First detection of the white dwarf cooling sequence of the galactic bulge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calamida, A.; Sahu, K. C.; Anderson, J.

2014-08-01

We present Hubble Space Telescope data of the low-reddening Sagittarius window in the Galactic bulge. The Sagittarius Window Eclipsing Extrasolar Planet Search field (∼3'× 3'), together with three more Advanced Camera for Surveys and eight Wide-Field Camera 3 fields, were observed in the F606W and F814W filters, approximately every two weeks for 2 yr, with the principal aim of detecting a hidden population of isolated black holes and neutron stars through astrometric microlensing. Proper motions were measured with an accuracy of ≈0.1 mas yr{sup –1} (≈4 km s{sup –1}) at F606W ≈ 25.5 mag, and better than ≈0.5 mas yr{supmore » –1} (≈20 km s{sup –1}) at F606W ≈ 28 mag, in both axes. Proper-motion measurements allowed us to separate disk and bulge stars and obtain a clean bulge color-magnitude diagram. We then identified for the first time a white dwarf (WD) cooling sequence in the Galactic bulge, together with a dozen candidate extreme horizontal branch stars. The comparison between theory and observations shows that a substantial fraction of the WDs (≈30%) are systematically redder than the cooling tracks for CO-core H-rich and He-rich envelope WDs. This evidence would suggest the presence of a significant number of low-mass WDs and WD-main-sequence binaries in the bulge. This hypothesis is further supported by the finding of two dwarf novae in outburst, two short-period (P ≲ 1 day) ellipsoidal variables, and a few candidate cataclysmic variables in the same field.« less

Cool Dwarfs 1o-7

NASA Astrophysics Data System (ADS)

Ambruster, Carol W.

Most of the cool dwarfs in the interesting age range 10^7-10^8 yr are too faint for IUE, yet such stars are critically important from the viewpoint of stellar evolution. Among stars of this age are the Pleiades K dwarfs, some of which appear to be on the main sequence, and some of which are still arriving there. Up until last year, only 2 stars in this age range had been observed by IUE, both recently: HD 36705 (AB Dor) and HD 17433. Three more stars were identified by the present investigators and observed with IUE during the past (11th) year: HD 129333, a single, nearby solar-type GOV star; HD 82558, a rapidly rotating, single, K2V star; and Ross 137B, the M dwarf common proper motion companion to AB Dor. We have since identified 5 more stars between 10^7 and 10^8 years old that are bright enough to be observed by IUE. They are physically associated, but distant, companions to main sequence O and B stars, identified in the survey of Lindroos (1986). Their ages are thus determined by the short main sequence lifetimes of the hot primaries. Rotational velocities are not yet known for our 5 proposed targets; we will be obtaining these and other data in the coming year. We therefore request time for basic IUE observations of these stars, an LWP-lo, LWP-hi and SWP-lo, for each star. This will ensure that crucial basic fluxes are in the IUE archives, should the satellite die in the coming year. Furthermore these data are immediately useful in filling the gap in the exhaustive study by Simon, Herbig and Boesgaard (1985) of the evolution of TR and chromospheric activity with age. More in-depth coverage will be proposed next year.

Using White Dwarf Companions of Blue Stragglers to Constrain Mass Transfer Physics

NASA Astrophysics Data System (ADS)

Gosnell, Natalie M.; Leiner, Emily; Geller, Aaron M.; Knigge, Christian; Mathieu, Robert D.; Sills, Alison; Leigh, Nathan

2018-06-01

Complete membership studies of old open clusters reveal that 25% of the evolved stars follow pathways in stellar evolution that are impacted by binary evolution. Recent studies show that the majority of blue straggler stars, traditionally defined to be stars brighter and bluer than the corresponding main sequence turnoff, are formed through mass transfer from a giant star onto a main sequence companion, resulting in a white dwarf in a binary system with a blue straggler. We will present constraints on the histories and mass transfer efficiencies for two blue straggler-white dwarf binaries in open cluster NGC 188. The constraints are a result of measuring white dwarf cooling temperatures and surface gravities with HST COS far-ultraviolet spectroscopy. This information sets both the timeline for mass transfer and the stellar masses in the pre-mass transfer binary, allowing us to constrain aspects of the mass transfer physics. One system is formed through Case C mass transfer, leaving a CO-core white dwarf, and provides an interesting test case for mass transfer from an asymptotic giant branch star in an eccentric system. The other system formed through Case B mass transfer, leaving a He-core white dwarf, and challenges our current understanding of the expected regimes for stable mass transfer from red giant branch stars.

Ultra-cool dwarfs viewed equator-on: surveying the best host stars for biosignature detection in transiting exoplanets

NASA Astrophysics Data System (ADS)

Miles-Paez, Paulo; Metchev, Stanimir; Burgasser, Adam; Apai, Daniel; Palle, Enric; Zapatero Osorio, Maria Rosa; Artigau, Etienne; Mace, Greg; Tannock, Megan; Triaud, Amaury

2018-05-01

There are about 150 known planets around M dwarfs, but only one system around an ultra-cool (>M7) dwarf: Trappist-1. Ultra-cool dwarfs are arguably the most promising hosts for atmospheric and biosignature detection in transiting planets because of the enhanced feature contrast in transit and eclipse spectroscopy. We propose a Spitzer survey to continuously monitor 15 of the brightest ultra-cool dwarfs over 3 days. To maximize the probability of detecting transiting planets, we have selected only targets seen close to equator-on. Spin-orbit alignment expectations dictate that the planetary systems around these ultra-cool dwarfs should also be oriented nearly edge-on. Any planet detections from this survey will immediately become top priority targets for JWST transit spectroscopy. No other telescope, present or within the foreseeable future, will be able to conduct a similarly sensitive and dedicated survey for characterizeable Earth analogs.

Examining Cloud, Metallicity, and Gravity signatures in Brown Dwarfs

NASA Astrophysics Data System (ADS)

Gonzales, Eileen; Faherty, Jacqueline K.; Gagné, Jonathan; Artigau, Étienne; BDNYC

2018-01-01

The nearby solar neighborhood is littered with low mass, low temperature objects called brown dwarfs. This population of ultracool objects do not have enough mass to sustain stable hydrogen burning so they never enter the main sequence and simply cool through time. Brown dwarfs span effective temperatures in the range 250 to 3000K. They also have age dependent observable properties. Young brown dwarfs appear to have redder near infrared colors than field age sources, while old objects tend to have bluer colors. Over the past several years, the research group entitled “Brown Dwarfs in New York City” (BDNYC) has been collecting optical, near and mid-infrared spectra, as well as photometry for sources that have well defined distances. In this poster, I will compare the distance calibrated spectral energy distributions of a sample of old, young, and field age brown dwarfs of the same effective temperature. In so doing, I will discern observables linked to gravity, atmosphere, metallicity and age effects.

The frequency of planetary debris around young white dwarfs

NASA Astrophysics Data System (ADS)

Koester, D.; Gänsicke, B. T.; Farihi, J.

2014-06-01

Context. Heavy metals in the atmospheres of white dwarfs are thought in many cases to be accreted from a circumstellar debris disk, which was formed by the tidal disruption of a rocky planetary body within the Roche radius of the star. The abundance analysis of photospheric elements and conclusions about the chemical composition of the accreted matter are a new and promising method of studying the composition of extrasolar planetary systems. However, ground-based searches for metal-polluted white dwarfs that rely primarily on the detection of the Ca ii K line become insensitive at Teff > 15 000 K because this ionization state depopulates. Aims: We present the results of the first unbiased survey for metal pollution among hydrogen-atmosphere (DA type) white dwarfs with cooling ages in the range 20-200 Myr and 17 000 K 23 000 K, in excellent agreement with the absence of infrared excess from dust around these warmer stars. The median, main sequence progenitor of our sample corresponds to an A-type star of ≈2 M⊙, and we find 13 of 23 white dwarfs descending from main sequence 2-3 M⊙, late B- and A-type stars to be currently accreting. Only one of 14 targets with Mwd > 0.8 M⊙ is found to be currently accreting, which suggests a large fraction of these stars result from double-degenerate mergers, and the merger disks do not commonly reform large planetesimals or otherwise pollute the remnant. We reconfirm our previous finding that two 625 Myr Hyades white dwarfs are currently accreting rocky planetary debris. Conclusions: At least 27% of all white dwarfs with cooling ages 20-200 Myr are accreting planetary debris, but that fraction could be as high as ≈50%. At Teff > 23 000 K, the luminosity of white dwarfs is probably sufficient to vaporize circumstellar dust grains, so no stars with strong metal-pollution are found. Planetesimal disruption events should occur in this cooling age and temperature range as well, and they are likely to result in short phases of high mass-transfer rates. It appears that the formation of rocky planetary material is common around 2-3 M⊙ late B- and A-type stars. Table 1 is available in electronic form at http://www.aanda.org

The luminosity function at the end of the main sequence: Results of a deep, large-area, CCD survey for cool dwarfs

NASA Technical Reports Server (NTRS)

Kirkpatrick, J. Davy; Mcgraw, John T.; Hess, Thomas R.; Liebert, James; Mccarthy, Donald W., Jr.

1994-01-01

The luminosity function at the end of the main sequence is determined from V, R, and I data taken by the charge coupled devices (CCD)/Transit Instrument, a dedicated telescope surveying an 8.25 min wide strip of sky centered at delta = +28 deg, thus sampling Galactic latitudes of +90 deg down to -35 deg. A selection of 133 objects chosen via R - I and V - I colors has been observed spectroscopically at the 4.5 m Multiple Mirror Telescope to assess contributions by giants and subdwarfs and to verify that the reddest targets are objects of extremely late spectral class. Eighteen dwarfs of type M6 or later have been discovered, with the latest being of type M8.5. Data used for the determination of the luminosity function cover 27.3 sq. deg down to a completeness limit of R = 19.0. This luminosity function, computed at V, I, and bolometric magnitudes, shows an increase at the lowest luminosities, corresponding to spectral types later than M6- an effect suggested in earlier work by Reid & Gilmore and Legget & Hawkins. When the luminosity function is segregated into north Galactic and south Galactic portions, it is found that the upturn at faint magnitudes exists only in the southern sample. In fact, no dwarfs with M(sub I) is greater than or equal to 12.0 are found within the limiting volume of the 19.4 sq deg northern sample, in stark contrast to the smaller 7.9 sq deg area at southerly latitudes where seven such dwarfs are found. This fact, combined with the fact that the Sun is located approximately 10-40 pc north of the midplane, suggests that the latest dwarfs are part of a young population with a scale height much smaller than the 350 pc value generally adopted for other M dwarfs. These objects comprise a young population either because the lower metallicities prevelant at earlier epochs inhibited the formation of late M dwarfs or because the older counterparts of this population have cooled beyond current detection limits. The latter scenario would hold if these late-type M dwarfs are substellar. The luminosity function data together with an empirical derivation of the mass-luminosity relation (from Henry & McCarthy) are used to compute a mass function independent of theory. This mass function increases toward the end of the main sequence, but the observed density of M dwarfs is still insufficient to account for the missing mass. If the increases seen in the luminosity and mass functions are indicative of a large, unseen, substellar population, brown dwarfs may yet add significantly to the mass of the Galaxy.

Race to the Top: Transiting Brown Dwarfs and Hot Jupiters

NASA Astrophysics Data System (ADS)

Beatty, Thomas G.

2015-12-01

There are currently twelve known transiting brown dwarfs, nine of which orbit single main-sequence stars. These systems give us one of the only ways in which we may directly measure the masses and radii brown dwarfs, which in turn provides strong constraints on theoretical models of brown dwarf interiors and atmospheres. In addition, the transiting brown dwarfs allow us to forge a link between our understanding of transiting hot Jupiters, and our understanding of the field brown dwarf population. Comparing the two gives us a unique avenue to explore the role and interaction of surface gravity and stellar irradiation in the atmospheres of sub-stellar objects. It also allows us to leverage the detailed spectroscopic information we have for field brown dwarfs to interpret the broadband colors of hot Jupiters. This provides us with insight into the L/T transition in brown dwarfs, and the atmospheric chemistry changes that occur in hot Jupiter atmospheres as they cool. I will discuss recent observational results, with a particular focus on the transiting brown dwarf KELT-1b, and suggest how more of these important systems may be discovered in the future.

A Catalog of Cool Dwarf Targets for the Transiting Exoplanet Survey Satellite

NASA Astrophysics Data System (ADS)

Muirhead, Philip S.; Dressing, Courtney D.; Mann, Andrew W.; Rojas-Ayala, Bárbara; Lépine, Sébastien; Paegert, Martin; De Lee, Nathan; Oelkers, Ryan

2018-04-01

We present a catalog of cool dwarf targets (V-J> 2.7, T eff ≲ 4000 K) and their stellar properties for the upcoming Transiting Exoplanet Survey Satellite (TESS), for the purpose of determining which cool dwarfs should be observed using two minute observations. TESS has the opportunity to search tens of thousands of nearby, cool, late K- and M-type dwarfs for transiting exoplanets, an order of magnitude more than current or previous transiting exoplanet surveys, such as Kepler, K2, and ground-based programs. This necessitates a new approach to choosing cool dwarf targets. Cool dwarfs are chosen by collating parallax and proper motion catalogs from the literature and subjecting them to a variety of selection criteria. We calculate stellar parameters and TESS magnitudes using the best possible relations from the literature while maintaining uniformity of methods for the sake of reproducibility. We estimate the expected planet yield from TESS observations using statistical results from the Kepler mission, and use these results to choose the best targets for two minute observations, optimizing for small planets for which masses can conceivably be measured using follow-up Doppler spectroscopy by current and future Doppler spectrometers. The catalog is available in machine readable format and is incorporated into the TESS Input Catalog and TESS Candidate Target List until a more complete and accurate cool dwarf catalog identified by ESA’s Gaia mission can be incorporated.

Searching for Partners of Cool Senior Citizens

NASA Astrophysics Data System (ADS)

Jao, Wei-Chun; Henry, T. J.

2012-01-01

Mass is one of the most fundamental parameters in stellar astronomy. In order to measure dynamical masses, one needs to find nearby binary systems that can be resolved and monitored, ideally with orbital periods that completely wrap in a reasonable amount of time. Many surveys have been made of nearby main sequence dwarfs, and their mass-luminosity relation is well established. As part of our Cool Subdwarf Investigations (CSI) program, we are searching for subdwarf binaries of spectral types K and M within 60 parsecs to measure their multiplicity rate and to reveal binaries appropriate for mass determinations. Here we present results of our CSI work using HST's Fine Guidance Sensors. When combined with previous CSI work and results in the literature, we find the multiplicity rate of subdwarfs, 21%, to be surprisingly low compared to that of similar main sequence K and M stars, 37%. This work has several implications, including that the star formation and/or evolution history of subdwarfs is different than for dwarfs, and that ideal systems for subdwarf mass determinations are difficult to find. This work is supported by HST grant GO-11943.

Infrared spectrum of an extremely cool white-dwarf star

PubMed

Hodgkin; Oppenheimer; Hambly; Jameson; Smartt; Steele

2000-01-06

White dwarfs are the remnant cores of stars that initially had masses of less than 8 solar masses. They cool gradually over billions of years, and have been suggested to make up much of the 'dark matter' in the halo of the Milky Way. But extremely cool white dwarfs have proved difficult to detect, owing to both their faintness and their anticipated similarity in colour to other classes of dwarf stars. Recent improved models indicate that white dwarfs are much more blue than previously supposed, suggesting that the earlier searches may have been looking for the wrong kinds of objects. Here we report an infrared spectrum of an extremely cool white dwarf that is consistent with the new models. We determine the star's temperature to be 3,500 +/- 200 K, making it the coolest known white dwarf. The kinematics of this star indicate that it is in the halo of the Milky Way, and the density of such objects implied by the serendipitous discovery of this star is consistent with white dwarfs dominating the dark matter in the halo.

OPTICAL IDENTIFICATION OF He WHITE DWARFS ORBITING FOUR MILLISECOND PULSARS IN THE GLOBULAR CLUSTER 47 TUCANAE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cadelano, M.; Pallanca, C.; Ferraro, F. R.

2015-10-10

We used ultra-deep UV observations obtained with the Hubble Space Telescope to search for optical companions to binary millisecond pulsars (MSPs) in the globular cluster 47 Tucanae. We identified four new counterparts (to MSPs 47TucQ, 47TucS, 47TucT, and 47TucY) and confirmed those already known (to MSPs 47TucU and 47TucW). In the color–magnitude diagram, the detected companions are located in a region between the main sequence and the CO white dwarf (WD) cooling sequences, consistent with the cooling tracks of He WDs with masses between 0.15 M{sub ⊙} and 0.20 M{sub ⊙}. For each identified companion, mass, cooling age, temperature, andmore » pulsar mass (as a function of the inclination angle) have been derived and discussed. For 47TucU we also found that the past accretion history likely proceeded at a sub-Eddington rate. The companion to the redback 47TucW is confirmed to be a non-degenerate star, with properties particularly similar to those observed for black widow systems. Two stars have been identified within the 2σ astrometric uncertainty from the radio positions of 47TucH and 47TucI, but the available data prevent us from firmly assessing whether they are the true companions of these two MSPs.« less

Cool White Dwarfs Found in the UKIRT Infrared Deep Sky Survey

NASA Astrophysics Data System (ADS)

Leggett, S. K.; Lodieu, N.; Tremblay, P.-E.; Bergeron, P.; Nitta, A.

2011-07-01

We present the results of a search for cool white dwarfs in the United Kingdom InfraRed Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS). The UKIDSS LAS photometry was paired with the Sloan Digital Sky Survey to identify cool hydrogen-rich white dwarf candidates by their neutral optical colors and blue near-infrared colors, as well as faint reduced proper motion magnitudes. Optical spectroscopy was obtained at Gemini Observatory and showed the majority of the candidates to be newly identified cool degenerates, with a small number of G- to K-type (sub)dwarf contaminants. Our initial search of 280 deg2 of sky resulted in seven new white dwarfs with effective temperature T eff ≈ 6000 K. The current follow-up of 1400 deg2 of sky has produced 13 new white dwarfs. Model fits to the photometry show that seven of the newly identified white dwarfs have 4120 K <=T eff <= 4480 K, and cooling ages between 7.3 Gyr and 8.7 Gyr; they have 40 km s-1 <= v tan <= 85 km s-1 and are likely to be thick disk 10-11 Gyr-old objects. The other half of the sample has 4610 K <=T eff <= 5260 K, cooling ages between 4.3 Gyr and 6.9 Gyr, and 60 km s-1 <= v tan <= 100 km s-1. These are either thin disk remnants with unusually high velocities, or lower-mass remnants of thick disk or halo late-F or G stars.

New Y and T Dwarfs from WISE Identified by Methane Imaging

NASA Astrophysics Data System (ADS)

Tinney, C. G.; Kirkpatrick, J. Davy; Faherty, Jacqueline K.; Mace, Gregory N.; Cushing, Mike; Gelino, Christopher R.; Burgasser, Adam J.; Sheppard, Scott S.; Wright, Edward L.

2018-06-01

We identify new Y- and T-type brown dwarfs from the WISE All Sky data release using images obtained in filters that divide the traditional near-infrared H and J bands into two halves—specifically {CH}}4{{s}} and CH4l in the H and J2, and J3 in the J. This proves to be very effective at identifying cool brown dwarfs via the detection of their methane absorption, as well as providing preliminary classification using methane colors and WISE -to-near-infrared colors. New and updated calibrations between T/Y spectral types and {CH}}4{{s}}–CH4l J3–W2, and {CH}}4{{s}}–W2 colors are derived, producing classification estimates good to a few spectral sub-types. We present photometry for a large sample of T and Y dwarfs in these filters, together with spectroscopy for 23 new ultra-cool dwarfs—2 Y dwarfs and 21 T dwarfs. We identify a further 8 new cool brown dwarfs, which we have high confidence are T dwarfs based on their methane photometry. We find that, for objects observed on a 4 m class telescope at J-band magnitudes of ∼20 or brighter, {CH}}4{{s}}–CH4l is the more powerful color for detecting objects and then estimating spectral types. Due to the lower sky background in the J-band, the J3 and J2 bands are more useful for identifying fainter cool dwarfs at J ≳ 22. The J3–J2 color is poor at estimating spectral types. But fortunately, once J3–J2 confirms that an object is a cool dwarf, the J3–W2 color is very effective at estimating approximate spectral types.

Chromospherically Active Stars in the RAVE Survey. II. Young Dwarfs in the Solar Neighborhood

NASA Astrophysics Data System (ADS)

Žerjal, M.; Zwitter, T.; Matijevič, G.; Grebel, E. K.; Kordopatis, G.; Munari, U.; Seabroke, G.; Steinmetz, M.; Wojno, J.; Bienaymé, O.; Bland-Hawthorn, J.; Conrad, C.; Freeman, K. C.; Gibson, B. K.; Gilmore, G.; Kunder, A.; Navarro, J.; Parker, Q. A.; Reid, W.; Siviero, A.; Watson, F. G.; Wyse, R. F. G.

2017-01-01

A large sample of over 38,000 chromospherically active candidate solar-like stars and cooler dwarfs from the RAVE survey is addressed in this paper. An improved activity identification with respect to the previous study was introduced to build a catalog of field stars in the solar neighborhood with an excess emission flux in the calcium infrared triplet wavelength region. The central result of this work is the calibration of the age-activity relation for main-sequence dwarfs in a range from a few 10 {Myr} up to a few Gyr. It enabled an order of magnitude age estimation of the entire active sample. Almost 15,000 stars are shown to be younger than 1 {Gyr} and ˜2000 younger than 100 {Myr}. The young age of the most active stars is confirmed by their position off the main sequence in the J - K versus {N}{UV}-V diagram showing strong ultraviolet excess, mid-infrared excess in the J - K versus {W}1-{W}2 diagram, and very cool temperatures (J-K> 0.7). They overlap with the reference pre-main-sequence RAVE stars often displaying X-ray emission. The activity level increasing with the color reveals their different nature from the solar-like stars and probably represents an underlying dynamo-generating magnetic fields in cool stars. Of the RAVE objects from DR5, 50% are found in the TGAS catalog and supplemented with accurate parallaxes and proper motions by Gaia. This makes the database of a large number of young stars in a combination with RAVE’s radial velocities directly useful as a tracer of the very recent large-scale star formation history in the solar neighborhood. The data are available online in the Vizier database.

Making Sense of Atmospheric Models and Fundamental Stellar Properties at the Bottom of the Main Sequence

NASA Astrophysics Data System (ADS)

Dieterich, Sergio; Henry, Todd; Jao, W.-C.; Washington, Robert; Silverstein, Michele; Winters, J.; RECONS

2018-01-01

We present a detailed comparison of atmospheric model predictions and photometric observations for late M and L dwarfs. We discuss which wavelength regions are best for determining the fundamental properties of these cool stellar and substellar atmospheres and use this analysis to refine the HR diagram for the hydrogen burning limit first presented in 2014. We also add several new objects to the HR diagram and find little qualitative difference in the HR diagram's overall morphology when compared to our 2014 results. The L2 dwarf 2MASS 0523-1403 remains the smallest hydrogen burning star for which we calculated a radius, thus likely indicating the end of the stellar main sequence. This work is supported by the NSF Astronomy and Astrophysics Postdoctoral Fellowship program through grant AST-1400680.

THE DISCOVERY OF SOLAR-LIKE ACTIVITY CYCLES BEYOND THE END OF THE MAIN SEQUENCE?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Route, Matthew, E-mail: mroute@purdue.edu

2016-10-20

The long-term magnetic behavior of objects near the cooler end of the stellar main sequence is poorly understood. Most theoretical work on the generation of magnetism in these ultracool dwarfs (spectral type ≥M7 stars and brown dwarfs) suggests that their magnetic fields should not change in strength and direction. Using polarized radio emission measurements of their magnetic field orientations, I demonstrate that these cool, low-mass, fully convective objects appear to undergo magnetic polarity reversals analogous to those that occur on the Sun. This powerful new technique potentially indicates that the patterns of magnetic activity displayed by the Sun continue tomore » exist, despite the fully convective interiors of these objects, in contravention of several leading theories of the generation of magnetic fields by internal dynamos.« less

ROSAT Pointed Observations of Cool Magnetic White Dwarfs

NASA Technical Reports Server (NTRS)

Musielak, Z. E.; Porter, J. G.; Davis, J. M.

1995-01-01

Observational evidence for the existence of a chromosphere on the cool magnetic white dwarf GD 356 has been reported. In addition, there has been theoretical speculations that cool magnetic white dwarfs may be sources of coronal X-ray emission. This emission, if it exists, would be distinct from the two types of X-ray emission (deep photospheric and shocked wind) that have already been observed from hot white dwarfs. We have used the PSPC instrument on ROSAT to observe three of the most prominent DA white dwarf candidates for coronal X-ray emission: GD 356, KUV 2316+123, and GD 90. The data show no significant emission for these stars. The derived upper limits for the X-ray luminosities provide constraints for a revision of current theories of the generation of nonradiative energy in white dwarfs.

Nearly simultaneous observations of chromospheric and coronal radiative losses of cool stars

NASA Technical Reports Server (NTRS)

Schrijver, C. J.; Dobson, A. K.; Radick, R. R.

1992-01-01

The flux-flux relationships of cool stars are studied on the basis of nearly simultaneous measurements of Ca II H+K, Mg II h+k, and soft X-ray fluxes. A linear relationship is derived between IUE Mg II h+k fluxes and Mount Wilson Ca II H+K fluxes which were obtained within 36 hr of each other for a sample of 26 F5-K3 main-sequence stars. Nearly simultaneous EXOSAT soft X-ray fluxes are compared with Ca II H+K fluxes for a sample of 20 dwarfs and gaints with spectral types ranging from F6 to K2, and 72 additional cool stars for which noncontemporaneous Ca II H+K and EINSTEIN soft X-ray fluxes are available are compared. It is confirmed that a nonradiatively heated chromosphere exists on even the least active main-sequence stars. This basal chromosphere is probably independent of stellar magnetic activity.

A Search for Variability in Warm and Cool C-rich DQ White Dwarfs

NASA Astrophysics Data System (ADS)

Dupuis, Christopher Michael; Williams, Kurtis A.

2018-01-01

Hot DQ white dwarfs are a rare class of white dwarfs that have atmospheres dominated by carbon with little to no hydrogen or helium. Recently it has been found that the majority of these stars are photometrically variable likely due to rapid rotation with star spots. The cool progeny of the hot DQs are expected to also be rapidly rotating as no strong braking mechanisms should be present. We present the time-series photometry of multiple warm and cool C-rich DQ white dwarfs as part of an ongoing search for variability in hot DQ white dwarfs and their progeny. This program will permit us to confirm rotation as the source of variability, compare the distribution of rotation rates to those of more common white dwarf spectral types, and constrain the evolutionary rates of hot DQ rotation. These data are one way to better understand the formation scenarios of these stars.

The coolest extremely low-mass white dwarfs

NASA Astrophysics Data System (ADS)

Calcaferro, Leila M.; Althaus, Leandro G.; Córsico, Alejandro H.

2018-06-01

Context. Extremely low-mass white dwarf (ELM WD; M⋆ ≲ 0.18-0.20 M⊙) stars are thought to be formed in binary systems via stable or unstable mass transfer. Although stable mass transfer predicts the formation of ELM WDs with thick hydrogen (H) envelopes that are characterized by dominant residual nuclear burning along the cooling branch, the formation of ELM WDs with thinner H envelopes from unstable mass loss cannot be discarded. Aims: We compute new evolutionary sequences for helium (He) core WD stars with thin H envelopes with the main aim of assessing the lowest Teff that could be reached by this type of stars. Methods: We generate a new grid of evolutionary sequences of He-core WD stars with thin H envelopes in the mass range from 0.1554 to 0.2025 M⊙, and assess the changes in both the cooling times and surface gravity induced by a reduction of the H envelope. We also determine, taking into account the predictions of progenitor evolution, the lowest Teff reached by the resulting ELM WDs. Results: We find that a slight reduction in the H envelope yields a significant increase in the cooling rate of ELM WDs. Because of this, ELM WDs with thin H envelopes could cool down to 2500 K, in contrast to their canonical counterparts that cool down to 7000 K. In addition, we find that a reduction of the thickness of the H envelope markedly increases the surface gravity (g) of these stars. Conclusions: If ELM WDs are formed with thin H envelopes, they could be detected at very low Teff. The detection of such cool ELM WDs would be indicative that they were formed with thin H envelopes, thus opening the possibility of placing constraints on the possible mechanisms of formation of this type of star. Last but not least, the increase in g due to the reduction of the H envelope leads to consequences in the spectroscopic determinations of these stars.

Luminosity and cooling of highly magnetized white dwarfs: suppression of luminosity by strong magnetic fields

NASA Astrophysics Data System (ADS)

Bhattacharya, Mukul; Mukhopadhyay, Banibrata; Mukerjee, Subroto

2018-06-01

We investigate the luminosity and cooling of highly magnetized white dwarfs with electron-degenerate cores and non-degenerate surface layers where cooling occurs by diffusion of photons. We find the temperature and density profiles in the surface layers or envelope of white dwarfs by solving the magnetostatic equilibrium and photon diffusion equations in a Newtonian framework. We also obtain the properties of white dwarfs at the core-envelope interface, when the core is assumed to be practically isothermal. With the increase in magnetic field, the interface temperature increases whereas the interface radius decreases. For a given age of the white dwarf and for fixed interface radius or interface temperature, we find that the luminosity decreases significantly from about 10-6 to 10-9 L⊙ as the magnetic field strength increases from about 109 to 1012 G at the interface and hence the envelope. This is remarkable because it argues that magnetized white dwarfs are fainter and can be practically hidden in an observed Hertzsprung-Russell diagram. We also find the cooling rates corresponding to these luminosities. Interestingly, the decrease in temperature with time, for the fields under consideration, is not found to be appreciable.

Photometric Calibrations of Gemini Images of NGC 6253

NASA Astrophysics Data System (ADS)

Pearce, Sean; Jeffery, Elizabeth

2017-01-01

We present preliminary results of our analysis of the metal-rich open cluster NGC 6253 using imaging data from GMOS on the Gemini-South Observatory. These data are part of a larger project to observe the effects of high metallicity on white dwarf cooling processes, especially the white dwarf cooling age, which have important implications on the processes of stellar evolution. To standardize the Gemini photometry, we have also secured imaging data of both the cluster and standard star fields using the 0.6-m SARA Observatory at CTIO. By analyzing and comparing the standard star fields of both the SARA data and the published Gemini zero-points of the standard star fields, we will calibrate the data obtained for the cluster. These calibrations are an important part of the project to obtain a standardized deep color-magnitude diagram to analyze the cluster. We present the process of verifying our standardization process. With a standardized CMD, we also present an analysis of the cluster's main sequence turn off age.

A Search for a Surviving White Dwarf Companion in SN 1006

NASA Astrophysics Data System (ADS)

Kerzendorf, W. E.; Strampelli, G.; Shen, K. J.; Schwab, J.; Pakmor, R.; Do, T.; Buchner, J.; Rest, A.

2018-05-01

Multiple channels have been proposed to produce Type Ia supernovae, with many scenarios suggesting that the exploding white dwarf accretes from a binary companion pre-explosion. In almost all cases, theory suggests that this companion will survive. However, no such companion has been unambiguously identified in ancient supernova remnants - possibly falsifying the accretion scenario. Existing surveys, however, have only looked for stars as faint as ≈0.1L⊙ and thus might have missed a surviving white dwarf companion. In this work, we present very deep DECAM imaging (u, g, r, z) of the Type Ia supernova remnant SN 1006 specifically to search for a potential surviving white dwarf companion. We find no object that is consistent with a relatively young cooling white dwarf within the inner half of the SN 1006 remnant. We find that if there is a companion white dwarf, it must be redder than the standard white dwarf cooling track, or it must have formed long ago and cooled undisturbed for >108 yr. We conclude that our findings are consistent with the complete destruction of the secondary (such as in a merger) or an anomalously red or very dim surviving companion white dwarf.

Solidification of carbon-oxygen white dwarfs

NASA Technical Reports Server (NTRS)

Schatzman, E.

1982-01-01

The internal structure of white dwarfs is discussed. Highly correlated plasmas are reviewed. Implications for phase separation in the core of cooling white dwarfs are considered. The consequences for evolution of white dwarfs are addressed.

The luminosities of the coldest brown dwarfs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tinney, C. G.; Faherty, Jacqueline K.; Kirkpatrick, J. Davy

2014-11-20

In recent years, brown dwarfs have been extended to a new Y-dwarf class with effective temperatures colder than 500 K and masses in the range of 5-30 Jupiter masses. They fill a crucial gap in observable atmospheric properties between the much colder gas-giant planets of our own solar system (at around 130 K) and both hotter T-type brown dwarfs and the hotter planets that can be imaged orbiting young nearby stars (both with effective temperatures in the range of 1500-1000 K). Distance measurements for these objects deliver absolute magnitudes that make critical tests of our understanding of very cool atmospheres.more » Here we report new distances for nine Y dwarfs and seven very late T dwarfs. These reveal that Y dwarfs do indeed represent a continuation of the T-dwarf sequence to both fainter luminosities and cooler temperatures. They also show that the coolest objects display a large range in absolute magnitude for a given photometric color. The latest atmospheric models show good agreement with the majority of these Y-dwarf absolute magnitudes. This is also the case for WISE0855-0714, the coldest and closest brown dwarf to the Sun, which shows evidence for water ice clouds. However, there are also some outstanding exceptions, which suggest either binarity or the presence of condensate clouds. The former is readily testable with current adaptive optics facilities. The latter would mean that the range of cloudiness in Y dwarfs is substantial with most hosting almost no clouds—while others have dense clouds, making them prime targets for future variability observations to study cloud dynamics.« less

The influence of H2O line blanketing on the spectra of cool dwarf stars

NASA Technical Reports Server (NTRS)

Allard, F.; Hauschildt, P. H.; Miller, S.; Tennyson, J.

1994-01-01

We present our initial results of model atmosphere calculations for cool M dwarfs using an opacity sampling method and a new list of H2O lines. We obtain significantly improved fits to the infrared spectrum of the M dwarf VB10 when compared to earlier models. H2O is by far the dominant opacity source in cool stars. To illustrate this, we show the Rosseland mean of the total extinction under various assumptions. Our calculations demonstrate the importance of a good treatment of the water opacities in cool stars and the improvements possible by using up-to-date data for the water line absorption.

DISCOVERY OF A POSSIBLE COOL WHITE DWARF COMPANION FROM THE AllWISE MOTION SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fajardo-Acosta, Sergio B.; Kirkpatrick, J. Davy; Gelino, Christopher R.

We present optical and near-infrared spectroscopy of WISEA J061543.91-124726.8, which we rediscovered as a high motion object in the AllWISE survey. The spectra of this object are unusual; while the red optical ( λ > 7000 Å) and near-infrared spectra exhibit characteristic TiO, VO, and H{sub 2}O bands of a late-M dwarf, the blue portion of its optical spectrum shows a significant excess of emission relative to late-M-type templates. The excess emission is relatively featureless, with the exception of a prominent and very broad Na i D doublet. We find that no single, ordinary star can reproduce these spectral characteristics.more » The most likely explanation is an unresolved binary system of an M7 dwarf and a cool white dwarf. The flux of a cool white dwarf drops in the optical red and near-infrared, due to collision-induced absorption, thus allowing the flux of a late-M dwarf to show through. This scenario, however, does not explain the Na D feature, which is unlike that of any known white dwarf, but which could perhaps be explained via unusual abundance or pressure conditions.« less

Detectable close-in planets around white dwarfs through late unpacking

NASA Astrophysics Data System (ADS)

Veras, Dimitri; Gänsicke, Boris T.

2015-02-01

Although 25-50 per cent of white dwarfs (WDs) display evidence for remnant planetary systems, their orbital architectures and overall sizes remain unknown. Vibrant close-in (≃1 R⊙) circumstellar activity is detected at WDs spanning many Gyr in age, suggestive of planets further away. Here we demonstrate how systems with 4 and 10 closely packed planets that remain stable and ordered on the main sequence can become unpacked when the star evolves into a WD and experience pervasive inward planetary incursions throughout WD cooling. Our full-lifetime simulations run for the age of the Universe and adopt main-sequence stellar masses of 1.5, 2.0 and 2.5 M⊙, which correspond to the mass range occupied by the progenitors of typical present-day WDs. These results provide (i) a natural way to generate an ever-changing dynamical architecture in post-main-sequence planetary systems, (ii) an avenue for planets to achieve temporary close-in orbits that are potentially detectable by transit photometry and (iii) a dynamical explanation for how residual asteroids might pollute particularly old WDs.

Three new cool brown dwarfs discovered with the wide-field infrared survey explorer (WISE) and an improved spectrum of the Y0 dwarf wise J041022.71+150248.4

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cushing, Michael C.; Kirkpatrick, J. Davy; Gelino, Christopher R.

2014-05-01

As part of a larger search of Wide-field Infrared Survey Explorer (WISE) data for cool brown dwarfs with effective temperatures less than 1000 K, we present the discovery of three new cool brown dwarfs with spectral types later than T7. Using low-resolution, near-infrared spectra obtained with the NASA Infrared Telescope Facility and the Hubble Space Telescope, we derive spectral types of T9.5 for WISE J094305.98+360723.5, T8 for WISE J200050.19+362950.1, and Y0: for WISE J220905.73+271143.9. The identification of WISE J220905.73+271143.9 as a Y dwarf brings the total number of spectroscopically confirmed Y dwarfs to 17. In addition, we present an improvedmore » spectrum (i.e., higher signal-to-noise ratio) of the Y0 dwarf WISE J041022.71+150248.4 that confirms the Cushing et al. classification of Y0. Spectrophotometric distance estimates place all three new brown dwarfs at distances less than 12 pc, with WISE J200050.19+362950.1 lying at a distance of only 3.9-8.0 pc. Finally, we note that brown dwarfs like WISE J200050.19+362950.1 that lie in or near the Galactic plane offer an exciting opportunity to directly measure the mass of a brown dwarf via astrometric microlensing.« less

Multiplicity of the Galactic Senior Citizens: A High-resolution Search for Cool Subdwarf Companions

NASA Astrophysics Data System (ADS)

Ziegler, Carl; Law, Nicholas M.; Baranec, Christoph; Riddle, Reed L.; Fuchs, Joshua T.

2015-05-01

Cool subdwarfs are the oldest members of the low-mass stellar population. Mostly present in the galactic halo, subdwarfs are characterized by their low-metallicity. Measuring their binary fraction and comparing it to solar-metallicity stars could give key insights into the star formation process early in the Milky Way’s history. However, because of their low luminosity and relative rarity in the solar neighborhood, binarity surveys of cool subdwarfs have suffered from small sample sizes and incompleteness. Previous surveys have suggested that the binary fraction of red subdwarfs is much lower than for their main-sequence cousins. Using the highly efficient Robo-AO system, we present the largest high-resolution survey of subdwarfs, sensitive to angular separations (ρ ≥slant 0.″ 15) and contrast ratios ({Δ }{{m}i} ≤slant 6) invisible in past surveys. Of 344 target cool subdwarfs, 43 are in multiple systems, 19 of which are newly discovered, for a binary fraction of 12.5 ± 1.9%. We also discovered seven triple star systems for a triplet fraction of 2.0 ± 0.8%. Comparisons to similar surveys of solar-metallicity dwarf stars gives a ∼3σ disparity in luminosity between companion stars, with subdwarfs displaying a shortage of low-contrast companions. We also observe a lack of close subdwarf companions in comparison to similar-mass dwarf multiple systems.

Is EG 50 a White or Strange Dwarf?

NASA Astrophysics Data System (ADS)

Hajyan, G. S.; Vartanyan, Yu. L.

2017-12-01

The time dependences of the luminosity of a white dwarf and four strange dwarfs with masses of 0.5 M (the mass of the white dwarf EG 50 with a surface temperature of 2.1·104 K) are determined taking neutrino energy losses into account. It was assumed that these configurations radiate only at the expense of thermal energy reserves. It is shown that the sources of thermal energy owing to nonequilibrium b-processes and the phenomenon of crystallization of electron-nuclear matter are insignificant in determining the cooling time of white and strange dwarfs with masses of 0.5 M⨀. It is shown that in this approximation the time dependences of the luminosity of white and strange dwarfs with masses of 0.5 M⨀ differ significantly only for surface temperatures TR≥7·104 K, so it is impossible to determine whether EG 50 is a white or strange dwarf based on the cooling time.

Stellar Evolution in NGC 6791: Mass Loss on the Red Giant Branch and the Formation of Low-Mass White Dwarfs

NASA Astrophysics Data System (ADS)

Kalirai, Jasonjot S.; Bergeron, P.; Hansen, Brad M. S.; Kelson, Daniel D.; Reitzel, David B.; Rich, R. Michael; Richer, Harvey B.

2007-12-01

We present the first detailed study of the properties (temperatures, gravities, and masses) of the NGC 6791 white dwarf population. This unique stellar system is both one of the oldest (8 Gyr) and most metal-rich ([Fe/H]~+0.4) open clusters in our Galaxy and has a color-magnitude diagram (CMD) that exhibits both a red giant clump and a much hotter extreme horizontal branch. Fitting the Balmer lines of the white dwarfs in the cluster using Keck/LRIS spectra suggests that most of these stars are undermassive, =0.43+/-0.06 Msolar, and therefore could not have formed from canonical stellar evolution involving the helium flash at the tip of the red giant branch. We show that at least 40% of NGC 6791's evolved stars must have lost enough mass on the red giant branch to avoid the flash and therefore did not convert helium into carbon-oxygen in their core. Such increased mass loss in the evolution of the progenitors of these stars is consistent with the presence of the extreme horizontal branch in the CMD. This unique stellar evolutionary channel also naturally explains the recent finding of a very young age (2.4 Gyr) for NGC 6791 from white dwarf cooling theory; helium-core white dwarfs in this cluster will cool ~3 times slower than carbon-oxygen-core stars, and therefore the corrected white dwarf cooling age is in fact >~7 Gyr, consistent with the well-measured main-sequence turnoff age. These results provide direct empirical evidence that mass loss is much more efficient in high-metallicity environments and therefore may be critical in interpreting the ultraviolet upturn in elliptical galaxies. Data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

Brown Dwarf Weather (Artist's Concept)

NASA Image and Video Library

2017-06-06

This artist's concept shows what the weather might look like on cool star-like bodies known as brown dwarfs. These giant balls of gas start out life like stars, but lack the mass to sustain nuclear fusion at their cores, and instead, fade and cool with time. Observations from NASA's Spitzer Space Telescope suggest that most brown dwarfs are roiling with one or more planet-size storms akin to Jupiter's "Great Red Spot." https://photojournal.jpl.nasa.gov/catalog/PIA21475

Not-So-Bright Bulbs

NASA Technical Reports Server (NTRS)

2008-01-01

This artist's concept shows the dimmest star-like bodies currently known -- twin brown dwarfs referred to as 2M 0939. The twins, which are about the same size, are drawn as if they were viewed close to one of the bodies.

Brown dwarfs are neither planets nor stars. They form like stars out of collapsing clouds of gas and dust, but they don't have enough mass to ignite nuclear burning in their cores and become full-blown stars. They are similar to Jupiter in that they are cool balls of gas, but they are warmer and heavier. Astronomers say that the universe is littered with these cosmic misfits, but because they are so dim, they are hard to find.

NASA's Spitzer Space Telescope is fitted with heat-seeking infrared eyes, which allow it to detect the minute glow of cool objects like brown dwarfs. Data from Spitzer and the Anglo-Australian Observatory in Australia together reveal that both of the brown dwarfs making up 2M 0939 share the title of dimmest known brown dwarfs. Their atmospheres are also among the coolest known for any brown dwarf (565 to 635 Kelvin or 560 to 680 degrees Fahrenheit).

The term 'brown dwarf' comes from the fact that these objects cool and change over time, and therefore do not have a definitive color. The 2M 0939 brown dwarfs, if we could see them directly, would have a dark magenta hue due to their cool temperatures and the presence of water, methane and ammonia gases in their atmospheres.

2M 0939's full name is 2MASS J09393548-2448279 after the partly NASA-funded infrared mission, the Two Micron All Sky Survey, or '2MASS,' which first detected the object in 1999.

Search for white dwarf companions of cool stars with peculiar element abundances

NASA Technical Reports Server (NTRS)

Boehm-Vitense, E.

1984-01-01

A search for a white dwarf companions of cool stars with peculiar element abundances was undertaken. One additional star the xi Cet, was found with a white dwarf companion. It was found that HR 1016, 56Uma, 16 Ser, have high excitation emission lines which indicate a high temperature object in the system. It is suggested that since these indications for high temperature companions were seen for all nearby Ba stars, it is highly probable that all Ba stars have white dwarf companions, and that the peculiar element abundances seen in the Ba stars are due to mass transfer. Observations, arguments and conclusions are presented. White dwarf companions were not found. Together with the Li and Be abundances and the chromospheric emission line spectra in these stars were studied. No white dwarf companions were seen for subgiant CH stars.

Definition and empirical structure of the range of stellar chromospheres-coronae across the H-R diagram: Cool stars

NASA Technical Reports Server (NTRS)

Linsky, J. L.

1986-01-01

Major advances in our understanding of non-radiative heating and other activity in stars cooler than T sub eff = 10,000K has occured in the last few years. This observational evidence is reviewed and the trends that are now becoming apparent are discussed. The evidence for non-radiatively heated outer atmospheric layers (chromospheres, transition regions, and coronae) in dwarf stars cooler than spectral type A7, in F and G giants, pre-main sequence stars, and close bindary systems is unambiguous, as is the evidence for chromospheres in the K and M giants and supergiants. The existence of non-radiative heating in the outer layers of the A stars remains undetermined despite repeated searches at all wavelengths. Two important trends in the data are the decrease in plasma emission measure with age on the main sequence and decreasing rotational velocity. Variability and atmospheric inhomogeneity are commonly seen, and there is considerable evidence that magnetic fields define the geometry and control the energy balance in the outer atmospheric layers. In addition, the microwave observations imply that non-thermal electrons are confined in coronal magnetic flux tubes in at least the cool dwarfs and RS CVn systems. The chromospheres in the K and M giants and supergiants are geometrically extended, as are the coronae in the RS CVn systems and probably also in other stars.

Planetary Engulfment as a Trigger for White Dwarf Pollution

NASA Astrophysics Data System (ADS)

Petrovich, Cristobal; Muñoz, Diego J.

2017-01-01

The presence of a planetary system can shield a planetesimal disk from the secular gravitational perturbations due to distant outer massive objects (planets or stellar companions). As the host star evolves off the main sequence to become a white dwarf, these planets can be engulfed during the giant phase, triggering secular instabilities and leading to the tidal disruptions of small rocky bodies. These disrupted bodies can feed the white dwarfs with rocky material and possibly explain the high-metallicity material in their atmospheres. We illustrate how this mechanism can operate when the gravitational perturbations are due to the KL mechanism from a stellar binary companion, a process that is activated only after the planet has been removed/engulfed. We show that this mechanism can explain the observed accretion rates if: (1) the planetary engulfment happens rapidly compared to the secular timescale, which is generally the case for wide binaries (> 100 au) and planetary engulfment during the asymptotic giant branch; (2) the planetesimal disk has a total mass of ˜ {10}-4-{10}-2{M}\\oplus . We show that this new mechanism can provide a steady supply of material throughout the entire life of the white dwarfs for all cooling ages and can account for a large fraction (up to nearly half) of the observed polluted white dwarfs.

Characterization of the Mysteriously Cool Brown Dwarf HD 4113

NASA Astrophysics Data System (ADS)

Ednie, Michaela; Follette, Katherine; Ward-Duong, Kimberly

2018-01-01

Characterizing the physical properties of brown dwarfs is necessary to expand and improve our understanding of low mass companions, including exoplanets. Systems with both close radial velocity companions and distant directly imaged companions are particularly powerful in understanding planet formation mechanisms. Early in 2017, members of the SPHERE team discovered a companion brown dwarf in the HD 4113 system, which also contains a known RV planet. Atmospheric model fits to the Y and J-band spectra and H2/H3 photometry of the brown dwarf suggested it is unusually cool. We obtained new Magellan data in the Z and K’ bands in mid-2017. This data will help us to complete a more detailed atmospheric and astrometric characterization of this unusually cool companion. Broader wavelength coverage will help in accurate spectral typing and estimations of luminosity, temperature, surface gravity, radius, and composition. Additionally, a second astrometric epoch will help constrain the architecture of the system.

The Continuing Search for Variability Among Cool White Dwarfs

NASA Astrophysics Data System (ADS)

Schaefer, J. J.; Oswalt, T. D.; Johnston, K. B.; Rudkin, M.; Heinz, T.

2002-12-01

The Continuing Search for Variability Among Cool White Dwarfs Justin J. Schaefer University of Wyoming Department of Physics and Astronomy P.O. Box 3905 Laramie, Wyoming 82071 USA (schaefju@uwyo.edu) Terry D. Oswalt, Kyle Johnston, Merissa Rudkin, Tamalyn Heinz Florida Institute of Technology and the SARA Observatory Department of Physics & Space Sciences 150 West University Boulevard Melbourne, Florida 32901 USA (oswalt@luyten.astro.fit.edu, kyjohnst@fit.edu, mrudkin@astro.fit.edu, theinz@fit.edu) ABSTRACT We present BVRI photometry of eleven binaries with white dwarf (WD) components. The observations were obtained at the SARA 0.9-meter telescope on Kitt Peak during the summer of 2002. Standard system (B-V), (V-R) and (R-I) color indices of four white dwarfs were determined. This data will be used to estimate the WD cooling ages in wide WD+dM binaries, as part of our ongoing research program to determine the chromospheric activity-age relation for M dwarf stars. Time-series differential photometry was also collected for eight cool white dwarfs as part of a program to explore the variability in the low luminosity, low temperature regime of the WD cooling track. We failed to detect any variability greater than ~0.04 magnitudes in these stars. Several nights of differential photometry data were collected on the DAO WD + K dwarf short-period variable HS1136+6646. From the light variations we determined a likely orbital period of 0.825 +/-0.009 days. Strong evidence is presented for two other possible periods within this light curve, possibly indicative of rotational modulation by the WD component. We gratefully acknowledge support from the National Science Foundation, which funds the SARA Research Experiences for Undergraduates program via grant AST-0097616 to Florida Tech. One of us (TDO) also acknowledges partial support for this work from NASA (subcontract Y701296) and the NSF (AST 0206115).

Lithium in M67

NASA Technical Reports Server (NTRS)

Hobbs, L. M.; Pilachowski, Catherine

1986-01-01

Echelle spectra recorded at the Li I 6707-A line are reported for seven main-sequence members and one cool subgiant in M67. The spectral types of the seven dwarfs studied range from about F8 at the turnoff point to about G5. The principal result is that the average lithium abundance in the three hottest main-sequence stars is 0.45 x 10 to the -9th. Any enrichment of lithium in the gas of the Galactic disk in the last 5 Gyr therefore has not exceeded a factor of about two and probably is entirely negligible, when the corresponding results for NGC 752 and the Hyades are taken into account.

The Temperature and Cooling Age of the White Dwarf Companion to the Millisecond Pulsar PSR B1855+09.

PubMed

van Kerkwijk MH; Bell; Kaspi; Kulkarni

2000-02-10

We report on Keck and Hubble Space Telescope observations of the binary millisecond pulsar PSR B1855+09. We detect its white dwarf companion and measure mF555W=25.90+/-0.12 and mF814W=24.19+/-0.11 (Vega system). From the reddening-corrected color, (mF555W-mF814W&parr0;0=1.06+/-0.21, we infer a temperature Teff=4800+/-800 K. The white dwarf mass is known accurately from measurements of the Shapiro delay of the pulsar signal, MC=0.258+0.028-0.016 M middle dot in circle. Hence, given a cooling model, one can use the measured temperature to determine the cooling age. The main uncertainty in the cooling models for such low-mass white dwarfs is the amount of residual nuclear burning, which is set by the thickness of the hydrogen layer surrounding the helium core. From the properties of similar systems, it has been inferred that helium white dwarfs form with thick hydrogen layers, with mass greater, similar3x10-3 M middle dot in circle, which leads to significant additional heating. This is consistent with expectations from simple evolutionary models of the preceding binary evolution. For PSR B1855+09, though, such models lead to a cooling age of approximately 10 Gyr, which is twice the spin-down age of the pulsar. It could be that the spin-down age were incorrect, which would call the standard vacuum dipole braking model into question. For two other pulsar companions, however, ages well over 10 Gyr are inferred, indicating that the problem may lie with the cooling models. There is no age discrepancy for models in which the white dwarfs are formed with thinner hydrogen layers ( less, similar3x10-4 M middle dot in circle).

The lithium-rotation connection in the 125 Myr-old Pleiades cluster

NASA Astrophysics Data System (ADS)

Bouvier, J.; Barrado, D.; Moraux, E.; Stauffer, J.; Rebull, L.; Hillenbrand, L.; Bayo, A.; Boisse, I.; Bouy, H.; DiFolco, E.; Lillo-Box, J.; Calderón, M. Morales

2018-06-01

Context. The evolution of lithium abundance over a star's lifetime is indicative of transport processes operating in the stellar interior. Aims: We revisit the relationship between lithium content and rotation rate previously reported for cool dwarfs in the Pleiades cluster. Methods: We derive new LiI 670.8 nm equivalent width measurements from high-resolution spectra obtained for low-mass Pleiades members. We combine these new measurements with previously published ones, and use the Kepler K2 rotational periods recently derived for Pleiades cool dwarfs to investigate the lithium-rotation connection in this 125 Myr-old cluster. Results: The new data confirm the correlation between lithium equivalent width and stellar spin rate for a sample of 51 early K-type members of the cluster, where fast rotating stars are systematically lithium-rich compared to slowly rotating ones. The correlation is valid for all stars over the (J-Ks) color range 0.50-0.70 mag, corresponding to a mass range from about 0.75 to 0.90 M⊙, and may extend down to lower masses. Conclusions: We argue that the dispersion in lithium equivalent widths observed for cool dwarfs in the Pleiades cluster reflects an intrinsic scatter in lithium abundances, and suggest that the physical origin of the lithium dispersion pattern is to be found in the pre-main sequence rotational history of solar-type stars. Based on observations made at Observatoire de Haute Provence (CNRS), France, at the Nordic Optical Telescope (IAC), Spain, and at the W. M. Keck Observatory, Hawaii, USA.Full Table B.1 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/613/A63

Characterizing K2 Planetary Systems Orbiting Cool Dwarfs

NASA Astrophysics Data System (ADS)

Dressing, Courtney D.; Newton, Elisabeth R.; Schlieder, Joshua; Vanderburg, Andrew; Charbonneau, David; Knutson, Heather; K2C2

2017-01-01

The NASA K2 mission is using the repurposed Kepler spacecraft to search for transiting planets in multiple fields along the ecliptic plane. K2 observes 10,000 - 30,000 stars in each field for roughly 80 days, which is too short to observe multiple transits of planets in the habitable zones of Sun-like stars, but long enough to detect potentially habitable planets orbiting low-mass dwarfs. Accordingly, M and K dwarfs are frequently nominated as K2 Guest Observer targets and K2 has already observed significantly more low-mass stars than the original Kepler mission. While the K2 data are therefore an enticing resource for studying the properties and frequency of planetary systems orbiting low-mass stars, many K2 cool dwarfs are not well-characterized. We are refining the properties of K2 planetary systems orbiting cool dwarfs by acquiring medium-resolution NIR spectra with SpeX on the IRTF and TripleSpec on the Palomar 200". In our initial sample of 144 potential cool dwarfs hosting candidate planetary systems detected by K2, we noted a high contamination rate from giants (16%) and reddened hotter dwarfs (31%). After employing empirically-based relations to determine the temperatures, radii, masses, luminosities, and metallicities of K2 planet candidate host stars, we found that our new cool dwarf radius estimates were 10-40% larger than the initial values, indicating that the radii of the associated planet candidates were also underestimated. Refining the stellar parameters allows us to identify astrophysical false positives and better constrain the radii and insolation flux environments of bona fide transiting planets. I will present our resulting catalog of system properties and highlight the most attractive K2 planets for radial velocity mass measurement and atmospheric characterization with Spitzer, HST, JWST, and the next generation of extremely large ground- and space-based telescopes. We gratefully acknowledge funding from the NASA Sagan Fellowship Program, the NASA K2 Guest Observer Program, the NASA XRP Program, the John Templeton Foundation, the National Science Foundation Astronomy & Astrophysics Postdoctoral Program, and the National Science Foundation Graduate Research Fellowship Program.

White Dwarf Stars

NASA Astrophysics Data System (ADS)

Kepler, S. O.

2014-10-01

White dwarfs are the evolutionary endpoint for nearly 95% of all stars born in our Galaxy, the final stages of evolution of all low- and intermediate mass stars, i.e., main sequence stars with masses below (8.5± 1.5) M_{odot}, depending on metallicity of the progenitor, mass loss and core overshoot. Massive white dwarfs are intrinsically rare objects, tand produce a gap in the determination of the initial vs. final mass relation at the high mass end (e.g. Weidemann 2000 A&A, 363, 647; Kalirai et al. 2008, ApJ, 676, 594; Williams, Bolte & Koester 2009, ApJ, 693, 355). Main sequences stars with higher masses will explode as SNII (Smartt S. 2009 ARA&A, 47, 63), but the limit does depend on the metallicity of the progenitor. Massive white dwarfs are probably SNIa progenitors through accretion or merger. They are rare, being the final product of massive stars (less common) and have smaller radius (less luminous). Kepler et al. 2007 (MNRAS, 375, 1315), Kleinman et al. 2013 (ApJS, 204, 5) estimate only 1-2% white dwarfs have masses above 1 M_{odot}. The final stages of evolution after helium burning are a race between core growth and loss of the H-rich envelope in a stellar wind. When the burning shell is exposed, the star rapidly cools and burning ceases, leaving a white dwarf. As they cool down, the magnetic field freezes in, ranging from a few kilogauss to a gigagauss. Peculiar type Ia SN 2006gz, SN 2007if, SN 2009dc, SN 2003fg suggest progenitors in the range 2.4-2.8 M_{odot}, and Das U. & Mukhopadhyay B. (2012, Phys. Rev. D, 86, 042001) estimate that the Chandrasekhar limit increases to 2.3-2.6 M_{odot} for extremely high magnetic field stars, but differential rotation induced by accretion could also increase it, according to Hachisu I. et al. 2012 (ApJ, 744, 69). García-Berro et al. 2012, ApJ, 749, 25, for example, proposes double degenerate mergers are the progenitors of high-field magnetic white dwarfs. We propose magnetic fields enhance the line broadening in WDs, causing an overestimated surface gravity, and ultimately determine if these magnetic fields are likely developed through the star's own surface convection zone, or inherited from massive Ap/Bp progenitors. We discovered around 20 000 spectroscopic white dwarfs with the Sloan Digital Sky Survey (SDSS), with a corresponding increase in relatively rare varieties of white dwarfs, including the massive ones (Kleinman et al. 2013, ApJS, 204, 5, Kepler et al. 2013, MNRAS, 439, 2934). The mass distributions of the hydrogen-rich (DA) measured from fitting the spectra with model atmospheres calculated using unidimensinal mixing lenght-theory (MLT) shows the average mass (as measured by the surface gravity) increases apparently below 13 000K for DAs (e.g. Bergeron et al. 1991, ApJ, 367, 253; Tremblay et al. 2011, ApJ, 730, 128; Kleinman et al. 2013). Only with the tridimensional (3D) convection calculations of Tremblay et al. 2011 (A&A, 531, L19) and 2013 (A&A, 552, 13; A&A, 557, 7; arXiv 1309.0886) the problem has finally been solved, but the effects of magnetic fields are not included yet in the mass determinations. Pulsating white dwarf stars are used to measure their interior and envelope properties through seismology, and together with the luminosity function of white dwarf stars in clusters and around the Sun are valuable tools for the study of high density physics, and the history of stellar formation.

Asteroseismology of White Dwarf Stars

NASA Technical Reports Server (NTRS)

Hansen, Carl J.

1997-01-01

The primary purpose of this investigation has been to study various aspects of multimode pulsations in variable white dwarfs. In particular, nonlinear interactions among pulsation modes in white dwarfs (and, to some extent, in other variable stars), analysis of recent observations where such interactions are important, and preliminary work on the effects of crystallization in cool white dwarfs are reported.

VizieR Online Data Catalog: NGC 6802 dwarf cluster members and non-members (Tang+, 2017)

NASA Astrophysics Data System (ADS)

Tang, B.; Geisler, D.; Friel, E.; Villanova, S.; Smiljanic, R.; Casey, A. R.; Randich, S.; Magrini, L.; San, Roman I.; Munoz, C.; Cohen, R. E.; Mauro, F.; Bragaglia, A.; Donati, P.; Tautvaisiene, G.; Drazdauskas, A.; Zenoviene, R.; Snaith, O.; Sousa, S.; Adibekyan, V.; Costado, M. T.; Blanco-Cuaresma, S.; Jimenez-Esteban, F.; Carraro, G.; Zwitter, T.; Francois, P.; Jofre, P.; Sordo, R.; Gilmore, G.; Flaccomio, E.; Koposov, S.; Korn, A. J.; Lanzafame, A. C.; Pancino, E.; Bayo, A.; Damiani, F.; Franciosini, E.; Hourihane, A.; Lardo, C.; Lewis, J.; Monaco, L.; Morbidelli, L.; Prisinzano, L.; Sacco, G.; Worley, C. C.; Zaggia, S.

2016-11-01

The dwarf stars in NGC 6802 observed by GIRAFFE spectrograph are separated into four tables: 1. cluster members in the lower main sequence; 2. cluster members in the upper main sequence; 3. non-member dwarfs in the lower main sequence; 4. non-member dwarfs in the upper main sequence. The star coordinates, V band magnitude, V-I color, and radial velocity are given. (4 data files).

Building Magnetic Fields in White Dwarfs

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-03-01

White dwarfs, the compact remnants left over at the end of low- and medium-mass stars lifetimes, are often found to have magnetic fields with strengths ranging from thousands to billions of times that of Earth. But how do these fields form?MultiplePossibilitiesAround 1020% of white dwarfs have been observed to have measurable magnetic fields with a wide range of strengths. There are several theories as to how these fields might be generated:The fields are fossil.The original weak magnetic fields of the progenitor stars were amplified as the stars cores evolved into white dwarfs.The fields are caused by binary interactions.White dwarfs that formed in the merger of a binary pair might have had a magnetic field amplified as a result of a dynamo that was generated during the merger.The fields were produced by some other internal physical mechanism during the cooling of the white dwarf itself.In a recent publication, a team of authors led by Jordi Isern (Institute of Space Sciences, CSIC, and Institute for Space Studies of Catalonia, Spain) explored this third possibility.Dynamos from CrystallizationThe inner and outer boundaries of the convective mantle of carbon/oxygen white dwarfs of two different masses (top vs. bottom panel) as a function of luminosity. As the white dwarf cools (toward the right), the mantle grows thinner due to the crystallization and settling of material. [Isern et al. 2017]As white dwarfs have no nuclear fusion at their centers, they simply radiate heat and gradually cool over time. The structure of the white dwarf undergoes an interesting change as it cools, however: though the object begins as a fluid composed primarily of an ionized mixture of carbon and oxygen (and a few minor species like nickel and iron), it gradually crystallizes as its temperature drops.The crystallized phase of the white dwarf is oxygen-rich which is denser than the liquid, so the crystallized material sinks to the center of the dwarf as it solidifies. As a result, the white dwarf forms a solid, oxygen-rich core with a liquid, carbon-rich mantle thats Rayleigh-Taylor unstable: as crystallization continues, the solids continue to sink out of the mantle.By analytically modeling this process, Isern and collaborators demonstrate that the Rayleigh-Taylor instabilities in the convective mantle can drive a dynamo large enough to generate the magnetic field strengths weve observed in white dwarfs.Magnetic field density as a function of the dynamo energy density. The plots show Earth and Jupiter (black dots), T Tauri stars (cyan), M dwarf stars (magenta), and two types of white dwarfs (blue and red). Do these lie on the same scaling relation? [Isern et al. 2017]A Universal Process?This setup the solid core with an unstable liquid mantle on top is exactly the structure expected to occur in planets such as Earth and Jupiter. These planets magnetic fields are similarly thought to be generated by convective dynamos powered by the cooling and chemical separation of their interiors and the process can also be scaled up to account for the magnetic fields of fully convective objects like T Tauri stars, as well.If white-dwarf magnetic fields are generated by the same type of dynamo, this may be a universal process for creating magnetic fields in astrophysical objects though other processes may well be at work too.CitationJordi Isern et al 2017 ApJL 836 L28. doi:10.3847/2041-8213/aa5eae

A Panchromatic View of Brown Dwarf Aurorae

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pineda, J. Sebastian; Hallinan, Gregg; Kao, Melodie M.

Stellar coronal activity has been shown to persist into the low-mass star regime, down to late M-dwarf spectral types. However, there is now an accumulation of evidence suggesting that at the end of the main sequence, there is a transition in the nature of the magnetic activity from chromospheric and coronal to planet-like and auroral, from local impulsive heating via flares and MHD wave dissipation to energy dissipation from strong large-scale magnetospheric current systems. We examine this transition and the prevalence of auroral activity in brown dwarfs through a compilation of multiwavelength surveys of magnetic activity, including radio, X-ray, andmore » optical. We compile the results of those surveys and place their conclusions in the context of auroral emission as a consequence of large-scale magnetospheric current systems that accelerate energetic electron beams and drive the particles to impact the cool atmospheric gas. We explore the different manifestations of auroral phenomena, like H α , in brown dwarf atmospheres and define their distinguishing characteristics. We conclude that large-amplitude photometric variability in the near-infrared is most likely a consequence of clouds in brown dwarf atmospheres, but that auroral activity may be responsible for long-lived stable surface features. We report a connection between auroral H α emission and quiescent radio emission in electron cyclotron maser instability pulsing brown dwarfs, suggesting a potential underlying physical connection between quiescent and auroral emissions. We also discuss the electrodynamic engines powering brown dwarf aurorae and the possible role of satellites around these systems both to power the aurorae and seed the magnetosphere with plasma.« less

A Panchromatic View of Brown Dwarf Aurorae

NASA Astrophysics Data System (ADS)

Pineda, J. Sebastian; Hallinan, Gregg; Kao, Melodie M.

2017-09-01

Stellar coronal activity has been shown to persist into the low-mass star regime, down to late M-dwarf spectral types. However, there is now an accumulation of evidence suggesting that at the end of the main sequence, there is a transition in the nature of the magnetic activity from chromospheric and coronal to planet-like and auroral, from local impulsive heating via flares and MHD wave dissipation to energy dissipation from strong large-scale magnetospheric current systems. We examine this transition and the prevalence of auroral activity in brown dwarfs through a compilation of multiwavelength surveys of magnetic activity, including radio, X-ray, and optical. We compile the results of those surveys and place their conclusions in the context of auroral emission as a consequence of large-scale magnetospheric current systems that accelerate energetic electron beams and drive the particles to impact the cool atmospheric gas. We explore the different manifestations of auroral phenomena, like Hα, in brown dwarf atmospheres and define their distinguishing characteristics. We conclude that large-amplitude photometric variability in the near-infrared is most likely a consequence of clouds in brown dwarf atmospheres, but that auroral activity may be responsible for long-lived stable surface features. We report a connection between auroral Hα emission and quiescent radio emission in electron cyclotron maser instability pulsing brown dwarfs, suggesting a potential underlying physical connection between quiescent and auroral emissions. We also discuss the electrodynamic engines powering brown dwarf aurorae and the possible role of satellites around these systems both to power the aurorae and seed the magnetosphere with plasma.

Could Ultracool Dwarfs Have Sun-Like Activity?

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-11-01

Solar-like stars exhibit magnetic cycles; our Sun, for instance, displays an 11-year period in its activity, manifesting as cyclic changes in radiation levels, the number of sunspots and flares, and ejection of solar material. Over the span of two activity cycles, the Suns magnetic field flips polarity and then returns to its original state.An artists illustration comparing the Sun to TRAPPIST-1, an ultracool dwarf star known to host several planets. [ESO]But what about the magnetic behavior of objects near the cooler end of the stellar main sequence do they exhibit similar activity cycles?Effects of a Convecting InteriorDwarf stars have made headlines in recent years due to their potential to harbor exoplanets. Because these cooler stars have lower flux levels compared to the Sun, their habitable zones lie much closer to the stars. The magnetic behavior of these stars is therefore important to understand: could ultracool dwarfs exhibit solar-like activity cycles that would affect planets with close orbits?The differences in internal structure between different mass stars. Ultracool dwarfs have fully convective interiors. [www.sun.org]Theres a major difference between ultracool dwarfs (stars of spectral type higher than M7 and brown dwarfs) and Sun-like stars: their internal structures. Sun-like stars have a convective envelope that surrounds a radiative core. The interiors of cool, low-mass objects, on the other hand, are fully convective.Based on theoretical studies of how magnetism is generated in stars, its thought that the fully convective interiors of ultracool dwarfs cant support large-scale magnetic field formation. This should prevent these stars from exhibiting activity cycles like the Sun. But recent radio observations of dwarf stars have led scientist Matthew Route (ITaP Research Computing, Purdue University) to question these models.A Reversing Field?During observations of the brown dwarf star J1047+21 in 20102011, radio flares were detected with emission primarily polarized in a single direction. The dwarfs flares in late 2013, however, all showed polarization in the opposite direction. Could this be an indication that J1047+21 has a stable, global dipolar field that flipped polarity in between the two sets of observations? If so, this could mean that the star has a magnetic cycle similar to the Suns.Artists impression showing the relative sizes and colors of the Sun, a red dwarf (M-dwarf), a hotter brown dwarf (L-dwarf), a cool brown dwarf (T-dwarf) similar to J1047+21, and the planet Jupiter [Credit: NASA/IPAC/R. Hurt (SSC)]Inspired by this possibility, Route conducted an investigation of the long-term magnetic behavior of all known radio-flaring ultracool dwarfs, a list of 14 stars. Using polarized radio emission measurements, he found that many of his targets exhibited similar polarity flips, which he argues is evidence that these dwarfs are undergoing magnetic field reversals on roughly decade-long timescales, analogous to those reversals that occur in the Sun.If this is indeed true, then we need to examine our models of how magnetic fields are generated in stars: the interface between the radiative and convective layers may not be necessary to produce large-scale magnetic fields. Understanding this process is certainly an important step in interpreting the potential habitability of planets around ultracool dwarfs.CitationMatthew Route 2016 ApJL 830 L27. doi:10.3847/2041-8205/830/2/L27

Atmospheric Properties Of T Dwarfs Inferred From Model Fits At Low Spectral Resolution

NASA Astrophysics Data System (ADS)

Giorla Godfrey, Paige A.; Rice, Emily L.; Filippazzo, Joseph C.; Douglas, Stephanie E.

2016-09-01

Brown dwarf spectral types (M, L, T, Y) correlate with spectral morphology, and generally appear to correspond with decreasing mass and effective temperature (Teff). Model fits to observed spectra suggest, however, that spectral subclasses do not share this monotonic temperature correlation, indicating that secondary parameters (gravity, metallicity, dust) significantly influence spectral morphology. We seekto disentangle the fundamental parameters that underlie the spectral type sequence of the coolest fully populated spectral class of brown dwarfs using atmosphere models. We investigate the relationship between spectral type and best fit model parameters for a sample of over 150 T dwarfs with low resolution (R 75-100) near-infrared ( 0.8-2.5 micron) SpeX Prism spectra. We use synthetic spectra from four model grids (Saumon & Marley 2008, Morley+ 2012, Saumon+ 2012, BT Settl 2013) and a Markov-Chain Monte Carlo (MCMC) analysis to determine robust best fit parameters and their uncertainties. We compare the consistency of each model grid by performing our analysis on the full spectrum and also on individual wavelength bands (Y,J,H,K). We find more consistent results between the J band and full spectrum fits and that our best fit spectral type-Teff results agree with the polynomial relationships of Stephens+2009 and Filippazzo+ 2015 using bolometric luminosities. Our analysis consists of the most extensive low resolution T dwarf model comparison to date, and lays the foundation for interpretation of cool brown dwarf and exoplanet spectra.

Some aspects of cool main sequence star ages derived from stellar rotation (gyrochronology)

NASA Astrophysics Data System (ADS)

Barnes, S. A.; Spada, F.; Weingrill, J.

2016-09-01

Rotation periods for cool stars can be measured with good precision by monitoring starspot light modulation. Observations have shown that the rotation periods of dwarf stars of roughly solar metallicity have such systematic dependencies on stellar age and mass that they can be used to derive reliable ages, a procedure called gyrochronology. We review the method and show illustrative cases, including recent ground- and space-based data. The age uncertainties approach 10 % in the best cases, making them a valuable complement to, and constraint on, asteroseismic or other ages. Edited, updated, and refereed version of a presentation at the WE-Heraeus-Seminar in Bad Honnef, Germany: Reconstructing the Milky Way's History: Spectroscopic Surveys, Asteroseismology and Chemodynamical Models

Collecting Brown Dwarfs in the Night Sky

NASA Image and Video Library

2010-11-09

The green dot in the middle of this image might look like an emerald amidst glittering diamonds, but is a dim star belonging to a class called brown dwarfs; it is the first ultra-cool brown dwarf discovered by NASA Wide-field Infrared Survey Explorer.

Stationary radiation hydrodynamics of accreting magnetic white dwarfs.

NASA Astrophysics Data System (ADS)

Woelk, U.; Beuermann, K.

1996-02-01

Using an artificial viscosity, we solved the one-dimensional time-independent two-fluid hydrodynamic equations simultaneously to the fully frequency and angle dependent radiation transport in an accretion flow directed towards the surface of a magnetic white dwarf. We consider energy transfer from ions to electrons by Coulomb encounters and cooling by bremsstrahlung and by cyclotron radiation in fields between B=5 and 70MG. Electron and ion temperatures relax in the post-shock regime and the cooling flow settles onto the white dwarf surface. For high mass flow rates ˙(m) (in g/cm^2^/s), cooling takes place mainly by bremsstrahlung and the solutions approach the non-magnetic case. For low ˙(m) and high B, cooling is dominated by cyclotron radiation which causes the thickness of the cooling region to collapse by 1-2 orders of magnitude compared to the non-magnetic case. The electron temperature behind the shock drops from a few 10^8^ to a few 10^7^K and the ratio of cyclotron vs. total radiative flux approaches unity. For high ˙(m) and low B values, bremsstrahlung dominates, but cyclotron losses can never be neglected. We find a smooth transition from particle-heated to shock-heated atmospheres in the maximum electron temperature and also in the thickness of the heated layer. With these results, the stationary radiation-hydrodynamics of accreting magnetic white dwarfs with cyclotron and bremsstrahlung cooling has been solved for the whole range of observed mass flow rates and field strengths.

Magnetic field evolution in white dwarfs: The hall effect and complexity of the field

NASA Technical Reports Server (NTRS)

Muslimov, A. G.; Van Horn, H. M.; Wood, M. A.

1995-01-01

We calculate the evolution of the magnetic fields in white dwarfs, taking into account the Hall effect. Because this effect depends nonlinearly upon the magnetic field strength B, the time dependences of the various multipole field components are coupled. The evolution of the field is thus significantly more complicated than has been indicated by previous investigations. Our calculations employ recent white dwarf evolutionary sequences computed for stars with masses 0.4, 0.6, 0.8, and 1.0 solar mass. We show that in the presence of a strong (up to approximately 10(exp 9) G) internal toroidal magnetic field; the evolution of even the lowest order poloidal modes can be substantially changed by the Hall effect. As an example, we compute the evolution of an initially weak quadrupole component, which we take arbitrarily to be approximately 0.1%-1% of the strength of a dominant dipole field. We find that coupling provided by the Hall effect can produce growth of the ratio of the quadrupole to the dipole component of the surface value of the magnetic field strength by more than a factor of 10 over the 10(exp 9) to 10(exp 10) year cooling lifetime of the white dwarf. Some consequences of these results for the process of magnetic-field evolution in white dwarfs are briefly discussed.

Evolution models of helium white dwarf-main-sequence star merger remnants: the mass distribution of single low-mass white dwarfs

NASA Astrophysics Data System (ADS)

Zhang, Xianfei; Hall, Philip D.; Jeffery, C. Simon; Bi, Shaolan

2018-02-01

It is not known how single white dwarfs with masses less than 0.5Msolar -- low-mass white dwarfs -- are formed. One way in which such a white dwarf might be formed is after the merger of a helium-core white dwarf with a main-sequence star that produces a red giant branch star and fails to ignite helium. We use a stellar-evolution code to compute models of the remnants of these mergers and find a relation between the pre-merger masses and the final white dwarf mass. Combining our results with a model population, we predict that the mass distribution of single low-mass white dwarfs formed through this channel spans the range 0.37 to 0.5Msolar and peaks between 0.45 and 0.46Msolar. Helium white dwarf--main-sequence star mergers can also lead to the formation of single helium white dwarfs with masses up to 0.51Msolar. In our model the Galactic formation rate of single low-mass white dwarfs through this channel is about 8.7X10^-3yr^-1. Comparing our models with observations, we find that the majority of single low-mass white dwarfs (<0.5Msolar) are formed from helium white dwarf--main-sequence star mergers, at a rate which is about $2$ per cent of the total white dwarf formation rate.

Spitzer Spectroscopy of Low-Mass Dwarfs - Clouds and Chemistry at the Bottom of the IMF

NASA Technical Reports Server (NTRS)

Roellig, Thomas L.

2006-01-01

Brown dwarfs and low-mass stars show evidence of complicated atmospheres, including a variety of molecular species and clouds. Infrared observations are one of the best probes of the physics of these objects, but up until recently these observations have been limited in studies from ground-based telescopes by atmospheric absorption and insufficient sensitivity. With the launch of the Spitzer Space Telescope with its Infrared Spectrograph (IRS) instrument we now have the capability to undertake a systematic study of the atmospheric structure and chemistry in these cool objects. The IRS Dim Suns team has compiled spectra from objects ranging from M1 dwarfs with effective temperatures 3,800K of down to T8 dwarfs with effective temperatures of 700. This talk will present these results and discuss their implications for our understanding of cool dwarf atmospheric physics and structure.

Project 1640 observations of the white dwarf HD 114174 B

NASA Astrophysics Data System (ADS)

Bacchus, E.; Parry, I. R.; Oppenheimer, R.; Aguilar, J.; Beichman, C.; Brenner, D.; Burruss, R.; Cady, E.; Luszcz-Cook, S.; Crepp, J.; Dekany, R.; Gianninas, A.; Hillenbrand, L.; Kilic, M.; King, D.; Lockhart, T. G.; Matthews, C. T.; Nilsson, R.; Pueyo, L.; Rice, E. L.; Roberts, L. C.; Sivaramakrishnan, A.; Soummer, R.; Vasisht, G.; Veicht, A.; Zhai, C.; Zimmerman, N. T.

2017-08-01

We present the first near infrared spectrum of the faint white dwarf companion HD 114174 B, obtained with Project 1640. Our spectrum, covering the Y, J and H bands, combined with previous TaRgetting bENchmark-objects with Doppler Spectroscopy (TRENDS) photometry measurements, allows us to place further constraints on this companion. We suggest two possible scenarios; either this object is an old, low-mass, cool H atmosphere white dwarf with Teff ˜ 3800 K or a high-mass white dwarf with Teff > 6000 K, potentially with an associated cool (Teff ˜ 700 K) brown dwarf or debris disc resulting in an infrared excess in the L΄ band. We also provide an additional astrometry point for 2014 June 12 and use the modelled companion mass combined with the radial velocity and direct imaging data to place constraints on the orbital parameters for this companion.

Clouds and hazes in exoplanets and brown dwarfs

NASA Astrophysics Data System (ADS)

Morley, Caroline Victoria

The formation of clouds significantly alters the spectra of cool substellar atmospheres from terrestrial planets to brown dwarfs. In cool planets like Earth and Jupiter, volatile species like water and ammonia condense to form ice clouds. In hot planets and brown dwarfs, iron and silicates instead condense, forming dusty clouds. Irradiated methane-rich planets may have substantial hydrocarbon hazes. During my dissertation, I have studied the impact of clouds and hazes in a variety of substellar objects. First, I present results for cool brown dwarfs including clouds previously neglected in model atmospheres. Model spectra that include sulfide and salt clouds can match the spectra of T dwarf atmospheres; water ice clouds will alter the spectra of the newest and coldest brown dwarfs, the Y dwarfs. These sulfide/salt and ice clouds potentially drive spectroscopic variability in these cool objects, and this variability should be distinguishable from variability caused by hot spots. Next, I present results for small, cool exoplanets between the size of Earth and Neptune. They likely have sulfide and salt clouds and also have photochemical hazes caused by stellar irradiation. Vast resources have been dedicated to characterizing the handful of super Earths and Neptunes accessible to current telescopes, yet of the planets smaller than Neptune studied to date, all have radii in the near-infrared consistent with being constant in wavelength, likely showing that these small planets are consistently enshrouded in thick hazes and clouds. For the super Earth GJ 1214b, very thick, lofted clouds of salts or sulfides in high metallicity (1000x solar) atmospheres create featureless transmission spectra in the near-infrared. Photochemical hazes also create featureless transmission spectra at lower metallicities. For the Neptune-sized GJ 436b, its thermal emission and transmission spectra combine indicate a high metallicity atmosphere, potentially heated by tides and affected by disequilibrium chemistry. I show that despite the challenges, there are promising avenues for understanding small planets: by observing thermal emission and reflected light, we can break the degeneracies and con- strain the atmospheric compositions. These future observations will provide rich diagnostics of molecules and clouds in small planets.

White Dwarfs in Wide Binaries and the Age of the Galaxy

NASA Astrophysics Data System (ADS)

Smith, John Allyn

A comprehensive study of common proper binary systems suspected of containing white dwarf stars is being conducted by Oswalt and collaborators (Oswalt et al. 1988). These systems usually contain a white dwarf and a main sequence star. In the present study, we use the white dwarf luminosity function to determine the age of the local Galactic disk as well as the local space density of white dwarfs. We obtained BVRI photometry of approximately 475 systems (of 512) which were found to contain about 325 white dwarfs. Of these white dwarfs, 152 met the selection criteria for our study and were used in the final analysis. Using this largest sample of cool white dwarfs in binary systems observed to date, we have determined an age for the Galactic disk of 9.7-0.8+0.9 Gyr which yields a lower limit age for the Universe of about 11.7 Gyr. Recent globular cluster studies agree to within ±1σ for the Galaxy age derived from our Disk age. The latest cosmologically derived age for the Universe, modified for the recently released Hipparcos data, is now in accordance with our age estimates for the Universe, for H o (69 km s-1 Mpc-1) and an inflationary cosmology. Further, our age is in accord with the ages derived for the Galaxy from nucleocomsochronology and meteoritic sample analyses. As a part of this work, we have determined the white dwarf space density to be 4.5 ± 1.0 10-3 pc-3, in accord with the results previously reported by Liebert, Dahn & Monet (1987). This space density corresponds to a white dwarf birthrate of 4.65 × 10-13 yr-1 pc-3. This research also details a unique approach to calculating and correcting for the incompleteness of a proper motion and magnitude selected stellar sample.

Climate model studies of synchronously rotating planets.

PubMed

Joshi, Manoj

2003-01-01

M stars constitute 75% of main sequence stars though, until recently, their star systems have not been considered suitable places for habitable planets to exist. In this study the climate of a synchronously rotating planet around an M dwarf star is evaluated using a three-dimensional global atmospheric circulation model. The presence of clouds and evaporative cooling at the surface of the planet result in a cooler surface temperature at the subsolar point. Water ice forms at the polar regions and on the dark side, where the minimum temperature lies between -30 degrees C and 0 degrees C. As expected, rainfall is extremely high on the starlit side and extremely low on the dark side. The presence of a dry continent causes higher temperatures on the dayside, and allows accumulation of snow on the nightside. The absence of any oceans leads to higher day-night temperature differences, consistent with previous work. The present study reinforces recent conclusions that synchronously rotating planets within the circumstellar habitable zones of M dwarf stars should be habitable, and therefore M dwarf systems should not be excluded in future searches for exoplanets.

A Chandra Search for Coronal X Rays from the Cool White Dwarf GD 356

NASA Technical Reports Server (NTRS)

Weisskopf, Martin C.; Wu, Kinwah; Trimble, Virginia; ODell, Stephen L.; Elsner, Ronald F.; Zavlin, Vyacheslav E.; Kouveliotou, Chryssa

2006-01-01

We report observations with the Chandra X-ray Observatory of the single, cool, magnetic white dwarf GD 356. For consistent comparison with other X-ray observations of single white dwarfs, we also re-analyzed archival ROSAT data for GD 356 (GJ 1205), G 99-47 (GR 290 = V1201 Ori), GD 90, G 195-19 (EG250 = GJ 339.1), and WD 2316+123 and archival Chandra data for LHS 1038 (GJ 1004) and GD 358 (V777 Her). Our Chandra observation detected no X rays from GD 356, setting the most restrictive upper limit to the X-ray luminosity from any cool white dwarf - Lx less than 6.0 x 10(exp 25) erg s(sup -1), at 99.7% confidence, for a 1- keV thermal-bremsstrahlung spectrum. The corresponding limit to the electron density is no less than 4.4x10(exp 11) per cubic centimeter. Our re-analysis of the archival data confirmed the non-detections reported by the original investigators. We discuss the implications of our and prior observations on models for coronal emission from white dwarfs. For magnetic white dwarfs, we emphasize the more stringent constraints imposed by cyclotron radiation. In addition, we describe (in an appendix) a statistical methodology for detecting a source and for constraining the strength of a source, which applies even when the number of source or background events is small.

Observations of the Ultraviolet Spectra of Carbon White Dwarfs

NASA Technical Reports Server (NTRS)

Wagner, G. A.

1982-01-01

Strong ultraviolet carbon lines were detected in additional white DC (continuous visual spectra) dwarfs using the IUE. These lines are not seen in the ultraviolet spectrum of the cool DC star Stein 2051 B. The bright DA white dwarf LB 3303 has a strong unidentified absorption near lambda 1400.

On the Spectral Evolution of Helium-atmosphere White Dwarfs Showing Traces of Hydrogen

NASA Astrophysics Data System (ADS)

Rolland, B.; Bergeron, P.; Fontaine, G.

2018-04-01

We present a detailed spectroscopic analysis of 115 helium-line (DB) and 28 cool, He-rich hydrogen-line (DA) white dwarfs based on atmosphere fits to optical spectroscopy and photometry. We find that 63% of our DB population show hydrogen lines, making them DBA stars. We also demonstrate the persistence of pure DB white dwarfs with no detectable hydrogen feature at low effective temperatures. Using state-of-the art envelope models, we next compute the total quantity of hydrogen, M H, that is contained in the outer convection zone as a function of effective temperature and atmospheric H/He ratio. We find that some (T eff, M H) pairs cannot physically exist as a homogeneously mixed structure; such a combination can only occur as stratified objects of the DA spectral type. On that basis, we show that the values of M H inferred for the bulk of the DBA stars are too large and incompatible with the convective dilution scenario. We also present evidence that the hydrogen abundances measured in DBA and cool, helium-rich white dwarfs cannot be globally accounted for by any kind of accretion mechanism onto a pure DB star. We suggest that cool, He-rich DA white dwarfs are most likely created by the convective mixing of a DA star with a thin hydrogen envelope; they are not cooled down DBAs. We finally explore several scenarios that could account for the presence of hydrogen in DBA stars.

White Dwarfs in the UKIRT Infrared Deep Sky Survey Data Release 9

NASA Astrophysics Data System (ADS)

Tremblay, P.-E.; Leggett, S. K.; Lodieu, N.; Freytag, B.; Bergeron, P.; Kalirai, J. S.; Ludwig, H.-G.

2014-06-01

We have identified 8 to 10 new cool white dwarfs from the Large Area Survey (LAS) Data Release 9 of the United Kingdom InfraRed Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS). The data set was paired with the Sloan Digital Sky Survey to obtain proper motions and a broad ugrizYJHK wavelength coverage. Optical spectroscopic observations were secured at Gemini Observatory and confirm the degenerate status for eight of our targets. The final sample includes two additional white dwarf candidates with no spectroscopic observations. We rely on improved one-dimensional model atmospheres and new multi-dimensional simulations with CO5BOLD to review the stellar parameters of the published LAS white dwarf sample along with our additional discoveries. Most of the new objects possess very cool atmospheres with effective temperatures below 5000 K, including two pure-hydrogen remnants with a cooling age between 8.5 and 9.0 Gyr, and tangential velocities in the range 40 km s-1 <=v tan <= 60 km s-1. They are likely thick disk 10-11 Gyr old objects. In addition, we find a resolved double degenerate system with v tan ~ 155 km s-1 and a cooling age between 3.0 and 5.0 Gyr. These white dwarfs could be disk remnants with a very high velocity or former halo G stars. We also compare the LAS sample with earlier studies of very cool degenerates and observe a similar deficit of helium-dominated atmospheres in the range 5000 < T eff (K) < 6000. We review the possible explanations for the spectral evolution from helium-dominated toward hydrogen-rich atmospheres at low temperatures.

DENIS J081730.0-615520: AN OVERLOOKED MID-T DWARF IN THE SOLAR NEIGHBORHOOD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Artigau, Etienne; Lafreniere, David; Doyon, Rene

2010-07-20

Recent wide-field near-infrared surveys have uncovered a large number of cool brown dwarfs (BDs), extending the temperature sequence down to less than 500 K and constraining the faint end of the luminosity function (LF). One interesting implication of the derived LF is that the BD census in the immediate (<10 pc) solar neighborhood is still largely incomplete, and some bright (J < 16) BDs remain to be identified in existing surveys. These objects are especially interesting as they are the ones that can be studied in most detail, especially with techniques that require large fluxes (e.g., time-variability, polarimetry, and high-resolutionmore » spectroscopy) that cannot realistically be applied to objects uncovered by deep surveys. By cross-matching the DEep Near-Infrared Survey of the Southern sky (DENIS) and the Two Micron All Sky Survey point-source catalogs, we have identified an overlooked BD-DENIS J081730.0-615520-that is the brightest field mid-T dwarf in the sky (J = 13.6). We present astrometry and spectroscopy follow-up observations of this BD. Our data indicate a spectral type T6 and a distance-from parallax measurement-of 4.9 {+-} 0.3 pc, placing this mid-T dwarf among the three closest isolated BDs to the Sun.« less

White dwarf evolution - Cradle-to-grave constraints via pulsation

NASA Technical Reports Server (NTRS)

Kawaler, Steven D.

1990-01-01

White dwarf evolution, particularly in the early phases, is not very strongly constrained by observation. Fortunately, white dwarfs undergo nonradial pulsation in three distinct regions of the H-R diagram. These pulsations provide accurate masses, surface compositional structure and rotation velocities, and help constrain other important physical properties. We demonstrate the application of the tools of stellar seismology to white dwarf evolution using the hot white dwarf star PG 1159-035 and the cool DAV (or ZZ Ceti) stars as examples. From pulsation studies, significant challenges to the theory of white dwarf evolution emerge.

Cool Companions of White Dwarfs from 2MASS

NASA Astrophysics Data System (ADS)

Hoard, D. W.; Wachter, S.; Sturch, L. K.; Widhalm, A. M.; Weiler, K. P.; Wellhouse, J. W.; Gibiansky, M.

2006-12-01

Detecting low mass stellar companions to white dwarfs (WDs) offers many advantages compared to main sequence primaries. In the latter case, faint low mass companions are often hidden in the glare of the more luminous main sequence primary, and radial velocity variations are small and, therefore, difficult to detect. Since WDs are less luminous than main sequence stars, the brightness contrast compared to a potential faint companion is significantly reduced. Most importantly, the markedly different spectral energy distributions of the WDs and their low mass companions makes the detection and separation of the two components relatively straightforward even with simple broad-band multi-color photometry. We have shown in Wachter et al. (2003) that the 2MASS near-IR color-color diagram can easily and efficiently identify candidates for unresolved WD + red dwarf binaries. Our follow-up observations (e.g., Farihi et al. 2006) have shown that a large fraction of these candidates are confirmed as previously unknown binary stars. Here, we present results from our full survey of the 2235 WDs from the McCook & Sion (1999) Catalog using the 2MASS All-Sky Data Release. We have identified an additional large sample of candidate WD + red dwarf binaries, as well as a number of systems that may contain extremely low mass stellar or substellar companions. Support for this work was provided by the National Aeronautics and Space Administration (NASA) under an Astrophysics Data Program grant issued through the Office of Space Science. This research made use of the NASA/Infrared Processing and Analysis Center (IPAC) Infrared Science Archive, which is operated by the Jet Propulsion Laboratory/California Institute of Technology (CIT), under contract with NASA, and data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and IPAC/CIT, funded by NASA and the National Science Foundation.

Multi-periodic pulsations of a stripped red-giant star in an eclipsing binary system.

PubMed

Maxted, Pierre F L; Serenelli, Aldo M; Miglio, Andrea; Marsh, Thomas R; Heber, Ulrich; Dhillon, Vikram S; Littlefair, Stuart; Copperwheat, Chris; Smalley, Barry; Breedt, Elmé; Schaffenroth, Veronika

2013-06-27

Low-mass white-dwarf stars are the remnants of disrupted red-giant stars in binary millisecond pulsars and other exotic binary star systems. Some low-mass white dwarfs cool rapidly, whereas others stay bright for millions of years because of stable fusion in thick surface hydrogen layers. This dichotomy is not well understood, so the potential use of low-mass white dwarfs as independent clocks with which to test the spin-down ages of pulsars or as probes of the extreme environments in which low-mass white dwarfs form cannot fully be exploited. Here we report precise mass and radius measurements for the precursor to a low-mass white dwarf. We find that only models in which this disrupted red-giant star has a thick hydrogen envelope can match the strong constraints provided by our data. Very cool low-mass white dwarfs must therefore have lost their thick hydrogen envelopes by irradiation from pulsar companions or by episodes of unstable hydrogen fusion (shell flashes). We also find that this low-mass white-dwarf precursor is a type of pulsating star not hitherto seen. The observed pulsation frequencies are sensitive to internal processes that determine whether this star will undergo shell flashes.

Parallaxes of Southern Extremely Cool Objects (PARSEC). II. Spectroscopic Follow-up and Parallaxes of 52 Targets

NASA Astrophysics Data System (ADS)

Marocco, F.; Andrei, A. H.; Smart, R. L.; Jones, H. R. A.; Pinfield, D. J.; Day-Jones, A. C.; Clarke, J. R. A.; Sozzetti, A.; Lucas, P. W.; Bucciarelli, B.; Penna, J. L.

2013-12-01

We present near-infrared spectroscopy for 52 ultracool dwarfs, including two newly discovered late-M dwarfs, one new late-M subdwarf candidate, three new L, and four new T dwarfs. We also present parallaxes and proper motions for 21 of them. Four of the targets presented here have previous parallax measurements, while all the others are new values. This allow us to populate further the spectral sequence at early types (L0-L4). Combining the astrometric parameters with the new near-infrared spectroscopy presented here, we are able to investigate further the nature of some of the objects. In particular, we find that the peculiar blue L1 dwarf SDSS J133148.92-011651.4 is a metal-poor object, likely a member of the galactic thick disk. We discover a new M subdwarf candidate, 2MASS J20115649-6201127. We confirm the low-gravity nature of EROS-MP J0032-4405, DENIS-P J035726.9-441730, and 2MASS J22134491-2136079. We present two new metal-poor dwarfs: the L4pec 2MASS J19285196-4356256 and the M7pec SIPS2346-5928. We also determine the effective temperature and bolometric luminosity of the 21 targets with astrometric measurements, and we obtain a new polynomial relation between effective temperature and near-infrared spectral type. The new fit suggests a flattening of the sequence at the transition between M and L spectral types. This could be an effect of dust formation, which causes a more rapid evolution of the spectral features as a function of the effective temperature. Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

A numerical study of the stability of radiative shocks. [in accretion flows onto white dwarf stars

NASA Technical Reports Server (NTRS)

Imamura, J. N.; Wolff, M. T.; Durisen, R. H.

1984-01-01

Attention is given to the oscillatory instability of optically thin radiative shocks in time-dependent numerical calculations of accretion flows onto degenerate dwarfs. The present nonlinear calculations yield good quantitative agreement with the linear results obtained for oscillation frequencies, damping rates, and critical alpha-values. The fundamental mode and the first overtone in the shock radius and luminosity variations can be clearly identified, and evidence is sometimes seen for the second overtone. Time-dependent calculations are also performed which include additional physics relevant to degenerate dwarf accretion, such as electron thermal conduction, unequal electron and ion temperatures, Compton cooling, and relativistic corrections to the bremsstrahlung cooling law. All oscillatory modes are found to be damped, and hence stable, in the case of a 1-solar mass white dwarf accreting in spherical symmetry.

White Dwarfs in Star Clusters: The Initial-Final Mass Relation for Stars from 0.85 to 8 M$_\\odot$

NASA Astrophysics Data System (ADS)

Cummings, Jeffrey; Kalirai, Jason; Tremblay, P.-E.; Ramírez-Ruiz, Enrico

2018-01-01

The spectroscopic study of white dwarfs provides both their mass, cooling age, and intrinsic photometric properties. For white dwarfs in the field of well-studied star clusters, this intrinsic photometry can be used to determine if they are members of that star cluster. Comparison of a member white dwarf's cooling age to its total cluster's age provides the evolutionary timescale of its progenitor star, and hence the mass. This is the initial-final mass relation (IFMR) for stars, which gives critical information on how a progenitor star evolves and loses mass throughout its lifetime, and how this changes with progenitor mass. Our work, for the first time, presents a uniform analysis of 85 white dwarf cluster members spanning from progenitor masses of 0.85 to 8 M$_\\odot$. Comparison of our work to theoretical IFMRs shows remarkable consistency in their shape but differences remain. We will discuss possible explanations for these differences, including the effects of stellar rotation.

Dynamically hot galaxies. I - Structural properties

NASA Technical Reports Server (NTRS)

Bender, Ralf; Burstein, David; Faber, S. M.

1992-01-01

Results are reported from an analysis of the structural properties of dynamically hot galaxies which combines central velocity dispersion, effective surface brightness, and effective radius into a new 3-space (k), in which the axes are parameters that are physically meaningful. Hot galaxies are found to divide into groups in k-space that closely parallel conventional morphological classifications, namely, luminous ellipticals, compacts, bulges, bright dwarfs, and dwarf spheroidals. A major sequence is defined by luminous ellipticals, bulges, and most compacts, which together constitute a smooth continuum in k-space. Several properties vary smoothly with mass along this continuum, including bulge-to-disk ratio, radio properties, rotation, degree of velocity anisotropy, and 'unrelaxed'. A second major sequence is comprised of dwarf ellipticals and dwarf spheroidals. It is suggested that mass loss is a major factor in hot dwarf galaxies, but the dwarf sequence cannot be simply a mass-loss sequence, as it has the wrong direction in k-space.

SEARCHING FOR BINARY Y DWARFS WITH THE GEMINI MULTI-CONJUGATE ADAPTIVE OPTICS SYSTEM (GeMS)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Opitz, Daniela; Tinney, C. G.; Faherty, Jacqueline K.

The NASA Wide-field Infrared Survey Explorer (WISE) has discovered almost all the known members of the new class of Y-type brown dwarfs. Most of these Y dwarfs have been identified as isolated objects in the field. It is known that binaries with L- and T-type brown dwarf primaries are less prevalent than either M-dwarf or solar-type primaries, they tend to have smaller separations and are more frequently detected in near-equal mass configurations. The binary statistics for Y-type brown dwarfs, however, are sparse, and so it is unclear if the same trends that hold for L- and T-type brown dwarfs alsomore » hold for Y-type ones. In addition, the detection of binary companions to very cool Y dwarfs may well be the best means available for discovering even colder objects. We present results for binary properties of a sample of five WISE Y dwarfs with the Gemini Multi-Conjugate Adaptive Optics System. We find no evidence for binary companions in these data, which suggests these systems are not equal-luminosity (or equal-mass) binaries with separations larger than ∼0.5–1.9 AU. For equal-mass binaries at an age of 5 Gyr, we find that the binary binding energies ruled out by our observations (i.e., 10{sup 42} erg) are consistent with those observed in previous studies of hotter ultra-cool dwarfs.« less

Superhumps and Repetitive Rebrightenings of the WZ Sge-Type Dwarf Nova, EG Cancri

NASA Astrophysics Data System (ADS)

Kato, Taichi; Nogami, Daisaku; Matsumoto, Katsura; Baba, Hajime

2004-03-01

We report on time-resolved photometric observations of the WZ Sge-type dwarf nova, EG Cnc (Huruhata's variable), during its superoutburst in 1996-1997. EG Cnc, after the main superoutburst accompanied by the development of superhumps typical of a WZ Sge-type dwarf nova, exhibited a series of six major rebrightenings. During these rebrightenings and the following long fading tail, EG Cnc persistently showed superhumps having a period equal to the superhump period observed during the main superoutburst. The persistent superhumps had a constant superhump flux with respect to the rebrightening phase. These findings suggest that the superhumps observed during the rebrightening stage and the fading tail are a ``remnant'' of the usual superhumps, and are not newly triggered by rebrightenings. By a comparison with the 1977 outburst of this object and outbursts of other WZ Sge-type dwarf novae, we propose an activity sequence of WZ Sge-type superoutbursts, in which the current outburst of EG Cnc is placed between a single-rebrightening event and distinct outbursts separated by a dip. The post-superoutburst behavior of WZ Sge-type dwarf novae can be understood in the presence of a considerable amount of remnant matter behind the cooling front in the outer accretion disk, even after the main superoutburst. We consider that a premature quenching of the hot state due to the weak tidal effect under the extreme mass ratio of the WZ Sge-type binary is responsible for the origin of the remnant mass.

The end of the White Dwarf Cooling Sequence of NGC 6752

NASA Astrophysics Data System (ADS)

Bedin, Luigi

2017-08-01

We propose to study the last HST-accessible white dwarf (WD) cooling sequence (CS) for a nearby globular cluster (GC), the chemically complex, extreme blue horizontal branch cluster NGC 6752. Over 97% of stars end their lives as WDs, and the WD CS provides constraints not only on the age, but also potentially the star formation history of a GC. The CS of WDs also lies in the least-explored region of the color-magnitude diagram of old stellar populations. Recent deep imaging with HST has successfully reached the end of the WD CS in only three classical old GCs, M4, NGC 6397 and 47 Tuc, and reveals an unexpectedly complex, and double-peaked, WD CS in the metal rich old open cluster NGC 6791. One more investigation is in progress on the massive globular Omega Centauri, where over 14 sub-populations are known to exist.While almost every cluster is known to host multiple populations, every single cluster is unique. NGC 6752 is a bridge between the relatively simple globular clusters, and Omega Cen, the most complex globular cluster known. NGC 6752 has an extended blue horizontal branch, a collapsed core and 3 chemically distinct populations. It is our last chance to add diversity to our very limited sample of WD CS, so far containing only 3 globular clusters, one old open cluster, and the complex Omega Cen system. We need to undertake this investigation while HST is still operational, as there is no foreseeable opportunity in the post-HST era to have one extra WD CS in the homogeneus optical photometric system of HST.

The Impact of Clouds and Hazes in Substellar Atmospheres

NASA Astrophysics Data System (ADS)

Morley, Caroline; Fortney, Jonathan J.; Marley, Mark S.

2016-01-01

The formation of clouds significantly alters the spectra of cool substellar atmospheres from terrestrial planets to brown dwarfs. In cool planets like Earth and Jupiter, volatile species like water and ammonia condense to form ice clouds. In hot planets and brown dwarfs, iron and silicates instead condense, forming dusty clouds. Irradiated methane-rich planets may have substantial hydrocarbon hazes. During my thesis, I have studied the impact of clouds and hazes in a variety of substellar objects. First, I present results for cool brown dwarfs including clouds previously neglected in model atmospheres. Model spectra that include sulfide and salt clouds can match the spectra of T dwarf atmospheres; water ice clouds will alter the spectra of the newest and coldest brown dwarfs, the Y dwarfs. These sulfide/salt and ice clouds potentially drive spectroscopic variability in these cool objects, and this variability should be distinguishable from variability caused by hot spots.Next, I present results for small, cool exoplanets between the size of Earth and Neptune, so-called super Earths. They likely have sulfide and salt clouds and also have photochemical hazes caused by stellar irradiation. Vast resources have been dedicated to characterizing the handful of super Earths accessible to current telescopes, yet of the planets smaller than Neptune studied to date, all have radii in the near-infrared consistent with being constant in wavelength, likely showing that these small planets are consistently enshrouded in thick hazes and clouds. Very thick, lofted clouds of salts or sulfides in high metallicity (1000× solar) atmospheres create featureless transmission spectra in the near-infrared. Photochemical hazes with a range of particle sizes also create featureless transmission spectra at lower metallicities. I show that despite these challenges, there are promising avenues for understanding this class of small planets: by observing the thermal emission and reflectivity of small planets, we can break the degeneracies and better constrain the atmospheric compositions. These observations may provide rich diagnostics of molecules and clouds in small planets, in contrast to the limited success to date.

Post-main-sequence Evolution of Icy Minor Planets. II. Water Retention and White Dwarf Pollution around Massive Progenitor Stars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malamud, Uri; Perets, Hagai B., E-mail: uri.mal@tx.technion.ac.il, E-mail: hperets@physics.technion.ac.il

Most studies suggest that the pollution of white dwarf (WD) atmospheres arises from the accretion of minor planets, but the exact properties of polluting material, and in particular the evidence for water in some cases, are not yet understood. Here we study the water retention of small icy bodies in exo-solar planetary systems, as their respective host stars evolve through and off the main sequence and eventually become WDs. We explore, for the first time, a wide range of star masses and metallicities. We find that the mass of the WD progenitor star is of crucial importance for the retentionmore » of water, while its metallicity is relatively unimportant. We predict that minor planets around lower-mass WD progenitors would generally retain more water and would do so at closer distances from the WD than compared with high-mass progenitors. The dependence of water retention on progenitor mass and other parameters has direct implications for the origin of observed WD pollution, and we discuss how our results and predictions might be tested in the future as more observations of WDs with long cooling ages become available.« less

Gaia Reveals Evidence for Merged White Dwarfs

NASA Astrophysics Data System (ADS)

Kilic, Mukremin; Hambly, N. C.; Bergeron, P.; Genest-Beaulieu, C.; Rowell, N.

2018-06-01

We use Gaia Data Release 2 to identify 13,928 white dwarfs within 100 pc of the Sun. The exquisite astrometry from Gaia reveals for the first time a bifurcation in the observed white dwarf sequence in both Gaia and the Sloan Digital Sky Survey (SDSS) passbands. The latter is easily explained by a helium atmosphere white dwarf fraction of 36%. However, the bifurcation in the Gaia colour-magnitude diagram depends on both the atmospheric composition and the mass distribution. We simulate theoretical colour-magnitude diagrams for single and binary white dwarfs using a population synthesis approach and demonstrate that there is a significant contribution from relatively massive white dwarfs that likely formed through mergers. These include white dwarf remnants of main-sequence (blue stragglers) and post-main sequence mergers. The mass distribution of the SDSS subsample, including the spectroscopically confirmed white dwarfs, also shows this massive bump. This is the first direct detection of such a population in a volume-limited sample.

MagAO Imaging of Long-period Objects (MILO). II. A Puzzling White Dwarf around the Sun-like Star HD 11112

NASA Astrophysics Data System (ADS)

Rodigas, Timothy J.; Bergeron, P.; Simon, Amélie; Arriagada, Pamela; Faherty, Jacqueline K.; Anglada-Escudé, Guillem; Mamajek, Eric E.; Weinberger, Alycia; Butler, R. Paul; Males, Jared R.; Morzinski, Katie; Close, Laird M.; Hinz, Philip M.; Bailey, Jeremy; Carter, Brad; Jenkins, James S.; Jones, Hugh; O'Toole, Simon; Tinney, C. G.; Wittenmyer, Rob; Debes, John

2016-11-01

HD 11112 is an old, Sun-like star that has a long-term radial velocity (RV) trend indicative of a massive companion on a wide orbit. Here we present direct images of the source responsible for the trend using the Magellan Adaptive Optics system. We detect the object (HD 11112B) at a separation of 2.″2 (100 au) at multiple wavelengths spanning 0.6-4 μm and show that it is most likely a gravitationally bound cool white dwarf. Modeling its spectral energy distribution suggests that its mass is 0.9-1.1 M ⊙, which corresponds to very high eccentricity, near edge-on orbits from a Markov chain Monte Carlo analysis of the RV and imaging data together. The total age of the white dwarf is >2σ, which is discrepant with that of the primary star under most assumptions. The problem can be resolved if the white dwarf progenitor was initially a double white dwarf binary that then merged into the observed high-mass white dwarf. HD 11112B is a unique and intriguing benchmark object that can be used to calibrate atmospheric and evolutionary models of cool white dwarfs and should thus continue to be monitored by RV and direct imaging over the coming years.

Too Cool for Stellar Rules: A Bayesian Exploration of Trends in Ultracool Magnetism

NASA Astrophysics Data System (ADS)

Cruz, Kelle L.; Schwab, Ellianna; Williams, Peter K. G.; Hogg, David W.; Rodriguez, David R.; BDNYC

2017-01-01

Ultracool dwarfs, the lowest mass red dwarfs and brown dwarfs (spectral types M7-Y9), are fully convective objects with electrically neutral atmospheres due to their extremely cool temperatures (500-3000 K). Radio observations of ultracool dwarfs indicate the presence of magnetic field strengths on the order of ~kG, however the dynamo driving these fields is not fully understood. To better understand ultracool dwarf magnetic behavior, we analyze photometric radio detections of 196 dwarfs (spectral types M7-T8), observed in the 4.5-8.5 GHz range on the Karl G. Jansky Very Large Array (VLA) and the Australia Telescope Compact Array (ATCA). The measurements in our sample are mostly upper limits, along with a small percentage of confirmed detections. The detections have both large uncertainties and high intrinsic scatter. Using Bayesian analysis to fully take advantage of the information available in these inherently uncertain measurements, we search for trends in radio luminosity as a function of several fundamental parameters: spectral type, effective temperature, and rotation rate. In this poster, we present the preliminary results of our efforts to investigate the possibility of subpopulations with different magnetic characteristics using Gaussian mixture models.

Cool Star Marked by Long-Lived Storm Artist Concept

NASA Image and Video Library

2015-12-10

This illustration shows a cool star, called W1906+40, marked by a raging storm near one of its poles. The storm is thought to be similar to the Great Red Spot on Jupiter. Scientists discovered it using NASA's Kepler and Spitzer space telescopes. The location of the storm is estimated to be near the north pole of the star based on computer models of the data. The telescopes cannot see the storm itself, but learned of its presence after observing how the star's light changes over time. The storm travels around with the star, making a full lap about every 9 hours. When it passes into a telescope's field of view, it causes light of particular infrared and visible wavelengths to dip in brightness. The storm has persisted for at least two years. Astronomers aren't sure why it has lasted so long. While planets are known to have cloudy storms, this is the best evidence yet for a star with the same type of storm. The star, W1906+40, belongs to a thermally cool class of objects called L-dwarfs. Some L-dwarfs are considered stars because they fuse atoms and generate light, as our sun does, while others, called brown dwarfs, are known as "failed stars" for their lack of atomic fusion. The L-dwarf W1906+40 is thought to be a star based on estimates of its age (the older the L-dwarf, the more likely it is a star). Its temperature is about 2,200 Kelvin (3,500 degrees Fahrenheit). That may sound scorching hot, but as far as stars go, it is relatively cool. Cool enough, in fact, for clouds to form in its atmosphere. W1906+40 is located 53 light-years away in the constellation Lyra. http://photojournal.jpl.nasa.gov/catalog/PIA20055

Exoplanet Meteorology: Characterizing the Atmospheres of Directly Imaged Sub-Stellar Objects

NASA Astrophysics Data System (ADS)

Rajan, Abhijith; Gemini Planet Imager, Extrasolar Planets and Systems Imaging Group

2018-01-01

I study the structure, composition and dynamic evolution of directly imaged exoplanet and brown dwarf atmospheres, using spectrophotometric data collected from a range of ground and space based instrumentation. As part of my dissertation, I led studies exploring the atmospheres of brown dwarfs to search for weather variations, and characterized the near and mid infrared SEDs of imaged exoplanets to estimate their fundamental parameters. To understand the evolution of weather on brown dwarfs we conducted a multi-epoch study monitoring of 4 ultracool, T5 - Y0, brown dwarfs in the J-band to search for photometric variability. These cool brown dwarfs are predicted to have salt and sulfide clouds condensing in their upper atmosphere. The study found that cool brown dwarfs, fit with higher opacity clouds, were more likely to be variable. Through data taken with the Hubble Space Telescope and Gemini telescope we characterized the atmospheres of directly imaged exoplanets. For HR 8799, in near IR wavelengths unobservable from the ground, we constrained the presence of clouds in the outer planets. As a member of the Gemini Planet Imager Exoplanet Survey team, I analyzed archival HST data and examined the near-infrared colors of HD 106906b as seen with GPI, concluding that the companion shows weak evidence of a circumplanetary dust disk or cloud. Finally, by combining data spanning 1 - 5 um for the low mass Jupiter-like exoplanet, 51 Eri b, we found a cool effective temperature best fit by a patchy cloud atmosphere. This makes the planet an excellent candidate for future variability studies with the James Webb Space Telescope.

De Novo Transcriptome Analysis for Kentucky Bluegrass Dwarf Mutants Induced by Space Mutation

PubMed Central

Gan, Lu; Di, Rong; Chao, Yuehui; Han, Liebao; Chen, Xingwu; Wu, Chao; Yin, Shuxia

2016-01-01

Kentucky bluegrass (Poa pratensis L.) is a major cool-season turfgrass requiring frequent mowing. Utilization of cultivars with slow growth is a promising method to decrease mowing frequency. In this study, two dwarf mutant selections of Kentucky bluegrass (A12 and A16) induced by space mutation were analyzed for the differentially expressed genes compared with the wild type (WT) by the high-throughput RNA-Seq technology. 253,909 unigenes were obtained by de novo assembly. 24.20% of the unigenes had a significant level of amino acid sequence identity to Brachypodium distachyon proteins, followed by Hordeum vulgare with 18.72% among the non-redundant (NR) Blastx top hits. Assembled unigenes were associated with 32 pathways using KEGG orthology terms and their respective KEGG maps. Between WT and A16 libraries, 4,203 differentially expressed genes (DEGs) were identified, whereas there were 883 DEGs between WT and A12 libraries. Further investigation revealed that the DEG pathways were mainly involved in terpenoid biosynthesis and plant hormone metabolism, which might account for the differences of plant height and leaf blade color between dwarf mutant and WT plants. Our study presents the first comprehensive transcriptomic data and gene function analysis of Poa pratensis L., providing a valuable resource for future studies in plant dwarfing breeding and comparative genome analysis for Pooideae plants. PMID:27010560

Evidence for a New Class of Extreme Ultraviolet Sources

NASA Technical Reports Server (NTRS)

Maoz, Dan; Ofek, Eran O.; Shemi, Amotz

1997-01-01

Most of the sources detected in the extreme ultraviolet (EUV; 100-600 A) by the ROSAT/WFC and EUVE all-sky surveys have been identified with active late-type stars and hot white dwarfs that are near enough to the Earth to escape absorption by interstellar gas. However, about 15 per cent of EUV sources are as yet unidentified with any optical counterparts. We examine whether the unidentified EUV sources may consist of the same population of late-type stars and white dwarfs. We present B and R photometry of stars in the fields of seven of the unidentified EUV sources. We detect in the optical the entire main-sequence and white dwarf population out to the greatest distances where they could still avoid absorption. We use color-magnitude diagrams to demonstrate that, in most of the fields, none of the observed stars has the colours and magnitudes of late-type dwarfs at distances less than 100 pc. Similarly, none of the observed stars is a white dwarf within 500 pc that is hot enough to be a EUV emitter. The unidentified EUV sources we study are not detected in X-rays, while cataclysmic variables, X-ray binaries, and active galactic nuclei generally are. We conclude that some of the EUV sources may be a new class of nearby objects, which are either very faint at optical bands or which mimic the colours and magnitudes of distant late-type stars or cool white dwarfs. One candidate for optically faint objects is isolated old neutron stars, slowly accreting interstellar matter. Such neutron stars are expected to be abundant in the Galaxy, and have not been unambiguously detected.

Pan-Planets: Searching for hot Jupiters around cool dwarfs

NASA Astrophysics Data System (ADS)

Obermeier, C.; Koppenhoefer, J.; Saglia, R. P.; Henning, Th.; Bender, R.; Kodric, M.; Deacon, N.; Riffeser, A.; Burgett, W.; Chambers, K. C.; Draper, P. W.; Flewelling, H.; Hodapp, K. W.; Kaiser, N.; Kudritzki, R.-P.; Magnier, E. A.; Metcalfe, N.; Price, P. A.; Sweeney, W.; Wainscoat, R. J.; Waters, C.

2016-03-01

The Pan-Planets survey observed an area of 42 sq deg. in the galactic disk for about 165 h. The main scientific goal of the project is the detection of transiting planets around M dwarfs. We establish an efficient procedure for determining the stellar parameters Teff and log g of all sources using a method based on SED fitting, utilizing a three-dimensional dust map and proper motion information. In this way we identify more than 60 000 M dwarfs, which is by far the largest sample of low-mass stars observed in a transit survey to date. We present several planet candidates around M dwarfs and hotter stars that are currently being followed up. Using Monte Carlo simulations we calculate the detection efficiency of the Pan-Planets survey for different stellar and planetary populations. We expect to find 3.0+3.3-1.6 hot Jupiters around F, G, and K dwarfs with periods lower than 10 days based on the planet occurrence rates derived in previous surveys. For M dwarfs, the percentage of stars with a hot Jupiter is under debate. Theoretical models expect a lower occurrence rate than for larger main sequence stars. However, radial velocity surveys find upper limits of about 1% due to their small sample, while the Kepler survey finds a occurrence rate that we estimate to be at least 0.17b(+0.67-0.04) %, making it even higher than the determined fraction from OGLE-III for F, G and K stellar types, 0.14 (+0.15-0.076) %. With the large sample size of Pan-Planets, we are able to determine an occurrence rate of 0.11 (+0.37-0.02) % in case one of our candidates turns out to be a real detection. If, however, none of our candidates turn out to be true planets, we are able to put an upper limit of 0.34% with a 95% confidence on the hot Jupiter occurrence rate of M dwarfs. This limit is a significant improvement over previous estimates where the lowest limit published so far is 1.1% found in the WFCAM Transit Survey. Therefore we cannot yet confirm the theoretical prediction of a lower occurrence rate for cool stars. Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.

A radio-pulsing white dwarf binary star.

PubMed

Marsh, T R; Gänsicke, B T; Hümmerich, S; Hambsch, F-J; Bernhard, K; Lloyd, C; Breedt, E; Stanway, E R; Steeghs, D T; Parsons, S G; Toloza, O; Schreiber, M R; Jonker, P G; van Roestel, J; Kupfer, T; Pala, A F; Dhillon, V S; Hardy, L K; Littlefair, S P; Aungwerojwit, A; Arjyotha, S; Koester, D; Bochinski, J J; Haswell, C A; Frank, P; Wheatley, P J

2016-09-15

White dwarfs are compact stars, similar in size to Earth but approximately 200,000 times more massive. Isolated white dwarfs emit most of their power from ultraviolet to near-infrared wavelengths, but when in close orbits with less dense stars, white dwarfs can strip material from their companions and the resulting mass transfer can generate atomic line and X-ray emission, as well as near- and mid-infrared radiation if the white dwarf is magnetic. However, even in binaries, white dwarfs are rarely detected at far-infrared or radio frequencies. Here we report the discovery of a white dwarf/cool star binary that emits from X-ray to radio wavelengths. The star, AR Scorpii (henceforth AR Sco), was classified in the early 1970s as a δ-Scuti star, a common variety of periodic variable star. Our observations reveal instead a 3.56-hour period close binary, pulsing in brightness on a period of 1.97 minutes. The pulses are so intense that AR Sco's optical flux can increase by a factor of four within 30 seconds, and they are also detectable at radio frequencies. They reflect the spin of a magnetic white dwarf, which we find to be slowing down on a 10 7 -year timescale. The spin-down power is an order of magnitude larger than that seen in electromagnetic radiation, which, together with an absence of obvious signs of accretion, suggests that AR Sco is primarily spin-powered. Although the pulsations are driven by the white dwarf's spin, they mainly originate from the cool star. AR Sco's broadband spectrum is characteristic of synchrotron radiation, requiring relativistic electrons. These must either originate from near the white dwarf or be generated in situ at the M star through direct interaction with the white dwarf's magnetosphere.

Evidence for a cool wind from the K2 dwarf in the detached binary V471 Tauri

NASA Technical Reports Server (NTRS)

Mullan, D. J.; Sion, E. M.; Bruhweiler, F. C.; Carpenter, K. G.

1989-01-01

Evidence for mass loss from the K2 dwarf in V471 Tauri is found in the form of discrete absorption features in lines of various elements (Mg, Fe, Cr, Mn) and ionization stages (Mg I, Mg II, Fe I, Fe II). Resonant Mg II absorption indicates a mass loss rate of at least 10 to the -11th solar masses per year. The wind appears to be cool (no more than a few times 10,000 K).

Computation of Collision-Induced Absorption by Simple Molecular Complexes, for Astrophysical Applications

NASA Astrophysics Data System (ADS)

Abel, Martin; Frommhold, Lothar; Li, Xiaoping; Hunt, Katharine L. C.

2012-06-01

The interaction-induced absorption by collisional pairs of H{_2} molecules is an important opacity source in the atmospheres of various types of planets and cool stars, such as late stars, low-mass stars, brown dwarfs, cool white dwarf stars, the ambers of the smaller, burnt out main sequence stars, exoplanets, etc., and therefore of special astronomical interest The emission spectra of cool white dwarf stars differ significantly in the infrared from the expected blackbody spectra of their cores, which is largely due to absorption by collisional H{_2}-H{_2}, H{_2}-He, and H{_2}-H complexes in the stellar atmospheres. Using quantum-chemical methods we compute the atmospheric absorption from hundreds to thousands of kelvin. Laboratory measurements of interaction-induced absorption spectra by H{_2} pairs exist only at room temperature and below. We show that our results reproduce these measurements closely, so that our computational data permit reliable modeling of stellar atmosphere opacities even for the higher temperatures. First results for H_2-He complexes have already been applied to astrophysical models have shown great improvements in these models. L. Frommhold, Collision-Induced Absorption in Gases, Cambridge University Press, Cambridge, New York, 1993 and 2006 X. Li, K. L. C. Hunt, F. Wang, M. Abel, and L. Frommhold, Collision-Induced Infrared Absorption by Molecular Hydrogen Pairs at Thousands of Kelvin, Int. J. of Spect., vol. 2010, Article ID 371201, 11 pages, 2010. doi: 10.1155/2010/371201 M. Abel, L. Frommhold, X. Li, and K. L. C. Hunt, Collision-induced absorption by H{_2} pairs: From hundreds to thousands of Kelvin, J. Phys. Chem. A, 115, 6805-6812, 2011} L. Frommhold, M. Abel, F. Wang, M. Gustafsson, X. Li, and K. L. C. Hunt, "Infrared atmospheric emission and absorption by simple molecular complexes, from first principles", Mol. Phys. 108, 2265, 2010 M. Abel, L. Frommhold, X. Li, and K. L. C. Hunt, Infrared absorption by collisional H_2-He complexes at temperatures up to 9000 K and frequencies from 0 to 20000 cm-1, J. Chem. Phys., 136, 044319, 2012 D. Saumon, M. S. Marley, M. Abel, L. Frommhold, and R. S. Freedman, New H_2 collision-induced absorption and NH_3 opacity and the spectra of the coolest brown dwarfs, Astrophysical Journal, 2012

Finding the elusive substellar members of young moving groups

NASA Astrophysics Data System (ADS)

Aller, Kimberly Mei

Young moving groups (YMGs) consist of coeval, comoving stars, with ages between 10-100Myrs, that have migrated from their origins after formation. They provide a valuable link between ongoing star formation in molecular clouds (˜1Myr) and old field stars (≥1Gyr). However, previous searches based on optical surveys such as Hipparcos and the Palomar Sky Survey were insensitive to these very faint cool dwarfs. More recent surveys with GALEX have begun to reveal the nearby (<25 pc) low-mass members (≥ 0.1 M solar massses) but the cool, substellar members have remained elusive. We have increased the search volume by a factor of ˜10 using a novel combination of photometry and proper motions from Pan-STARRS, WISE, and 2MASS in order to uncover the missing substellar members down to ≥ 00.1 M solar massses (at 10Myr). We have obtained NIR low-resolution spectroscopy and confirmed the youth of 65 new ultracool dwarf YMG candidates. We also obtained high-resolution NIR spectroscopy to determine radial velocities for our young brown dwarfs. With our RVs and PS1 parallaxes, we have nearly doubled the number of confirmed bona fide substellar YMG members, which are also brown dwarf age benchmarks. Our new young brown dwarfs empirically define the substellar spectral evolution with age and provide us with a snapshot of brown dwarf evolution. Finally, our resulting young brown dwarfs will be valuable targets for future surveys of brown dwarf binarity and young exoplanet characterization.

NEW INSIGHTS INTO THE PROBLEM OF THE SURFACE GRAVITY DISTRIBUTION OF COOL DA WHITE DWARFS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tremblay, P.-E.; Bergeron, P.; Gianninas, A.

2010-04-01

We review at length the longstanding problem in the spectroscopic analysis of cool hydrogen-line (DA) white dwarfs (T{sub eff}< 13,000 K) where gravities are significantly higher than those found in hotter DA stars. The first solution that has been proposed for this problem is a mild and systematic helium contamination from convective mixing that would mimic the high gravities. We constrain this scenario by determining the helium abundances in six cool DA white dwarfs using high-resolution spectra from the Keck I 10 m telescope. We obtain no detections, with upper limits as low as He/H = 0.04 in some cases.more » This allows us to put this scenario to rest for good. We also extend our model grid to lower temperatures using improved Stark profiles with non-ideal gas effects from Tremblay and Bergeron and find that the gravity distribution of cool objects remains suspiciously high. Finally, we find that photometric masses are, on average, in agreement with expected values, and that the high-log g problem is so far unique to the spectroscopic approach.« less

MagAO IMAGING OF LONG-PERIOD OBJECTS (MILO). II. A PUZZLING WHITE DWARF AROUND THE SUN-LIKE STAR HD 11112

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodigas, Timothy J.; Arriagada, Pamela; Faherty, Jacqueline K.

HD 11112 is an old, Sun-like star that has a long-term radial velocity (RV) trend indicative of a massive companion on a wide orbit. Here we present direct images of the source responsible for the trend using the Magellan Adaptive Optics system. We detect the object (HD 11112B) at a separation of 2.″2 (100 au) at multiple wavelengths spanning 0.6–4 μ m and show that it is most likely a gravitationally bound cool white dwarf. Modeling its spectral energy distribution suggests that its mass is 0.9–1.1 M {sub ⊙}, which corresponds to very high eccentricity, near edge-on orbits from amore » Markov chain Monte Carlo analysis of the RV and imaging data together. The total age of the white dwarf is >2 σ , which is discrepant with that of the primary star under most assumptions. The problem can be resolved if the white dwarf progenitor was initially a double white dwarf binary that then merged into the observed high-mass white dwarf. HD 11112B is a unique and intriguing benchmark object that can be used to calibrate atmospheric and evolutionary models of cool white dwarfs and should thus continue to be monitored by RV and direct imaging over the coming years.« less

Dark-ages Reionization and Galaxy Formation Simulation - XIV. Gas accretion, cooling, and star formation in dwarf galaxies at high redshift

NASA Astrophysics Data System (ADS)

Qin, Yuxiang; Duffy, Alan R.; Mutch, Simon J.; Poole, Gregory B.; Geil, Paul M.; Mesinger, Andrei; Wyithe, J. Stuart B.

2018-06-01

We study dwarf galaxy formation at high redshift (z ≥ 5) using a suite of high-resolution, cosmological hydrodynamic simulations and a semi-analytic model (SAM). We focus on gas accretion, cooling, and star formation in this work by isolating the relevant process from reionization and supernova feedback, which will be further discussed in a companion paper. We apply the SAM to halo merger trees constructed from a collisionless N-body simulation sharing identical initial conditions to the hydrodynamic suite, and calibrate the free parameters against the stellar mass function predicted by the hydrodynamic simulations at z = 5. By making comparisons of the star formation history and gas components calculated by the two modelling techniques, we find that semi-analytic prescriptions that are commonly adopted in the literature of low-redshift galaxy formation do not accurately represent dwarf galaxy properties in the hydrodynamic simulation at earlier times. We propose three modifications to SAMs that will provide more accurate high-redshift simulations. These include (1) the halo mass and baryon fraction which are overestimated by collisionless N-body simulations; (2) the star formation efficiency which follows a different cosmic evolutionary path from the hydrodynamic simulation; and (3) the cooling rate which is not well defined for dwarf galaxies at high redshift. Accurate semi-analytic modelling of dwarf galaxy formation informed by detailed hydrodynamical modelling will facilitate reliable semi-analytic predictions over the large volumes needed for the study of reionization.

The brightest pure-H ultracool white dwarf

NASA Astrophysics Data System (ADS)

Catalán, S.; Tremblay, P.-E.; Pinfield, D. J.; Smith, L. C.; Zhang, Z. H.; Napiwotzki, R.; Marocco, F.; Day-Jones, A. C.; Gomes, J.; Forde, K. P.; Lucas, P. W.; Jones, H. R. A.

2012-10-01

We report the identification of LSR J0745+2627 in the United Kingdom InfraRed Telescope Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) as a cool white dwarf with kinematics and age compatible with the thick-disk/halo population. LSR J0745+2627 has a high proper motion (890 mas/yr) and a high reduced proper motion value in the J band (HJ = 21.87). We show how the infrared-reduced proper motion diagram is useful for selecting a sample of cool white dwarfs with low contamination. LSR J0745+2627 is also detected in the Sloan Digital Sky Survey (SDSS) and the Wide-field Infrared Survey Explorer (WISE). We have spectroscopically confirmed this object as a cool white dwarf using X-Shooter on the Very Large Telescope. A detailed analysis of its spectral energy distribution reveals that its atmosphere is compatible with a pure-H composition model with an effective temperature of 3880 ± 90 K. This object is the brightest pure-H ultracool white dwarf (Teff < 4000 K) ever identified. We have constrained the distance (24-45 pc), space velocities and age considering different surface gravities. The results obtained suggest that LSR J0745+2627 belongs to the thick-disk/halo population and is also one of the closest ultracool white dwarfs. Based on observations made with ESO telescopes at the Paranal Observatory under programme ID 088.C-0048(B).FITS version of the reduced spectrum is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/L3

Linking Dynamical and Stellar Evolution in the Metal-Poor Globular Cluster M92

NASA Astrophysics Data System (ADS)

Kalirai, Jason

2017-08-01

We propose a 5 orbit HST program to acquire UV imaging at the center of the ancient, metal-poor globular cluster NGC 6341 (M92). Our program is designed to achieve two science goals with a single data set, 1.) to directly measure the diffusion of stars through the massive cluster's core, 2.) to pinpoint the phase of post main-sequence evolution at which [Fe/H] = -2.3 stars lose their mass. Our novel technique will achieve these goals by using the full power of WFC3's exquisite UV sensitivity at <0.3 microns combined with its high spatial resolution. We will uncover 1000 newly-formed white dwarfs in the center of M92 and track how their spatial distribution changes as they get older on the cooling sequence. Having just experienced significant mass loss, the youngest remnants with ages <10s of Myr will still be moving slowly like their 0.8 Msun progenitors, whereas the older remnants with t_cool > 100s Myr will be fully relaxed. Using the methodology we developed and successfully applied to 47 Tuc (Heyl et al. 2015a; 2015b), we will watch this dynamical evolution to measure the diffusion coefficient due to gravitational relaxation in the cluster's core and the past timing of stellar mass loss that was responsible for the current cluster mass segregation profile. M92 is the ideal target for this study as it complements our existing study of the relatively metal-rich cluster 47 Tuc; it has an extremely low metallicity of [Fe/H] = -2.3, very low foreground reddening (E(B-V) = 0.02), moderate concentration index, and a theoretically-expected relaxation timescale in its core of 90 Myr, which nicely splits the young and old white dwarfs that can be observed with Hubble.

The problem of the barium stars

NASA Technical Reports Server (NTRS)

Bohm-Vitense, E.; Nemec, J.; Proffitt, C.

1984-01-01

Ultraviolet observations of barium stars and other cool stars with peculiar element abundances are reported. Those observations attempted to find hot white dwarf companions. Among six real barium stars studied, only Zeta Cap was found to have a white dwarf companion. Among seven mild, or marginal, barium stars studied, at least three were found to have hot subluminous companions. It is likely that all of them have white dwarf companions.

Thermal evolution of old white dwarfs

NASA Astrophysics Data System (ADS)

Kozhberov, Andrew

2017-11-01

This work is devoted to a description of thermodynamic properties of Coulomb crystals which are expected to form in white dwarf interiors. Effects of magnetic field, isotopic impurities, polarization of the electron background and crystal lattice type on the thermal evolution of white dwarfs are discussed. It is shown that the electron polarization could play a noticeable role in the cooling process. While other parameters in concern do not make a significant impact.

Analyzing the Effects of Stellar Evolution on White Dwarf Ages

NASA Astrophysics Data System (ADS)

Moss, Adam; Von Hippel, Ted, Dr.

2018-01-01

White dwarfs are among the oldest objects in our Galaxy, thus if we can determine their ages, we can derive the star formation history of our Galaxy. As part of a larger project that will use Gaia parallaxes to derive the ages of tens of thousands of white dwarfs, we explore the impact on the total white dwarf age of various modern models of main sequence and red giant branch stellar evolution, as well as uncertainties in progenitor metallicity. In addition, we study the effect on white dwarf ages caused by uncertainties in the Initial Final Mass Relation, which is the mapping between zero age main sequence and white dwarf masses. We find that for old and high mass white dwarfs, uncertainties in these factors have little effect on the total white dwarf age.

A global cloud map of the nearest known brown dwarf.

PubMed

Crossfield, I J M; Biller, B; Schlieder, J E; Deacon, N R; Bonnefoy, M; Homeier, D; Allard, F; Buenzli, E; Henning, Th; Brandner, W; Goldman, B; Kopytova, T

2014-01-30

Brown dwarfs--substellar bodies more massive than planets but not massive enough to initiate the sustained hydrogen fusion that powers self-luminous stars--are born hot and slowly cool as they age. As they cool below about 2,300 kelvin, liquid or crystalline particles composed of calcium aluminates, silicates and iron condense into atmospheric 'dust', which disappears at still cooler temperatures (around 1,300 kelvin). Models to explain this dust dispersal include both an abrupt sinking of the entire cloud deck into the deep, unobservable atmosphere and breakup of the cloud into scattered patches (as seen on Jupiter and Saturn). However, hitherto observations of brown dwarfs have been limited to globally integrated measurements, which can reveal surface inhomogeneities but cannot unambiguously resolve surface features. Here we report a two-dimensional map of a brown dwarf's surface that allows identification of large-scale bright and dark features, indicative of patchy clouds. Monitoring suggests that the characteristic timescale for the evolution of global weather patterns is approximately one day.

Detection of lithium in the cool halo dwarfs Groombridge 1830 and HD 134439: Implications for internal stellar mixing and cosmology

NASA Technical Reports Server (NTRS)

Deliyannis, Constantine P.; Ryan, Sean G.; Beers, Timothy C.; Thorburn, Julie A.

1994-01-01

Lithium abundances in halo stars, when interpreted correctly, hold the key to uncovering the primordial Li abundance Li(sub p). However, whereas standard stellar evolutionary models imply consistency in standard big bang nucleosynthesis (BBN), models with rotationally induced mixing imply a higher Li(sub p), possibly implying an inconsistency in standard BBN. We report here Li detections in two cool halo dwarfs, Gmb 1830 and HD 134439. These are the coolest and lowest Li detections in halo dwarfs to date, and are consistent with the metallicity dependence of Li depletion in published models. If the recent report of a beryllium deficiency in Gmb 1830 represents a real Be depletion, then the rotational models would be favored. We propose tests to reduce critical uncertainties.

Direct imaging and new technologies to search for substellar companions around MGs cool dwarfs

NASA Astrophysics Data System (ADS)

Gálvez-Ortiz, M. C.; Clarke, J. R. A.; Pinfield, D. J.; Folkes, S. L.; Jenkins, J. S.; García Pérez, A. E.; Burningham, B.; Day-Jones, A. C.; Jones, H. R. A.

2011-07-01

We describe here our project based in a search for sub-stellar companions (brown dwarfs and exo-planets) around young ultra-cool dwarfs (UCDs) and characterise their properties. We will use current and future technology (high contrast imaging, high-precision Doppler determinations) from the ground and space (VLT, ELT and JWST), to find companions to young objects. Members of young moving groups (MGs) have clear advantages in this field. We compiled a catalogue of young UCD objects and studied their membership to five known young moving groups: Local Association (Pleiades moving group, 20-150 Myr), Ursa Mayor group (Sirius supercluster, 300 Myr), Hyades supercluster (600 Myr), IC 2391 supercluster (35 Myr) and Castor moving group (200 Myr). To assess them as members we used different kinematic and spectroscopic criteria.

Measuring Atmospheric Abundances and Rotation of a Brown Dwarf with a Measured Mass and Radius

NASA Astrophysics Data System (ADS)

Birkby, Jayne

2015-08-01

There are no cool brown dwarfs with both a well-characterized atmosphere and a measured mass and radius. LHS 6343, a brown dwarf transiting one member of an M+M binary in the Kepler field, provides the first opportunity to tie theoretical atmospheric models to the observed brown dwarf mass-radius diagram. We propose four half-nights of observations with NIRSPAO in 2015B to measure spectral features in LHS 6343 C by detecting the relative motions of absorption features during the system's orbit. In addition to abundances, we will directly measure the brown dwarf's projected rotational velocity and mass.

New Observational Evidence of Flash Mixing on the White Dwarf Cooling Curve

NASA Technical Reports Server (NTRS)

Brown, T. M.; Lanz, T.; Sweigart, A. V.; Cracraft, Misty; Hubeny, Ivan; Landsman, W. B.

2011-01-01

Blue hook stars are a class of subluminous extreme horizontal branch stars that were discovered in UV images of the massive globular clusters w Cen and NGC 2808. These stars occupy a region of the HR diagram that is unexplained by canonical stellar evolution theory. Using new theoretical evolutionary and atmospheric models, we have shown that the blue hook stars are very likely the progeny of stars that undergo extensive internal mixing during a late helium-core flash on the white dwarf cooling curve. This "flash mixing" produces hotter-than-normal EHB stars with atmospheres significantly enhanced in helium and carbon. The larger bolometric correction, combined with the decrease in hydrogen opacity, makes these stars appear sub luminous in the optical and UV. Flash mixing is more likely to occur in stars born with a high helium abundance, due to their lower mass at the main sequence turnoff. For this reason, the phenomenon is more common in those massive globular clusters that show evidence for secondary populations enhanced in helium. However, a high helium abundance does not, by itself, explain the presence of blue hook stars in massive globular clusters. Here, we present new observational evidence for flash mixing, using recent HST observations. These include UV color-magnitude diagrams of six massive globular clusters and far-UV spectroscopy of hot subdwarfs in one of these clusters (NGC 2808).

A strange dwarf scenario for the formation of the peculiar double white dwarf binary SDSS J125733.63+542850.5

NASA Astrophysics Data System (ADS)

Jiang, Long; Chen, Wen-Cong; Li, Xiang-Dong

2018-05-01

The Hubble Space Telescope observation of the double white dwarf (WD) binary SDSS J125733.63+542850.5 reveals that the massive WD has a surface gravity log g1 ˜ 8.7 (which implies a mass of M1 ˜ 1.06 M⊙) and an effective temperature T1 ˜ 13 000 K, while the effective temperature of the low-mass WD (M2 < 0.24 M⊙) is T2 ˜ 6400K. Therefore, the massive and the low-mass WDs have a cooling age τ1 ˜ 1 Gyr and τ2 ≥ 5 Gyr, respectively. This is in contradiction with traditional binary evolution theory. In this paper, we propose a strange dwarf (SD) scenario to explain the formation of this double WD binary. We assume that the massive WD is a SD originating from a phase transition (PT) in a ˜1.1 M⊙ WD, which has experienced accretion and spin-down processes. Its high effective temperature could arise from the heating process during the PT. Our simulations suggest that the progenitor of SDSS J125733.63+542850.5 can be a binary system consisting of a 0.65 M⊙ WD and a 1.5 M⊙ main-sequence star in a 1.492 d orbit. Especially, the secondary star (i.e. the progenitor of the low-mass WD) is likely to have an ultra-low metallicity of Z = 0.0001.

VizieR Online Data Catalog: NIR spectroscopy of new L and T dwarf candidates (Kellogg+, 2017)

NASA Astrophysics Data System (ADS)

Kellogg, K.; Metchev, S.; Miles-Paez, P. A.; Tannock, M. E.

2018-02-01

We implemented a photometric search for peculiar L and T dwarfs using combined optical (SDSS), near-infrared (2MASS) and mid-infrared (WISE) fluxes. In Paper I (Kellogg et al. 2015AJ....150..182K), we reported a sample of 314 objects that passed all of our selection criteria and visual verification. After refining our visual verification, our total candidate L and T dwarf list was cut to 156 objects including 104 new candidates. We obtained near-infrared spectroscopic observations of the remaining 104 objects in our survey (66 peculiarly red, 13 candidate binary, and 25 general ultra-cool dwarf candidates) using the SpeX instrument on the NASA Infrared Telescope Facility (IRTF) and the Gemini Near-Infrared Spectrograph (GNIRS) instrument on the Gemini North telescope. We obtained the majority of our follow-up observations (91 of 104) with the SpeX spectrograph on the IRTF in prism mode (0.75-2.5μm; R~75-150), between 2014 October and 2016 April. The observing sequences and instrument settings were the same as those in Paper I (Kellogg et al. 2015AJ....150..182K). Table1 gives observation epochs and SpeX instrument settings for each science target. We followed-up the remaining 13 objects in our candidate list using the Gemini Near-Infrared Spectrograph (GNIRS) on Gemini North (0.9-2.5μm). We observed these objects in queue mode between 2015 October and 2017 May. We took the observations in cross-dispersed mode with the short-blue camera with 32l/mm grating and a 1.0''*7.0'' slit, resulting in a resolution of R~500. We used a standard A-B-B-A nodding sequence along the slit to record object and sky spectra. Individual exposure times were 120s per pointing. Table2 gives Gemini/GNIRS observation epochs for each science target. (4 data files).

Is the SDSS ZZ Ceti instability strip really pure?

NASA Astrophysics Data System (ADS)

de Souza Oliveira, Kepler

2006-08-01

We propose to obtain SNR > 60 optical spectra of the DA white dwarf stars for which the Sloan Digital Sky Survey spectra indicated temperatures inside de ZZ Ceti instability strip, but time series photometry show they are not variables. The Sloan spectra have insufficient SNR, specially below 4000A, where there are hydrogen lines whose strength can be used to measure surface gravity accurately. Theoretically and observationally, the location of the instability strip depends both on temperature and mass. To use the properties derived from the pulsating stars as applying to all white dwarf stars, and their progenitors, we must demonstrate pulsation is a normal evolutionary state. As the instability strip is only 1200K wide, accurate temperatures and log g must be obtained and therefore the spectra must include the log g sensitive lines Hgamma to H9. White dwarf stars, the objects of this proposal, are the end point of evolution of around 97% of all stars born. As they cool, they pass through instability strips, where they are seen as multi-periodic pulsators. Each pulsation is an independent measurement, placing another constraint on the stellar properties. Pulsations allow the determination of the stellar compositional layers, including the core, crucial to understand the progenitor's evolution, from AGB to planetary nebulae nuclei, "born again" phase, and their possible evolution to SNIa through accretion. As white dwarf progenitors lose at least half of their masses before turning into white dwarfs, they contribute to the interstellar medium enrichment, and measuring their structure in detail will allow us to decode nuclear reaction rates and convection, which determine their evolution. Pulsating white dwarf stars are also laboratories for physics at high densities as crystallization, neutrino cooling, and axion emission. White dwarf cooling, also measured through pulsations, allows an independent measurement of the age of the galactic components and was the first to indicate an age of 13 Gyr to the Universe, back in 1987. Now that we have observed white dwarf stars in all the components of our galaxy, possible differences in component ages are detectable. Our goal is to determine if the instalibity strip is pure, implying the information we obtain on the variables applies to white dwarf stars in general. As these stars are on average fainter than g=18.2, we require blue sensitive 8m class telescope.

The complete nucleotide sequence of the Barley yellow dwarf virus-RMV genome reveals it to be a new Polerovirus distantly related to other yellow dwarf viruses

USDA-ARS?s Scientific Manuscript database

The yellow dwarf viruses (YDVs) of the Luteoviridae family represent the most widespread group of cereal viruses worldwide. They include the Barley yellow dwarf viruses (BYDVs) of genus Luteovirus, the Cereal yellow dwarf viruses (CYDVs) and Wheat yellow dwarf virus (WYDV) of genus Polerovirus. All ...

Innocent Bystanders: Carbon Stars from the Sloan Digital Sky Survey

NASA Astrophysics Data System (ADS)

Green, Paul

2013-03-01

Among stars showing carbon molecular bands (C stars), the main-sequence dwarfs, likely in post-mass transfer binaries, are numerically dominant in the Galaxy. Via spectroscopic selection from the Sloan Digital Sky Survey, we retrieve 1220 high galactic latitude C stars, ~5 times more than previously known, including a wider variety than past techniques such as color or grism selection have netted, and additionally yielding 167 DQ white dwarfs. Of the C stars with proper motion measurements, we identify 69% clearly as dwarfs (dCs), while ~7% are giants. The dCs likely span absolute magnitudes Mi from ~6.5 to 10.5. "G-type" dC stars with weak CN and relatively blue colors are probably the most massive dCs still cool enough to show C2 bands. We report Balmer emission in 22 dCs, none of which are G-types. We find 8 new DA/dC stars in composite spectrum binaries, quadrupling the total sample of these "smoking guns" for AGB binary mass transfer. Eleven very red C stars with strong red CN bands appear to be "N"-type AGB stars at large Galactocentric distances, one likely a new discovery in the dIrr galaxy Leo A. Two such stars within 30' of each other may trace a previously unidentified dwarf galaxy or tidal stream at ~40 kpc. We explore the multiwavelength properties of the sample and report the first X-ray detection of a dC star, which shows strong Balmer emission. Our own spectroscopic survey additionally provides the dC surface density from a complete sample of dwarfs limited by magnitude, color, and proper motion.

The Origin and Evolution of the White-Dwarf Stars

NASA Astrophysics Data System (ADS)

Clemens, J. C.

1994-12-01

The secret of how white dwarf stars form and evolve is hidden in their interiors. There, gravity separates the constituent elements into layers; the lighter elements float to the top and the heavier ones sink. Consequently, a white dwarf's structure depends on the quantity of the elements present. Measuring that structure can tell us about the processes which formed white dwarfs and allow us to calculate how fast they cool. The latter is indispensable for measuring the age of our galaxy using the oldest white dwarfs as chronometers. Because some white dwarfs pulsate, we can exploit the resulting luminosity variations to measure their internal structure using "asteroseismology," a procedure analogous to terrestrial seismology. Exploring white dwarf structure via asteroseismology poses a difficult observational task: acquiring essentially uninterrupted time series measurements of the brightness changes of pulsating white dwarf stars. We have accomplished this task using an instrument we developed for this purpose, the Whole Earth Telescope. By combining data from the Whole Earth Telescope with published measurements, we have detected a common pattern in the pulsation spectra of all the variable, hydrogen spectra white dwarfs (DAVs), implying that they have similar surface hydrogen layer masses. Because we have identified the degree (l) and the radial overtone (k) of the modes in the pattern detected, we have been able to compare their periods to published pulsation models to find the mass of the hydrogen layer; it is about 10^-4 times the total stellar mass. This result will require adjustments to published estimates of the age of the galaxy which use theoretical cooling times of the oldest white dwarfs as a time standard; the theoretical models typically assume much thinner hydrogen layers. We have also investigated the two classes of pulsating helium spectra white dwarfs (DOVs and DBVs). From their pulsation properties, and the mass of the hydrogen layer measured for the DAVs, we have concluded that the helium surface white dwarfs do not form via the same process as the hydrogen surface stars. There must be at least two separate channels for white dwarf formation. (SECTION: Dissertation Summary)

The Origin and Evolution of the White Dwarf Stars

NASA Astrophysics Data System (ADS)

Clemens, J. C.

1994-05-01

The secret of how white dwarf stars form and evolve is hidden in their interiors. There, gravity separates the constituent elements into layers; the lighter elements float to the top and the heavier ones sink. Consequently, a white dwarf's structure depends on the quantity of the elements present. Measuring that structure can tell us about the processes which formed white dwarfs and allow us to calculate how fast they cool. The latter is indispensable for measuring the age of our galaxy using the oldest white dwarfs as chronometers. Because some white dwarfs pulsate, we can exploit the resulting luminosity variations to measure their internal structure using asteroseismology. Exploring white dwarf structure via asteroseismology poses a difficult observational task: acquiring essentially uninterrupted time series measurements of the brightness changes of pulsating white dwarf stars. We have accomplished this task using an instrument we call the Whole Earth Telescope (WET). By combining data from the WET with published measurements, we have detected a common pattern in the pulsation spectra of all the variable, hydrogen spectra white dwarfs (DAVs), implying that they have similar surface hydrogen layer masses. Because we have identified the degree (l) and the radial overtone (k) of the modes in the pattern detected, we have been able to compare their periods to published pulsation models to find the mass of the hydrogen layer; it is about 10(-4) times the total stellar mass. This result will require adjustments to published estimates of the age of the galaxy which use theoretical cooling times of the oldest white dwarfs as a time standard; the theoretical models typically assume much thinner hydrogen layers. We have also investigated the two classes of pulsating helium spectra white dwarfs (DOVs and DBVs). From their pulsation properties, and the mass of the hydrogen layer measured for the DAVs, we have concluded that the helium surface white dwarfs do not form via the same process as the hydrogen surface stars. There must be at least two separate channels for white dwarf formation.

The origin and evolution of the white dwarf stars

NASA Astrophysics Data System (ADS)

Clemens, James Christopher

1994-01-01

The secret of how white dwarf stars form and evolve is hidden in their interiors. There, gravity separates the constituent elements into layers; the lighter elements float to the top and the heavier ones sink. Consequently, a white dwarf's structure depends on the quantity of the elements present. Measuring that structure can tell Us about the processes which formed white dwarfs and allow us to calculate how fast they cool. The latter is indispensable for measuring the age of our galaxy using the oldest white dwarfs as chronometers. Because some white dwarfs pulsate, we can exploit the resulting luminosity variations to measure their internal structure using 'asteroseismology', a procedure analogous to terrestrial seismology. Exploring white dwarf structure via asteroseismology poses a difficult observational task: acquiring essentially uninterrupted time series measurements of the brightness changes of pulsating white dwarf stars. We have accomplished this task using an instrument we developed for this purpose, the Whole Earth Telescope. By combining data from the Whole Earth Telescope with published measurements, we have detected a common pattern in the pulsation spectra of all the variable, hydrogen spectra white dwarfs (DAVs), implying that they have similar surface hydrogen layer masses. Because we have identified the degree (l) and the radial overtone (k) of the modes in the pattern detected, we have been able to compare their periods to published pulsation models to find the mass of the hydrogen layer, it is about 10-4 times the total stellar mass. This result will require adjustments to published estimates of the age of the galaxy which use theoretical cooling times of the oldest white dwarfs as a time standard; the theoretical models typically assume much thinner hydrogen layers. We have also investigated the two classes of pulsating helium spectra white dwarfs (DOVs and DBVs). From their pulsation properties and the mass of the hydrogen layer measured for the DAVs, we have concluded that the helium surface white dwarfs do not form via the same process as the hydrogen surface stars. There must be at least two separate channels for white dwarf formation.

Properties of quasi-periodic oscillations in accreting magnetic white dwarfs

NASA Technical Reports Server (NTRS)

Wu, Kinwah; Chanmugam, G.; Shaviv, G.

1992-01-01

Previous studies of time-dependent accretion onto magnetic white dwarfs, in which the cooling was assumed to be due to bremsstrahlung emission, have shown that the accretion shock undergoes oscillations. However, when cyclotron cooling is also included, the oscillations are damped for sufficiently strong magnetic fields. Here we demonstrate that the oscillations can be sustained by accretion-fluctuation-induced excitations. The frequency of the QPOs are shown to increase quadratically with the magnetic field strength. We interpret the oscillations as a two-phase process in which bremsstrahlung cooling dominates in one half-cycle and cyclotron cooling in the other. Such a process may have very different consequences compared to a single-phase process where the functional form of the cooling is essentially the same throughout the cycle. If in the two-phase process damping occurs mainly in the cyclotron cooling half-cycle, there will be a universal effective damping factor which tends to suppress all oscillation modes indiscriminately. The oscillations of the accretion shock also could be a limit cycle process in which the system vacillates between two branches.

The onset of planet formation in brown dwarf disks.

PubMed

Apai, Dániel; Pascucci, Ilaria; Bouwman, Jeroen; Natta, Antonella; Henning, Thomas; Dullemond, Cornelis P

2005-11-04

The onset of planet formation in protoplanetary disks is marked by the growth and crystallization of sub-micrometer-sized dust grains accompanied by dust settling toward the disk mid-plane. Here, we present infrared spectra of disks around brown dwarfs and brown dwarf candidates. We show that all three processes occur in such cool disks in a way similar or identical to that in disks around low- and intermediate-mass stars. These results indicate that the onset of planet formation extends to disks around brown dwarfs, suggesting that planet formation is a robust process occurring in most young circumstellar disks.

Three very cool degenerate stars in Luyten common proper motion binaries - Implications for the age of the galactic disk

NASA Technical Reports Server (NTRS)

Hintzen, Paul; Oswalt, Terry D.; Liebert, James; Sion, Edward M.

1989-01-01

During the course of a spectroscopic study of Luyten common proper motion (CPM) stars, spectrophotometric observations have been obtained of three binaries containing degenerate stars with estimated absolute magnitudes M(V) of about 16. Each of the three pairs consists of a yellow degenerate star primary and a DC 13 + secondary 1.4-2.3 mag fainter. One of the primary stars is spectral class DC 7, another is a sharp-lined DA 8, and the third shows peculiar broad absorption features which we interpret as pressure-shifted C2 Swan bands. The LP 701 - 69/70 system has survived for over 8 billion years without disruption by passing stars, despite its 1500 a.u. orbital major axis. The three cool degenerate companions nearly double the available sample of stars at the low-luminosity terminus of the white dwarf cooling sequence. These findings appear consistent with the conclusion that degenerate stars in the old disk population have not had time to evolve to a luminosity fainter than M(V) about 16.2.

The complete nucleotide sequence of the genome of Barley yellow dwarf virus-RMV reveals it to be a new Polerovirus distantly related to other yellow dwarf viruses

PubMed Central

Krueger, Elizabeth N.; Beckett, Randy J.; Gray, Stewart M.; Miller, W. Allen

2013-01-01

The yellow dwarf viruses (YDVs) of the Luteoviridae family represent the most widespread group of cereal viruses worldwide. They include the Barley yellow dwarf viruses (BYDVs) of genus Luteovirus, the Cereal yellow dwarf viruses (CYDVs) and Wheat yellow dwarf virus (WYDV) of genus Polerovirus. All of these viruses are obligately aphid transmitted and phloem-limited. The first described YDVs (initially all called BYDV) were classified by their most efficient vector. One of these viruses, BYDV-RMV, is transmitted most efficiently by the corn leaf aphid, Rhopalosiphum maidis. Here we report the complete 5612 nucleotide sequence of the genomic RNA of a Montana isolate of BYDV-RMV (isolate RMV MTFE87, Genbank accession no. KC921392). The sequence revealed that BYDV-RMV is a polerovirus, but it is quite distantly related to the CYDVs or WYDV, which are very closely related to each other. Nor is BYDV-RMV closely related to any other particular polerovirus. Depending on the gene that is compared, different poleroviruses (none of them a YDV) share the most sequence similarity to BYDV-RMV. Because of its distant relationship to other YDVs, and because it commonly infects maize via its vector, R. maidis, we propose that BYDV-RMV be renamed Maize yellow dwarf virus-RMV (MYDV-RMV). PMID:23888156

The complete nucleotide sequence of the genome of Barley yellow dwarf virus-RMV reveals it to be a new Polerovirus distantly related to other yellow dwarf viruses.

PubMed

Krueger, Elizabeth N; Beckett, Randy J; Gray, Stewart M; Miller, W Allen

2013-01-01

The yellow dwarf viruses (YDVs) of the Luteoviridae family represent the most widespread group of cereal viruses worldwide. They include the Barley yellow dwarf viruses (BYDVs) of genus Luteovirus, the Cereal yellow dwarf viruses (CYDVs) and Wheat yellow dwarf virus (WYDV) of genus Polerovirus. All of these viruses are obligately aphid transmitted and phloem-limited. The first described YDVs (initially all called BYDV) were classified by their most efficient vector. One of these viruses, BYDV-RMV, is transmitted most efficiently by the corn leaf aphid, Rhopalosiphum maidis. Here we report the complete 5612 nucleotide sequence of the genomic RNA of a Montana isolate of BYDV-RMV (isolate RMV MTFE87, Genbank accession no. KC921392). The sequence revealed that BYDV-RMV is a polerovirus, but it is quite distantly related to the CYDVs or WYDV, which are very closely related to each other. Nor is BYDV-RMV closely related to any other particular polerovirus. Depending on the gene that is compared, different poleroviruses (none of them a YDV) share the most sequence similarity to BYDV-RMV. Because of its distant relationship to other YDVs, and because it commonly infects maize via its vector, R. maidis, we propose that BYDV-RMV be renamed Maize yellow dwarf virus-RMV (MYDV-RMV).

Ultracool Dwarfs in the Ukirt Infrared Deep Sky Survey (UKIDSS)

NASA Astrophysics Data System (ADS)

Burningham, Ben; Pinfield, D.; Leggett, S. K.; Lodieu, N.; Warren, S. J.; Lucas, P. W.; Tamura, M.; Mortlock, D.; Kendall, T. R.; Jones, H. R.; Jameson, R. F.; Richard, M.; Martin, E. L.; UKIDSS Cool Dwarf Science Working Group

2007-05-01

The UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) presents an unparallelled resource for the study of field brown dwarfs. The UKIDSS Cool Dwarf Science Working Group (CDSWG) is carrying out a search for the lowest temperature brown dwarfs ever discovered, with the possibility of identifying a new spectral class of ultracool dwarf: the Y dwarf. CDSWG members identified 10 new T dwarfs in the early and first data releases of the LAS, including 2 objects with spectral types later than T7.5. One of these is thought to be the coolest T dwarf ever found with a spectral type of T8.5, and an estimated temperature of 650K. Data release 2 (DR2) took place on 1st March 2007, and already the most promising objects have been selected and followed-up photometrically and spectroscopically. In this contribution I will discuss the capabilities of UKIDSS for identifying ultracool dwarfs and summarise our latest results.

IUE spectrophotometry of the DA4 primary in the short-period white dwarf-red dwarf spectroscopic binary Case 1

NASA Technical Reports Server (NTRS)

Sion, E. M.; Guinan, E. F.; Wesemael, F.

1984-01-01

Low-resolution ultraviolet International Ultraviolet Explorer spectra of the DA white dwarf Case 1 are presented. The spectra show the presence of the 1400 A feature, already discovered in several other DA stars, and of a shallower trough in the 1550-1700 A range. A model atmosphere analysis of the ultraviolet energy distribution of the Ly-alpha red wing yields T(e) = 13,000 + or - 500 K. Possible interpretations of the 1400 A feature are reviewed. Case 1 is the coolest white dwarf found in a short-period, detached white dwarf-red dwarf binary, and its cooling time is consistent with estimates of the efficiency of angular momentum removal mechanisms in the phases subsequent to common envelope binary evolution.

The complete nucleotide sequence of the barley yellow dwarf GPV isolate from China shows that it is a new member of the genus Polerovirus.

PubMed

Zhang, Wenwei; Cheng, Zhuomin; Xu, Lei; Wu, Maosen; Waterhouse, Peter; Zhou, Guanghe; Li, Shifang

2009-01-01

The complete nucleotide sequence of the ssRNA genome of a Chinese GPV isolate of barley yellow dwarf virus (BYDV) was determined. It comprised 5673 nucleotides, and the deduced genome organization resembled that of members of the genus Polerovirus. It was most closely related to cereal yellow dwarf virus-RPV (77% nt identity over the entire genome; coat protein amino acid identity 79%). The GPV isolate also differs in vector specificity from other BYDV strains. Biological properties, phylogenetic analyses and detailed sequence comparisons suggest that GPV should be considered a member of a new species within the genus, and the name Wheat yellow dwarf virus-GPV is proposed.

The ultracool-field dwarf luminosity-function and space density from the Canada-France Brown Dwarf Survey

NASA Astrophysics Data System (ADS)

Reylé, C.; Delorme, P.; Willott, C. J.; Albert, L.; Delfosse, X.; Forveille, T.; Artigau, E.; Malo, L.; Hill, G. J.; Doyon, R.

2010-11-01

Context. Thanks to recent and ongoing large scale surveys, hundreds of brown dwarfs have been discovered in the last decade. The Canada-France Brown Dwarf Survey is a wide-field survey for cool brown dwarfs conducted with the MegaCam camera on the Canada-France-Hawaii Telescope. Aims: Our objectives are to find ultracool brown dwarfs and to constrain the field brown-dwarf luminosity function and the mass function from a large and homogeneous sample of L and T dwarfs. Methods: We identify candidates in CFHT/MegaCam i' and z' images and follow them up with pointed near infrared (NIR) imaging on several telescopes. Halfway through our survey we found ~50 T dwarfs and ~170 L or ultra cool M dwarfs drawn from a larger sample of 1400 candidates with typical ultracool dwarfs i'-z' colours, found in 780 square degrees. Results: We have currently completed the NIR follow-up on a large part of the survey for all candidates from mid-L dwarfs down to the latest T dwarfs known with utracool dwarfs' colours. This allows us to draw on a complete and well defined sample of 102 ultracool dwarfs to investigate the luminosity function and space density of field dwarfs. Conclusions: We found the density of late L5 to T0 dwarfs to be 2.0+0.8-0.7 × 10-3 objects pc-3, the density of T0.5 to T5.5 dwarfs to be 1.4+0.3-0.2 × 10-3 objects pc-3, and the density of T6 to T8 dwarfs to be 5.3+3.1-2.2 × 10-3 objects pc-3. We found that these results agree better with a flat substellar mass function. Three latest dwarfs at the boundary between T and Y dwarfs give the high density 8.3+9.0-5.1 × 10-3 objects pc-3. Although the uncertainties are very large this suggests that many brown dwarfs should be found in this late spectral type range, as expected from the cooling of brown dwarfs, whatever their mass, down to very low temperature. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at TERAPIX and the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS. Based on observations made with the ESO New Technology Telescope at the La Silla Observatory. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil) and CONICET (Argentina). Based on observations with the Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. Based on observations made at The McDonald Observatory of the University of Texas at Austin.Tables 3, 5 and 8 are only available in electronic form at http://www.aanda.org

Axions and the luminosity function of white dwarfs. The thin and thick disks, and the halo

NASA Astrophysics Data System (ADS)

Isern, J.; García-Berro, E.; Torres, S.; Cojocaru, R.; Catalán, S.

2018-05-01

The evolution of white dwarfs is a simple gravothermal process of cooling. Since the shape of their luminosity function is sensitive to the characteristic cooling time, it is possible to use its slope to test the existence of additional sources or sinks of energy, such as those predicted by alternative physical theories. The aim of this paper is to study if the changes in the slope of the white dwarf luminosity function around bolometric magnitudes ranging from 8 to 10 and previously attributed to axion emission are, effectively, a consequence of the existence of axions and not an artifact introduced by the star formation rate. We compute theoretical luminosity functions of the thin and thick disk, and of the stellar halo including axion emission and we compare them with the existing observed luminosity functions. Since these stellar populations have different star formation histories, the slope change should be present in all of them at the same place if it is due to axions or any other intrinsic cooling mechanism. The signature of an unexpected cooling seems to be present in the luminosity functions of the thin and thick disks, as well as in the halo luminosity function. This additional cooling is compatible with axion emission, thus supporting to the idea that DFSZ axions, with a mass in the range of 4 to 10 meV, could exist. If this were the case, these axions could be detected by the future solar axioscope IAXO.

Metal Accretion onto White Dwarfs. I. The Approximate Approach Based on Estimates of Diffusion Timescales

NASA Astrophysics Data System (ADS)

Fontaine, G.; Brassard, P.; Dufour, P.; Tremblay, P.-E.

2015-06-01

The accretion-diffusion picture is the model par excellence for describing the presence of planetary debris polluting the atmospheres of relatively cool white dwarfs. Some important insights into the process may be derived using an approximate approach which combines static stellar models with estimates of diffusion timescales at the base of the outer convection zone or, in its absence, at the photosphere. Until recently, and to our knowledge, values of diffusion timescales in white dwarfs have all been obtained on the basis of the same physics as that developed initially by Paquette et al., including their diffusion coefficients and thermal diffusion coefficients. In view of the recent exciting discoveries of a plethora of metals (including some never seen before) polluting the atmospheres of an increasing number of cool white dwarfs, we felt that a new look at the estimates of settling timescales would be worthwhile. We thus provide improved estimates of diffusion timescales for all 27 elements from Li to Cu in the periodic table in a wide range of the surface gravity-effective temperature domain and for both DA and non-DA stars.

Accretional Heating by Periodic Dwarf Nova Outburst Events

NASA Astrophysics Data System (ADS)

Godon, P.; Sion, E. M.

2001-12-01

We carry out simulations of evolutionary models of accreting white dwarfs in dwarf novae to assess the combined effect of boundary layer irradiation and compressional heating on the accreting star. We focus on the behavior of the surface observables of the accreting white dwarf for different value of the mass accretion rate and accretor mass. Outburst of days to weeks are followed by a shut off of the radial infall during quiescences lasting weeks to months. Preliminary results indicate that after a long evolution time of many accretion cycles, the effective surface temperature of the white dwarf will increase substantially. The purpose of this work is to generate a grid of models that will then be used to compared with observations of white dwarf heating and cooling in dwarf nova systems. This work is supported by NASA HST grant GO-8139 and in part by NSF grant AST99-01955 and NASA grant NAG5-8388.

Polycistronic artificial miRNA-mediated resistance to Wheat dwarf virus in barley is highly efficient at low temperature.

PubMed

Kis, András; Tholt, Gergely; Ivanics, Milán; Várallyay, Éva; Jenes, Barnabás; Havelda, Zoltán

2016-04-01

Infection of Wheat dwarf virus (WDV) strains on barley results in dwarf disease, imposing severe economic losses on crop production. As the natural resistance resources against this virus are limited, it is imperative to elaborate a biotechnological approach that will provide effective and safe immunity to a wide range of WDV strains. Because vector insect-mediated WDV infection occurs during cool periods in nature, it is important to identify a technology which is effective at lower temperature. In this study, we designed artificial microRNAs (amiRNAs) using a barley miRNA precursor backbone, which target different conservative sequence elements of the WDV strains. Potential amiRNA sequences were selected to minimize the off-target effects and were tested in a transient sensor system in order to select the most effective constructs at low temperature. On the basis of the data obtained, a polycistronic amiRNA precursor construct (VirusBuster171) was built expressing three amiRNAs simultaneously. The construct was transformed into barley under the control of a constitutive promoter. The transgenic lines were kept at 12-15 °C to mimic autumn and spring conditions in which major WDV infection and accumulation take place. We were able to establish a stable barley transgenic line displaying resistance to insect-mediated WDV infection. Our study demonstrates that amiRNA technology can be an efficient tool for the introduction of highly efficient resistance in barley against a DNA virus belonging to the Geminiviridae family, and this resistance is effective at low temperature where the natural insect vector mediates the infection process. © 2015 BSPP and John Wiley & Sons Ltd.

Stellar activity with LAMOST - II. Chromospheric activity in open clusters

NASA Astrophysics Data System (ADS)

Fang, Xiang-Song; Zhao, Gang; Zhao, Jing-Kun; Bharat Kumar, Yerra

2018-05-01

We use the LAMOST spectra of member stars in Pleiades, M34, Praesepe, and Hyades to study how chromospheric activity varies as a function of mass and rotation at different age. We measured excess equivalent widths of H α, H β, and Ca II K based on estimated chromospheric contributions from old and inactive field dwarfs, and excess luminosities are obtained by normalizing bolometric luminosity, for more than 700 late-type stars in these open clusters. Results indicate two activity sequences in cool spot coverage and H α excess emission among GK dwarfs in Pleiades and M dwarfs in Praesepe and Hyades, paralleling with well-known rotation sequences. A weak dependence of chromospheric emission on rotation exists among ultrafast rotators in saturated regime with Rossby number Ro ≲ 0.1. In the unsaturated regime, chromospheric and coronal emission show similar dependence on Ro, but with a shift towards larger Ro, indicating chromospheric emission gets easily saturated than coronal emission, and/or convective turnover time-scales based on X-ray data do not work well with chromospheric emission. More interestingly, our analysis shows fully convective slow rotators obey the rotation-chromospheric activity relation similar to hotter stars, confirming the previous finding. We found correlations among H α, H β, and Ca II K emissions, in which H α losses are more important than Ca II K for cooler and more active stars. In addition, a weak correlation is seen between chromospheric emission and photospheric activity that shows dependence on stellar spectral type and activity level, which provides some clues on how spot configuration varies as a function of mass and activity level.

Weather on Other Worlds. IV. Hα Emission and Photometric Variability Are Not Correlated in L0–T8 Dwarfs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miles-Páez, Paulo A.; Metchev, Stanimir A.; Heinze, Aren

Recent photometric studies have revealed that surface spots that produce flux variations are present on virtually all L and T dwarfs. Their likely magnetic or dusty nature has been a much-debated problem, the resolution to which has been hindered by paucity of diagnostic multi-wavelength observations. To test for a correlation between magnetic activity and photometric variability, we searched for H α emission among eight L3–T2 ultra-cool dwarfs with extensive previous photometric monitoring, some of which are known to be variable at 3.6 μ m or 4.5 μ m. We detected H α only in the non-variable T2 dwarf 2MASS J12545393−0122474.more » The remaining seven objects do not show H α emission, even though six of them are known to vary photometrically. Combining our results with those for 86 other L and T dwarfs from the literature show that the detection rate of H α emission is very high (94%) for spectral types between L0 and L3.5 and much smaller (20%) for spectral types ≥L4, while the detection rate of photometric variability is approximately constant (30%–55%) from L0 to T8 dwarfs. We conclude that chromospheric activity, as evidenced by H α emission, and large-amplitude photometric variability are not correlated. Consequently, dust clouds are the dominant driver of the observed variability of ultra-cool dwarfs at spectral types, at least as early as L0.« less

Diffusion of neon in white dwarf stars.

PubMed

Hughto, J; Schneider, A S; Horowitz, C J; Berry, D K

2010-12-01

Sedimentation of the neutron rich isotope 22Ne may be an important source of gravitational energy during the cooling of white dwarf stars. This depends on the diffusion constant for 22Ne in strongly coupled plasma mixtures. We calculate self-diffusion constants D(i) from molecular dynamics simulations of carbon, oxygen, and neon mixtures. We find that D(i) in a mixture does not differ greatly from earlier one component plasma results. For strong coupling (coulomb parameter Γ> few), D(i) has a modest dependence on the charge Z(i) of the ion species, D(i)∝Z(i)(-2/3). However, D(i) depends more strongly on Z(i) for weak coupling (smaller Γ). We conclude that the self-diffusion constant D(Ne) for 22Ne in carbon, oxygen, and neon plasma mixtures is accurately known so that uncertainties in D(Ne) should be unimportant for simulations of white dwarf cooling.

Variability and periodicity of field M dwarfs revealed by multichannel monitoring

NASA Astrophysics Data System (ADS)

Rockenfeller, B.; Bailer-Jones, C. A. L.; Mundt, R.

2006-03-01

We present simultaneous, multiband photometric monitoring of 19 field dwarfs covering most of the M spectral sequence (M2-M9). Significant variability was found in seven objects in at least one out of the three channels I, R and G. Periodic variability was tested with a CLEAN power spectral analysis. Two objects, LHS370 (M5V) and 2M1707+64 (M9V), show periods of 5.9± 2.0 and 3.65± 0.1 h respectively. On account of the agreement with the typical values of v sin i published for M dwarfs (Mohanty & Basri 2003, ApJ, 583, 451), we claim these to be the objects' rotation periods. Three further objects show possible periods of a few hours. Comparing the variability amplitude in each channel with predictions based on the synthetic spectra of Allard et al. (2001, ApJ, 556, 357), we investigated the source of variability in LHS370 and 2M1707+64. For the latter, we find evidence for the presence of magnetically-induced cool spots at a temperature contrast of 4-8%, with a projected surface coverage factor of less than 0.075. Moreover, we can rule out dust clouds (as represented by the COND or DUSTY models) as the cause of the variability. No conclusion can be drawn in the case of LHS370. Comparing the frequency of occurrence of variability in this and various L dwarf samples published over the past few years, we find that variability is more common in field L dwarfs than in field M dwarfs (for amplitudes larger than 0.005 mag on timescales of 0.5 to 20 h). Using the homogeneous data sets of this work and Bailer-Jones & Mundt (2001, A&A, 367, 218), we find fractions of variable objects of 0.21± 0.11 among field M dwarfs and 0.70± 0.26 among field L dwarfs (and 0.29± 0.13, 0.48± 0.12 respectively if we take into account a larger yet more inhomogeneous sample). This is marginally significant (2σ deviation) and implies a change in the physical nature and/or extent of surface features when moving from M to L dwarfs.

DWARF – a data warehouse system for analyzing protein families

PubMed Central

Fischer, Markus; Thai, Quan K; Grieb, Melanie; Pleiss, Jürgen

2006-01-01

Background The emerging field of integrative bioinformatics provides the tools to organize and systematically analyze vast amounts of highly diverse biological data and thus allows to gain a novel understanding of complex biological systems. The data warehouse DWARF applies integrative bioinformatics approaches to the analysis of large protein families. Description The data warehouse system DWARF integrates data on sequence, structure, and functional annotation for protein fold families. The underlying relational data model consists of three major sections representing entities related to the protein (biochemical function, source organism, classification to homologous families and superfamilies), the protein sequence (position-specific annotation, mutant information), and the protein structure (secondary structure information, superimposed tertiary structure). Tools for extracting, transforming and loading data from public available resources (ExPDB, GenBank, DSSP) are provided to populate the database. The data can be accessed by an interface for searching and browsing, and by analysis tools that operate on annotation, sequence, or structure. We applied DWARF to the family of α/β-hydrolases to host the Lipase Engineering database. Release 2.3 contains 6138 sequences and 167 experimentally determined protein structures, which are assigned to 37 superfamilies 103 homologous families. Conclusion DWARF has been designed for constructing databases of large structurally related protein families and for evaluating their sequence-structure-function relationships by a systematic analysis of sequence, structure and functional annotation. It has been applied to predict biochemical properties from sequence, and serves as a valuable tool for protein engineering. PMID:17094801

Habitable planets around white and brown dwarfs: the perils of a cooling primary.

PubMed

Barnes, Rory; Heller, René

2013-03-01

White and brown dwarfs are astrophysical objects that are bright enough to support an insolation habitable zone (IHZ). Unlike hydrogen-burning stars, they cool and become less luminous with time; hence their IHZ moves in with time. The inner edge of the IHZ is defined as the orbital radius at which a planet may enter a moist or runaway greenhouse, phenomena that can remove a planet's surface water forever. Thus, as the IHZ moves in, planets that enter it may no longer have any water and are still uninhabitable. Additionally, the close proximity of the IHZ to the primary leads to concern that tidal heating may also be strong enough to trigger a runaway greenhouse, even for orbital eccentricities as small as 10(-6). Water loss occurs due to photolyzation by UV photons in the planetary stratosphere, followed by hydrogen escape. Young white dwarfs emit a large amount of these photons, as their surface temperatures are over 10(4) K. The situation is less clear for brown dwarfs, as observational data do not constrain their early activity and UV emission very well. Nonetheless, both types of planets are at risk of never achieving habitable conditions, but planets orbiting white dwarfs may be less likely to sustain life than those orbiting brown dwarfs. We consider the future habitability of the planet candidates KOI 55.01 and 55.02 in these terms and find they are unlikely to become habitable.

Gaia Confirms that SDSS J102915+172927 is a Dwarf Star

NASA Astrophysics Data System (ADS)

Bonifacio, P.; Caffau, E.; Spite, M.; Spite, F.; François, P.; Zaggia, S.; Arenou, F.; Haigron, R.; Leclerc, N.; Marchal, O.; Panuzzo, P.; Plum, G.; Sartoretti, P.

2018-05-01

The Gaia Data Release 2 provides a parallax of 0.734+/-0.073 mas for SDSS J102915+172927, currently the most metal-poor known object. This parallax implies that it is dwarf star, ruling out the scenario that it is a subgiant. The subgiant scenario had as a corollary that the star had been formed in a medium highly enriched in C, thus making line cooling efficient during the collapse, that was also highly enriched in Fe by Type Ia SNe. This scenario can also now be ruled out for this star, reinforcing the need of dust cooling and fragmentation to explain its formation.

The `DODO' survey - I. Limits on ultra-cool substellar and planetary-mass companions to van Maanen's star (vMa2)

NASA Astrophysics Data System (ADS)

Burleigh, M. R.; Clarke, F. J.; Hogan, E.; Brinkworth, C. S.; Bergeron, P.; Dufour, P.; Dobbie, P. D.; Levan, A. J.; Hodgkin, S. T.; Hoard, D. W.; Wachter, S.

2008-05-01

We report limits in the planetary-mass regime for companions around the nearest single white dwarf to the Sun, van Maanen's star (vMa2), from deep J-band imaging with Gemini North and Spitzer Infrared Array Camera (IRAC) mid-IR photometry. We find no resolved common proper motion companions to vMa2 at separations from 3 to 45 arcsec, at a limiting magnitude of J ~ 23. Assuming a total age for the system of 4.1 +/- 1Gyr, and utilizing the latest evolutionary models for substellar objects, this limit is equivalent to companion masses >7 +/- 1MJup(Teff ~ 300K). Taking into account the likely orbital evolution of very low mass companions in the post-main-sequence phase, these J-band observations effectively survey orbits around the white dwarf progenitor from 3 to 50au. There is no flux excess detected in any of the complimentary Spitzer IRAC mid-IR filters. We fit a white dwarf model atmosphere to the optical BVRI, JHK and IRAC photometry. The best solution gives Teff = 6030 +/- 240K, logg = 8.10 +/- 0.04 and, hence, M = 0.633 +/- 0.022Msolar. We then place a 3σ upper limit of 10 +/- 2MJup on the mass of any unresolved companion in the 4.5μm band.

M dwarf spectra from 0.6 to 1.5 micron - A spectral sequence, model atmosphere fitting, and the temperature scale

NASA Technical Reports Server (NTRS)

Kirkpatrick, J. D.; Kelly, Douglas M.; Rieke, George H.; Liebert, James; Allard, France; Wehrse, Rainer

1993-01-01

Red/infrared (0.6-1.5 micron) spectra are presented for a sequence of well-studied M dwarfs ranging from M2 through M9. A variety of temperature-sensitive features useful for spectral classification are identified. Using these features, the spectral data are compared to recent theoretical models, from which a temperature scale is assigned. The red portion of the model spectra provide reasonably good fits for dwarfs earlier than M6. For layer types, the infrared region provides a more reliable fit to the observations. In each case, the wavelength region used includes the broad peak of the energy distribution. For a given spectral type, the derived temperature sequence assigns higher temperatures than have earlier studies - the difference becoming more pronounced at lower luminosities. The positions of M dwarfs on the H-R diagram are, as a result, in closer agreement with theoretical tracks of the lower main sequence.

The temperature and radius of the white dwarf Stein 2051B

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liebert, J.

1976-12-15

The temperature, radius, and other atmospheric parameters are derived for the cool DC white dwarf Stein 2051B (=G175-34B=EG 180), whose mass was recently determined by Strand. New spectrophotometric scans of this star and its dwarf M companion are discussed; these and existing Stroemgren photometry are fitted to model atmospheres with hydrogen/metal deficient compositions, and a temperature of 7050 +- 400 K is determined. The resulting radius of 0.0111 +- 0.0015 R/sub sun/ is marginally smaller than that of 40 Eri B. (AIP)

Icy Dwarf Planets: Colored Popsicles in the Outer Solar System

NASA Astrophysics Data System (ADS)

Pinilla-Alonso, Noemi

2016-10-01

We update the list of candidates to be considered by the IAU as dwarf planets using the criterium suggested by Tancredi & Favre (2008). We add here the information collected in the last 10 years (mostly the sizes and albedos by the herschel hey program TNOs Are Cool). We compare the physical characteristics of these candidates with the physical characteristics of the rest of the TNOs. Our goal is to study if there are common physical properties among the candidates that enable the identification of a dwarf planet.

The Extent of Chemically Enriched Gas around Star-forming Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Johnson, Sean D.; Chen, Hsiao-Wen; Mulchaey, John S.; Schaye, Joop; Straka, Lorrie A.

2017-11-01

Supernova driven winds are often invoked to remove chemically enriched gas from dwarf galaxies to match their low observed metallicities. In such shallow potential wells, outflows may produce massive amounts of enriched halo gas (circumgalactic medium, CGM) and pollute the intergalactic medium (IGM). Here, we present a survey of the CGM and IGM around 18 star-forming field dwarfs with stellar masses of {log} {M}* /{M}⊙ ≈ 8{--}9 at z≈ 0.2. Eight of these have CGM probed by quasar absorption spectra at projected distances, d, less than that of the host virial radius, {R}{{h}}. Ten are probed in the surrounding IGM at d/{R}{{h}}=1{--}3. The absorption measurements include neutral hydrogen, the dominant silicon ions for diffuse cool gas (T ˜ 104 K; Si II, Si III, and Si IV), moderately ionized carbon (C IV), and highly ionized oxygen (O VI). Metal absorption from the CGM of the dwarfs is less common and ≈ 4× weaker compared to massive star-forming galaxies, though O VI absorption is still common. None of the dwarfs probed at d/{R}{{h}}=1{--}3 have definitive metal-line detections. Combining the available silicon ions, we estimate that the cool CGM of the dwarfs accounts for only 2%-6% of the expected silicon budget from the yields of supernovae associated with past star formation. The highly ionized O VI accounts for ≈8% of the oxygen budget. As O VI traces an ion with expected equilibrium ion fractions of ≲0.2, the highly ionized CGM may represent a significant metal reservoir even for dwarfs not expected to maintain gravitationally shock heated hot halos.

Building an Unusual White-Dwarf Duo

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-09-01

A new study has examined how the puzzling wide binary system HS 2220+2146 which consists of two white dwarfs orbiting each other might have formed. This system may be an example of a new evolutionary pathway for wide white-dwarf binaries.Evolution of a BinaryMore than 100 stellar systems have been discovered consisting of two white dwarfs in a wide orbit around each other. How do these binaries form? In the traditional picture, the system begins as a binary consisting of two main-sequence stars. Due to the large separation between the stars, the stars evolve independently, each passing through the main-sequence and giant branches and ending their lives as white dwarfs.An illustration of a hierarchical triple star system, in which two stars orbit each other, and a third star orbits the pair. [NASA/JPL-Caltech]Because more massive stars evolve more quickly, the most massive of the two stars in a binary pair should be the first to evolve into a white dwarf. Consequently, when we observe a double-white-dwarf binary, its usually a safe bet that the more massive of the two white dwarfs will also be the older and cooler of the pair, since it should have formed first.But in the case of the double-white-dwarf binary HS 2220+2146, the opposite is true: the more massive of the two white dwarfs appears to be the younger and hotter of the pair. If it wasnt created in the traditional way, then how did this system form?Two From Three?Led by Jeff Andrews (Foundation for Research and Technology-Hellas, Greece and Columbia University), a team of scientists recently examined this system more carefully, analyzing its spectra to confirm our understanding of the white dwarfs temperatures and masses.Based on their observations, Andrews and collaborators determined that there are no hidden additional companions that could have caused the unusual evolution of this system. Instead, the team proposed that this unusual binary might be an example of an evolutionary channel that involves three stars.The authors proposed formation scenario for H220+2146. In this picture, the inner binary merges to form a blue straggler. This star and the remaining main-sequence star then evolve independently into white dwarfs, forming the system observed today. [Andrews et al. 2016]An Early MergerIn the model the authors propose for HS 2220+2146, the binary system began as a hierarchical triple system of main-sequence stars. The innermost binary then merged to form a large star known as a blue straggler a star that, due to the merger, will evolve more slowly than its larger mass implies it should.The blue straggler and the remaining main-sequence star, still in a wide orbit, then continued to evolve independently of each other. The smaller star ended its main-sequence lifetime and became a white dwarf first, followed by the more massive but slowly evolving blue straggler thus forming the system we observe today.If the authors model is correct, then HS 2220+2146 would be the first binary double white dwarf known to have formed through this channel. ESAs Gaia mission, currently underway, is expected to discover up to a million new white dwarfs, many of which will likely be in wide binary systems. Among these, we may well find many other systems like HS 2220+2146 that formed in the same way.CitationJeff J. Andrews et al 2016 ApJ 828 38. doi:10.3847/0004-637X/828/1/38

THE SPECTRAL EVOLUTION OF CONVECTIVE MIXING WHITE DWARFS, THE NON-DA GAP, AND WHITE DWARF COSMOCHRONOLOGY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Eugene Y.; Hansen, Brad M. S., E-mail: eyc@mail.utexas.edu, E-mail: hansen@astro.ucla.edu

The spectral distribution of field white dwarfs shows a feature called the 'non-DA gap'. As defined by Bergeron et al., this is a temperature range (5100-6100 K) where relatively few non-DA stars are found, even though such stars are abundant on either side of the gap. It is usually viewed as an indication that a significant fraction of white dwarfs switch their atmospheric compositions back and forth between hydrogen-rich and helium-rich as they cool. In this Letter, we present a Monte Carlo model of the Galactic disk white dwarf population, based on the spectral evolution model of Chen and Hansen.more » We find that the non-DA gap emerges naturally, even though our model only allows white dwarf atmospheres to evolve monotonically from hydrogen-rich to helium-rich through convective mixing. We conclude by discussing the effects of convective mixing on the white dwarf luminosity function and the use thereof for Cosmochronology.« less

Thermonuclear Explosions from Hybrid C/O/Ne White Dwarf Progenitors Ignited Centrally After Interior Mixing

NASA Astrophysics Data System (ADS)

Augustine, Carlyn

2018-01-01

Type Ia Supernovae are thermonuclear explosions of white dwarf (WD) stars. Past studies predict the existence of "hybrid" white dwarfs, made of a C/O/Ne core with a O/Ne shell, and that these are viable progenitors for supernovae. More recent work found that the C/O core is mixed with the surrounding O/Ne while the WD cools. Inspired by this scenario, we performed simulations of thermonuclear supernovae in the single degenerate paradigm from these hybrid progenitors. Our investigation began by constructing a hybrid white dwarf model with the one-dimensional stellar evolution code MESA. The model was allowed to go through unstable interior mixing ignite carbon burning centrally. The MESA model was then mapped to a two-dimensional initial condition and an explosion simulated from that with FLASH. For comparison, a similar simulation of an explosion was performed from a traditional C/O progenitor WD. Comparing the yields produced by explosion simulations allows us to determine which model produces more 56Ni, and therefore brighter events, and how explosions from these models differ from explosions from previous models without the mixing during the WD cooling.

Studies of Binary Pulsar Evolution Through Hubble Space Telescope Imaging of White Dwarf Companions

NASA Astrophysics Data System (ADS)

Lundgren, S. C.; Foster, R. S.; Camilo, F.

1995-12-01

In observations of six binary millisecond pulsars with the Hubble Space Telescope, we have discovered white dwarf companions to PSRs J0034-0534, J1022+1001, and J1713+0747 and improved photometry on PSRs J1640+2224 and J2145-0750. The companion to PSR J2019+2425 was not detected down to m_I=25.4. For the five companions detected, effective temperatures were estimated for the colors measured. Two of the white dwarfs, J0034-0534 and J1713+0747, are among the coolest and oldest known. Using distance estimates to the pulsars, the absolute luminosities were determined. Constrains on the masses and cooling times were obtained from the luminosities and temperatures. The results for each pulsar were related to expectations based on models for white dwarf cooling, Roche lobe overflow in the preceding low-mass X-ray binary phase, and mass accretion rate/neutron star spin period relations. Precision pulsar astrophysics at the Naval Research Laboratory is supported by the Office of Naval Research. SL is supported by a post-doctoral fellowship through the National Research Council. FC acknowledges support from NSF grant AST 91-15103 and a fellowship under the auspices of the European Commission.

Evidence for halo kinematics among cool carbon-rich dwarfs

NASA Astrophysics Data System (ADS)

Farihi, J.; Arendt, A. R.; Machado, H. S.; Whitehouse, L. J.

2018-07-01

This paper reports preliminary, yet compelling, kinematical inferences for N≳ 600 carbon-rich dwarf stars that demonstrate around 30-60 per cent are members of the Galactic halo. The study uses a spectroscopically and non-kinematically selected sample of stars from the SDSS, and cross-correlates these data with three proper motion catalogues based on Gaia DR1 astrometry to generate estimates of their 3D space velocities. The fraction of stars with halo-like kinematics is roughly 30 per cent for distances based on a limited number of parallax measurements, with the remainder dominated by the thick disc, but close to 60 per cent of the sample lies below an old, metal-poor disc isochrone in reduced proper motion. An ancient population is consistent with an extrinsic origin for C/O >1 in cool dwarfs, where a fixed mass of carbon pollution more readily surmounts lower oxygen abundance and with a lack of detectable ultraviolet-blue flux from younger white dwarf companions. For an initial stellar mass function that favours low-mass stars as in the Galactic disc, the dC stars are likely to be the dominant source of carbon-enhanced, metal-poor stars in the Galaxy.

Evidence for halo kinematics among cool carbon-rich dwarfs

NASA Astrophysics Data System (ADS)

Farihi, J.; Arendt, A. R.; Machado, H. S.; Whitehouse, L. J.

2018-04-01

This paper reports preliminary yet compelling kinematical inferences for N ≳ 600 carbon-rich dwarf stars that demonstrate around 30% to 60% are members of the Galactic halo. The study uses a spectroscopically and non-kinematically selected sample of stars from the SDSS, and cross-correlates these data with three proper motion catalogs based on Gaia DR1 astrometry to generate estimates of their 3-D space velocities. The fraction of stars with halo-like kinematics is roughly 30% for distances based on a limited number of parallax measurements, with the remainder dominated by the thick disk, but close to 60% of the sample lie below an old, metal-poor disk isochrone in reduced proper motion. An ancient population is consistent with an extrinsic origin for C/O >1 in cool dwarfs, where a fixed mass of carbon pollution more readily surmounts lower oxygen abundances, and with a lack of detectable ultraviolet-blue flux from younger white dwarf companions. For an initial stellar mass function that favors low-mass stars as in the Galactic disk, the dC stars are likely to be the dominant source of carbon-enhanced, metal-poor stars in the Galaxy.

Outbursts in Symbiotic Binaries

NASA Technical Reports Server (NTRS)

Mushotzky, Richard (Technical Monitor); Kenyon, Scott J.

2003-01-01

Two models have been proposed for the outbursts of symbiotic stars. In the thermonuclear model, outbursts begin when the hydrogen burning shell of a hot white dwarf reaches a critical mass. After a rapid increase in the luminosity and effective temperature, the white dwarf evolves at constant luminosity to lower effective temperatures, remains at optical maximum for several years, and then returns to quiescence along a white dwarf cooling curve. In disk instability models, the brightness rises when the accretion rate from the disk onto the central white dwarf abruptly increases by factors of 5-20. After a few month to several year period at maximum, both the luminosity and the effective temperature of the disk decline as the system returns to quiescence.

Weighing Ultra-Cool Stars

NASA Astrophysics Data System (ADS)

2004-05-01

Large Ground-Based Telescopes and Hubble Team-Up to Perform First Direct Brown Dwarf Mass Measurement [1] Summary Using ESO's Very Large Telescope at Paranal and a suite of ground- and space-based telescopes in a four-year long study, an international team of astronomers has measured for the first time the mass of an ultra-cool star and its companion brown dwarf. The two stars form a binary system and orbit each other in about 10 years. The team obtained high-resolution near-infrared images; on the ground, they defeated the blurring effect of the terrestrial atmosphere by means of adaptive optics techniques. By precisely determining the orbit projected on the sky, the astronomers were able to measure the total mass of the stars. Additional data and comparison with stellar models then yield the mass of each of the components. The heavier of the two stars has a mass around 8.5% of the mass of the Sun and its brown dwarf companion is even lighter, only 6% of the solar mass. Both objects are relatively young with an age of about 500-1,000 million years. These observations represent a decisive step towards the still missing calibration of stellar evolution models for very-low mass stars. PR Photo 19a/04: Orbit of the ultra-cool stars in 2MASSW J0746425+2000321. PR Photo 19b/04: Animated Gif of the orbital motion. Telephone number star Even though astronomers have found several hundreds of very low mass stars and brown dwarfs, the fundamental properties of these extreme objects, such as masses and surface temperatures, are still not well known. Within the cosmic zoo, these ultra-cool stars represent a class of "intermediate" objects between giant planets - like Jupiter - and "normal" stars less massive than our Sun, and to understand them well is therefore crucial to the field of stellar astrophysics. The problem with these ultra-cool stars is that contrary to normal stars that burn hydrogen in their central core, no unique relation exists between the luminosity of the star and its mass. Indeed, luminosities and surface temperatures of ultra-cool dwarf stars depend both on their age and their mass. An older, somewhat more massive ultra-cool dwarf can thus have exactly the same temperature as a younger, less massive one. It is therefore a basic goal of modern astrophysics to obtain independently the masses of an ultra-cool dwarf star. This is in principle possible by studying such objects that are members in a binary system. This is precisely what an international team of astronomers [2] has now done in a four-year long study of a binary stellar system with an ultra-cool dwarf star, using a plethora of top telescopic facilities, including ESO's Very Large Telescope, as well as Keck I and Gemini North in Hawaii and also the Hubble Space Telescope. This system - with the telephone number name of 2MASSW J0746425+2000321 [3]- is located at a distance of 40 light-years. Beating the seeing ESO PR Photo 19a/04 ESO PR Photo 19a/04 Orbit of the ultra-cool stars in 2MASSW J0746425+2000321 [Preview - JPEG: 400 x 548 pix - 121k] [Normal - JPEG: 800 x 1095 pix - 320k] [Hires - JPEG: 2591 x 3546 pix - 1.8M] [Hires - TIFF: 2591 x 3546 pix - 36.8M] ESO PR Photo 19b/04 ESO PR Photo 19b/04 Animated GIF showing the orbital motion (size: 416 kb) Caption: ESO PR Photo 19a/04 shows the orbit of the brown dwarf around the ultra-cool dwarf. Each red dot on the orbit corresponds to one observation made with a ground- or space-based telescope. The observations cover 60% of the whole orbit. ESO PR Photo 19b/04 is an animated Gif showing the motion of the brown dwarf and the various high-resolution images obtained by the astronomers. The astronomers used high-angular-resolution imaging to see both stars in the binary system and to measure their motion over a four-year period. However, this is more easily said than done, as the separation on the sky between the two stars is quite small: between 0.13 and 0.22 arcsec. This corresponds to the size of a 1-Euro coin, seen at a distance of about 25 km. This separation is so small that it is normally not possible to differentiate the two stars due to the blurring effect of atmospheric turbulence (the "seeing"). It is therefore necessary to use the technique of adaptive optics. This wonderful method is based on the measurement of the image quality in real-time and sending corresponding corrective signals up to 100 times every second to a small deformable mirror, located in front of the detector. As the mirror continuously modifies its shape, the disturbing effect of the turbulence is neutralised. Applied at the VLT, this technique has resulted in images which are at least ten times sharper than the "seeing" and which therefore show many more details in the observed objects. At the Very Large Telescope, the astronomers used the state-of-the-art adaptive optics NACO instrument [4]. Says Hervé Bouy, principal author of the paper presenting the results described here: "NACO offers the possibility to work in the infrared and is therefore ideally suited for the study of ultra-cool stars, which emit most of their light in this wavelength range. With the combination of the high efficiency of NACO and the VLT, and the excellent atmospheric conditions prevailing at Paranal, we were able to achieve very sharp images of this binary stellar system, almost as good as if the telescope were located in space." Ultra-cool and on diet During their four-year long study, seven different relative positions of the two components of the binary system were measured and Hervé Bouy and his co-workers were able to determine with good precision the stellar orbits. They find that the two stars revolve around each other once every 10 years and that their physical separation is only 2.5 times the distance of the Earth to the Sun - as astronomers say, 2.5 Astronomical Units. Using Kepler's laws, it is then straightforward to derive the total mass of the system. The obtained value is less than 15 % of the mass of the Sun. The astronomers then used the photometric data of each star obtained in several wavebands, as well as spectra obtained with the Hubble Space Telescope to study the two objects in more detail. Using the latest stellar models of the group of the Ecole Normale Supérieure de Lyon, they found that both stars have roughly the same surface temperature, around 1500 °C (1800 K). For a star, this is ultra-cool indeed - by comparison, the surface temperature of the Sun is more than three times higher. Using theoretical models, the team also found that the two stars are rather young (in astrophysical terms) - their age is between 500 and 1,000 million years only. The more massive of the two has a mass between 7.5 and 9.5% the mass of the Sun, while its companion has a mass between 5 and 7% of the solar mass. Objects weighing less than about 7% of our Sun have been variously called "Brown Dwarfs", "Failed Stars" or "Super Planets". Indeed, since they have no sustained energy generation by thermal nuclear reactions in their interior, many of their properties are more similar to those of giant gas planets in our own solar system such as Jupiter, than to stars like the Sun. The system 2MASSW J0746425+2000321 is thus apparently made up of a brown dwarf orbiting a slightly more massive ultra-cool dwarf star. It is a true "Rosetta stone" in the new field of low-mass stellar astrophysics and further studies will surely provide more valuable information about these objects in the transitional zone between stars and planets. More information The research described in this press release is published in the research journal Astronomy & Astrophysics ("First determination of the dynamical mass of a binary L1.5 dwarf" by H. Bouy et al.). The paper is available in PDF format on the publisher web site.

Parallaxes for the Coldest Brown Dwarfs

NASA Astrophysics Data System (ADS)

Dupuy, Trent; Kraus, Adam; Liu, Michael

2014-12-01

Understanding extremely cool atmospheres is a major goal of both brown dwarf and exoplanet studies. The WISE all-sky survey has uncovered the coolest brown dwarfs to date including the first unambiguous Y dwarfs. These discoveries are spectroscopically estimated to have temperatures of ~300-500 K and masses of ~5-20 Mjup, overlapping discoveries from radial velocity exoplanet surveys. However, direct distances are needed to determine model-independent temperatures and to test the observed properties against theoretical models in this new physical frontier. From our Cycle 8 program, we have successfully measured the first robust parallaxes for these extremely low-luminosity objects using Spitzer [3.6]-band astrometry, made possible with our improved distortion solution for IRAC. Our results, comprising less than half the currently known late-T/Y census, have uncovered a number of puzzles. Perhaps the most intriguing is the possibility that the observed near-IR spectral types and spectral energy distributions do not follow a simple correspondence with temperature, in contrast to all other (hotter) substellar and stellar objects. We propose here to obtain definitive parallaxes and temperatures to the ~2 dozen known coldest brown dwarfs. For our Cycle 8 sample, these new data will double the time baseline, leading to major improvements over our preliminary results. We will also double the total sample with parallaxes for more recent discoveries. Altogether, our work will establish the temperature scale as a function of spectral type, delineate the cooling (and intrinsic scatter) through the T/Y transition, and enable strong test of theoretical models for these coldest brown dwarfs, which are ~100x fainter than previously known objects at near-IR wavelengths.

Habitable Planets Around White and Brown Dwarfs: The Perils of a Cooling Primary

PubMed Central

Heller, René

2013-01-01

Abstract White and brown dwarfs are astrophysical objects that are bright enough to support an insolation habitable zone (IHZ). Unlike hydrogen-burning stars, they cool and become less luminous with time; hence their IHZ moves in with time. The inner edge of the IHZ is defined as the orbital radius at which a planet may enter a moist or runaway greenhouse, phenomena that can remove a planet's surface water forever. Thus, as the IHZ moves in, planets that enter it may no longer have any water and are still uninhabitable. Additionally, the close proximity of the IHZ to the primary leads to concern that tidal heating may also be strong enough to trigger a runaway greenhouse, even for orbital eccentricities as small as 10−6. Water loss occurs due to photolyzation by UV photons in the planetary stratosphere, followed by hydrogen escape. Young white dwarfs emit a large amount of these photons, as their surface temperatures are over 104 K. The situation is less clear for brown dwarfs, as observational data do not constrain their early activity and UV emission very well. Nonetheless, both types of planets are at risk of never achieving habitable conditions, but planets orbiting white dwarfs may be less likely to sustain life than those orbiting brown dwarfs. We consider the future habitability of the planet candidates KOI 55.01 and 55.02 in these terms and find they are unlikely to become habitable. Key Words: Extrasolar terrestrial planets—Habitability—Habitable zone—Tides—Exoplanets. Astrobiology 13, 279–291. PMID:23537137

The Solar Neighborhood. XLII. Parallax Results from the CTIOPI 0.9 m Program—Identifying New Nearby Subdwarfs Using Tangential Velocities and Locations on the H–R Diagram

NASA Astrophysics Data System (ADS)

Jao, Wei-Chun; Henry, Todd J.; Winters, Jennifer G.; Subasavage, John P.; Riedel, Adric R.; Silverstein, Michele L.; Ianna, Philip A.

2017-11-01

Parallaxes, proper motions, and optical photometry are presented for 51 systems consisting of 37 cool subdwarf and 14 additional high proper motion systems. Thirty-seven systems have parallaxes reported for the first time, 15 of which have proper motions of at least 1″ yr‑1. The sample includes 22 newly identified cool subdwarfs within 100 pc, of which three are within 25 pc, and an additional five subdwarfs from 100 to 160 pc. Two systems—LSR 1610-0040 AB and LHS 440 AB—are close binaries exhibiting clear astrometric perturbations that will ultimately provide important masses for cool subdwarfs. We use the accurate parallaxes and proper motions provided here, combined with additional data from our program and others, to determine that effectively all nearby stars with tangential velocities greater than 200 km s‑1 are subdwarfs. We compare a sample of 167 confirmed cool subdwarfs to nearby main sequence dwarfs and Pleiades members on an observational Hertzsprung–Russell diagram using M V versus (V ‑ K s ) to map trends of age and metallicity. We find that subdwarfs are clearly separated for spectral types K5–M5, indicating that the low metallicities of subdwarfs set them apart in the H–R diagram for (V ‑ K s ) = 3–6. We then apply the tangential velocity cutoff and the subdwarf region of the H–R diagram to stars with parallaxes from Gaia Data Release 1 and the MEarth Project to identify a total of 29 new nearby subdwarf candidates that fall clearly below the main sequence.

Deposition of steeply infalling debris - pebbles, boulders, snowballs, asteroids, comets - around stars

NASA Astrophysics Data System (ADS)

Brown, J. C.; Veras, D.; Gänsicke, B. T.

2017-09-01

When Comet Lovejoy plunged into the Sun, and survived, questions arose about the physics of infall of small bodies. [1,2] has already described this infall in detail. However, a more general analysis for any type of star has been missing. [3] generalized previous studies, with specific applications to white dwarfs. High-metallicity pollution is common in white dwarf stars hosting remnant planetary systems. However, they rarely have detectable debris accretion discs, possibly because much of the influx is fast steeply infalling debris in star-grazing orbits, producing a more tenuous signature than a slowly accreting disc. Processes governing such deposition between the Roche radius and photosphere have so far received little attention and we model them here analytically by extending recent work on sun-grazing comets to white dwarf systems. We find that the evolution of cm-to-km size infallers most strongly depends on two combinations of parameters, which effectively measure sublimation rate and binding strength. We then provide an algorithm to determine the fate of infallers for any white dwarf, and apply the algorithm to four limiting combinations of hot versus cool (young/old) white dwarfs with snowy (weak, volatile) versus rocky (strong, refractory) infallers. We find: (i) Total sublimation above the photosphere befalls all small infallers across the entire white dwarf temperature range, the threshold size rising with it and 100× larger for rock than snow. (ii) All very large objects fragment tidally regardless of temperature: for rock, a0 ≽ 105 cm; for snow, a0 ≽ 103 - 3 × 104 cm across all white dwarf cooling ages. (iii) A considerable range of infaller sizes avoids fragmentation and total sublimation, yielding impacts or grazes with cold white dwarfs. This range rapidly narrows with increasing temperature, especially for snowy bodies. Finally, we briefly discuss how the various forms of deposited debris may finally reach the photosphere surface itself.

Outer atmospheres of cool stars. XII - A survey of IUE ultraviolet emission line spectra of cool dwarf stars

NASA Technical Reports Server (NTRS)

Linsky, J. L.; Bornmann, P. L.; Carpenter, K. G.; Hege, E. K.; Wing, R. F.; Giampapa, M. S.; Worden, S. P.

1982-01-01

Quantitative information is obtained on the chromospheres and transition regions of M dwarf stars, in order to determine how the outer atmospheres of dMe stars differ from dM stars and how they compare with the outer atmospheres of quiet and active G and K type dwarfs. IUE spectra of six dMe and four dM stars, together with ground-based photometry and spectroscopy of the Balmer and Ca II H and K lines, show no evidence of flares. It is concluded, regarding the quiescent behavior of these stars, that emission-line spectra resemble that of the sun and contain emission lines formed in regions with 4000-20,000 K temperatures that are presumably analogous to the solar chromosphere, as well as regions with temperatures of 20,000-200,000 K that are presumably analogous to the solar transition region. Emission-line surface fluxes are proportional to the emission measure over the range of temperatures at which the lines are formed.

Hubble Space Telescope observations of cool white dwarf stars: Detection of new species of heavy elements

NASA Technical Reports Server (NTRS)

Shipman, Harry; Barnhill, Maurice; Provencal, Judi; Roby, Scott; Bues, Irmela; Cordova, France; Hammond, Gordon; Hintzen, Paul; Koester, Detlev; Liebert, James

1995-01-01

Observations of cool white dwarf stars with the Hubble Space Telescope (HST) has uncovered a number of spectral features from previouslly unobserved species. In this paper we present the data on four cool white dwarfs. We present identifications, equivalent width measurements, and brief summaries of the significance of our findings. The four stars observed are GD 40 (DBZ3, G 74-7 (DAZ), L 745-46A (DZ), and LDS 749B (DBA). Many additional species of heavey elements were detected in GD 40 and G 74-7. In L 745-46A, while the detections are limited to Fe 1, Fe II, and Mg II, the quality of the Mg II h and K line profiles should permit a test of the line broadening theories, which are so crucial to abundance determinations. The clear detection of Mg II h and k in LDS 749 B should, once an abundance determination is made, provide a clear test of the hypothesis that the DBA stars are the result of accretion from the interstellar medium. This star contains no other clear features other than a tantalizing hint of C II 1335 with a P Cygni profile, and some expected He 1 lines.

Convection Destroys the Core/Mantle Structure in Hybrid C/O/Ne White Dwarfs

NASA Astrophysics Data System (ADS)

Brooks, Jared; Schwab, Josiah; Bildsten, Lars; Quataert, Eliot; Paxton, Bill

2017-01-01

A hybrid C/O/Ne white dwarf (WD)—an unburned C/O core surrounded by an O/Ne/Na mantle—can be formed if the carbon flame is quenched in a super-AGB star or white dwarf merger remnant. We show that this segregated hybrid structure becomes unstable to rapid mixing within 2000 years of the onset of WD cooling. Carbon burning includes a weak reaction that removes electrons, resulting in a lower electron-to-baryon ratio ({Y}{{e}}) in the regions processed by carbon burning compared to the unburned C/O core, making the O/Ne mantle denser than the C/O core as the WD cools. This is unstable to efficient mixing. We use the results of {\\mathtt{MESA}} models with different size C/O cores to quantify the rate at which the cores mix with the mantle as they cool. In all cases, we find that the WDs undergo significant core/mantle mixing on timescales shorter than the time available to grow the WD to the Chandrasekhar mass (MCh) by accretion. As a result, hybrid WDs that reach MCh due to later accretion will have lower central carbon fractions than assumed thus far. We briefly discuss the implications of these results for the possibility of SNe Ia from hybrid WDs.

J-Band Infrared Spectroscopy of a Sample of Brown Dwarfs Using NIRSPEC on Keck II.

PubMed

McLean; Wilcox; Becklin; Figer; Gilbert; Graham; Larkin; Levenson; Teplitz; Kirkpatrick

2000-04-10

Near-infrared spectroscopic observations of a sample of very cool, low-mass objects are presented with higher spectral resolution than in any previous studies. Six of the objects are L dwarfs, ranging in spectral class from L2 to L8/9, and the seventh is a methane or T dwarf. These new observations were obtained during commissioning of the near-infrared spectrometer (NIRSPEC), the first high-resolution near-infrared cryogenic spectrograph for the Keck II 10 m telescope on Mauna Kea, Hawaii. Spectra with a resolving power of R approximately 2500 from 1.135 to 1.360 µm (approximately J band) are presented for each source. At this resolution, a rich spectral structure is revealed, much of which is due to blending of unresolved molecular transitions. Strong lines due to neutral potassium (K i) and bands due to iron hydride (FeH) and steam (H2O) change significantly throughout the L sequence. Iron hydride disappears between L5 and L8, the steam bands deepen, and the K i lines gradually become weaker but wider because of pressure broadening. An unidentified feature occurs at 1.22 µm that has a temperature dependence like FeH but has no counterpart in the available FeH opacity data. Because these objects are 3-6 mag brighter in the near-infrared compared with the I band, spectral classification is efficient. One of the objects studied (2MASSW J1523+3014) is the coolest L dwarf discovered so far by the 2 Micron All-Sky Survey (2MASS), but its spectrum is still significantly different from the methane-dominated objects such as Gl 229B or SDSS 1624+0029.

Formation of high-field magnetic white dwarfs from common envelopes

PubMed Central

Nordhaus, Jason; Wellons, Sarah; Spiegel, David S.; Metzger, Brian D.; Blackman, Eric G.

2011-01-01

The origin of highly magnetized white dwarfs has remained a mystery since their initial discovery. Recent observations indicate that the formation of high-field magnetic white dwarfs is intimately related to strong binary interactions during post-main-sequence phases of stellar evolution. If a low-mass companion, such as a planet, brown dwarf, or low-mass star, is engulfed by a post-main-sequence giant, gravitational torques in the envelope of the giant lead to a reduction of the companion’s orbit. Sufficiently low-mass companions in-spiral until they are shredded by the strong gravitational tides near the white dwarf core. Subsequent formation of a super-Eddington accretion disk from the disrupted companion inside a common envelope can dramatically amplify magnetic fields via a dynamo. Here, we show that these disk-generated fields are sufficiently strong to explain the observed range of magnetic field strengths for isolated, high-field magnetic white dwarfs. A higher-mass binary analogue may also contribute to the origin of magnetar fields. PMID:21300910

The Cosmological Impact of Luminous TeV Blazars. III. Implications for Galaxy Clusters and the Formation of Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Pfrommer, Christoph; Chang, Philip; Broderick, Avery E.

2012-06-01

A subset of blazars are powerful TeV emitters, dominating the extragalactic component of the very high energy gamma-ray universe (E >~ 100 GeV). These TeV gamma rays generate ultrarelativistic electron-positron pairs via pair production with the extragalactic background light. While it has generally been assumed that the kinetic energy of these pairs cascades to GeV gamma rays via inverse Compton scattering, we have argued in Broderick et al. (Paper I in this series) that plasma beam instabilities are capable of dissipating the pairs' energy locally on timescales short in comparison to the inverse Compton cooling time, heating the intergalactic medium (IGM) with a rate that is independent of density. This dramatically increases the entropy of the IGM after redshift z ~ 2, with a number of important implications for structure formation: (1) this suggests a scenario for the origin of the cool core (CC)/non-cool core (NCC) bimodality in galaxy clusters and groups. Early-forming galaxy groups are unaffected because they can efficiently radiate the additional entropy, developing a CC. However, late-forming groups do not have sufficient time to cool before the entropy is gravitationally reprocessed through successive mergers—counteracting cooling and potentially raising the core entropy further. This may result in a population of X-ray dim groups/clusters, consistent with X-ray stacking analyses of optically selected samples. Hence, blazar heating works differently than feedback by active galactic nuclei, which we show can balance radiative cooling but is unable to transform CC into NCC clusters on the buoyancy timescale due to the weak coupling between the mechanical energy to the cluster gas. (2) We predict a suppression of the Sunyaev-Zel'dovich (SZ) power spectrum template on angular scales smaller than 5' due to the globally reduced central pressure of groups and clusters forming after z ~ 1. This allows for a larger rms amplitude of the density power spectrum, σ8, and may reconcile SZ-inferred values with those by other cosmological probes even after allowing for a contribution due to patchy reionization. (3) Our redshift-dependent entropy floor increases the characteristic halo mass below which dwarf galaxies cannot form by a factor of approximately 10 (50) at mean density (in voids) over that found in models that include photoionization alone. This prevents the formation of late-forming dwarf galaxies (z <~ 2) with masses ranging from 1010 to 1011 M ⊙ for redshifts z ~ 2 to 0, respectively. This may help resolve the "missing satellite problem" in the Milky Way of the low observed abundances of dwarf satellites compared to cold dark matter simulations and may bring the observed early star formation histories into agreement with galaxy formation models. At the same time, it explains the "void phenomenon" by suppressing the formation of galaxies within existing dwarf halos of masses <3 × 1010 M ⊙ with a maximum circular velocity <60 km s-1 for z <~ 2, hence reconciling the number of dwarfs in low-density regions in simulations and the paucity of those in observations.

Prof. Hayashi's work on the pre-main sequence evolution and brown dwarfs

NASA Astrophysics Data System (ADS)

Nakano, Takenori

2012-09-01

Prof. Hayashi's work on the evolution of stars in the pre-main sequence stage is reviewed. The historical background and the process of finding the Hayashi phase are mentioned. The work on the evolution of low-mass stars is also reviewed including the determination of the bottom of the main sequence and evolution of brown dwarfs, and comparison is made with the other works in the same period.

Wave energy in white dwarf atmospheres. I - Magnetohydrodynamic energy spectra for homogeneous DB and layered DA stars

NASA Technical Reports Server (NTRS)

Musielak, Zdzislaw E.

1987-01-01

The radiative damping of acoustic and MHD waves that propagate through white dwarf photospheric layers is studied, and other damping processes that may be important for the propagation of the MHD waves are calculated. The amount of energy remaining after the damping processes have occurred in different types of waves is estimated. The results show that lower acoustic fluxes should be expected in layered DA and homogeneous DB white dwarfs than had previously been estimated. Acoustic emission manifests itself in an enhancement of the quadrupole term, but this term may become comparable to or even lower than the dipole term for cool white dwarfs. Energy carried by the acoustic waves is significantly dissipated in deep photospheric layers, mainly because of radiative damping. Acoustically heated corona cannot exist around DA and DB white dwarfs in a range T(eff) = 10,000-30,000 K and for log g = 7 and 8. However, relatively hot and massive white dwarfs could be exceptions.

Chandra Observations of Magnetic White Dwarfs and Their Theoretical Implications

NASA Technical Reports Server (NTRS)

Musielak, Z. E.; Noble, M.; Porter, J. G.; Winget, D. E.; Six, N. Frank (Technical Monitor)

2002-01-01

Observations of cool DA and DB white dwarfs have not yet been successful in detecting coronal X-ray emission but observations of late-type dwarfs and giants show that coronae are common for these stars. To produce coronal X-rays, a star must have dynamo-generated surface magnetic fields and a well-developed convection zone. There is strong observational evidence that the DA star LHS 1038 and the DB star GD 358 have weak and variable surface magnetic fields. Since these fields are likely to be generated by dynamo action and since both stars have well-developed convection zones, theory predicts detectable levels of coronal X-rays from these white dwarfs. However, we present analysis of Chandra observations of both stars showing no detectable X-ray emission. The derived upper limits for the X-ray fluxes provide strong constraints on theories of formation of coronae around magnetic white dwarfs.

Faint blue counts from formation of dwarf galaxies at z approximately equals 1

NASA Technical Reports Server (NTRS)

Babul, Arif; Rees, Martin J.

1993-01-01

The nature of faint blue objects (FBO's) has been a source of much speculation since their detection in deep CCD images of the sky. Their high surface density argues against them being progenitors of present-day bright galaxies and since they are only weakly clustered on small scales, they cannot be entities that merged together to form present-day galaxies. Babul & Rees (1992) have suggested that the observed faint blue counts may be due to dwarf elliptical galaxies undergoing their initial starburst at z is approximately equal to 1. In generic hierarchical clustering scenarios, however, dwarf galaxy halos (M is approximately 10(exp 9) solar mass) are expected to form at an earlier epoch; for example, typical 10(exp 9) solar mass halos will virialize at z is approximately equal to 2.3 if the power-spectrum for the density fluctuations is that of the standard b = 2 cold dark matter (CDM) model. Under 'ordinary conditions' the gas would rapidly cool, collect in the cores, and undergo star-formation. Conditions at high redshifts are far from 'ordinary'. The intense UV background will prevent the gas in the dwarf halos from cooling, the halos being released from their suspended state only when the UV flux has diminished sufficiently.

The MEarth Project: Finding the Best Targets for Atmospheric Characterization with JWST

NASA Astrophysics Data System (ADS)

Berta-Thompson, Z.

2014-04-01

If we want to directly observe the radius, orbit, mass, and atmosphere of a small, cool, habitable exoplanet, our best opportunity is to find such a planet transiting a small, cool, nearby M dwarf star. The MEarth Project is an ongoing all-sky survey for Earth-like planets transiting the closest, smallest M dwarfs in the Galaxy. MEarth aims to find good targets for atmospheric characterization with JWST and the next generation of enormous ground-based telescopes. This poster provides a status update on the MEarth Project, including the progress we've made over the past five years with 8 telescopes in the Northern hemisphere and promising early results from our new installation of 8 more telescopes in the Southern hemisphere.

The dusty atmosphere of the brown dwarf Gliese 229B.

PubMed

Griffith, C A; Yelle, R V; Marley, M S

1998-12-11

The brown dwarf Gliese 229B has an observable atmosphere too warm to contain ice clouds like those on Jupiter and too cool to contain silicate clouds like those on low-mass stars. These unique conditions permit visibility to higher pressures than possible in cool stars or planets. Gliese 229B's 0.85- to 1.0-micrometer spectrum indicates particulates deep in the atmosphere (10 to 50 bars) having optical properties of neither ice nor silicates. Their reddish color suggests an organic composition characteristic of aerosols in planetary stratospheres. The particles' mass fraction (10(-7)) agrees with a photochemical origin caused by incident radiation from the primary star and suggests the occurrence of processes native to planetary stratospheres.

Properties of an eclipsing double white dwarf binary NLTT 11748

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaplan, David L.; Walker, Arielle N.; Marsh, Thomas R.

2014-01-10

We present high-quality ULTRACAM photometry of the eclipsing detached double white dwarf binary NLTT 11748. This system consists of a carbon/oxygen white dwarf and an extremely low mass (<0.2 M {sub ☉}) helium-core white dwarf in a 5.6 hr orbit. To date, such extremely low-mass white dwarfs, which can have thin, stably burning outer layers, have been modeled via poorly constrained atmosphere and cooling calculations where uncertainties in the detailed structure can strongly influence the eventual fates of these systems when mass transfer begins. With precise (individual precision ≈1%), high-cadence (≈2 s), multicolor photometry of multiple primary and secondary eclipsesmore » spanning >1.5 yr, we constrain the masses and radii of both objects in the NLTT 11748 system to a statistical uncertainty of a few percent. However, we find that overall uncertainty in the thickness of the envelope of the secondary carbon/oxygen white dwarf leads to a larger (≈13%) systematic uncertainty in the primary He WD's mass. Over the full range of possible envelope thicknesses, we find that our primary mass (0.136-0.162 M {sub ☉}) and surface gravity (log (g) = 6.32-6.38; radii are 0.0423-0.0433 R {sub ☉}) constraints do not agree with previous spectroscopic determinations. We use precise eclipse timing to detect the Rømer delay at 7σ significance, providing an additional weak constraint on the masses and limiting the eccentricity to ecos ω = (– 4 ± 5) × 10{sup –5}. Finally, we use multicolor data to constrain the secondary's effective temperature (7600 ± 120 K) and cooling age (1.6-1.7 Gyr).« less

The extent of chemically enriched gas around star-forming dwarf galaxies

NASA Astrophysics Data System (ADS)

Johnson, Sean

2018-01-01

Supernovae driven winds are often invoked to remove chemically enriched gas from galaxies to match the low metallicities of dwarf galaxies. In such shallow potential wells, outflows may produce massive amounts of enriched halo gas (circum-galactic medium or CGM) and pollute the intergalactic medium (IGM). I will present a survey of the CGM and IGM around 18 star-forming field dwarf galaxies with stellar masses of log M*/M⊙ ≈ 8 ‑ 9 at z ≈ 0.2. Eight of these have CGM probed by quasar absorption spectra at projected distances, d, less than the host virial radius, Rh. Ten are probed at d/Rh = 1 ‑ 3 to study the surrounding IGM. The absorption measurements include neutral hydrogen (H I), the dominant silicon ions for diffuse cool gas (T ∼ 104 K; Si II, Si III, and Si IV), more highly ionized carbon (C IV), and highly ionized oxygen (O VI). The metal absorption from the CGM of the dwarf galaxies is less common and ≈ 4× weaker compared to massive star-forming galaxies though O VI absorption is still common. None of the dwarfs probed at d/Rh = 1 ‑ 3 have definitive metal-line detections. Combining the available silicon ions, we estimate that the cool CGM accounts for only 2 ‑ 6% of the expected silicon budget. CGM absorption from O VI can account for ≈ 8% of the expected oxygen budget. As O VI traces an ion with expected equilibrium ion fractions of 0.2, this highly ionized phase of the CGM may represent a significant metal reservoir even for dwarf galaxies not expected to maintain gravitationally shock heated hot halos.

Light-curve Modulation of Low-mass Stars in K2. I. Identification of 481 Fast Rotators in the Solar Neighborhood

NASA Astrophysics Data System (ADS)

Saylor, Dicy; Lepine, Sebastien; Crossfield, Ian; Petigura, Erik A.

2018-01-01

The K2 mission is targeting large numbers of nearby (d < 100 pc) GKM dwarfs selected from the SUPERBLINK proper motion survey (μ > 40 mas yr‑1, V < 20). Additionally, the mission is targeting low-mass, high proper motion stars associated with the local (d < 500 pc) Galactic halo population also selected from SUPERBLINK. K2 campaigns 0 through 8 monitored a total of 26,518 of these cool main-sequence stars. We used the auto-correlation function to search for fast rotators by identifying short-period photometric modulations in the K2 light curves. We identified 481 candidate fast rotators with rotation periods <4 days that show light-curve modulations consistent with starspots. Their kinematics show low average transverse velocities, suggesting that they are part of the young disk population. A subset (13) of the fast rotators is found among those targets with colors and kinematics consistent with the local Galactic halo population and may represent stars spun up by tidal interactions in close binary systems. We further demonstrate that the M dwarf fast rotators selected from the K2 light curves are significantly more likely to have UV excess and discuss the potential of the K2 mission to identify new nearby young GKM dwarfs on the basis of their fast rotation rates. Finally, we discuss the possible use of local halo stars as fiducial, non-variable sources in the Kepler fields.

THE EFFECTS OF CLOSE COMPANIONS (AND ROTATION) ON THE MAGNETIC ACTIVITY OF M DWARFS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morgan, Dylan P.; West, Andrew A.; Dhital, Saurav

2012-10-01

We present a study of close white dwarf and M dwarf (WD+dM) binary systems and examine the effect that a close companion has on the magnetic field generation in M dwarfs. We use a base sample of 1602 white dwarf main-sequence binaries from Rebassa-Mansergas et al. to develop a set of color cuts in GALEX, SDSS, UKIDSS, and 2MASS color space. Then using the SDSS Data Release 8 spectroscopic database, we construct a sample of 1756 WD+dM high-quality pairs from our color cuts and previous catalogs. We separate the individual WD and dM from each spectrum using an iterative techniquemore » that compares the WD and dM components to best-fit templates. Using the absolute height above the Galactic plane as a proxy for age, and the H{alpha} emission line as an indicator for magnetic activity, we investigate the age-activity relation for our sample for spectral types {<=} M7. Our results show that early-type M dwarfs ({<=}M4) in close binary systems are more likely to be active and have longer activity lifetimes compared to their field counterparts. However, at a spectral type of M5 (just past the onset of full convection in M dwarfs), the activity fraction and lifetimes of WD+dM binary systems become more comparable to that of the field M dwarfs. One of the implications of having a close binary companion is presumed to be increased stellar rotation through disk disruption, tidal effects, or angular momentum exchange. Thus, we interpret the similarity in activity behavior between late-type dMs in WD+dM pairs and late-type field dMs to be due to a decrease in sensitivity in close binary companions (or stellar rotation), which has implications for the nature of magnetic activity in fully convective stars. Using the WD components of the pairs, we find WD cooling ages to use as an additional constraint on the age-activity relation for our sample. We find that, on average, active early-type dMs tend to be younger and that active late-type dMs span a much broader age regime making them indistinguishable from the inactive late-type population. We also show that magnetic strength, as measured by H{alpha}, is comparable between paired and field M dwarfs until a spectral type of M6/M7 where M dwarf activity for stars with close companions becomes much stronger. In addition, we present 37 very close candidate pairs with fast-moving orbits that display radial velocity changes over hour timescales.« less

The Effects of Close Companions (and Rotation) on the Magnetic Activity of M Dwarfs

NASA Astrophysics Data System (ADS)

Morgan, Dylan P.; West, Andrew A.; Garcés, Ane; Catalán, Silvia; Dhital, Saurav; Fuchs, Miriam; Silvestri, Nicole M.

2012-10-01

We present a study of close white dwarf and M dwarf (WD+dM) binary systems and examine the effect that a close companion has on the magnetic field generation in M dwarfs. We use a base sample of 1602 white dwarf main-sequence binaries from Rebassa-Mansergas et al. to develop a set of color cuts in GALEX, SDSS, UKIDSS, and 2MASS color space. Then using the SDSS Data Release 8 spectroscopic database, we construct a sample of 1756 WD+dM high-quality pairs from our color cuts and previous catalogs. We separate the individual WD and dM from each spectrum using an iterative technique that compares the WD and dM components to best-fit templates. Using the absolute height above the Galactic plane as a proxy for age, and the Hα emission line as an indicator for magnetic activity, we investigate the age-activity relation for our sample for spectral types <= M7. Our results show that early-type M dwarfs (<=M4) in close binary systems are more likely to be active and have longer activity lifetimes compared to their field counterparts. However, at a spectral type of M5 (just past the onset of full convection in M dwarfs), the activity fraction and lifetimes of WD+dM binary systems become more comparable to that of the field M dwarfs. One of the implications of having a close binary companion is presumed to be increased stellar rotation through disk disruption, tidal effects, or angular momentum exchange. Thus, we interpret the similarity in activity behavior between late-type dMs in WD+dM pairs and late-type field dMs to be due to a decrease in sensitivity in close binary companions (or stellar rotation), which has implications for the nature of magnetic activity in fully convective stars. Using the WD components of the pairs, we find WD cooling ages to use as an additional constraint on the age-activity relation for our sample. We find that, on average, active early-type dMs tend to be younger and that active late-type dMs span a much broader age regime making them indistinguishable from the inactive late-type population. We also show that magnetic strength, as measured by Hα, is comparable between paired and field M dwarfs until a spectral type of M6/M7 where M dwarf activity for stars with close companions becomes much stronger. In addition, we present 37 very close candidate pairs with fast-moving orbits that display radial velocity changes over hour timescales.

Helium shell flashes and evolution of accreting white dwarfs

NASA Astrophysics Data System (ADS)

Fujimoto, M. Y.; Sugimoto, D.

1982-06-01

The evolution of accreting white dwarfs is investigated from the onset of accretion through the helium shell flash. Properties of the helium shell flashes are studied by means of a generalized theory of shell flash and by numerical computations, and it is found that the shell flash grows up to the strength of a supernova explosion when the mass of the helium zone is large enough on a massive white dwarf. Although accretion onto a hot white dwarf causes a weaker shell flash than those onto cool ones, a strong tendency exists for the strength to be determined mainly by the accretion rate. For fast accretion, the shell flashes are weak and triggered recurrently, while for slow accretion the helium shell flash, once triggered, develops into a detonation supernova.

On the Detection and Characterization of Polluted White Dwarfs

NASA Astrophysics Data System (ADS)

Steele, Amy; Debes, John H.; Deming, Drake

2017-06-01

There is evidence of circumstellar material around main sequence, giant, and white dwarf stars. What happens to this material after the main sequence? With this work, we focus on the characterization of the material around WD 1145+017. The goals are to monitor the white dwarf—which has a transiting, disintegrating planetesimal and determine the composition of the evaporated material for that same white dwarf by looking at high-resolution spectra. We also present preliminary results of follow-up photometric observations of known polluted WDs. If rocky bodies survive red giant branch evolution, then the material raining down on a WD atmosphere is a direct probe of main sequence cosmochemistry. If rocky bodies do not survive the evolution, then this informs the degree of post-main-sequence processing. These case studies will provide the community with further insight about debris disk modeling, the degree of post-main-sequence processing of circumstellar material, and the composition of a disintegrating planetesimal.

POPULATION PROPERTIES OF BROWN DWARF ANALOGS TO EXOPLANETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faherty, Jacqueline K.; Gagne, Jonathan; Weinberger, Alycia

2016-07-01

We present a kinematic analysis of 152 low surface gravity M7-L8 dwarfs by adding 18 new parallaxes (including 10 for comparative field objects), 38 new radial velocities, and 19 new proper motions. We also add low- or moderate-resolution near-infrared spectra for 43 sources confirming their low surface gravity features. Among the full sample, we find 39 objects to be high-likelihood or new bona fide members of nearby moving groups, 92 objects to be ambiguous members and 21 objects that are non-members. Using this age-calibrated sample, we investigate trends in gravity classification, photometric color, absolute magnitude, color–magnitude, luminosity, and effective temperature.more » We find that gravity classification and photometric color clearly separate 5–130 Myr sources from >3 Gyr field objects, but they do not correlate one to one with the narrower 5–130 Myr age range. Sources with the same spectral subtype in the same group have systematically redder colors, but they are distributed between 1 and 4 σ from the field sequences and the most extreme outlier switches between intermediate- and low-gravity sources either confirmed in a group or not. The absolute magnitudes of low-gravity sources from the J band through W 3 show a flux redistribution when compared to equivalently typed field brown dwarfs that is correlated with spectral subtype. Low-gravity, late-type L dwarfs are fainter at J than the field sequence but brighter by W 3. Low-gravity M dwarfs are >1 mag brighter than field dwarfs in all bands from J through W 3. Clouds, which are a far more dominant opacity source for L dwarfs, are the likely cause. On color–magnitude diagrams, the latest-type, low-gravity L dwarfs drive the elbow of the L/T transition up to 1 mag redder and 1 mag fainter than field dwarfs at M{sub J} but are consistent with or brighter than the elbow at M{sub W1} and M{sub W2}. We conclude that low-gravity dwarfs carry an extreme version of the cloud conditions of field objects to lower temperatures, which logically extends into the lowest-mass, directly imaged exoplanets. Furthermore, there is an indication on color-magnitude diagrams (CMDs; such as M{sub J} versus (J – W 2)) of increasingly redder sequences separated by gravity classification, although it is not consistent across all CMD combinations. Examining bolometric luminosities for planets and low-gravity objects, we confirm that (in general) young M dwarfs are overluminous while young L dwarfs are normal compared to the field. Using model extracted radii, this translates into normal to slightly warmer M dwarf temperatures compared to the field sequence and lower temperatures for L dwarfs with no obvious correlation with the assigned moving group.« less

A detection of the evolutionary time scale of the DA white dwarf G117 - B15A with the Whole Earth Telescope

NASA Technical Reports Server (NTRS)

Kepler, S. O.; Fontaine, G.; Bergeron, P.; Winget, D. E.; Nather, R. E.; Bradley, P. A.; Claver, C. F.; Grauer, A. D.; Vauclair, G.; Marar, T. M. K.

1991-01-01

The time rate of change for the main pulsation period of the 13,000 K DA white dwarf G117 - B15A has been detected using the Whole Earth Telescope (WET). The observed rate of period change, P(dot) = (12.0 + or - 3.5) x 10 to the -15th s/s, is somewhat larger than the published theoretical calculations of the rate of period change due to cooling, based on carbon core white dwarf models. Other effects that could contribute to the observed rate of period change are discussed.

A NEAR-INFRARED SPECTROSCOPIC SURVEY OF COOL WHITE DWARFS IN THE SLOAN DIGITAL SKY SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kilic, Mukremin; Kowalski, Piotr M.; Von Hippel, Ted

2009-07-15

We present near-infrared photometric observations of 15 and spectroscopic observations of 38 cool white dwarfs (WDs). This is the largest near-infrared spectroscopic survey of cool WDs to date. Combining the Sloan Digital Sky Survey photometry and our near-infrared data, we perform a detailed model atmosphere analysis. The spectral energy distributions of our objects are explained fairly well by model atmospheres with temperatures ranging from 6300 K down to 4200 K. Two WDs show significant absorption in the infrared, and are best explained with mixed H/He atmosphere models. Based on the up-to-date model atmosphere calculations by Kowalski and Saumon, we findmore » that the majority of the stars in our sample have hydrogen-rich atmospheres. We do not find any pure helium atmosphere WDs below 5000 K, and we find a trend of increasing hydrogen to helium ratio with decreasing temperature. These findings present an important challenge to understanding the spectral evolution of WDs.« less

High-throughput discovery of mutations in tef semi-dwarfing genes by next-generation sequencing analysis.

PubMed

Zhu, Qihui; Smith, Shavannor M; Ayele, Mulu; Yang, Lixing; Jogi, Ansuya; Chaluvadi, Srinivasa R; Bennetzen, Jeffrey L

2012-11-01

Tef (Eragrostis tef) is a major cereal crop in Ethiopia. Lodging is the primary constraint to increasing productivity in this allotetraploid species, accounting for losses of ∼15-45% in yield each year. As a first step toward identifying semi-dwarf varieties that might have improved lodging resistance, an ∼6× fosmid library was constructed and used to identify both homeologues of the dw3 semi-dwarfing gene of Sorghum bicolor. An EMS mutagenized population, consisting of ∼21,210 tef plants, was planted and leaf materials were collected into 23 superpools. Two dwarfing candidate genes, homeologues of dw3 of sorghum and rht1 of wheat, were sequenced directly from each superpool with 454 technology, and 120 candidate mutations were identified. Out of 10 candidates tested, six independent mutations were validated by Sanger sequencing, including two predicted detrimental mutations in both dw3 homeologues with a potential to improve lodging resistance in tef through further breeding. This study demonstrates that high-throughput sequencing can identify potentially valuable mutations in under-studied plant species like tef and has provided mutant lines that can now be combined and tested in breeding programs for improved lodging resistance.

Evolution of chromospheres and coronae in solar mass stars - A far-ultraviolet and soft X-ray comparison of Arcturus /K2 III/ and Alpha Centauri A /G2 V/

NASA Technical Reports Server (NTRS)

Ayres, T. R.; Simon, T.; Linsky, J. L.

1982-01-01

IUE far-UV and Einstein Observatory soft X-ray observations for the red giant Arcturus and the nearby yellow dwarf Alpha-Centauri A, which are archetypes of solar mass stars in different stages of evolution, are compared. Evidence is found for neither coronal soft X-ray emission from the red giant, at surface flux levels of only 0.0006 that detected previously for the yellow dwarf, nor C II and IV resonance line emission at surface flux levels of only 0.02 those of the yellow dwarf. The resonance line upper limits and previous detections of the C II intersystem UV multiplet 0.01 near 2325 A provide evidence for an Arcturus outer atmosphere that is geometrically extended, tenuous and cool. The red giant has, in addition, a prominent cool stellar wind. An extensive tabulation of line identifications, widths and fluxes for the IUE far-UV echelle spectra of the two stars is given, and two competing explanations for the Wilson-Bappu effect are discussed.

Characterizing K2 Candidate Planetary Systems Orbiting Low-Mass Stars. I. Classifying Low-Mass Host Stars Observed During Campaigns 1-7

NASA Technical Reports Server (NTRS)

Dressing, Courtney D.; Newton, Elisabeth R.; Schlieder, Joshua E.; Charbomeau, David; Krutson, Heather A.; Vanderburg, Andrew; Sinukoff, Evan

2017-01-01

We present near-infrared spectra for 144 candidate planetary systems identified during Campaigns 1-7 of the NASA K2 Mission. The goal of the survey was to characterize planets orbiting low-mass stars, but our Infrared Telescope Facility/SpeX and Palomar/TripleSpec spectroscopic observations revealed that 49% of our targets were actually giant stars or hotter dwarfs reddened by interstellar extinction. For the 72 stars with spectra consistent with classification as cool dwarfs (spectral types K3-M4), we refined their stellar properties by applying empirical relations based on stars with interferometric radius measurements. Although our revised temperatures are generally consistent with those reported in the Ecliptic Plane Input Catalog (EPIC), our revised stellar radii are typically 0.13 solar radius (39%) larger than the EPIC values, which were based on model isochrones that have been shown to underestimate the radii of cool dwarfs. Our improved stellar characterizations will enable more efficient prioritization of K2 targets for follow-up studies.

2MASS J06562998+3002455: Not a Cool White Dwarf Candidate, but a Population II Halo Star

NASA Astrophysics Data System (ADS)

de la Fuente Marcos, Raúl; de la Fuente Marcos, Carlos

2018-06-01

2MASS J06562998+3002455 or PSS 309-6 is a high proper-motion star that was discovered during a survey with the 2.1 m telescope at Kitt Peak National Observatory. Here, we reevaluate the status of this interesting star using Gaia DR2. Our results strongly suggest that PSS 309-6 could be a Population II star as the value of its V component is close to -220 km/s, which is typical for halo stars in the immediate solar neighborhood. Kapteyn's star is the nearest known halo star and PSS 309-6 exhibits similar kinematic and photometric signatures. Its properties also resemble those of 2MASS J15484023-3544254, which was once thought to be the nearest cool white dwarf but was later reclassified as K-type subdwarf. Although it is virtually certain that PSS 309-6 is not a nearby white dwarf but a more distant Population II subdwarf, further spectroscopic information, including radial velocity measurements, is necessary to fully characterize this probable member of the Galactic halo.

APOKASC 2.0: Asteroseismology and Spectroscopy for Cool Stars

NASA Astrophysics Data System (ADS)

Pinsonneault, Marc H.; Elsworth, Yvonne P.; APOKASC

2017-01-01

The APOGEE survey has obtained and analyzed high resolution H band spectra of more than 10,000 cool dwarfs and giants in the original Kepler fields. The APOKASC effort combines this data with asteroseismology and star spot studies, resulting in more than 7,000 stellar mass estimates for dwarfs and giants with high quality abundances, temperatures, and surface gravities. We highlight the main results from this effort so far, which include a tight correlation between surface abundances in giants and stellar mass, precise absolute gravity calibrations, and the discovery of unexpected stellar populations, such as young alpha-enhanced stars. We discuss grid modeling estimates for stellar masses and compare the absolute asteroseismic mass scale to calibrators in star clusters and the halo Directions for future efforts are discussed.

LRG-BEASTS III: ground-based transmission spectrum of the gas giant orbiting the cool dwarf WASP-80

NASA Astrophysics Data System (ADS)

Kirk, J.; Wheatley, P. J.; Louden, T.; Skillen, I.; King, G. W.; McCormac, J.; Irwin, P. G. J.

2018-02-01

We have performed ground-based transmission spectroscopy of the hot Jupiter orbiting the cool dwarf WASP-80 using the ACAM instrument on the William Herschel Telescope (WHT) as part of the Low-Resolution Ground-Based Exoplanet Atmosphere Survey using Transmission Spectroscopy programme. This is the third paper of a ground-based transmission spectroscopy survey of hot Jupiters using low-resolution grism spectrographs. We observed two transits of the planet and have constructed transmission spectra spanning a wavelength range of 4640-8840 Å. Our transmission spectrum is inconsistent with a previously claimed detection of potassium in WASP-80b's atmosphere, and is instead most consistent with a haze. We also do not see evidence for sodium absorption at a resolution of 100 Å.

THE COSMOLOGICAL IMPACT OF LUMINOUS TeV BLAZARS. III. IMPLICATIONS FOR GALAXY CLUSTERS AND THE FORMATION OF DWARF GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pfrommer, Christoph; Chang, Philip; Broderick, Avery E., E-mail: christoph.pfrommer@h-its.org, E-mail: aeb@cita.utoronto.ca, E-mail: pchang@cita.utoronto.ca

2012-06-10

A subset of blazars are powerful TeV emitters, dominating the extragalactic component of the very high energy gamma-ray universe (E {approx}> 100 GeV). These TeV gamma rays generate ultrarelativistic electron-positron pairs via pair production with the extragalactic background light. While it has generally been assumed that the kinetic energy of these pairs cascades to GeV gamma rays via inverse Compton scattering, we have argued in Broderick et al. (Paper I in this series) that plasma beam instabilities are capable of dissipating the pairs' energy locally on timescales short in comparison to the inverse Compton cooling time, heating the intergalactic mediummore » (IGM) with a rate that is independent of density. This dramatically increases the entropy of the IGM after redshift z {approx} 2, with a number of important implications for structure formation: (1) this suggests a scenario for the origin of the cool core (CC)/non-cool core (NCC) bimodality in galaxy clusters and groups. Early-forming galaxy groups are unaffected because they can efficiently radiate the additional entropy, developing a CC. However, late-forming groups do not have sufficient time to cool before the entropy is gravitationally reprocessed through successive mergers-counteracting cooling and potentially raising the core entropy further. This may result in a population of X-ray dim groups/clusters, consistent with X-ray stacking analyses of optically selected samples. Hence, blazar heating works differently than feedback by active galactic nuclei, which we show can balance radiative cooling but is unable to transform CC into NCC clusters on the buoyancy timescale due to the weak coupling between the mechanical energy to the cluster gas. (2) We predict a suppression of the Sunyaev-Zel'dovich (SZ) power spectrum template on angular scales smaller than 5' due to the globally reduced central pressure of groups and clusters forming after z {approx} 1. This allows for a larger rms amplitude of the density power spectrum, {sigma}{sub 8}, and may reconcile SZ-inferred values with those by other cosmological probes even after allowing for a contribution due to patchy reionization. (3) Our redshift-dependent entropy floor increases the characteristic halo mass below which dwarf galaxies cannot form by a factor of approximately 10 (50) at mean density (in voids) over that found in models that include photoionization alone. This prevents the formation of late-forming dwarf galaxies (z {approx}< 2) with masses ranging from 10{sup 10} to 10{sup 11} M{sub Sun} for redshifts z {approx} 2 to 0, respectively. This may help resolve the 'missing satellite problem' in the Milky Way of the low observed abundances of dwarf satellites compared to cold dark matter simulations and may bring the observed early star formation histories into agreement with galaxy formation models. At the same time, it explains the 'void phenomenon' by suppressing the formation of galaxies within existing dwarf halos of masses <3 Multiplication-Sign 10{sup 10} M{sub Sun} with a maximum circular velocity <60 km s{sup -1} for z {approx}< 2, hence reconciling the number of dwarfs in low-density regions in simulations and the paucity of those in observations.« less

Dwarf galaxy populations in present-day galaxy clusters - II. The history of early-type and late-type dwarfs

NASA Astrophysics Data System (ADS)

Lisker, Thorsten; Weinmann, Simone M.; Janz, Joachim; Meyer, Hagen T.

2013-06-01

How did the dwarf galaxy population of present-day galaxy clusters form and grow over time? We address this question by analysing the history of dark matter subhaloes in the Millennium II cosmological simulation. A semi-analytic model serves as the link to observations. We argue that a reasonable analogue to early morphological types or red-sequence dwarf galaxies are those subhaloes that experienced strong mass-loss, or alternatively those that have spent a long time in massive haloes. This approach reproduces well the observed morphology-distance relation of dwarf galaxies in the Virgo and Coma clusters, and thus provides insight into their history. Over their lifetime, present-day late types have experienced an amount of environmental influence similar to what the progenitors of dwarf ellipticals had already experienced at redshifts above 2. Therefore, dwarf ellipticals are more likely to be a result of early and continuous environmental influence in group- and cluster-size haloes, rather than a recent transformation product. The observed morphological sequences of late-type and early-type galaxies have developed in parallel, not consecutively. Consequently, the characteristics of today's late-type galaxies are not necessarily representative for the progenitors of today's dwarf ellipticals. Studies aiming to reproduce the present-day dwarf population thus need to start at early epochs, model the influence of various environments, and also take into account the evolution of the environments themselves.

A Population Study of Wide-Separation Brown Dwarf Companions to Main Sequence Stars

NASA Technical Reports Server (NTRS)

Smith, Jeffrey J.

2005-01-01

Increased interest in infrared astronomy has opened the frontier to study cooler objects that shed significant light on the formation of planetary systems. Brown dwarf research provides a wealth of information useful for sorting through a myriad of proposed formation theories. Our study combines observational data from 2MASS with rigorous computer simulations to estimate the true population of long-range (greater than 1000 AU) brown dwarf companions in the solar neighborhood (less than 25 pc from Earth). Expanding on Gizis et al. (2001), we have found the margin of error in previous estimates to be significantly underestimated after we included orbit eccentricity, longitude of pericenter, angle of inclination, field star density, and primary and secondary luminosities as parameters influencing the companion systems in observational studies. We apply our simulation results to current L- and T-dwarf catalogs to provide updated estimates on the frequency of wide-separation brown dwarf companions to main sequence stars.

The detectability of brown dwarfs - Predictions and uncertainties

NASA Technical Reports Server (NTRS)

Nelson, L. A.; Rappaport, S.; Joss, P. C.

1993-01-01

In order to determine the likelihood for the detection of isolated brown dwarfs in ground-based observations as well as in future spaced-based astronomy missions, and in order to evaluate the significance of any detections that might be made, we must first know the expected surface density of brown dwarfs on the celestial sphere as a function of limiting magnitude, wavelength band, and Galactic latitude. It is the purpose of this paper to provide theoretical estimates of this surface density, as well as the range of uncertainty in these estimates resulting from various theoretical uncertainties. We first present theoretical cooling curves for low-mass stars that we have computed with the latest version of our stellar evolution code. We use our evolutionary results to compute theoretical brown-dwarf luminosity functions for a wide range of assumed initial mass functions and stellar birth rate functions. The luminosity functions, in turn, are utilized to compute theoretical surface density functions for brown dwarfs on the celestial sphere. We find, in particular, that for reasonable theoretical assumptions, the currently available upper bounds on the brown-dwarf surface density are consistent with the possibility that brown dwarfs contribute a substantial fraction of the mass of the Galactic disk.

The white dwarf luminosity function - A possible probe of the galactic halo

NASA Technical Reports Server (NTRS)

Tamanaha, Christopher M.; Silk, Joseph; Wood, M. A.; Winget, D. E.

1990-01-01

The dynamically inferred dark halo mass density, amounting to above 0.01 solar masses/cu pc at the sun's Galactocentric radius, can be composed of faint white dwarfs provided that the halo formed in a sufficiently early burst of star formation. The model is constrained by the observed disk white dwarf luminosity function which falls off below log (L/solar L) = -4.4, due to the onset of star formation in the disk. By using a narrow range for the initial mass function and an exponentially decaying halo star formation rate with an e-folding time equal to the free-fall time, all the halo dark matter is allowed to be in cool white dwarfs which lie beyond the falloff in the disk luminosity function. Although it is unlikely that all the dark matter is in these dim white dwarfs, a definite signature in the low-luminosity end of the white dwarf luminosity function is predicted even if they comprise only 1 percent of the dark matter. Current CCD surveys should answer the question of the existence of this population within the next few years.

Genome sequence variation in the constricta strain dramatically alters the protein interaction and localization map of Potato yellow dwarf virus

USDA-ARS?s Scientific Manuscript database

The genome sequence of the constricta strain of Potato yellow dwarf virus (CYDV) was determined to be 12,792 nucleotides long and organized into seven open reading frames with the gene order 3’-N-X-P-Y-M-G-L-5’, which encodes the nucleocapsid, phosphoprotein, movement, matrix, glycoprotein and RNA-d...

Ultraviolet Spectra of Two Magnetic White Dwarfs and Ultraviolet Spectra of Subluminous Objects Found in the Kiso Schmidt Survey

NASA Technical Reports Server (NTRS)

Wegner, Gary A.

1987-01-01

Low resolution International Ultraviolet Explorer (IUE) spectroscopic observations of two magnetic white dwarfs BPM25114 and K813-14 were obtained using both the SWP and LWP cameras. The first object has an observed magnetic field of 4 x 10(7) Gauss and the second has one of 3 x 10(7) Gauss. Both objects have overall spectral energy distributions appropriate for cool DA white dwarfs with T(eff) near 10,000 K and accordingly show strong lambda lambda 1400 and 1600 absorption in their spectra. Compared to non-magnetic DA white dwarfs of comparable effective temperature, there are some differences in the profiles, presumably produced by the magnetic fields in these objects. In addition, the ultraviolet spectra of a number of hot subluminous stars in the Kiso Schmidt survey were observed.

The Fate of Exoplanetary Systems and the Implications for White Dwarf Pollution

NASA Astrophysics Data System (ADS)

Veras, D.; Mustill, A. J.; Bonsor, A.; Wyatt, M. C.

2013-09-01

Mounting discoveries of extrasolar planets orbiting post-main-sequence stars motivate studies to understand the fate of these planets. Also, polluted white dwarfs (WDs) likely represent dynamically active systems at late times. Here, we perform full-lifetime simulations of one-, two- and three-planet systems from the endpoint of formation to several Gyr into the WD phase of the host star. We outline the physical and computational processes which must be considered for post-main-sequence planetary studies, and characterize the challenges in explaining the robust observational signatures of infrared excess in white dwarfs by appealing to late-stage planetary systems.

The evolution of the lithium abundances of solar-type stars. II - The Ursa Major Group

NASA Technical Reports Server (NTRS)

Soderblom, David R.; Pilachowski, Catherine A.; Fedele, Stephen B.; Jones, Burton F.

1993-01-01

We draw upon a recent study of the membership of the Ursa Major Group (UMaG) to examine lithium among 0.3 Gyr old solar-type stars. For most G and K dwarfs, Li confirms the conclusions about membership in UMaG reached on the basis of kinematics and chromospheric activity. G and K dwarfs in UMaG have less Li than comparable stars in the Pleiades. This indicates that G and K dwarfs undergo Li depletion while they are on the main sequence, in addition to any pre-main-sequence depletion they may have experienced. Moreover, the Li abundances of the Pleiades K dwarfs cannot be attributed to main-sequence depletion alone, demonstrating that pre-main-sequence depletion of Li also takes place. The sun's Li abundance implies that the main-sequence mechanism becomes less effective with age. The hottest stars in UMaG have Li abundances like those of hot stars in the Pleiades and Hyades and in T Tauris, and the two genuine UMaG members with temperatures near Boesgaard's Li chasm have Li abundances consistent with that chasm developing fully by 0.3 Gyr for stars with UMaG's metallicity. We see differences in the abundance of Li between UMaG members of the same spectral types, indicating that a real spread in the lithium abundance exists within this group.

Precise Ages for the Benchmark Brown Dwarfs HD 19467 B and HD 4747 B

NASA Astrophysics Data System (ADS)

Wood, Charlotte; Boyajian, Tabetha; Crepp, Justin; von Braun, Kaspar; Brewer, John; Schaefer, Gail; Adams, Arthur; White, Tim

2018-01-01

Large uncertainty in the age of brown dwarfs, stemming from a mass-age degeneracy, makes it difficult to constrain substellar evolutionary models. To break the degeneracy, we need ''benchmark" brown dwarfs (found in binary systems) whose ages can be determined independent of their masses. HD~19467~B and HD~4747~B are two benchmark brown dwarfs detected through the TRENDS (TaRgeting bENchmark objects with Doppler Spectroscopy) high-contrast imaging program for which we have dynamical mass measurements. To constrain their ages independently through isochronal analysis, we measured the radii of the host stars with interferometry using the Center for High Angular Resolution Astronomy (CHARA) Array. Assuming the brown dwarfs have the same ages as their host stars, we use these results to distinguish between several substellar evolutionary models. In this poster, we present new age estimates for HD~19467 and HD~4747 that are more accurate and precise and show our preliminary comparisons to cooling models.

Application of screened Coulomb potential in fitting DBV star PG 0112+104

NASA Astrophysics Data System (ADS)

Chen, Y. H.

2018-03-01

With 78.7 d of observations for PG 0112+104, a pulsating DB star, from Campaign 8 of Kepler 2 mission, Hermes et al. made a detailed mode identification. A reliable mode identification, with 5 l = 1 modes, 3 l = 2 modes, and 3 l = 1 or 2 modes, was identified. Grids of DBV star models are evolved by WDEC with element diffusion effect of pure Coulomb potential and screened Coulomb potential. Fitting the identified modes of PG 0112+104 by the calculated ones, we studied the difference of element diffusion effect between adopting pure Coulomb potential and screened Coulomb potential. Our aim is to reduce the fitting error by studying new input physics. The starting models including their chemical composition profile are from white dwarf models evolved by MESA. They were calculated following the stellar evolution from the main sequence to the start of the white dwarf cooling sequences. The optimal parameters are basically consistent with that of previous spectroscopic and asteroseismological studies. The pure and screened Coulomb potential lead to different composition profiles of the C/O-He interface area. High k modes are very sensitive to the area. However, most of the observed modes for PG 0112+104 are low k modes. The σRMS taking the screened Coulomb potential is reduced by 4 per cent compared with taking the pure Coulomb potential when fitting the identified low k modes of PG 0112+104. Fitting the Kepler 2 data with our models improved the σRMS of the fit by 27 per cent.

A New Sample of Cool Subdwarfs from SDSS: Properties and Kinematics

NASA Astrophysics Data System (ADS)

Savcheva, Antonia; West, Andrew A.; Bochanski, John J.

2014-06-01

We present a new sample of M subdwarfs compiled from the 7th data re- lease of the Sloan Digital Sky Survey. With 3517 new subdwarfs, this new sample significantly increases the number the existing sample of low-mass subdwarfs. This catalog includes unprecedentedly large numbers of extreme and ultra sudwarfs. Here, we present the catalog and the statistical analysis we perform. Subdwarf template spectra are derived. We show color-color and reduced proper motion diagrams of the three metallicity classes, which are shown to separate from the disk dwarf population. The extreme and ultra subdwarfs are seen at larger values of reduced proper motion as expected for more dynamically heated populations. We determine 3D kinematics for all of the stars with proper motions. The color-magnitude diagrams show a clear separation of the three metallicity classes with the ultra and extreme subdwarfs being significantly closer to the main sequence than the ordinary subdwarfs. All subdwarfs lie below and to the blue of the main sequence. Based on the average (U, V, W ) velocities and their dispersions, the extreme and ultra subdwarfs likely belong to the Galactic halo, while the ordinary subdwarfs are likely part of the old Galactic (or thick) disk. An extensive activity analy- sis of subdwarfs is performed using chromospheric Hα emission and 208 active subdwarfs are found. We show that while the activity fraction of subdwarfs rises with spectral class and levels off at the latest spectral classes, consistent with the behavior of M dwarfs, the extreme and ultra subdwarfs are basically flat.

A New Sample of Cool Subdwarfs from SDSS: Properties and Kinematics

NASA Astrophysics Data System (ADS)

Savcheva, Antonia S.; West, Andrew A.; Bochanski, John J.

2014-10-01

We present a new sample of M subdwarfs compiled from the seventh data release of the Sloan Digital Sky Survey. With 3517 new subdwarfs, this new sample significantly increases the number of spectroscopically confirmed low-mass subdwarfs. This catalog also includes 905 extreme and 534 ultra sudwarfs. We present the entire catalog, including observed and derived quantities, and template spectra created from co-added subdwarf spectra. We show color-color and reduced proper motion diagrams of the three metallicity classes, which are shown to separate from the disk dwarf population. The extreme and ultra subdwarfs are seen at larger values of reduced proper motion, as expected for more dynamically heated populations. We determine 3D kinematics for all of the stars with proper motions. The color-magnitude diagrams show a clear separation of the three metallicity classes with the ultra and extreme subdwarfs being significantly closer to the main sequence than the ordinary subdwarfs. All subdwarfs lie below (fainter) and to the left (bluer) of the main sequence. Based on the average (U, V, W) velocities and their dispersions, the extreme and ultra subdwarfs likely belong to the Galactic halo, while the ordinary subdwarfs are likely part of the old Galactic (or thick) disk. An extensive activity analysis of subdwarfs is performed using Hα emission, and 208 active subdwarfs are found. We show that while the activity fraction of subdwarfs rises with spectral class and levels off at the latest spectral classes, consistent with the behavior of M dwarfs, the extreme and ultra subdwarfs are basically flat.

Frontiers of stellar evolution

NASA Technical Reports Server (NTRS)

Lambert, David L. (Editor)

1991-01-01

The present conference discusses theoretical and observational views of star formation, spectroscopic constraints on the evolution of massive stars, very low mass stars and brown dwarfs, asteroseismology, globular clusters as tests of stellar evolution, observational tests of stellar evolution, and mass loss from cool evolved giant stars. Also discussed are white dwarfs and hot subdwarfs, neutron stars and black holes, supernovae from single stars, close binaries with evolved components, accretion disks in interacting binaries, supernovae in binary systems, stellar evolution and galactic chemical evolution, and interacting binaries containing compact components.

Two peculiar subclasses of cool DB stars - The DBA's and the DBZ's

NASA Technical Reports Server (NTRS)

Shipman, Harry L.

1987-01-01

This paper reviews several recent observational investigations which have demonstrated that a significant number of white dwarfs with He-dominated photospheres contain trace hydrogen. In addition, follow-up work on the Case Blue Star survey has uncovered an analog of GD 40 - another DBZ star. Various scenarios for their origin are discussed. The paper concludes with a brief synopsis of a discussion of how many more subclasses of white dwarf stars might exist and what it would take to discover them.

Get Ready for Gaia: Cool White Dwarfs in Common Proper Motion with Tycho Stars

NASA Astrophysics Data System (ADS)

Hambly, N.; Rowell, N.; Lam, M.

2017-03-01

We discuss the Gaia Data Release 1 (September 2016) and preliminary work on maximising the benefit for cool white dwarf (WD) science in advance of the full parallax catalogue which will appear around one year later in DR2. The Tycho catalogue is used in conjunction with the all-sky ground based astrometric/ photometric SuperCOSMOS Sky Survey in order to identify candidate faint common proper motion objects to the Tycho stars. Gaia DR1 is supplemented by the Tycho-Gaia Astrometric Solution catalogue containing some 2 million parallaxes with Hipparcos-like precision for Tycho stars. While hotter, brighter WDs are present in Tycho, cooler examples are much rarer (if present at all) and CPM offers one method to infer precision distances for a statistically useful sample of these very faint WDs.

The Dwarf Nova SY Cancri and its Environs

NASA Astrophysics Data System (ADS)

Landolt, A. U.; Clem, J. L.

2018-06-01

Multicolor UBVRI photometry, collected intermittedly over a period of 22 years, is presented for the dwarf nova SY Cancri. Additional UBVRI photometry for a handful of sequence stars in the vicinity of SY Cancri is also presented.

Genomic and phylogenetic evidence that Maize rough dwarf and Rice black-streaked dwarf fijiviruses should be classified as different geographic strains of a single species.

PubMed

Xie, L; Lv, M-F; Yang, J; Chen, J-P; Zhang, H-M

Maize rough dwarf disease (MRDD) has long been known as one of the most devastating viral diseases of maize worldwide and is caused by single or complex infection by four fijiviruses: Maize rough dwarf virus (MRDV) in Europe and the Middle East, Mal de Rio Cuarto virus (MRCV) in South America, rice black-streaked dwarf virus (RBSDV), and Southern rice black-streaked dwarf virus (SRBSDV or Rice black-streaked dwarf virus 2, RBSDV-2) in East Asia. These are currently classified as four distinct species in the genus Fijivirus, family Reoviridae, but their taxonomic status has been questioned. To help resolve this, the nucleotide sequences of the ten genomic segments of an Italian isolate of MRDV have been determined, providing the first complete genomic sequence of this virus. Its genome has 29144 nucleotides and is similar in organization to those of RBSDV, SRBSDV, and MRCV. The 13 ORFs always share highest identities (81.3-97.2%) with the corresponding ORFs of RBSDV and phylogenetic analyses of the different genome segments and ORFs all confirm that MRDV clusters most closely with RBSDV and that MRCV and SRBSDV are slightly more distantly related. The results suggest that MRDV and RBSDV should be classified as different geographic strains of the same virus species and we suggest the name cereal black-streaked dwarf fijivirus (CBSDV) for consideration.

Thermoregulatory challenges in the habitat of the world's smallest tortoise, Chersobius signatus.

PubMed

Loehr, Victor J T

2018-01-01

Ectotherms have various means of dealing with low environmental temperatures, but relatively few species have been rigorously investigated. Consequently, we have little information to predict how ectotherm populations might respond to global temperature changes. Tortoises from temperate and subtropical regions often overcome periodically cool conditions by hibernation, but speckled dwarf tortoises (Chersobius signatus) need to remain active to exploit ephemeral resources in their arid winter-rainfall habitat. This study investigated how dwarf tortoises cope with low temperatures in winter and spring, by measuring thermal habitat quality and thermoregulation based on differently-sized operative temperature models in sun, shade, and in deep crevices. Investigations continued in summer and autumn to obtain a year-round picture of thermoregulatory challenges. Although large models (i.e., larger than dwarf tortoises) were expected to have lower operative temperatures than smaller models, due to the former's larger thermal inertia, all model sizes had similar temperatures. Hence, the species' small body size does not appear constrained by obtainable body temperatures in cool seasons. Nevertheless, low operative temperatures in winter posed a challenge for the tortoises, which reached their field-preferred body temperature for an average of only 0.8-0.9h per day. Moreover, a low thermoregulation effectiveness suggested that tortoises traded-off physiological benefits of favourable body temperatures against predation risk. Spring and autumn provided higher temperatures, but summer caused the greatest thermoregulatory challenge. Although summer body temperatures were closer to field-preferred body temperature than in any other season, tortoises required rock crevices to avoid overheating. The small size of dwarf tortoises might help them utilise crevices. In summer, maximum operative temperatures in crevices were similar to field-preferred body temperature, indicating that an increase in environmental temperatures might be detrimental to dwarf tortoises. In light of projected temperature rises, future studies should assess if dwarf tortoises can cope with higher environmental temperatures in summer. Copyright © 2017 Elsevier Ltd. All rights reserved.

CARMENES. Mining public archives for stellar parameters and spectra of M dwarfs with master thesis students

NASA Astrophysics Data System (ADS)

Caballero, J. A.; Montes, D.; Alonso-Floriano, F. J.; Cortés-Contreras, M.; González-Álvarez, E.; Hidalgo, D.; Holgado, G.; Martínez-Rodríguez, H.; Sanz-Forcada, J.; López-Santiago, J.

2015-05-01

We are compiling the most comprehensive database of M dwarfs ever built, CARMENCITA, the CARMENES Cool dwarf Information and daTa Archive, which will be the CARMENES 'input catalogue'. In addition to the science preparation with low- and high-resolution spectrographs and lucky imagers, we compile a huge pile of public data on over 2200 M dwarfs, and analyse them, mostly using virtual-observatory tools. Here we describe four specific actions carried out by master students. They mine public archives for additional high-resolution spectroscopy (UVES, FEROS and HARPS), multi-band photometry (FUV-NUV-u-B-g-V-r-R-i-J-H-Ks-W1-W2-W3-W4), X-ray data (ROSAT, XMM-Newton and Chandra), and periods, rotational velocities and Hα pseudo-equivalent widths. As described, there are many interdependences between all these data.

Skylab ultraviolet stellar spectra - A new white dwarf, HD 149499 B

NASA Technical Reports Server (NTRS)

Parsons, S. B.; Wray, J. D.; Benedict, G. F.; Henize, K. G.; Laget, M.

1976-01-01

The letter reports the discovery of a cool star with excess brightness in the vacuum ultraviolet on an objective-prism photograph obtained during the second Skylab mission. This star, HD 149499, is of type K0 V and has a companion with an apparent magnitude of about 11.8; the relatively flat UV spectrum observed at the position of HD 149499 is characteristic of a 10th or 11th magnitude unreddened O- or early B-type star. It is shown that the excess VUV brightness is due to the companion, HD 149499B, which probably lies in the region of the H-R diagram occupied by the hot white dwarfs. Inspection of white dwarf lists indicates that this star is the sixth or seventh brightest white dwarf known. A maximum orbital motion of 0.025 arcsec/yr is estimated along with a period of just under 500 yr.

Stellar coronae at the end of the main sequence - A ROSAT survey of the late M dwarfs

NASA Technical Reports Server (NTRS)

Fleming, Thomas A.; Giampapa, Mark S.; Schmitt, J. H. M. M.; Bookbinder, Jay A.

1993-01-01

We present X-ray data, both detections and upper limits, from the ROSAT all-sky survey for most known M dwarfs later than type M5, as well as from selected ROSAT pointed observations of some of these stars. We compare these data with similar data for early M dwarfs in an attempt to probe the nature of the magnetic dynamo and coronal heating mechanism for the very late M dwarfs, which are presumably totally convective. Our results indicate that late M dwarfs can have coronae which are just as active as those for the early M dwarfs and that coronal heating efficiency for 'saturated' stars does not drop at spectral type M6.

Stellar coronae at the end of the main sequence: A Rosat survey of the late M dwarfs

NASA Technical Reports Server (NTRS)

Fleming, T. A.; Giampapa, M. S.; Schmitt, J. H. M. M.; Bookbinder, J. A.

1993-01-01

X-ray data, both detections and upper limits, from the Rosat all sky survey for most known M dwarfs later than type M5 are presented. Selected Rosat pointed observations of some of these stars are included. These data are compared to similar data for early M dwarfs in an attempt to probe the nature of the magnetic dynamo and coronal heating mechanism for the very late M dwarfs, which are presumably totally convective. The results indicate that late M dwarfs can have coronae which are just as active as those for the early M dwarfs and that coronal heating efficiency for 'saturated' stars does not drop at spectral type M6.

AN M DWARF COMPANION TO AN F-TYPE STAR IN A YOUNG MAIN-SEQUENCE BINARY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eigmüller, Ph.; Csizmadia, Sz.; Erikson, A.

2016-03-15

Only a few well characterized very low-mass M dwarfs are known today. Our understanding of M dwarfs is vital as these are the most common stars in our solar neighborhood. We aim to characterize the properties of a rare F+dM stellar system for a better understanding of the low-mass end of the Hertzsprung–Russel diagram. We used photometric light curves and radial velocity follow-up measurements to study the binary. Spectroscopic analysis was used in combination with isochrone fitting to characterize the primary star. The primary star is an early F-type main-sequence star with a mass of (1.493 ± 0.073) M{sub ⊙}more » and a radius of (1.474 ± 0.040) R{sub ⊙}. The companion is an M dwarf with a mass of (0.188 ± 0.014) M{sub ⊙} and a radius of (0.234 ± 0.009) R{sub ⊙}. The orbital period is (1.35121 ± 0.00001) days. The secondary star is among the lowest-mass M dwarfs known to date. The binary has not reached a 1:1 spin–orbit synchronization. This indicates a young main-sequence binary with an age below ∼250 Myr. The mass–radius relation of both components are in agreement with this finding.« less

EX-111 Thermal Emission from Hot White Dwarfs: The Suggested He Abundance-Temperature Correlation. EX-112: The Unique Emission Line White Dwarf Star GD 356

NASA Technical Reports Server (NTRS)

Shipman, H. L.

1986-01-01

Progress in the EXOSAT data analysis program is reported. EXOSAT observations for four white dwarfs (WD1031-115, WD0004+330, WD1615-154, and WD0109-264) were obtained. Counting rates were unexpectedly low, indicating that these objects have a substantial amount of x-ray absorbing matter in their photosheres. In addition, soft x-ray pulsations characterized by a 9.25 minute cycle were discovered in the DA white dwarf V471 Tauri. A residual x-ray flux from the K dwarf companion can be seen during the white dwarf eclipse at orbital phase 0.0. Pronounced dips in the soft x-ray light curve occur at orbital phases 0.15, 0.18, and 0.85. The dips may be correlated with the triangular Lagrangian points of the binary orbit. Smaller dips at phases near the eclipse may be associated with cool loops in the K star corona. Data for the white dwarf H1504+65 was also analyzed. This object is particularly unusual in that its photoshere is devoid of hydrogen and helium. Finally, existing data on the white dwarf Sirius B were analyzed to see what constraints from other data can be placed on the properties of this star. Interrelationships between radius, rotational velocity, and effective temperature were derived.

Circumstellar Material on and off the Main Sequence

NASA Astrophysics Data System (ADS)

Steele, Amy; Debes, John H.; Deming, Drake

2017-06-01

There is evidence of circumstellar material around main sequence, giant, and white dwarf stars that originates from the small-body population of planetary systems. These bodies tell us something about the chemistry and evolution of protoplanetary disks and the planetary systems they form. What happens to this material as its host star evolves off the main sequence, and how does that inform our understanding of the typical chemistry of rocky bodies in planetary systems? In this talk, I will discuss the composition(s) of circumstellar material on and off the main sequence to begin to answer the question, “Is Earth normal?” In particular, I look at three types of debris disks to understand the typical chemistry of planetary systems—young debris disks, debris disks around giant stars, and dust around white dwarfs. I will review the current understanding on how to infer dust composition for each class of disk, and present new work on constraining dust composition from infrared excesses around main sequence and giant stars. Finally, dusty and polluted white dwarfs hold a unique key to our understanding of the composition of rocky bodies around other stars. In particular, I will discuss WD1145+017, which has a transiting, disintegrating planetesimal. I will review what we know about this system through high speed photometry and spectroscopy and present new work on understanding the complex interplay of physics that creates white dwarf pollution from the disintegration of rocky bodies.

Discovery of White Dwarfs in the Globular Clusters M13 and M22 Using HST ACS Photometric Data

NASA Astrophysics Data System (ADS)

Cho, Dong-Hwan; Yoon, Tae Seog; Lee, Sang-Gak; Sung, Hyun-Il

2015-12-01

A search for hot and bright white dwarfs (WDs) in the Milky Way globular clusters M13 (NGC 6205) and M22 (NGC 6656) is carried out using the deep and homogeneous VI photometric catalog of Anderson et al. and and Sarajedini et al., based on data taken with the ACS/WFC aboard the Hubble Space Telescope (HST). V versus V-I color-magnitude diagrams (CMDs) of M13 and M22 are constructed and numerous spurious detections are rejected according to their photometric quality parameters qfit(V) and qfit(I). In the case of M13, further radial restriction is applied to reject central stars with higher photometric errors due to central crowding. From each resultant V versus V-I CMD, sixteen and thirteen WD candidates are identified in M13 and M22, respectively. They are identified as stellar objects in the accompanying ACS/WFC images and are found to be randomly distributed across the central regions of M13 and M22. Their positions in the CMDs are in the bright part of the DA WD cooling sequences indicating that they are true WDs. In order to confirm their nature, follow-up spectroscopic observations are needed.

Characterizing the Cool KOIs. VII. Refined Physical Properties of the Transiting Brown Dwarf LHS 6343 C

NASA Astrophysics Data System (ADS)

Montet, Benjamin T.; Johnson, John Asher; Muirhead, Philip S.; Villar, Ashley; Vassallo, Corinne; Baranec, Christoph; Law, Nicholas M.; Riddle, Reed; Marcy, Geoffrey W.; Howard, Andrew W.; Isaacson, Howard

2015-02-01

We present an updated analysis of LHS 6343, a triple system in the Kepler field which consists of a brown dwarf transiting one member of a widely separated M+M binary system. By analyzing the full Kepler data set and 34 Keck/HIgh Resolution Echelle Spectrometer radial velocity observations, we measure both the observed transit depth and Doppler semiamplitude to 0.5% precision. With Robo-AO and Palomar/PHARO adaptive optics imaging as well as TripleSpec spectroscopy, we measure a model-dependent mass for LHS 6343 C of 62.1 ± 1.2 M Jup and a radius of 0.783 ± 0.011 R Jup. We detect the secondary eclipse in the Kepler data at 3.5σ, measuring ecos ω = 0.0228 ± 0.0008. We also derive a method to measure the mass and radius of a star and transiting companion directly, without any direct reliance on stellar models. The mass and radius of both objects depend only on the orbital period, stellar density, reduced semimajor axis, Doppler semiamplitude, eccentricity, and inclination, as well as the knowledge that the primary star falls on the main sequence. With this method, we calculate a mass and radius for LHS 6343 C to a precision of 3% and 2%, respectively.

Activity in Very Cool Stars: Magnetic Dissipation in Late M and L Dwarf Atmospheres

NASA Astrophysics Data System (ADS)

Mohanty, Subhanjoy; Basri, Gibor; Shu, Frank; Allard, France; Chabrier, Gilles

2002-05-01

Recent observations show that chromospheric Hα activity in late M and L dwarfs is much lower than in the earlier M types. This is particularly surprising given that the late M and L dwarfs are comparatively very rapid rotators: in the early M dwarfs, rapid rotation is associated with high activity levels. One possibility is that the drop-off in activity in the late M and L dwarfs is a result of very high electrical resistivities in their dense, cool, and predominantly neutral atmospheres.We calculate the magnetic field diffusivity in the atmospheres of objects with Teff in the range 3000-1500 K (mid M to late L) using the atmospheric structure models of Allard and Hauschildt. We find that the combination of very low ionization fraction and high density in these atmospheres results in very large resistivities and thus efficient field diffusion. While both ambipolar diffusion and Ohmic decay of currents due to ion-electron collisions occur, the primary diffusion effects are due to current decay through collisions of charged particles with neutrals. Moreover, the latter resistivity is a strong function of both effective temperature and optical depth, increasing rapidly as either Teff or optical depth decreases. This has two implications: (1) Any magnetic field present is increasingly decoupled from atmospheric fluid motions as one moves from mid M to L. In the late M and L dwarfs, atmospheric motions cannot lead to equilibrium field configurations very different from potential ones. That is, the magnitude of magnetic stresses generated by atmospheric motions is very small in these objects. We quantify this effect by a simple Reynolds number calculation. (2) Even if magnetic stresses are easily produced by fluid motions in the hot interior (where the coupling between field and matter is good), their propagation up through the atmosphere will be increasingly hampered by the growing atmospheric resistivity as one moves from mid M to late L. Thus both the generation and propagation of magnetic stresses are increasingly damped with decreasing Teff in these cool dwarfs. As a result, the magnetic free energy available for the support of a chromosphere, and activity becomes smaller and smaller with later type. This can account for the observed drop in Hα activity from mid M to L, assuming that activity in these dwarfs is magnetically driven. To check the latter assumption, we estimate the emergent acoustic fluxes in these objects through a Lighthill-Proudman calculation. While the acoustic fluxes also decrease with decreasing Teff, they appear inadequate to explain the observed Hα fluxes in mid M to L dwarfs. In the absence of acoustic heating, magnetic heating indeed seems the most viable way of generating activity. We emphasize that our calculations are equilibrium ones and do not address time-dependent phenomena. We also do not examine the highest atmospheric layers, where correction is not expected, but which we show are rarefied enough to permit charged particles to remain coupled to the field. Finally, while our calculations do not address flares in late M and L dwarfs, we speculate that the latter could be created by buoyant flux tubes that are generated in the interior and rise rapidly through the atmosphere, dissipating their associated currents in the upper atmospheric layers.

Star Formation in Dwarf-Dwarf Mergers: Fueling Hierarchical Assembly

NASA Astrophysics Data System (ADS)

Stierwalt, Sabrina; Johnson, K. E.; Kallivayalil, N.; Patton, D. R.; Putman, M. E.; Besla, G.; Geha, M. C.

2014-01-01

We present early results from the first systematic study a sample of isolated interacting dwarf pairs and the mechanisms governing their star formation. Low mass dwarf galaxies are ubiquitous in the local universe, yet the efficiency of gas removal and the enhancement of star formation in dwarfs via pre-processing (i.e. dwarf-dwarf interactions occurring before the accretion by a massive host) are currently unconstrained. Studies of Local Group dwarfs credit stochastic internal processes for their complicated star formation histories, but a few intriguing examples suggest interactions among dwarfs may produce enhanced star formation. We combine archival UV imaging from GALEX with deep optical broad- and narrow-band (Halpha) imaging taken with the pre- One Degree Imager (pODI) on the WIYN 3.5-m telescope and with the 2.3-m Bok telescope at Steward Observatory to confirm the presence of stellar bridges and tidal tails and to determine whether dwarf-dwarf interactions alone can trigger significant levels of star formation. We investigate star formation rates and global galaxy colors as a function of dwarf pair separation (i.e. the dwarf merger sequence) and dwarf-dwarf mass ratio. This project is a precursor to an ongoing effort to obtain high spatial resolution HI imaging to assess the importance of sequential triggering caused by dwarf-dwarf interactions and the subsequent affect on the more massive hosts that later accrete the low mass systems.

Cool carbon stars in the halo and in dwarf galaxies: Hα, colours, and variability

NASA Astrophysics Data System (ADS)

Mauron, N.; Gigoyan, K. S.; Berlioz-Arthaud, P.; Klotz, A.

2014-02-01

The population of cool carbon (C) stars located far from the galactic plane is probably made of debris of small galaxies such as the Sagittarius dwarf spheroidal galaxy (Sgr), which are disrupted by the gravitational field of the Galaxy. We aim to know this population better through spectroscopy, 2MASS photometric colours, and variability data. When possible, we compared the halo results to C star populations in the Fornax dwarf spheroidal galaxy, Sgr, and the solar neighbourhood. We first present a few new discoveries of C stars in the halo and in Fornax. The number of spectra of halo C stars is now 125. Forty percent show Hα in emission. The narrow location in the JHK diagram of the halo C stars is found to differ from that of similar C stars in the above galaxies. The light curves of the Catalina and LINEAR variability databases were exploited to derive the pulsation periods of 66 halo C stars. A few supplementary periods were obtained with the TAROT telescopes. We confirm that the period distribution of the halo strongly resembles that of Fornax, and we found that it is very different from the C stars in the solar neighbourhood. There is a larger proportion of short-period Mira/SRa variables in the halo than in Sgr, but the survey for C stars in this dwarf galaxy is not complete, and the study of their variability needs to be continued to investigate the link between Sgr and the cool halo C stars. Based on observations made with the NTT and 3.6 m telescope at the European Southern Observatory (La Silla, Chile; programs 084.D-0302 and 070.D-0203), with the TAROT telescopes at La Silla and at Observatoire de la Côte d'Azur (France), and on the exploitation of the Catalina Sky Survey and the LINEAR variability databases.Appendix A is available in electronic form at http://www.aanda.org

On the decay of outbursts in dwarf novae nad X-ray novae

NASA Technical Reports Server (NTRS)

Cannizzo, John K.

1994-01-01

We perform computations using a time-dependent model for the accretion disk limit-cycle mechanism to examine the decay of the optical light following the peak of a dwarf nova outburst. We present the results of a parameter study of the physical input variables which affect the decay rate. In the model, the decay is brought about by a cooling transition front which begins at large radii in the disk and moves inward. The nature of the decay is strongly influenced by the radial dependence of the accretion disk viscosity parameter alpha. To obtain exponential decays for typical dwarf nova parameters, we require alpha proportional to r(exp epsilon(sub 0)), where epsilon(sub 0) approximately = 0.3-0.4. The exact value of epsilon(sub 0) which produces exponential decays depends on factors such as the mass of the accreting star and the inner radius of the accretion disk. Therefore, the observed ubiquity of exponential decays in two different types of systems (dwarf novae and X-ray novae) leads us to believe that alpha is an unnatural scaling for the viscosity. The physics of the cooling transition front must be self-regulating in that the timescale (-parital derivative of lnSigma(r)/partial derivative +)(exp -1) (where Sigma is the surface density) for mass extraction across the front remains constant. This may be consistent with a scaling alpha proportional to (h/r)(exp n), where h is the local disk semi-thickness and n approximately 1-2. As regards the speed of the cooling front, we find v(sub F)(r) proportional to r(exp p), where p approximately 3 at large radii, with an abrupt transition to p approximately 0 at some smaller radius. The r(exp 3) dependence is much steeper than has been found by previous workers and appears to result from the strong variation of specific heat within the cooling front when the front resides at a large radius in the disk. The outflow of disk material across the cooling front causes a significant departure of dln T(sub dff0/dln r from the standard value of -0.75 (expected from steady state accretion) within about 0.2 dex in radius of the break associated with the cooling front -- T(sub eff) aproximately 10(exp 3.9) K (r/10(exp 10 cm)) (exp -0.1). These effects should be observable with eclipse mapping. Finally, it appears that the relatively slow decay rate for the optical flux in the 1975 outburst of A0620-00 can be accounted for if the primary is a approximately 10 Solar mass black hole.

The sdA problem - I. Physical properties

NASA Astrophysics Data System (ADS)

Pelisoli, Ingrid; Kepler, S. O.; Koester, D.

2018-04-01

The so-called sdA stars are defined by having H-rich spectra and surface gravities similar to hot subdwarf stars, but effective temperature below the zero-age horizontal branch. Their evolutionary history is an enigma: their surface gravity is too high for main-sequence stars, but too low for single evolution white dwarfs. They are most likely byproducts of binary evolution, including blue-stragglers, extremely-low mass white dwarf stars (ELMs) and their precursors (pre-ELMs). A small number of ELMs with similar properties to sdAs is known. Other possibilities include metal-poor A/F dwarfs, second generation stars, or even stars accreted from dwarf galaxies. In this work, we analyse colours, proper motions, and spacial velocities of a sample of sdAs from the Sloan Digital Sky Survey to assess their nature and evolutionary origin. We define a probability of belonging to the main sequence and a probability of being a (pre-)ELM based on these properties. We find that 7 per cent of the sdAs are more likely to be (pre-)ELMs than main-sequence stars. However, the spacial velocity distribution suggests that over 35 per cent of them cannot be explained as single metal-poor A/F stars.

A hydrodynamic study of a slow nova outburst. [computerized simulation of thermonuclear runaway in white dwarf envelope

NASA Technical Reports Server (NTRS)

Sparks, W. M.; Starrfield, S.; Truran, J. W.

1978-01-01

The paper reports use of a Lagrangian implicit hydrodynamics computer code incorporating a full nuclear-reaction network to follow a thermonuclear runaway in the hydrogen-rich envelope of a 1.25 solar-mass white dwarf. In this evolutionary sequence the envelope was assumed to be of normal (solar) composition and the resulting outburst closely resembles that of the slow nova HR Del. In contrast, previous CNO-enhanced models resemble fast nova outbursts. The slow-nova model ejects material by radiation pressure when the high luminosity of the rekindled hydrogen shell source exceeds the local Eddington luminosity of the outer layers. This is in contrast to the fast nova outburst where ejection is caused by the decay of the beta(+)-unstable nuclei. Nevertheless, radiation pressure probably plays a major role in ejecting material from the fast nova remnants. Therefore, the sequence from slow to fast novae can be interpreted as a sequence of white dwarfs with increasing amounts of enhanced CNO nuclei in their hydrogen envelopes, although other parameters such as the white-dwarf mass and accretion rate probably contribute to the observed variation between novae.

The Effects of Ram-pressure Stripping and Supernova Winds on the Tidal Stirring of Disky Dwarfs: Enhanced Transformation into Dwarf Spheroidals

NASA Astrophysics Data System (ADS)

Kazantzidis, Stelios; Mayer, Lucio; Callegari, Simone; Dotti, Massimo; Moustakas, Leonidas A.

2017-02-01

A conclusive model for the formation of dwarf spheroidal (dSph) galaxies still remains elusive. Owing to their proximity to the massive spirals Milky Way (MW) and M31, various environmental processes have been invoked to explain their origin. In this context, the tidal stirring model postulates that interactions with MW-sized hosts can transform rotationally supported dwarfs, resembling present-day dwarf irregular (dIrr) galaxies, into systems with the kinematic and structural properties of dSphs. Using N-body+SPH simulations, we investigate the dependence of this transformation mechanism on the gas fraction, f gas, in the disk of the progenitor dwarf. Our numerical experiments incorporate for the first time the combined effects of radiative cooling, ram-pressure stripping, star formation, supernova (SN) winds, and a cosmic UV background. For a given orbit inside the primary galaxy, rotationally supported dwarfs with gas fractions akin to those of observed dIrrs (f gas ≳ 0.5), demonstrate a substantially enhanced likelihood and efficiency of transformation into dSphs relative to their collisionless (f gas = 0) counterparts. We argue that the combination of ram-pressure stripping and SN winds causes the gas-rich dwarfs to respond more impulsively to tides, augmenting their transformation. When f gas ≳ 0.5, disky dwarfs on previously unfavorable low-eccentricity or large-pericenter orbits are still able to transform. On the widest orbits, the transformation is incomplete; the dwarfs retain significant rotational support, a relatively flat shape, and some gas, naturally resembling transition-type systems. We conclude that tidal stirring constitutes a prevalent evolutionary mechanism for shaping the structure of dwarf galaxies within the currently favored CDM cosmological paradigm.

The Effects of Ram-pressure Stripping and Supernova Winds on the Tidal Stirring of Disky Dwarfs: Enhanced Transformation into Dwarf Spheroidals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kazantzidis, Stelios; Mayer, Lucio; Callegari, Simone

A conclusive model for the formation of dwarf spheroidal (dSph) galaxies still remains elusive. Owing to their proximity to the massive spirals Milky Way (MW) and M31, various environmental processes have been invoked to explain their origin. In this context, the tidal stirring model postulates that interactions with MW-sized hosts can transform rotationally supported dwarfs, resembling present-day dwarf irregular (dIrr) galaxies, into systems with the kinematic and structural properties of dSphs. Using N -body+SPH simulations, we investigate the dependence of this transformation mechanism on the gas fraction, f {sub gas}, in the disk of the progenitor dwarf. Our numerical experimentsmore » incorporate for the first time the combined effects of radiative cooling, ram-pressure stripping, star formation, supernova (SN) winds, and a cosmic UV background. For a given orbit inside the primary galaxy, rotationally supported dwarfs with gas fractions akin to those of observed dIrrs ( f {sub gas} ≳ 0.5), demonstrate a substantially enhanced likelihood and efficiency of transformation into dSphs relative to their collisionless ( f {sub gas} = 0) counterparts. We argue that the combination of ram-pressure stripping and SN winds causes the gas-rich dwarfs to respond more impulsively to tides, augmenting their transformation. When f {sub gas} ≳ 0.5, disky dwarfs on previously unfavorable low-eccentricity or large-pericenter orbits are still able to transform. On the widest orbits, the transformation is incomplete; the dwarfs retain significant rotational support, a relatively flat shape, and some gas, naturally resembling transition-type systems. We conclude that tidal stirring constitutes a prevalent evolutionary mechanism for shaping the structure of dwarf galaxies within the currently favored CDM cosmological paradigm.« less

The Extended Region Around the Planetary Nebula NGC 3242

NASA Technical Reports Server (NTRS)

2009-01-01

This ultraviolet image from NASA's Galaxy Evolution Explorer shows NGC 3242, a planetary nebula frequently referred to as 'Jupiter's Ghost.'

The unfortunate name of 'planetary nebula' for this class of celestial object is a historical legacy credited to William Herschel during the 18th century a time when telescopes where small and objects like these, at least the central region, looked very similar to gas-giant planets such as Saturn and Jupiter. In fact, NGC 3242 has no relation to Jupiter or any other planet.

Telescopes and their detectors have dramatically improved over the past few centuries. Our understanding of what planetary nebulae truly are has improved accordingly.

When stars with a mass similar to our sun approach the end of their lives by exhausting supplies of hydrogen and helium fuel in their cores, they swell up into cool red-giant stars. In a last gasp before death, they expel the layers of gas in their outer atmosphere. This exposes the core of the dying star, a dense hot ball of carbon and oxygen called a white dwarf. The white dwarf is so hot that it shines very brightly in the ultraviolet. The ultraviolet light from the white dwarf, in turn, ionizes the gaseous material expelled by the star causing it to glow. A planetary nebula is really the death of a low-mass star.

Although low-mass stars like our sun live for billions of years, planetary nebulae only last for about ten thousand years. As the central white dwarf quickly cools and the ultraviolet light dwindles, the surrounding gas also cools and fades.

In this image of NGC 3242 from the Galaxy Evolution Explorer, the extended region around the planetary nebula is shown in dramatic detail. The small circular white and blue area at the center of the image is the well-known portion of the famous planetary nebula. The precise origin and composition of the extended wispy white features is not known for certain. It is most likely material ejected during the star's red-giant phase before the white dwarf was exposed. However, it may be possible that the extended material is simply interstellar gas that, by coincidence, is located close enough to the white dwarf to be energized by it, and induced to glow with ultraviolet light.

NGC 3242 is located 1,400 to 2,500 light-years away in the constellation Hydra. It was discovered by William Herschel in 1785.

Whole-genome sequencing reveals a potential causal mutation for dwarfism in the Miniature Shetland pony.

PubMed

Metzger, Julia; Gast, Alana Christina; Schrimpf, Rahel; Rau, Janina; Eikelberg, Deborah; Beineke, Andreas; Hellige, Maren; Distl, Ottmar

2017-04-01

The Miniature Shetland pony represents a horse breed with an extremely small body size. Clinical examination of a dwarf Miniature Shetland pony revealed a lowered size at the withers, malformed skull and brachygnathia superior. Computed tomography (CT) showed a shortened maxilla and a cleft of the hard and soft palate which protruded into the nasal passage leading to breathing difficulties. Pathological examination confirmed these findings but did not reveal histopathological signs of premature ossification in limbs or cranial sutures. Whole-genome sequencing of this dwarf Miniature Shetland pony and comparative sequence analysis using 26 reference equids from NCBI Sequence Read Archive revealed three probably damaging missense variants which could be exclusively found in the affected foal. Validation of these three missense mutations in 159 control horses from different horse breeds and five donkeys revealed only the aggrecan (ACAN)-associated g.94370258G>C variant as homozygous wild-type in all control samples. The dwarf Miniature Shetland pony had the homozygous mutant genotype C/C of the ACAN:g.94370258G>C variant and the normal parents were heterozygous G/C. An unaffected full sib and 3/5 unaffected half-sibs were heterozygous G/C for the ACAN:g.94370258G>C variant. In summary, we could demonstrate a dwarf phenotype in a miniature pony breed perfectly associated with a missense mutation within the ACAN gene.

Procesos cuasi-moleculares en enanas blancas frías

NASA Astrophysics Data System (ADS)

Rohrmann, R. D.; Althaus, L. G.; Kepler, S. O.

We show that the radiation emitted by very cool white dwarf stars (Teff ~< 3000 K) with pure hydrogen atmospheres, is fully formed by radiative processes induced by atomic and molecular collisions. FULL TEXT IN SPANISH

A Photometric (griz) Metallicity Calibration for Cool Stars

NASA Astrophysics Data System (ADS)

West, Andrew A.; Davenport, James R. A.; Dhital, Saurav; Mann, Andrew; Massey, Angela P

2014-06-01

We present results from a study that uses wide pairs as tools for estimating and constraining the metal content of cool stars from their spectra and broad band colors. Specifically, we will present results that optimize the Mann et al. M dwarf metallicity calibrations (derived using wide binaries) for the optical regime covered by SDSS spectra. We will demonstrate the robustness of the new calibrations using a sample of wide, low-mass binaries for which both components have an SDSS spectrum. Using these new spectroscopic metallicity calibrations, we will present relations between the metallicities (from optical spectra) and the Sloan colors derived using more than 20,000 M dwarfs in the SDSS DR7 spectroscopic catalog. These relations have important ramifications for studies of Galactic chemical evolution, the search for exoplanets and subdwarfs, and are essential for surveys such as Pan-STARRS and LSST, which use griz photometry but have no spectroscopic component.

Time-resolved IUE studies of cataclysmic variables. I - Eclipsing systems IP Peg, PG 1030+590, and V1315 Aql

NASA Technical Reports Server (NTRS)

Szkody, Paula

1987-01-01

IUE time-resolved spectra of the high-inclination cataclysmic variables IP Peg, PG 1030+590, and V1315 Aql are analyzed in order to determine the characteristics of the disk, hotspots, and white dwarfs. The UV continuum flux distributions are generally flatter than systems of low inclination and high mass-transfer rate, and the white dwarfs/inner disk appear to be relatively cool (15,000-19,000 K) for their orbital periods, possibly because the boundary layers are blocked from view. The continuum fluxes increase at spot phases, with the spot providing the dominant flux in IP Peg. The spot temperatures range from hot (20,000 K) in IP Peg, and perhaps in PG 1030+590, to cool (11,000 K) in V1315 Aql. The C IV emission lines show slightly larger decreases at spot phases than during eclipse, which implies an extended stream area.

Brown Dwarfs: Discovery and Detailed Studies

NASA Technical Reports Server (NTRS)

Kulkarni, Shrinivas R.

2001-01-01

We obtained the optical and IR spectra of Gliese 229B and identified Cs, I, and CO features - as expected in theoretical models. Our optical IR spectrum showed that most of the refractory metals have condensed out of the atmosphere and the presence of Cs, I and CO shows evidence for disequilibrium chemistry. We reported orbital evidence for Gliese 229B. The HST measured optical magnitudes provide additional evidence for the absence of dust in the atmosphere of this cool object. The luminosity of brown dwarfs depend on their masses and ages and in order to interpret the results of the survey we have carried out an extensive Monte Carlo analysis. Our conclusion is that warm brown dwarfs are rare, as companions in the orbital period range beyond approximately 30 - 50 AU. The Palomer survey poses no constraint for brown dwarfs in planetary orbits similar to those of the outer planets. We have just started a program of imaging nearby stars with the newly commissioned AO system at Palomar and Keck and have already found a brown dwarf candidate.

FIRE Spectroscopy Of The Ultracool Brown Dwarf, UGPS 0722-05

NASA Astrophysics Data System (ADS)

Bochanski, John J.; Burgasser, A. J.; Simcoe, R. A.

2011-05-01

We present FIRE spectroscopic observations of the ultracool (T ˜ 520 K) brown dwarf, UGPS 0722-05, obtained during instrument commissioning on the 6.5m Baade Magellan Telescope at Las Campanas Observatory. At a distance of 4.1 pc, this cool brown dwarf is well-suited for detailed followup, and represents a keystone at the transition between the lowest-mass brown dwarfs and exoplanets. Our spectrum of UGPS 0722-05 covers the 0.8-2.5 micron bandpasses at a resolution of R ˜ 6,000, and is measured to high signal-to-noise, peaking at 80 near 1.27 microns. We derive radial and rotational velocities for the isolated brown dwarf, and examine its space motion and Galactic orbit. The spectrum of UGPS 0722-05 is also compared to theoretical spectral models to constrain its atmospheric parameters. Finally, we comment on the presence of unidentified absorption features reported in the discovery spectrum of Lucas et al. (2010). We thank Mauricio Martinez and the entire Magellan staff for assistance during FIRE commissioning and observations. JJB acknowledges the support of Kevin Luhman.

Doppler Imaging of Exoplanets and Brown Dwarfs

NASA Astrophysics Data System (ADS)

Crossfield, I.; Biller, B.; Schlieder, J.; Deacon, N.; Bonnefoy, M.; Homeier, D.; Allard, F.; Buenzli, E.; Henning, T.; Brandner, W.; Goldman, Bertr; Kopytova, T.

2014-03-01

Doppler Imaging produces 2D global maps. When applied to cool planets or more massive brown dwarfs, it can map atmospheric features and track global weather patterns. The first substellar map, of the 2pc-distant brown dwarf Luhman 16B (Crossfeld et al. 2014), revealed patchy regions of thin & thick clouds. Here, I investigate the feasibility of future Doppler Imaging of additional objects. Searching the literature, I find that all 3 of P, v sin i, and variability are published for 22 brown dwarfs. At least one datum exists for 333 targets. The sample is very incomplete below ~L5; we need more surveys to find the best targets for Doppler Imaging! I estimate limiting magnitudes for Doppler Imaging with various hi-resolution near-infrared spectrographs. Only a handful of objects - at the M/L and L/T transitions - can be mapped with current tools. Large telescopes such as TMT and GMT will allow Doppler Imaging of many dozens of brown dwarfs and the brightest exoplanets. More targets beyond type L5 likely remain to be found. Future observations will let us probe the global atmospheric dynamics of many diverse objects.

TOWARD HIGH-PRECISION SEISMIC STUDIES OF WHITE DWARF STARS: PARAMETRIZATION OF THE CORE AND TESTS OF ACCURACY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Giammichele, N.; Fontaine, G.; Brassard, P.

We present a prescription for parametrizing the chemical profile in the core of white dwarfs in light of the recent discovery that pulsation modes may sometimes be deeply confined in some cool pulsating white dwarfs. Such modes may be used as unique probes of the complicated chemical stratification that results from several processes that occurred in previous evolutionary phases of intermediate-mass stars. This effort is part of our ongoing quest for more credible and realistic seismic models of white dwarfs using static, parametrized equilibrium structures. Inspired by successful techniques developed in design optimization fields (such as aerodynamics), we exploit Akimamore » splines for the tracing of the chemical profile of oxygen (carbon) in the core of a white dwarf model. A series of tests are then presented to better seize the precision and significance of the results that can be obtained in an asteroseismological context. We also show that the new parametrization passes an essential basic test, as it successfully reproduces the chemical stratification of a full evolutionary model.« less

A Common Origin of Magnetism from Planets to White Dwarfs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Isern, Jordi; Külebi, Baybars; García-Berro, Enrique

Isolated magnetic white dwarfs have field strengths ranging from kilogauss to gigagauss. However, the origin of the magnetic field has not been hitherto elucidated. Whether these fields are fossil, hence the remnants of original weak magnetic fields amplified during the course of the evolution of their progenitor stars, or are the result of binary interactions, or, finally, they are produced by other internal physical mechanisms during the cooling of the white dwarf itself, remains a mystery. At sufficiently low temperatures, white dwarfs crystallize. Upon solidification, phase separation of its main constituents, {sup 12}C and {sup 16}O, and of the impuritiesmore » left by previous evolution occurs. This process leads to the formation of a Rayleigh–Taylor unstable liquid mantle on top of a solid core. This convective region, as it occurs in solar system planets like the Earth and Jupiter, can produce a dynamo able to yield magnetic fields of strengths of up to 0.1 MG, thus providing a mechanism that could explain magnetism in single white dwarfs.« less

Toward High-precision Seismic Studies of White Dwarf Stars: Parametrization of the Core and Tests of Accuracy

NASA Astrophysics Data System (ADS)

Giammichele, N.; Charpinet, S.; Fontaine, G.; Brassard, P.

2017-01-01

We present a prescription for parametrizing the chemical profile in the core of white dwarfs in light of the recent discovery that pulsation modes may sometimes be deeply confined in some cool pulsating white dwarfs. Such modes may be used as unique probes of the complicated chemical stratification that results from several processes that occurred in previous evolutionary phases of intermediate-mass stars. This effort is part of our ongoing quest for more credible and realistic seismic models of white dwarfs using static, parametrized equilibrium structures. Inspired by successful techniques developed in design optimization fields (such as aerodynamics), we exploit Akima splines for the tracing of the chemical profile of oxygen (carbon) in the core of a white dwarf model. A series of tests are then presented to better seize the precision and significance of the results that can be obtained in an asteroseismological context. We also show that the new parametrization passes an essential basic test, as it successfully reproduces the chemical stratification of a full evolutionary model.

Chandra Observations of Magnetic White Dwarfs and their Theoretical Implications

NASA Technical Reports Server (NTRS)

Musielak, Z. E.; Noble, M.; Porter, J. G.; Winget, D. E.

2003-01-01

Observations of cool DA and DB white dwarfs have not yet been successful in detecting coronal X-ray emission, but observations of late-type dwarfs and giants show that coronae are common for these stars. To produce coronal X-rays, a star must have dynamo-generated surface magnetic fields and a well-developed convection zone. There is some observational evidence that the DA star LHS 1038 and the DB star GD 358 have weak and variable surface magnetic fields. It has been suggested that such fields can be generated by dynamo action, and since both stars have well-developed convection zones, theory predicts detectable levels of coronal X-rays from these white dwarfs. However, we present analysis of Chandra observations of both stars showing no detectable X-ray emission. The derived upper limits for the X-ray fluxes provide strong constraints on theories of formation of coronae around magnetic white dwarfs. Another important implication of our negative Chandra observations is the possibility that the magnetic fields of LHS 1038 and GD 358 are fossil fields.

Contribution of Primordial Binary Evolution to the Two Blue-straggler Sequences in Globular Cluster M30

NASA Astrophysics Data System (ADS)

Jiang, Dengkai; Chen, Xuefei; Li, Lifang; Han, Zhanwen

2017-11-01

Two blue-straggler sequences discovered in globular cluster M30 provide a strong constraint on the formation mechanisms of blue stragglers. We study the formation of blue-straggler binaries through binary evolution, and find that binary evolution can contribute to the blue stragglers in both of the sequences. Whether a blue-straggler is located in the blue sequence or red sequence depends on the contribution of the mass donor to the total luminosity of the binary, which is generally observed as a single star in globular clusters. The blue stragglers in the blue sequence have a cool white dwarf companion, while the majority (˜60%) of the objects in the red sequence are binaries that are still experiencing mass transfer. However, there are also some objects for which the donors have just finished the mass transfer (the stripped-core stars, ˜10%) or the blue stragglers (the accretors) have evolved away from the blue sequence (˜30%). Meanwhile, W UMa contact binaries found in both sequences may be explained by various mass ratios, that is, W UMa contact binaries in the red sequence have two components with comparable masses (e.g., mass ratio q ˜ 0.3-1.0), while those in the blue sequence have low mass ratios (e.g., q< 0.3). However, the fraction of the blue sequence in M30 cannot be reproduced by binary population synthesis if we assumed the initial parameters of a binary sample to be the same as those of the field. This possibly indicates that dynamical effects on binary systems are very important in globular clusters.

The Star-forming Main Sequence of Dwarf Low Surface Brightness Galaxies

NASA Astrophysics Data System (ADS)

McGaugh, Stacy S.; Schombert, James M.; Lelli, Federico

2017-12-01

We explore the star-forming properties of late-type, low surface brightness (LSB) galaxies. The star-forming main sequence ({SFR}-{M}* ) of LSB dwarfs has a steep slope, indistinguishable from unity (1.04 ± 0.06). They form a distinct sequence from more massive spirals, which exhibit a shallower slope. The break occurs around {M}* ≈ {10}10 {M}⊙ , and can also be seen in the gas mass—stellar mass plane. The global Kennicutt-Schmidt law ({SFR}-{M}g) has a slope of 1.47 ± 0.11 without the break seen in the main sequence. There is an ample supply of gas in LSB galaxies, which have gas depletion times well in excess of a Hubble time, and often tens of Hubble times. Only ˜ 3 % of this cold gas needs be in the form of molecular gas to sustain the observed star formation. In analogy with the faint, long-lived stars of the lower stellar main sequence, it may be appropriate to consider the main sequence of star-forming galaxies to be defined by thriving dwarfs (with {M}* < {10}10 {M}⊙ ), while massive spirals (with {M}* > {10}10 {M}⊙ ) are weary giants that constitute more of a turn-off population.

Evolutionary sequences of very hot, low-mass, accreting white dwarfs with application to symbiotic variables and ultrasoft/supersoft low-luminosity x-ray sources

NASA Technical Reports Server (NTRS)

Sion, Edward M.; Starrfield, Sumner G.

1994-01-01

We present the first detailed model results of quasi-static evolutionary sequences of very hot low-mass white dwarfs accreting hydrogen-rich material at rates between 1 x 10(exp -7) and 1 x 10(exp -9) solar mass/yr. Most of the sequences were generated from starting models whose core thermal structures were not thermally relaxed in the thermal pulse cycle-averaged sense of an asymptotic giant branch stellar core. Hence, the evolution at constant accretion rate was not invariably characterized by series of identical shell flashes. Sequences exhibiting stable steady state nuclear burning at the accretion supply rate as well as sequences exhibiting recurrent thermonuclear shell flashes are presented and discussed. In some cases, the white dwarf accretors remain small (less than 10(exp 11) cm) and very hot even during the shell flash episode. They then experience continued but reduced hydrogen shell burning during the longer quiescent intervals while their surface temperatures increase both because of compressional heating and envelope structure readjustment in response to accretion over thousands of years. Both accretion and continued hydrogen burning power these models with luminosities of a few times 10(exp 37) ergs/s. We suggest that the physical properties of these model sequences are of considerable relevance to the observed outburst and quiescent behavior of those symbiotic variables and symbiotic novae containing low-mass white dwarfs. We also suggest that our models are relevant to the observational characteristics of the growing class of low-luminosity, supersoft/ultrasoft X-ray sources in globular clusters, and the Magellanic Clouds.

Spot temperatures and area coverages on active dwarf stars

NASA Technical Reports Server (NTRS)

Sarr, Steven H.; Neff, James E.

1990-01-01

Two active K dwarfs are examined to determine the temperatures of the stars and to estimate the locations and sizes of cool spots on the stellar surfaces. Two wavelength regions with TiO absorption bands at different temperature sensitivities are modeled simultaneously using the method developed by Huenemoerder and Ramsey (1987). The spectrum of BD +26deg730 shows excess absorption in the TiO band, and the absence of the 8860 A band in HD 82558 indicates that its spots are warmer than those of BD +26deg730.

A new benchmark T8-9 brown dwarf and a couple of new mid-T dwarfs from the UKIDSS DR5+ LAS

NASA Astrophysics Data System (ADS)

Goldman, B.; Marsat, S.; Henning, T.; Clemens, C.; Greiner, J.

2010-06-01

Benchmark brown dwarfs are those objects for which fiducial constraints are available, including effective temperature, parallax, age and metallicity. We searched for new cool brown dwarfs in 186deg2 of the new area covered by the data release DR5+ of the UKIRT Deep Infrared Sky Survey (UKIDSS) Large Area Survey. Follow-up optical and near-infrared broad-band photometry, and methane imaging of four promising candidates, revealed three objects with distinct methane absorption, typical of mid- to late-T dwarfs and one possibly T4 dwarf. The latest-type object, classified as T8-9, shares its large proper motion with Ross 458 (BD+13o2618), an active M0.5 binary which is 102arcsec away, forming a hierarchical low-mass star+brown dwarf system. Ross 458C has an absolute J-band magnitude of 16.4, and seems overluminous, particularly in the K band, compared to similar field brown dwarfs. We estimate the age of the system to be less than 1Gyr, and its mass to be as low as 14 Jupiter masses for the age of 1Gyr. At 11.4pc, this new late-T benchmark dwarf is a promising target to constrain the evolutionary and atmospheric models of very low-mass brown dwarfs. We present proper motion measurements for our targets and for 13 known brown dwarfs. Two brown dwarfs have velocities typical of the thick disc and may be old brown dwarfs. Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, jointly operated by the Max-Planck Institut für Astronomie Heidelberg and the Instituto de Astrofísica de Andaluc'a (CSIC), and on observations made with ESO/MPG Telescope at the La Silla Observatory under programme ID 081.A-9012 and 081.A-9014. E-mail: goldman@mpia.de

Stars of type MS with evidence of white dwarf companions. [IUE, Main Sequence (MS)

NASA Technical Reports Server (NTRS)

Peery, Benjamin F., Jr.

1986-01-01

A search for white dwarf companions of MS-type stars was conducted, using IUE. The overendowments of these stars in typical S-process nuclides suggest that they, like the Ba II stars, may owe their peculiar compositions to earlier mass transfer. Short-wavelength IUE spectra show striking emission line variability in HD35155, HD61913, and 4 Ori; HD35155 and 4 Ori show evidence of white dwarf companions.

The intermediate-age pre-cataclysmic variables SDSS J172406+562003 and RE J2013+4002

NASA Astrophysics Data System (ADS)

Shimansky, V. V.; Borisov, N. V.; Nurtdinova, D. N.; Mitrofanova, A. A.; Vlasyuk, V. V.; Spiridonova, O. I.

2012-06-01

We have analyzed the physical status of the pre-cataclysmic variables SDSSJ172406+562003 and RE J2013+4002, which have evolved after their common-envelope stage a time t = 106-107 years. Spectroscopy and photometry of these systems were performed with the 6-m and 1-m telescopes of the Special Astrophysical Observatory. We demonstrate that emission lines in the spectra were formed solely by the reflection of radiation emitted by the white dwarfs on the surfaces of their cool companions, under conditions close to local thermodynamic equilibrium. These effects are also responsible for most of the objects' photometric variability amplitude. However, comparing the light curves of SDSS 172406 from different epochs, we find aperiodic brightness variations, probably due to spottedness of the surface of the secondary. Jointly analyzing the spectra, radial-velocity curves, and light curves of the pre-cataclysmic variables and modeling the reflection effects, we have derived their fundamental parameters. We demonstrate that the secondaries in these systems are consistent with evolutionary models for main-sequence stars and do not have the luminosity excesses characteristic of cool stars in young pre-cataclysmic variables.

Two white dwarfs in ultrashort binaries with detached, eclipsing, likely sub-stellar companions detected by K2

NASA Astrophysics Data System (ADS)

Parsons, S. G.; Hermes, J. J.; Marsh, T. R.; Gänsicke, B. T.; Tremblay, P.-E.; Littlefair, S. P.; Sahman, D. I.; Ashley, R. P.; Green, M.; Rattanasoon, S.; Dhillon, V. S.; Burleigh, M. R.; Casewell, S. L.; Buckley, D. A. H.; Braker, I. P.; Irawati, P.; Dennihy, E.; Rodríguez-Gil, P.; Winget, D. E.; Winget, K. I.; Bell, Keaton J.; Kilic, Mukremin

2017-10-01

Using data from the extended Kepler mission in K2 Campaign 10, we identify two eclipsing binaries containing white dwarfs with cool companions that have extremely short orbital periods of only 71.2 min (SDSS J1205-0242, a.k.a. EPIC 201283111) and 72.5 min (SDSS J1231+0041, a.k.a. EPIC 248368963). Despite their short periods, both systems are detached with small, low-mass companions, in one case a brown dwarf and in the other case either a brown dwarf or a low-mass star. We present follow-up photometry and spectroscopy of both binaries, as well as phase-resolved spectroscopy of the brighter system, and use these data to place preliminary estimates on the physical and binary parameters. SDSS J1205-0242 is composed of a 0.39 ± 0.02 M⊙ helium-core white dwarf that is totally eclipsed by a 0.049 ± 0.006 M⊙ (51 ± 6MJ) brown-dwarf companion, while SDSS J1231+0041 is composed of a 0.56 ± 0.07 M⊙ white dwarf that is partially eclipsed by a companion of mass ≲0.095 M⊙. In the case of SDSS J1205-0242, we look at the combined constraints from common-envelope evolution and brown-dwarf models; the system is compatible with similar constraints from other post-common-envelope binaries, given the current parameter uncertainties, but has potential for future refinement.

Dusty Dwarfs Galaxies Occulting A Bright Background Spiral

NASA Astrophysics Data System (ADS)

Holwerda, Benne

2017-08-01

The role of dust in shaping the spectral energy distributions of low mass disk galaxies remains poorly understood. Recent results from the Herschel Space Observatory imply that dwarf galaxies contain large amounts of cool (T 20K) dust, coupled with very modest optical extinctions. These seemingly contradictory conclusions may be resolved if dwarfs harbor a variety of dust geometries, e.g., dust at larger galactocentric radii or in quiescent dark clumps. We propose HST observations of six truly occulting dwarf galaxies drawn from the Galaxy Zoo catalog of silhouetted galaxy pairs. Confirmed, true occulting dwarfs are rare as most low-mass disks in overlap are either close satellites or do not have a confirmed redshift. Dwarf occulters are the key to determining the spatial extent of dust, the small scale structure introduced by turbulence, and the prevailing dust attenuation law. The recent spectroscopic confirmation of bona-fide low mass occulting dwarfs offers an opportunity to map dust in these with HST. What is the role of dust in the SED of these dwarf disk galaxies? With shorter feedback scales, how does star-formation affect their morphology and dust composition, as revealed from their attenuation curve? The resolution of HST allows us to map the dust disks down to the fine scale structure of molecular clouds and multi-wavelength imaging maps the attenuation curve and hence dust composition in these disks. We therefore ask for 2 orbits on each of 6 dwarf galaxies in F275W, F475W, F606W, F814W and F125W to map dust from UV to NIR to constrain the attenuation curve.

A GA-insensitive dwarf mutant of Brassica napus L. correlated with mutation in pyrimidine box in the promoter of GID1.

PubMed

Li, Huapeng; Wang, Yun; Li, Xiaocheng; Gao, Yong; Wang, Zhijun; Zhao, Yun; Wang, Maolin

2011-01-01

A dwarf mutant from Brassica napus, namely NDF-1, which was derived from a high doubled haploid (DH) line '3529'(Brassica napus L.) of which seeds were jointly treated with chemical inducers and fast neutron bombardment, was revealed that dwarfism is under the control of a major gene(designated as ndf1) with a mainly additive effect and non-significant dominance effect. The germination and hypocotyls elongation response of dwarf mutants after exogenous GA and uniconazol application showed NDF-1 was a gibberellin insensitive dwarf. We cloned the Brassica napus GID1 gene, named BnGID1, and found it was the ortholog of AtGID1a. The sequence blasting of the BnGID1 genes from NDF-1 and wild type showed there was no mutant in the gene. But the quantitative RT-PCR analysis of GID1 EST pointed out the mutation was caused by the low-level expression of BnGID1 gene. After sequenced the BnGID1 gene's upstream, we found three bases mutated in the pyrimidine box (P-box) of the BnGID1 promoter, which is linkage with the dwarf mutant.

Future Interstellar Travel Destinations: Assessing the Suitability of Nearby Red Dwarf Stars as Hosts to Habitable Life-bearing Planets

NASA Astrophysics Data System (ADS)

Guinan, Edward F.; Engle, S. G.

2013-01-01

As part of our NSF/NASA sponsored “Living with a Red Dwarf Star” program, we are carrying out a comprehensive study of red dwarf stars across the electromagnetic spectrum to assess their suitability as hosts for habitable planets. These cool, dim, long-lived, low mass stars comprise >75% of the stars in our Galaxy. Moreover an increasing number of (potentially habitable) large Earth-size planets are being found hosted by red dwarfs. With intrinsically low luminosities (L < 0.02 Lsun), the habitable zones (HZs) of hosted planets are close to their host stars (typically 0.05 AU < HZ <0.4 AU). Our study indicates red dwarf HZ planets without strong (protective) magnetic fields are especially susceptible to atmospheric erosion & loss by the star’s X-UV and wind fluxes. Also, the frequent flaring of young red dwarf stars and tidal-locking of close-in planets could challenge the development of life. But tidal locking of these planets could have some advantages for the developmenet of life. The long lifetimes of the red dwarfs (> 50 BY) could be favorable for the development of complex (possibly even intelligent) life. We discuss our results in the context of nearby red dwarfs as possible destinations for future interstellar missions program. We illustrate this with examples of the red dwarf exoplanet systems: GJ 581 and HD 85512 (both with large HZ Earth-size planets). Also we discuss the nearest star (4.3 LY) - the red dwarf - Proxima Centauri as a potential destination for future interstellar missions such proposed by Icarus Interstellar and the 100-Year Starship and StarVoyager programs. We gratefully acknowledge the support from NSF-Grant AST-10-09903, Chandra Grants GO1-12124X & GO2-13020X and HST Grant GO-10920.

Discovery of Nearest Known Brown Dwarf

NASA Astrophysics Data System (ADS)

2003-01-01

Bright Southern Star Epsilon Indi Has Cool, Substellar Companion [1] Summary A team of European astronomers [2] has discovered a Brown Dwarf object (a 'failed' star) less than 12 light-years from the Sun. It is the nearest yet known. Now designated Epsilon Indi B, it is a companion to a well-known bright star in the southern sky, Epsilon Indi (now "Epsilon Indi A"), previously thought to be single. The binary system is one of the twenty nearest stellar systems to the Sun. The brown dwarf was discovered from the comparatively rapid motion across the sky which it shares with its brighter companion : the pair move a full lunar diameter in less than 400 years. It was first identified using digitised archival photographic plates from the SuperCOSMOS Sky Surveys (SSS) and confirmed using data from the Two Micron All Sky Survey (2MASS). Follow-up observations with the near-infrared sensitive SOFI instrument on the ESO 3.5-m New Technology Telescope (NTT) at the La Silla Observatory confirmed its nature and has allowed measurements of its physical properties. Epsilon Indi B has a mass just 45 times that of Jupiter, the largest planet in the Solar System, and a surface temperature of only 1000 °C. It belongs to the so-called 'T dwarf' category of objects which straddle the domain between stars and giant planets. Epsilon Indi B is the nearest and brightest T dwarf known. Future studies of the new object promise to provide astronomers with important new clues as to the formation and evolution of these exotic celestial bodies, at the same time yielding interesting insights into the border zone between planets and stars. TINY MOVING NEEDLES IN GIANT HAYSTACKS ESO PR Photo 03a/03 ESO PR Photo 03a/03 [Preview - JPEG: 400 x 605 pix - 92k [Normal - JPEG: 1200 x 1815 pix - 1.0M] Caption: PR Photo 03a/03 shows Epsilon Indi A (the bright star at far right) and its newly discovered brown dwarf companion Epsilon Indi B (circled). The upper image comes from one of the SuperCOSMOS Sky Surveys (SSS) optical photographic plates (I-band, centred at wavelength 0.7 µm) on which this very high proper motion object was discovered. The lower image is the 'Quicklook atlas' infrared image (Ks-band, 2.1 µm) from the Two Micron All Sky Survey (2MASS). Epsilon Indi B is much brighter in the near-infrared than at optical wavelengths, indicating that it is a very cool object. Both images cover roughly 7 x 5 arcmin. Imagine you are a professional ornithologist, recently returned home from an expedition to the jungles of South America, where you spent long weeks using your high-powered telephoto lenses searching for rare species of birds. Relaxing, you take a couple of wide-angle snapshots of the blooming flowers in your back garden, undistracted by the common blackbird flying across your viewfinder. Only later, when carefully comparing those snaps, you notice something tiny and unusually coloured, flittering close behind the blackbird: you've discovered an exotic, rare bird, right there at home. In much the same way, a team of astronomers [2] has just found one of the closest neighbours to the Sun, an exotic 'failed star' known as a 'brown dwarf', moving rapidly across the sky in the southern constellation Indus (The Indian). Interestingly, at a time when telescopes are growing larger and are equipped with ever more sophisticated electronic detectors, there is still much to be learned by combining old photographic plates with this modern technology. Photographic plates taken by wide-field ("Schmidt") telescopes over the past decades have been given a new lease on life through being digitised by automated measuring machines, allowing computers to trawl effectively through huge and invaluable data archives that are by far not yet fully exploited [3]. For the Southern Sky, the Institute for Astronomy in Edinburgh (Scotland, UK) has recently released scans made by the SuperCOSMOS machine of plates spanning several decades in three optical passbands. These data are perfectly suited to the search for objects with large proper motions and extreme colours, such as brown dwarfs in the Solar vicinity. Everything is moving - a question of perspective In astronomy, the `proper motion' of a star signifies its apparent motion on the celestial sphere; it is usually expressed in arcseconds per year [4]. The corresponding, real velocity of a star (in kilometres per second) can only be estimated if the distance is known. A star with a large proper motion may indicate a real large velocity or simply that the star is close to us. By analogy, an airplane just after takeoff has a much lower true speed than when it's cruising at high altitude, but to an observer watching near an airport, the departing airplane seems to be moving much more quickly across the sky. Proxima Centauri, our nearest stellar neighbour, is just 4.2 light-years away (cf. ESO PR 22/02) and has a proper motion of 3.8 arcsec/year (corresponding to 23 km/sec relative to the Sun, in the direction perpendicular to the line-of-sight). The highest known proper motion star is Barnard's Star at 6 light-years distance and moving 10 arcsec/year (87 km/sec relative to the Sun). All known stars within 30 light-years are high-proper-motion objects and move at least 0.2 arcsec/year. Trawling for fast moving objects For some time, astronomers at the Astrophysical Institute in Potsdam have been making a systematic computerised search for high-proper-motion objects which appear on red photographic sky plates, but not on the equivalent blue plates. Their goal is to identify hitherto unknown cool objects in the Solar neighbourhood. They had previously found a handful of new objects within 30 light-years in this way, but nothing as red or moving remotely as fast as the one they have now snared in the constellation of Indus in the southern sky. This object was only seen on the very longest-wavelength plates in the SuperCOSMOS Sky Survey database. It was moving so quickly that on plates taken just two years apart in the 1990s, it had moved almost 10 arcseconds on the sky, giving a proper motion of 4.7 arcsec/year. It was also very faint at optical wavelengths, the reason why it had never been spotted before. However, when confirmed in data from the digital Two Micron All Sky Survey (2MASS), it was seen to be much brighter in the infrared, with the typical colour signature of a cool brown dwarf. At this point, the object was thought to be an isolated traveller. However, a search through available online catalogues quickly revealed that just 7 arcminutes away was a well-known star, Epsilon Indi. The two share exactly the same very large proper motion, and thus it was immediately clear the two must be related, forming a wide binary system separated by more than 1500 times the distance between the Sun and the Earth. Epsilon Indi is one of the 20 nearest stars to the Sun at just 11.8 light years [5]. It is a dwarf star (of spectral type K5) and with a surface temperature of about 4000 °C, somewhat cooler than the Sun. As such, it often appears in science fiction as the home of a habitable planetary system [6]. That all remains firmly in the realm of speculation, but nevertheless, we now know that it most certainly has a very interesting companion. This is a remarkable discovery: Epsilon Indi B is the nearest star-like source to the Sun found in 15 years, the highest proper motion source found in over 70 years, and with a total luminosity just 0.002% that of the Sun, one of the intrinsically faintest sources ever seen outside the Solar System! After Proxima and Alpha Centauri, the Epsilon Indi system is also just the second known wide binary system within 15 light years. However, unlike Proxima Centauri, Epsilon Indi B is no ordinary star. BROWN DWARFS: COOLING, COOLING, COOLING... ESO PR Photo 03b/03 ESO PR Photo 03b/03 [Preview - JPEG: 480 x 400 pix - 41k [Normal - JPEG: 960 x 800 pix - 120k] [Full-Res - JPEG: 2200 x 1834 pix - 304k] Caption: PR Photo 03b/03 shows the near-infrared (0.9-2.5 µm) spectrum of Epsilon Indi B, obtained on November 16-17, 2002, with the SOFI multi-mode instrument on the ESO 3.5-m New Technology Telescope (NTT) at the La Silla Observatory (Chile) The total integration time is 360 sec. Regions of strong absorption in the Earth's atmosphere have been removed for clarity. The locations of prominent molecular absorption bands from water (H2O), methane (CH4) and carbon monoxide (CO) in the atmosphere of Epsilon Indi B are indicated. Also labelled are some spectral lines from potassium (KI, at 1.25 and 1.52 µm) and sodium (NaI, at 2.33 µm) atoms. From these data, the spectral type of Epsilon Indi B is determined as T2.5V, corresponding to an effective temperature of 'just' 1000 ± 60 °C. Within days of its discovery in the database, the astronomers managed to secure an infrared spectrum of Epsilon Indi B using the SOFI instrument on the ESO 3.5-m New Technology Telescope (NTT) at the La Silla Observatory (Chile). The spectrum showed the broad absorption features due to methane and water steam in its upper atmosphere, indicating a temperature of 'only' 1000 °C. Ordinary stars are never this cool - Epsilon Indi B was confirmed as a brown dwarf. Brown dwarfs are thought to form in much the same way as stars, by the gravitational collapse of clumps of cold gas and dust in dense molecular clouds. However, for reasons not yet entirely clear, some clumps end up with masses less than about 7.5% of that of our Sun, or 75 times the mass of planet Jupiter. Below that boundary, there is not enough pressure in the core to initiate nuclear hydrogen fusion, the long-lasting and stable source of power for ordinary stars like the Sun. Except for a brief early phase where some deuterium is burned, these low-mass objects simply continue to cool and fade slowly away while releasing the heat left-over from their birth. Theoretical discussions of such objects began some 40 years ago. They were first named 'black dwarfs' and later 'brown dwarfs', in recognition of their predicted very cool temperatures. However, they were also predicted to be very faint and very red, and it was only in 1995 that such objects began to be detected. The first were seen as faint companions to nearby stars, and then later, some were found floating freely in the Solar neighbourhood. Most brown dwarfs belong to the recently classified spectral types L and T, below the long-known cool dwarfs of type M. These are very red to human eyes, but L and T dwarfs are cooler still, so much so that they are almost invisible at optical wavelengths, with most of their emission coming out in the infrared. [7]. How massive is Epsilon Indi B? The age of most brown dwarfs detected to date is unknown and thus it is hard to estimate their masses. However, it may be assumed that the age of Epsilon Indi B is the same as that of Epsilon Indi A, whose age is estimated to be 1.3 billion years based on its rotational speed. Combining this information with the measured temperature, brightness, and distance, it is then possible to determine the mass of Epsilon Indi B using theoretical models of brown dwarfs. Two independent sets of models yield the same result: Epsilon Indi B must have a mass somewhere between 4-6% of that of the Sun, or 40-60 Jupiter masses. The most likely value is around 45 Jupiter masses, i.e. well below the hydrogen fusion limit, and definitively confirming this new discovery as a bona-fide brown dwarf. THE IMPORTANCE OF EPSILON INDI B ESO PR Photo 03c/03 ESO PR Photo 03c/03 [Preview - JPEG: 469 x 400 pix - 77k [Normal - JPEG: 937 x 800 pix - 328k] [Full-Res - JPEG: 2718 x 2321 pix - 3.1M] [Java Applet] Caption: PR Photo 03c/03 displays a 3D map of all known stellar systems in the solar neighbourhood within a radius of 12.5 light-years. The Sun is at the centre and the Epsilon Indi binary system with the newly found brown dwarf Epsilon Indi B lies near the bottom. The colour is indicative of the temperature and the spectral class - white stars are (main-sequence) A and F dwarfs; yellow stars like the Sun are G dwarfs; orange stars are K dwarfs; and red stars are M dwarfs, by far the most common type of star in the solar neighbourhood. The blue axes are oriented along the galactic coordinate system, and the radii of the rings are 5, 10, and 15 light-years, respectively. The Java Applet conveniently provides detailed information about the stars in the figure - just move the cursor over the field. The figure is adapted from a diagram by Richard Powell. PR Photo 03c/03 shows the current census of the stars in the solar neighbourhood. All these stars have been known for many years, including GJ1061, which, however, only had its distance firmly established in 1997. The discovery of Epsilon Indi B, however, is an extreme case, never before catalogued, and the first brown dwarf to be found within the 12.5 light year horizon. If current predictions are correct, there should be twice as many brown dwarfs as main sequence stars. Consequently, Epsilon Indi B may be the first of perhaps 100 brown dwarfs within this distance, still waiting to be discovered! Epsilon Indi B is an important catch well beyond the cataloguing the Solar neighbourhood. As the nearest and brightest known brown dwarf and with a very accurately measured distance, it can be subjected to a wide variety of detailed observational studies. It may thus serve as a template for more distant members of its class. With the help of Epsilon Indi B, astronomers should now be able to see further into the mysteries surrounding the formation and evolution of the exotic objects known as brown dwarfs, halfway between stars and giant planets, the physics of their inner cores, and the weather and chemistry of their atmospheres. AN HISTORICAL NOTE - THE SOUTHERN CONSTELLATION INDUS ESO PR Photo 03d/03 ESO PR Photo 03d/03 [Preview - JPEG: 478 x 400 pix - 91k [Normal - JPEG: 956 x 800 pix - 952k] [Full-Res - JPEG: 2260 x 1892 pix - 3.2M] Caption: PR Photo 03d/03 shows the southern constellation Indus (The Indian) and its surroundings, as drawn in the famous Uranographia published 1801 of German astronomer Johann Elert Bode. This reproduction was made from original printing plates held by the library of the Astrophysical Institute Potsdam (Germany). The binary stellar system Epsilon Indi is associated with one of the arrows in the Indian's hand. However, because of its proximity, only 12 light-years away, it is moving so fast across the sky that it is now located someway below the arrows. In only a few thousand years, it will have moved out of the Indus constellation and into the neighbouring constellation Tucana (The Toucan). The constellation Indus lies deep in the southern sky, nestled between three birds, Grus (The Crane), Tucana (The Toucan) and Pavo (The Peacock), cf. PR Photo 03d/03. First catalogued in 1595-1597 by the Dutch navigators Pieter Dirkszoon Keyser and Frederick de Houtman, this constellation was added to the southern sky by Johann Bayer in his book 'Uranometria' (1603) to honour the Native Americans that European explorers had encountered on their travels. In particular, it has been suggested that it is specifically the native peoples of Tierra del Fuego and Patagonia that are represented in Indus, just over two thousand kilometres south of La Silla where the first spectroscopic observations of Epsilon Indi B were made some 400 years later. In the later drawing by Bode shown here, Epsilon Indi, the fifth brightest star in Indus, is associated with one of the arrows in the Indian's hand. More information The information in this press release is based on a paper ("Epsilon Indi B: a new benchmark T dwarf" by Ralf-Dieter Scholz and co-authors), soon to be published in the European journal Astronomy & Astrophysics (Letters). It is available on the web in preprint form at http://babbage.sissa.it/abs/astro-ph/0212487.

The Star, the Dwarf and the Planet

NASA Astrophysics Data System (ADS)

2006-10-01

Astronomers have detected a new faint companion to the star HD 3651, already known to host a planet. This companion, a brown dwarf, is the faintest known companion of an exoplanet host star imaged directly and one of the faintest T dwarfs detected in the Solar neighbourhood so far. The detection yields important information on the conditions under which planets form. "Such a system is an interesting example that might prove that planets and brown dwarfs can form around the same star", said Markus Mugrauer, lead author of the paper presenting the discovery. ESO PR Photo 39a/06 ESO PR Photo 39a/06 The Companion to HD 3651 HD 3651 is a star slightly less massive than the Sun, located 36 light-years away in the constellation Pisces (the "Fish"). For several years, it has been known to harbour a planet less massive than Saturn, sitting closer to its parent star than Mercury is from the Sun: the planet accomplishes a full orbit in 62 days. Mugrauer and his colleagues first spotted the faint companion in 2003 on images from the 3.8-m United Kingdom Infrared Telescope (UKIRT) in Hawaii. Observations in 2004 and 2006 using ESO's 3.6 m New Technology Telescope (NTT) at La Silla provided the crucial confirmation that the speck of light is not a spurious background star, but indeed a true companion. The newly found companion, HD 3651B, is 16 times further away from HD 3651 than Neptune is from the Sun. HD 3651B is the dimmest directly imaged companion of an exoplanet host star. Furthermore, as it is not detected on the photographic plates of the Palomar All Sky Survey, the companion must be even fainter in the visible spectral range than in the infrared, meaning it is a very cool low-mass sub-stellar object. Comparing its characteristics with theoretical models, the astronomers infer that the object has a mass between 20 and 60 Jupiter masses, and a temperature between 500 and 600 degrees Celsius. It is thus ten times colder and 300 000 less luminous than the Sun. These properties place it in the category of cool T-type brown dwarfs. ESO PR Photo 38b/06 ESO PR Photo 39b/06 The Relative Position of the Companion to HD 3651 "Due to their faintness even in the infrared, these cool T dwarfs are very difficult to find", said Mugrauer. "Only two other brown dwarfs with similar brightness are presently known. Their study will provide important insights into the atmospheric properties of cool sub-stellar objects." More than 170 stars are currently known to host exoplanets. In some cases, these stars were also found to have one or several stellar companions, showing that planet formation can also take place in a dynamically more complex environment than our own Solar System where planet formation occurred around an isolated single star. In 2001, Mugrauer and his colleagues started an observational programme to find out whether exoplanet host stars are single or married. In this programme, known exoplanet host stars are systematically imaged at two different epochs, at least several months apart. True companions can be distinguished from coincidental background objects as only they move together with the stars over time. With this effective search strategy several new companions of exoplanet host stars have been detected. Most of the detected companions are low-mass stars in the same evolutionary state as the Sun. In two cases, however, the astronomers found the companions to be white dwarfs, that is, stars at the end of their life. These intriguing systems bear evidence that planets can even survive the troubled last moments in the life of a nearby star. The planet host star HD 3651 is thus surrounded by two sub-stellar objects. The planet, HD 3651b, is very close, while the newly found brown dwarf companion revolves around the star 1500 times farther away than the planet. This system is the first imaged example that planets and brown dwarfs can form around the same star.

The complete genome sequence of a virus associated with cotton blue disease, cotton leafroll dwarf virus, confirms that it is a new member of the genus Polerovirus.

PubMed

Distéfano, Ana J; Bonacic Kresic, Ivan; Hopp, H Esteban

2010-11-01

Cotton blue disease is the most important virus disease of cotton in the southern part of America. The complete nucleotide sequence of the ssRNA genome of the cotton blue disease-associated virus was determined for the first time. It comprised 5,866 nucleotides, and the deduced genomic organization resembled that of members of the genus Polerovirus. Sequence homology comparison and phylogenetic analysis confirm that this virus (previous proposed name cotton leafroll dwarf virus) is a member of a new species within the genus Polerovirus.

On the Nature of Ultra-faint Dwarf Galaxy Candidates. II. The Case of Cetus II

NASA Astrophysics Data System (ADS)

Conn, Blair C.; Jerjen, Helmut; Kim, Dongwon; Schirmer, Mischa

2018-04-01

We obtained deep Gemini GMOS-S g, r photometry of the ultra-faint dwarf galaxy candidate Cetus II with the aim of providing stronger constraints on its size, luminosity, and stellar population. Cetus II is an important object in the size–luminosity plane, as it occupies the transition zone between dwarf galaxies and star clusters. All known objects smaller than Cetus II (r h ∼ 20 pc) are reported to be star clusters, while most larger objects are likely dwarf galaxies. We found a prominent excess of main-sequence stars in the color–magnitude diagram of Cetus II, best described by a single stellar population with an age of 11.2 Gyr, metallicity of [Fe/H] = ‑1.28 dex, an [α/Fe] = 0.0 dex at a heliocentric distance of 26.3 ± 1.2 kpc. As well as being spatially located within the Sagittarius dwarf tidal stream, these properties are well matched to the Sagittarius galaxy’s Population B stars. Interestingly, like our recent findings on the ultra-faint dwarf galaxy candidate Tucana V, the stellar field in the direction of Cetus II shows no evidence of a concentrated overdensity despite tracing the main sequence for over six magnitudes. These results strongly support the picture that Cetus II is not an ultra-faint stellar system in the Milky Way halo, but made up of stars from the Sagittarius tidal stream.

Preparation of the CARMENES Input Catalogue: Mining Public Archives for Stellar Parameters and Spectra of M Dwarfs with Master Thesis Students

NASA Astrophysics Data System (ADS)

Montes, D.; Caballero, J. A.; Alonso-Floriano, F. J.; Cortes Contreras, M.; Gonzalez-Alvarez, E.; Hidalgo, D.; Holgado, G.; Llamas, M.; Martinez-Rodriguez, H.; Sanz-Forcada, J.

2015-01-01

We help compiling the most comprehensive database of M dwarfs ever built, CARMENCITA, the CARMENES Cool dwarf Information and daTa Archive, which will be the CARMENES `input catalogue'. In addition to the science preparation with low- and high-resolution spectrographs and lucky imagers (see the other contributions in this volume), we compile a huge pile of public data on over 2100 M dwarfs, and analyze them, mostly using virtual-observatory tools. Here we describe four specific actions carried out by master and grade students. They mine public archives for additional high-resolution spectroscopy (UVES, FEROS and HARPS), multi-band photometry (FUV-NUV-u-B-g-V-r-R-i-J-H-Ks-W1-W2-W3-W4), X-ray data (ROSAT, XMM-Newton and Chandra), periods, rotational velocities and Hα pseudo-equivalent widths. As described, there are many interdependences between all these data.

EC 10246-2707: an eclipsing subdwarf B + M dwarf binary

NASA Astrophysics Data System (ADS)

Barlow, B. N.; Kilkenny, D.; Drechsel, H.; Dunlap, B. H.; O'Donoghue, D.; Geier, S.; O'Steen, R. G.; Clemens, J. C.; LaCluyze, A. P.; Reichart, D. E.; Haislip, J. B.; Nysewander, M. C.; Ivarsen, K. M.

2013-03-01

We announce the discovery of a new eclipsing hot subdwarf B + M dwarf binary, EC 10246-2707, and present multicolour photometric and spectroscopic observations of this system. Similar to other HW Vir-type binaries, the light curve shows both primary and secondary eclipses, along with a strong reflection effect from the M dwarf; no intrinsic light contribution is detected from the cool companion. The orbital period is 0.118 507 9936 ± 0.000 000 0009 d, or about 3 h. Analysis of our time series spectroscopy reveals a velocity semi-amplitude of K1 = 71.6 ± 1.7 km s-1 for the sdB and best-fitting atmospheric parameters of Teff = 28 900 ± 500 K, log g = 5.64 ± 0.06 and log N(He)/N(H) = -2.5 ± 0.2. Although we cannot claim a unique solution from modelling the light curve, the best-fitting model has an sdB mass of 0.45 M⊙ and a cool companion mass of 0.12 M⊙. These results are roughly consistent with a canonical-mass sdB and M dwarf separated by a ˜ 0.84 R⊙. We find no evidence of pulsations in the light curve and limit the amplitude of rapid photometric oscillations to <0.08 per cent. Using 15 yr of eclipse timings, we construct an observed minus calculated (O - C) diagram but find no statistically significant period changes; we rule out |dot{P}| > 7.2 × 10^{-12}. If EC 10246-2707 evolves into a cataclysmic variable, its period should fall below the famous cataclysmic variable period gap.

Rose spring dwarf-associated virus has RNA structural and gene-expression features like those of Barley yellow dwarf virus

PubMed Central

Salem, Nida’ M.; Miller, W. Allen; Rowhani, Adib; Golino, Deborah A.; Moyne, Anne-Laure; Falk, Bryce W.

2015-01-01

We determined the complete nucleotide sequence of the Rose spring dwarf-associated virus (RSDaV) genomic RNA (GenBank accession no. EU024678) and compared its predicted RNA structural characteristics affecting gene expression. A cDNA library was derived from RSDaV double-stranded RNAs (dsRNAs) purified from infected tissue. Nucleotide sequence analysis of the cloned cDNAs, plus for clones generated by 5′- and 3′-RACE showed the RSDaV genomic RNA to be 5,808 nucleotides. The genomic RNA contains five major open reading frames (ORFs), and three small ORFs in the 3′-terminal 800 nucleotides, typical for viruses of genus Luteovirus in the family Luteoviridae. Northern blot hybridization analysis revealed the genomic RNA and two prominent subgenomic RNAs of approximately 3 kb and 1 kb. Putative 5′ ends of the sgRNAs were predicted by identification of conserved sequences and secondary structures which resembled the Barley yellow dwarf virus (BYDV) genomic RNA 5′ end and subgenomic RNA promoter sequences. Secondary structures of the BYDV-like ribosomal frameshift elements and cap-independent translation elements, including long-distance base pairing spanning four kb were identified. These contain similarities but also informative differences with the BYDV structures, including a strikingly different structure predicted for the 3′ cap-independent translation element. These analyses of the RSDaV genomic RNA show more complexity for the RNA structural elements for members of the Luteoviridae. PMID:18329064

Rose spring dwarf-associated virus has RNA structural and gene-expression features like those of Barley yellow dwarf virus.

PubMed

Salem, Nida' M; Miller, W Allen; Rowhani, Adib; Golino, Deborah A; Moyne, Anne-Laure; Falk, Bryce W

2008-06-05

We determined the complete nucleotide sequence of the Rose spring dwarf-associated virus (RSDaV) genomic RNA (GenBank accession no. EU024678) and compared its predicted RNA structural characteristics affecting gene expression. A cDNA library was derived from RSDaV double-stranded RNAs (dsRNAs) purified from infected tissue. Nucleotide sequence analysis of the cloned cDNAs, plus for clones generated by 5'- and 3'-RACE showed the RSDaV genomic RNA to be 5808 nucleotides. The genomic RNA contains five major open reading frames (ORFs), and three small ORFs in the 3'-terminal 800 nucleotides, typical for viruses of genus Luteovirus in the family Luteoviridae. Northern blot hybridization analysis revealed the genomic RNA and two prominent subgenomic RNAs of approximately 3 kb and 1 kb. Putative 5' ends of the sgRNAs were predicted by identification of conserved sequences and secondary structures which resembled the Barley yellow dwarf virus (BYDV) genomic RNA 5' end and subgenomic RNA promoter sequences. Secondary structures of the BYDV-like ribosomal frameshift elements and cap-independent translation elements, including long-distance base pairing spanning four kb were identified. These contain similarities but also informative differences with the BYDV structures, including a strikingly different structure predicted for the 3' cap-independent translation element. These analyses of the RSDaV genomic RNA show more complexity for the RNA structural elements for members of the Luteoviridae.

THREE NEW ECLIPSING WHITE-DWARF-M-DWARF BINARIES DISCOVERED IN A SEARCH FOR TRANSITING PLANETS AROUND M-DWARFS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Law, Nicholas M.; Kraus, Adam L.; Street, Rachel

2012-10-01

We present three new eclipsing white-dwarf/M-dwarf binary systems discovered during a search for transiting planets around M-dwarfs. Unlike most known eclipsing systems of this type, the optical and infrared emission is dominated by the M-dwarf components, and the systems have optical colors and discovery light curves consistent with being Jupiter-radius transiting planets around early M-dwarfs. We detail the PTF/M-dwarf transiting planet survey, part of the Palomar Transient Factory (PTF). We present a graphics processing unit (GPU)-based box-least-squares search for transits that runs approximately 8 Multiplication-Sign faster than similar algorithms implemented on general purpose systems. For the discovered systems, we decomposemore » low-resolution spectra of the systems into white-dwarf and M-dwarf components, and use radial velocity measurements and cooling models to estimate masses and radii for the white dwarfs. The systems are compact, with periods between 0.35 and 0.45 days and semimajor axes of approximately 2 R{sub Sun} (0.01 AU). The M-dwarfs have masses of approximately 0.35 M{sub Sun }, and the white dwarfs have hydrogen-rich atmospheres with temperatures of around 8000 K and have masses of approximately 0.5 M{sub Sun }. We use the Robo-AO laser guide star adaptive optics system to tentatively identify one of the objects as a triple system. We also use high-cadence photometry to put an upper limit on the white-dwarf radius of 0.025 R{sub Sun} (95% confidence) in one of the systems. Accounting for our detection efficiency and geometric factors, we estimate that 0.08%{sub -0.05%}{sup +0.10%} (90% confidence) of M-dwarfs are in these short-period, post-common-envelope white-dwarf/M-dwarf binaries where the optical light is dominated by the M-dwarf. The lack of detections at shorter periods, despite near-100% detection efficiency for such systems, suggests that binaries including these relatively low-temperature white dwarfs are preferentially found at relatively large orbital radii. Similar eclipsing binary systems can have arbitrarily small eclipse depths in red bands and generate plausible small-planet-transit light curves. As such, these systems are a source of false positives for M-dwarf transiting planet searches. We present several ways to rapidly distinguish these binaries from transiting planet systems.« less

Parallax measurements of cool brown dwarfs

NASA Astrophysics Data System (ADS)

Manjavacas, E.; Goldman, B.; Reffert, S.; Henning, T.

2013-12-01

Context. Accurate parallax measurements allow us to determine physical properties of brown dwarfs and help us constrain evolutionary and atmospheric models, break age-mass degeneracy, and reveal unresolved binaries. Aims: We measured absolute trigonometric parallaxes and proper motions of six cool brown dwarfs using background galaxies to establish an absolute reference frame. We derive the absolute J-band magnitude. The six T brown dwarfs in our sample have spectral types between T2.5 and T8 and magnitudes between 13.9 and 18.0 in the Two Micron All Sky Survey (2MASS) with photometric distances below 25 pc. Methods: The observations were taken in the J-band with the Omega-2000 camera on the 3.5 m telescope at Calar Alto during a time period of 27 months between March 2011 and June 2013. The number of epochs varied between 11 and 12 depending on the object. The reduction of the astrometric measurements was carried out with respect to the field stars. The relative parallax and proper motions were transformed into absolute measurements using the background galaxies in our fields. Results: We obtained absolute parallaxes for our six brown dwarfs with a precision between 3 and 6 mas. We compared our results in a color-magnitude diagram with other brown dwarfs with determined parallax and with the BT-Settl 2012 atmospheric models. For four of the six targets, we found a good agreement in luminosity with objects of similar spectral types. We obtained an improved accuracy in the parallaxes and proper motions in comparison to previous works. The object 2MASS J11061197+2754225 is more than 1 mag overluminous in all bands, which point to binarity or high order multiplicity. Based on observations taken with Omega-2000 at the 3.5 m telescope at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated by the Max Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).Appendix A is available in electronic form at http://www.aanda.org

HUBBLE SPIES BROWN DWARFS IN NEARBY STELLAR NURSERY

NASA Technical Reports Server (NTRS)

2002-01-01

Probing deep within a neighborhood stellar nursery, NASA's Hubble Space Telescope uncovered a swarm of newborn brown dwarfs. The orbiting observatory's near-infrared camera revealed about 50 of these objects throughout the Orion Nebula's Trapezium cluster [image at right], about 1,500 light-years from Earth. Appearing like glistening precious stones surrounding a setting of sparkling diamonds, more than 300 fledgling stars and brown dwarfs surround the brightest, most massive stars [center of picture] in Hubble's view of the Trapezium cluster's central region. All of the celestial objects in the Trapezium were born together in this hotbed of star formation. The cluster is named for the trapezoidal alignment of those central massive stars. Brown dwarfs are gaseous objects with masses so low that their cores never become hot enough to fuse hydrogen, the thermonuclear fuel stars like the Sun need to shine steadily. Instead, these gaseous objects fade and cool as they grow older. Brown dwarfs around the age of the Sun (5 billion years old) are very cool and dim, and therefore are difficult for telescopes to find. The brown dwarfs discovered in the Trapezium, however, are youngsters (1 million years old). So they're still hot and bright, and easier to see. This finding, along with observations from ground-based telescopes, is further evidence that brown dwarfs, once considered exotic objects, are nearly as abundant as stars. The image and results appear in the Sept. 20 issue of the Astrophysical Journal. The brown dwarfs are too dim to be seen in a visible-light image taken by the Hubble telescope's Wide Field and Planetary Camera 2 [picture at left]. This view also doesn't show the assemblage of infant stars seen in the near-infrared image. That's because the young stars are embedded in dense clouds of dust and gas. The Hubble telescope's near-infrared camera, the Near Infrared Camera and Multi-Object Spectrometer, penetrated those clouds to capture a view of those objects. The brown dwarfs are the faintest objects in the image. Surveying the cluster's central region, the Hubble telescope spied brown dwarfs with masses equaling 10 to 80 Jupiters. Researchers think there may be less massive brown dwarfs that are beyond the limits of Hubble's vision. The near-infrared image was taken Jan. 17, 1998. Two near-infrared filters were used to obtain information on the colors of the stars at two wavelengths (1.1 and 1.6 microns). The Trapezium picture is 1 light-year across. This composite image was made from a 'mosaic' of nine separate, but adjoining images. In this false-color image, blue corresponds to warmer, more massive stars, and red to cooler, less massive stars and brown dwarfs, and stars that are heavily obscured by dust. The visible-light data were taken in 1994 and 1995. Credits for near-infrared image: NASA; K.L. Luhman (Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.); and G. Schneider, E. Young, G. Rieke, A. Cotera, H. Chen, M. Rieke, R. Thompson (Steward Observatory, University of Arizona, Tucson, Ariz.) Credits for visible-light picture: NASA, C.R. O'Dell and S.K. Wong (Rice University)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barnes, Sydney A.; Weingrill, Joerg; Fritzewski, Dario

We report rotation periods for 20 cool (FGK) main sequence member stars of the 4 Gyr-old open cluster M67 (=NGC 2682), obtained by analyzing data from Campaign 5 of the K2 mission with the Kepler Space Telescope . The rotation periods delineate a sequence in the color–period diagram (CPD) of increasing period with redder color. This sequence represents a cross-section at the cluster age of the surface P = P ( t , M ), suggested in prior work to extend to at least solar age. The current Sun is located marginally (approximately 1 σ ) above M67 in themore » CPD, as its relative age leads us to expect, and lies on the P = P ( t , M ) surface to within measurement precision. We therefore conclude that the solar rotation rate is normal as compared with cluster stars, a fact that strengthens the solar–stellar connection. The agreement between the M67 rotation period measurements and prior predictions further implies that rotation periods, especially when coupled with appropriate supporting work such as spectroscopy, can provide reliable ages via gyrochronology for other similar FGK dwarfs from the early main sequence to solar age and likely until the main sequence turnoff. The M67 rotators have a rotational age of 4.2 Gyr with a standard deviation of 0.7 Gyr, implying that similar field stars can be age-dated to precisions of ∼17%. The rotational age of the M67 cluster as a whole is therefore 4.2 Gyr, but with a lower (averaged) uncertainty of 0.2 Gyr.« less

The Unevenly Distributed Nearest Brown Dwarfs

NASA Astrophysics Data System (ADS)

Bihain, Gabriel; Scholz, Ralf-Dieter

2016-08-01

To address the questions of how many brown dwarfs there are in the Milky Way, how do these objects relate to star formation, and whether the brown dwarf formation rate was different in the past, the star-to-brown dwarf number ratio can be considered. While main sequence stars are well known components of the solar neighborhood, lower mass, substellar objects increasingly add to the census of the nearest objects. The sky projection of the known objects at <6.5 pc shows that stars present a uniform distribution and brown dwarfs a non-uniform distribution, with about four times more brown dwarfs behind than ahead of the Sun relative to the direction of rotation of the Galaxy. Assuming that substellar objects distribute uniformly, their observed configuration has a probability of 0.1 %. The helio- and geocentricity of the configuration suggests that it probably results from an observational bias, which if compensated for by future discoveries, would bring the star-to-brown dwarf ratio in agreement with the average ratio found in star forming regions.

Galaxias enanas: las voces de la mayoría

NASA Astrophysics Data System (ADS)

Cellone, S. A.

More than twenty years after photographic surveys of nearby clusters of galaxies revealed that low-luminosity, or ``dwarf'', galaxies (M_B ≳ -18 mag) are the numerically dominant population, research on these objects has been boosted by new instrumental and theoretical developments. Among several breakthroughs that have re-shaped our knowledge abut dwarf galaxies, we should point out: the detection of underlying spiral structure, disks/bars in dwarf ``elliptical'' galaxies; the possible evolutionary relation between (some?) dwarf ellipticals and spiral galaxies; the discoveries of ultra-compact and ultra-faint dwarfs; the universality of the color-luminosity relation extending along ˜ 10 mag. A brief review on these subjects is presented, with emphasis on early-type dwarfs and their possible evolutionary relations with other galaxy types. I will particularly address the controversy about which are the objects that extend the E sequence down to the lowest luminosities (if such objects really exist). FULL TEXT IN SPANISH

Measuring Sirius: An Exercise in Patience

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-05-01

Sometimes important astronomical advances require the newest and fanciest observatories and technologies but sometimes they just require decades of work and a lot of patience. Patience is finally paying off for a team of scientists who have been observing the Sirius star system for nearly 20 years.Historical (black, blue and green) and Hubble (red) observations of the relative orbit of Sirius B around Sirius A. [Adapted from Bond et al. 2017]Bright NeighborsLocated a mere 8.5 light-years away, the Sirius system consists of the main-sequence star Sirius A and its white-dwarf companion Sirius B. Sirius A is the brightest star in our sky, and Sirius B is the brightest and nearest white dwarf weve observed. The unusual proximity and brightness of these stars make them excellent targets for learning about stellar and white-dwarf astrophysics.In order to interpret our observations, however, we first need to pin down the basic information about these stars. In particular, we want to measure the precise masses and orbital elements for the system but because the stars orbit each other only once every 50 years, these properties take time to measure well!Toward this end, a team of scientists began an observing campaign in 2001 to regularly image the Sirius system using the Hubble Space Telescope. Now, 16 years later, they have enough data to make precise statements about the system.Precision Measurements at LastIn a recent publication led by Howard Bond (Pennsylvania State University and Space Telescope Science Institute), the team details nearly two decades of precise photometric and astrometric measurements using Hubble. In addition, they supplemented these data by dredging through 150 years worth of historical observations of Sirius and critically analyzing 2,300 of these as well.Comparisons of white-dwarf theory with the observed parameters of Sirius B, both on the H-R diagram (top) and in a mass-radius plot of cooling white dwarfs (bottom). Sirius Bs measured parameters matches the theoretical models very well. [Bond et al. 2017]The result? Bond and collaborators were able to make very precise measurements of the masses of Sirius A and Sirius B 2.063 0.023 and 1.018 0.011 solar masses, respectively and of their orbital elements. They find that the position of Sirius B on the Hertzsprung-Russell diagram is beautifully consistent with models based on cooling white dwarfs of Sirius Bs measured mass. Similarly, stellar models of Sirius A are nicely consistent with Bond and collaborators measurements if the star has a slightly low metallicity of 85% that of the Sun.The high-precision measurements also allowed the authors rule out the possibility of a third body in the system an idea thats been tossed around for decades unless the third body is smaller than 1525 Jupiter masses.Bond and collaborators enumerate some open puzzles of the Sirius system, such as like conflicting signs that the two stars might have interacted, long ago. Though these puzzles remain unresolved, the painstaking decades of observations of Sirius have already revealed much about the system and improved our understanding of stellar evolution. Whats more, these measurements give us an ideal launching point for future studies of these two objects. In the case of the Sirius system, patience has definitely paid off.CitationHoward E. Bond et al 2017 ApJ 840 70. doi:10.3847/1538-4357/aa6af8

Reversal of Fortune: Increased Star Formation Efficiencies in the Early Histories of Dwarf Galaxies?

NASA Astrophysics Data System (ADS)

Madau, Piero; Weisz, Daniel R.; Conroy, Charlie

2014-08-01

On dwarf galaxy scales, the different shapes of the galaxy stellar mass function and the dark halo mass function require a star-formation efficiency (SFE) in these systems that is currently more than 1 dex lower than that of Milky Way-size halos. Here, we argue that this trend may actually be reversed at high redshift. Specifically, by combining the resolved star-formation histories of nearby isolated dwarfs with the simulated mass-growth rates of dark matter halos, we show that the assembly of these systems occurs in two phases: (1) an early, fast halo accretion phase with a rapidly deepening potential well, characterized by a high SFE; and (2) a late, slow halo accretion phase where, perhaps as a consequence of reionization, the SFE is low. Nearby dwarfs have more old stars than predicted by assuming a constant or decreasing SFE with redshift, a behavior that appears to deviate qualitatively from the trends seen among more massive systems. Taken at face value, the data suggest that at sufficiently early epochs, dwarf galaxy halos above the atomic cooling mass limit can be among the most efficient sites of star formation in the universe.

Radial velocity studies of cool stars.

PubMed

Jones, Hugh R A; Barnes, John; Tuomi, Mikko; Jenkins, James S; Anglada-Escude, Guillem

2014-04-28

Our current view of exoplanets is one derived primarily from solar-like stars with a strong focus on understanding our Solar System. Our knowledge about the properties of exoplanets around the dominant stellar population by number, the so-called low-mass stars or M dwarfs, is much more cursory. Based on radial velocity discoveries, we find that the semi-major axis distribution of M dwarf planets appears to be broadly similar to those around more massive stars and thus formation and migration processes might be similar to heavier stars. However, we find that the mass of M dwarf planets is relatively much lower than the expected mass dependency based on stellar mass and thus infer that planet formation efficiency around low-mass stars is relatively impaired. We consider techniques to overcome the practical issue of obtaining good quality radial velocity data for M dwarfs despite their faintness and sustained activity and emphasize (i) the wavelength sensitivity of radial velocity signals, (ii) the combination of radial velocity data from different experiments for robust detection of small amplitude signals, and (iii) the selection of targets and radial velocity interpretation of late-type M dwarfs should consider Hα behaviour.

Are sdAs helium core stars?

NASA Astrophysics Data System (ADS)

Pelisoli, Ingrid; Kepler, S. O.; Koester, Detlev

2017-12-01

Evolved stars with a helium core can be formed by non-conservative mass exchange interaction with a companion or by strong mass loss. Their masses are smaller than 0.5 M⊙. In the database of the Sloan Digital Sky Survey (SDSS), there are several thousand stars which were classified by the pipeline as dwarf O, B and A stars. Considering the lifetimes of these classes on the main sequence, and their distance modulus at the SDSS bright saturation, if these were common main sequence stars, there would be a considerable population of young stars very far from the galactic disk. Their spectra are dominated by Balmer lines which suggest effective temperatures around 8 000-10 000 K. Several thousand have significant proper motions, indicative of distances smaller than 1 kpc. Many show surface gravity in intermediate values between main sequence and white dwarf, 4.75 < log g < 6.5, hence they have been called sdA stars. Their physical nature and evolutionary history remains a puzzle. We propose they are not H-core main sequence stars, but helium core stars and the outcomes of binary evolution. We report the discovery of two new extremely-low mass white dwarfs among the sdAs to support this statement.

Wolf 1130: A Nearby Triple System Containing a Cool, Ultramassive White Dwarf

NASA Astrophysics Data System (ADS)

Mace, Gregory N.; Mann, Andrew W.; Skiff, Brian A.; Sneden, Christopher; Kirkpatrick, J. Davy; Schneider, Adam C.; Kidder, Benjamin; Gosnell, Natalie M.; Kim, Hwihyun; Mulligan, Brian W.; Prato, L.; Jaffe, Daniel

2018-02-01

Following the discovery of the T8 subdwarf WISE J200520.38+542433.9 (Wolf 1130C), which has a proper motion in common with a binary (Wolf 1130AB) consisting of an M subdwarf and a white dwarf, we set out to learn more about the old binary in the system. We find that the A and B components of Wolf 1130 are tidally locked, which is revealed by the coherence of more than a year of V-band photometry phase-folded to the derived orbital period of 0.4967 days. Forty new high-resolution, near-infrared spectra obtained with the Immersion Grating Infrared Spectrometer provide radial velocities and a projected rotational velocity (v sin i) of 14.7 ± 0.7 {km} {{{s}}}-1 for the M subdwarf. In tandem with a Gaia parallax-derived radius and verified tidal locking, we calculate an inclination of i = 29° ± 2°. From the single-lined orbital solution and the inclination we derive an absolute mass for the unseen primary ({1.24}-0.15+0.19 M ⊙). Its non-detection between 0.2 and 2.5 μm implies that it is an old (>3.7 Gyr) and cool (T eff < 7000 K) ONe white dwarf. This is the first ultramassive white dwarf within 25 pc. The evolution of Wolf 1130AB into a cataclysmic variable is inevitable, making it a potential SN Ia progenitor. The formation of a triple system with a primary mass >100 times the tertiary mass and the survival of the system through the common-envelope phase, where ∼80% of the system mass was lost, is remarkable. Our analysis of Wolf 1130 allows us to infer its formation and evolutionary history, which has unique implications for understanding low-mass star and brown dwarf formation around intermediate-mass stars.

76 T dwarfs from the UKIDSS LAS: benchmarks, kinematics and an updated space density

NASA Astrophysics Data System (ADS)

Burningham, Ben; Cardoso, C. V.; Smith, L.; Leggett, S. K.; Smart, R. L.; Mann, A. W.; Dhital, S.; Lucas, P. W.; Tinney, C. G.; Pinfield, D. J.; Zhang, Z.; Morley, C.; Saumon, D.; Aller, K.; Littlefair, S. P.; Homeier, D.; Lodieu, N.; Deacon, N.; Marley, M. S.; van Spaandonk, L.; Baker, D.; Allard, F.; Andrei, A. H.; Canty, J.; Clarke, J.; Day-Jones, A. C.; Dupuy, T.; Fortney, J. J.; Gomes, J.; Ishii, M.; Jones, H. R. A.; Liu, M.; Magazzú, A.; Marocco, F.; Murray, D. N.; Rojas-Ayala, B.; Tamura, M.

2013-07-01

We report the discovery of 76 new T dwarfs from the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS). Near-infrared broad- and narrow-band photometry and spectroscopy are presented for the new objects, along with Wide-field Infrared Survey Explorer (WISE) and warm-Spitzer photometry. Proper motions for 128 UKIDSS T dwarfs are presented from a new two epoch LAS proper motion catalogue. We use these motions to identify two new benchmark systems: LHS 6176AB, a T8p+M4 pair and HD 118865AB, a T5.5+F8 pair. Using age constraints from the primaries and evolutionary models to constrain the radii, we have estimated their physical properties from their bolometric luminosity. We compare the colours and properties of known benchmark T dwarfs to the latest model atmospheres and draw two principal conclusions. First, it appears that the H - [4.5] and J - W2 colours are more sensitive to metallicity than has previously been recognized, such that differences in metallicity may dominate over differences in Teff when considering relative properties of cool objects using these colours. Secondly, the previously noted apparent dominance of young objects in the late-T dwarf sample is no longer apparent when using the new model grids and the expanded sample of late-T dwarfs and benchmarks. This is supported by the apparently similar distribution of late-T dwarfs and earlier type T dwarfs on reduced proper motion diagrams that we present. Finally, we present updated space densities for the late-T dwarfs, and compare our values to simulation predictions and those from WISE.

PROBING TRAPPIST-1-LIKE SYSTEMS WITH K2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Demory, Brice-Olivier; Queloz, Didier; Gillen, Ed

2016-07-10

The search for small planets orbiting late M dwarfs holds the promise of detecting Earth-size planets for which their atmospheres could be characterized within the next decade. The recent discovery of TRAPPIST-1 entertains hope that these systems are common around hosts located at the bottom of the main sequence. In this Letter, we investigate the ability of the repurposed Kepler mission ( K2 ) to probe planetary systems similar to TRAPPIST-1. We perform a consistent data analysis of 189 spectroscopically confirmed M5.5 to M9 late M dwarfs from Campaigns 1–6 to search for planet candidates and inject transit signals withmore » properties matching TRAPPIST-1b and c. We find no transiting planet candidates across our K2 sample. Our injection tests show that K2 is able to recover both TRAPPIST-1 planets for 10% of the sample only, mainly because of the inefficient throughput at red wavelengths resulting in Poisson-limited performance for these targets. Increasing injected planetary radii to match GJ 1214b’s size yields a recovery rate of 70%. The strength of K2 is its ability to probe a large number of cool hosts across the different campaigns, out of which the recovery rate of 10% may turn into bona fide detections of TRAPPIST-1-like systems within the next two years.« less

Genesis of magnetic fields in isolated white dwarfs

NASA Astrophysics Data System (ADS)

Briggs, Gordon P.; Ferrario, Lilia; Tout, Christopher A.; Wickramasinghe, Dayal T.

2018-05-01

A dynamo mechanism driven by differential rotation when stars merge has been proposed to explain the presence of strong fields in certain classes of magnetic stars. In the case of the high field magnetic white dwarfs (HFMWDs), the site of the differential rotation has been variously thought to be the common envelope, the hot outer regions of a merged degenerate core or an accretion disc formed by a tidally disrupted companion that is subsequently accreted by a degenerate core. We have shown previously that the observed incidence of magnetism and the mass distribution in HFMWDs are consistent with the hypothesis that they are the result of merging binaries during common envelope evolution. Here we calculate the magnetic field strengths generated by common envelope interactions for synthetic populations using a simple prescription for the generation of fields and find that the observed magnetic field distribution is also consistent with the stellar merging hypothesis. We use the Kolmogorov-Smirnov test to study the correlation between the calculated and the observed field strengths and find that it is consistent for low envelope ejection efficiency. We also suggest that field generation by the plunging of a giant gaseous planet on to a white dwarf may explain why magnetism among cool white dwarfs (including DZ white dwarfs) is higher than among hot white dwarfs. In this picture a super-Jupiter residing in the outer regions of the white dwarf's planetary system is perturbed into a highly eccentric orbit by a close stellar encounter and is later accreted by the white dwarf.

Genesis of magnetic fields in isolated white dwarfs

NASA Astrophysics Data System (ADS)

Briggs, Gordon P.; Ferrario, Lilia; Tout, Christopher A.; Wickramasinghe, Dayal T.

2018-07-01

A dynamo mechanism driven by differential rotation when stars merge has been proposed to explain the presence of strong fields in certain classes of magnetic stars. In the case of the high-field magnetic white dwarfs (HFMWDs), the site of the differential rotation has been variously thought to be the common envelope, the hot outer regions of a merged degenerate core or an accretion disc are formed by a tidally disrupted companion that is subsequently accreted by a degenerate core. We have shown previously that the observed incidence of magnetism and the mass distribution in HFMWDs are consistent with the hypothesis that they are the result of merging binaries during common envelope evolution. Here, we calculate the magnetic field strengths generated by common envelope interactions for synthetic populations using a simple prescription for the generation of fields and find that the observed magnetic field distribution is also consistent with the stellar merging hypothesis. We use the Kolmogorov-Smirnov test to study the correlation between the calculated and the observed field strengths and find that it is consistent for low envelope ejection efficiency. We also suggest that the field generation by the plunging of a giant gaseous planet on to a white dwarf may explain why magnetism among cool white dwarfs (including DZ white dwarfs) is higher than among hot white dwarfs. In this picture, a super-Jupiter residing in the outer regions of the white dwarf's planetary system is perturbed into a highly eccentric orbit by a close stellar encounter and is later accreted by the white dwarf.

The discontinuity near 1600 A in the spectra of DA white dwarfs

NASA Technical Reports Server (NTRS)

Wegner, G.

1984-01-01

Ultraviolet spectroscopic observations of two relatively cool DA white dwarfs, L481 - 60 (= WD 1544 - 37) and BPM 1266 ( = WD 2105 - 82), with the International Ultraviolet Explorer (IUE) satellite show a strong drop in their spectral energy distributions below 1600 A. Published model atmospheres and thier visual spectra suggest that these two stars have effective temperatures in the vicinity of 9,000-10,000 K, and it is proposed that the 1600 A feature could be due to the 342(1S) 3s2(1S) photoionization edge of Mg I.

UKIRT's Wide Field Camera and the Detection of 10 MJupiter Objects

NASA Astrophysics Data System (ADS)

WFCAM Team; UKIDSS Team

2004-06-01

In mid-2004 a near-infrared wide field camera will be commissioned on UKIRT. About 40% of all UKIRT time will go into sky surveys and one of these, the Large Area Survey using YJHK filters, will extend the field brown dwarf population to temperatures and masses significantly lower than those of the T dwarf population discovered by the Sloan and 2MASS surveys. The LAS should find objects as cool as 450 K and as low mass as 10 MJupiter at 10 pc. These planetary-mass objects will possibly require a new spectral type designation.

Precipitating Condensation Clouds in Substellar Atmospheres

NASA Technical Reports Server (NTRS)

Ackerman, Andrew S.; Marley, Mark S.; Gore, Warren J. (Technical Monitor)

2000-01-01

We present a method to calculate vertical profiles of particle size distributions in condensation clouds of giant planets and brown dwarfs. The method assumes a balance between turbulent diffusion and precipitation in horizontally uniform cloud decks. Calculations for the Jovian ammonia cloud are compared with previous methods. An adjustable parameter describing the efficiency of precipitation allows the new model to span the range of predictions from previous models. Calculations for the Jovian ammonia cloud are found to be consistent with observational constraints. Example calculations are provided for water, silicate, and iron clouds on brown dwarfs and on a cool extrasolar giant planet.

Wide cool and ultracool companions to nearby stars from Pan-STARRS 1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deacon, Niall R.; Liu, Michael C.; Magnier, Eugene A.

2014-09-10

We present the discovery of 57 wide (>5'') separation, low-mass (stellar and substellar) companions to stars in the solar neighborhood identified from Pan-STARRS 1 (PS1) data and the spectral classification of 31 previously known companions. Our companions represent a selective subsample of promising candidates and span a range in spectral type of K7-L9 with the addition of one DA white dwarf. These were identified primarily from a dedicated common proper motion search around nearby stars, along with a few as serendipitous discoveries from our Pan-STARRS 1 brown dwarf search. Our discoveries include 23 new L dwarf companions and one knownmore » L dwarf not previously identified as a companion. The primary stars around which we searched for companions come from a list of bright stars with well-measured parallaxes and large proper motions from the Hipparcos catalog (8583 stars, mostly A-K dwarfs) and fainter stars from other proper motion catalogs (79170 stars, mostly M dwarfs). We examine the likelihood that our companions are chance alignments between unrelated stars and conclude that this is unlikely for the majority of the objects that we have followed-up spectroscopically. We also examine the entire population of ultracool (>M7) dwarf companions and conclude that while some are loosely bound, most are unlikely to be disrupted over the course of ∼10 Gyr. Our search increases the number of ultracool M dwarf companions wider than 300 AU by 88% and increases the number of L dwarf companions in the same separation range by 82%. Finally, we resolve our new L dwarf companion to HIP 6407 into a tight (0.''13, 7.4 AU) L1+T3 binary, making the system a hierarchical triple. Our search for these key benchmarks against which brown dwarf and exoplanet atmosphere models are tested has yielded the largest number of discoveries to date.« less

CARMENES: A Spectroscopic Survey of M Dwarfs and their Planets

NASA Astrophysics Data System (ADS)

Quirrenbach, Andreas; Consortium, CARMENES

2015-08-01

CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs) is a next-generation instrument currently under construction for the 3.5m telescope at the Calar Alto Observatory by a consortium of eleven Spanish and German institutions. Commissioning of CARMENES will start in April 2015. CARMENES will conduct a 600-night exoplanet survey targeting ~300 M dwarfs. An important and unique feature of the CARMENES instrument is that it consists of two separate échelle spectrographs, which together cover the wavelength range from 0.55 to 1.7 μm at a spectral resolution of R = 82,000. The spectrographs are fed by fibers from the Cassegrain focus of the telescope.The main scientific objective of CARMENES is to carry out a survey of late-type main sequence stars with the goal of detecting low-mass planets in their habitable zones (HZs). In the focus of the project are very cool stars later than spectral type M4 and moderately active stars. We aim at being able to detect a 2M⊕ planet in the HZ of an M5 star, which requires a long-term radial velocity precision of 1ms-1 per measurement. For stars later than M4 (M < 0.25M⊙), such precision will yield detections of super-Earths of 5M⊕ and smaller inside the entire width of the HZ. The CARMENES survey will thus provide a comprehensive overview of planetary systems around nearby Northern M dwarfs. By reaching into the realm of Earth-like planets, it will provide a treasure trove for follow-up studies probing their habitability.At the same time, the CARMENES survey will generate a unique data set for studies of M star atmospheres, rotation, and activity. The spectra will cover important diagnostic lines for activity (Hα, Na I D1 and D2, and the Ca II infrared triplet), as well as FeH lines around 10,000Å, from which the magnetic field can be inferred. Correlating the time series of these features with each other, and with wavelength-dependent radial velocities, will provide new insight into the physical properties of M dwarf atmospheres, and will provide excellent discrimination between planetary companions and stellar radial velocity "noise".

A temperate rocky super-Earth transiting a nearby cool star

NASA Astrophysics Data System (ADS)

Dittmann, Jason A.; Irwin, Jonathan M.; Charbonneau, David; Bonfils, Xavier; Astudillo-Defru, Nicola; Haywood, Raphaëlle D.; Berta-Thompson, Zachory K.; Newton, Elisabeth R.; Rodriguez, Joseph E.; Winters, Jennifer G.; Tan, Thiam-Guan; Almenara, Jose-Manuel; Bouchy, François; Delfosse, Xavier; Forveille, Thierry; Lovis, Christophe; Murgas, Felipe; Pepe, Francesco; Santos, Nuno C.; Udry, Stephane; Wünsche, Anaël; Esquerdo, Gilbert A.; Latham, David W.; Dressing, Courtney D.

2017-04-01

M dwarf stars, which have masses less than 60 per cent that of the Sun, make up 75 per cent of the population of the stars in the Galaxy. The atmospheres of orbiting Earth-sized planets are observationally accessible via transmission spectroscopy when the planets pass in front of these stars. Statistical results suggest that the nearest transiting Earth-sized planet in the liquid-water, habitable zone of an M dwarf star is probably around 10.5 parsecs away. A temperate planet has been discovered orbiting Proxima Centauri, the closest M dwarf, but it probably does not transit and its true mass is unknown. Seven Earth-sized planets transit the very low-mass star TRAPPIST-1, which is 12 parsecs away, but their masses and, particularly, their densities are poorly constrained. Here we report observations of LHS 1140b, a planet with a radius of 1.4 Earth radii transiting a small, cool star (LHS 1140) 12 parsecs away. We measure the mass of the planet to be 6.6 times that of Earth, consistent with a rocky bulk composition. LHS 1140b receives an insolation of 0.46 times that of Earth, placing it within the liquid-water, habitable zone. With 90 per cent confidence, we place an upper limit on the orbital eccentricity of 0.29. The circular orbit is unlikely to be the result of tides and therefore was probably present at formation. Given its large surface gravity and cool insolation, the planet may have retained its atmosphere despite the greater luminosity (compared to the present-day) of its host star in its youth. Because LHS 1140 is nearby, telescopes currently under construction might be able to search for specific atmospheric gases in the future.

Alkali Halide Opacity in Brown Dwarf and Cool Stellar Atmospheres: A Study of Lithium Chloride

NASA Astrophysics Data System (ADS)

Kirby, K.; Weck, P. F.; Schweitzer, A.; Stancil, P. C.; Hauschildt, P. H.

2003-12-01

Recent thermochemical equilibrium calculations have revealed the important role played by lithium chloride in the lithium chemistry of cool dwarf atmospheres (K. Lodders 1999, ApJ 519, 793). Indeed, LiCl appears to be the dominant Li-bearing gas over an extended domain of the (P,T) diagram, typically for temperatures below 1500 K. LiCl has a large dipole moment in its ground electronic state which can give rise to intense rovibrational line spectra. In addition, LiCl can make dipole transitions to several low-lying unbound excited states, causing dissociation of the molecule. For these reasons, LiCl may be a significant source of line and continuum opacity in brown dwarf and cool stellar atmospheres. In this work, we report calculations of complete lists of line oscillator strengths and photodissociation cross sections for the low-lying electronic states of LiCl. We have performed single- and double-excitation configuration interaction calculations using the ALCHEMY ab initio package (Mc Lean et al. 1991, MOTECC 91, Elsevier, Leiden) and obtained the potential curves and the corresponding dipole transition moment functions between the X 1Σ ^+ ground state and the B 1Σ ^+ and A 1Π excited states. The resulting line oscillator strengths and molecular photodissociation cross sections have been included in the PHOENIX stellar atmosphere code (Hauschildt & Baron 1999, J. Comput. App. Math. 102, 41). The new models, calculated using spherical geometry for all gravities considered, also incorporate our latest database of nearly 670 million molecular lines, and updated equations of state (EOS). This work was supported in part by NSF grants AST-9720704 and AST-0086246, NASA grants NAG5-8425, NAG5-9222, and NAG5-10551 as well as NASA/JPL grant 961582.

A temperate rocky super-Earth transiting a nearby cool star.

PubMed

Dittmann, Jason A; Irwin, Jonathan M; Charbonneau, David; Bonfils, Xavier; Astudillo-Defru, Nicola; Haywood, Raphaëlle D; Berta-Thompson, Zachory K; Newton, Elisabeth R; Rodriguez, Joseph E; Winters, Jennifer G; Tan, Thiam-Guan; Almenara, Jose-Manuel; Bouchy, François; Delfosse, Xavier; Forveille, Thierry; Lovis, Christophe; Murgas, Felipe; Pepe, Francesco; Santos, Nuno C; Udry, Stephane; Wünsche, Anaël; Esquerdo, Gilbert A; Latham, David W; Dressing, Courtney D

2017-04-19

M dwarf stars, which have masses less than 60 per cent that of the Sun, make up 75 per cent of the population of the stars in the Galaxy. The atmospheres of orbiting Earth-sized planets are observationally accessible via transmission spectroscopy when the planets pass in front of these stars. Statistical results suggest that the nearest transiting Earth-sized planet in the liquid-water, habitable zone of an M dwarf star is probably around 10.5 parsecs away. A temperate planet has been discovered orbiting Proxima Centauri, the closest M dwarf, but it probably does not transit and its true mass is unknown. Seven Earth-sized planets transit the very low-mass star TRAPPIST-1, which is 12 parsecs away, but their masses and, particularly, their densities are poorly constrained. Here we report observations of LHS 1140b, a planet with a radius of 1.4 Earth radii transiting a small, cool star (LHS 1140) 12 parsecs away. We measure the mass of the planet to be 6.6 times that of Earth, consistent with a rocky bulk composition. LHS 1140b receives an insolation of 0.46 times that of Earth, placing it within the liquid-water, habitable zone. With 90 per cent confidence, we place an upper limit on the orbital eccentricity of 0.29. The circular orbit is unlikely to be the result of tides and therefore was probably present at formation. Given its large surface gravity and cool insolation, the planet may have retained its atmosphere despite the greater luminosity (compared to the present-day) of its host star in its youth. Because LHS 1140 is nearby, telescopes currently under construction might be able to search for specific atmospheric gases in the future.

The Productivity of Oxygenic Photosynthesis around Cool, M Dwarf Stars

NASA Astrophysics Data System (ADS)

Lehmer, Owen R.; Catling, David C.; Parenteau, Mary N.; Hoehler, Tori M.

2018-06-01

In the search for life around cool stars, the presence of atmospheric oxygen is a prominent biosignature, as it may indicate oxygenic photosynthesis (OP) on the planetary surface. On Earth, most oxygenic photosynthesizing organisms (OPOs) use photons between 400 and 750 nm, which have sufficient energy to drive the photosynthetic reaction that generates O2 from H2O and CO2. OPOs around cool stars may evolve similar biological machinery capable of producing oxygen from water. However, in the habitable zones (HZs) of the coolest M dwarf stars, the flux of 400–750 nm photons may be just a few percent that of Earth’s. We show that the reduced flux of 400–750 nm photons around M dwarf stars could result in Earth-like planets being growth limited by light, unlike the terrestrial biosphere, which is limited by nutrient availability. We consider stars with photospheric temperatures between 2300 and 4200 K and show that such light-limited worlds could occur at the outer edge of the HZ around TRAPPIST-1-like stars. We find that even if OP can use photons longer than 750 nm, there would still be insufficient energy to sustain the Earth’s extant biosphere throughout the HZ of the coolest stars. This is because such stars emit largely in the infrared and near-infrared, which provide sufficient energy to make the planet habitable, but limits the energy available for OP. TRAPPIST-1f and g may fall into this category. Biospheres on such planets, potentially limited by photon availability, may generate small biogenic signals, which could be difficult for future observations to detect.

Universal Dark Halo Scaling Relation for the Dwarf Spheroidal Satellites

NASA Astrophysics Data System (ADS)

Hayashi, Kohei; Ishiyama, Tomoaki; Ogiya, Go; Chiba, Masashi; Inoue, Shigeki; Mori, Masao

2017-07-01

Motivated by a recently found interesting property of the dark halo surface density within a radius, {r}\\max , giving the maximum circular velocity, {V}\\max , we investigate it for dark halos of the Milky Way’s and Andromeda’s dwarf satellites based on cosmological simulations. We select and analyze the simulated subhalos associated with Milky-Way-sized dark halos and find that the values of their surface densities, {{{Σ }}}{V\\max }, are in good agreement with those for the observed dwarf spheroidal satellites even without employing any fitting procedures. Moreover, all subhalos on the small scales of dwarf satellites are expected to obey the universal relation, irrespective of differences in their orbital evolutions, host halo properties, and observed redshifts. Therefore, we find that the universal scaling relation for dark halos on dwarf galaxy mass scales surely exists and provides us with important clues for understanding fundamental properties of dark halos. We also investigate orbital and dynamical evolutions of subhalos to understand the origin of this universal dark halo relation and find that most subhalos evolve generally along the {r}\\max \\propto {V}\\max sequence, even though these subhalos have undergone different histories of mass assembly and tidal stripping. This sequence, therefore, should be the key feature for understanding the nature of the universality of {{{Σ }}}{V\\max }.

Spectroscopic investigation of stars on the lower main sequence

NASA Astrophysics Data System (ADS)

Mishenina, T. V.; Soubiran, C.; Bienaymé, O.; Korotin, S. A.; Belik, S. I.; Usenko, I. A.; Kovtyukh, V. V.

2008-10-01

Aims: The aim of this paper is to provide fundamental parameters and abundances with a high accuracy for a large sample of cool main sequence stars. This study is part of wider project, in which the metallicity distribution of the local thin disc is investigated from a complete sample of G and K dwarfs within 25 pc. Methods: The stars were observed at high resolution and a high signal-to-noise ratio with the ELODIE echelle spectrograph. The V sin i were obtained with a calibration of the cross-correlation function. Effective temperatures were estimated by the line depth ratio method. Surface gravities (log g) were determined by two methods: parallaxes and ionization balance of iron. The Mg and Na abundances were derived using a non-LTE approximation. Abundances of other elements were obtained by measuring equivalent widths. Results: Rotational velocities, atmospheric parameters (T_eff, log g, [Fe/H], V_t), and Li, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Co, Ni, and Zn abundances are provided for 131 stars. Among them, more than 30 stars are active stars with a fraction of BY Dra and RS CVn type stars for which spectral peculiarities were investigated. We find the mean abundances of the majority of elements in active and nonactive stars to be similar, except for Li, and possibly for Zn and Co. The lithium is reliably detected in 54% of active stars but only in 20% of nonactive stars. No correlation is found between Li abundances and rotational velocities. A possible anticorrelation of log A(Li) with the index of chromospheric activity GrandS is observed. Conclusions: Active and nonactive cool dwarfs show similar dependencies of most elemental ratios vs. [Fe/H]. This allows us to use such abundance ratios to study the chemical and dynamical evolution of the Galaxy. Among active stars, no clear correlation has been found between different indicators of activity for our sample stars. Based on spectra collected with the ELODIE spectrograph at the 1.93-m telescope of the Observatoire de Haute Provence (France). Tables A.1-A3 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/489/923

T dwarfs all the way to 550 K?

NASA Astrophysics Data System (ADS)

Burningham, Ben; Pinfield, D. J.; Leggett, S. K.; Tamura, M.; Lucas, P. W.; Homeier, D.

2009-02-01

We highlight recent results from the UKIDSS Large Area Survey (LAS) including a T dwarf with an estimated Teff = 550-600 K and new constraints on the substellar mass function in the field. We also define the T9 subtype as an extension to the T spectral sequence defined by Burgasser et al. (2006).

CGM Evolution of a Simulated Dwarf Galaxy

NASA Astrophysics Data System (ADS)

Sheehan-Klenk, Patrick; Christensen, Charlotte

2018-06-01

The circumgalactic medium (CGM), which is fed by galactic outflows, is intrinsically connected to star formation and galactic evolution. We followed the evolution of the CGM of a simulated dwarf galaxy of mass 4.75 × 1010 solar masses., through five timesteps corresponding to z = 3, 2, 1, 0.5, 0.15. The simulation includes metal line cooling, metal diffusion, and supernova feedback, and the resulting galaxy has a realistic stellar mass and metallicity. We measured the surface densities of HI, CIV and OVI in the CGM gas composition and analyzed their trends in relation to the galaxy's evolution. Additionally, we created mock absorption line spectra, which we used to find the mean equivalent width for sight lines spaced 0.1R/Rvir apart. From this analysis, we saw there was high metallicity at large radii, and over time the CGM cooled and became more ordered. We note the impact of a merger with a smaller galaxy at z = 0.5. We compare these results to observations.

Dynamics of exoplanetary systems, links to their habitability

NASA Astrophysics Data System (ADS)

Bolmont, E.; Raymond, S. N.; Selsis, F.

2014-12-01

Our knowledge of planets' orbital dynamics, which was based on Solar System studies, has been challenged by the diversity of exoplanetary systems. Around cool and ultra cool dwarfs, the influence of tides on the orbital and spin evolution of planets can strongly affect their climate and their capacity to host surface liquid water. We illustrate the role of tides and dynamics with the extreme case of planets orbiting around brown dwarfs. In multiple planet systems, the eccentricity is excited by planet-planet interactions. Planets are therefore heated up from the inside by the tidally-induced friction. This process can heat a habitable zone planet to such a level that surface liquid water cannot exist. We also talk about the newly discovered potentially habitable Earth-sized planet Kepler-186f. Given the poorly estimated age of the system, the planet could still be evolving towards synchronization and have a high obliquity or be pseudo-synchronized with a zero obliquity. These two configurations would have a different effect on the climate of this planet.

Li I AND K I SCATTER IN COOL PLEIADES DWARFS

DOE Office of Scientific and Technical Information (OSTI.GOV)

King, Jeremy R.; Schuler, Simon C.; Hobbs, L. M.

2010-02-20

We utilize high-resolution (R {approx} 60,000), high signal-to-noise ratio ({approx}100) spectroscopy of 17 cool Pleiades dwarfs to examine the confounding star-to-star scatter in the lambda6707 Li I line strengths in this young cluster. Our Pleiades, selected for their small projected rotational velocity and modest chromospheric emission, evince substantial scatter in the line strengths of lambda6707 Li I feature that is absent in the lambda7699 K I resonance line. The Li I scatter is not correlated with that in the high-excitation lambda7774 O I feature, and the magnitude of the former is greater than the latter despite the larger temperature sensitivitymore » of the O I feature. These results suggest that systematic errors in line strength measurements due to blending, color (or color-based T{sub eff}) errors, or line formation effects related to an overlying chromosphere are not the principal source of Li I scatter in our stars. There do exist analytic spot models that can produce, via line formation effects, the observed Li scatter without introducing scatter in the K I line strengths or the color-magnitude diagram. However, these models predict factor of >=3 differences in abundances derived from the subordinate lambda6104 and resonance lambda6707 Li I features; we find no difference in the abundances determined from these two features. These analytic spot models also predict CN line strengths significantly larger than we observe in our spectra. The simplest explanation of the Li, K, CN, and photometric data is that there must be a real abundance component to the Pleiades Li dispersion. We suggest that this real abundance component is the manifestation of relic differences in erstwhile pre-main-sequence Li burning caused by effects of surface activity on stellar structure. We discuss observational predictions of these effects, which may be related to other anomalous stellar phenomena.« less

Genetic analysis of a novel Alaska barley yellow dwarf virus in the family Luteoviridae.

PubMed

Robertson, N L; French, R

2007-02-01

A new plant virus belonging to the family Luteoviridae and isolated from diseased oat (Avena sativa L.) plants was discovered in Alaska in 2003. Even though plants with red/orange leaves were indicative of barley yellow dwarf disease, they were not reactive to specific antibodies corresponding to barley yellow dwarf virus (BYDV)-MAV, -PAV, -SGV, and cereal yellow dwarf virus-RPV from enzyme-linked immunosorbent assays (ELISA). An alternative RT-PCR assay that incorporated Shu-F/Yan-R primers for detection of BYDV-MAV, -PAS, -PAV, and SGV was effective in producing approximately 830-nt fragments that contained genomic sequences to the 3'-terminus of the polymerase gene (ORF 2), the intergenic region ( approximately 113 nt), the coat protein gene (ORF 3), and the putative movement gene (ORF 4). The Alaskan isolates were most similar to BYDV-MAV with only about 77 and 80% amino acid identity in the CP and ORF 4, respectively. The Alaska isolates coat protein gene sequences differed in several regions that otherwise are conserved among BYDV-MAV isolates, and may be important in serological variations, accounting for the negative ELISA results. Based upon sequence and serological differences, we concluded that the Alaskan BYDV-MAV-like isolates formed a novel species tentatively in the genus Luteovirus, and propose the name BYDV-ORV (oat red-leaf virus).

Deciphering IR Excess Observed by the Spitzer Space Telescope in Short Period Interacting Cataclysmic Binaries

NASA Astrophysics Data System (ADS)

Chun, Howard; Brinkworth, Carolyn; Ciardi, David; Hoard, Don; Howell, Steve; Stefaniak, Linda; Thomas, Beth

2006-03-01

During the first year of the Spitzer Space Telescope Observing Program for Students and Teachers, our team observed a small sample of short orbital period interacting white dwarf binaries. Our scientific investigation was aimed at detection and characterization of the low mass, cool, brown dwarf-like mass donors in these systems. We used the Infrared Array Camera to obtain photometric observations of the polars EF Eri, GG Leo, V347 Pav, and RX J0154.0-5947 at 3.6, 4.5, 5.8, and 8.0 microns. In all our targets, we detected excess emission in the 3-8 micron region over that expected from a brown dwarf alone. One of the exciting discoveries we made with our IRAC observations is that the star EF Eri was found to be unexpectedly bright in the mid-IR (compared to its 2MASS magnitudes). This fact highlights an opportunity for us to observe EF Eri with the IRS as a follow-up proposal. EF Eri has a flux level of ~700 ?Jy at 8 microns. Thus, we are asking for time to obtain IRS data for only this star, our brightest source. We plan to obtain SL1 (7.4-14.5 microns) and SL2 (5.2-8.7 microns) spectroscopy only. We know the IRAC fluxes so our integration toies are well constrained and the spectral region covered by SL1, SL2 will yield sufficient S/N to differentiate between cool dust (rising BB like spectrum with PAH and other molecular features allowing us to determine dust size, temperature, and disk extent) and a T type dwarf showing characteristic spectral signatures and a falling Rayleigh-Jeans tail.

A novel strategy for the determination of a rhabdovirus genome and its application to sequencing of Eggplant mottled dwarf virus.

PubMed

Pappi, Polyxeni G; Dovas, Chrysostomos I; Efthimiou, Konstantinos E; Maliogka, Varvara I; Katis, Nikolaos I

2013-08-01

A novel strategy employing the rhabdovirus untranslated conserved intergenic regions was developed and applied successfully for the determination of the complete nucleotide sequence of Eggplant mottled dwarf virus (EMDV). The EMDV genome contains seven open reading frames with the same organization as Potato yellow dwarf virus (PYDV), the type species of the genus Nucleorhabdovirus. These two species encode five core genes [nucleocapsid (N), phosphoprotein (P), matrix (M), glycoprotein (G), and the polymerase (L)] like other viruses of the genus and an additional one (X), located between N and P, giving rise to a protein with currently unknown function. Furthermore, both EMDV and PYDV contain a gene (Y), inserted between P and M, which probably encodes the virus movement protein, in concordance with the rest of the plant-infecting rhabdoviruses. Phylogenetic analysis of the polymerase gene confirmed the classification of EMDV within the genus Nucleorhabdovirus and showed a close evolutionary relationship to PYDV. The novel sequencing strategy developed is a useful tool for the genome determination of yet uncharacterized rhabdoviruses.

Asteroseismology of ZZ Ceti stars with full evolutionary white dwarf models. II. The impact of AGB thermal pulses on the asteroseismic inferences of ZZ Ceti stars

NASA Astrophysics Data System (ADS)

De Gerónimo, F. C.; Althaus, L. G.; Córsico, A. H.; Romero, A. D.; Kepler, S. O.

2018-05-01

Context. The thermally pulsing phase on the asymptotic giant branch (TP-AGB) is the last nuclear burning phase experienced by most low- and intermediate-mass stars. During this phase, the outer chemical stratification above the C/O core of the emerging white dwarf (WD) is built up. The chemical structure resulting from progenitor evolution strongly impacts the whole pulsation spectrum exhibited by ZZ Ceti stars, which are pulsating C/O core white dwarfs located on a narrow instability strip at Teff 12 000 K. Several physical processes occurring during progenitor evolution strongly affect the chemical structure of these stars; those found during the TP-AGB phase are the most relevant for the pulsational properties of ZZ Ceti stars. Aims: We present a study of the impact of the chemical structure built up during the TP-AGB evolution on the stellar parameters inferred from asteroseismological fits of ZZ Ceti stars. Methods: Our analysis is based on a set of carbon-oxygen core white dwarf models with masses from 0.534 to 0.6463 M⊙ derived from full evolutionary computations from the ZAMS to the ZZ Ceti domain. We computed evolutionary sequences that experience different number of thermal pulses (TP). Results: We find that the occurrence or not of thermal pulses during AGB evolution implies an average deviation in the asteroseimological effective temperature of ZZ Ceti stars of at most 8% and on the order of ≲5% in the stellar mass. For the mass of the hydrogen envelope, however, we find deviations up to 2 orders of magnitude in the case of cool ZZ Ceti stars. Hot and intermediate temperature ZZ Ceti stars show no differences in the hydrogen envelope mass in most cases. Conclusions: Our results show that, in general, the impact of the occurrence or not of thermal pulses in the progenitor stars is not negligible and must be taken into account in asteroseismological studies of ZZ Ceti stars.

THE ACS LCID PROJECT: ON THE ORIGIN OF DWARF GALAXY TYPES—A MANIFESTATION OF THE HALO ASSEMBLY BIAS?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gallart, Carme; Monelli, Matteo; Aparicio, Antonio

We discuss how knowledge of the whole evolutionary history of dwarf galaxies, including details on the early star formation events, can provide insight on the origin of the different dwarf galaxy types. We suggest that these types may be imprinted by the early conditions of formation rather than only being the result of a recent morphological transformation driven by environmental effects. We present precise star formation histories of a sample of Local Group dwarf galaxies, derived from color–magnitude diagrams reaching the oldest main-sequence turnoffs. We argue that these galaxies can be assigned to two basic types: fast dwarfs that startedmore » their evolution with a dominant and short star formation event and slow dwarfs that formed a small fraction of their stars early and have continued forming stars until the present time (or almost). These two different evolutionary paths do not map directly onto the present-day morphology (dwarf spheroidal versus dwarf irregular). Slow and fast dwarfs also differ in their inferred past location relative to the Milky Way and/or M31, which hints that slow dwarfs were generally assembled in lower-density environments than fast dwarfs. We propose that the distinction between a fast and slow dwarf galaxy primarily reflects the characteristic density of the environment where they form. At a later stage, interaction with a large host galaxy may play a role in the final gas removal and ultimate termination of star formation.« less

Mesa Isochrones and Stellar Tracks (MIST). I. Solar-scaled Models

NASA Astrophysics Data System (ADS)

Choi, Jieun; Dotter, Aaron; Conroy, Charlie; Cantiello, Matteo; Paxton, Bill; Johnson, Benjamin D.

2016-06-01

This is the first of a series of papers presenting the Modules for Experiments in Stellar Astrophysics (MESA) Isochrones and Stellar Tracks (MIST) project, a new comprehensive set of stellar evolutionary tracks and isochrones computed using MESA, a state-of-the-art open-source 1D stellar evolution package. In this work, we present models with solar-scaled abundance ratios covering a wide range of ages (5≤slant {log}({Age}) [{year}]≤slant 10.3), masses (0.1≤slant M/{M}⊙ ≤slant 300), and metallicities (-2.0≤slant [{{Z}}/{{H}}]≤slant 0.5). The models are self-consistently and continuously evolved from the pre-main sequence (PMS) to the end of hydrogen burning, the white dwarf cooling sequence, or the end of carbon burning, depending on the initial mass. We also provide a grid of models evolved from the PMS to the end of core helium burning for -4.0≤slant [{{Z}}/{{H}}]\\lt -2.0. We showcase extensive comparisons with observational constraints as well as with some of the most widely used existing models in the literature. The evolutionary tracks and isochrones can be downloaded from the project website at http://waps.cfa.harvard.edu/MIST/.

Beyond the T Dwarfs: Theoretical Spectra, Colors, and Detectability of the Coolest Brown Dwarfs

NASA Astrophysics Data System (ADS)

Burrows, Adam; Sudarsky, David; Lunine, Jonathan I.

2003-10-01

We explore the spectral and atmospheric properties of brown dwarfs cooler than the latest known T dwarfs. Our focus is on the yet-to-be-discovered free-floating brown dwarfs in the Teff range from ~800 to ~130 K and with masses from 25 to 1 MJ. This study is in anticipation of the new characterization capabilities enabled by the launch of the Space Infrared Telescope Facility (SIRTF) and the eventual launch of the James Webb Space Telescope (JWST). In addition, it is in support of the continuing ground-based searches for the coolest substellar objects. We provide spectra from ~0.4 to 30 μm, highlight the evolution and mass dependence of the dominant H2O, CH4, and NH3 molecular bands, consider the formation and effects of water ice clouds, and compare our theoretical flux densities with the putative sensitivities of the instruments on board SIRTF and JWST. The latter can be used to determine the detection ranges from space of cool brown dwarfs. In the process, we determine the reversal point of the blueward trend in the near-infrared colors with decreasing Teff (a prominent feature of the hotter T dwarf family), the Teff's at which water and ammonia clouds appear, the strengths of gas-phase ammonia and methane bands, the masses and ages of the objects for which the neutral alkali metal lines (signatures of L and T dwarfs) are muted, and the increasing role as Teff decreases of the mid-infrared fluxes longward of 4 μm. These changes suggest physical reasons to expect the emergence of at least one new stellar class beyond the T dwarfs. Furthermore, studies in the mid-infrared could assume a new, perhaps transformational, importance in the understanding of the coolest brown dwarfs. Our spectral models populate, with cooler brown dwarfs having progressively more planet-like features, the theoretical gap between the known T dwarfs and the known giant planets. Such objects likely inhabit the Galaxy, but their numbers are as yet unknown.

Complete genomic characterization of milk vetch dwarf virus isolates from cowpea and broad bean in Anhui province, China.

PubMed

Zhang, Chenhua; Zheng, Hongying; Yan, Dankan; Han, Kelei; Song, Xijiao; Liu, Yong; Zhang, Dongfang; Chen, Jianping; Yan, Fei

2017-08-01

Cowpea and broad bean plants showing severe stunting and leaf rolling symptoms were observed in Hefei city, Anhui province, China, in 2014. Symptomatic plants from both species were shown to be infected with milk vetch dwarf virus (MDV) by PCR. The complete genomes of MDV isolates from cowpea and broad bean were sequenced. Each of them had eight genomic DNAs that differed between the two isolates by 10.7% in their overall nucleotide sequences. In addition, the MDV genomes from cowpea and broad bean were associated with two and three alphasatellite DNAs, respectively. This is the first report of MDV on cowpea in China and the first complete genome sequences of Chinese MDV isolates.

GW LIBRAE: STILL HOT EIGHT YEARS POST-OUTBURST

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szkody, Paula; Mukadam, Anjum S.; Gänsicke, Boris T.

We report continued Hubble Space Telescope ( HST ) ultraviolet spectra and ground-based optical photometry and spectroscopy of GW Librae eight years after its largest known dwarf nova outburst in 2007. This represents the longest cooling timescale measured for any dwarf nova. The spectra reveal that the white dwarf still remains about 3000 K hotter than its quiescent value. Both ultraviolet and optical light curves show a short period of 364–373 s, similar to one of the non-radial pulsation periods present for years prior to the outburst, and with a similar large UV/optical amplitude ratio. A large modulation at amore » period of 2 hr (also similar to that observed prior to outburst) is present in the optical data preceding and during the HST observations, but the satellite observation intervals did not cover the peaks of the optical modulation, and so it is not possible to determine its corresponding UV amplitude. The similarity of the short and long periods to quiescent values implies that the pulsating, fast spinning white dwarf in GW Lib may finally be nearing its quiescent configuration.« less

K-H2 line shapes for the spectra of cool brown dwarfs

NASA Astrophysics Data System (ADS)

Allard, N. F.; Spiegelman, F.; Kielkopf, J. F.

2016-05-01

Observations of cooler and cooler brown dwarfs show that the contribution from broadening at many bars pressure is becoming important. The opacity in the red optical to near-IR region under these conditions is dominated by the extremely pressure-broadened wings of the alkali resonance lines, in particular, the K I resonance doublet at 0.77 μm. Collisions with H2 are preponderant in brown dwarf atmospheres at an effective temperature of about 1000 K; the H2 perturber densities reach several 1019 even in Jupiter-mass planets and exceed 1020 for super-Jupiters and older Y dwarfs. As a consequence, it appears that when the far wing absorption due to alkali atoms in a dense H2 atmosphere is significant, accurate pressure broadened profiles that are valid at high densities of H2 should be incorporated into spectral models. The opacity tables are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A21

Outbursts in Symbiotic Binaries

NASA Technical Reports Server (NTRS)

Sonneborn, George (Technical Monitor); Kenyon, Scott J.

2004-01-01

Two models have been proposed for the outbursts of symbiotic stars. In the thermonuclear model, outbursts begin when the hydrogen burning shell of a hot white dwarf reaches a critical mass. After a rapid increase in the luminosity and effective temperature, the white dwarf evolves at constant luminosity to lower effective temperatures, remains at optical maximum for several years, and then returns to quiescence along a white dwarf cooling curve. In disk instability models, the brightness rises when the accretion rate from the disk onto the central white dwarf abruptly increases by factors of 5-20. After a few month to several year period at maximum, both the luminosity and the effective temperature of the disk decline as the system returns to quiescence. If most symbiotic stars undergo thermonuclear eruptions, then symbiotics are probably poor candidates for type I supernovae. However, they can then provide approx. 10% of the material which stars recycle back into the interstellar medium. If disk instabilities are the dominant eruption mechanism, symbiotics are promising type Ia candidates but recycle less material into the interstellar medium.

Chemical Soups Around Cool Stars

NASA Technical Reports Server (NTRS)

2009-01-01

This artist's conception shows a young, hypothetical planet around a cool star. A soupy mix of potentially life-forming chemicals can be seen pooling around the base of the jagged rocks. Observations from NASA's Spitzer Space Telescope hint that planets around cool stars the so-called M-dwarfs and brown dwarfs that are widespread throughout our galaxy might possess a different mix of life-forming, or prebiotic, chemicals than our young Earth.

Life on our planet is thought to have arisen out of a pond-scum-like mix of chemicals. Some of these chemicals are thought to have come from a planet-forming disk of gas and dust that swirled around our young sun. Meteorites carrying the chemicals might have crash-landed on Earth.

Astronomers don't know if these same life-generating processes are taking place around stars that are cooler than our sun, but the Spitzer observations show their disk chemistry is different. Spitzer detected a prebiotic molecule, called hydrogen cyanide, in the disks around yellow stars like our sun, but found none around cooler, less massive, reddish stars. Hydrogen cyanide is a carbon-containing, or organic compound. Five hydrogen cyanide molecules can join up to make adenine a chemical element of the DNA molecule found in all living organisms on Earth.

The Discovery of a Companion to the Very Cool Dwarf Gliese 569B with the Keck Adaptive Optics Facility.

PubMed

Martín; Koresko; Kulkarni; Lane; Wizinowich

2000-01-20

We report observations obtained with the Keck adaptive optics facility of the nearby (d=9.8 pc) binary Gl 569. The system was known to be composed of a cool primary (dM2) and a very cool secondary (dM8.5) with a separation of 5&arcsec; (49 AU). We have found that Gl 569B is itself double with a separation of only 0&farcs;101+/-0&farcs;002 (1 AU). This detection demonstrates the superb spatial resolution that can be achieved with adaptive optics at Keck. The difference in brightness between Gl 569B and the companion is approximately 0.5 mag in the J, H, and K&arcmin; bands. Thus, both objects have similarly red colors and very likely constitute a very low mass binary system. For reasonable assumptions about the age (0.12-1.0 Gyr) and total mass of the system (0.09-0.15 M middle dot in circle), we estimate that the orbital period is approximately 3 yr. Follow-up observations will allow us to obtain an astrometric orbit solution and will yield direct dynamical masses that can constrain evolutionary models of very low mass stars and brown dwarfs.

PHYSICAL PROPERTIES OF THE CURRENT CENSUS OF NORTHERN WHITE DWARFS WITHIN 40 pc OF THE SUN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Limoges, M.-M.; Bergeron, P.; Lépine, S., E-mail: limoges@astro.umontreal.ca, E-mail: bergeron@astro.umontreal.ca, E-mail: slepine@chara.gsu.edu

We present a detailed description of the physical properties of our current census of white dwarfs within 40 pc of the Sun, based on an exhaustive spectroscopic survey of northern hemisphere candidates from the SUPERBLINK proper motion database. Our method for selecting white dwarf candidates is based on a combination of theoretical color–magnitude relations and reduced proper motion diagrams. We reported in an earlier publication the discovery of nearly 200 new white dwarfs, and we present here the discovery of an additional 133 new white dwarfs, among which we identify 96 DA, 3 DB, 24 DC, 3 DQ, and 7more » DZ stars. We further identify 178 white dwarfs that lie within 40 pc of the Sun, representing a 40% increase of the current census, which now includes 492 objects. We estimate the completeness of our survey at between 66% and 78%, allowing for uncertainties in the distance estimates. We also perform a homogeneous model atmosphere analysis of this 40 pc sample and find a large fraction of massive white dwarfs, indicating that we are successfully recovering the more massive, and less luminous objects often missed in other surveys. We also show that the 40 pc sample is dominated by cool and old white dwarfs, which populate the faint end of the luminosity function, although trigonometric parallaxes will be needed to shape this part of the luminosity function more accurately. Finally, we identify 4 probable members of the 20 pc sample, 4 suspected double degenerate binaries, and we also report the discovery of two new ZZ Ceti pulsators.« less

Detection of Accretion X-Rays from QS Vir: Cataclysmic or a Lot of Hot Air?

NASA Astrophysics Data System (ADS)

Matranga, Marco; Drake, Jeremy J.; Kashyap, Vinay; Steeghs, Danny

2012-03-01

An XMM-Newton observation of the nearby "pre-cataclysmic" short-period (P orb = 3.62 hr) binary QS Vir (EC 13471-1258) revealed regular narrow X-ray eclipses when the white dwarf passed behind its M2-4 dwarf companion. The X-ray emission provides a clear signature of mass transfer and accretion onto the white dwarf. The low-resolution XMM-Newton EPIC spectra are consistent with a cooling flow model and indicate an accretion rate of \\dot{M} = 1.7 \\times 10^{-13} \\,M_\\odot yr-1. At 48 pc distant, QS Vir is then the second nearest accreting cataclysmic variable known, with one of the lowest accretion rates found to date for a non-magnetic system. To feed this accretion through a wind would require a wind mass-loss rate of \\dot{M}\\sim 2\\times 10^{-12}\\,M_\\odot yr-1 if the accretion efficiency is of the order of 10%. Consideration of likely mass-loss rates for M dwarfs suggests this is improbably high and pure wind accretion unlikely. A lack of accretion disk signatures also presents some difficulties for direct Roche lobe overflow. We speculate that QS Vir is on the verge of Roche lobe overflow, and that the observed mass transfer could be supplemented by upward chromospheric flows on the M dwarf, analogous to spicules and mottles on the Sun, that escape the Roche surface to be subsequently swept up into the white dwarf Roche lobe. If so, QS Vir would be in a rare evolutionary phase lasting only a million years. The X-ray luminosity of the M dwarf estimated during primary eclipse is LX = 3 × 1028 erg s-1, which is consistent with that of rapidly rotating "saturated" K and M dwarfs.

The L dwarf/T dwarf transition: Multiplicity, magnetic activity and mineral meteorology across the hydrogen burning limit

NASA Astrophysics Data System (ADS)

Burgasser, A. J.

2013-02-01

The transition between the L dwarf and T dwarf spectral classes is one of the most remarkable along the stellar/brown dwarf main sequence, separating sources with photospheres containing mineral condensate clouds from those containing methane and ammonia gases. Unusual characteristics of this transition include a 1 μm brightening between late L and early T dwarfs observed in both parallax samples and coeval binaries; a spike in the multiplicity fraction; evidence of increased photometric variability, possibly arising from patchy cloud structures; and a delayed transition for young, planetary-mass objects. All of these features can be explained if this transition is governed by the ``rapid'' (nonequlibrium) rainout of clouds from the photosphere, triggered by temperature, surface gravity, metallicity and (perhaps) rotational effects. While the underlying mechanism of this rainout remains under debate, the transition is now being exploited to discover and precisely characterize tight (<1 AU) very low-mass binaries that can be used to test brown dwarf evolutionary and atmospheric theories, and resolved binaries that further constrain the properties of this remarkable transition.

[Searching for Rare Celestial Objects Automatically from Stellar Spectra of the Sloan Digital Sky Survey Data Release Eight].

PubMed

Si, Jian-min; Luo, A-li; Wu, Fu-zhao; Wu, Yi-hong

2015-03-01

There are many valuable rare and unusual objects in spectra dataset of Sloan Digital Sky Survey (SDSS) Data Release eight (DR8), such as special white dwarfs (DZ, DQ, DC), carbon stars, white dwarf main-sequence binaries (WDMS), cataclysmic variable (CV) stars and so on, so it is extremely significant to search for rare and unusual celestial objects from massive spectra dataset. A novel algorithm based on Kernel dense estimation and K-nearest neighborhoods (KNN) has been presented, and applied to search for rare and unusual celestial objects from 546 383 stellar spectra of SDSS DR8. Their densities are estimated using Gaussian kernel density estimation, the top 5 000 spectra in descend order by their densities are selected as rare objects, and the top 300 000 spectra in ascend order by their densities are selected as normal objects. Then, KNN were used to classify the rest objects, and simultaneously K nearest neighbors of the 5 000 rare spectra are also selected as rare objects. As a result, there are totally 21 193 spectra selected as initial rare spectra, which include error spectra caused by deletion, redden, bad calibration, spectra consisting of different physically irrelevant components, planetary nebulas, QSOs, special white dwarfs (DZ, DQ, DC), carbon stars, white dwarf main-sequence binaries (WDMS), cataclysmic variable (CV) stars and so on. By cross identification with SIMBAD, NED, ADS and major literature, it is found that three DZ white dwarfs, one WDMS, two CVs with company of G-type star, three CVs candidates, six DC white dwarfs, one DC white dwarf candidate and one BL Lacertae (BL lac) candidate are our new findings. We also have found one special DA white dwarf with emission lines of Ca II triple and Mg I, and one unknown object whose spectrum looks like a late M star with emission lines and its image looks like a galaxy or nebula.

On the nature of the dwarf carbon star G77-61

NASA Technical Reports Server (NTRS)

Dearborn, D. S. P.; Liebert, J.; Aaronson, M.; Dahn, C. C.; Harrington, R.

1986-01-01

In the present study of astrometric, photometric, and spectrophotometric data for the low luminosity carbon star G77-61, radial velocity variations are detected which have a binary period of 245 days. The unseen companion is probably a cool white dwarf of much higher mass than the visible object. The most straightforward evolutionary hypothesis is that this star has an extremely metal-poor composition, and that it accreted a small amount of carbon-rich material when the now-unseen primary was at maximum radius. This may have inverted the C/O abundance of the secondary without achieving common envelope evolution and a sorter period.

Parallax measurements of six brown dwarfs.

NASA Astrophysics Data System (ADS)

Manjavacas, E.; Goldman, B.; Reffert, S.; Henning, T.

Accurate parallax measurements allow us to determine physical properties of brown dwarfs, and help us to constrain evolutionary and atmospheric models and reveal unresolved binaries. We measured absolute trigonometric parallaxes and proper motions of six cool brown dwarfs using background galaxies to establish an absolute reference frame. The brown dwarfs in our sample have spectral types between T2.5 and T7.5. The observations were taken in the J-band with the Omega2000 camera at the 3.5 m telescope at CAHA during a time period of 27 months. We obtained absolute parallaxes for our 6 brown dwarfs with a precision between 3 and 6 mas. We compared our results with the study by \\cite{Dupuy} and with the evolutionary models of \\cite{Allard}. For four of the six targets we found a good agreement in luminosity among objects of similar spectral types. The object 2MASS J11061197+2754225 is more than 1 mag overluminous in all bands pointing to binarity or higher order multiplicity. Based on observations taken with Omega-2000 at the 3.5 m telescope at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated by the Max Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).

8-12 GHz Radio Observations of Flare Activity On M dwarf CN Leo

NASA Astrophysics Data System (ADS)

Wofford, Alia; Villadsen, Jackie; Quintana, Elisa; Barclay, Thomas; Thackeray, Beverly

2018-01-01

Red dwarfs are cool stars that make up 70% of all stars. Red dwarfs can be utilized to detect potentially habitable planets but they have particularly strong magnetic activity that can be detrimental to orbiting planets’ atmospheres and habitability. A coronal mass ejection (CME) is an eruption of magnetized plasma from the star that is ejected into the interplanetary medium which can erode a planet’s atmosphere daily. Based on the sun CMEs are expected to produce very bright radio bursts along with optical flares. We are using M dwarf CN Leo, a well studied flare star that was in the K2 campaign field in summer 2017, as a template to understand the relationship between radio and optical flares and the space weather conditions impacting M dwarf planets. Using radio frequencies ranging from 0.22 GHz-12 GHz we search for simultaneous radio bursts and optical flares to infer if CMEs, flares or aurorae are occurring on the star. I will present the 8-12 GHz radio data from eight 1.5-hour observations with simultaneous optical data. CN Leo produced a bright non-thermal radio flare that lasted approximately for a day during two consecutive observations, with a gyrosynchrotron emission mechanism.

Unstable low-mass planetary systems as drivers of white dwarf pollution

NASA Astrophysics Data System (ADS)

Mustill, Alexander J.; Villaver, Eva; Veras, Dimitri; Gänsicke, Boris T.; Bonsor, Amy

2018-05-01

At least 25 {per cent} of white dwarfs show atmospheric pollution by metals, sometimes accompanied by detectable circumstellar dust/gas discs or (in the case of WD 1145+017) transiting disintegrating asteroids. Delivery of planetesimals to the white dwarf by orbiting planets is a leading candidate to explain these phenomena. Here, we study systems of planets and planetesimals undergoing planet-planet scattering triggered by the star's post-main-sequence mass loss, and test whether this can maintain high rates of delivery over the several Gyr that they are observed. We find that low-mass planets (Earth to Neptune mass) are efficient deliverers of material and can maintain the delivery for Gyr. Unstable low-mass planetary systems reproduce the observed delayed onset of significant accretion, as well as the slow decay in accretion rates at late times. Higher-mass planets are less efficient, and the delivery only lasts a relatively brief time before the planetesimal populations are cleared. The orbital inclinations of bodies as they cross the white dwarf's Roche limit are roughly isotropic, implying that significant collisional interactions of asteroids, debris streams and discs can be expected. If planet-planet scattering is indeed responsible for the pollution of white dwarfs, many such objects, and their main-sequence progenitors, can be expected to host (currently undetectable) super-Earth planets on orbits of several au and beyond.

Infrared Detection of Very Low Mass Stars.

NASA Astrophysics Data System (ADS)

Probst, Ronald George

We present in this thesis a review of very-low -mass ((TURN)0.1 M(,0)) star research, and results of two observational programs directed at the photometric detection of low mass binary companions in the infrared. Present theoretical desiderata are model atmospheres for very cool dwarf stars and determination of the minimum protostellar mass with all relevant physics included. Luminosities for these stars are well determined, but the effective temperature scale is uncertain and abundance analyses are lacking. Masses are known for very few, and with large relative errors. The luminosity function for M(,v) > 13 is very uncertain. Astrometric methods provide at present the only means of detecting very low mass objects in significant numbers. Completion of the near-star parallax catalogue and measurement of additional low-mass binaries are important observational programs. The potential of photometric selection of red dwarf binaries is explored in Chapter II. Separation of binaries from single stars by color anomalies alone is found impractical. Detection by overluminosity in the HR diagram is hampered by the intrinsic spread of the field star population. However, we find that application of both kinematic and photometric criteria allows binaries to be detected with only moderate contamination by single stars; we discuss several binary suspects selected in this way. Our approach uses an infrared bandpass to provide temperature resolution in the color baseline, and we present JHK photometry for 60 stars, including recent parallax stars with M(,v)>14. We examine the status of the least luminous stars; there is no conclusive evidence that they are not hydrogen-burning objects. Chapter III presents a survey of (TURN)100 white dwarfs at 2 (mu) for infrared excess indicative of low -luminosity cool companions. White dwarf-red dwarf composites are detectable by infared color anomalies down to M(,v)(TURN)21 for the red dwarf component, and our survey is complete to absolute magnitudes on this level. Candidates for astrometric mass determination are suggested. Several stars are found to be composites containing an accretion disk or a hot subdwarf + dK secondary. We find very few new low-luminosity companions to normal white dwarfs. This does not appear to be a selection effect, nor is there reason to believe that all parent systems have been altered or destroyed in the mass loss phase. Our strongly negative result constrains the luminosity function for red dwarf companions to decline steeply past M(,v) (DBLTURN) 13. This may reflect a general decline in the initial mass function for star formation, or a failure of systems with large mass ratios to form or remain bound in the parent star-forming regions.

Testing the Planet-Metallicity Correlation in M-dwarfs with Gemini GNIRS Spectra

NASA Astrophysics Data System (ADS)

Hobson, M. J.; Jofré, E.; García, L.; Petrucci, R.; Gómez, M.

2018-04-01

While the planet-metallicity correlation for FGK main-sequence stars hosting giant planets is well established, it is less clear for M-dwarf stars. We determine stellar parameters and metallicities for 16 M-dwarf stars, 11 of which host planets, with near-infrared spectra from the Gemini Near-Infrared Spectrograph (GNIRS). We find that M-dwarfs with planets are preferentially metal-rich compared to those without planets. This result is supported by the analysis of a larger catalogue of 18 M stars with planets and 213 M stars without known planets T15, and demonstrates the utility of GNIRS spectra to obtain reliable stellar parameters of M stars. We also find that M dwarfs with giant planets are preferentially more metallic than those with low-mass planets, in agreement with previous results for solar-type stars. These results favor the core accretion model of planetary formation.

Photometry, Astrometry, and Discoveries of Ultracool Dwarfs in the Pan-STARRS 3π Survey

NASA Astrophysics Data System (ADS)

Best, William M. J.; Magnier, Eugene A.; Liu, Michael C.; Deacon, Niall; Aller, Kimberly; Zhang, Zhoujian; Pan-STARRS1 Builders

2018-01-01

The Pan-STARRS1 3π Survey (PS1)'s far-red optical sensitivity makes it an exceptional new resource for discovering and characterizing ultracool dwarfs. We present a PS1-based catalog of photometry and proper motions of nearly 10,000 M, L, and T dwarfs, along with our analysis of the kinematics of nearby M6-T9 dwarfs, building a comprehensive picture of the local ultracool population. We highlight some especially interesting ultracool discoveries made with PS1, including brown dwarfs with spectral types in the enigmatic L/T transition, wide companions to main sequence stars that serve as age and metallicity bechmarks for substellar models, and free-floating members of the nearby young moving groups and star-forming regions with masses down to ≈5 MJup. With its public release, PS1 will continue to be a vital tool for studying the ultracool population.

The discovery of a very cool binary system

NASA Astrophysics Data System (ADS)

Burningham, Ben; Leggett, S. K.; Lucas, P. W.; Pinfield, D. J.; Smart, R. L.; Day-Jones, A. C.; Jones, H. R. A.; Murray, D.; Nickson, E.; Tamura, M.; Zhang, Z.; Lodieu, N.; Tinney, C. G.; Zapatero Osorio, M. R.

2010-06-01

We report the discovery of a very cool d/sdL7+T7.5p common proper motion binary system, SDSS J1416+13AB, found by cross-matching the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) Large Area Survey Data Release 5 (UKIDSS LAS DR4) against the Sloan Digital Sky Survey Data Release 7. The d/sdL7 is blue in J - H and H - K and has other features suggestive of low metallicity and/or high gravity. The T7.5p displays spectral peculiarity seen before in earlier type dwarfs discovered in UKIDSS LAS DR4, and referred to as CH4-J-early peculiarity, where the CH4-J index, based on the absorption to the red side of the J-band peak, suggests an earlier spectral type than the H2O-J index, based on the blue side of the J-band peak, by ~2 subtypes. We suggest that CH4-J-early peculiarity arises from low metallicity and/or high gravity, and speculate as to its use for classifying T dwarfs. UKIDSS and follow-up United Kingdom Infrared Telescope/Wide Field CAMera (UKIRT/WFCAM) photometry shows the T dwarf to have the bluest near-infrared colours yet seen for such an object with H - K = -1.31 +/- 0.17. Warm Spitzer IRAC photometry shows the T dwarf to have extremely red H - [4.5] = 4.86 +/- 0.04, which is the reddest yet seen for a substellar object. The lack of parallax measurement for the pair limits our ability to estimate parameters for the system. However, applying a conservative distance estimate of 5-15 pc suggests a projected separation in range 45-135 au. By comparing H - K:H - [4.5] colours of the T dwarf to spectral models, we estimate that Teff = 500 K and [M/H] ~ - 0.30, with logg ~ 5.0. This suggests a mass of ~30 MJupiter for the T dwarf and an age of ~10 Gyr for the system. The primary would then be a 75 MJupiter object with logg ~ 5.5 and a relatively dust-free Teff ~ 1500K atmosphere. Given the unusual properties of the system we caution that these estimates are uncertain. We eagerly await parallax measurements and high-resolution imaging which will constrain the parameters further.

Hot subdwarfs in (eclipsing) binaries with brown dwarf or low-mass main-sequence companions

NASA Astrophysics Data System (ADS)

Schaffenroth, Veronika; Geier, Stephan; Heber, Uli

2014-09-01

The formation of hot subdwarf stars (sdBs), which are core helium-burning stars located on the extended horizontal branch, is not yet understood. Many of the known hot subdwarf stars reside in close binary systems with short orbital periods of between a few hours and a few days, with either M-star or white-dwarf companions. Common-envelope ejection is the most probable formation channel. Among these, eclipsing systems are of special importance because it is possible to constrain the parameters of both components tightly by combining spectroscopic and light-curve analyses. They are called HW Virginis systems. Soker (1998) proposed that planetary or brown-dwarf companions could cause the mass loss necessary to form an sdB. Substellar objects with masses greater than >10 M_J were predicted to survive the common-envelope phase and end up in a close orbit around the stellar remnant, while planets with lower masses would entirely evaporate. This raises the question if planets can affect stellar evolution. Here we report on newly discovered eclipsing or not eclipsing hot subdwarf binaries with brown-dwarf or low-mass main-sequence companions and their spectral and photometric analysis to determine the fundamental parameters of both components.

From Globular Clusters to Tidal Dwarfs: Structure Formation in Tidal Tails

NASA Astrophysics Data System (ADS)

Knierman, K.; Hunsberger, S.; Gallagher, S.; Charlton, J.; Whitmore, B.; Hibbard, J.; Kundu, A.; Zaritsky, D.

1999-12-01

Galaxy interactions trigger star formation in tidal debris. How does this star formation depend on the local and global physical conditions? Using WFPC2/HST images, we investigate the range of structure within tidal tails of four classic ``Toomre Sequence'' mergers: NGC 4038/9 (``Antennae''), NGC 7252 (``Atoms for Peace''), NGC 3921, and NGC 3256. These tails contain a variety of stellar associations with sizes from globular clusters up to dwarf Irregulars. We explore whether there is a continuum between the two extremes. Our eight fields sample seven tidal tails at a variety of stages in the evolutionary sequence. Some of these tails are rich in HI while others are HI poor. Large tidal dwarfs are embedded in three of the tails. Using V and I WFPC2 images, we measure luminosities and colors of substructures within the tidal tails. The properties of globular cluster candidates in the tails will be contrasted with those of the hundreds of young clusters in the central regions of these mergers. We address whether globular clusters form and survive in the tidal tails and whether tidal dwarfs are composed of only young stars. By comparing the properties of structures in the tails of the four mergers with different ages, we examine systematic evolution of structure along the evolutionary sequence and as a function of HI content. We acknowledge support from NASA through STScI, and from NSF for an REU supplement for Karen Knierman.

The dynamics of post-main sequence planetary systems

NASA Astrophysics Data System (ADS)

Mustill, Alexander James

2017-06-01

The study of planetary systems after their host stars have left the main sequence is of fundamental importance for exoplanet science, as the most direct determination of the compositions of extra-Solar planets, asteroids and comets is in fact made by an analysis of the elemental abundances of the remnants of these bodies accreted into the atmospheres of white dwarfs.To understand how the accreted bodies relate to the source populations in the planetary system, and to model their dynamical delivery to the white dwarf, it is necessary to understand the effects of stellar evolution on bodies' orbits. On the red giant branch (RGB) and asymptotic giant branch (AGB) prior to becoming a white dwarf, stars expand to a large size (>1 au) and are easily deformed by orbiting planets, leading to tidal energy dissipation and orbital decay. They also lose half or more of their mass, causing the expansion of bodies' orbits. This mass loss increases the planet:star mass ratio, so planetary systems orbiting white dwarfs can be much less stable than those orbiting their main-sequence progenitors. Finally, small bodies in the system experience strong non-gravitational forces during the RGB and AGB: aerodynamic drag from the mass shed by the star, and strong radiation forces as the stellar luminosity reaches several thousand Solar luminosities.I will review these effects, focusing on planet--star tidal interactions and planet--asteroid interactions, and I will discuss some of the numerical challenges in modelling systems over their entire lifetimes of multiple Gyr.

New nearby white dwarfs from Gaia DR1 TGAS and UCAC5/URAT

NASA Astrophysics Data System (ADS)

Scholz, R.-D.; Meusinger, H.; Jahreiß, H.

2018-05-01

Aims: Using an accurate Tycho-Gaia Astrometric Solution (TGAS) 25 pc sample that is nearly complete for GK stars and selecting common proper motion (CPM) candidates from the 5th United States Naval Observatory CCD Astrograph Catalog (UCAC5), we search for new white dwarf (WD) companions around nearby stars with relatively small proper motions. Methods: To investigate known CPM systems in TGAS and to select CPM candidates in TGAS+UCAC5, we took into account the expected effect of orbital motion on the proper motion and proper motion catalogue errors. Colour-magnitude diagrams (CMDs) MJ /J - Ks and MG /G - J were used to verify CPM candidates from UCAC5. Assuming their common distance with a given TGAS star, we searched for candidates that occupied similar regions in the CMDs as the few known nearby WDs (four in TGAS) and WD companions (three in TGAS+UCAC5). The CPM candidates with colours and absolute magnitudes corresponding neither to the main sequence nor to the WD sequence were considered as doubtful or subdwarf candidates. Results: With a minimum proper motion of 60 mas yr-1, we selected three WD companion candidates; two of which are also confirmed by their significant parallaxes measured in URAT data, whereas the third may also be a chance alignment of a distant halo star with a nearby TGAS star that has an angular separation of about 465 arcsec. One additional nearby WD candidate was found from its URAT parallax and GJKs photometry. With HD 166435 B orbiting a well-known G1 star at ≈24.6 pc with a projected physical separation of ≈700 AU, we discovered one of the hottest WDs, classified by us as DA2.0 ± 0.2, in the solar neighbourhood. We also found TYC 3980-1081-1 B, a strong cool WD companion candidate around a recently identified new solar neighbour with a TGAS parallax corresponding to a distance of ≈8.3 pc and our photometric classification as ≈M2 dwarf. This raises the question of whether previous assumptions on the completeness of the WD sample to a distance of 13 pc were correct. Partly based on observations with the 2.2 m telescope of the German-Spanish Astronomical Centre at Calar Alto, Spain

SPLAT: Using Spectral Indices to Identify and Characterize Ultracool Stars, Brown Dwarfs and Exoplanets in Deep Surveys and as Companions to Nearby Stars

NASA Astrophysics Data System (ADS)

Aganze, Christian; Burgasser, Adam J.; Martin, Eduardo; Konopacky, Quinn; Masters, Daniel C.

2016-06-01

The majority of ultracool dwarf stars and brown dwarfs currently known were identified in wide-field red optical and infrared surveys, enabling measures of the local, typically isolated, population in a relatively shallow (<100 pc radius) volume. Constraining the properties of the wider Galactic population (scale height, radial distribution, Population II sources), and close brown dwarf and exoplanet companions to nearby stars, requires specialized instrumentation, such as high-contrast, coronagraphic spectrometers (e.g., Gemini/GPI, VLT/Sphere, Project 1640); and deep spectral surveys (e.g., HST/WFC3 parallel fields, Euclid). We present a set of quantitative methodologies to identify and robustly characterize sources for these specific populations, based on templates and tools developed as part of the SpeX Prism Library Analysis Toolkit. In particular, we define and characterize specifically-tuned sets spectral indices that optimize selection of cool dwarfs and distinguish rare populations (subdwarfs, young planetary-mass objects) based on low-resolution, limited-wavelength-coverage spectral data; and present a template-matching classification method for these instruments. We apply these techniques to HST/WFC3 parallel fields data in the WISPS and HST-3D programs, where our spectral index set allows high completeness and low contamination for searches of late M, L and T dwarfs to distances out to ~3 kpc.The material presented here is based on work supported by the National Aeronautics and Space Administration under Grant No. NNX15AI75G.

Complete genome sequence and integrated protein localization and interaction map for alfalfa dwarf virus, which combines properties of both cytoplasmic and nuclear plant rhabdoviruses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bejerman, Nicolás, E-mail: n.bejerman@uq.edu.au; Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, St Lucia, QLD 4072; Giolitti, Fabián

Summary: We have determined the full-length 14,491-nucleotide genome sequence of a new plant rhabdovirus, alfalfa dwarf virus (ADV). Seven open reading frames (ORFs) were identified in the antigenomic orientation of the negative-sense, single-stranded viral RNA, in the order 3′-N-P-P3-M-G-P6-L-5′. The ORFs are separated by conserved intergenic regions and the genome coding region is flanked by complementary 3′ leader and 5′ trailer sequences. Phylogenetic analysis of the nucleoprotein amino acid sequence indicated that this alfalfa-infecting rhabdovirus is related to viruses in the genus Cytorhabdovirus. When transiently expressed as GFP fusions in Nicotiana benthamiana leaves, most ADV proteins accumulated in the cellmore » periphery, but unexpectedly P protein was localized exclusively in the nucleus. ADV P protein was shown to have a homotypic, and heterotypic nuclear interactions with N, P3 and M proteins by bimolecular fluorescence complementation. ADV appears unique in that it combines properties of both cytoplasmic and nuclear plant rhabdoviruses. - Highlights: • The complete genome of alfalfa dwarf virus is obtained. • An integrated localization and interaction map for ADV is determined. • ADV has a genome sequence similarity and evolutionary links with cytorhabdoviruses. • ADV protein localization and interaction data show an association with the nucleus. • ADV combines properties of both cytoplasmic and nuclear plant rhabdoviruses.« less

AN EMPIRICAL CALIBRATION TO ESTIMATE COOL DWARF FUNDAMENTAL PARAMETERS FROM H-BAND SPECTRA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Newton, Elisabeth R.; Charbonneau, David; Irwin, Jonathan

Interferometric radius measurements provide a direct probe of the fundamental parameters of M dwarfs. However, interferometry is within reach for only a limited sample of nearby, bright stars. We use interferometrically measured radii, bolometric luminosities, and effective temperatures to develop new empirical calibrations based on low-resolution, near-infrared spectra. We find that H-band Mg and Al spectral features are good tracers of stellar properties, and derive functions that relate effective temperature, radius, and log luminosity to these features. The standard deviations in the residuals of our best fits are, respectively, 73 K, 0.027 R {sub ☉}, and 0.049 dex (an 11% error on luminosity).more » Our calibrations are valid from mid K to mid M dwarf stars, roughly corresponding to temperatures between 3100 and 4800 K. We apply our H-band relationships to M dwarfs targeted by the MEarth transiting planet survey and to the cool Kepler Objects of Interest (KOIs). We present spectral measurements and estimated stellar parameters for these stars. Parallaxes are also available for many of the MEarth targets, allowing us to independently validate our calibrations by demonstrating a clear relationship between our inferred parameters and the stars' absolute K magnitudes. We identify objects with magnitudes that are too bright for their inferred luminosities as candidate multiple systems. We also use our estimated luminosities to address the applicability of near-infrared metallicity calibrations to mid and late M dwarfs. The temperatures we infer for the KOIs agree remarkably well with those from the literature; however, our stellar radii are systematically larger than those presented in previous works that derive radii from model isochrones. This results in a mean planet radius that is 15% larger than one would infer using the stellar properties from recent catalogs. Our results confirm the derived parameters from previous in-depth studies of KOIs 961 (Kepler-42), 254 (Kepler-45), and 571 (Kepler-186), the latter of which hosts a rocky planet orbiting in its star's habitable zone.« less

Cut from the same cloth: The convergent evolution of dwarf morphotypes of the Carex flava group (Cyperaceae) in Circum-Mediterranean mountains

PubMed Central

Benítez-Benítez, Carmen; Fernández-Mazuecos, Mario; Martín-Bravo, Santiago

2017-01-01

Plants growing in high-mountain environments may share common morphological features through convergent evolution resulting from an adaptative response to similar ecological conditions. The Carex flava species complex (sect. Ceratocystis, Cyperaceae) includes four dwarf morphotypes from Circum-Mediterranean mountains whose taxonomic status has remained obscure due to their apparent morphological resemblance. In this study we investigate whether these dwarf mountain morphotypes result from convergent evolution or common ancestry, and whether there are ecological differences promoting differentiation between the dwarf morphotypes and their taxonomically related large, well-developed counterparts. We used phylogenetic analyses of nrDNA (ITS) and ptDNA (rps16 and 5’trnK) sequences, ancestral state reconstruction, multivariate analyses of macro- and micromorphological data, and species distribution modeling. Dwarf morphotype populations were found to belong to three different genetic lineages, and several morphotype shifts from well-developed to dwarf were suggested by ancestral state reconstructions. Distribution modeling supported differences in climatic niche at regional scale between the large forms, mainly from lowland, and the dwarf mountain morphotypes. Our results suggest that dwarf mountain morphotypes within this sedge group are small forms of different lineages that have recurrently adapted to mountain habitats through convergent evolution. PMID:29281689

A system of three transiting super-Earths in a cool dwarf star

NASA Astrophysics Data System (ADS)

Díez Alonso, E.; Suárez& Gómez, S. L.; González Hernández, J. I.; Suárez Mascareño, A.; González Gutiérrez, C.; Velasco, S.; Toledo-Padrón, B.; de Cos Juez, F. J.; Rebolo, R.

2018-05-01

We present the detection of three super-Earths transiting the cool star LP415-17, monitored by K2 mission in its 13th campaign. High-resolution spectra obtained with High Accuracy Radial velocity Planet Searcher-North/Telescopio Nazionale Galileo (HARPS-N/TNG) showed that the star is a mid-late K dwarf. Using spectral synthesis models, we infer its effective temperature, surface gravity, and metallicity, and subsequently determined from evolutionary models a stellar radius of 0.58 R⊙. The planets have radii of 1.8, 2.6, and 1.9 R⊕ and orbital periods of 6.34, 13.85, and 40.72 d. High-resolution images discard any significant contamination by an intervening star in the line of sight. The orbit of the furthest planet has radius of 0.18 au, close to the inner edge of the habitable zone. The system is suitable to improve our understanding of formation and dynamical evolution of super-Earth systems in the rocky-gaseous threshold, their atmospheres, internal structure, composition, and interactions with host stars.

Prominence formation and ejection in cool stars

NASA Astrophysics Data System (ADS)

Villarreal D'Angelo, Carolina; Jardine, Moira; See, Victor

2018-03-01

The observational signatures of prominences have been detected in single and binary G and K type stars for many years now, but recently this has been extended to the M dwarf regime. Prominences carry away both mass and angular momentum when they are ejected and the impact of this mass on any orbiting planets may be important for the evolution of exoplanetary atmospheres. By means of the classification used in the massive star community, that involves knowledge of two parameters (the co-rotation and Alfvén radii, rK and rA), we have determined which cool stars could support prominences. From a model of mechanical support, we have determined that the prominence mass mp/M⋆ = (EM/EG)(r⋆/rK)2F where E_MB_\\star ^2r_\\star ^3 and E_G = GM_\\star ^2/r_\\star are magnetic and gravitational energies and F is a geometric factor. Our calculated masses and ejection frequencies (typically 1016 - 1017 g and 0.4 d, respectively) are consistent with observations and are sufficient to ensure that an exoplanet orbiting in the habitable zone of an M dwarf could suffer frequent impacts.

Activity of the M8 Dwarf TRAPPIST-1

NASA Astrophysics Data System (ADS)

Dmitrienko, E. S.; Savanov, I. S.

2018-06-01

The results of an analysis of observations of the cool (M8) dwarf TRAPPIST-1 obtained on the Kepler Space Telescope (the K2 continuation mission) are presented. TRAPPIST-1 possesses a planetary system containing at least seven planets. In all, the observations consist of 105 584 individual brightness measurements made over a total duration of 79 days. Brightness power spectra computed for TRAPPIST-1 exhibit a peak corresponding to P 0 = 3.296 ± 0.007 d . There are also two peaks with lower significances at P 1 = 2.908 d and P 2 = 2.869 d , which cannot be explained by the presence of differential rotation. The observational material available for TRAPPIST-1 is subdivided into 21 datasets, each covering one stellar rotation period. Each of the individual light curves was used to construct a map of the star's temperature inhomogeneities. On average, the total spotted area of TRAPPIST-1 was S = 5% of the entire visible area. The difference between the angular rotation rates at the equator and at the pole is estimated to be ΔΩ = 0.006. The new results obtained together with data from the literature are used to investigate the properties of this unique star and compare them to the properties of other cool dwarfs. Special attention is paid to the star's evolutionary status (its age). All age estimates for TRAPPIST-1 based on its activity characteristics (rotation, spot coverage, UV and X-ray flux, etc.) indicate that the star is young.

The Solar Neighborhood. XXVII. Discovery of New Proper Motion Stars with μ >= 0farcs18 yr-1 in the Southern Sky with 16.5 < R 59F <= 18.0

NASA Astrophysics Data System (ADS)

Boyd, Mark R.; Henry, Todd J.; Jao, Wei-Chun; Subasavage, John P.; Hambly, Nigel C.

2011-09-01

Here we present 1584 new southern proper motion systems with μ >= 0farcs18 yr-1 and 16.5 > R 59F >= 18.0. This search complements the six previous SuperCOSMOS-RECONS (SCR) proper motion searches of the southern sky for stars within the same proper motion range, but with R 59F <= 16.5. As in previous papers, we present distance estimates for these systems and find that three systems are estimated to be within 25 pc, including one, SCR 1546-5534, possibly within the RECONS 10 pc horizon at 6.7 pc, making it the second nearest discovery of the searches. We find 97 white dwarf candidates with distance estimates between 10 and 120 pc, as well as 557 cool subdwarf candidates. The subdwarfs found in this paper make up nearly half of the subdwarf systems reported from our SCR searches and are significantly redder than those discovered thus far. The SCR searches have now found 155 red dwarfs estimated to be within 25 pc, including 10 within 10 pc. In addition, 143 white dwarf candidates and 1155 cool subdwarf candidates have been discovered. The 1584 systems reported here augment the sample of 4724 systems previously discovered in our SCR searches and imply that additional systems fainter than R 59F = 18.0 are yet to be discovered.

Atmospheric Habitable Zones in Y Dwarf Atmospheres

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yates, Jack S.; Palmer, Paul I.; Biller, Beth

We use a simple organism lifecycle model to explore the viability of an atmospheric habitable zone (AHZ), with temperatures that could support Earth-centric life, which sits above an environment that does not support life. To illustrate our model, we use a cool Y dwarf atmosphere, such as WISE J085510.83–0714442.5, whose 4.5–5.2 μ m spectrum shows absorption features consistent with water vapor and clouds. We allow organisms to adapt to their atmospheric environment (described by temperature, convection, and gravity) by adopting different growth strategies that maximize their chance of survival and proliferation. We assume a constant upward vertical velocity through themore » AHZ. We found that the organism growth strategy is most sensitive to the magnitude of the atmospheric convection. Stronger convection supports the evolution of more massive organisms. For a purely radiative environment, we find that evolved organisms have a mass that is an order of magnitude smaller than terrestrial microbes, thereby defining a dynamical constraint on the dimensions of life that an AHZ can support. Based on a previously defined statistical approach, we infer that there are of the order of 10{sup 9} cool Y brown dwarfs in the Milky Way, and likely a few tens of these objects are within 10 pc from Earth. Our work also has implications for exploring life in the atmospheres of temperate gas giants. Consideration of the habitable volumes in planetary atmospheres significantly increases the volume of habitable space in the galaxy.« less

A Raspberry bushy dwarf virus isolate from Ecuadorean Rubus glaucus contains an additional RNA that is a rearrangement of RNA 2

USDA-ARS?s Scientific Manuscript database

A new Raspberry bushy dwarf virus isolate was found in commercial blackberry (Rubus glaucus) in Azuay, province of Ecuador and named RBDV-Ec-Az. The complete bipartite genome was sequenced using dsRNA as initial template. RNA 1 was 5449 nucleotides (nt) long and the normal RBDV RNA 2 was 2231 nt lon...

An expanded set of brown dwarf and very low mass star models

NASA Technical Reports Server (NTRS)

Burrows, A.; Hubbard, W. B.; Saumon, D.; Lunine, J. I.

1993-01-01

We present in this paper updated and improved theoretical models of brown dwarfs and late M dwarfs. The evolution and characteristics of objects between 0.01 and 0.2 solar mass are exhaustively investigated and special emphasis is placed on their properties at early ages. The dependence on the helium fraction, deuterium fraction, and metallicity of the masses, effective temperature and luminosities at the edge of the hydrogen main sequence are calculated. We derive luminosity functions for representative mass functions and compare our predictions to recent cluster data. We show that there are distinctive features in the theoretical luminosity functions that can serve as diagnostics of brown dwarf physics. A zero-metallicity model is presented as a bound to or approximation of a putative extreme halo population.

Prospecting in Ultracool Dwarfs: Measuring the Metallicities of Mid- and Late-M Dwarfs

NASA Astrophysics Data System (ADS)

Mann, Andrew W.; Deacon, Niall R.; Gaidos, Eric; Ansdell, Megan; Brewer, John M.; Liu, Michael C.; Magnier, Eugene A.; Aller, Kimberly M.

2014-06-01

Metallicity is a fundamental parameter that contributes to the physical characteristics of a star. The low temperatures and complex molecules present in M dwarf atmospheres make it difficult to measure their metallicities using techniques that have been commonly used for Sun-like stars. Although there has been significant progress in developing empirical methods to measure M dwarf metallicities over the last few years, these techniques have been developed primarily for early- to mid-M dwarfs. We present a method to measure the metallicity of mid- to late-M dwarfs from moderate resolution (R ~ 2000) K-band (sime 2.2 μm) spectra. We calibrate our formula using 44 wide binaries containing an F, G, K, or early-M primary of known metallicity and a mid- to late-M dwarf companion. We show that similar features and techniques used for early-M dwarfs are still effective for late-M dwarfs. Our revised calibration is accurate to ~0.07 dex for M4.5-M9.5 dwarfs with -0.58 < [Fe/H] < +0.56 and shows no systematic trends with spectral type, metallicity, or the method used to determine the primary star metallicity. We show that our method gives consistent metallicities for the components of M+M wide binaries. We verify that our new formula works for unresolved binaries by combining spectra of single stars. Lastly, we show that our calibration gives consistent metallicities with the Mann et al. study for overlapping (M4-M5) stars, establishing that the two calibrations can be used in combination to determine metallicities across the entire M dwarf sequence.

HUNTING THE COOLEST DWARFS: METHODS AND EARLY RESULTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schneider, A.; Song, Inseok; Melis, Carl

2011-12-20

We present the methods and first results of a survey of nearby high proper motion main-sequence stars to probe for cool companions with the Gemini camera at Lick Observatory. This survey uses a sample of old (age > 2 Gyr) stars as targets to probe for companions down to temperatures of 500 K. Multi-epoch observations allow us to discriminate comoving companions from background objects. So far, our survey has successfully rediscovered the wide T8.5 companion to GJ 1263 and has discovered a companion to the nearby M0V star GJ 660.1. The companion to GJ 660.1 (GJ 660.1B) is {approx}4 magmore » fainter than its host star in the J-band and is located at a projected separation of {approx}120 AU. Known trigonometric parallax and Two Micron All Sky Survey magnitudes for the GJ 660.1 system indicate a spectral type for the companion of M9 {+-} 2.« less

TRAPPIST-1 Planet Animations

NASA Image and Video Library

2018-02-05

This still from a video shows illustrations of the seven Earth-size planets of TRAPPIST-1, an exoplanet system about 40 light-years away, based on data current as of February 2018. Each planet is shown in sequence, starting with the innermost TRAPPIST-1b and ending with the outermost TRAPPIST-1h. The video presents the planets' relative sizes as well as the relative scale of the central star as seen from each planet. The art highlights possibilities for how the surfaces of these intriguing worlds might look based on their newly calculated properties. The seven planets of TRAPPIST-1 are all Earth-sized and terrestrial. TRAPPIST-1 is an ultra-cool dwarf star in the constellation Aquarius, and its planets orbit very close to it. In the background, slightly distorted versions our familiar constellations, including Orion and Taurus, are shown as they would appear from the location of TRAPPIST-1 (backdrop image courtesy California Academy of Sciences/Dan Tell). An animation is available at https://photojournal.jpl.nasa.gov/catalog/PIA22098

In search of Nemesis

NASA Technical Reports Server (NTRS)

Carlson, S.; Culler, T.; Muller, R. A.; Tetreault, M.; Perlmutter, S.

1994-01-01

The parallax of all stars of visual magnitude greater than about 6.5 has already been measured. If Nemesis is a main-sequence star 1 parsec away, this requires Nemesis's mass to be less than about 0.4 solar masses. If it were less than about 0.05 solar masses its gravity would be too weak to trigger a comet storm. If Nemesis is on the main sequence, this mass range requires it to be a red dwarf. A red dwarf companion would probably have been missed by standard astronomical surveys. Nearby stars are usually found because they are bright or have high proper motion. However, Nemesis's proper motion would now be 0.01 arcsec/yr, and if it is a red dwarf its magnitude is about 10 - too dim to attract attention. Unfortunately, standard four-color photometry does not distinguish between red dwarfs and giants. So although surveys such as the Dearborn Red Star Catalog list stars by magnitude and spectral type, they do not identify the dwarfs. Every star of the correct spectral type and magnitude must be scrutinized. Our candidate list is a hybrid; candidate red stars are identified in the astrometrically poor Dearborn Red Star Catalog and their positions are corrected using the Hubble Guide Star Catalog. When errors in the Dearborn catalog make it impossible to identify the corresponding Hubble star, the fields are split so that we have one centering on each possible candidate. We are currently scrutinizing 3098 fields, which we believe contain all possible red dwarf candidates in the northern hemisphere. Since our last report the analysis and database software has been completely rebuilt to take advantage of updated hardware, to make the data more accessible, and to implement improved methods of data analysis. The software is now completed and we are eliminating stars every clear night.

The WFCAM Transit Survey: A Search for Rocky Planets Around Cool Stars

NASA Astrophysics Data System (ADS)

Birkby, J.; Hodgkin, S.; Pinfield, D.; WTS Consortium

2011-12-01

We report on the WFCAM Transit Survey which is a near-infrared photometric monitoring campaign designed primarily to test the predictions of planet formation theory. We monitor a statisically significant sample of ˜6,000 M-dwarfs (M<0.6M⊙) across 6 sq. deg of the sky, by taking advantage of the highly-efficient queue-scheduled operational mode of the 3.8m United Kingdom Infrared Telescope. Our light curves have RMS < 1% between 13 < J < 16 magnitudes and preliminary simulations indicate the survey is sensitive to at least Jupiter-like transits of M-dwarfs. The survey is approximately 25% complete and within this dataset we find i) no planet-like transit events, despite thorough and extensive follow-up this summer and ii) 32 new M-dwarf eclipsing binaries. We do not speculate on the planet fraction of M-dwarfs at this incomplete stage of our survey, but once we achieve 1,000 epochs of observation on our entire M-dwarf sample, we will have a significant observational constraint to place on occurrence of planets around M-dwarfs. We report masses and radii for three of our newly discovered eclipsing binary, with errors of 3-7%, which all show inflated radii when compared to stellar evolution models (e.g. Baraffe et al. (1998)). Our results support the growing body of observations with inflated M-dwarf radii, which may be caused by increased magnetic activity inhibiting the convection efficiency or increased star spot coverage (e.g. Chabrier et al. (2007); Jackson et al. (2009)). Finally, we present preliminary mass and radius estimates of a fourth new eclipsing binary, which is one of the lowest mass binary systems ever discovered and will provide a calibrating point in the desert of observations between 0.1-0.2M⊙.

THE CENTRAL SLOPE OF DARK MATTER CORES IN DWARF GALAXIES: SIMULATIONS VERSUS THINGS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oh, Se-Heon; De Blok, W. J. G.; Brook, Chris

2011-07-15

We make a direct comparison of the derived dark matter (DM) distributions between hydrodynamical simulations of dwarf galaxies assuming a {Lambda}CDM cosmology and the observed dwarf galaxies sample from the THINGS survey in terms of (1) the rotation curve shape and (2) the logarithmic inner density slope {alpha} of mass density profiles. The simulations, which include the effect of baryonic feedback processes, such as gas cooling, star formation, cosmic UV background heating, and most importantly, physically motivated gas outflows driven by supernovae, form bulgeless galaxies with DM cores. We show that the stellar and baryonic mass is similar to thatmore » inferred from photometric and kinematic methods for galaxies of similar circular velocity. Analyzing the simulations in exactly the same way as the observational sample allows us to address directly the so-called cusp/core problem in the {Lambda}CDM model. We show that the rotation curves of the simulated dwarf galaxies rise less steeply than cold dark matter rotation curves and are consistent with those of the THINGS dwarf galaxies. The mean value of the logarithmic inner density slopes {alpha} of the simulated galaxies' DM density profiles is {approx}-0.4 {+-} 0.1, which shows good agreement with {alpha} = -0.29 {+-} 0.07 of the THINGS dwarf galaxies. The effect of non-circular motions is not significant enough to affect the results. This confirms that the baryonic feedback processes included in the simulations are efficiently able to make the initial cusps with {alpha} {approx}-1.0 to -1.5 predicted by DM-only simulations shallower and induce DM halos with a central mass distribution similar to that observed in nearby dwarf galaxies.« less

The Chromospheric Activity and Ages of M Dwarf Stars in Wide Binary Systems

NASA Astrophysics Data System (ADS)

Silvestri, Nicole M.; Hawley, Suzanne L.; Oswalt, Terry D.

2005-05-01

We investigate the relationship between age and chromospheric activity for 139 M dwarf stars in wide binary systems with white dwarf companions. The age of each system is determined from the cooling age of its white dwarf component. The current limit for activity-age relations found for M dwarfs in open clusters is 4 Gyr. Our unique approach to finding ages for M stars allows for the exploration of this relationship at ages older than 4 Gyr. The general trend of stars remaining active for a longer time at a later spectral type is confirmed. However, our larger sample and greater age range reveal additional complexity in assigning age based on activity alone. We find that M dwarfs in wide binaries older than 4 Gyr depart from the loglinear relation for clusters and are found to have activity at magnitudes, colors, and masses that are brighter, bluer, and more massive than predicted by the cluster relation. In addition to our activity-age results, we present the measured radial velocities and complete space motions for 161 white dwarf stars in wide binaries. Based on observations obtained with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium; the Cerro Tololo Inter-American Observatory 4.0 m telescope, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under a cooperative agreement with the National Science Foundation (NSF) as part of the National Optical Astronomy Observatory (NOAO), which also operates Kitt Peak National Observatory in Tucson, Arizona; and the SARA Observatory 0.9 m telescope at Kitt Peak, which is owned and operated by the Southeastern Association for Research in Astronomy (http://www.saraobservatory.org).

Do all barium stars have a white dwarf companion?

NASA Technical Reports Server (NTRS)

Dominy, J. F.; Lambert, D. L.

1983-01-01

International Ultraviolet Explorer short-wavelength, low-dispersion spectra were analyzed for four barium, two mild barium, and one R-type carbon star in order to test the hypothesis that the barium and related giants are produced by mass transfer from a companion now present as a white dwarf. An earlier tentative identification of a white dwarf companion to the mild barium star Zeta Cyg is confirmed. For the other stars, no ultraviolet excess attributable to a white dwarf is seen. Limits are set on the bolometric magnitude and age of a possible white dwarf companion. Since the barium stars do not have obvious progenitors among main-sequence and subgiant stars, mass transfer must be presumed to occur when the mass-gaining star is already on the giant branch. This restriction, and the white dwarf's minimum age, which is greater than 8 x 10 to the 8th yr, determined for several stars, effectively eliminates the hypothesis that mass transfer from an asymptotic giant branch star creates a barium star. Speculations are presented on alternative methods of producing a barium star in a binary system.

A novel hypothyroid dwarfism due to the missense mutation Arg479Cys of the thyroid peroxidase gene in the mouse.

PubMed

Takabayashi, Shuji; Umeki, Kazumi; Yamamoto, Etsuko; Suzuki, Tohru; Okayama, Akihiko; Katoh, Hideki

2006-10-01

Recently, we found a novel dwarf mutation in an ICR closed colony. This mutation was governed by a single autosomal recessive gene. In novel dwarf mice, plasma levels of the thyroid hormones, T3 and T4, were reduced; however, TSH was elevated. Their thyroid glands showed a diffuse goiter exhibiting colloid deficiency and abnormal follicle epithelium. The dwarfism was improved by adding thyroid hormone in the diet. Gene mapping revealed that the dwarf mutation was closely linked to the thyroid peroxidase (Tpo) gene on chromosome 12. Sequencing of the Tpo gene of the dwarf mice demonstrated a C to T substitution at position 1508 causing an amino acid change from arginine (Arg) to cysteine (Cys) at codon 479 (Arg479Cys). Western blotting revealed that TPO protein of the dwarf mice was detected in a microsomal fraction of thyroid tissue, but peroxidase activity was not detected. These findings suggested that the dwarf mutation caused a primary congenital hypothyroidism by TPO deficiency, resulting in a defect of thyroid hormone synthesis.

The ultracool dwarf DENIS-P J104814.7-395606. Chromospheres and coronae at the low-mass end of the main-sequence

NASA Astrophysics Data System (ADS)

Stelzer, B.; Alcalá, J.; Biazzo, K.; Ercolano, B.; Crespo-Chacón, I.; López-Santiago, J.; Martínez-Arnáiz, R.; Schmitt, J. H. M. M.; Rigliaco, E.; Leone, F.; Cupani, G.

2012-01-01

Context. Several diagnostics ranging from the radio to the X-ray band are suitable for investigating the magnetic activity of late-type stars. Empirical connections between the emission at different wavelengths place constraints on the nature and efficiency of the emission mechanism and the physical conditions in different atmospheric layers. The activity of ultracool dwarfs, at the low-mass end of the main-sequence, is poorly understood. Aims: We perform a multi-wavelength study of one of the nearest M9 dwarfs, DENIS-P J104814.7-395606 (4 pc), to examine its position within the group of magnetically active ultracool dwarfs, and, in general, advance our understanding of these objects by comparing them to early-M type dwarf stars and the Sun. Methods: We obtained an XMM-Newton observation of DENIS-P J104814.7-395606 and a broad-band spectrum from the ultraviolet to the near-infrared with X-Shooter. From this dataset, we derive the X-ray properties, stellar parameters, kinematics, and the emission-line spectrum tracing chromospheric activity. We integrate these data by compiling the activity parameters of ultracool dwarfs from the literature. Results: Our deep XMM-Newton observation provides the first X-ray detection of DENIS-P J104814.7-395606 (log Lx = 25.1), as well as the first measurement of its V band brightness (V = 17.35 mag). The flux-flux relations between X-ray and chromospheric activity indicators are here for the first time extended into the regime of the ultracool dwarfs. The approximate agreement of DENIS-P J104814.7-395606 and other ultracool dwarfs with flux-flux relations for early-M dwarfs suggests that the same heating mechanisms work in the atmospheres of ultracool dwarfs, albeit weaker as judged from their lower fluxes. The observed Balmer decrements of DENIS 1048-3956 are compatible with optically thick plasma in local thermal equilibrium (LTE) at low, nearly photospheric temperature or optically thin LTE plasma at 20 000 K. Describing the decrements with case B recombination requires different emitting regions for Hα and the higher Balmer lines. The high observed Hα/Hβ flux ratio is also poorly fitted by the optically thin models. We derive a similarly high value for the Hα/Hβ ratio of vB 10 and LHS 2065 and conclude that this may be a characteristic of ultracool dwarfs. We add DENIS-P J104814.7-395606 to the list of ultracool dwarfs detected in both the radio and the X-ray band. The Benz-Güdel relation between radio and X-ray luminosity of late-type stars is well-known to be violated by ultracool dwarfs. We speculate on the presence of two types of ultracool dwarfs with distinct radio and X-ray behaviors.

Age of Local Galactic Disk from the Wdlf for Cpmbs

NASA Astrophysics Data System (ADS)

Smith, J. Allyn; Oswalt, Terry D.; Wood, Matt A.; Silvestri, Nicole M.

We present the white dwarf luminosity function (WDLF) for common proper motion systems. This WDLF was derived using the 1/Vmax method pioneered by Schmidt (1975) and detailed by Liebert Dahn and Monet (1988). New cooling models were used to determine the luminosities of the white dwarfs and the age of the local Galactic disk. Comparison to WDLFs developed using older colling models (Wood 1995) will be examined for changes in the derived disk age. Kinematic data is available for a subset of the WDs in the sample. Separate luminosity functions will be examined for each of the statistically significant subsets. JAS acknowledges support from NASA GSRP Fellowship NGT-51086.

IUE observations of the M dwarfs CM Draconis and Rossiter 137 B - Magnetic activity at saturated levels

NASA Technical Reports Server (NTRS)

Vilhu, O.; Brandenburg, A.; Ambruster, C. W.; Neff, J. E.; Linsky, J. L.

1989-01-01

IUE observations of two active M dwarfs with known rotation rate or age and presumed to be almost totally convective are presented. The first of these stars, CM Draconis (Gl 630.1), is an old Population II binary with its components in tidally induced rapid rotation (P = 1.27 d, dM 4 + dM 4). The other one, Rossiter 137 B, forms with HD 36705 (AB Dor) a visual pair of young active stars. The activity of CM Dra is due to the forced rotation in a close binary, while Rst 137 B is assumed to rotate fast enough to generate its magnetica activity. These results are compared with those for M dwarfs, particularly AU Mic and YZ CMi, that have known rotational periods and measured ultraviolet emission line fluxes. The chromospheric-coronal saturation levels of cool dwarfs between 0.3 less than B-V less than 1.6 is determined. It is found that saturated F stars have stronger chromospheres than saturated M stars, but the opposite is true for the corona. Results of these observations seem to favor a rotation-dependent distributed dynamo generating magnetic flux in totally convective stars.

Hydrodynamic models for novae with ejecta rich in oxygen, neon and magnesium

NASA Technical Reports Server (NTRS)

Starrfield, S.; Sparks, W. M.; Truran, J. W.

1985-01-01

The characteristics of a new class of novae are identified and explained. This class consists of those objects that have been observed to eject material rich in oxygen, neon, magnesium, and aluminum at high velocities. We propose that for this class of novae the outburst is occurring not on a carbon-oxygen white dwarf but on an oxygen-neon-magnesium white dwarf which has evolved from a star which had a main sequence mass of approx. 8 solar masses to approx. 12 solar masses. An outburst was simulated by evolving 1.25 solar mass white dwarfs accreting hydrogen rich material at various rates. The effective enrichment of the envelope by ONeMg material from the core is simulated by enhancing oxygen in the accreted layers. The resulting evolutionary sequences can eject the entire accreted envelope plus core material at high velocities. They can also become super-Eddington at maximum bolometric luminosity. The expected frequency of such events (approx. 1/4) is in good agreement with the observed numbers of these novae.

The interacting binary white dwarf systems

NASA Astrophysics Data System (ADS)

Provencal, Judith Lucille

1994-01-01

Interacting binary white dwarfs are believed to contain two white dwarfs of extreme mass ratio, one of which is filling its Roche Lobe, transferring material to its companion via an accretion disk. The defining characteristic of an IBWD is the nondetection of hydrogen in the system. IBWD's represent the culmination of binary star evolution. In this final death dance, two degenerate objects are entangled, the massive white dwarf tidally stripping and devouring its helpless companion's outer layers. Because a white dwarf expands as it loses mass, the end result of this process is the complete absorption of one star by the other . My goal in the examination of these systems is to understand their photometric behavior and determine the best model of these objects. The IBWD's represent the endpoint of binary evolution. Knowledge of the physical properties of these objects will provide constraints on theories of binary evolution, white dwarf formation, the thermal and physical structure of accreting white dwarfs, and nucleosynthesis. To achieve this goal, I have analyzed the most comprehensive high speed photometric data sets available on 5 of the 6 known objects: AM CVn, PG1346+082, CP Eri, V803 Cen, and G61-29. AM CVn and PG1346+0S2 were targets of the Whole Earth Telescope in 1988 and 1990 respectively. We find a range of variation timescales, from minutes to days, and a range of physical behaviour. Most importantly, we measure a rate of period change of P = 1.68 +/- 0.03 x 10-11s/s for the dominant variation in AM CVn. We also find the differences in behavior can be attributed to a difference in mass transfer rate that may be evolutionary in origin. Finally, I discuss in detail the observational characteristics of each object, and overall properties of the IBWD family. In conclusion, I discuss past and future history of these objects, and touch on their possible influence on our knowledge of white dwarf evolution and formation. The IBWD's are possible progenitors of helium white dwarfs. If this hypothesis is correct, these systems represent a second entry point onto the white dwarf cooling curve.

Hypothetical Rejuvenated Planets Artist Concept

NASA Image and Video Library

2015-06-25

This artist's concept shows a hypothetical "rejuvenated" planet -- a gas giant that has reclaimed its youthful infrared glow. NASA's Spitzer Space Telescope found tentative evidence for one such planet around a dead star, or white dwarf, called PG 0010+280 (depicted as white dot in illustration). When planets are young, they are warm and toasty due to internal heat left over from their formation. Planets cool over time -- until they are possibly rejuvenated. The theory goes that this Jupiter-like planet, which orbits far from its star, would accumulate some of the material sloughed off by its star as the star was dying. The material would cause the planet to swell in mass. As the material fell onto the planet, it would heat up due to friction and glow with infrared light. The final result would be an old planet, billions of years in age, radiating infrared light as it did in its youth. Spitzer detected an excess infrared light around the white dwarf PG 0010+280. Astronomers aren't sure where the light is coming from, but one possibility is a rejuvenated planet. Future observations may help solve the mystery. A Jupiter-like planet is about ten times the size of a white dwarf. White dwarfs are about the size of Earth, so one white dwarf would easily fit into the Great Red Spot on Jupiter! http://photojournal.jpl.nasa.gov/catalog/PIA19346

The 25 parsec local white dwarf population

NASA Astrophysics Data System (ADS)

Holberg, J. B.; Oswalt, T. D.; Sion, E. M.; McCook, G. P.

2016-11-01

We have extended our detailed survey of the local white dwarf population from 20 to 25 pc, effectively doubling the sample volume, which now includes 232 stars. In the process, new stars within 20 pc have been added, a more uniform set of distance estimates as well as improved spectral and binary classifications are available. The present 25 pc sample is estimated to be about 68 per cent complete (the corresponding 20 pc sample is now 86 per cent complete). The space density of white dwarfs is unchanged at 4.8 ± 0.5 × 10-3 pc-3. This new study includes a white dwarf mass distribution and luminosity function based on the 232 stars in the 25 pc sample. We find a significant excess of single stars over systems containing one or more companions (74 per cent versus 26 per cent). This suggests mechanisms that result in the loss of companions during binary system evolution. In addition, this updated sample exhibits a pronounced deficiency of nearby `Sirius-like' systems. 11 such systems were found within the 20 pc volume versus only one additional system found in the volume between 20 and 25 pc. An estimate of white dwarf birth rates during the last ˜8 Gyr is derived from individual remnant cooling ages. A discussion of likely ways new members of the local sample may be found is provided.

Faint blue galaxies revisited

NASA Astrophysics Data System (ADS)

Ferguson, Henry C.

If dwarf-elliptical galaxies formed their stars very rapdily (on timescales of less than 1 Gyr), they may in principle be detectable out to high redshift. Prior to the discovery of cosmic acceleration, it appeared that rapid and late formation dwarf elliptical galaxies might be required to explain the number counts of faint galaxies. A plausible hypothesis emerged: that photoionization by the UV background prevents gas cooling in low-mass halos until z ≲ 1.5. The discovery of cosmic acceleration eased the tension between predicted galaxy number counts and galaxy-evolution models. Nevertheless, there is some evidence for relatively late star formation in nearby dE's, and the photoionization delay mechanism still appears to have some merit. It is thus of interest to look back in time to see if we can find starbursting dwarf galaxies at moderate redshift. We review the connection between faint-blue galaxies and bursting-dwarf galaxies and discuss some attempts to identify progenitors to dE galaxies in the Hubble Ultra Deep Field (HUDF) observations. We find roughly 85 galaxies in the HUDF with redshifts 0.6 that appear to have formed most of their stars at z. Of these, 70% have half-light radii less than 1.5 kpc. These are thus "smoking gun" candidates for dwarf galaxies that are either collapsing for the first time at moderate redshifts or have otherwise been unable to form stars for more than 1/3 of a Hubble time.

SPIRou Input Catalogue: global properties of 440 M dwarfs observed with ESPaDOnS at CFHT

NASA Astrophysics Data System (ADS)

Fouqué, Pascal; Moutou, Claire; Malo, Lison; Martioli, Eder; Lim, Olivia; Rajpurohit, Arvind; Artigau, Etienne; Delfosse, Xavier; Donati, Jean-François; Forveille, Thierry; Morin, Julien; Allard, France; Delage, Raphaël; Doyon, René; Hébrard, Elodie; Neves, Vasco

2018-04-01

Present and future high-precision radial-velocity spectrometers dedicated to the discovery of low-mass planets orbiting low-mass dwarfs need to focus on the best selected stars to make an efficient use of telescope time. In the framework of the preparation of the SPIRou Input Catalogue (SPIC), the CoolSnap program aims at screening M dwarfs in the solar neighbourhood against binarity, rapid rotation, activity, etc. To optimize the selection, this paper describes the methods used to compute effective temperature, metallicity, projected rotation velocity of a large sample of 440 M dwarfs observed in the visible with the high-resolution spectropolarimeter Echelle SpectroPolArimetric Device for the ObservatioN of Stars (ESPaDOnS) at Canada-France-Hawaii Telescope. It also summarizes known and newly discovered spectroscopic binaries, and stars known to belong to visual multiple systems. A calibration of the projected rotation velocity versus measured line widths for M dwarfs observed by the ESPaDOnS spectropolarimeter is derived, and the resulting values are compared to equatorial rotation velocities deduced from rotation periods and radii. A comparison of the derived effective temperatures and metallicities with literature values is also conducted. Finally, the radial-velocity uncertainty of each star in the sample is estimated, to narrow down the selection of stars to be included into the SPIC.

Does the 43 bp sequence from an 800,000 year old cretan dwarf elephantid really rewrite the textbook on mammoths?

PubMed

Orlando, Ludovic; Pagés, Marie; Calvignac, Sébastien; Hughes, Sandrine; Hänni, Catherine

2007-02-22

Pigmy elephants inhabited the islands from the Mediterranean region during the Pleistocene period but became extinct in the course of the Holocene. Despite striking distinctive anatomical characteristics related to insularity, some similarities with the lineage of extant Asian elephants have suggested that pigmy elephants could be most probably seen as members of the genus Elephas. Poulakakis et al (2006) have recently challenged this view by recovering a short mtDNA sequence from an 800 000 year old fossil of the Cretan pigmy elephant (Elephas creticus). According to the authors of this study, a deep taxonomic revision of Cretan dwarf elephants would be needed, as the sequence exhibits clear affinities with woolly mammoth haplotypes. However, we point here many aspects that seriously weaken the strength of the ancient DNA evidence reported.

Spectral comparison of directly imaged, young substellar companions using integral field spectroscopy - construction of an empiric log g sequence

NASA Astrophysics Data System (ADS)

Schmidt, T.; Neuhaüser, R.; Seifahrt, A.

2010-10-01

About 15 substellar companions with large separations (>∼50 AU) to their young primary stars and brown dwarfs are confirmed by both common proper motion and late-M / early-L type spectra. The origin and early evolution of these objects is still under debate. While often these substellar companions are regarded as brown dwarfs, they could possibly also be massive planets, the mass estimates are very uncertain so far. They are companions to primary stars or brown dwarfs in young associations and star forming regions like the TW Hya association, Upper Scorpius, Taurus, Beta Pic moving group, TucHor association, Lupus, Ophiuchus, and Chamaeleon, hence their ages and distances are well known, in contrast to free-floating brown dwarfs. An empirical classification is not possible, because a spectral sequence that is taking the lower gravity into account, is not existing. This problem leads to an apparent mismatch between spectra of old field type objects and young low-mass companions at the same effective temperature, hampering a determination of temperature and surface gravity independent from models. Now that about 15 such substellar candidates are found in associations of different ages, 1 - 35 Myrs, it is possible to study their spectra in comparison to each other using the advantage of light concentration by an adaptive optics system with their primary as guide star. Therefore we have begun the construction of an empirical log g sequence from beginning to observe all these substellar companions homogeneously using the AO-assisted integral field spectrograph SINFONI at VLT (ESO).

Mapping a disordered portion of the Brz2001-binding site on a plant monooxygenase, DWARF4, using a quartz-crystal microbalance biosensor-based T7 phage display.

PubMed

Takakusagi, Yoichi; Manita, Daisuke; Kusayanagi, Tomoe; Izaguirre-Carbonell, Jesus; Takakusagi, Kaori; Kuramochi, Kouji; Iwabata, Kazuki; Kanai, Yoshihiro; Sakaguchi, Kengo; Sugawara, Fumio

2013-04-01

In small-molecule/protein interaction studies, technical difficulties such as low solubility of small molecules or low abundance of protein samples often restrict the progress of research. Here, we describe a quartz-crystal microbalance (QCM) biosensor-based T7 phage display in combination use with a receptor-ligand contacts (RELIC) bioinformatics server for application in a plant Brz2001/DWARF4 system. Brz2001 is a brassinosteroid biosynthesis inhibitor in the less-soluble triazole series of compounds that targets DWARF4, a cytochrome P450 (Cyp450) monooxygenase containing heme and iron. Using a Brz2001 derivative that has higher solubility in 70% EtOH and forms a self-assembled monolayer on gold electrode, we selected 34 Brz2001-recognizing peptides from a 15-mer T7 phage-displayed random peptide library using a total of four sets of one-cycle biopanning. The RELIC/MOTIF program revealed continuous and discontinuous short motifs conserved within the 34 Brz2001-selected 15-mer peptide sequences, indicating the increase of information content for Brz2001 recognition. Furthermore, an analysis of similarity between the 34 peptides and the amino-acid sequence of DWARF4 using the RELIC/MATCH program generated a similarity plot and a cluster diagram of the amino-acid sequence. Both of these data highlighted an internally located disordered portion of a catalytic site on DWARF4, indicating that this portion is essential for Brz2001 recognition. A similar trend was also noted by an analysis using another 26 Brz2001-selected peptides, and not observed using the 27 gold electrode-recognizing control peptides, demonstrating the reproducibility and specificity of this method. Thus, this affinity-based strategy enables high-throughput detection of the small-molecule-recognizing portion on the target protein, which overcomes technical difficulties such as sample solubility or preparation that occur when conventional methods are used.

Did A Planet Survive A Post-Main Sequence Evolutionary Event?

NASA Astrophysics Data System (ADS)

Sorber, Rebecca; Jang-Condell, Hannah; Zimmerman, Mara

2018-06-01

The GL86 is star system approximately 10 pc away with a main sequence K- type ~ 0.77 M⊙ star (GL 86A) with a white dwarf ~0.49 M⊙ companion (GL86 B). The system has a ~ 18.4 AU semi-major axis, an orbital period of ~353 yrs, and an eccentricity of ~ 0.39. A 4.5 MJ planet orbits the main sequence star with a semi-major axis of 0.113 AU, an orbital period of 15.76 days, in a near circular orbit with an eccentricity of 0.046. If we assume that this planet was formed during the time when the white dwarf was a main sequence star, it would be difficult for the planet to have remained in a stable orbit during the post-main sequence evolution of GL86 B. The post-main sequence evolution with planet survival will be examined by modeling using the program Mercury (Chambers 1999). Using the model, we examine the origins of the planet: whether it formed before or after the post-main sequence evolution of GL86B. The modeling will give us insight into the dynamical evolution of, not only, the binary star system, but also the planet’s life cycle.

Supernova SN 2011fe from an exploding carbon-oxygen white dwarf star.

PubMed

Nugent, Peter E; Sullivan, Mark; Cenko, S Bradley; Thomas, Rollin C; Kasen, Daniel; Howell, D Andrew; Bersier, David; Bloom, Joshua S; Kulkarni, S R; Kandrashoff, Michael T; Filippenko, Alexei V; Silverman, Jeffrey M; Marcy, Geoffrey W; Howard, Andrew W; Isaacson, Howard T; Maguire, Kate; Suzuki, Nao; Tarlton, James E; Pan, Yen-Chen; Bildsten, Lars; Fulton, Benjamin J; Parrent, Jerod T; Sand, David; Podsiadlowski, Philipp; Bianco, Federica B; Dilday, Benjamin; Graham, Melissa L; Lyman, Joe; James, Phil; Kasliwal, Mansi M; Law, Nicholas M; Quimby, Robert M; Hook, Isobel M; Walker, Emma S; Mazzali, Paolo; Pian, Elena; Ofek, Eran O; Gal-Yam, Avishay; Poznanski, Dovi

2011-12-14

Type Ia supernovae have been used empirically as 'standard candles' to demonstrate the acceleration of the expansion of the Universe even though fundamental details, such as the nature of their progenitor systems and how the stars explode, remain a mystery. There is consensus that a white dwarf star explodes after accreting matter in a binary system, but the secondary body could be anything from a main-sequence star to a red giant, or even another white dwarf. This uncertainty stems from the fact that no recent type Ia supernova has been discovered close enough to Earth to detect the stars before explosion. Here we report early observations of supernova SN 2011fe in the galaxy M101 at a distance from Earth of 6.4 megaparsecs. We find that the exploding star was probably a carbon-oxygen white dwarf, and from the lack of an early shock we conclude that the companion was probably a main-sequence star. Early spectroscopy shows high-velocity oxygen that slows rapidly, on a timescale of hours, and extensive mixing of newly synthesized intermediate-mass elements in the outermost layers of the supernova. A companion paper uses pre-explosion images to rule out luminous red giants and most helium stars as companions to the progenitor.

Seek a Minor Sun: The Distribution of Habitable Planets in the Hertzsprung-Russell-Rosenberg Diagram

NASA Astrophysics Data System (ADS)

Gaidos, Eric

2015-07-01

The Sun-Earth systems has long been used as a template to understand habitable planets around other stars and to develop missions to seek them. However, two decades of exoplanet studies have shown that many, if not most planetary systems around G dwarf stars do not resemble the Solar System. Moreover, an objective census of our Galaxy might ignore solar- type stars and focus on M dwarfs, which constitute some 80% of all stars in the neighborhood. Recent work has shown that M dwarfs have more close-in planets than solar-type stars, and perhaps more planets in the "habitable zone" defined by stellar irradiation. M dwarfs also burn hydrogen over a vastly longer time; slow evolution on the main sequence means a planet can remain habitable for much longer, providing a more permissive environment for the evo- lution of life and intelligence. If M dwarfs are such compelling locales to look for life, why are we ourselves not orbiting a red Sun?

Effects of Main-Sequence Mass Loss on Stellar and Galactic Chemical Evolution.

NASA Astrophysics Data System (ADS)

Guzik, Joyce Ann

1988-06-01

L. A. Willson, G. H. Bowen and C. Struck -Marcell have proposed that 1 to 3 solar mass stars may experience evolutionarily significant mass loss during the early part of their main-sequence phase. The suggested mass-loss mechanism is pulsation, facilitated by rapid rotation. Initial mass-loss rates may be as large as several times 10^{-9}M o/yr, diminishing over several times 10^8 years. We attempted to test this hypothesis by comparing some theoretical implications with observations. Three areas are addressed: Solar models, cluster HR diagrams, and galactic chemical evolution. Mass-losing solar models were evolved that match the Sun's luminosity and radius at its present age. The most extreme viable models have initial mass 2.0 M o, and mass-loss rates decreasing exponentially over 2-3 times 10^8 years. Compared to a constant -mass model, these models require a reduced initial ^4He abundance, have deeper envelope convection zones and higher ^8B neutrino fluxes. Early processing of present surface layers at higher interior temperatures increases the surface ^3He abundance, destroys Li, Be and B, and decreases the surface C/N ratio following first dredge-up. Evolution calculations incorporating main-sequence mass loss were completed for a grid of models with initial masses 1.25 to 2.0 Mo and mass loss timescales 0.2 to 2.0 Gyr. Cluster HR diagrams synthesized with these models confirm the potential for the hypothesis to explain observed spreads or bifurcations in the upper main sequence, blue stragglers, anomalous giants, and poor fits of main-sequence turnoffs by standard isochrones. Simple closed galactic chemical evolution models were used to test the effects of main-sequence mass loss on the F and G dwarf distribution. Stars between 3.0 M o and a metallicity -dependent lower mass are assumed to lose mass. The models produce a 30 to 60% increase in the stars to stars-plus -remnants ratio, with fewer early-F dwarfs and many more late-F dwarfs remaining on the main sequence to the present. The ratio of stars to stellar remnants and the white dwarf age distribution may prove valuable in distinguishing between explanations for the observed bimodal present-day stellar mass function.

Observing exoplanet populations with high-precision astrometry

NASA Astrophysics Data System (ADS)

Sahlmann, Johannes

2012-06-01

This thesis deals with the application of the astrometry technique, consisting in measuring the position of a star in the plane of the sky, for the discovery and characterisation of extra-solar planets. It is feasible only with a very high measurement precision, which motivates the use of space observatories, the development of new ground-based astronomical instrumentation and of innovative data analysis methods: The study of Sun-like stars with substellar companions using CORALIE radial velocities and HIPPARCOS astrometry leads to the determination of the frequency of close brown dwarf companions and to the discovery of a dividing line between massive planets and brown dwarf companions; An observation campaign employing optical imaging with a very large telescope demonstrates sufficient astrometric precision to detect planets around ultra-cool dwarf stars and the first results of the survey are presented; Finally, the design and initial astrometric performance of PRIMA, ! a new dual-feed near-infrared interferometric observing facility for relative astrometry is presented.

The CI pressure shift and gravitational redshift of the cool DBQA5 white dwarf LDS678A

NASA Technical Reports Server (NTRS)

Sion, E. M.; Vauclair, G.; Oswalt, T. D.; Hammond, G.; Liebert, J.; Koester, D.; Wegner, G.; Marcum, P.

1990-01-01

A high resolution ultraviolet spectrum of the helium rich degenerate LDS 678A, obtained with the International Ultraviolet Explorer (IUE) satellite is presented. LDS 678A is the coolest metallic line generate (DQ or DZ) yet observed with the IUE scale. These observations provide a detailed line profile of the strong C I 2479 absorption line with equivalent width (W sub 2479 = 2.35 plus or minus 0.06 angstroms) from which theoretical line profile fits yield a C abundance (log C/He = 6.4). The presence of carbon in a helium rich atmosphere lends credence to the notion that LDS 678A is a transitional case between the DB white dwarfs with nearly pure helium atmospheres and the helium rich DQ white dwarfs which exhibit carbon bands. Corrected for an inferred pressure shift for the C I line, a gravitational redshift is deduced from which a most probable mass of 0.55 solar mass is derived.

HUBBLE SPACE TELESCOPE AND GROUND-BASED OBSERVATIONS OF V455 ANDROMEDAE POST-OUTBURST

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szkody, Paula; Mukadam, Anjum S.; Brown, Justin

2013-09-20

Hubble Space Telescope spectra obtained in 2010 and 2011, 3 and 4 yr after the large amplitude dwarf nova outburst of V455 And, were combined with optical photometry and spectra to study the cooling of the white dwarf, its spin, and possible pulsation periods after the outburst. The modeling of the ultraviolet (UV) spectra shows that the white dwarf temperature remains ∼600 K hotter than its quiescent value at 3 yr post-outburst, and still a few hundred degrees hotter at 4 yr post-outburst. The white dwarf spin at 67.6 s and its second harmonic at 33.8 s are visible inmore » the optical within a month of outburst and are obvious in the later UV observations in the shortest wavelength continuum and the UV emission lines, indicating an origin in high-temperature regions near the accretion curtains. The UV light curves folded on the spin period show a double-humped modulation consistent with two-pole accretion. The optical photometry 2 yr after outburst shows a group of frequencies present at shorter periods (250-263 s) than the periods ascribed to pulsation at quiescence, and these gradually shift toward the quiescent frequencies (300-360 s) as time progresses past outburst. The most surprising result is that the frequencies near this period in the UV data are only prominent in the emission lines, not the UV continuum, implying an origin away from the white dwarf photosphere. Thus, the connection of this group of periods with non-radial pulsations of the white dwarf remains elusive.« less

Spitzer Photometry of WISE-Selected Brown Dwarf and Hyper-Lumninous Infrared Galaxy Candidates

NASA Technical Reports Server (NTRS)

Griffith, Roger L.; Kirkpatrick, J. Davy; Eisenhardt, Peter R. M.; Gelino, Christopher R.; Cushing, Michael C.; Benford, Dominic; Blain, Andrew; Bridge, Carrie R.; Cohen, Martin; Cutri, Roc M.;

Slowly Spinning Southern M Dwarfs

NASA Astrophysics Data System (ADS)

Newton, Elisabeth; Mondrik, Nicholas; Irwin, Jonathan; Charbonneau, David

2018-01-01

M dwarf stars are the most common type of star in the galaxy, but their ages are challenging to determine due to their trillion-year lifetimes on the main sequence. Consequently, the evolution of rotation and magnetism at field ages is difficult to investigate observationally. M dwarfs in the Solar Neighborhood provide a unique opportunity to make progress in this area due to the availability of parallaxes and the accessibility of spectroscopy. We have used new rotation period measurements and our compilation of H-alpha emission for nearby M dwarfs to explore two questions: 1) What is the longest rotation period an M dwarf can have? And 2) Do M dwarfs undergo an era of rapid angular momentum evolution? Here, we focus on the view from the Southern hemisphere, presenting approximately 200 new rotation periods for fully convective M dwarfs. Amongst the highest-quality datasets, we identify rotation periods in three-quarters of all stars; of these, half have rotation periods longer than 70 days. The longest rotation period we detect is 148 days, which is for a 0.15 solar-mass star. The lack of M dwarfs with intermediate rotation periods that we previously identified persists, supporting our hypothesis that M dwarfs rapidly spin down from 10-day to 100-day periods.ERN is supported by the National Science Foundation Astronomy & Astrophysics Postdoctoral Fellowship. We gratefully acknowledge support from the David and Lucille Packard Foundation, the National Science Foundation, and the John Templeton Foundation.

Atmospheric studies of C2 white dwarfs

NASA Astrophysics Data System (ADS)

Swanson, Steven Roger

Model atmosphere and line formation calculations for the delta nu = + 1 Swan bands of the C2 molecule are presented for seven white dwarfs and are compared to high resolution optical spectra. Limits on the C-12 to C-13 ratio are computed for highly pressure broadened lines and are used to analyze the observed spectra for any sign of absorption by the (C-12)(C-13) molecule. The metal abundances in cool white dwarf atmospheres and the usefulness of the determination of the C-12 to C-13 ratio are discussed. The line center shift and the pressure broadening are used to determine a value for the van der Waals interaction constant, C6. This is done using a detailed line modelling program which explicitly includes approximately 2000 rotational transition lines within the vibrational bands, in conjunction with atmospheric models calculated by the LUCIFER atmosphere modelling program. The isotopic shift of the vibrational and rotational lines is also included in the model to compare the detectability of various C-12 to C-13 ratios. The line models fit the observed spectra with varying degrees of accuracy. One star, WD0548-001, shows an unusually small pressure shift and broadening for the high pressures that the atmospheric model predicts. The results show that only in the hottest stars with the least pressure broadened lines in this study can the isotopic effect be seen. With the data available, the best limit on the C-12 to C-13 ratio is a minimum of 40 for WD0856 + 331. The models show that even for very high signal to noise data, the isotopic shift in the Swan bands in very cool white dwarfs would be difficult to separate from the pressure broadening effects. It is shown that the isotopic ratio is high enough to rule out the possibility that the carbon is a relic from previous CNO burning.

A Revised Estimate of the Occurrence Rate of Terrestrial Planets in the Habitable Zones around Kepler M-dwarfs

NASA Astrophysics Data System (ADS)

Kopparapu, Ravi Kumar

2013-04-01

Because of their large numbers, low-mass stars may be the most abundant planet hosts in our Galaxy. Furthermore, terrestrial planets in the habitable zones (HZs) around M-dwarfs can potentially be characterized in the near future and hence may be the first such planets to be studied. Recently, Dressing & Charbonneau used Kepler data and calculated the frequency of terrestrial planets in the HZ of cool stars to be 0.15^{+0.13}_{-0.06} per star for Earth-size planets (0.5-1.4 R ⊕). However, this estimate was derived using the Kasting et al. HZ limits, which were not valid for stars with effective temperatures lower than 3700 K. Here we update their result using new HZ limits from Kopparapu et al. for stars with effective temperatures between 2600 K and 7200 K, which includes the cool M stars in the Kepler target list. The new HZ boundaries increase the number of planet candidates in the HZ. Assuming Earth-size planets as 0.5-1.4 R ⊕, when we reanalyze their results, we obtain a terrestrial planet frequency of 0.48^{+0.12}_{-0.24} and 0.53^{+0.08}_{-0.17} planets per M-dwarf star for conservative and optimistic limits of the HZ boundaries, respectively. Assuming Earth-size planets as 0.5-2 R ⊕, the frequency increases to 0.51^{+0.10}_{-0.20} per star for the conservative estimate and to 0.61^{+0.07}_{-0.15} per star for the optimistic estimate. Within uncertainties, our optimistic estimates are in agreement with a similar optimistic estimate from the radial velocity survey of M-dwarfs (0.41^{+0.54}_{-0.13}). So, the potential for finding Earth-like planets around M stars may be higher than previously reported.

A REVISED ESTIMATE OF THE OCCURRENCE RATE OF TERRESTRIAL PLANETS IN THE HABITABLE ZONES AROUND KEPLER M-DWARFS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kopparapu, Ravi Kumar

Because of their large numbers, low-mass stars may be the most abundant planet hosts in our Galaxy. Furthermore, terrestrial planets in the habitable zones (HZs) around M-dwarfs can potentially be characterized in the near future and hence may be the first such planets to be studied. Recently, Dressing and Charbonneau used Kepler data and calculated the frequency of terrestrial planets in the HZ of cool stars to be 0.15{sup +0.13}{sub -0.06} per star for Earth-size planets (0.5-1.4 R{sub Circled-Plus }). However, this estimate was derived using the Kasting et al. HZ limits, which were not valid for stars with effectivemore » temperatures lower than 3700 K. Here we update their result using new HZ limits from Kopparapu et al. for stars with effective temperatures between 2600 K and 7200 K, which includes the cool M stars in the Kepler target list. The new HZ boundaries increase the number of planet candidates in the HZ. Assuming Earth-size planets as 0.5-1.4 R{sub Circled-Plus }, when we reanalyze their results, we obtain a terrestrial planet frequency of 0.48{sup +0.12}{sub -0.24} and 0.53{sup +0.08}{sub -0.17} planets per M-dwarf star for conservative and optimistic limits of the HZ boundaries, respectively. Assuming Earth-size planets as 0.5-2 R{sub Circled-Plus }, the frequency increases to 0.51{sup +0.10}{sub -0.20} per star for the conservative estimate and to 0.61{sup +0.07}{sub -0.15} per star for the optimistic estimate. Within uncertainties, our optimistic estimates are in agreement with a similar optimistic estimate from the radial velocity survey of M-dwarfs (0.41{sup +0.54}{sub -0.13}). So, the potential for finding Earth-like planets around M stars may be higher than previously reported.« less

Surveying Nearby M dwarfs with Gaia: A Treasure Trove for Exoplanet Astrophysics

NASA Astrophysics Data System (ADS)

Sozzetti, A.; Tinetti, G.; Lattanzi, M. G.; Micela, G.; Morbidelli, R.; Giacobbe, P.

2011-10-01

Cool, nearby M dwarfs within a few tens of parsecs from the Sun are today becoming the focus of dedicated experiments in the realm of exoplanets astrophysics. This is due to the shift in theoretical paradigms in light of new observations, and thanks to the improved understanding of the observational opportunities for planet detection and characterization provided by this sample. Gaia, in its all-sky survey, will deliver precision astrometry for a magnitude-limited (V=20) sample of M dwarfs in the vicinity of the Sun, providing an inventory of cool nearby stars with a much higher degree of completeness (particularly for late sub-types) with respect to currently available catalogs. We gauge the Gaia potential for precision astrometry of exoplanets orbiting a sample of actual M stars within 30 pc from the Sun. The stellar reservoir is carefully selected based on cross-correlation among catalogs in the literature (e.g., Lepine, PMSU).We express Gaia sensitivity thresholds as a function of system parameters and in view of the latest mission profile, including the most up-to-date astrometric error model. The simulations also provide insight on the capability of high-precision astrometry to reconstruct the underlying orbital elements and mass distributions of the generated companions. We investigate the synergy between the Gaia data on nearby M dwarfs and other ground-based and spaceborne programs for planet detection and characterization, with a particular focus on: a) the improvements in the determination of transiting planet parameters thanks to the exquisitely precise stellar distances determined by Gaia; b) the betterment in orbit modeling when Gaia astrometry and precision radial-velocities are available for the same targets; and c) the ability of Gaia to carefully predict the ephemerides of detected (transiting and non-transiting) planets aroundM stars, for the purpose of spectroscopic characterization of their atmospheres with dedicated observatories in space, such as EChO.

The Gaia Astrometric Survey of Nearby M Dwarfs: A Treasure Trove for Exoplanet Astrophysics

NASA Astrophysics Data System (ADS)

Sozzetti, Alessandro; Giacobbe, P.; Lattanzi, M. G.; Micela, G.; Tinetti, G.

2011-09-01

Cool, nearby M dwarfs within a few tens of parsecs from the Sun are becoming the focus of dedicated experiments in the realm of exoplanets astrophysics. This is due to the shift in theoretical paradigms in light of new observations, and to the improved understanding of the observational opportunities for planet detection and characterization provided by this sample. Gaia, in its all-sky survey, will deliver precision astrometry for a magnitude-limited (V=20) sample of M dwarfs, providing an inventory of cool nearby stars with a much higher degree of completeness (particularly for late sub-types) with respect to currently available catalogs. We gauge the Gaia potential for precision astrometry of exoplanets orbiting a sample of already known dM stars within 30 pc from the Sun, carefully selected based on cross-correlation among catalogs in the literature (e.g., Lepine, PMSU). We express Gaia sensitivity thresholds as a function of system parameters and in view of the latest mission profile, including the most up-to-date astrometric error model. The simulations also provide insight on the capability of high-precision astrometry to reconstruct the underlying orbital elements and mass distributions of the generated companions. These results will help in evaluating the complete expected Gaia planet population around late-type stars. We investigate the synergy between the Gaia data on nearby M dwarfs and other ground-based and space-borne programs for planet detection and characterization, with a particular focus on: a) the improvements in the determination of transiting planet parameters thanks to the exquisitely precise stellar distances determined by Gaia; b) the betterment in orbit modeling when Gaia astrometry and precision radial-velocities are available for the same targets; and c) the ability of Gaia to carefully predict the ephemerides of (transiting and non-transiting) planets around M stars, for spectroscopic characterization of their atmospheres with dedicated observatories in space, such as EChO.

A Detailed Model Atmosphere Analysis of Cool White Dwarfs in the Sloan Digital Sky Survey

DTIC Science & Technology

2010-09-01

Road, Flagstaff, AZ 86001, USA 6 Department of Astronomy, 1 University Station C1400, Austin, TX 78712, USA 7 Kavli Institute for Cosmological Physics...with the Leggett et al. (1998) result, but the lack of infrared photometry prevented Harris et al. (2006) from a definite conclusion about the implied

A Very Cool Pair of Brown Dwarfs

NASA Astrophysics Data System (ADS)

2011-03-01

Observations with the European Southern Observatory's Very Large Telescope, along with two other telescopes, have shown that there is a new candidate for the coldest known star: a brown dwarf in a double system with about the same temperature as a freshly made cup of tea - hot in human terms, but extraordinarily cold for the surface of a star. This object is cool enough to begin crossing the blurred line dividing small cold stars from big hot planets. Brown dwarfs are essentially failed stars: they lack enough mass for gravity to trigger the nuclear reactions that make stars shine. The newly discovered brown dwarf, identified as CFBDSIR 1458+10B, is the dimmer member of a binary brown dwarf system located just 75 light-years from Earth [1]. The powerful X-shooter spectrograph on ESO's Very Large Telescope (VLT) was used to show that the composite object was very cool by brown dwarf standards. "We were very excited to see that this object had such a low temperature, but we couldn't have guessed that it would turn out to be a double system and have an even more interesting, even colder component," said Philippe Delorme of the Institut de planétologie et d'astrophysique de Grenoble (CNRS/Université Joseph Fourier), a co-author of the paper. CFBDSIR 1458+10 is the coolest brown dwarf binary found to date. The dimmer of the two dwarfs has now been found to have a temperature of about 100 degrees Celsius - the boiling point of water, and not much different from the temperature inside a sauna [2]. "At such temperatures we expect the brown dwarf to have properties that are different from previously known brown dwarfs and much closer to those of giant exoplanets - it could even have water clouds in its atmosphere," said Michael Liu of the University of Hawaii's Institute for Astronomy, who is lead author of the paper describing this new work. "In fact, once we start taking images of gas-giant planets around Sun-like stars in the near future, I expect that many of them will look like CFBDSIR 1458+10B." Unravelling the secrets of this unique object involved exploiting the power of three different telescopes. CFBDSIR 1458+10 was first found to be a binary using the Laser Guide Star (LGS) Adaptive Optics system on the Keck II Telescope in Hawaii [3]. Liu and his colleagues then employed the Canada-France-Hawaii Telescope, also in Hawaii, to determine the distance to the brown dwarf duo using an infrared camera [4]. Finally the ESO VLT was used to study the object's infrared spectrum and measure its temperature. The hunt for cool objects is a very active astronomical hot topic. The Spitzer Space Telescope has recently identified two other very faint objects as other possible contenders for the coolest known brown dwarfs, although their temperatures have not been measured so precisely. Future observations will better determine how these objects compare to CFBDSIR 1458+10B. Liu and his colleagues are planning to observe CFBDSIR 1458+10B again to better determine its properties and to begin mapping the binary's orbit, which, after about a decade of monitoring, should allow astronomers to determine the binary's mass. Notes [1] CFBDSIR 1458+10 is the name of the binary system. The two components are known as CFBDSIR 1458+10A and CFBDSIR 1458+10B, with the latter the fainter and cooler of the two. They seem to be orbiting each other at a separation of about three times the distance between the Earth and the Sun in a period of about thirty years. [2] By comparison the temperature of the surface of the Sun is about 5500 degrees Celsius. [3] Adaptive optics cancels out much of Earth's atmospheric interference, improving the image sharpness by a factor of ten and enabling the very small separation binary to be resolved. [4] The astronomers measured the apparent motion of the brown dwarfs against the background of more distant stars caused by Earth's changing position in its orbit around the Sun. The effect, known as parallax, allowed them to determine the distance to the brown dwarfs. More information This research was presented in a paper, "CFBDSIR J1458+1013B: A Very Cold (>T10) Brown Dwarf in a Binary System", Liu et al. to appear in the Astrophysical Journal. The team is composed of Michael C. Liu (Institute for Astronomy [IfA], University of Hawaii, USA), Philippe Delorme (Institut de planétologie et d'astrophysique de Grenoble, CNRS/Université Joseph Fourier, France [IPAG]), Trent J. Dupuy (Harvard-Smithsonian Center for Astrophysics, Cambridge, USA), Brendan P. Bowler (IfA), Loic Albert (Canada-France-Hawaii Telescope Corporation, Hawaii, USA), Etienne Artigau (Université de Montréal, Canada), Celine Reylé (Observatoire de Besançon, France), Thierry Forveille (IPAG) and Xavier Delfosse (IPAG). ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world's most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory and VISTA, the world's largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become "the world's biggest eye on the sky".

VizieR Online Data Catalog: USNO Photographic Parallaxes. I. (Monet+, 1992)

NASA Astrophysics Data System (ADS)

Monet, D. G.; Dahn, C. C.; Vrba, F. J.; Harris, H. C.; Pier, J. R.; Luginbuhl, C. B.; Ables, H. D.

2000-11-01

The U.S. Naval Observatory CCD trigonometric parallax program is described in detail, including the instrumentation employed, observing procedures followed, and reduction procedures applied. Astrometric results are presented for 72 stars ranging in apparent brightness from V=15.16 to 19.58. Photometry (V and V-I on the Kron-Cousins system) is presented for the parallax stars and for all 426 individual reference stars employed in the astrometric solutions. Corrections for differential color refraction, calibrated to the observed V-I colors, have been applied to all astrometric measures. The mean errors in the relative parallaxes range from ±0.0005" to ±0.0027" with a median value of ±0.0010". Seventeen of the 23 stars with Vtan>200km/s form a well-delineated sequence of extreme subdwarfs covering 11.5

HADES RV Programme with HARPS-N at TNG . III. Flux-flux and activity-rotation relationships of early-M dwarfs

NASA Astrophysics Data System (ADS)

Maldonado, J.; Scandariato, G.; Stelzer, B.; Biazzo, K.; Lanza, A. F.; Maggio, A.; Micela, G.; González-Álvarez, E.; Affer, L.; Claudi, R. U.; Cosentino, R.; Damasso, M.; Desidera, S.; González Hernández, J. I.; Gratton, R.; Leto, G.; Messina, S.; Molinari, E.; Pagano, I.; Perger, M.; Piotto, G.; Rebolo, R.; Ribas, I.; Sozzetti, A.; Suárez Mascareño, A.; Zanmar Sanchez, R.

2017-02-01

Context. Understanding stellar activity in M dwarfs is crucial for the physics of stellar atmospheres and for ongoing radial velocity exoplanet programmes. Despite the increasing interest in M dwarfs, our knowledge of the chromospheres of these stars is far from being complete. Aims: We test whether the relations between activity, rotation, and stellar parameters and flux-flux relationships previously investigated for main-sequence FGK stars and for pre-main-sequence M stars also hold for early-M dwarfs on the main-sequence. Although several attempts have been made so far, here we analyse a large sample of stars undergoing relatively low activity. Methods: We analyse in a homogeneous and coherent way a well-defined sample of 71 late-K/early-M dwarfs that are currently being observed in the framework of the HArps-N red Dwarf Exoplanet Survey (HADES). Rotational velocities are derived using the cross-correlation technique, while emission flux excesses in the Ca II H & K and Balmer lines from Hα up to Hɛ are obtained by using the spectral subtraction technique. The relationships between the emission excesses and the stellar parameters (projected rotational velocity, effective temperature, kinematics, and age) are studied. Relations between pairs of fluxes of different chromospheric lines (flux-flux relationships) are also studied and compared with the literature results for other samples of stars. Results: We find that the strength of the chromospheric emission in the Ca II H & K and Balmer lines is roughly constant for stars in the M0-M3 spectral range. Although our sample is likely to be biased towards inactive stars, our data suggest that a moderate but significant correlation between activity and rotation might be present, as well as a hint of kinematically selected young stars showing higher levels of emission in the calcium line and in most of the Balmer lines. We find our sample of M dwarfs to be complementary in terms of chromospheric and X-ray fluxes with those of the literature, extending the analysis of the flux-flux relationships to the very low flux domain. Conclusions: Our results agree with previous works suggesting that the activity-rotation-age relationship known to hold for solar-type stars also applies to early-M dwarfs. We also confirm previous findings that the field stars which deviate from the bulk of the empirical flux-flux relationships show evidence of youth. Based on observations made with the Italian Telescopio Nazionale Galileo (TNG), operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

The complete mitochondrial genome of the dwarf tapeworm Hymenolepis nana--a neglected zoonotic helminth.

PubMed

Cheng, Tian; Liu, Guo-Hua; Song, Hui-Qun; Lin, Rui-Qing; Zhu, Xing-Quan

2016-03-01

Hymenolepis nana, commonly known as the dwarf tapeworm, is one of the most common tapeworms of humans and rodents and can cause hymenolepiasis. Although this zoonotic tapeworm is of socio-economic significance in many countries of the world, its genetics, systematics, epidemiology, and biology are poorly understood. In the present study, we sequenced and characterized the complete mitochondrial (mt) genome of H. nana. The mt genome is 13,764 bp in size and encodes 36 genes, including 12 protein-coding genes, 2 ribosomal RNA, and 22 transfer RNA genes. All genes are transcribed in the same direction. The gene order and genome content are completely identical with their congener Hymenolepis diminuta. Phylogenetic analyses based on concatenated amino acid sequences of 12 protein-coding genes by Bayesian inference, Maximum likelihood, and Maximum parsimony showed the division of class Cestoda into two orders, supported the monophylies of both the orders Cyclophyllidea and Pseudophyllidea. Analyses of mt genome sequences also support the monophylies of the three families Taeniidae, Hymenolepididae, and Diphyllobothriidae. This novel mt genome provides a useful genetic marker for studying the molecular epidemiology, systematics, and population genetics of the dwarf tapeworm and should have implications for the diagnosis, prevention, and control of hymenolepiasis in humans.

THE SOLAR NEIGHBORHOOD. XXVIII. THE MULTIPLICITY FRACTION OF NEARBY STARS FROM 5 TO 70 AU AND THE BROWN DWARF DESERT AROUND M DWARFS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dieterich, Sergio B.; Henry, Todd J.; Golimowski, David A.

2012-08-15

We report on our analysis of Hubble Space Telescope/NICMOS snapshot high-resolution images of 255 stars in 201 systems within {approx}10 pc of the Sun. Photometry was obtained through filters F110W, F180M, F207M, and F222M using NICMOS Camera 2. These filters were selected to permit clear identification of cool brown dwarfs through methane contrast imaging. With a plate scale of 76 mas pixel{sup -1}, NICMOS can easily resolve binaries with subarcsecond separations in the 19.''5 Multiplication-Sign 19.''5 field of view. We previously reported five companions to nearby M and L dwarfs from this search. No new companions were discovered during themore » second phase of data analysis presented here, confirming that stellar/substellar binaries are rare. We establish magnitude and separation limits for which companions can be ruled out for each star in the sample, and then perform a comprehensive sensitivity and completeness analysis for the subsample of 138 M dwarfs in 126 systems. We calculate a multiplicity fraction of 0.0{sup +3.5}{sub -0.0}% for L companions to M dwarfs in the separation range of 5-70 AU, and 2.3{sup +5.0}{sub -0.7}% for L and T companions to M dwarfs in the separation range of 10-70 AU. We also discuss trends in the color-magnitude diagrams using various color combinations and present astrometry for 19 multiple systems in our sample. Considering these results and results from several other studies, we argue that the so-called brown dwarf desert extends to binary systems with low-mass primaries and is largely independent of primary mass, mass ratio, and separations. While focusing on companion properties, we discuss how the qualitative agreement between observed companion mass functions and initial mass functions suggests that the paucity of brown dwarfs in either population may be due to a common cause and not due to binary formation mechanisms.« less

Complete Sequence and Comparative Analysis of the Chloroplast Genome of Coconut Palm (Cocos nucifera)

PubMed Central

Huang, Ya-Yi; Matzke, Antonius J. M.; Matzke, Marjori

2013-01-01

Coconut, a member of the palm family (Arecaceae), is one of the most economically important trees used by mankind. Despite its diverse morphology, coconut is recognized taxonomically as only a single species (Cocos nucifera L.). There are two major coconut varieties, tall and dwarf, the latter of which displays traits resulting from selection by humans. We report here the complete chloroplast (cp) genome of a dwarf coconut plant, and describe the gene content and organization, inverted repeat fluctuations, repeated sequence structure, and occurrence of RNA editing. Phylogenetic relationships of monocots were inferred based on 47 chloroplast protein-coding genes. Potential nodes for events of gene duplication and pseudogenization related to inverted repeat fluctuation were mapped onto the tree using parsimony criteria. We compare our findings with those from other palm species for which complete cp genome sequences are available. PMID:24023703

Complete sequence and comparative analysis of the chloroplast genome of coconut palm (Cocos nucifera).

PubMed

Huang, Ya-Yi; Matzke, Antonius J M; Matzke, Marjori

2013-01-01

Coconut, a member of the palm family (Arecaceae), is one of the most economically important trees used by mankind. Despite its diverse morphology, coconut is recognized taxonomically as only a single species (Cocos nucifera L.). There are two major coconut varieties, tall and dwarf, the latter of which displays traits resulting from selection by humans. We report here the complete chloroplast (cp) genome of a dwarf coconut plant, and describe the gene content and organization, inverted repeat fluctuations, repeated sequence structure, and occurrence of RNA editing. Phylogenetic relationships of monocots were inferred based on 47 chloroplast protein-coding genes. Potential nodes for events of gene duplication and pseudogenization related to inverted repeat fluctuation were mapped onto the tree using parsimony criteria. We compare our findings with those from other palm species for which complete cp genome sequences are available.

Secular Resonances During Main-Sequence and Post-Main-Sequence Planetary System Dynamics

NASA Astrophysics Data System (ADS)

Smallwood, Jeremy L.

We investigate gravitational perturbations of an asteroid belt by secular resonances. We ap- ply analytic and numerical models to main-sequence and post-main-sequence planetary systems. First, we investigate how the asteroid impact rate on the Earth is affected by the architecture of the planetary system. We find that the nu6 resonance plays an important role in the asteroid collision rate with the Earth. Compared to exoplanetary systems, the solar system is somewhat special in its lack of a super-Earth mass planet in the inner solar system. We therefore consider the effects of the presence of a super-Earth in the terrestrial planet region. We find a significant effect for super-Earths with a mass of around 10 M_{Earth} and a separation greater than about 0.7 AU. These results have implications for the habitability of exoplanetary systems. Secondly, we model white dwarf pollution by asteroids from secular resonances. In the past few decades, observations have revealed signatures of metals polluting the atmospheres of white dwarfs that require a continu- ous accretion of asteroids. We show that secular resonances driven by two outer companions can provide a source of pollution if an inner terrestrial planet is engulfed during the red-giant branch phase. Secular resonances may be a viable mechanism for the pollution of white dwarfs in a variety of exoplanetary system architectures including systems with two giant planets and systems with one giant planet and a binary star companion.

Rotational Modulation and Activity Cycles at Rotational Extremes: 25 yrs of NURO Photometry for HII 1883

NASA Astrophysics Data System (ADS)

Milingo, Jackie; Saar, Steven; Marschall, Laurence

2018-01-01

We present a 25 yr compilation of V-band differential photometry for the Pleiades K dwarf HII 1883 (V660 Tau). HII 1883 has a rotational period of ~ 0.24 d and displays significant rotational modulation due to non-uniform surface brightness or "starspots". Preliminary work yields a cycle period of ~ 9 yrs and rotational shear (ΔP_rot/) considerably less than solar. HII 1883 is one of the fastest rotating single stars with a known cycle. With additional data available we compare newly determined P_cyc and ΔP_rot/ values with those of other stars, putting HII 1883 into the broader context of dynamo properties in single cool dwarfs.

Dwarfs and Giants in the local flows of galaxies.

NASA Astrophysics Data System (ADS)

Chernin, A. D.; Emelyanov, N. V.; Karachentsev, I. D.

We use recent Hubble Space Telescope data on nearby dwarf and giant galaxies to study the dynamical structure and evolutionary trends of the local expansion flows of galaxies. It is found that antigravity of dark energy dominates the force field of the flows and makes them expand with acceleration. It also cools the flows and introduces to them the nearly linear velocity-distance relation with the time-rate close to the global Hubble's factor. There are grounds to expect that this is the universal physical regularity that is common not only for the nearby flows we studied here, but also for all the expansion flows of various spatial scales from the 1 Mpc scale and up to the scale of the global cosmological expansion.

TRAPPIST-1 Compared to Jovian Moons and Inner Solar System - Updated Feb. 2018

NASA Image and Video Library

2018-02-05

All seven planets discovered in orbit around the red dwarf star TRAPPIST-1 could easily fit inside the orbit of Mercury, the innermost planet of our solar system. In fact, they would have room to spare. TRAPPIST-1 also is only a fraction of the size of our Sun; it isn't much larger than Jupiter. So, the TRAPPIST-1 system's proportions look more like Jupiter and its moons than those of our solar system. The seven planets of TRAPPIST-1 are all Earth-sized and terrestrial. TRAPPIST-1 is an ultra-cool dwarf star in the constellation Aquarius, and its planets orbit very close to it. https://photojournal.jpl.nasa.gov/catalog/PIA22096

Gas clump formation via thermal instability in high-redshift dwarf galaxy mergers

NASA Astrophysics Data System (ADS)

Arata, Shohei; Yajima, Hidenobu; Nagamine, Kentaro

2018-04-01

Star formation in high-redshift dwarf galaxies is a key to understand early galaxy evolution in the early Universe. Using the three-dimensional hydrodynamics code GIZMO, we study the formation mechanism of cold, high-density gas clouds in interacting dwarf galaxies with halo masses of ˜3 × 107 M⊙, which are likely to be the formation sites of early star clusters. Our simulations can resolve both the structure of interstellar medium on small scales of ≲ 0.1 pc and the galactic disc simultaneously. We find that the cold gas clouds form in the post-shock region via thermal instability due to metal-line cooling, when the cooling time is shorter than the galactic dynamical time. The mass function of cold clouds shows almost a power-law initially with an upper limit of thermally unstable scale. We find that some clouds merge into more massive ones with ≳104 M⊙ within ˜ 2 Myr. Only the massive cold clouds with ≳ 103 M⊙ can keep collapsing due to gravitational instability, resulting in the formation of star clusters. We find that the clump formation is more efficient in the prograde-prograde merger than the prograde-retrograde case due to the difference in the degree of shear flow. In addition, we investigate the dependence of cloud mass function on metallicity and H2 abundance, and show that the cases with low metallicities (≲10-2 Z⊙) or high H2 abundance (≳10-3) cannot form massive cold clouds with ≳103 M⊙.

Spectral Sequences of Type Ia Supernovae. I. Connecting Normal and Subluminous SNe Ia and the Presence of Unburned Carbon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heringer, E.; Kerkwijk, M. H. van; Sim, S. A.

2017-09-01

Type Ia supernovae (SNe Ia) are generally agreed to arise from thermonuclear explosions of carbon–oxygen white dwarfs. The actual path to explosion, however, remains elusive, with numerous plausible parent systems and explosion mechanisms suggested. Observationally, SNe Ia have multiple subclasses, distinguished by their light curves and spectra. This raises the question of whether these indicate that multiple mechanisms occur in nature or that explosions have a large but continuous range of physical properties. We revisit the idea that normal and 91bg-like SNe can be understood as part of a spectral sequence in which changes in temperature dominate. Specifically, we findmore » that a single ejecta structure is sufficient to provide reasonable fits of both the normal SN Ia SN 2011fe and the 91bg-like SN 2005bl, provided that the luminosity and thus temperature of the ejecta are adjusted appropriately. This suggests that the outer layers of the ejecta are similar, thus providing some support for a common explosion mechanism. Our spectral sequence also helps to shed light on the conditions under which carbon can be detected in premaximum SN Ia spectra—we find that emission from iron can “fill in” the carbon trough in cool SNe Ia. This may indicate that the outer layers of the ejecta of events in which carbon is detected are relatively metal-poor compared to events in which carbon is not detected.« less

The brown dwarf kinematics project

NASA Astrophysics Data System (ADS)

Faherty, Jackie K.

2010-10-01

Brown dwarfs are a recent addition to the plethora of objects studied in Astronomy. With theoretical masses between 13 and 75 MJupiter , they lack sustained stable Hydrogen burning so they never join the stellar main sequence. They have physical properties similar to both planets and low-mass stars so studies of their population inform on both. The distances and kinematics of brown dwarfs provide key statistical constraints on their ages, moving group membership, absolute brightnesses, evolutionary trends, and multiplicity. Yet, until my thesis, fundamental measurements of parallax and proper motion were made for only a relatively small fraction of the known population. To address this deficiency, I initiated the Brown Dwarf Kinematics (BDKP). Over the past four years I have re-imaged the majority of spectroscopically confirmed field brown dwarfs (or ultracool dwarfs---UCDs) and created the largest proper motion catalog for ultracool dwarfs to date. Using new astrometric information I examined population characteristics such as ages calculated from velocity dispersions and correlations between kinematics and colors. Using proper motions, I identified several new wide co-moving companions and investigated binding energy (and hence formation) limitations as well as the frequency of hierarchical companions. Concurrently over the past four years I have been conducting a parallax survey of 84 UCDs including those showing spectral signatures of youth, metal-poor brown dwarfs, and those within 20 pc of the Sun. Using absolute magnitude relations in J,H, and K, I identified overluminous binary candidates and investigated known flux-reversal binaries. Using current evolutionary models, I compared the MK vs J-K color magnitude diagram to model predictions and found that the low-surface gravity dwarfs are significantly red-ward and underluminous of predictions and a handful of late-type T dwarfs may require thicker clouds to account for their scatter.

Dwarfism and Altered Craniofacial Development in Rabbits Is Caused by a 12.1 kb Deletion at the HMGA2 Locus.

PubMed

Carneiro, Miguel; Hu, Dou; Archer, John; Feng, Chungang; Afonso, Sandra; Chen, Congying; Blanco-Aguiar, José A; Garreau, Hervé; Boucher, Samuel; Ferreira, Paula G; Ferrand, Nuno; Rubin, Carl-Johan; Andersson, Leif

2017-02-01

The dwarf phenotype characterizes the smallest of rabbit breeds and is governed largely by the effects of a single dwarfing allele with an incompletely dominant effect on growth. Dwarf rabbits typically weigh under 1 kg and have altered craniofacial morphology. The dwarf allele is recessive lethal and dwarf homozygotes die within a few days of birth. The dwarf phenotype is expressed in heterozygous individuals and rabbits from dwarf breeds homozygous for the wild-type allele are normal, although smaller when compared to other breeds. Here, we show that the dwarf allele constitutes a ∼12.1 kb deletion overlapping the promoter region and first three exons of the HMGA2 gene leading to inactivation of this gene. HMGA2 has been frequently associated with variation in body size across species. Homozygotes for null alleles are viable in mice but not in rabbits and probably not in humans. RNA-sequencing analysis of rabbit embryos showed that very few genes (4-29 genes) were differentially expressed among the three HMGA2/dwarf genotypes, suggesting that dwarfism and inviability in rabbits are caused by modest changes in gene expression. Our results show that HMGA2 is critical for normal expression of IGF2BP2, which encodes an RNA-binding protein. Finally, we report a catalog of regions of elevated genetic differentiation between dwarf and normal-size rabbits, including LCORL-NCAPG, STC2, HOXD cluster, and IGF2BP2 Levels and patterns of genetic diversity at the LCORL-NCAPG locus further suggest that small size in dwarf breeds was enhanced by crosses with wild rabbits. Overall, our results imply that small size in dwarf rabbits results from a large effect, loss-of-function (LOF) mutation in HMGA2 combined with polygenic selection. Copyright © 2017 by the Genetics Society of America.

Dwarfism and Altered Craniofacial Development in Rabbits Is Caused by a 12.1 kb Deletion at the HMGA2 Locus

PubMed Central

Hu, Dou; Archer, John; Feng, Chungang; Afonso, Sandra; Chen, Congying; Blanco-Aguiar, José A.; Garreau, Hervé; Boucher, Samuel; Ferreira, Paula G.; Ferrand, Nuno; Rubin, Carl-Johan

2017-01-01

The dwarf phenotype characterizes the smallest of rabbit breeds and is governed largely by the effects of a single dwarfing allele with an incompletely dominant effect on growth. Dwarf rabbits typically weigh under 1 kg and have altered craniofacial morphology. The dwarf allele is recessive lethal and dwarf homozygotes die within a few days of birth. The dwarf phenotype is expressed in heterozygous individuals and rabbits from dwarf breeds homozygous for the wild-type allele are normal, although smaller when compared to other breeds. Here, we show that the dwarf allele constitutes a ∼12.1 kb deletion overlapping the promoter region and first three exons of the HMGA2 gene leading to inactivation of this gene. HMGA2 has been frequently associated with variation in body size across species. Homozygotes for null alleles are viable in mice but not in rabbits and probably not in humans. RNA-sequencing analysis of rabbit embryos showed that very few genes (4–29 genes) were differentially expressed among the three HMGA2/dwarf genotypes, suggesting that dwarfism and inviability in rabbits are caused by modest changes in gene expression. Our results show that HMGA2 is critical for normal expression of IGF2BP2, which encodes an RNA-binding protein. Finally, we report a catalog of regions of elevated genetic differentiation between dwarf and normal-size rabbits, including LCORL-NCAPG, STC2, HOXD cluster, and IGF2BP2. Levels and patterns of genetic diversity at the LCORL-NCAPG locus further suggest that small size in dwarf breeds was enhanced by crosses with wild rabbits. Overall, our results imply that small size in dwarf rabbits results from a large effect, loss-of-function (LOF) mutation in HMGA2 combined with polygenic selection. PMID:27986804

High-cadence spectroscopy of M-dwarfs - II. Searching for stellar pulsations with HARPS

NASA Astrophysics Data System (ADS)

Berdiñas, Z. M.; Rodríguez-López, C.; Amado, P. J.; Anglada-Escudé, G.; Barnes, J. R.; MacDonald, J.; Zechmeister, M.; Sarmiento, L. F.

2017-08-01

Stellar oscillations appear all across the Hertzsprung-Russell diagram. Recent theoretical studies support their existence also in the atmosphere of M dwarfs. These studies predict for them short periodicities ranging from 20 min to 3 h. Our Cool Tiny Beats (CTB) programme aims at finding these oscillations for the very first time. With this goal, CTB explores the short time domain of M dwarfs using radial velocity data from the High Accuracy Radial velocity Planet Searcher (HARPS)-European Southern Observatory and HARPS-N high-precision spectrographs. Here we present the results for the two most long-term stable targets observed to date with CTB, GJ 588 and GJ 699 (I.e. Barnard's star). In the first part of this work we detail the correction of several instrumental effects. These corrections are especially relevant when searching for subnight signals. Results show no significant signals in the range where M dwarfs pulsations were predicted. However, we estimate that stellar pulsations with amplitudes larger than ˜0.5 m s-1 can be detected with a 90 per cent completeness with our observations. This result, along with the excess of power regions detected in the periodograms, opens the possibility of non-resolved very low amplitude pulsation signals. Next generation more precise instrumentation would be required to detect such oscillations. However, the possibility of detecting pulsating M-dwarf stars with larger amplitudes is feasible due to the short size of the analysed sample. This motivates the need for completeness of the CTB survey.

Late Holocene expansion of Siberian dwarf pine (Pinus pumila) in Kamchatka in response to increased snow cover as inferred from lacustrine oxygen-isotope records

NASA Astrophysics Data System (ADS)

Hammarlund, Dan; Klimaschewski, Andrea; St. Amour, Natalie A.; Andrén, Elinor; Self, Angela E.; Solovieva, Nadia; Andreev, Andrei A.; Barnekow, Lena; Edwards, Thomas W. D.

2015-11-01

Holocene records of cellulose-inferred lake-water δ18O were produced from two lake-sediment sequences obtained in central and northern Kamchatka, Russian Far East. The sediment records share similar fluctuations in δ18O during the interval of ca. 5000-800 cal yr BP that correspond (inversely) with changes in K+ content of the GISP2 ice-core record from Greenland, a proxy for the relative strength of the Siberian High, suggesting control by climate-related variability in δ18O of regional precipitation. The dramatic expansion of Siberian dwarf pine (Pinus pumila) in northern and central Kamchatka between ca. 5000 and 4000 cal yr BP, as inferred from pollen records from the same and neighbouring sites, appears to have occurred at a time of progressively declining δ18O of precipitation. This development is interpreted as reflecting a regional cooling trend accompanied by increasing winter snowfall related to gradual intensification of the Siberian High from ca. 5000 to ca. 3000 cal yr BP. A thicker and more long-lasting snow cover can be assumed to have favoured P. pumila by providing a competitive advantage over other boreal and subalpine tree and shrub species in the region during the later part of the Holocene. These results, which are the first of their kind from Kamchatka, provide novel insight into the Holocene vegetational and climatic development in easternmost Asia, as well as long-term atmospheric circulation dynamics in Beringia.

Cloud Atlas: Rotational Modulations in the L/T Transition Brown Dwarf Companion HN Peg B

NASA Technical Reports Server (NTRS)

Zhou, Yifan; Apai, Daniel; Metchev, Stanimir; Lew, Ben W. P.; Schneider, Glenn; Marley, Mark S.; Karalidi, Theodora; Manjavacas, Elena; Bedin, Luigi R.; Cowan, Nicolas B.;

H2 Fluorescence in M dwarf Systems: A Stellar Origin

NASA Astrophysics Data System (ADS)

Kruczek, Nicholas; France, Kevin; Evonosky, William; Youngblood, Allison; Loyd, R. O. Parke

2017-01-01

Observations of Lyα-driven H2 fluorescence can be a useful tool for measuring the abundance of H2 in exoplanet atmospheres. This emission has been previously observed in M dwarfs with planetary systems but at too low of a signal to determine its origin. It may have been originating in the atmospheres of planets, but conditions within these systems also mean that the H2 could be residing on the stellar surface or in a circumstellar disk. We use observations from the ``Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanet Host Stars" (MUSCLES) Hubble Space Telescope (HST) Treasury Survey to study H2 fluorescence in M dwarfs with and without confirmed planets to determine the origin of the emission. The results are further supported by the direct imaging of a candidate M dwarf system using the HST-Advanced Camera for Surveys/Solar Blind Channel. We constrain the location of the fluorescing H2 through analysis of the line profiles and determine that the emission is originating on the star. We verify that this interpretation is consistent with 1D radiative transfer models that are optimized using the spectra of the MUSCLES stars and find that the H2 likely resides in starspots or a cool region of the lower chromosphere.

Innocent Bystanders and Smoking Guns: Dwarf Carbon Stars

NASA Astrophysics Data System (ADS)

Green, Paul J.

2014-01-01

As far as we know, most carbon throughout the Universe is created and dispersed by AGB stars. So it was at first surprising to find that the carbon stars most prevalent in the Galaxy are in fact dwarfs. We suspect that dC stars are most likely innocent bystanders in post-mass transfer binaries, and may be predominantly metal-poor. Among 1200 C stars found in the SDSS (Green 2013), we confirm 724 dCs, of which a dozen are DA/dC stars in composite spectrum binaries, quadrupling the total sample of these "smoking guns" for AGB binary mass transfer. The dCs likely span absolute magnitudes M_i from about 6.5 to 10.5. G-type dC stars with weak CN and relatively blue colors are probably the most massive dCs still cool enough to show C_2 bands. Eleven very red C stars with strong red CN bands appear to be N-type AGB stars at large Galactocentric distances, one likely a new discovery in the dIrr galaxy Le A. Two such stars within 30arcmin of each other may trace a previously unidentified dwarf galaxy or tidal stream at ~40 kpc. We describe follow-up projects to study the spatial, kinematic, and binary properties of these C-enriched dwarfs.

Search for pulsations in M dwarfs in the Kepler short-cadence data base

NASA Astrophysics Data System (ADS)

Rodríguez, E.; Rodríguez-López, C.; López-González, M. J.; Amado, P. J.; Ocando, S.; Berdiñas, Z. M.

2016-04-01

The results of a search for stellar pulsations in M dwarf stars in the Kepler short-cadence (SC) data base are presented. This investigation covers all the cool and dwarf stars in the list of Dressing & Charbonneau, which were also observed in SC mode by the Kepler satellite. The sample has been enlarged via selection of stellar parameters (temperature, surface gravity and radius) with available Kepler Input Catalogue values together with JHK and riz photometry. In total, 87 objects observed by the Kepler mission in SC mode were selected and analysed using Fourier techniques. The detection threshold is below 10 μmag for the brightest objects and below 20 μmag for about 40 per cent of the stars in the sample. However, no significant signal in the [˜10,100] cd-1 frequency domain that can be reliably attributable to stellar pulsations has been detected. The periodograms have also been investigated for solar-like oscillations in the >100 cd-1 region, but with unsuccessful results too. Despite these inconclusive photometric results, M dwarfs pulsation amplitudes may still be detected in radial velocity searches. State-of-the-art coming instruments, like CARMENES near-infrared high-precision spectrograph, will play a key role in the possible detection.

The unstable fate of the planet orbiting the A star in the HD 131399 triple stellar system

NASA Astrophysics Data System (ADS)

Veras, Dimitri; Mustill, Alexander J.; Gänsicke, Boris T.

2017-02-01

Validated planet candidates need not lie on long-term stable orbits, and instability triggered by post-main-sequence stellar evolution can generate architectures which transport rocky material to white dwarfs, hence polluting them. The giant planet HD 131399Ab orbits its parent A star at a projected separation of about 50-100 au. The host star, HD 131399A, is part of a hierarchical triple with HD 131399BC being a close binary separated by a few hundred au from the A star. Here, we determine the fate of this system, and find the following: (I) Stability along the main sequence is achieved only for a favourable choice of parameters within the errors. (II) Even for this choice, in almost every instance, the planet is ejected during the transition between the giant branch and white dwarf phases of HD 131399A. This result provides an example of both how the free-floating planet population may be enhanced by similar systems and how instability can manifest in the polluted white dwarf progenitor population.

Surface Magnetic Field Strengths: New Tests of Magnetoconvective Models of M Dwarfs

NASA Astrophysics Data System (ADS)

MacDonald, James; Mullan, D. J.

2014-05-01

Precision modeling of M dwarfs has become worthwhile in recent years due to the increasingly precise values of masses and radii which can be obtained from eclipsing binary studies. In a recent paper, Torres has identified four prime M dwarf pairs with the most precise empirical determinations of masses and radii. The measured radii are consistently larger than standard stellar models predict by several percent. These four systems potentially provide the most challenging tests of precision evolutionary models of cool dwarfs at the present time. We have previously modeled M dwarfs in the context of a criterion due to Gough & Tayler in which magnetic fields inhibit the onset of convection according to a physics-based prescription. In the present paper, we apply our magnetoconvective approach to the four prime systems in the Torres list. Going a step beyond what we have already modeled in CM Dra (one of the four Torres systems), we note that new constraints on magnetoconvective models of M dwarfs are now available from empirical estimates of magnetic field strengths on the surfaces of these stars. In the present paper, we consider how well our magnetoconvective models succeed when confronted with this new test of surface magnetic field strengths. Among the systems listed by Torres, we find that plausible magnetic models work well for CM Dra, YY Gem, and CU Cnc. (The fourth system in Torres's list does not yet have enough information to warrant magnetic modeling.) Our magnetoconvection models of CM Dra, YY Gem, and CU Cnc yield predictions of the magnetic fluxes on the stellar surface which are consistent with the observed correlation between magnetic flux and X-ray luminosity.

Surface magnetic field strengths: New tests of magnetoconvective models of M dwarfs

DOE Office of Scientific and Technical Information (OSTI.GOV)

MacDonald, James; Mullan, D. J., E-mail: jimmacd@udel.edu, E-mail: mullan@udel.edu

2014-05-20

Precision modeling of M dwarfs has become worthwhile in recent years due to the increasingly precise values of masses and radii which can be obtained from eclipsing binary studies. In a recent paper, Torres has identified four prime M dwarf pairs with the most precise empirical determinations of masses and radii. The measured radii are consistently larger than standard stellar models predict by several percent. These four systems potentially provide the most challenging tests of precision evolutionary models of cool dwarfs at the present time. We have previously modeled M dwarfs in the context of a criterion due to Goughmore » and Tayler in which magnetic fields inhibit the onset of convection according to a physics-based prescription. In the present paper, we apply our magnetoconvective approach to the four prime systems in the Torres list. Going a step beyond what we have already modeled in CM Dra (one of the four Torres systems), we note that new constraints on magnetoconvective models of M dwarfs are now available from empirical estimates of magnetic field strengths on the surfaces of these stars. In the present paper, we consider how well our magnetoconvective models succeed when confronted with this new test of surface magnetic field strengths. Among the systems listed by Torres, we find that plausible magnetic models work well for CM Dra, YY Gem, and CU Cnc. (The fourth system in Torres's list does not yet have enough information to warrant magnetic modeling.) Our magnetoconvection models of CM Dra, YY Gem, and CU Cnc yield predictions of the magnetic fluxes on the stellar surface which are consistent with the observed correlation between magnetic flux and X-ray luminosity.« less

Pulsating low-mass white dwarfs in the frame of new evolutionary sequences. V. Asteroseismology of ELMV white dwarf stars

NASA Astrophysics Data System (ADS)

Calcaferro, Leila M.; Córsico, Alejandro H.; Althaus, Leandro G.

2017-11-01

Context. Many pulsating low-mass white dwarf stars have been detected in the past years in the field of our Galaxy. Some of them exhibit multiperiodic brightness variation, therefore it is possible to probe their interiors through asteroseismology. Aims: We present a detailed asteroseismological study of all the known low-mass variable white dwarf stars based on a complete set of fully evolutionary models that are representative of low-mass He-core white dwarf stars. Methods: We employed adiabatic radial and nonradial pulsation periods for low-mass white dwarf models with stellar masses ranging from 0.1554 to 0.4352 M⊙ that were derived by simulating the nonconservative evolution of a binary system consisting of an initially 1 M⊙ zero-age main-sequence (ZAMS) star and a 1.4 M⊙ neutron star companion. We estimated the mean period spacing for the stars under study (where this was possible), and then we constrained the stellar mass by comparing the observed period spacing with the average of the computed period spacings for our grid of models. We also employed the individual observed periods of every known pulsating low-mass white dwarf star to search for a representative seismological model. Results: We found that even though the stars under analysis exhibit few periods and the period fits show multiplicity of solutions, it is possible to find seismological models whose mass and effective temperature are in agreement with the values given by spectroscopy for most of the cases. Unfortunately, we were not able to constrain the stellar masses by employing the observed period spacing because, in general, only few periods are exhibited by these stars. In the two cases where we were able to extract the period spacing from the set of observed periods, this method led to stellar mass values that were substantially higher than expected for this type of stars. Conclusions: The results presented in this work show the need for further photometric searches, on the one hand, and that some improvements of the theoretical models are required on the other hand in order to place the asteroseismological results on a firmer ground.

Morphological and molecular variation in Mitchella undulata, with special reference to the systematic treatment of the dwarf form from Yakushima.

PubMed

Yokoyama, Jun; Fukuda, Tatsuya; Tsukaya, Hirokazu

2003-08-01

Morphological and molecular variation in Mitchella undulata Siebold et Zucc. was examined to evaluate the genetic basis for recognizing the dwarf variety, M. undulata var. minor Masamune. Considerable variation in leaf size in M. undulata, but no obvious morphological discontinuities, were found between the normal and dwarf varieties. Instead, a weak cline running from the Pacific Ocean to the Sea of Japan was found. Anatomical observations of leaf blades revealed that the large variation in leaf size can be attributed to variation in the number of leaf cells and not to differences in cell size. A molecular analysis based on sequences of rDNA internal transcribed spacer regions indicated that there were two major genotypes in M. undulata with minor variation in haplotypes resulting from additional substitutions or putative recombination. The dwarf form from Yakushima was neither genetically uniform nor apparently differentiated from other populations. From these results, we conclude that the dwarf form of M. undulata should be treated at the rank of forma.

Stellar and Planetary Parameters for K2 's Late-type Dwarf Systems from C1 to C5

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martinez, Arturo O.; Crossfield, Ian J. M.; Peacock, Sarah

The NASA K2 mission uses photometry to find planets transiting stars of various types. M dwarfs are of high interest since they host more short-period planets than any other type of main-sequence star and transiting planets around M dwarfs have deeper transits compared to other main-sequence stars. In this paper, we present stellar parameters from K and M dwarfs hosting transiting planet candidates discovered by our team. Using the SOFI spectrograph on the European Southern Observatory’s New Technology Telescope, we obtained R ≈ 1000 J -, H -, and K -band (0.95–2.52 μ m) spectra of 34 late-type K2 planetmore » and candidate planet host systems and 12 bright K4–M5 dwarfs with interferometrically measured radii and effective temperatures. Out of our 34 late-type K2 targets, we identify 27 of these stars as M dwarfs. We measure equivalent widths of spectral features, derive calibration relations using stars with interferometric measurements, and estimate stellar radii, effective temperatures, masses, and luminosities for the K2 planet hosts. Our calibrations provide radii and temperatures with median uncertainties of 0.059 R {sub ⊙} (16.09%) and 160 K (4.33%), respectively. We then reassess the radii and equilibrium temperatures of known and candidate planets based on our spectroscopically derived stellar parameters. Since a planet’s radius and equilibrium temperature depend on the parameters of its host star, our study provides more precise planetary parameters for planets and candidates orbiting late-type stars observed with K2 . We find a median planet radius and an equilibrium temperature of approximately 3 R {sub ⊕} and 500 K, respectively, with several systems (K2-18b and K2-72e) receiving near-Earth-like levels of incident irradiation.« less

The SOHO-Stellar Connection

NASA Technical Reports Server (NTRS)

Ayres, Thomas R.

1999-01-01

I discusses practical aspects of the so-called "solar-stellar" connection; namely, the fundamental principles, the tools at the disposal of the stellar astronomer, and a few recent examples of the connection in action. I provide an overall evolutionary context for coronal activity, calling attention to the very different circumstances of low mass main sequence stars like the Sun, which are active mainly early in their lives; compared with more massive stars, whose coronally active phase occurs near the end of their lives, during their brief incursion into the cool half of the Hertzsprung-Russell diagram as yellow and then red giants. On the instrumental slide, I concentrate primarily on spectroscopy, in the ultraviolet and X-ray bands where coronae leave their most obvious signatures. I present an early glimpse of the type of moderate resolution spectra we can expect from the recently launched Chandra observatory, and contemporaneous HST STIS high-resolution UV measurements of the CXO calibration star Capella (alpha Aur; G8 III + G1 III). I compare STIS spectra of solar-type dwarfs-zeta Dor (F7 V), an active coronal source; and alpha Cen A (G2 V), a near twin of the Sun-to a trace obtained with the SOHO SUMER imaging UV spectrometer. I also compare STIS line profiles of the active coronal dwarf to the corresponding features in the mixed-activity "hybrid-chromosphere" bright giant alpha TrA (K2 II) and the archetype "noncoronal" red giant Arcturus (alpha Boo; K2 III). The latter shows dramatic evidence for a "cool absorber" in its outer atmosphere that is extinguishing the "hot lines" (like Si IV lambda1393 and N V lambda1238) below about 1500 A, probably through absorption in the Si I lambda1525 and C I lambda1240 photoionization continua. The disappearance of coronae across the "Linsky-Haisch" dividing line near K1 III thus apparently is promoted by a dramatic overturning in the outer atmospheric structure, namely the coronae of the red giants seem to lie beneath their extended chromospheres, rather than outside as in the Sun. I then discuss an intriguing long-slit STIS low-resolution observation of an X-ray active late-A dwarf in the nearby Hyades cluster: the spatially resolved UV spectroscopy clearly shows that a previously unseen close companion (a dKe or dMe) likely is responsible for the coronal activity, rather than some unexplained departure of the A dwarf from its expected state of X-ray dormancy. Finally, I describe early results from a joint observing campaign involving SOHO SUMER, TRACE, and the Kitt Peak Infrared Imaging Spectrometer, conducted May 1999, to explore the dynamics of the quiet solar atmosphere through the key "magnetic transition zone" that separates the kinetically dominated deep photosphere from the magnetically dominated coronal regime. Linking spatially and temporally resolved solar properties to aspects of the averaged lineshapes (for example: widths, asymmetries, intensity ratios, and Doppler shifts) is a crucial step in carrying any physical wisdom we develop in the solar setting to the distant stars.

Digging for substellar objects in the stellar graveyard

NASA Astrophysics Data System (ADS)

Debes, John H., IV

2005-11-01

White dwarfs, the endpoint of stellar evolution for stars with mass < 8 [Special characters omitted.] , possess several attributes favorable for studying planet and brown dwarf formation around stars with primordial masses 1 [Special characters omitted.] . This thesis explores the consequences of post-main-sequence evolution on the dynamics of a planetary system and the observational signatures that arise from such evolution. These signatures are then specifically tested with a direct imaging survey of nearby white dwarfs. Finally, new techniques for high contrast imaging are discussed and placed in the context of further searches for planets and brown dwarfs in the stellar graveyard. While planets closer than ~ 5 AU will most likely not survive the post-main sequence evolution of its parent star, any planet with semimajor axis > 5 AU will survive, and its semimajor axis will increase as the central star loses mass. The stability of adjacent orbits to mutual planet-planet perturbations depends on the ratio of the planet mass to the central star's mass, and I demonstrate that some planets in previously stable orbits around a star undergoing mass loss will become unstable. If pollution of a white dwarf's atmosphere is caused by relic planetary systems, any white dwarf with photospheric absorption due to metals can be searched for substellar companions. Hydrogen white dwarfs with metal absorption, so called DAZ white dwarfs, are hard to explain by simple ISM accretion, and present an opportunity to test the observational signatures of unstable planetary systems. Additionally, field white dwarfs can be searched for substellar companions as well. The search for planetary companions to stars requires further development of high contrast imaging techniques. This thesis studies Gaussian aperture pupil masks (GAPMs) which in theory can achieve the contrast requisite for directly imaging an extrasolar planet around a nearby solar type star. I outline the process of designing, fabricating, and testing a GAPM for use on current telescopes and specifically the Penn State near-IR Imager and Spectrograph (PIRIS) at the Mt. Wilson 100" telescope. I find that observations with a prototype are quite successful, achieving a contrast similar to a traditional Lyot coronagraph without blocking any light from a central object and useful for finding faint companions to nearby young solar analogues. In the lab I can reproduce the expected PSF reasonably well and with a single aperture design which achieves ~ 4 x 10 -5 contrast at 10l/ D . I find that small inaccuracies in the mask fabrication process and insufficient correction of the atmosphere contribute the most degradation to contrast at these levels. (Abstract shortened by UMI.)

The WFCAM Transit Survey: a search for rocky planets around cool stars

NASA Astrophysics Data System (ADS)

Birkby, Jayne

2010-09-01

The theory of core accretion makes two intriguing, observable predictions: i) that the formation of rocky/icy planets is common around M-dwarfs, and ii) that hot-Jupiters are extremely difficult to produce around low-mass stars. Furthermore, due to their small physical size and lower bolometric luminosity, M-dwarfs are up to 300? more sensitive to planetary transits in their habitable zones than solar-type stars. We present here the WFCAM Transit Survey (WTS); an ambitious, near- infrared photometric monitoring campaign of ˜6000 M-dwarfs across four 1.5 sq deg fields situated >5 degrees above and below the galactic plane. We utilise a unique opportunity provided by the highly efficient queue-scheduled operational mode of the UKIRT to observe our fields, with at least one visible at any time, when atmospheric conditions and RA coverage are unsuitable for other ongoing UKIRT programs. By probing the peak of the M-dwarf spectral energy distribution (13<17), we obtain a statistically significant sample of low-mass stars, which allows us to place meaningful constraints on the occurrence and formation of planets around M-dwarfs. The WTS has achieved one thousand epochs after 2 years in one of our target fields and will continue until April 2012. Our light curves have a per datapoint photometric precision of ˜3-4 mmag for the brightest objects, with RMS scatter < 1% for J<16, sufficient to detect Earth-like transits around M-dwarfs. I report here on the goals of our survey, our most recent results and the properties of our M-dwarf target sample. I also discuss our processing methods and how we combat the challenges encountered when observing occultations of faint red stars and the spectroscopic follow-up required to confirm them. (http://www.ast.cam.ac.uk/˜sth/wts/index.html)

Follow-up spectroscopic observations of HD 107148 B: A new white dwarf companion of an exoplanet host star

NASA Astrophysics Data System (ADS)

Mugrauer, M.; Dinçel, B.

2016-06-01

We report on our follow-up spectroscopy of HD 1071478 B, a recently detected faint co-moving companion of the exoplanet host star HD 107148 A. The companion is separated from its primary star by about 35 arcsec (or 1790 AU of projected separation) and its optical and near infrared photometry is consistent with a white dwarf, located at the distance of HD 107148 A. In order to confirm the white dwarf nature of the co-moving companion, we obtained follow-up spectroscopic observations of HD 107148 B with CAFOS at the CAHA 2.2 m telescope. According to our CAFOS spectroscopy HD 107148 B is a DA white dwarf with an effective temperature in the range between 5900 and 6400 K. The properties of HD 107148 B can further be constrained with the derived effective temperature and the known visual and infrared photometry of the companion, using evolutionary models of DA white dwarfs. We obtain for HD 107148 B a mass of 0.56±0.05 M_⊙, a luminosity of (2.0±0.2)×10-4 L_⊙, log g [cm s-2])=7.95±0.09, and a cooling age of 2100±270 Myr. With its white dwarf companion the exoplanet host star HD 107148 A forms an evolved stellar system, which hosts at least one exoplanet. So far, only few of these evolved systems are known, which represent only about 5 % of all known exoplanet host multiple stellar systems. HD 107148 B is the second confirmed white dwarf companion of an exoplanet host star with a projected separation to its primary star of more than 1000 AU. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).

K2 Ultracool Dwarfs Survey. II. The White Light Flare Rate of Young Brown Dwarfs

NASA Astrophysics Data System (ADS)

Gizis, John E.; Paudel, Rishi R.; Mullan, Dermott; Schmidt, Sarah J.; Burgasser, Adam J.; Williams, Peter K. G.

2017-08-01

We use Kepler K2 Campaign 4 short-cadence (one-minute) photometry to measure white light flares in the young, moving group brown dwarfs 2MASS J03350208+2342356 (2M0335+23) and 2MASS J03552337+1133437 (2M0355+11), and report on long-cadence (thirty-minute) photometry of a superflare in the Pleiades M8 brown dwarf CFHT-PL-17. The rotation period (5.24 hr) and projected rotational velocity (45 km s-1) confirm 2M0335+23 is inflated (R≥slant 0.20 {R}⊙ ) as predicted for a 0.06 {M}⊙ , 24 Myr old brown dwarf βPic moving group member. We detect 22 white light flares on 2M0335+23. The flare frequency distribution follows a power-law distribution with slope -α =-1.8+/- 0.2 over the range 1031 to 1033 erg. This slope is similar to that observed in the Sun and warmer flare stars, and is consistent with lower-energy flares in previous work on M6-M8 very-low-mass stars; taking the two data sets together, the flare frequency distribution for ultracool dwarfs is a power law over 4.3 orders of magnitude. The superflare (2.6× {10}34 erg) on CFHT-PL-17 shows higher-energy flares are possible. We detect no flares down to a limit of 2× {10}30 erg in the nearby L5γ AB Dor moving group brown dwarf 2M0355+11, consistent with the view that fast magnetic reconnection is suppressed in cool atmospheres. We discuss two multi-peaked flares observed in 2M0335+23, and argue that these complex flares can be understood as sympathetic flares, in which fast-mode magnetohydrodynamic waves similar to extreme-ultraviolet waves in the Sun trigger magnetic reconnection in different active regions.

Low-mass White Dwarfs with Hydrogen Envelopes as a Missing Link in the Tidal Disruption Menu

NASA Astrophysics Data System (ADS)

Law-Smith, Jamie; MacLeod, Morgan; Guillochon, James; Macias, Phillip; Ramirez-Ruiz, Enrico

2017-06-01

We construct a menu of objects that can give rise to bright flares when disrupted by massive black holes (BHs), ranging from planets to evolved stars. Through their tidal disruption, main sequence and evolved stars can effectively probe the existence of otherwise quiescent supermassive BHs, and white dwarfs can probe intermediate mass BHs. Many low-mass white dwarfs possess extended hydrogen envelopes, which allow for the production of prompt flares in disruptive encounters with moderately massive BHs of 105-{10}7 {M}⊙ —masses that may constitute the majority of massive BHs by number. These objects are a missing link in two ways: (1) for probing moderately massive BHs and (2) for understanding the hydrodynamics of the disruption of objects with tenuous envelopes. A flare arising from the tidal disruption of a 0.17 {M}⊙ white dwarf by a {10}5 {M}⊙ {BH} reaches a maximum between 0.6 and 11 days, with a peak fallback rate that is usually super-Eddington and results in a flare that is likely brighter than a typical tidal disruption event. Encounters stripping only the envelope can provide hydrogen-only fallback, while encounters disrupting the core evolve from H- to He-rich fallback. While most tidal disruption candidates observed thus far are consistent with the disruptions of main sequence stars, the rapid timescales of nuclear transients such as Dougie and PTF10iya are naturally explained by the disruption of low-mass white dwarfs. As the number of observed flares continues to increase, the menu presented here will be essential for characterizing nuclear BHs and their environments through tidal disruptions.

A burst from a thermonuclear runaway on an ONeMg white dwarf

NASA Technical Reports Server (NTRS)

Starrfield, S.; Politano, M.; Truran, J. W.; Sparks, W. M.

1992-01-01

Studies which examine the consequences of accretion, at rates of 10(exp -9) solar mass/yr and 10(exp -10) solar mass/yr, onto an ONeMg white dwarf with a mass of 1.35 solar masses are performed. In these studies, a Lagrangian, hydrodynamic, one-dimensional computer code was used. The code now includes a network with 89 nuclei up to Ca-40, elemental diffusion, new opacities, and new equation of state. The initial abundance distribution corresponded to a mixture that was enriched to either 25, 50, or 75 percent in products of carbon burning. The remaining material in each case is assumed to have a solar composition. The evolution of the thermonuclear runaway in the 1.35 solar mass white dwarf, with M = 10(exp -9) solar mass, produced peak temperatures in the shell source exceeding 300 million degrees. The sequence produced significant amounts of Na-22 from proton captures onto Ne-20 and significant amounts of Al-26 from proton captures on Mg-24. This sequence ejected 5.2 x 10(exp -6) solar mass moving with speeds from approximately 100 km/s to 2300 km/s. When the mass accretion rate was decreased to 10(exp -10) solar mass, the resulting thermonuclear runaway produced a shock that moved through the outer envelope of the white dwarf and raised the surface luminosity to L greater than 10(exp 7) solar luminosity and the effective temperature to values exceeding 10(exp 7) K. The interaction of the material expanding from off of the white dwarf with the accretion disk should produce a burst of gamma-rays.

Isolation and characterization of a Ds-tagged rice (Oryza sativa L.) GA-responsive dwarf mutant defective in an early step of the gibberellin biosynthesis pathway.

PubMed

Margis-Pinheiro, Marcia; Zhou, Xue-Rong; Zhu, Qian-Hao; Dennis, Elizabeth S; Upadhyaya, Narayana M

2005-03-01

We have isolated a severe dwarf transposon (Ds) insertion mutant in rice (Oryza sativa L.), which could be differentiated early in the seedling stage by reduced shoot growth and dark green leaves, and later by severe dwarfism and failure to initiate flowering. These mutants, however, showed normal seed germination and root growth. One of the sequences flanking Ds, rescued from the mutant, was of a chromosome 4-located putative ent-kaurene synthase (KS) gene, encoding the enzyme catalyzing the second step of the gibberellin (GA) biosynthesis pathway. Dwarf mutants were always homozygous for this Ds insertion and no normal plants homozygous for this mutation were recovered in the segregating progeny, indicating that the Ds insertion mutation is recessive. As mutations in three recently reported rice GA-responsive dwarf mutant alleles and the dwarf mutation identified in this study mapped to the same locus, we designate the corresponding gene OsKS1. The osks1 mutant seedlings were responsive to exogenous gibberellin (GA3). OsKS1 transcripts of about 2.3 kb were detected in leaves and stem of wild-type plants, but not in germinating seeds or roots, suggesting that OsKS1 is not involved in germination or root growth. There are at least five OsKS1-like genes in the rice genome, four of which are also represented in rice expressed sequence tag (EST) databases. All OsKS1-like genes are transcribed with different expression patterns. ESTs corresponding to all six OsKS genes are represented in other cereal databases including barley, wheat and maize, suggesting that they are biologically active.

2MASS Photometry of the Hot DA White Dwarf Stars in the Palomar Green Survey

NASA Astrophysics Data System (ADS)

Holberg, J. B.; Magargal, K.

2003-12-01

The Palomar Green (PG) Survey is a complete, magnitude limited survey of UV excess objects that continues to provide well-defined sample populations for many types of objects, in particular hot white dwarf stars. The 2MASS All-Sky Survey limiting JHK magnitudes are reasonably well matched to the B magnitude limits of the PG survey. The 2MASS survey, therefore, constitutes an excellent source of uniform, high-quality of photometry, that can be used in conjunction with the PG Survey. The 2MASS Point Source Catalog in the All-Sky Data Release was searched for over 340 hot DA white dwarfs in the PG sample. The resulting JHK colors and apparent magnitudes are used to determine photometric distances for these stars and to place limits on the existence of possible cool binary companions. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.

UV observations of the cool DBQA5 white dwarf LDS 678A - Limits on the atmospheric composition, pressure shift, and gravitational redshift derived from C I 2479

NASA Technical Reports Server (NTRS)

Oswalt, Terry D.; Sion, Edward M.; Hammond, Gordon; Vauclair, Gerard; Liebert, James W.

1991-01-01

A high-resolution ultraviolet spectrum of the helium-rich degenerate LDS 678A, obtained with the International Ultraviolet Explorer (IUE) satellite, is presented. LDS 678A is the coolest metallic line degenerate (DQ or DZ) yet observed with the IUE echelle. These observations provide a detailed line profile of the strong C I 2479 absorption line and equivalent width W2479 = 2.35 + or - 0.06 A from which theoretical profile fits yield a carbon abundance of log C/He = (-6.7 + or- 0.2). The presence of carbon in a He-rich atmosphere lends credence to the notion that LDS 678A is a transitional case between the DB white dwarfs with nearly pure helium atmospheres and the helium-rich DQ white dwarfs which exhibit carbon bands. Corrected for an inferred pressure shift Vp = + 38 + or - 4 km/s for the C I 2479 line, a gravitational redshift of Vrs = + 26 + or - 13 km/s is deduced from which a most probable mass of 0.55 solar mass is derived.

X-rays from accretion of red giant winds

NASA Technical Reports Server (NTRS)

Jura, M.; Helfand, D. J.

1984-01-01

X-ray observations of the late-type red giants Mira and R Aqr obtained with the Einstein Observatory are presented, and the general problems of white dwarf accretion from late-type giant winds is considered. The extremely low measured luminosities obtained for the two systems leads to the conclusion that the companions of Mira and R Aqr are most likely low-mass main sequence objects rather than white dwarfs as is usually assumed. The expected X-ray luminosities of true red giant/white dwarf systems are considered, and it is concluded that far too few have been detected if the canonical accretion scenario is adopted. A possible explanation of this situation in terms of grain-dominated Eddington-limited accretion is proposed.

POST-MAIN SEQUENCE EVOLUTION OF ICY MINOR PLANETS: IMPLICATIONS FOR WATER RETENTION AND WHITE DWARF POLLUTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malamud, Uri; Perets, Hagai B., E-mail: uri.mal@tx.technion.ac.il, E-mail: hperets@physics.technion.ac.il

Most observations of polluted white dwarf atmospheres are consistent with accretion of water-depleted planetary material. Among tens of known cases, merely two involve accretion of objects that contain a considerable mass fraction of water. The purpose of this study is to investigate the relative scarcity of these detections. Based on a new and highly detailed model, we evaluate the retention of water inside icy minor planets during the high-luminosity stellar evolution that follows the main sequence. Our model fully considers the thermal, physical, and chemical evolution of icy bodies, following their internal differentiation as well as water depletion, from themore » moment of their birth and through all stellar evolution phases preceding the formation of the white dwarf. We also account for different initial compositions and formation times. Our results differ from previous studies, which have either underestimated or overestimated water retention. We show that water can survive in a variety of circumstances and in great quantities, and therefore other possibilities are discussed in order to explain the infrequency of water detection. We predict that the sequence of accretion is such that water accretes earlier, and more rapidly, than the rest of the silicate disk, considerably reducing the chance of its detection in H-dominated atmospheres. In He-dominated atmospheres, the scarcity of water detections could be observationally biased. It implies that the accreted material is typically intrinsically dry, which may be the result of the inside-out depopulation sequence of minor planets.« less

A new three-locus model for rootstock-induced dwarfing in apple revealed by genetic mapping of root bark percentage

PubMed Central

Harrison, Nicola; Harrison, Richard J.; Barber-Perez, Nuria; Cascant-Lopez, Emma; Cobo-Medina, Magdalena; Lipska, Marzena; Conde-Ruíz, Rebeca; Brain, Philip; Gregory, Peter J.; Fernández-Fernández, Felicidad

2016-01-01

Rootstock-induced dwarfing of apple scions revolutionized global apple production during the twentieth century, leading to the development of modern intensive orchards. A high root bark percentage (the percentage of the whole root area constituted by root cortex) has previously been associated with rootstock-induced dwarfing in apple. In this study, the root bark percentage was measured in a full-sib family of ungrafted apple rootstocks and found to be under the control of three loci. Two quantitative trait loci (QTLs) for root bark percentage were found to co-localize to the same genomic regions on chromosome 5 and chromosome 11 previously identified as controlling dwarfing, Dw1 and Dw2, respectively. A third QTL was identified on chromosome 13 in a region that has not been previously associated with dwarfing. The development of closely linked sequence-tagged site markers improved the resolution of allelic classes, thereby allowing the detection of dominance and epistatic interactions between loci, with high root bark percentage only occurring in specific allelic combinations. In addition, we report a significant negative correlation between root bark percentage and stem diameter (an indicator of tree vigour), measured on a clonally propagated grafted subset of the mapping population. The demonstrated link between root bark percentage and rootstock-induced dwarfing of the scion leads us to propose a three-locus model that is able to explain levels of dwarfing from the dwarf ‘M.27’ to the semi-invigorating rootstock ‘M.116’. Moreover, we suggest that the QTL on chromosome 13 (Rb3) might be analogous to a third dwarfing QTL, Dw3, which has not previously been identified. PMID:26826217

Apple dwarfing rootstocks exhibit an imbalance in carbohydrate allocation and reduced cell growth and metabolism

PubMed Central

Foster, Toshi M; McAtee, Peter A; Waite, Chethi N; Boldingh, Helen L; McGhie, Tony K

2017-01-01

Apple dwarfing rootstocks cause earlier shoot termination and reduced root and shoot mass. To identify physiological factors responsible for rootstock-induced growth restriction, we compared vascular-enriched gene expression between two dwarfing rootstocks (‘M27’ and ‘M9’) and the vigorous rootstock ‘M793’ using RNA sequencing and quantitative reverse transcriptase PCR. Differentially expressed genes common to both dwarfing rootstocks belonged to five main biological processes: (1) primary metabolism, (2) cell wall synthesis and modification, (3) secondary metabolism, (4) hormone signalling and response and (5) redox homeostasis. Genes promoting the biosynthesis of amino acids, lipids and cell walls were downregulated in dwarfing rootstocks, whereas genes promoting the breakdown of these compounds were upregulated. The only exception to this trend was the upregulation of starch synthesis genes in dwarfing rootstocks. Non-structural carbohydrate analysis demonstrated that starch concentrations in ‘M9’ roots, stems and grafted ‘Royal Gala’ (‘RG’) scions were double that of equivalent tissues from ‘RG’ homo-grafted trees (‘RG’/‘RG’). Fructose and glucose concentrations were much lower in all three tissues of the ‘RG’/‘M9’ trees. Together, these data indicate that dwarfing rootstocks are in a state of sugar depletion and reduced cellular activity despite having large starch reserves. Another significant finding was the over-accumulation of flavonoids and the downregulation of auxin influx transporters MdAUX1 and MdLAX2 in dwarfing rootstocks. We propose that both factors reduce polar auxin transport. The results of this study contribute novel information about the physiological state of dwarfing rootstocks. PMID:28435686

The Near-Infrared Na I Doublet Feature in M Stars

NASA Astrophysics Data System (ADS)

Schiavon, R. P.; Barbuy, B.; Rossi, S. C. F.; Milone; A.

1997-04-01

The Na I near-infrared feature has been used to indicate the dwarf/giant population in composite systems, but its interpretation is still an issue of contention. In order to try to understand the behavior of this controversial feature, we study the spectra of cool stars by means of both observed and synthetic spectra. We conclude that the Na I infrared feature can be used as a dwarf/giant indicator. We propose a modified definition of the Na I index by defining a red continuum at 8234 Å and by measuring the equivalent width in the range 8172-8197 Å, avoiding the region at λ > 8197 Å, which contains V I, Zr I, Fe I, and TiO lines. Observations collected at the European Southern Observatory, La Silla, Chile.

IUE observations of the 1987 superoutburst of the dwarf nova Z Cha

NASA Technical Reports Server (NTRS)

Harlaftis, E.; Hassall, B. J. M.; Sonneborn, G.; Naylor, T.; Charles, P. A.

1988-01-01

Low resolution IUE observations of the dwarf nova Z Cha during superoutburst are presented. These cover most of the development of the outburst and have sufficient time resolution to probe continuum and line behavior on orbital phase. The observed modulation on this phase is very similar to that observed in the related object OY Car. The results imply the presence of a cool spot on the edge of the edge of the accretion disk, which periodically occults the brighter inner disk. Details of the line behavior suggest that the line originated in an extended wind-emitting region. In contrast to archive spectra obtained in normal outburst, the continuum is fainter and redder, indicating that the entire superoutburst disk may be geometrically thicker than during a normal outburst.

Serendipitous discovery of a faint dwarf galaxy near a Local Volume dwarf

NASA Astrophysics Data System (ADS)

Makarova, L. N.; Makarov, D. I.; Antipova, A. V.; Karachentsev, I. D.; Tully, R. B.

2018-03-01

A faint dwarf irregular galaxy has been discovered in the HST/ACS field of LV J1157+5638. The galaxy is resolved into individual stars, including the brightest magnitude of the red giant branch. The dwarf is very likely a physical satellite of LV J1157+5638. The distance modulus of LV J1157+5638 using the tip of the red giant branch (TRGB) distance indicator is 29.82 ± 0.09 mag (D = 9.22 ± 0.38 Mpc). The TRGB distance modulus of LV J1157+5638 sat is 29.76 ± 0.11 mag (D = 8.95 ± 0.42 Mpc). The distances to the two galaxies are consistent within the uncertainties. The projected separation between them is only 3.9 kpc. LV J1157+5638 has a total absolute V magnitude of -13.26 ± 0.10 and linear Holmberg diameter of 1.36 kpc, whereas its faint satellite LV J1157+5638 sat has MV = -9.38 ± 0.13 mag and Holmberg diameter of 0.37 kpc. Such a faint dwarf was discovered for the first time beyond the nearest 4 Mpc from us. The presence of main-sequence stars in both galaxies unambiguously indicates the classification of the objects as dwarf irregulars with recent or ongoing star formation events in both galaxies.

White dwarf stars with carbon atmospheres.

PubMed

Dufour, P; Liebert, J; Fontaine, G; Behara, N

2007-11-22

White dwarfs represent the endpoint of stellar evolution for stars with initial masses between approximately 0.07 and 8-10, where is the mass of the Sun (more massive stars end their life as either black holes or neutron stars). The theory of stellar evolution predicts that the majority of white dwarfs have a core made of carbon and oxygen, which itself is surrounded by a helium layer and, for approximately 80 per cent of known white dwarfs, by an additional hydrogen layer. All white dwarfs therefore have been traditionally found to belong to one of two categories: those with a hydrogen-rich atmosphere (the DA spectral type) and those with a helium-rich atmosphere (the non-DAs). Here we report the discovery of several white dwarfs with atmospheres primarily composed of carbon, with little or no trace of hydrogen or helium. Our analysis shows that the atmospheric parameters found for these stars do not fit satisfactorily in any of the currently known theories of post-asymptotic giant branch evolution, although these objects might be the cooler counterpart of the unique and extensively studied PG 1159 star H1504+65 (refs 4-7). These stars, together with H1504+65, might accordingly form a new evolutionary sequence that follows the asymptotic giant branch.

CARMENES input catalogue of M dwarfs. I. Low-resolution spectroscopy with CAFOS

NASA Astrophysics Data System (ADS)

Alonso-Floriano, F. J.; Morales, J. C.; Caballero, J. A.; Montes, D.; Klutsch, A.; Mundt, R.; Cortés-Contreras, M.; Ribas, I.; Reiners, A.; Amado, P. J.; Quirrenbach, A.; Jeffers, S. V.

2015-05-01

Context. CARMENES is a stabilised, high-resolution, double-channel spectrograph at the 3.5 m Calar Alto telescope. It is optimally designed for radial-velocity surveys of M dwarfs with potentially habitable Earth-mass planets. Aims: We prepare a list of the brightest, single M dwarfs in each spectral subtype observable from the northern hemisphere, from which we will select the best planet-hunting targets for CARMENES. Methods: In this first paper on the preparation of our input catalogue, we compiled a large amount of public data and collected low-resolution optical spectroscopy with CAFOS at the 2.2 m Calar Alto telescope for 753 stars. We derived accurate spectral types using a dense grid of standard stars, a double least-squares minimisation technique, and 31 spectral indices previously defined by other authors. Additionally, we quantified surface gravity, metallicity, and chromospheric activity for all the stars in our sample. Results: We calculated spectral types for all 753 stars, of which 305 are new and 448 are revised. We measured pseudo-equivalent widths of Hα for all the stars in our sample, concluded that chromospheric activity does not affect spectral typing from our indices, and tabulated 49 stars that had been reported to be young stars in open clusters, moving groups, and stellar associations. Of the 753 stars, two are new subdwarf candidates, three are T Tauri stars, 25 are giants, 44 are K dwarfs, and 679 are M dwarfs. Many of the 261 investigated dwarfs in the range M4.0-8.0 V are among the brightest stars known in their spectral subtype. Conclusions: This collection of low-resolution spectroscopic data serves as a candidate target list for the CARMENES survey and can be highly valuable for other radial-velocity surveys of M dwarfs and for studies of cool dwarfs in the solar neighbourhood. Full Tables A.1, A.2, and A.3 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/577/A128

Old Star's "Rebirth" Gives Astronomers Surprises

NASA Astrophysics Data System (ADS)

2005-04-01

Astronomers using the National Science Foundation's Very Large Array (VLA) radio telescope are taking advantage of a once-in-a-lifetime opportunity to watch an old star suddenly stir back into new activity after coming to the end of its normal life. Their surprising results have forced them to change their ideas of how such an old, white dwarf star can re-ignite its nuclear furnace for one final blast of energy. Sakurai's Object Radio/Optical Images of Sakurai's Object: Color image shows nebula ejected thousands of years ago. Contours indicate radio emission. Inset is Hubble Space Telescope image, with contours indicating radio emission; this inset shows just the central part of the region. CREDIT: Hajduk et al., NRAO/AUI/NSF, ESO, StSci, NASA Computer simulations had predicted a series of events that would follow such a re-ignition of fusion reactions, but the star didn't follow the script -- events moved 100 times more quickly than the simulations predicted. "We've now produced a new theoretical model of how this process works, and the VLA observations have provided the first evidence supporting our new model," said Albert Zijlstra, of the University of Manchester in the United Kingdom. Zijlstra and his colleagues presented their findings in the April 8 issue of the journal Science. The astronomers studied a star known as V4334 Sgr, in the constellation Sagittarius. It is better known as "Sakurai's Object," after Japanese amateur astronomer Yukio Sakurai, who discovered it on February 20, 1996, when it suddenly burst into new brightness. At first, astronomers thought the outburst was a common nova explosion, but further study showed that Sakurai's Object was anything but common. The star is an old white dwarf that had run out of hydrogen fuel for nuclear fusion reactions in its core. Astronomers believe that some such stars can undergo a final burst of fusion in a shell of helium that surrounds a core of heavier nuclei such as carbon and oxygen. However, the outburst of Sakurai's Object is the first such blast seen in modern times. Stellar outbursts observed in 1670 and 1918 may have been caused by the same phenomenon. Astronomers expect the Sun to become a white dwarf in about five billion years. A white dwarf is a dense core left after a star's normal, fusion-powered life has ended. A teaspoon of white dwarf material would weigh about 10 tons. White dwarfs can have masses up to 1.4 times that of the Sun; larger stars collapse at the end of their lives into even-denser neutron stars or black holes. Computer simulations indicated that heat-spurred convection (or "boiling") would bring hydrogen from the star's outer envelope down into the helium shell, driving a brief flash of new nuclear fusion. This would cause a sudden increase in brightness. The original computer models suggested a sequence of observable events that would occur over a few hundred years. "Sakurai's object went through the first phases of this sequence in just a few years -- 100 times faster than we expected -- so we had to revise our models," Zijlstra said. The revised models predicted that the star should rapidly reheat and begin to ionize gases in its surrounding region. "This is what we now see in our latest VLA observations," Zijlstra said. "It's important to understand this process. Sakurai's Object has ejected a large amount of the carbon from its inner core into space, both in the form of gas and dust grains. These will find their way into regions of space where new stars form, and the dust grains may become incorporated in new planets. Some carbon grains found in a meteorite show isotope ratios identical to those found in Sakurai's Object, and we think they may have come from such an event. Our results suggest this source for cosmic carbon may be far more important than we suspected before," Zijlstra added. The scientists continue to observe Sakurai's Object to take advantage of the rare opportunity to learn about the process of re-ignition. They are making new VLA observations just this month. Their new models predict that the star will heat very quickly, then slowly cool again, cooling back to its current temperature about the year 2200. They think there will be one more reheating episode before it starts its final cooling to a stellar cinder. Zijlstra worked with Marcin Hajduk of the University of Manchester and Nikolaus Copernicus University, Torun, Poland; Falk Herwig of Los Alamos National Laboratory; Peter A.M. van Hoof of Queen's University in Belfast and the Royal Observatory of Belgium; Florian Kerber of the European Southern Observatory in Germany; Stefan Kimeswenger of the University of Innsbruck, Austria; Don Pollacco of Queen's University in Belfast; Aneurin Evans of Keele University in Staffordshire, UK; Jose Lopez of the National Autonomous University of Mexico in Ensenada; Myfanwy Bryce of Jodrell Bank Observatory in the UK; Stewart P.S. Eyres of the University of Central Lancashire in the UK; and Mikako Matsuura of the University of Manchester. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Search for Variables in the Kepler Field on DASCH Plates

NASA Astrophysics Data System (ADS)

Tang, Sumin; Grindlay, J.; Los, E.; Servillat, M.

2011-01-01

The Digital Access to a Sky Century @ Harvard (DASCH) is a project to digitize the half a million glass photographic plates over the period 1880s-1980s. This 100 year coverage is a unique resource for studying temporal variations in the universe. Here we present our variable search algorithms and variable catalog in the Kepler fields based on 3000 scanned plates. We use the KIC spectral classifications to search for long-term variability of any main sequence stars, particularly M dwarfs. We apply a variability search technique developed for DASCH and set limits on the fraction of main sequence stars, by spectral type, which show detectable (>0.2mag) variability on timescales 10-100y. Such limits are of particular interest for M dwarfs given the recent discoveries of their planet systems.

Astrophysical Implications of a New Dynamical Mass for the Nearby White Dwarf 40 Eridani B

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bond, Howard E.; Bergeron, P.; Bédard, A., E-mail: heb11@psu.edu

The bright, nearby DA-type white dwarf (WD) 40 Eridani B is orbited by the M dwarf 40 Eri C, allowing determination of the WD’s mass. Until recently, however, the mass depended on orbital elements determined four decades ago, and that mass was so low that it created several astrophysical puzzles. Using new astrometric measurements, the binary-star group at the U.S. Naval Observatory has revised the dynamical mass upward, to 0.573 ± 0.018 M {sub ☉}. In this paper, we use model-atmosphere analysis to update other parameters of the WD, including effective temperature, surface gravity, radius, and luminosity. We then comparemore » these results with WD interior models. Within the observational uncertainties, theoretical cooling tracks for CO-core WDs of its measured mass are consistent with the position of 40 Eri B in the H-R diagram; equivalently, the theoretical mass–radius relation (MRR) is consistent with the star’s location in the mass–radius plane. This consistency is, however, achieved only if we assume a “thin” outer hydrogen layer, with q {sub H} = M {sub H}/ M {sub WD} ≃ 10{sup −10}. We discuss other evidence that a significant fraction of DA WDs have such thin H layers, in spite of the expectation from canonical stellar-evolution theory of “thick” H layers with q {sub H} ≃ 10{sup −4}. The cooling age of 40 Eri B is ∼122 Myr, and its total age is ∼1.8 Gyr. We present the MRRs for 40 Eri B and three other nearby WDs in visual binaries with precise mass determinations, and show that the agreement of current theory with observations is excellent in all cases.« less

Astrophysical Implications of a New Dynamical Mass for the Nearby White Dwarf 40 Eridani B

NASA Astrophysics Data System (ADS)

Bond, Howard E.; Bergeron, P.; Bédard, A.

2017-10-01

The bright, nearby DA-type white dwarf (WD) 40 Eridani B is orbited by the M dwarf 40 Eri C, allowing determination of the WD’s mass. Until recently, however, the mass depended on orbital elements determined four decades ago, and that mass was so low that it created several astrophysical puzzles. Using new astrometric measurements, the binary-star group at the U.S. Naval Observatory has revised the dynamical mass upward, to 0.573 ± 0.018 M ⊙. In this paper, we use model-atmosphere analysis to update other parameters of the WD, including effective temperature, surface gravity, radius, and luminosity. We then compare these results with WD interior models. Within the observational uncertainties, theoretical cooling tracks for CO-core WDs of its measured mass are consistent with the position of 40 Eri B in the H-R diagram; equivalently, the theoretical mass-radius relation (MRR) is consistent with the star’s location in the mass-radius plane. This consistency is, however, achieved only if we assume a “thin” outer hydrogen layer, with q H = M H/M WD ≃ 10-10. We discuss other evidence that a significant fraction of DA WDs have such thin H layers, in spite of the expectation from canonical stellar-evolution theory of “thick” H layers with q H ≃ 10-4. The cooling age of 40 Eri B is ˜122 Myr, and its total age is ˜1.8 Gyr. We present the MRRs for 40 Eri B and three other nearby WDs in visual binaries with precise mass determinations, and show that the agreement of current theory with observations is excellent in all cases.

Analysis of cataclysmic variable GSC02197-00886 evolution

NASA Astrophysics Data System (ADS)

Mitrofanova, A. A.; Borisov, N. V.; Shimansky, V. V.

2014-01-01

We present the spectral analysis of the physical state and evolution of the WZSge-type cataclysmic variable GSC02197-00886. The spectra of the system, covering the total orbital period at the time of the outburst on May 8, 2010, at the late relaxation stage, and in the quiescent state, were obtained at the SAO RAS 6-m BTA telescope in 2010-2012. From the absorption and emission HI, He I, and Fe II lines, we have determined the radial velocities for all the nights of observations and constructed the maps of Doppler tomography for the quiescent state. It was found that during the outburst the spectra of the object were formed in an optically thick accretion disk with an effective temperature of T eff ≈ 45 000 K and in a hotter boundary layer. During the relaxation of the system, the accretion disk gradually became optically thinner in the continuum and in the emission lines. In the quiescent state (July 2012), the continuous spectrum was dominated by the radiation of the cooling white dwarf with T eff = 18 000 K. The emission lines are formed on the surface of the cool star by the X-ray irradiation of the 1RXSJ213807.1+261958 source. We propose a method for determining the parameters of the white dwarf, based on the numerical modeling of the system spectra in the quiescent state and their comparison with the observed spectra. It is shown that the effective temperature of white dwarf has decreased by Δ T eff = 6000 K during the relaxation from August 2010 to July 2012. We have obtained a set of parameters for GSC02197-00886 and shown their good agreement with the average parameters of the W Z Sge-type systems, presented in the literature.

Flash Mixing on the White-Dwarf Cooling Curve: Understanding Hot Horizontal Branch Anomalies in NGC 2808

NASA Technical Reports Server (NTRS)

Brown, Thomas M.; Sweigart, Allen V.; Lanz, Thierry; Landsman, Wayne B.; Hubeny, Ivan; Fisher, Richard R. (Technical Monitor)

2001-01-01

We present an ultraviolet color-magnitude diagram (CMD) spanning the hot horizontal branch (HB), blue straggler, and white dwarf populations of the globular cluster NGC 2808. These data, obtained with the Space Telescope Imaging Spectrograph (STIS), demonstrate that NGC 2808 harbors a significant population of hot subluminous HB stars, an anomaly only previously reported for the globular cluster omega Cen. Our theoretical modeling indicates that the location of these subluminous stars in the CMD, as well as the high temperature gap along the HB of NGC 2808, can be explained if these stars underwent a late helium-core flash while descending the white dwarf cooling curve. We show that the convective zone produced by such a late helium flash will penetrate into the hydrogen envelope, thereby mixing hydrogen into the hot helium-burning interior, where it is rapidly consumed. This phenomenon is analogous to the "born again" scenario for producing hydrogen-deficient stars following a late helium-shell flash. The flash mixing of the envelope greatly enhances the envelope helium and carbon abundances that, in turn, leads to a discontinuous increase in the HB effective temperatures. We argue that the hot HB gap is associated with this theoretically predicted dichotomy in the HB properties. Moreover, the changes in the emergent spectral energy distribution caused by these abundance changes are primarily responsible for explaining the hot subluminous HB stars. Although further evidence is needed to confirm that a late helium-core flash can account for the subluminous HB stars and the hot HB gap, we demonstrate that an understanding of these stars requires the use of appropriate theoretical models for their evolution, atmospheres, and spectra.

Hazy Archean Earth as an Analog for Hazy Earthlike Exoplanets

NASA Astrophysics Data System (ADS)

Arney, Giada; Meadows, Victoria; Domagal-Goldman, Shawn; Claire, Mark; Schwieterman, Edward

2015-01-01

Hazy exoplanets may be common (Bean et al. 2010, Sing et al. 2011, Kreidberg et al 2014), and in our solar system, Venus and Titan have photochemically-produced hazes. There is evidence that Earth itself had a hydrocarbon haze in the Archean (Zerkle et al. 2012, Domagal-Goldman et al. 2008) with important climatic effects (Pavlov et al. 2001, Trainer et al. 2006, Haqq-Misra et al. 2008, Wolf and Toon 2012). We use a 1D coupled photochemical-climate model and a line-by-line radiative transfer model to investigate the climactic and spectral impacts of a fractal hydrocarbon haze on Archean Earth. The haze absorbs significantly at shorter wavelengths and can strongly suppress the Rayleigh scattering tail, a broadband effect that would be remotely detectable at low spectral resolution at wavelengths less than 0.5 μm. Hazes may have a more significant impact on transit transmission spectra. Using the transit transmission radiative transfer model developed by Misra et al. (2014) to generate hazy Archean spectra, we find that even a thin hydrocarbon haze masks the lower atmosphere from the visible into the near infrared where the haze optical depth exceeds unity. The transit transmission spectra we generate for hazy Archean Earth are steeply sloped like the Titan solar occultation spectrum observed by Robinson et al. (2014). Thick hazes can also cool the planet significantly: for example, the thick fractal haze generated around Archean Earth with 0.3% CH4, 1% CO2 and 1 ppm C2H6 cools the planet from roughly 290 K without the haze to below freezing with the haze. Finally, we investigate the impact of host star spectral type on haze formation, comparing the hazes generated around a solar-type star to those generated at an Earth analog planet around the M dwarf AD Leo. Our results indicate hazes around M dwarfs for the same initial atmospheric composition may be thinner due to decreased UV photolysis of methane and other hydrocarbons needed for haze formation. Earthlike planets around M dwarfs may therefore be more likely to remain haze-free than those around G dwarfs; therefore, they may be easier to examine spectrally.

CFBDSIR 2149-0403: young isolated planetary-mass object or high-metallicity low-mass brown dwarf?

NASA Astrophysics Data System (ADS)

Delorme, P.; Dupuy, T.; Gagné, J.; Reylé, C.; Forveille, T.; Liu, M. C.; Artigau, E.; Albert, L.; Delfosse, X.; Allard, F.; Homeier, D.; Malo, L.; Morley, C.; Naud, M. E.; Bonnefoy, M.

2017-06-01

Aims: We conducted a multi-wavelength, multi-instrument observational characterisation of the candidate free-floating planet CFBDSIR J214947.2-040308.9, a late T-dwarf with possible low-gravity features, in order to constrain its physical properties. Methods: We analysed nine hours of X-shooter spectroscopy with signal detectable from 0.8 to 2.3 μm, as well as additional photometry in the mid-infrared using the Spitzer Space Telescope. Combined with a VLT/HAWK-I astrometric parallax, this enabled a full characterisation of the absolute flux from the visible to 5 μm, encompassing more than 90% of the expected energy emitted by such a cool late T-type object. Our analysis of the spectrum also provided the radial velocity and therefore the determination of its full 3D kinematics. Results: While our new spectrum confirms the low gravity and/or high metallicity of CFBDSIR 2149, the parallax and kinematics safely rule out membership to any known young moving group, including AB Doradus. We use the equivalent width of the K I doublet at 1.25 μm as a promising tool to discriminate the effects of low-gravity from the effects of high-metallicity on the emission spectra of cool atmospheres. In the case of CFBDSIR 2149, the observed K I doublet clearly favours the low-gravity solution. Conclusions: CFBDSIR 2149 is therefore a peculiar late-T dwarf that is probably a young, planetary-mass object (2-13 MJup, <500 Myr) possibly similar to the exoplanet 51 Eri b, or perhaps a 2-40 MJup brown dwarf with super-solar metallicity. Based on observations obtained with X-shooter on VLT-UT2 at ESO-Paranal (run 091.D-0723). Based on observations obtained with HAWKI on VLT-UT4 (run 089.C-0952, 090.C-0483, 091.C-0543,092.C-0548,293.C-5019(A) and run 086.C-0655(A)). Based on observations obtained with ISAAC on VLT-UT3 at ESO-Paranal (run 290.C-5083). Based on observation obtained with WIRCam at CFHT (program 2012BF12). Based on Spitzer Space telescope DDT observation (program 10166).

A New Milky Way Satellite Discovered in the Subaru/Hyper Suprime-Cam Survey

NASA Astrophysics Data System (ADS)

Homma, Daisuke; Chiba, Masashi; Okamoto, Sakurako; Komiyama, Yutaka; Tanaka, Masayuki; Tanaka, Mikito; Ishigaki, Miho N.; Akiyama, Masayuki; Arimoto, Nobuo; Garmilla, José A.; Lupton, Robert H.; Strauss, Michael A.; Furusawa, Hisanori; Miyazaki, Satoshi; Murayama, Hitoshi; Nishizawa, Atsushi J.; Takada, Masahiro; Usuda, Tomonori; Wang, Shiang-Yu

2016-11-01

We report the discovery of a new ultra-faint dwarf satellite companion of the Milky Way (MW) based on the early survey data from the Hyper Suprime-Cam Subaru Strategic Program. This new satellite, Virgo I, which is located in the constellation of Virgo, has been identified as a statistically significant (5.5σ) spatial overdensity of star-like objects with a well-defined main sequence and red giant branch in the color-magnitude diagram. The significance of this overdensity increases to 10.8σ when the relevant isochrone filter is adopted for the search. Based on the distribution of the stars around the likely main-sequence turnoff at r ˜ 24 mag, the distance to Virgo I is estimated as 87 kpc, and its most likely absolute magnitude calculated from a Monte Carlo analysis is M V = -0.8 ± 0.9 mag. This stellar system has an extended spatial distribution with a half-light radius of {38}-11+12 pc, which clearly distinguishes it from a globular cluster with comparable luminosity. Thus, Virgo I is one of the faintest dwarf satellites known and is located beyond the reach of the Sloan Digital Sky Survey. This demonstrates the power of this survey program to identify very faint dwarf satellites. This discovery of Virgo I is based only on about 100 square degrees of data, thus a large number of faint dwarf satellites are likely to exist in the outer halo of the MW.

On the Li and Be tests for brown dwarfs

NASA Technical Reports Server (NTRS)

Nelson, L. A.; Rappaport, S.; Chiang, E.

1993-01-01

We present the results of stellar evolution calculations which show quantitatively how the measured abundances of Li and Be in low-mass stellar objects can be used to discriminate between brown dwarfs and low-mass main-sequence stars. The evolution of B, although less useful, is also studied. We define a transition mass range, below which at least 50 percent of the light element remains at the end of nuclear burning, and above which no more than 10 percent remains. We find that the transition mass range for Li burning is 0.059-0.062 solar mass, while for Be the range is 0.075-0.077 solar mass. Using these results, we then examine the factors (e.g., age and luminosity) that affect our ability to identify low-luminosity objects as brown dwarfs. In particular, we show that the Li test would be well suited for brown dwarf candidates located in nearby open clusters with ages in the range of 2 x 10 exp 8 to 5 x 10 exp 8 yr.

A Search for Metal Lines in the Spectra of DA White Dwarfs

NASA Technical Reports Server (NTRS)

Wegner, G. A.

1986-01-01

A theoretical analysis was carried out in order to interpret the ultraviolet spectra of DB white dwarfs obtained earlier with the International Ultraviolet Explorer (IUE) satellite. Here the results of the IUE ultraviolet spectroscopy combined with visual data and model atmospheres of DB white dwarfs are reported. In particular, a search for spectra lines due to the element carbon using the ultraviolet was made. In no case is there a positive detection of carbon and from these data, and upper limits for carbon by number relative to helium are derived in the range of C: He 10 to the minus 5 power to 10 to the minus 7 power for the 16 DB stars with ultraviolet spectra in the temperature range 11400 K T sub EFF less than 2300 K. The low carbon abundances found in the atmospheres of the DB stars agree well with the hypothesis that the atmospheric carbon observed in the cooler DQ members of the helium-rich white dwarf sequence is produced by a convective dredging mechanism.

Complete genome sequence of a divergent strain of lettuce chlorosis virus from Periwinkle in China

USDA-ARS?s Scientific Manuscript database

A novel strain of Lettuce chlorosis virus (LCV) was identified from periwinkle in China (PW) with foliar interveinal chlorosis and plant dwarfing. Complete nucleotide (nt) sequences of genomic RNA1 and RNA2 of the virus are 8,602 nt and 8,456 nt, respectively. The genomic organization of LCV-PW rese...

VO-compliant libraries of high resolution spectra of cool stars

NASA Astrophysics Data System (ADS)

Montes, D.

2008-10-01

In this contribution we describe a Virtual Observatory (VO) compliant version of the libraries of high resolution spectra of cool stars described by Montes et al. (1997; 1998; and 1999). Since their publication the fully reduced spectra in FITS format have been available via ftp and in the World Wide Web. However, in the VO all the spectra will be accessible using a common web interface following the standards of the International Virtual Observatory Alliance (IVOA). These libraries include F, G, K and M field stars, from dwarfs to giants. The spectral coverage is from 3800 to 10000 Å, with spectral resolution ranging from 0.09 to 3.0 Å.

Barium Stars: Theoretical Interpretation

NASA Astrophysics Data System (ADS)

Husti, Laura; Gallino, Roberto; Bisterzo, Sara; Straniero, Oscar; Cristallo, Sergio

2009-09-01

Barium stars are extrinsic Asymptotic Giant Branch (AGB) stars. They present the s-enhancement characteristic for AGB and post-AGB stars, but are in an earlier evolutionary stage (main sequence dwarfs, subgiants, red giants). They are believed to form in binary systems, where a more massive companion evolved faster, produced the s-elements during its AGB phase, polluted the present barium star through stellar winds and became a white dwarf. The samples of barium stars of Allen & Barbuy (2006) and of Smiljanic et al. (2007) are analysed here. Spectra of both samples were obtained at high-resolution and high S/N. We compare these observations with AGB nucleosynthesis models using different initial masses and a spread of 13C-pocket efficiencies. Once a consistent solution is found for the whole elemental distribution of abundances, a proper dilution factor is applied. This dilution is explained by the fact that the s-rich material transferred from the AGB to the nowadays observed stars is mixed with the envelope of the accretor. We also analyse the mass transfer process, and obtain the wind velocity for giants and subgiants with known orbital period. We find evidence that thermohaline mixing is acting inside main sequence dwarfs and we present a method for estimating its depth.

WFPC2 Observations of the URSA Minor Dwarf Spheroidal Galaxy

NASA Technical Reports Server (NTRS)

Mighell, Kenneth J.; Burke, Christopher J.

1999-01-01

We present our analysis of archival Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) observations in F555W (approximately V) and F814W (approximately I) of the central region of the Ursa Minor dwarf spheroidal galaxy. The V versus V - I color-magnitude diagram features a sparsely populated blue horizontal branch, a steep thin red giant branch, and a narrow subgiant branch. The main sequence reaches approximately 2 magnitudes below the main-sequence turnoff (V(sup UMi, sub TO) approximately equals 23.27 +/- 0.11 mag) of the median stellar population. We compare the fiducial sequence of the Galactic globular cluster M92 (NGC 6341). The excellent match between Ursa Minor and M92 confirms that the median stellar population of the UMi dSph galaxy is metal poor ([Fe/H](sub UMi) approximately equals [Fe/H](sub M92) approximately equals -2.2 dex) and ancient (age(sub UMi)approximately equalsage(sub M92) approximately equals 14 Gyr). The B - V reddening and the absorption in V are estimated to be E(B - V) = 0.03 +/- 0.01 mag and A(sup UMi, sub V) = 0.09 +/- 0.03 mag. A new estimate of the distance modulus of Ursa Minor, (m - M)(sup UMi, sub 0) = 19.18 +/- 0.12 mag, has been derived based on fiducial-sequence fitting M92 [DELTA.V(sub UMi - M92) = 4.60 +/- 0.03 mag and DELTA(V - I)(sub UMi - M92) = 0.010 +/- 0.005 mag] and the adoption of the apparent V distance modulus for M92 of (m - M)(sup M92, sub V) = 14.67 +/- 0.08 mag (Pont et al. 1998, A&A, 329, 87). The Ursa Minor dwarf spheroidal galaxy is then at a distance of 69 +/- 4 kpc from the Sun. These HST observations indicate that Ursa Minor has had a very simple star formation history consisting mainly of a single major burst of star formation about 14 Gyr ago which lasted approximately < 2 Gyr. While we may have missed minor younger stellar populations due to the small field-of-view of the WFPC2 instrument, these observations clearly show that most of the stars in the central region Ursa Minor dwarf spheroidal galaxy are ancient. If the ancient Galactic globular clusters, like M92, formed concurrently with the early formation of the Milky Way galaxy itself, then the Ursa Minor dwarf spheroidal is probably as old as the Milky Way.

Optical Searches for Baryonic Dark Matter

NASA Astrophysics Data System (ADS)

Graff, David Steven

1997-08-01

Microlensing results suggest that a good fraction of the halo is composed of massive chunks (0.1-1 Msolar) called MACHOs. I examine several optical searches for dim stars to constrain the local density of MACHOs. These searches show that (1) there are few red dwarfs in the galactic halo, and (2) they suggest that there are few brown dwarfs. I also find that (3) there may be sufficiently many white dwarfs in the halo to account for the microlensing results, but only if certain interesting conditions are met. (1) I examine a deep search for halo red dwarfs (Bahcall, Flynn, Gould & Kirhakos 1994). Using new stellar models and parallax observations of low mass, low metallicity stars, I find the halo red dwarf density to be <1% of the halo, while my best estimate of this value is 0.14-0.37%. (2) I derive mass functions (MF) for halo red dwarfs (the faintest hydrogen burning stars) and then extrapolate to place limits on the total mass of halo brown dwarfs (stars not quite massive enough to burn hydrogen). I find that the MF for halo red dwarfs cannot rise more quickly than 1/m2 as one approaches the hydrogen burning limit. Using recent results from star formation theory, I extrapolate the MF into the brown-dwarf regime. Likely extrapolations imply that the total mass of brown dwarfs in the halo is less than ~3% of the local mass density of the halo (~0.3% for the more realistic models I consider). My limits apply to brown dwarfs in the halo that come from the same stellar population as the red dwarfs. (3) A ground based search by Liebert, Dahn & Monet (1988) and a search of the Hubble Deep Field by Flynn, Bahcall & Gould (1996) have found no evidence for a substantial halo population of white dwarfs, implying that the putative halo population is either dim enough or sparse enough to elude detection. I use white dwarf luminosity functions calculated from various main sequence progenitor mass functions to re-examine the implications of these searches in light of recent microlensing results. I show that the minimum age of the white dwarf population depends upon assumptions regarding the initial mass function, atmospheric composition, and their total density. When I compare various theoretical white dwarf luminosity functions in which I vary these three parameters with the non detections of Liebert et al. and Flynn et al., I conclude that if white dwarfs constitute a significant portion of the halo then (I) the Universe must be 11 Gyr old and (II) they must have helium dominated atmospheres. Thus, white dwarfs could be the MACHOs and could make a significant contribution to galactic dark matter.

Precision Spectral Variability of L Dwarfs from the Ground

NASA Astrophysics Data System (ADS)

Burgasser, Adam J.; Schlawin, Everett; Teske, Johanna K.; Karalidi, Theodora; Gizis, John

2017-01-01

L dwarf photospheres (1500 K < T < 2500 K) contain mineral and metal condensates, which appear to organize into cloud structures as inferred from observed periodic photometric variations with amplitudes of <1%-30%. Studying the vertical structure, composition, and long-term evolution of these clouds necessitates precision spectroscopic monitoring, until recently limited to space-based facilities. Building on techniques developed for ground-based exoplanet transit spectroscopy, we present a method for precision spectral monitoring of L dwarfs with nearby visual companions. Using IRTF/SpeX, we demonstrate <0.5% spectral variability precision across the 0.9-2.4 micron band, and present results for two known L5 dwarf variables, J0835-0819 and J1821+1414, both of which show evidence of 3D cloud structure similar to that seen in space-based observations. We describe a survey of 30 systems which would sample the full L dwarf sequence and allow characterization of temperature, surface gravity, metallicity, rotation period and orientation effects on cloud structure, composition and evolution.This research is supported by funding from the National Science Foundation under award No. AST-1517177, and the National Aeronautics and Space Administration under Grant No. NNX15AI75G.

Stripped Red Giants - Helium Core White Dwarf Progenitors and their sdB Siblings

NASA Astrophysics Data System (ADS)

Heber, U.

2017-03-01

Some gaps in the mosaic of binary star evolution have recently been filled by the discoveries of helium-core white dwarf progenitors (often called extremely low mass (ELM) white dwarfs) as stripped cores of first-giant branch objects. Two varieties can be distinguished. One class is made up by SB1 binaries, companions being white dwarfs as well. Another class, the so-called EL CVn stars, are composite spectrum binaries, with A-Type companions. Pulsating stars are found among both classes. A riddle is posed by the apparently single objects. There is a one-to-one correspondence of the phenomena found for these new classes of star to those observed for sdB stars. In fact, standard evolutionary scenarios explain the origin of sdB stars as red giants that have been stripped close to the tip of first red giant branch. A subgroup of subluminous B stars can also be identified as stripped helium-cores of red giants. They form an extension of the ELM sequence to higher temperatures. Hence low mass white dwarfs of helium cores and sdB stars in binaries are close relatives in terms of stellar evolution.

Evolutionary Grids of Accreting White Dwarf Companions in Cataclysmic Variables

NASA Astrophysics Data System (ADS)

Benjamin, J.; Jensen, M.; Nadeau, S.; Nelson, L. A.

2003-12-01

We analyze the evolution of accreting white dwarfs in binary systems for a wide range of initial conditions. Specifically, evolutionary tracks are calculated for CO white dwarfs with masses in the range of 0.6 - 1.3 solar masses and accreting H-rich gas at rates of between 10-6 to 10-10 solar masses per year. Since the white dwarfs in these binaries could be very young or very old at the onset of mass transfer we simulated this possibility by investigating the evolution for a large range of internal temperatures. Thus most of the sequences generated were not thermally relaxed at the onset of mass transfer (and the thermonuclear flashes were not cyclic). We discuss the temporal dependence of the interior properties (envelope readjustment on a thermal timescale and compressional heating) on the initial conditions. Particular attention is paid to the white dwarfs accretors that remained small (relative to the Roche lobe radius) during the shell flash event. Finally, we use the results of these models to comment on the observed properties of Supersoft X-ray sources. This research was supported in part by funds from the Natural Sciences and Engineering Research Council (Canada).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clements, Tiffany D.; Jao, Wei-Chun; Silverstein, Michele L.

We report findings from a long-term photometric variability study of M dwarfs carried out at the SMARTS 0.9 m telescope at the Cerro Tololo Inter-American Observatory. As part of a multi-faceted effort to investigate the range of luminosities of M dwarfs of a given color on the Hertzsprung–Russell Diagram, 76 M dwarfs have been observed for 3–17 years in the Johnson–Kron–Cousins V band. We find that stars elevated above the center of the main sequence distribution tend to have higher levels of variability, likely caused by magnetic activity, than their fainter counterparts below the center. This study provides insight intomore » how the long-term magnetic activity of these stars may be affecting their sizes, luminosities, and thus positions on the H-R Diagram.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barlow, Brad N.; Wade, Richard A.; Liss, Sandra E.

The eclipsing binary system 2M 1938+4603 consists of a pulsating hot subdwarf B star and a cool M dwarf companion in an effectively circular three-hour orbit. The light curve shows both primary and secondary eclipses, along with a strong reflection effect from the cool companion. Here, we present constraints on the component masses and eccentricity derived from the Romer delay of the secondary eclipse. Using six months of publicly available Kepler photometry obtained in short-cadence mode, we fit model profiles to the primary and secondary eclipses to measure their centroid values. We find that the secondary eclipse arrives on averagemore » 2.06 {+-} 0.12 s after the midpoint between primary eclipses. Under the assumption of a circular orbit, we calculate from this time delay a mass ratio of q = 0.2691 {+-} 0.0018 and individual masses of M{sub sd} = 0.372 {+-} 0.024 M{sub Sun} and M{sub c} = 0.1002 {+-} 0.0065 M{sub Sun} for the sdB and M dwarf, respectively. These results differ slightly from those of a previously published light-curve modeling solution; this difference, however, may be reconciled with a very small eccentricity, ecos {omega} Almost-Equal-To 0.00004. We also report a decrease in the orbital period of P-dot = (-1.23 {+-} 0.07) Multiplication-Sign 10{sup -10}.« less

Constraining the Evolution of ZZ Ceti

NASA Technical Reports Server (NTRS)

Mukadam, Anjum S.; Kepler, S. O.; Winget, D. E.; Nather, R. E.; Kilic, M.; Mullally, F.; vonHippel, T.; Kleinman, S. J.; Nitta, A.; Guzik, J. A.

2003-01-01

We report our analysis of the stability of pulsation periods in the DAV star (pulsating hydrogen atmosphere white dwarf) ZZ Ceti, also called R548. On the basis of observations that span 31 years, we conclude that the period 213.13 s observed in ZZ Ceti drifts at a rate dP/dt 5 (5.5 plus or minus 1.9) x 10(exp -15) ss(sup -1), after correcting for proper motion. Our results are consistent with previous P values for this mode and an improvement over them because of the larger time base. The characteristic stability timescale implied for the pulsation period is |P||P(raised dot)|greater than or equal to 1.2 Gyr, comparable to the theoretical cooling timescale for the star. Our current stability limit for the period 213.13 s is only slightly less than the present measurement for another DAV, G117-B15A, for the period 215.2 s, establishing this mode in ZZ Ceti as the second most stable optical clock known, comparable to atomic clocks and more stable than most pulsars. Constraining the cooling rate of ZZ Ceti aids theoretical evolutionary models and white dwarf cosmochronology. The drift rate of this clock is small enough that we can set interesting limits on reflex motion due to planetary companions.

A Comprehensive COS Study of the Magnetic Dynamos, Rotations, UV Irradiances and Habitability of dM Stars with a Broad Span of Ages

NASA Astrophysics Data System (ADS)

Guinan, Edward

2012-10-01

We propose HST/COS FUV spectrophotometry of a carefully selected sample of 9 dM1-5 stars with recently reliably determined ages ranging from 1-12 Gyr. This program complements our Chandra Cycle 13 program of the same targets to determine their coronal X-ray properties. Ages {of all but one star} have recently been firmly determined from memberships in wide binaries with white dwarf {WD} companions having reliable cooling time+main-sequence evolution ages {Zhao et al. 2012, Garces et al 2011}. Until these studies, reliable age determinations for dM stars >2 Gyr were nearly impossible. However, we can now carry out a comprehensive UV study of dM star atmospheres across nearly the full age-range of the current Universe. The primary goals are 1} to study the evolution of their dynamo-generated X-ray and UV {XUV} emissions with age/rotation and to better define the heating and energetics of their atmospheres {via Age-Rotation-Activity-XUV Irradiance relations} and 2} to study the effects of the XUV radiation on planets hosted by red dwarfs. The COS UV spectral region contains numerous important diagnostic emission lines for characterizing the energy transfer and atmospheric structure, while line ratios yield valuable information about the electron density. Further, these data {when combined with our coronal X-ray measures} are also important for gauging dM star XUV emissions - critical for assessing the photochemical & photoionization evolution of planetary atmospheres and ionospheres that in turn strongly affect the possible development of life on hosted extrasolar planets. We are requesting a total of 19 HST orbits to achieve the science goals of the program.

Simulations of Magnetic Flux Emergence in Cool, Low-Mass Stars: Toward Linking Dynamo Action with Starspots

NASA Astrophysics Data System (ADS)

Weber, Maria Ann; Browning, Matthew; Nelson, Nicholas

2018-01-01

Starspots are windows into a star’s internal dynamo mechanism. However, the manner by which the dynamo-generated magnetic field traverses the stellar interior to emerge at the surface is not especially well understood. Establishing the details of magnetic flux emergence plays a key role in deciphering stellar dynamos and observed starspot properties. In the solar context, insight into this process has been obtained by assuming the magnetism giving rise to sunspots consists partly of idealized thin flux tubes (TFTs). Here, we present three sets of TFT simulations in rotating spherical shells of convection: one representative of the Sun, the second of a solar-like rapid rotator, and the third of a fully convective M dwarf. Our solar simulations reproduce sunspot observables such as low-latitude emergence, tilting action toward the equator following the Joy’s Law trend, and a phenomenon akin to active longitudes. Further, we compare the evolution of rising flux tubes in our (computationally inexpensive) TFT simulations to buoyant magnetic structures that arise naturally in a unique global simulation of a rapidly rotating Sun. We comment on the role of rapid rotation, the Coriolis force, and external torques imparted by the surrounding convection in establishing the trajectories of the flux tubes across the convection zone. In our fully convective M dwarf simulations, the expected starspot latitudes deviate from the solar trend, favoring significantly poleward latitudes unless the differential rotation is sufficiently prograde or the magnetic field is strongly super-equipartition. Together our work provides a link between dynamo-generated magnetic fields, turbulent convection, and observations of starspots along the lower main sequence.

Towards new generation spectroscopic models of cool stars

NASA Astrophysics Data System (ADS)

Bergemann, Maria

2018-06-01

Abstract: Spectroscopy is a unique tool to determine the physical parameters of stars. Knowledge of stellar chemical abundances, masses, and ages is the key to understanding the evolution of their host populations. I will focus on the current outstanding problems in spectroscopy of cool stars, which are the most useful objects in studies of our local Galactic neighborhood but also very distant systems, like faint dwarf Spheroidal galaxies. Among the most debated issues is to what extent can we trust the techniques, which rely on the classical assumptions of local thermodynamic equilibrium and hydrostatic balance. I will summarise the ongoing efforts to improve the models of cool stars, with the emphasis on NLTE and 3D modelling. I will then discuss how these exciting observations impact our knowledge of abundances in the Milky Way and in dSph systems, and present outlook for the future studies.

From Globular Clusters to Tidal Dwarfs: Structure Formation in the Tidal Tails of Merging Galaxies

NASA Astrophysics Data System (ADS)

Knierman, Karen A.; Gallagher, Sarah C.; Charlton, Jane C.; Hunsberger, Sally D.; Whitmore, Bradley; Kundu, Arunav; Hibbard, J. E.; Zaritsky, Dennis

2003-09-01

Using V and I images obtained with the Wide Field Planetary Camera 2 (WFPC2) of the Hubble Space Telescope, we investigate compact stellar structures within tidal tails. Six regions of tidal debris in the four classic ``Toomre sequence'' mergers: NGC 4038/39 (``Antennae''), NGC 3256, NGC 3921, and NGC 7252 (``Atoms for Peace'') have been studied in order to explore how the star formation depends on the local and global physical conditions. These mergers sample a range of stages in the evolutionary sequence and tails with and without embedded tidal dwarf galaxies. The six tails are found to contain a variety of stellar structures, with sizes ranging from those of globular clusters up to those of dwarf galaxies. From V and I WFPC2 images, we measure the luminosities and colors of the star clusters. NGC 3256 is found to have a large population of blue clusters (0.2<~V-I<~0.9), particularly in its western tail, similar to those found in the inner region of the merger. In contrast, NGC 4038/39 has no clusters in the observed region of the tail, only less luminous point sources likely to be individual stars. NGC 3921 and NGC 7252 have small populations of clusters along their tails. A significant cluster population is clearly associated with the prominent tidal dwarf candidates in the eastern and western tails of NGC 7252. The cluster-rich western tail of NGC 3256 is not distinguished from the others by its dynamical age or by its total H I mass. However, the mergers that have few clusters in the tail all have tidal dwarf galaxies, while NGC 3256 does not have prominent tidal dwarfs. We speculate that star formation in tidal tails may manifest itself either in small structures like clusters along the tail or in large structures such as dwarf galaxies, but not in both. Also, NGC 3256 has the highest star formation rate of the four mergers studied, which may contribute to the high number of star clusters in its tidal tails. Based in part on observations obtained with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555.

The K Dwarf Advantage for Biosignatures

NASA Astrophysics Data System (ADS)

Arney, Giada; Domagal-Goldman, Shawn David; Meadows, Victoria

2018-01-01

Biosignature detection is typically studied in the context of an atmosphere in chemical disequilibrium. Oxygen (O2) and methane (CH4) are generally considered the “canonical” biosignature disequilibrium pair. However, the modern CH4 concentration poses a major detection challenge to future direct imaging telescopes, and it has been difficult for Earth to accumulate spectrally detectable quantities of O2 and CH4 over its history (Olson et al 2016, Reinhard et al 2017). Even the lower atmospheric levels of O2 typical of the Earth’s Proterozoic eon (0.01-1% of the modern O2 amount) may have resulted in a reduced photochemical lifetime of CH4 due to decreased UV shielding of CH4 (Claire et al 2006, Goldblatt et al 2006). However, while the above is true for an Earthlike planet orbiting a sunlike star, the situation changes for other stars. For instance, Segura et al (2005) found longer photochemical lifetimes for CH4 in the atmospheres of Earthlike planets orbiting M dwarfs. M dwarfs, however, present several barriers to planetary habitability including desiccation during the stellar super-luminous pre-main sequence phase (Lugar and Barnes 2015) and tidal locking. K dwarfs, which comprise about 12% of all main sequence stars, avoid these M dwarf hazards, and will be important targets for future exoplanet direct imaging missions. Using a photochemical model, we find CH4 and O2 are simultaneously detectable in the atmospheres of K dwarf planets with various O2 concentrations ranging between Proterozoic levels and modern O2 amounts. For instance, for a planet with an Earth-like CH4 surface flux (1 x 1011 molecules/cm2/s) and a Proterozoic-like O2 level (1% of modern), the planet generates a CH4 surface mixing ratio of 1x10-5 for a planet orbiting the sun, and 1.5x10-4 – an order of magnitude more CH4 – for a planet orbiting a K6V star. This is enough to produce detectable CH4 and O2 for the planet orbiting the K6V star. We discuss the implications of this “K dwarf advantage” for biosignature searches in the context of potential future direct imaging exoplanet missions currently under study such as HabEx and LUVOIR.

Observationally Testing the Triple Origin of Blue Straggler Stars with Near-Infrared Spectroscopy

NASA Astrophysics Data System (ADS)

Kohler, Jacob P.; Gosnell, Natalie M.; Sokal, Kimberly R.; Mace, Gregory N.

2018-01-01

Presented are results to constrain blue straggler star (BSS) formation mechanisms in open cluster NGC 188 using data from the Immersion Grating INfrared Spectrometer (IGRINS) while at the Discovery Channel Telescope. The majority (at least 16 of 21) of NGC 188s BSSs are binaries, and, to date, seven white dwarf (WD) companions have been detected. This leaves at least nine undetected companion stars. Observations show a sharp peak of the BSSs companion mass distribution at 0.5 solar masses, highly suggestive of a WD or M-type main sequence (MS) star. Under our tested formation mechanism, the progenitors of BSSs are arranged in primordial hierarchical triple star systems that dynamically evolve through the Kozai-cycle tidal friction (KCTF) process into a binary composed of a BSS and, statistically, an M dwarf companion. We test for the presence of an M dwarf by cross-correlating a near-IR spectrum with both a BSS template and an M dwarf template. We present, for the first time, a preliminary detection of a 3800K, 0.5 solar mass M dwarf companion in each of the long period (log[P(d)]=3), single-lined binaries WOCS 451 and WOCS 5671 in NGC 188. To assess the possibility of a false M dwarf detection, we carry out Monte Carlo simulations cross-correlating an M dwarf template with a BSS-only spectrum with a signal-to-noise ratio matching our observations. Theoretical detection limits for various BSS-M dwarf pairs are reported. In the case of a non-detection, such as in WOCS 4970, we are able to place an upper limit on the mass, and thus temperature, of the companion star. Current and future research goals aim for further insight into the BSS formation mechanism frequencies of NGC 188.

Fundmental Parameters of Low-Mass Stars, Brown Dwarfs, and Planets

NASA Astrophysics Data System (ADS)

Montet, Benjamin; Johnson, John A.; Bowler, Brendan; Shkolnik, Evgenya

2016-01-01

Despite advances in evolutionary models of low-mass stars and brown dwarfs, these models remain poorly constrained by observations. In order to test these predictions directly, masses of individual stars must be measured and combined with broadband photometry and medium-resolution spectroscopy to probe stellar atmospheres. I will present results from an astrometric and spectroscopic survey of low-mass pre-main sequence binary stars to measure individual dynamical masses and compare to model predictions. This is the first systematic test of a large number of stellar systems of intermediate age between young star-forming regions and old field stars. Stars in our sample are members of the Tuc-Hor, AB Doradus, and beta Pictoris moving groups, the last of which includes GJ 3305 AB, the wide binary companion to the imaged exoplanet host 51 Eri. I will also present results of Spitzer observations of secondary eclipses of LHS 6343 C, a T dwarf transiting one member of an M+M binary in the Kepler field. By combining these data with Kepler photometry and radial velocity observations, we can measure the luminosity, mass, and radius of the brown dwarf. This is the first non-inflated brown dwarf for which all three of these parameters have been measured, providing the first benchmark to test model predictions of the masses and radii of field T dwarfs. I will discuss these results in the context of K2 and TESS, which will find additional benchmark transiting brown dwarfs over the course of their missions, including a description of the first planet catalog developed from K2 data and a program to search for transiting planets around mid-M dwarfs.

Precision asteroseismology of the pulsating white dwarf GD 1212 using a two-wheel-controlled Kepler spacecraft

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hermes, J. J.; Charpinet, S.; Barclay, Thomas

We present a preliminary analysis of the cool pulsating white dwarf (WD) GD 1212, enabled by more than 11.5 days of space-based photometry obtained during an engineering test of the two-reaction-wheel-controlled Kepler spacecraft. We detect at least 19 independent pulsation modes, ranging from 828.2-1220.8 s, and at least 17 nonlinear combination frequencies of those independent pulsations. Our longest uninterrupted light curve, 9.0 days in length, evidences coherent difference frequencies at periods inaccessible from the ground, up to 14.5 hr, the longest-period signals ever detected in a pulsating WD. These results mark some of the first science to come from amore » two-wheel-controlled Kepler spacecraft, proving the capability for unprecedented discoveries afforded by extending Kepler observations to the ecliptic.« less

Synthetic Stromgren photometry for F dwarf stars

NASA Technical Reports Server (NTRS)

Bell, R. A.

1988-01-01

Recent synthetic spectrum and color calculations for cool dwarf star models are tested by comparison with observation. The accuracy of the computed dependence of the thermal colors B-V and b-y on effective temperature is examined, and H-beta indices are presented and compared with observed values. The accuracy of the predictions of the Stromgren uvby system metal-abundance indicator m1 and luminosity indicator c1 are tested. A new calibration of the c1, b-y diagram in terms of absolute magnitudes is given, making use of recent calculations of stellar isochrones. Observations of very metal-poor subdwarfs are used to study the accuracy of the isochrones. The c1, b-y diagram of the subdwarfs is compared with that of the turnoff-region stars in the very metal-poor globular cluster NGC 6397.

The effect of starspots on the radii of low-mass pre-main-sequence stars

NASA Astrophysics Data System (ADS)

Jackson, R. J.; Jeffries, R. D.

2014-07-01

A polytropic model is used to investigate the effects of dark photospheric spots on the evolution and radii of magnetically active, low-mass (M < 0.5 M⊙), pre-main-sequence (PMS) stars. Spots slow the contraction along Hayashi tracks and inflate the radii of PMS stars by a factor of (1 - β)-N compared to unspotted stars of the same luminosity, where β is the equivalent covering fraction of dark starspots and N ≃ 0.45 ± 0.05. This is a much stronger inflation than predicted by Spruit & Weiss for main-sequence stars with the same β, where N ˜ 0.2-0.3. These models have been compared to radii determined for very magnetically active K- and M-dwarfs in the young Pleiades and NGC 2516 clusters, and the radii of tidally locked, low-mass eclipsing binary components. The binary components and zero-age main-sequence K-dwarfs have radii inflated by ˜10 per cent compared to an empirical radius-luminosity relation that is defined by magnetically inactive field dwarfs with interferometrically measured radii; low-mass M-type PMS stars, that are still on their Hayashi tracks, are inflated by up to ˜40 per cent. If this were attributable to starspots alone, we estimate that an effective spot coverage of 0.35 < β < 0.51 is required. Alternatively, global inhibition of convective flux transport by dynamo-generated fields may play a role. However, we find greater consistency with the starspot models when comparing the loci of active young stars and inactive field stars in colour-magnitude diagrams, particularly for the highly inflated PMS stars, where the large, uniform temperature reduction required in globally inhibited convection models would cause the stars to be much redder than observed.

CARMENES: First Results from the CAHA 3.5m Telescope

NASA Astrophysics Data System (ADS)

Quirrenbach, Andreas; Consortium, CARMENES

2015-12-01

CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs) is a next-generation instrument currently undergoing commissioning at the 3.5m telescope at the Calar Alto Observatory. It has been developed by a consortium of eleven Spanish and German institutions (see also Quirrenbach et al. 2010; 2012; 2014). CARMENES will conduct a 600-night exoplanet survey targeting ~300 M dwarfs. An important and unique feature of the CARMENES instrument is that it consists of two separate échelle spectrographs, which together cover the wavelength range from 0.55 to 1.7 μm at a spectral resolution of R = 82,000. The spectrographs are fed by fibers from the Cassegrain focus of the telescope.The main scientific objective of the CARMENES project is to carry out a survey of late-type main sequence stars with the goal of detecting low-mass planets in their habitable zones (HZs). In the focus of the project are very cool stars later than spectral type M4 and moderately active stars. We aim at being able to detect a 2M⊕ planet in the HZ of an M5 star. A long-term radial velocity precision of 1ms-1 per measurement will permit to attain such goals. For stars later than M4 (M < 0.25M⊙), such precision will yield detections of super-Earths of 5M⊕ and smaller inside the entire width of the HZ. The CARMENES survey will thus provide a comprehensive overview of planetary systems around nearby Northern M dwarfs. By reaching into the realm of Earth-like planets, it will provide a treasure trove for follow-up studies probing their habitability.Quirrenbach, A., Amado, P.J., Mandel, H., et al. (2010). CARMENES: Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs. In Ground-based and airborne instrumentation for astronomy III. Eds. McLean, I.S., Ramsay, S.K., & Takami, H., SPIE 773513Quirrenbach, A., Amado, P.J., Seifert, W., et al. (2012). CARMENES. I: Instrument and survey overview. In Ground-based and airborne instrumentation for astronomy IV. Eds. McLean, I.S., Ramsay, S.K., & Takami, H., SPIE 84460RQuirrenbach, A., Amado, P.J., Caballero, J.A., et al. (2014). CARMENES instrument overview. In Ground-based and airborne instrumentation for astronomy V. Eds. Ramsay, S.K., McLean, I.S., & Takami, H., SPIE 91471F

A white dwarf companion to the main-sequence star 4 Omicron(1) Orionis and the binary hypothesis for the origin of peculiar red giants

NASA Technical Reports Server (NTRS)

Ake, Thomas B.; Johnson, Hollis R.

1988-01-01

Ultraviolet spectra of the peculiar red giants (PRGs) called MS stars are investigated, and the discovery of a white dwarf (WD) companion to the MS star 4 Omicron(1) Orionis is reported. The observations and data analysis are discussed and compared with those for field WDs in order to derive parameters for the WD and the luminosity of the primary. Detection limits for the other MS stars investigated are derived, and the binary hypothesis for PRGs is reviewed.

Rapid Rotation of a Heavy White Dwarf

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-05-01

New Kepler observations of a pulsating white dwarf have revealed clues about the rotation of intermediate-mass stars.Learning About ProgenitorsStars weighing in at under 8 solar masses generally end their lives as slowly cooling white dwarfs. By studying the rotation of white dwarfs, therefore, we are able to learn about the final stages of angular momentum evolution in these progenitor stars.Most isolated field white dwarfs cluster in mass around 0.62 solar masses, which corresponds to a progenitor mass of around 2.2 solar masses. This abundance means that weve already learned a good deal about the final rotation of low-mass (13 solar-mass) stars. Our knowledge about the angular momentum of intermediate-mass (38 solar-mass) stars, on the other hand, remains fairly limited.Fourier transform of the pulsations from SDSSJ0837+1856. The six frequencies of stellar variability, marked with red dots, reveal a rotation period of 1.13 hours. [Hermes et al. 2017]Record-Breaking FindA newly discovered white dwarf, SDSSJ0837+1856, is now helping to shed light on this mass range. SDSSJ0837+1856 appears to be unusually massive: its measured at 0.87 solar masses, which corresponds to a progenitor mass of roughly 4.0 solar masses. Determining the rotation of this white dwarf would therefore tell us about the final stages of angular momentum in an intermediate-mass star.In a new study led by J.J. Hermes (Hubble Fellow at University of North Carolina, Chapel Hill), a team of scientists presents a series of measurements of SDSSJ0837+1856 that suggest its the highest-mass and fastest-rotating isolated pulsating white dwarf known.Histogram of rotation rates determined from the asteroseismology of pulsating white dwarfs (marked in red). SDSSJ0837+1856 (indicated in black) is more massive and rotates faster than any other known pulsating white dwarf. [Hermes et al. 2017]Rotation from PulsationsWhy pulsating? In the absence of measurable spots and other surface features, the way we measure the rotation rate of a star is using asteroseismology. In this process, observations of a stars tiny oscillations can reveal information about its internal structure and rotation.Hermes and collaborators used Kepler K2 observations spanning nearly 75 days in addition to ground-based follow-up and spectroscopy to estimate the white dwarfs rotation period based on its observed internal pulsations. The resulting rotation rate, 1.13 0.02 hours, is the fastest rotation period ever measured for an isolated pulsating white dwarf.Placing SDSSJ0837+1856 in the context of other white dwarfs with measured rotation periods, the authors argue that there seems to be a connection between the highest-mass white dwarfs and the fastest rotators. More observations of this kind will help us to determine whether this is a general trend that tells us something significant about the angular momentum evolution of intermediate-mass stars.CitationJ. J. Hermes et al 2017 ApJL 841 L2. doi:10.3847/2041-8213/aa6ffc

Diagnostics of models and observations in the contexts of exoplanets, brown dwarfs, and very low-mass stars.

NASA Astrophysics Data System (ADS)

Kopytova, Taisiya

2016-01-01

When studying isolated brown dwarfs and directly imaged exoplanets with insignificant orbital motion,we have to rely on theoretical models to determine basic parameters such as mass, age, effective temperature, and surface gravity.While stellar and atmospheric models are rapidly evolving, we need a powerful tool to test and calibrate them.In my thesis, I focussed on comparing interior and atmospheric models with observational data, in the effort of taking into account various systematic effects that can significantly influence the data analysis.As a first step, about 460 candidate member os the Hyades were screened for companions using diffraction limited imaging observation (both our own data and archival data). As a result I could establish the single star sequence for the Hyades comprising about 250 stars (Kopytova et al. 2015, accepted to A&A). Open clusters contain many coeval objects of the same chemical composition and age, and spanning a range of masses. We compare the obtained sequence with a set of theoretical isochrones identifying systematic offsets and revealing probable issues in the models.However, there are many cases when it is impossible to test models before comparing them with observations.As a second step, we apply atmospheric models for constraining parameters of WISE 0855-07, the coolest known Y dwarf(Kopytova et al. 2014, ApJ 797, 3). We demonstrate the limits of constraining effective temperature and the presence/absence of water clouds.As a third step, we introduce a novel method to take into account the above-mentioned systematics. We construct a "systematics vector" that allows us to reveal problematic wavelength ranges when fitting atmospheric models to observed near-infrared spectraof brown dwarfs and exoplanets (Kopytova et al., in prep.). This approach plays a crucial role when retrieving abundances for these objects, in particularly, a C/O ratio. The latter parameter is an important key to formation scenarios of brown dwarf and exoplanets. We show the way to constrain a C/O ratio while eliminating systematics effects, which significantly improves the reliability of a final result and our conclusions about formation history of certain exoplanets and brown dwarfs.

Pollen evidence for late pleistocene bering land bridge environments from Norton Sound, Northeastern Bering Sea, Alaska

USGS Publications Warehouse

Ager, T.A.; Phillips, R.L.

2008-01-01

After more than half a century of paleoenvironmental investigations, disagreements persist as to the nature of vegetation type and climate of the Bering land bridge (BLB) during the late Wisconsin (Sartan) glacial interval. Few data exist from sites on the former land bridge, now submerged under the Bering and Chukchi Seas. Two hypotheses have emerged during the past decade. The first, based on pollen data from Bering Sea islands and adjacent mainlands of western Alaska and Northeast Siberia, represents the likely predominant vegetation on the Bering land bridge during full-glacial conditions: graminoid-herb-willow tundra vegetation associated with cold, dry winters and cool, dry summer climate. The second hypothesis suggests that dwarf birch-shrub-herb tundra formed a broad belt across the BLB, and that mesic vegetation was associated with cold, snowier winters and moist, cool summers. As a step towards resolving this controversy, a sediment core from Norton Sound, northeastern Bering Sea was radiocarbon dated and analyzed for pollen content. Two pollen zones were identified. The older, bracketed by radiocarbon ages of 29,500 and 11,515 14C yr BP, contains pollen assemblages composed of grass, sedge, wormwood, willow, and a variety of herb (forb) taxa. These assemblages are interpreted to represent graminoid-herb-willow tundra vegetation that developed under an arid, cool climate regime. The younger pollen zone sediments were deposited about 11,515 14C yr BP, when rising sea level had begun to flood the BLB. This younger pollen zone contains pollen of birch, willow, heaths, aquatic plants, and spores of sphagnum moss. This is interpreted to represent a Lateglacial dwarf birch-heath-willow-herb tundra vegetation, likely associated with a wetter climate with deeper winter snows, and moist, cool summers. This record supports the first hypothesis, that graminoid-herb-willow tundra vegetation extended into the lowlands of the BLB during full glacial conditions of the late Wisconsin. ?? 2008 Regents of the University of Colorado.

Model atmospheres for M (sub)dwarf stars. 1: The base model grid

NASA Technical Reports Server (NTRS)

Allard, France; Hauschildt, Peter H.

1995-01-01

We have calculated a grid of more than 700 model atmospheres valid for a wide range of parameters encompassing the coolest known M dwarfs, M subdwarfs, and brown dwarf candidates: 1500 less than or equal to T(sub eff) less than or equal to 4000 K, 3.5 less than or equal to log g less than or equal to 5.5, and -4.0 less than or equal to (M/H) less than or equal to +0.5. Our equation of state includes 105 molecules and up to 27 ionization stages of 39 elements. In the calculations of the base grid of model atmospheres presented here, we include over 300 molecular bands of four molecules (TiO, VO, CaH, FeH) in the JOLA approximation, the water opacity of Ludwig (1971), collision-induced opacities, b-f and f-f atomic processes, as well as about 2 million spectral lines selected from a list with more than 42 million atomic and 24 million molecular (H2, CH, NH, OH, MgH, SiH, C2, CN, CO, SiO) lines. High-resolution synthetic spectra are obtained using an opacity sampling method. The model atmospheres and spectra are calculated with the generalized stellar atmosphere code PHOENIX, assuming LTE, plane-parallel geometry, energy (radiative plus convective) conservation, and hydrostatic equilibrium. The model spectra give close agreement with observations of M dwarfs across a wide spectral range from the blue to the near-IR, with one notable exception: the fit to the water bands. We discuss several practical applications of our model grid, e.g., broadband colors derived from the synthetic spectra. In light of current efforts to identify genuine brown dwarfs, we also show how low-resolution spectra of cool dwarfs vary with surface gravity, and how the high-regulation line profile of the Li I resonance doublet depends on the Li abundance.

Stellar Oxygen Abundances.V.Abundances of Two Hyades Dwarfs Derived from the 6300 Angstroms [OI] Line

NASA Astrophysics Data System (ADS)

King, Jeremy R.; Hiltgen, Daniel D.

1996-12-01

We present observations of the 6300 Å [O I] spectral region in two cool Hyades dwarfs, vB 79 and vB 25. We derive a mean iron abundance, [Fe/H]˜+0.11, in good agreement with recent analyses of F and G Hyades dwarfs. The O abundance derived from spectrum synthesis, [O/H]˜+0.15, is between the values deduced by Garcia Lopez et al. (1993, ApJ, 412, 173; [O/H]=-0.05 to -0.10) and King (1993, Ph. D. Dissertation, University of Hawaii; [O/H]=+0.26), who employed the 7774 Å O I triplet in hotter Hyades dwarfs. An accounting of differences between these two 7774 Å analyses is given. Our [O I]-based determination suggests the Hyades O abundance itself is super-solar, though [O/Fe]˜0.0; however, systematic errors as large as 0.10-0.15 dex cannot be ruled out. The Hyades giants show an unexpected ˜0.23 dex O deficit relative to our dwarf value. While some suggestive evidence for non-standard nuclear processing and mixing in the Hyades giants may exist, we find it unconvincing. Rather, model atmosphere deficiencies or [O I] -region blending features that are still unrecognized by laboratory and theoretical efforts may contribute to the giant-dwarf O discrepancy. Finally, our high O abundance is marginally consistent with values claimed to provide a solution to the Hyades Li problem from standard stellar models. However, it is not clear that these models do in fact reproduce the extant Li data. Our Li abundance upper limit for vB 25 is at least 0.5 dex lower than the abundances of two tidally locked binaries of similar Teff. Standard stellar models of uniform composition and age are not able to reproduce such scatter in Li.

The Origin of Ultra-Faint Galaxies

NASA Astrophysics Data System (ADS)

Sand, David

2017-08-01

We request 24 orbits of HST/ACS to obtain imaging in F606W and F814W of apparent tidal features in two ultra-faint dwarf galaxies: Hercules and Leo V. This will enable us to test whether the stars in ultra- faint galaxies-as a population-have been affected by Galactic tides. Most of the new dwarfs show signs of tidal interaction in ground-based photometry, several have measured ellipticities greater than 0.5, and kinematics of a subset show velocity gradients. These ubiquitous hints for tidal effects among distant dwarfs is particularly surprising and suggestive. If most ultra-faint dwarfs are disturbed by tides, then recent tests of galaxy formation in the near field have unstable foundations.HST resolution provides an opportunity to assess whether tidal features (accompanied by tentative kinematic gradients) seen in ground-based observations of Hercules and Leo V are genuine or are instead clumps of compact background galaxies masquerading as stellar debris. In Hercules, a further test is possible: searching for a distance gradient along the stretched body of the galaxy. Parallel pointings will sample similar dwarf-centric radii away from the tidal features, assuring an unambiguous result. Whether we confirm or rule out the presence of stellar loss in these objects, the consequences are important-the origin of the ultra-faint dwarfs tells us the lower limit to both galaxy formation and the number of dark matter subhalos inhabiting the Milky Way.This program is only possible with HST: its exquisite resolution can separate compact galaxies from main sequence dwarf stars at faint magnitudes, which even the best multi-band ground-based schemes struggle with.

Photospheric properties and fundamental parameters of M dwarfs

NASA Astrophysics Data System (ADS)

Rajpurohit, A. S.; Allard, F.; Teixeira, G. D. C.; Homeier, D.; Rajpurohit, S.; Mousis, O.

2018-02-01

Context. M dwarfs are an important source of information when studying and probing the lower end of the Hertzsprung-Russell (HR) diagram, down to the hydrogen-burning limit. Being the most numerous and oldest stars in the galaxy, they carry fundamental information on its chemical history. The presence of molecules in their atmospheres, along with various condensed species, complicates our understanding of their physical properties and thus makes the determination of their fundamental stellar parameters more challenging and difficult. Aim. The aim of this study is to perform a detailed spectroscopic analysis of the high-resolution H-band spectra of M dwarfs in order to determine their fundamental stellar parameters and to validate atmospheric models. The present study will also help us to understand various processes, including dust formation and depletion of metals onto dust grains in M dwarf atmospheres. The high spectral resolution also provides a unique opportunity to constrain other chemical and physical processes that occur in a cool atmosphere. Methods: The high-resolution APOGEE spectra of M dwarfs, covering the entire H-band, provide a unique opportunity to measure their fundamental parameters. We have performed a detailed spectral synthesis by comparing these high-resolution H-band spectra to that of the most recent BT-Settl model and have obtained fundamental parameters such as effective temperature, surface gravity, and metallicity (Teff, log g, and [Fe/H]), respectively. Results: We have determined Teff, log g, and [Fe/H] for 45 M dwarfs using high-resolution H-band spectra. The derived Teff for the sample ranges from 3100 to 3900 K, values of log g lie in the range 4.5 ≤ log g ≤ 5.5, and the resulting metallicities lie in the range ‑0.5 ≤ [Fe/H] ≤ +0.5. We have explored systematic differences between effective temperature and metallicity calibrations with other studies using the same sample of M dwarfs. We have also shown that the stellar parameters determined using the BT-Settl model are more accurate and reliable compared to other comparative studies using alternative models.

THE EXTREMELY RED, YOUNG L DWARF PSO J318.5338–22.8603: A FREE-FLOATING PLANETARY-MASS ANALOG TO DIRECTLY IMAGED YOUNG GAS-GIANT PLANETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Michael C.; Magnier, Eugene A.; Kotson, Michael C.

2013-11-10

We have discovered using Pan-STARRS1 an extremely red late-L dwarf, which has (J – K){sub MKO} = 2.78 and (J – K){sub 2MASS} = 2.84, making it the reddest known field dwarf and second only to 2MASS J1207–39b among substellar companions. Near-IR spectroscopy shows a spectral type of L7 ± 1 and reveals a triangular H-band continuum and weak alkali (K I and Na I) lines, hallmarks of low surface gravity. Near-IR astrometry from the Hawaii Infrared Parallax Program gives a distance of 24.6 ± 1.4 pc and indicates a much fainter J-band absolute magnitude than field L dwarfs. Themore » position and kinematics of PSO J318.5–22 point to membership in the β Pic moving group. Evolutionary models give a temperature of 1160{sup +30}{sub -40} K and a mass of 6.5{sup +1.3}{sub -1.0} M {sub Jup}, making PSO J318.5–22 one of the lowest mass free-floating objects in the solar neighborhood. This object adds to the growing list of low-gravity field L dwarfs and is the first to be strongly deficient in methane relative to its estimated temperature. Comparing their spectra suggests that young L dwarfs with similar ages and temperatures can have different spectral signatures of youth. For the two objects with well constrained ages (PSO J318.5–22 and 2MASS J0355+11), we find their temperatures are ≈400 K cooler than field objects of similar spectral type but their luminosities are similar, i.e., these young L dwarfs are very red and unusually cool but not 'underluminous'. Altogether, PSO J318.5–22 is the first free-floating object with the colors, magnitudes, spectrum, luminosity, and mass that overlap the young dusty planets around HR 8799 and 2MASS J1207–39.« less

Looking for the Coldest Atmospheres: a Search for Planetary Mass Companions around T and Y Brown Dwarfs

NASA Astrophysics Data System (ADS)

Fontanive, Clemence

2017-08-01

We propose to obtain WFC3/IR imaging of the very coolest brown dwarfs (T < 800 K) to search for substellar and planetary-mass companions to these objects. Companions discovered by this program would likely be analogues of the 250 K brown dwarf WISE 0855 and would provide vital benchmark objects for theoretical models, closing the gap in mass and temperature between brown dwarfs and planets. Finding such an object as a member of a binary system would be even more valuable as it would allow for the measurement of dynamical masses. We recently placed the first constraints to date on the binary frequency for brown dwarfs with spectral types >T8. This program will triple our current sample size, a requirement in order to confirm our current results and compare substellar binary properties for various spectral type and age populations. The WFC3/IR plate will allow us to probe near equal-mass binaries down to separations of 0.2 (2-3 AU for the typical distances of our targets). True cool companions should show strong absorption around 1.4 um as a result of the deep water absorption band observed at that wavelength in substellar spectra. We therefore propose observations in the WFC3 F127M and F139M filters which will allow us to robustly identify bona fide candidates and distinguish them from background stars based on this spectral feature. Most of our targets lack suitable NGS AO guide stars or LGS AO tip-tilt stars to be observed with ground-based telescopes, and the 1.4 um water band is often unobservable from the ground due to telluric water absorption. WFC3 on HST is thus the only instrument suitable for these observations.

Effect of UV Radiation on the Spectral Fingerprints of Earth-like Planets Orbiting M Stars

NASA Astrophysics Data System (ADS)

Rugheimer, S.; Kaltenegger, L.; Segura, A.; Linsky, J.; Mohanty, S.

2015-08-01

We model the atmospheres and spectra of Earth-like planets orbiting the entire grid of M dwarfs for active and inactive stellar models with Teff = 2300 K to Teff = 3800 K and for six observed MUSCLES M dwarfs with UV radiation data. We set the Earth-like planets at the 1 AU equivalent distance and show spectra from the visible to IR (0.4-20 μm) to compare detectability of features in different wavelength ranges with the James Webb Space Telescope and other future ground- and spaced-based missions to characterize exo-Earths. We focus on the effect of UV activity levels on detectable atmospheric features that indicate habitability on Earth, namely, H2O, O3, CH4, N2O, and CH3Cl. To observe signatures of life—O2/O3 in combination with reducing species like CH4—we find that early and active M dwarfs are the best targets of the M star grid for future telescopes. The O2 spectral feature at 0.76 μm is increasingly difficult to detect in reflected light of later M dwarfs owing to low stellar flux in that wavelength region. N2O, another biosignature detectable in the IR, builds up to observable concentrations in our planetary models around M dwarfs with low UV flux. CH3Cl could become detectable, depending on the depth of the overlapping N2O feature. We present a spectral database of Earth-like planets around cool stars for directly imaged planets as a framework for interpreting future light curves, direct imaging, and secondary eclipse measurements of the atmospheres of terrestrial planets in the habitable zone to design and assess future telescope capabilities.

LIVING WITH A RED DWARF: ROTATION AND X-RAY AND ULTRAVIOLET PROPERTIES OF THE HALO POPULATION KAPTEYN’S STAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guinan, Edward F.; Engle, Scott G.; Durbin, Allyn, E-mail: scott.engle@villanova.edu

As part of Villanova’s Living with a Red Dwarf program, we have obtained UV, X-ray, and optical data of the Population II red dwarf—Kapteyn’s Star. Kapteyn’s Star is noteworthy for its large proper motions and high radial velocity of ∼+245 km s{sup −1}. As the nearest Pop II red dwarf, it serves as an old age anchor for calibrating activity/irradiance–rotation–age relations, and an important test bed for stellar dynamos and the resulting X-ray–UV emissions of slowly rotating, near-fully convective red dwarf stars. Adding to the notoriety, Kapteyn’s Star has recently been reported to host two super-Earth candidates, one of whichmore » (Kapteyn b) is orbiting within the habitable zone. However, Robertson et al. questioned the planet’s existence since its orbital period may be an artifact of activity, related to the star’s rotation period. Because of its large Doppler-shift, measures of the important, chromospheric H i Lyα 1215.67 Å emission line can be reliably made, because it is mostly displaced from ISM and geo-coronal sources. Lyα emission dominates the FUV region of cool stars. Our measures can help determine the X-ray–UV effects on planets hosted by Kapteyn’s Star, and planets hosted by other old red dwarfs. Stellar X-ray and Lyα emissions have strong influences on the heating and ionization of upper planetary atmospheres and can (with stellar winds and flares) erode or even eliminate planetary atmospheres. Using our program stars, we have reconstructed the past exposures of Kapteyn’s Star's planets to coronal—chromospheric XUV emissions over time.« less

Meeting the Cool Neighbors. XII. An Optically Anchored Analysis of the Near-infrared Spectra of L Dwarfs

NASA Astrophysics Data System (ADS)

Cruz, Kelle L.; Núñez, Alejandro; Burgasser, Adam J.; Abrahams, Ellianna; Rice, Emily L.; Reid, I. Neill; Looper, Dagny

2018-01-01

Discrepancies between competing optical and near-infrared (NIR) spectral typing systems for L dwarfs have motivated us to search for a classification scheme that ties the optical and NIR schemes together, and addresses complexities in the spectral morphology. We use new and extant optical and NIR spectra to compile a sample of 171 L dwarfs, including 27 low-gravity β and γ objects, with spectral coverage from 0.6–2.4 μm. We present 155 new low-resolution NIR spectra and 19 new optical spectra. We utilize a method for analyzing NIR spectra that partially removes the broad-band spectral slope and reveals similarities in the absorption features between objects of the same optical spectral type. Using the optical spectra as an anchor, we generate near-infrared spectral average templates for L0–L8, L0–L4γ, and L0–L1β type dwarfs. These templates reveal that NIR spectral morphologies are correlated with the optical types. They also show the range of spectral morphologies spanned by each spectral type. We compare low-gravity and field-gravity templates to provide recommendations on the minimum required observations for credibly classifying low-gravity spectra using low-resolution NIR data. We use the templates to evaluate the existing NIR spectral standards and propose new ones where appropriate. Finally, we build on the work of Kirkpatrick et al. to provide a spectral typing method that is tied to the optical and can be used when only H or K band data are available. The methods we present here provide resolutions to several long-standing issues with classifying L dwarf spectra and could also be the foundation for a spectral classification scheme for cloudy exoplanets.

Rotation periods for nearby, mid-to-late M dwarfs estimated from the MEarth Project

NASA Astrophysics Data System (ADS)

Newton, Elisabeth R.; Irwin, Jonathan; Charbonneau, David; Berta-Thompson, Zachory K.; Dittmann, Jason

2015-01-01

Knowledge of M dwarfs' rotation is essential to understanding the generation of their magnetic fields and the mechanism by which they lose angular momentum. It is also important for characterizing the environment of planets that might orbit them. The most direct way to infer rotation periods is from variations in stars' brightnesses as dark spots rotate in and out of view. Most rotation periods estimated prior to this decade are the result of dedicated photometric studies. If care is taken to preserve astrophysical variability and limit systematics, transiting planet surveys generate the high-cadence monitoring required to estimate stellar rotation periods. While targeted surveys of clusters have provided data at young ages, observations of field M dwarfs are required to constrain their late-term evolution. Rotation periods of the smallest stars are also needed: the Kepler mission produced exquisite light curves of several thousand cool dwarfs, but field stars below 0.3 solar masses are not well-represented in the sample. The MEarth Project is a transiting planet survey targeting mid-to-late M dwarfs within 33 parsecs; it provides a unique data set for exploring rotation in a large sample of fully convective stars. We present a catalog of rotation periods for these stars. Our measurements are particularly useful because many of the MEarth targets have parallaxes, multi-wavelength photometry, and optical and near-infrared spectra. We present our methods for estimating rotation periods and quantifying our uncertainties, and discuss our results in the context of other surveys.The MEarth project gratefully acknowledges funding from the David and Lucile Packard Fellowship for Science and Engineering, the National Science Foundation under grants AST-0807690, AST-1109468, and AST-1004488, and the John Templeton Foundation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rugheimer, S.; Kaltenegger, L.; Segura, A.

We model the atmospheres and spectra of Earth-like planets orbiting the entire grid of M dwarfs for active and inactive stellar models with T{sub eff} = 2300 K to T{sub eff} = 3800 K and for six observed MUSCLES M dwarfs with UV radiation data. We set the Earth-like planets at the 1 AU equivalent distance and show spectra from the visible to IR (0.4–20 μm) to compare detectability of features in different wavelength ranges with the James Webb Space Telescope and other future ground- and spaced-based missions to characterize exo-Earths. We focus on the effect of UV activity levels onmore » detectable atmospheric features that indicate habitability on Earth, namely, H{sub 2}O, O{sub 3}, CH{sub 4}, N{sub 2}O, and CH{sub 3}Cl. To observe signatures of life—O{sub 2}/O{sub 3} in combination with reducing species like CH{sub 4}—we find that early and active M dwarfs are the best targets of the M star grid for future telescopes. The O{sub 2} spectral feature at 0.76 μm is increasingly difficult to detect in reflected light of later M dwarfs owing to low stellar flux in that wavelength region. N{sub 2}O, another biosignature detectable in the IR, builds up to observable concentrations in our planetary models around M dwarfs with low UV flux. CH{sub 3}Cl could become detectable, depending on the depth of the overlapping N{sub 2}O feature. We present a spectral database of Earth-like planets around cool stars for directly imaged planets as a framework for interpreting future light curves, direct imaging, and secondary eclipse measurements of the atmospheres of terrestrial planets in the habitable zone to design and assess future telescope capabilities.« less

Two-phase ultraviolet spectrophotometry of the pulsating white dwarf ZZ Piscium

NASA Technical Reports Server (NTRS)

Bond, H. E.; Kemper, E.; Grauer, A. D.; Holm, A. V.; Panek, R. J.; Schiffer, F. H., III

1985-01-01

Spectra of the pulsating white dwarf ZZ Psc (= G29-38) were obtained using the International Ultraviolet Explorer. By using a multiple-exposure technique in conjunction with simultaneous ground-based exposure-metering photometry, it was possible to obtain mean on-pulse and off-pulse spectra in the 1950-1310 A wavelength range. The ratio of the time-averaged on-pulse to off-pulse spectra is best fitted by a temperature variation that is in phase with the optical light variation. This result is consistent with the hypothesis that the observed variation is due to a high-order nonradial pulsation. Conventional ultraviolet spectra of ZZ Psc showed broad absorption features at 1390 and 1600 A. These features are also found in the spectra of the cool DA-type white dwarfs G226-29 and G67-23, and appear to increase in strength with decreasing temperature. A possible explanation for the 1600 A feature is absorption by the satellite band of resonance-broadened hydrogen Ly-alpha. Such absorption would also help explain a discrepancy between the observed pulsation amplitude shortward of 1650 A and the predicted amplitudes based on model atmospheres.

Finding ultracool brown dwarfs with MegaCam on CFHT: method and first results

NASA Astrophysics Data System (ADS)

Delorme, P.; Willott, C. J.; Forveille, T.; Delfosse, X.; Reylé, C.; Bertin, E.; Albert, L.; Artigau, E.; Robin, A. C.; Allard, F.; Doyon, R.; Hill, G. J.

2008-06-01

Aims: We present the first results of a wide field survey for cool brown dwarfs with the MegaCam camera on the CFHT telescope, the Canada-France Brown Dwarf Survey, hereafter CFBDS. Our objectives are to find ultracool brown dwarfs and to constrain the field-brown dwarf mass function thanks to a larger sample of L and T dwarfs. Methods: We identify candidates in CFHT/MegaCam i' and z' images using optimised psf-fitting within Source Extractor, and follow them up with pointed near-infrared imaging on several telescopes. Results: We have so far analysed over 350 square degrees and found 770 brown dwarf candidates brighter than z'_AB=22.5. We currently have J-band photometry for 220 of these candidates, which confirms 37% as potential L or T dwarfs. Some are among the reddest and farthest brown dwarfs currently known, including an independent identification of the recently published ULAS J003402.77-005206.7 and the discovery of a second brown dwarf later than T8, CFBDS J005910.83-011401.3. Infrared spectra of three T dwarf candidates confirm their nature, and validate the selection process. Conclusions: The completed survey will discover ~100 T dwarfs and ~500 L dwarfs or M dwarfs later than M8, approximately doubling the number of currently known brown dwarfs. The resulting sample will have a very well-defined selection function, and will therefore produce a very clean luminosity function. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at TERAPIX and the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS. Based on observations made with the ESO New Technology Telescope at the La Silla Observatory under programme ID 76.C-0540(A), 77.C-0594, 77.A-0707, 78.A-0651, 78.C-0629 and 79.A-0663. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), CNPq (Brazil) and CONICET (Argentina). Based on observations with the Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. This paper includes data taken at The McDonald Observatory of The University of Texas at Austin.

Identification and characterization of low mass stars and brown dwarfs using Virtual Observatory tools

NASA Astrophysics Data System (ADS)

Aberasturi, Miriam

2015-11-01

Context: Two thirds of the stars in our galactic neighborhood (d < 10 pc) are M-dwarfs which also constitute the most common stellar objects in the Milky Way. This property, combined with their small stellar masses and radii, increases the likelihood of detecting terrestrial planets through radial velocity and transit techniques, making them very adequate targets for the exoplanet hunting projects. Nevertheless, M dwarfs have associated different observational difficulties. They are cool objects whose emission radiation peaks at infrared wavelengths and, thus, with a low surface brightness in the optical range. Also, the photometric variability as well as the significant chromospheric activity hinder the radial velocity and transit determinations. It is necessary, therefore, to carry out a detailed characterization of M-dwarfs before building a shortlist with the best possible candidates for exoplanet searches. Brown dwarfs (BDs) are self-gravitating objects that do not get enough mass to maintain a sufficiently high temperature in their core for stable hydrogen fusion. They represent the link between low-mass stars and giant planets. Due to their low temperatures, BDs emit significant flux at mid-infrared wavelength which makes this range very adequate to look for this type of objects. The Virtual Observatory (VO) is an international initiative designed to help the astronomical community in the exploitation of the multi-wavelength information that resides in data archives. In the last years the Spanish Virtual Observatory is conducting a number of projects focused on the study of substellar objects taking advantage of Virtual Observatory tools for an easy data access and analysis of large area surveys. This is the framework where this thesis has been carried out. This dissertation addresses three problems in the framework of low-mass stars and brown dwarfs, namely, the search for brown dwarf candidates crossmatching catalogues (Chapter 4), the search for nearby bright M dwarfs and the subsequent spectroscopic characterization (Chapter 5), and a study of binarity in mid to late-T brown dwarfs (Chapter 6); the first two topics use Virtual Observatory tools. Aims and methodology:In the first paper we carried out a search of brown dwarfs in the sky area in common to the WISE, 2MASS Point Source and SDSS catalogues. A VO-workflow with the criteria that must accomplish our candidates was built using STILTS. The workflow returned 138 sources that were visually inspected. For the six new candidates that passed the inspection, proper motions were calculated using the positions and the different observing epochs of the catalogues previously quoted. Effective temperatures were estimated using VOSA and spectral types and distances using appropriate photometric calibrations. In the second publication we conducted an all-sky photometric search by cross correlating the Carlsberg Meridian Catalogue (CMC14) and the 2MASS Point Source Catalogue with the aim of increasing the number of known, nearby M dwarfs that could be used as targets for exoplanet searches in general and CARMENES in particular. This VO search was combined with low-resolution spectroscopic followup of 27 objects using the IDS spectrograph at the Isaac Newton telescope at La Palma, as well as with an astrometric and photometric study. In the third paper we attempted to refine the multiplicity properties of T dwarfs studying the largest sample so far observed with high angular resolution imaging. We undertook two parallel programs using the Wide Field Camera 3 (WFC3) installed on the Hubble Space Telescope (HST). We used a PSF-fitting subtraction technique to reveal the presence of any close companion to the sources in our sample. Monte Carlo simulations were carried out to estimate the capability of WFC3 to detect close binaries in terms of angular separation and magnitude difference. Simulations were also used to determine the fraction of binaries that would have been detected around each source based on assumed separations, mass ratio distributions and orientations of the systems. Results: The main conclusion from this dissertation is that the Virtual Observatory has proved to be an excellent research methodology in the field of low mass stars and brown dwarfs. In particular, it allowed an efficient management of the queries to different catalogues and archives as well as the estimation of physical parameters through VO-tools. In the first publication we present the identification of 31 brown dwarf (25 known and 6 strong candidates not previously reported in the literature) identified in the sky area in common toWISE, 2MASS and SDSS. This is a remarkable number considering that 2MASS has been extensively searched for ultracool dwarfs and clearly show how new surveys and the use of VO tools can help to mine older surveys. The robustness of our methodology was confirmed with the spectroscopic confirmation of our candidate targets making it an ideal technique to identify brown dwarfs and, by extension, other rare objects. In the second paper, we show the potential of the VO and a purely photometric approach for finding new bright, nearby M dwarfs that escaped previous surveys mostly based on proper motions. We discover 24 new potential targets for exoplanet hunting (7 at less than 20 pc), 12 of which have been included in the CARMENES input catalogue of M dwarfs. We also identify three young very low-mass stars (M4-M5 spectral types) in the Taurus-Auriga region and a wide (110 AU) binary system. In the third paper we infer an upper limit for the binary fraction of >T5 dwarfs of <16 - < 25% depending of the underlying mass ratio distribution. This binary fraction is consistent with previous estimations. From this work we also conclude that theWFC3 is more sensitive to cool companions than otherHST instruments like NICMOS or WFPC2 but its lower angular resolution makes it unsuitable to detect tight brown dwarf binary systems.

V and K-band Mass-Luminosity Relations for M Dwarf Stars

NASA Astrophysics Data System (ADS)

Benedict, George Frederick; Henry, Todd J.; McArthur, Barbara E.; Franz, Otto; Wasserman, Larry H.; Dieterich, Sergio

2015-08-01

Applying Hubble Space Telescope Fine Guidance Sensor astrometric techniques developed to establish relative orbits for binary stars (Franz et al. 1998, AJ, 116, 1432), determine masses of binary components (Benedict et al. 2001, AJ, 121, 1607), and measure companion masses of exoplanet host stars (McArthur et al. 2010, ApJ, 715, 1203), we derive masses with an average 2% error for 28 components of 14 M dwarf binary star systems. With these and other published masses we update the lower Main Sequence V-band Mass-Luminosity Relation first shown in Henry et al. 1999, ApJ, 512, 864. We demonstrate that a Mass-Luminosity Relation in the K-band has far less scatter. These relations can be used to estimate the masses of the ubiquitous red dwarfs (75% of all stars) to an accuracy of better than 5%.

Efectos difusivos en la formación de enanas blancas de Helio de baja masa en sistemas binarios cerrados

NASA Astrophysics Data System (ADS)

De Vito, M. A.; Benvenuto, O. G.

In the last years, and thanks to advances in observational techniques, many astronomers have discovered in a great number of binary radio-pulsars the presence of a helium white dwarf resulting from a previous evolutionary state in which the progenitor of this star experienced one or more episodes of mass transfer to the compact component in the pair. That is the case for PSR B1855+09 (van Kerkwijk, M. H., Bell, J. F, Kaspi, V. M., & Kulkarni, S. R. 2000, ApJ 530, L37), where the mass for the white dwarf is known accurately from measurements of the Shapiro delay of the pulsar signal, MWD = 0.258+0.028-0.016 M⊙; for PSR J02018 + 4232 (Bassa, C. G., van Kerkwijk, M. H., & Kulkarni, S. R. 2003, A&A, 403, 1067), the spectra confirm that the companion is a helium-core white dwarf of ≈ 0.2 M⊙. On the other hand, there are several authors (Ferraro, F., Possenti, A., Sabbi, E., & D'Amico, N. 2003, ApJ, 596, L211; Bassa et al. 2003) that have identified the optical binary companion to the BMSP PSR J1911 - 5958A, located in the halo of the Galactic globular cluster NGC 6752, like a blue star whose position in the color-magnitude diagram is consistent with the cooling sequence of a low-mass, ≈ 0.17 - 0.20 M⊙, low metallicity helium white dwarf at the cluster distance. Finally, the color and magnitude of the stellar companion for B 1620-26 indicate that is a white dwarf of 0.34 ± 0.04 M⊙ (Sigurdson, S., Richer, H. B., Hansen, B. M., Stairs, I. H. & Thorset, S. E. 2003, Science, 301, 193S). This has motivated us to study the formation of low mass helium white dwarfs in the context of binary evolution. For that purpose, using the code of binary evolution, entirely developed in the Facultad de Ciencias Astronómicas y Geofísicas of the Universidad Nacional de La Plata, Argentina, we have investigated the effects of diffusive processes on the evolution of a star member of a close binary system. A similar study was performed for Althaus, L. G., Serenelli, A. M., & Benvenuto, O. G. (2001, MNRAS, 323, 471) but in that paper the mass transfer was mimicked by subtracting mass to a progenitor of 1 M⊙ to obtain the mass for the desired object. Actually, our binary code has a full nuclear reactions network for hydrogen and helium burning that allowed us to follow the abundances of fifteen isotopes throughout the entire evolution of the star. We have also included a detailed equation of state. The mass loss treatment is non conservative. We have modified the conditions for the beginning and end of mass transfer episodes. In our previous version, we assumed it to occur when the stellar radius was greater or smaller, respectively, that the Roche Lobe radius for the star. This introduced numerical problems, especially at the end of mass transfer phases. We adopted H. Ritter (1988, A&A, 202, 93) formulation that considers a finite scale height in the stellar atmosphere. The numerical behaviour in much more satisfactory, besides that it constitutes a more appropriate description for the physical problem. We perform the calculations for the evolution of the primary star in a close binary system of initial mass 2 M⊙, initial period of 1 day, initial mass ratio of 1.4142 and solar metallicity. We have done the calculations in four cases: A) with diffusion and all Roche Lobe overflows, B) with diffusion and only the first Roche Lobe overflow, C) without diffusion and all Roche Lobe overflows, D) without diffusion and only the first Roche Lobe overflow. Cases B) and D) where performed to compare with results obtained for Althaus et al. (2001). The main conclusion of this work is that the age of these objects is mainly determined by diffusive effects, and the late stages of mass transfer, not considered in Althaus et al. (2001), constituted a minor effect on the scales of cooling times.

Li I and K I Scatter in Cool Pleiades Dwarfs

NASA Astrophysics Data System (ADS)

King, Jeremy R.; Schuler, Simon C.; Hobbs, L. M.; Pinsonneault, Marc H.

2010-02-01

We utilize high-resolution (R ~ 60,000), high signal-to-noise ratio (~100) spectroscopy of 17 cool Pleiades dwarfs to examine the confounding star-to-star scatter in the λ6707 Li I line strengths in this young cluster. Our Pleiades, selected for their small projected rotational velocity and modest chromospheric emission, evince substantial scatter in the line strengths of λ6707 Li I feature that is absent in the λ7699 K I resonance line. The Li I scatter is not correlated with that in the high-excitation λ7774 O I feature, and the magnitude of the former is greater than the latter despite the larger temperature sensitivity of the O I feature. These results suggest that systematic errors in line strength measurements due to blending, color (or color-based T eff) errors, or line formation effects related to an overlying chromosphere are not the principal source of Li I scatter in our stars. There do exist analytic spot models that can produce, via line formation effects, the observed Li scatter without introducing scatter in the K I line strengths or the color-magnitude diagram. However, these models predict factor of >=3 differences in abundances derived from the subordinate λ6104 and resonance λ6707 Li I features; we find no difference in the abundances determined from these two features. These analytic spot models also predict CN line strengths significantly larger than we observe in our spectra. The simplest explanation of the Li, K, CN, and photometric data is that there must be a real abundance component to the Pleiades Li dispersion. We suggest that this real abundance component is the manifestation of relic differences in erstwhile pre-main-sequence Li burning caused by effects of surface activity on stellar structure. We discuss observational predictions of these effects, which may be related to other anomalous stellar phenomena. Based on observations obtained with the High Resolution Spectrograph on the Hobby-Eberly Telescope, which is operated by McDonald Observatory on behalf of the University of Texas at Austin, Pennsylvania State University, Stanford University, the Ludwig-Maximillians-Universitaet, Munich, and the George-August-Universitaet, Goettingen. Public Access time was available on the Hobby-Eberly Telescope through an agreement with the National Science Foundation.

Disks around Failed Stars - a Question of Age

NASA Astrophysics Data System (ADS)

2002-08-01

First Ground-Based Mid-Infrared Observations of Brown Dwarfs [1] Summary A team of European astronomers [2] have observed eight Brown Dwarfs, i.e., small and faint objects also known as "failed stars", with the TIMMI2 infrared sensitive instrument at the ESO 3.6-m telescope on La Silla. From two of these, mid-infrared radiation is detected - for the first time ever from such objects with a ground-based telescope . While the younger Brown Dwarf, aged a few million years, is found to be surrounded by a dusty disk, no warm dust is present around the older ones. The new observations support the following formation hypothesis for Brown Dwarfs: they are born in the same way as "real" stars, by contraction in interstellar clouds of gas and dust . During the later stages of this process, the infalling material is transferred onto the star via a gas and dust disk . This disk - in which planets may possibly form - then disperses with time. PR Photo 17a/02 : Image of Brown Dwarf LP 944-20 PR Photo 17b/02 : Models of the disk around Brown Dwarf Cha HA 2 Brown Dwarfs are faint and cool objects Astronomical objects known as "Brown Dwarfs" are "failed stars" . Their comparatively small mass, less than about 7% of that of our Sun (or about 75 times the mass of planet Jupiter), is too small to achieve sufficiently high pressure and temperature at their centre to ignite energy-producing nuclear processes. Some astronomers also refer to Brown Dwarfs as a "missing link" between planets and stars, being neither one nor the other, yet with similarities to both. They do not burn hydrogen to helium as "real" stars do, but continue to emit faint light as they slowly contract and cool during millions of years. They end their inglorious life with a whimper and finally fade into eternal insignificance. Although Brown Dwarfs were theoretically predicted already in 1963, astronomers had to wait until 1995 for the first one to be discovered. This was mainly due to their extreme faintness as compared to normal stars - even the most nearby Brown Dwarfs shine so faintly that they can only be observed with relatively large telescopes. As they are rather cool objects, they emit mostly in the infrared spectral region; hence they are best observed with astronomical instruments that operate at those wavelengths. With improved techniques, however, more and more Brown Dwarfs have been found and the count has now reached several hundred. Many of these are located in the well-known Orion Nebula. Others move through interstellar space, like the lonely KELU-1 first discovered in 1997 at the ESO La Silla Observatory by Chilean astronomers, cf. ESO PR 07/97.With a distance of only 33 light-years from the Sun, it was one of the closest Brown Dwarfs known at that time. Formation of Brown Dwarfs Astronomers are still doubtful about the way Brown Dwarfs form. Among the numerous suggestions are the star-like contraction from an interstellar cloud of gas and dust and also another based on "ejected stellar embryos" . This latter scenario says that very young stars that are still accreting material are "kicked out of the nest" by their more massive brothers in multiple stellar systems. In this dramatic process, the unlucky objects are stripped of their surrounding disks. This effectively halts their further growth by accretion and they end up as underweight Brown Dwarfs. Recent observations at ESO have shown that the Brown Dwarfs in the Orion Nebula most likely have formed as stars do, i.e. by contraction in a cloud of dust and gas, cf. ESO PR 14/01. The clue to this was the observation of an excess of near-infrared radiation from many of these objects, interpreted as the presence of dusty disks around them. The astronomers then argued that if the young Brown Dwarfs possess such disks exactly like real stars do, then they must also form in the same way. Infrared observations of Brown Dwarfs Those observations were carried out in the near-infrared spectral region (in the 1.2 - 2.2 µm wavelength interval) with the ESO 3.5-m New Technology Telescope (NTT) . However, dusty disks around young stars (and presumably, those around Brown Dwarfs) radiate mostly at longer wavelengths. A detailed study of those disks is therefore best done with instruments that are sensitive to even longer wavelengths, e.g., in the mid-infrared to the sub-millimetre spectral region (10 - 1000 µm). This is in fact the only spectral interval where emission emanating from solid particles can be directly observed and their (mineral) composition thus be analysed. Pioneering observations in this wavelength interval of some Brown Dwarfs were made in mid-1995 by the ESA Infrared Space Observatory. However, the ISO instruments provided comparatively low image sharpness and these observations were hampered by confusion with the radiation from other objects in the same sky field. And the ISO mission was over before Brown Dwarf objects were discovered in larger numbers. Astronomers have therefore long wanted to observe Brown Dwarfs with large ground-based telescopes in the mid-infrared spectral region. But these objects are faint and few suitable instruments that work at these wavelengths are available at the world's large astronomical telescopes. Long exposures are necessary to record the faint emissions and until now, it had not been possible to perform such highly demanding observations of Brown Dwarfs. TIMMI2 observes Brown Dwarfs ESO PR Photo 17a/02 ESO PR Photo 17a/02 [Preview - JPEG: 874 x 400 pix - 75k [Normal - JPEG: 1747 x 800 pix - 752k] ESO PR Photo 17b/02 ESO PR Photo 17b/02 [Preview - JPEG: 400 x 451 pix - 48k] [Normal - JPEG: 800 x 901 pix - 200k] Caption : PR Photo 17a/02 shows the sky field with the nearby Brown Dwarf LP 944-20 at the centre, as photographed in blue (B), red (R) and near-infrared (IR) light (reproduced from the Digital Sky Survey [STScI Digitized Sky Survey, (C) 1993, 1994, AURA, Inc. all rights reserved - cf. http://archive.eso.org/dss/dss]). The object (at the arrow) is obviously very red. Observations with the TIMMI2 instrument at the ESO 3.6-m telescope on La Silla have shown that this comparatively old object does not possess a surrounding disk of dust and gas. Another much younger Brown Dwarf, Cha HA 2 , has one. The new measurements show that this object has a flat, dense disk (lower diagramme in PR Photo 17b/02 ), unlike the hotter (solar-like), young stars, that harbour "flared" disks with a diluted, very hot top layer (upper diagramme). Now, however, the first ground-based detection of mid-infrared radiation from two Brown Dwarfs has been achieved by a team of European astronomers [2], using the Thermal Infrared Multimode Instrument (TIMMI2) on the ESO 3.6-m telescope at the La Silla Observatory (Chile). They pointed the telescope towards a total of eight Brown Dwarf objects and recorded the emission at three different mid-infrared wavelengths (5, 9.8 and 11.9 µm). "We were delighted" , says team leader Daniel Apai, "to detect radiation from two of these with TIMMI2. These are the first observations of their kind with a ground-based instrument. And although we could only establish upper limits for the radiation from the five other objects, these results are highly significant for our attempts to understand the formation and evolution of Brown Dwarfs." One of the objects, known as Cha HA 2 and located in the southern constellation Chamaeleon [3], had earlier been observed with ISO. It is a bona-fide Brown Dwarf object and an image obtained with the Hubble Space Telescope indicates that it may possibly be double. It is a relatively young Brown Dwarf and is a member of the very young Cha I star-forming region - the age has been estimated at 2 - 4.5 million years. The ISO observations hinted at the presence of a dust disk around this object - this is fully confirmed by the new TIMMI2 observations. Moreover, the mid-IR radiation measured with this instrument interestingly shows the absence of a strong emission feature from silicates (at about 10 µm wavelength). According to the astronomers, this indicates that the disk around Cha HA 2 is comparatively dense and flat, and without a heated outer layer, cf. PR Photo 17b/02 . The other Brown Dwarf from which TIMMI2 has now detected mid-infrared radiation is one of the closest of its type. Designated LP 944-20 , it is located in the southern constellation Fornax (The Oven) at a distance of only ~15 light-years. It is much older than Cha HA 2 , though, probably 500 - 650 million years. In this case, the age was determined by measuring the strengths of spectral lines of the element Lithium; the older the object, the less is the content of Lithium. The observations show that the radiation from LP 944-20 comes from the cool star itself - it does not possess a surrounding disk as does the much younger Cha HA 2 [4]. Evolution of Brown Dwarfs Daniel Apai explains: "This all fits very nicely into the current picture of the evolution of Brown Dwarfs. They are born like stars by contraction in an interstellar cloud of gas and dust. At least some of them acquire a surrounding disk during this process. But that disk disperses after some time and we therefore only find it around relatively young Brown Dwarfs, not around older ones." . Nobody knows yet whether planets form in those disks around young Brown Dwarfs (as this was the case in the disk around the young Sun and other stars), but it might happen. Only future observations with much more sensitive instruments will be able to cast more light on this intriguing question. Future observations ESO's Very Large Telescope (VLT) will soon be equipped with the VLT Mid Infrared Spectrometer/Imager (VISIR) , an extremely powerful mid-infrared sensitive instrument that is well suited for this kind of studies. Further into the future, the Atacama Large Millimeter Array (ALMA) will provide excellent opportunities for in-depth investigations of Brown Dwarfs. With unequalled sensitivity and very good image sharpness, ALMA will be able to image disks around the nearest Brown Dwarfs and possibly, to detect signs of (forming) planets in them. More information The information presented in this Press Release is based on a Letter to the Editor in the research journal "Astrophysical Journal" ("Probing Dust around Brown Dwarfs: The Naked LP 944-20 and the Disk of Chamaeleon H-alpha 2" by D. Apai and co-authors (Vol. 573, pp. L115-L117; July 10, 2002). It is available on the web at http://arXiv.org/abs/astro-ph/0206210. Notes [1]: This press release is issued in coordination between ESO and the Max-Planck-Institut für Astronomie (Heidelberg, Germany). A German version is available at the MPIA website ( http://www.mpia.de/Public/Aktuelles/index_de.html ). [2]: The team consists of Daniel Apai , Ilaria Pascucci and Thomas Henning (all at Astrophysikalisches Institut und Universitätssternwarte, Jena, Germany, and Max-Planck-Institut für Astronomie, Heidelberg, Germany), Michael Sterzik (ESO-Chile), Randolf Klein and Dimitri Semenov (Astrophysikalisches Institut und Universitätssternwarte, Jena, Germany), Eike Günther and Bringfried Stecklum (Thüringer Landessternwarte Tautenburg, Germany). [3]: Cha HA 2 stands for "H-alpha emitting object no. 2 in the Chamaeleon I Dark Cloud". [4]: The photosphere of the young Brown Dwarf Cha HA 2 also emits mid-IR radiation. However, it is quite far away - about 500 light-years, or more than 30 times more distant than LP 944-20 - and that radiation is too weak to be detected with TIMMI2.

ASASSN-16ae: A POWERFUL WHITE-LIGHT FLARE ON AN EARLY-L DWARF

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmidt, Sarah J.; Shappee, Benjamin J.; Seibert, Mark

2016-09-10

We report the discovery and classification of SDSS J053341.43+001434.1 (SDSS0533), an early-L dwarf first discovered during a powerful Δ V< −11 magnitude flare observed as part of the ASAS-SN survey. Optical and infrared spectroscopy indicate a spectral type of L0 with strong H α emission and a blue NIR spectral slope. Combining the photometric distance, proper motion, and radial velocity of SDSS0533 yields three-dimensional velocities of ( U , V , W ) = (14 ± 13, −35 ± 14, −94 ± 22) km s{sup −1}, indicating that it is most likely part of the thick disk population and probablymore » old. The three detections of SDSS0533 obtained during the flare are consistent with a total V -band flare energy of at least 4.9 × 10{sup 33} erg (corresponding to a total thermal energy of at least E {sub tot} > 3.7 × 10{sup 34} erg), placing it among the strongest detected M dwarf flares. The presence of this powerful flare on an old L0 dwarf may indicate that stellar-type magnetic activity persists down to the end of the main sequence and on older ML transition dwarfs.« less

Iridovirus disease in two ornamental tropical freshwater fishes: African lampeye and dwarf gourami.

PubMed

Sudthongkong, Chaiwud; Miyata, Masato; Miyazaki, Teruo

2002-04-05

Many species of ornamental freshwater fishes are imported into Japan from all over the world. We found African lampeye Aplocheilichthys normani and dwarf gourami Colisa lalia suffering from an iridovirus infection just after being imported by tropical fish wholesalers from Singapore. African lampeye were cultured on the Indonesian Island of Sumatra and dwarf gourami were cultured in Malaysia before export. Diseased fishes displayed distinct histopathological signs of iridovirus infection: systemic appearance of inclusion body-bearing cells, and necrosis of splenocytes and hematopoietic cells. Electron microscopy revealed viral particles (African lampeye:180 to 200 nm in edge to edge diameter; dwarf gourami: 140 to 150 nm in diameter) in an inclusion body within the cytoplasm of inclusion body-bearing cells as well as in the cytoplasm of necrotized cells. Experimental infection with an iridovirus isolate from African lampeye (ALIV) revealed pathogenicity of ALIV to African lampeye and pearl gourami Trichogaster leeri. Polymerase chain reaction (PCR) products from ALIV and an iridovirus isolate from dwarf gourami (DGIV) using iridovirus-specific primers were indistinguishable. The nucleotide sequence of PCR products derived from ALIV (696 base pairs) and DGIV (701 base pairs) had 95.3% identity. These results indicate that ALIV and DGIV have a single origin.

Orbital misalignment of the Neptune-mass exoplanet GJ 436b with the spin of its cool star

NASA Astrophysics Data System (ADS)

Bourrier, Vincent; Lovis, Christophe; Beust, Hervé; Ehrenreich, David; Henry, Gregory W.; Astudillo-Defru, Nicola; Allart, Romain; Bonfils, Xavier; Ségransan, Damien; Delfosse, Xavier; Cegla, Heather M.; Wyttenbach, Aurélien; Heng, Kevin; Lavie, Baptiste; Pepe, Francesco

2018-01-01

The angle between the spin of a star and the orbital planes of its planets traces the history of the planetary system. Exoplanets orbiting close to cool stars are expected to be on circular, aligned orbits because of strong tidal interactions with the stellar convective envelope. Spin–orbit alignment can be measured when the planet transits its star, but such ground-based spectroscopic measurements are challenging for cool, slowly rotating stars. Here we report the three-dimensional characterization of the trajectory of an exoplanet around an M dwarf star, derived by mapping the spectrum of the stellar photosphere along the chord transited by the planet. We find that the eccentric orbit of the Neptune-mass exoplanet GJ 436b is nearly perpendicular to the stellar equator. Both eccentricity and misalignment, surprising around a cool star, can result from dynamical interactions (via Kozai migration) with a yet-undetected outer companion. This inward migration of GJ 436b could have triggered the atmospheric escape that now sustains its giant exosphere.

HIGH-RESOLUTION SPECTROSCOPY DURING ECLIPSE OF THE YOUNG SUBSTELLAR ECLIPSING BINARY 2MASS 0535-0546. II. SECONDARY SPECTRUM: NO EVIDENCE THAT SPOTS CAUSE THE TEMPERATURE REVERSAL

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohanty, Subhanjoy; Stassun, Keivan G., E-mail: s.mohanty@imperial.ac.uk, E-mail: keivan.stassun@vanderbilt.edu

2012-10-10

We present high-resolution optical spectra of the young brown dwarf eclipsing binary 2M0535-05, obtained during eclipse of the higher-mass (primary) brown dwarf. Combined with our previous spectrum of the primary alone (Paper I), the new observations yield the spectrum of the secondary alone. We investigate, through a differential analysis of the two binary components, whether cool surface spots are responsible for suppressing the temperature of the primary. In Paper I, we found a significant discrepancy between the empirical surface gravity of the primary and that inferred via fine analysis of its spectrum. Here we find precisely the same discrepancy inmore » surface gravity, both qualitatively and quantitatively. While this may again be ascribed to either cool spots or model opacity errors, it implies that cool spots cannot be responsible for preferentially lowering the temperature of the primary: if they were, spot effects on the primary spectrum should be preferentially larger, and they are not. The T{sub eff}'s we infer for the primary and secondary, from the TiO-{epsilon} bands alone, show the same reversal, in the same ratio, as is empirically observed, bolstering the validity of our analysis. In turn, this implies that if suppression of convection by magnetic fields on the primary is the fundamental cause of the T{sub eff} reversal, then it cannot be a local suppression yielding spots mainly on the primary (though both components may be equally spotted), but a global suppression in the interior of the primary. We briefly discuss current theories of how this might work.« less

A Multiwavelength Study of Nearby Millisecond Pulsar PSR J1400-1431: Improved Astrometry and an Optical Detection of Its Cool White Dwarf Companion

NASA Astrophysics Data System (ADS)

Swiggum, J. K.; Kaplan, D. L.; McLaughlin, M. A.; Lorimer, D. R.; Bogdanov, S.; Ray, P. S.; Lynch, R.; Gentile, P.; Rosen, R.; Heatherly, S. A.; Barlow, B. N.; Hegedus, R. J.; Vasquez Soto, A.; Clancy, P.; Kondratiev, V. I.; Stovall, K.; Istrate, A.; Penprase, B.; Bellm, E. C.

2017-09-01

In 2012, five high-school students involved in the Pulsar Search Collaboratory discovered the millisecond pulsar (MSP) PSR J1400-1431, and initial timing parameters were published in Rosen et al. a year later. Since then, we have obtained a phase-connected timing solution spanning five years, resolving a significant position discrepancy and measuring \\dot{P}, proper motion, parallax, and a monotonic slope in dispersion measure over time. Due to PSR J1400-1431’s proximity and significant proper motion, we use the Shklovskii effect and other priors to determine a 95% confidence interval for PSR J1400-1431’s distance, d={270}-80+130 pc. With an improved timing position, we present the first detection of the pulsar’s low-mass white dwarf (WD) companion using the Goodman Spectrograph on the 4.1 m SOAR telescope. Deeper imaging suggests that it is a cool DA-type WD with {T}{eff}=3000+/- 100 K and R/{R}⊙ =(2.19+/- 0.03)× {10}-2 (d/270 {pc}). We show a convincing association between PSR J1400-1431 and a γ-ray point source, 3FGL J1400.5-1437, but only weak (3.3σ) evidence of pulsations after folding γ-ray photons using our radio timing model. We detect an X-ray counterpart with XMM-Newton, but the measured X-ray luminosity (1×1029 erg s-1) makes PSR J1400-1431 the least X-ray luminous rotation-powered MSP detected to date. Together, our findings present a consistent picture of a nearby (d≈ 230 pc) MSP in a 9.5-day orbit around a cool ˜0.3 M ⊙ WD companion, with orbital inclination I≳ 60^\\circ .

The distribution of rotational velocities for low-mass stars in the Pleiades

NASA Technical Reports Server (NTRS)

Stauffer, John R.; Hartmann, Lee W.

1987-01-01

The available spectral type and color data for late-type Pleiades members have been reanalyzed, and new reddening estimates are obtained. New photometry for a small number of stars and a compilation of H-alpha equivalent widths for Pleiades dwarfs are presented. These data are used to examine the location of the rapid rotators in color-magnitude diagrams and the correlation between chromospheric activity and rotation. It is shown that the wide range of angular momenta exhibited by Pleiades K and M dwarfs is not necessarily produced by a combination of main-sequence spin-downs and a large age spread; it can also result from a plausible spread in initial angular momenta, coupled with initial main-sequence spin-down rates that are only weakly dependent on rotation. The new reddening estimates confirm Breger's (1985) finding of large extinctions confined to a small region in the southern portion of the Merope nebula.

The CYP88A cytochrome P450, ent-kaurenoic acid oxidase, catalyzes three steps of the gibberellin biosynthesis pathway

PubMed Central

Helliwell, Chris A.; Chandler, Peter M.; Poole, Andrew; Dennis, Elizabeth S.; Peacock, W. James

2001-01-01

We have shown that ent-kaurenoic acid oxidase, a member of the CYP88A subfamily of cytochrome P450 enzymes, catalyzes the three steps of the gibberellin biosynthetic pathway from ent-kaurenoic acid to GA12. A gibberellin-responsive barley mutant, grd5, accumulates ent-kaurenoic acid in developing grains. Three independent grd5 mutants contain mutations in a gene encoding a member of the CYP88A subfamily of cytochrome P450 enzymes, defined by the maize Dwarf3 protein. Mutation of the Dwarf3 gene gives rise to a gibberellin-responsive dwarf phenotype, but the lesion in the gibberellin biosynthesis pathway has not been identified. Arabidopsis thaliana has two CYP88A genes, both of which are expressed. Yeast strains expressing cDNAs encoding each of the two Arabidopsis and the barley CYP88A enzymes catalyze the three steps of the GA biosynthesis pathway from ent-kaurenoic acid to GA12. Sequence comparison suggests that the maize Dwarf3 locus also encodes ent-kaurenoic acid oxidase. PMID:11172076

Exploring Substellar Evolution with the Coldest Brown Dwarfs

NASA Astrophysics Data System (ADS)

Dupuy, Trent J.

2017-01-01

The coldest brown dwarfs are our best analogs to extrasolar gas-giant planets, representing the lowest mass products of star formation. Our view of such objects has been transformed over the last few years as new observations have revealed that the solar neighborhood is populated by much colder objects than previously recognized. At the center of efforts to discover and characterize these coldest substellar objects have been observations from NASA missions (WISE, Spitzer, HST) and the Keck Telescopes. I will review the tremendous progress made in this field over just the last few years thanks to major community efforts to overcome observational challenges in obtaining spectroscopy, photometry, and astrometry of these infrared-faint, optically invisible objects. Spectra from HST and Keck were key in establishing the much anticipated "Y" spectral type, extending the classic stellar classification scheme to atmospheres as cool as 300-400 K. Parallaxes and photometry from Spitzer and Keck have provided absolute fluxes, enabling robust temperature determinations and critical tests of model atmopheres. High-resolution imaging with Keck laser guide star adaptive optics (LGS AO) has been the most prolific resource for revealing tight companions among the coldest brown dwarfs. In fact, with continued orbit monitoring with Keck LGS AO and HST, these binary systems will ultimately provide dynamical masses that will allow the strongest tests of models and reveal if the coldest brown dwarfs are indeed "planetary mass" (less than about 13 Jupiter masses) as is currently thought.

IRAC Photometry of the Coldest CatWISE-selected Brown Dwarfs

NASA Astrophysics Data System (ADS)

Meisner, Aaron; Kirkpatrick, J. Davy; Kirkpatrick, J. Davy; Eisenhardt, Peter; Marocco, Federico; Faherty, Jacqueline; Cushing, Michael; Wright, Edward

2018-05-01

We will obtain IRAC [3.6] and [4.5] photometry of 250 extremely cool brown dwarfs newly revealed by the powerful combination of WISE and NEOWISE imaging at 4.6 microns. Our CatWISE effort, which is an archival data analysis program using WISE and NEOWISE data, will improve upon the motion selection of AllWISE by enabling a >10x time baseline enhancement, from 0.5 years (AllWISE) to 6.5 years (CatWISE). As a result, CatWISE motion selection is expected to yield a dramatic 8-fold increase in the sample of known brown dwarfs at spectral types T5 and later (T < 1,200 K). Many of the coolest such CatWISE discoveries will be detected exclusively in the WISE 4.6 micron (W2) channel. WISE W1 (3.4 micron) nondetections, which we expect for the majority of our most interesting sources, will provide only limits on mid-infrared color. Spitzer can supply this critical datum by measuring accurate [3.6]-[4.5] colors of our discoveries. These Spitzer color measurements will permit photometric spectral type estimates, which in turn yield estimates for critical parameters including luminosity, distance, and near-infrared flux. Using large [3.6]-[4.5] color to pinpoint the coldest late T and Y dwarfs among our CatWISE sample will enable us to prioritize these objects for spectroscopic follow-up, better understand the bottom of the substellar mass function, and identify nearby giant planet analogs suitable for future atmospheric studies with JWST.

The First Brown Dwarf/Planetary-mass Object in the 32 Orionis Group

NASA Astrophysics Data System (ADS)

Burgasser, Adam J.; Lopez, Mike A.; Mamajek, Eric E.; Gagné, Jonathan; Faherty, Jacqueline K.; Tallis, Melisa; Choban, Caleb; Tamiya, Tomoki; Escala, Ivanna; Aganze, Christian

2016-03-01

The 32 Orionis group is a co-moving group of roughly 20 young (24 Myr) M3-B5 stars 100 pc from the Sun. Here we report the discovery of its first substellar member, WISE J052857.69+090104.2. This source was previously reported to be an M giant star based on its unusual near-infrared spectrum and lack of measureable proper motion. We re-analyze previous data and new moderate-resolution spectroscopy from Magellan/Folded-port InfraRed Echellette to demonstrate that this source is a young near-infrared L1 brown dwarf with very low surface gravity features. Spectral model fits indicate Teff = 1880{}-70+150 K and {log}g = 3.8{}-0.2+0.2, consistent with a 15-22 Myr object with a mass near the deuterium-burning limit. Its sky position, estimated distance, kinematics (both proper motion and radial velocity), and spectral characteristics are all consistent with membership in 32 Orionis, and its temperature and age imply a mass (M = {14}-3+4 MJ) that straddles the brown dwarf/planetary-mass object boundary. The source has a somewhat red J-W2 color compared to other L1 dwarfs, but this is likely a low-gravity-related temperature offset; we find no evidence of significant excess reddening from a disk or cool companion in the 3-5 μm waveband. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Contrasting growth responses of dominant peatland plants to warming and vegetation composition.

PubMed

Walker, Tom N; Ward, Susan E; Ostle, Nicholas J; Bardgett, Richard D

2015-05-01

There is growing recognition that changes in vegetation composition can strongly influence peatland carbon cycling, with potential feedbacks to future climate. Nevertheless, despite accelerated climate and vegetation change in this ecosystem, the growth responses of peatland plant species to combined warming and vegetation change are unknown. Here, we used a field warming and vegetation removal experiment to test the hypothesis that dominant species from the three plant functional types present (dwarf-shrubs: Calluna vulgaris; graminoids: Eriophorum vaginatum; bryophytes: Sphagnum capillifolium) contrast in their growth responses to warming and the presence or absence of other plant functional types. Warming was accomplished using open top chambers, which raised air temperature by approximately 0.35 °C, and we measured air and soil microclimate as potential mechanisms through which both experimental factors could influence growth. We found that only Calluna growth increased with experimental warming (by 20%), whereas the presence of dwarf-shrubs and bryophytes increased growth of Sphagnum (46%) and Eriophorum (20%), respectively. Sphagnum growth was also negatively related to soil temperature, which was lower when dwarf-shrubs were present. Dwarf-shrubs may therefore promote Sphagnum growth by cooling the peat surface. Conversely, the effect of bryophyte presence on Eriophorum growth was not related to any change in microclimate, suggesting other factors play a role. In conclusion, our findings reveal contrasting abiotic and biotic controls over dominant peatland plant growth, suggesting that community composition and carbon cycling could be modified by simultaneous climate and vegetation change.

A new Böhm-Vitense gap in the temperature range 5560 to 5610 K in the main sequence hm-Vitense gap in the main sequence

NASA Astrophysics Data System (ADS)

Kovtyukh, V. V.; Soubiran, C.; Belik, S. I.

2004-12-01

Highly precise temperatures (σ = 10-15 K) have been determined from line depth ratios for a set of 248 F-K field dwarfs of about solar metallicity (-0.5 < [Fe/H] < +0.4), based on high resolution (R=42 000), high S/N echelle spectra. A new gap has been discovered in the distribution of stars on the Main Sequence in the temperature range 5560 to 5610 K. This gap coincides with a jump in the microturbulent velocity Vt and the well-known Li depression near 5600 K in field dwarfs and open clusters. As the principal cause of the observed discontinuities in stellar properties we propose the penetration of the convective zone into the inner layers of stars slightly less massive than the Sun and related to it, a change in the temperature gradient. Based on spectra collected with the ELODIE spectrograph at the 1.93-m telescope of the Observatoire de Haute-Provence (France). Full Table 1 is only available in electronic form at http://www.edpsciences.org

Characterization of the N-terminal segment used by the barley yellow dwarf virus movement protein to promote interaction with the nuclear membrane of host plant cells.

PubMed

Dennison, Sarah Rachel; Harris, Frederick; Brandenburg, Klaus; Phoenix, David Andrew

2007-11-01

The barley yellow dwarf virus movement protein (BYDV-MP) requires its N-terminal sequence to promote the transport of viral RNA into the nuclear compartment of host plant cells. Here, graphical analysis predicts that this sequence would form a membrane interactive amphiphilic alpha-helix. Confirming this prediction, NT1, a peptide homologue of the BYDV-MP N-terminal sequence, was found to be alpha-helical (65%) in the presence of vesicles mimics of the nuclear membrane. The peptide increased the fluidity of these nuclear membrane mimics (rise in wavenumber of circa 0.5-1.0 cm(-1)) and induced surface pressure changes of 2 mN m(-1) in lipid monolayers with corresponding compositions. Taken with isotherm analysis these results suggest that BYDV-MP forms an N-terminal amphiphilic alpha-helix, which partitions into the nuclear membrane primarily through thermodynamically stable associations with the membrane lipid headgroup region. We speculate that these associations may play a role in targeting of the nuclear membrane by BYDM-MP.

The CV period minimum

NASA Astrophysics Data System (ADS)

Kolb, Ulrich; Baraffe, Isabelle

Using improved, up-to-date stellar input physics tested against observations of low-mass stars and brown dwarfs we calculate the secular evolution of low-donor-mass CVs, including those which form with a brown dwarf donor star. Our models confirm the mismatch between the calculated minimum period (plus or minus in ~= 70 min) and the observed short-period cut-off (~= 80 min) in the CV period histogram. Theoretical period distributions synthesized from our model sequences always show an accumulation of systems at the minimum period, a feature absent in the observed distribution. We suggest that non-magnetic CVs become unobservable as they are effectively trapped in permanent quiescence before they reach plus or minus in, and that small-number statistics may hide the period spike for magnetic CVs. We calculate the minimum period for high mass transfer rate sequences and discuss the relevance of these for explaining the location of CV secondaries in the orbital-period-spectral-type diagram. We also show that a recently suggested revised mass-radius relation for low-mass main-sequence stars cannot explain the CV period gap.

THE HAWAII INFRARED PARALLAX PROGRAM. II. YOUNG ULTRACOOL FIELD DWARFS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Michael C.; Dupuy, Trent J.; Allers, Katelyn N., E-mail: mliu@ifa.hawaii.edu

We present a large, uniform analysis of young (≈10–150 Myr) ultracool dwarfs, based on new high-precision infrared (IR) parallaxes for 68 objects. We find that low-gravity (vl-g) late-M and L dwarfs form a continuous sequence in IR color–magnitude diagrams, separate from the field population and from current theoretical models. These vl-g objects also appear distinct from young substellar (brown dwarf and exoplanet) companions, suggesting that the two populations may have a different range of physical properties. In contrast, at the L/T transition, young, old, and spectrally peculiar objects all span a relatively narrow range in near-IR absolute magnitudes. At a given spectralmore » type, the IR absolute magnitudes of young objects can be offset from ordinary field dwarfs, with the largest offsets occurring in the Y and J bands for late-M dwarfs (brighter than the field) and mid-/late-L dwarfs (fainter than the field). Overall, low-gravity (vl-g) objects have the most uniform photometric behavior, while intermediate gravity (int-g) objects are more diverse, suggesting a third governing parameter beyond spectral type and gravity class. We examine the moving group membership for all young ultracool dwarfs with parallaxes, changing the status of 23 objects (including 8 previously identified planetary-mass candidates) and fortifying the status of another 28 objects. We use our resulting age-calibrated sample to establish empirical young isochrones and show a declining frequency of vl-g objects relative to int-g objects with increasing age. Notable individual objects in our sample include high-velocity (≳100 km s{sup −1}) int-g objects, very red late-L dwarfs with high surface gravities, candidate disk-bearing members of the MBM20 cloud and β  Pic moving group, and very young distant interlopers. Finally, we provide a comprehensive summary of the absolute magnitudes and spectral classifications of young ultracool dwarfs, using a combined sample of 102 objects found in the field and as substellar companions to young stars.« less

Accretion signatures in the X-shooter spectrum of the substellar companion to SR12

NASA Astrophysics Data System (ADS)

Santamaría-Miranda, Alejandro; Cáceres, Claudio; Schreiber, Matthias R.; Hardy, Adam; Bayo, Amelia; Parsons, Steven G.; Gromadzki, Mariusz; Aguayo Villegas, Aurora Belén

2018-04-01

About a dozen substellar companions orbiting young stellar objects or pre-main sequence stars at several hundred au have been identified in the last decade. These objects are interesting both due to the uncertainties surrounding their formation, and because their large separation from the host star offers the potential to study the atmospheres of young giant planets and brown dwarfs. Here, we present X-shooter spectroscopy of SR 12 C, a ˜2 Myr young brown dwarf orbiting SR 12 at an orbital separation of 1083 au. We determine the spectral type, gravity, and effective temperature via comparison with models and observational templates of young brown dwarfs. In addition, we detect and characterize accretion using several accretion tracers. We find SR 12 C to be a brown dwarf of spectral type L0 ± 1, log g = 4 ± 0.5, an effective temperature of 2600 ± 100 K. Our spectra provide clear evidence for accretion at a rate of ˜10-10 M⊙ yr-1. This makes SR 12 one of the few sub-stellar companions with a reliable estimate for its accretion rate. A comparison of the ages and accretion rates of sub-stellar companions with young isolated brown dwarfs does not reveal any significant differences. If further accretion rate measurements of a large number of substellar companions can confirm this trend, this would hint towards a similar formation mechanism for substellar companions at large separations and isolated brown dwarfs.

The Multiple-component Binary Hyad, vA 351 - a Progress Report

NASA Astrophysics Data System (ADS)

Benedict, George Fritz; Franz, Otto G.; Wasserman, Lawrence H.

2017-06-01

We extend results first announced by Franz et al. (1998) in the abstract, http://adsabs.harvard.edu/abs/1998AAS...19310207F ,that identified vA 351 = H346 in the Hyades as a multiple star system containing a white dwarf. With HST/FGS fringe tracking and scanning, spanning four years, we establish a parallax, relative orbit, and mass fraction for the A-B components, with a period, P~5.47y. With ground-based radial velocities from the McDonald Observatory Struve 2.1m telescope and Sandiford Spectrograph, spanning 14 years, we find that component B consists of BC, two M dwarf stars orbiting with a very short period (P(BC)~0.75 days), having a mass ratio C/B~0.94. We confirm that the total mass of the system can only be reconciled with the distance and component photometry by including a fainter, higher mass component, proposed to be a ~0.8Msun white dwarf. Thus, the quadruple system consists of three M dwarfs (A,B,C) and one white dwarf (D). The M dwarf masses and absolute magnitudes are consistent with the Benedict et al. (2016, http://adsabs.harvard.edu/abs/2016AJ....152..141B) lower Main Sequence Mass-Luminosity Relation. The radial velocity signal has so far yielded a signature only for the short-period BC orbital motion. Velocities from H-α and He I emission lines confirm the BC period from absorption lines, with similar (He I) and higher (H-α) velocity amplitudes.

70 DA White Dwarfs Identified in LAMOST Pilot Survey

NASA Astrophysics Data System (ADS)

Zhao, J. K.; Luo, A. L.; Oswalt, T. D.; Zhao, G.

2013-06-01

We present a spectroscopically identified catalog of 70 DA white dwarfs (WDs) from the LAMOST pilot survey. Thirty-five are found to be new identifications after cross-correlation with the Eisenstein et al. and Villanova catalogs. The effective temperature and gravity of these WDs are estimated by Balmer lines fitting. Most of them are hot WDs. The cooling times and masses of these WDs are estimated by interpolation in theoretical evolution tracks. The peak of the mass distribution is found to be ~0.6 M ⊙, which is consistent with prior work in the literature. The distances of these WDs are estimated using the method of synthetic spectral distances. All of these WDs are found to be in the Galactic disk from our analysis of space motions. Our sample supports the expectation that WDs with high mass are concentrated near the plane of the Galactic disk.

A NEW TIMESCALE FOR PERIOD CHANGE IN THE PULSATING DA WHITE DWARF WD 0111+0018

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hermes, J. J.; Montgomery, M. H.; Winget, D. E.

2013-03-20

We report the most rapid rate of period change measured to date for a pulsating DA (hydrogen atmosphere) white dwarf (WD), observed in the 292.9 s mode of WD 0111+0018. The observed period change, faster than 10{sup -12} s s{sup -1}, exceeds by more than two orders of magnitude the expected rate from cooling alone for this class of slow and simply evolving pulsating WDs. This result indicates the presence of an additional timescale for period evolution in these pulsating objects. We also measure the rates of period change of nonlinear combination frequencies and show that they share the evolutionarymore » characteristics of their parent modes, confirming that these combination frequencies are not independent modes but rather artifacts of some nonlinear distortion in the outer layers of the star.« less

70 DA WHITE DWARFS IDENTIFIED IN LAMOST PILOT SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, J. K.; Luo, A. L.; Zhao, G.

2013-06-01

We present a spectroscopically identified catalog of 70 DA white dwarfs (WDs) from the LAMOST pilot survey. Thirty-five are found to be new identifications after cross-correlation with the Eisenstein et al. and Villanova catalogs. The effective temperature and gravity of these WDs are estimated by Balmer lines fitting. Most of them are hot WDs. The cooling times and masses of these WDs are estimated by interpolation in theoretical evolution tracks. The peak of the mass distribution is found to be {approx}0.6 M {sub Sun }, which is consistent with prior work in the literature. The distances of these WDs aremore » estimated using the method of synthetic spectral distances. All of these WDs are found to be in the Galactic disk from our analysis of space motions. Our sample supports the expectation that WDs with high mass are concentrated near the plane of the Galactic disk.« less

The solar neighborhood, 1: Standard spectral types (K5-M8) for northern dwarfs within eight parsecs

NASA Technical Reports Server (NTRS)

Henry, Todd J.; Kirkpatrick, J. Davy; Simons, Douglas A.

1994-01-01

Spectral types on a standard system are presented for late-type dwarfs within 8 pc. All known main-sequence stars north of -25 deg and with M(sub V) greater than or = 8.00 have been observed, resulting in 92 spectra. Based upon the stellar system density to 5 pc, we estimate that approximately 35 systems in the 8 pc sample are 'missing.' In an effort to reveal these systems, we use an empirical spectral type-M(sub V) relation to estimate distances to additional stars that may lie within 8 pc.

The origin of ultra-compact binaries

NASA Technical Reports Server (NTRS)

Hachisu, Izumi; Miyaji, Shigeki; Saio, Hideyuki

1987-01-01

The origin of ultra-compact binaries composed of a neutron star and a low-mass (about 0.06 solar mass) white dwarf is considered. Taking account of the systemic losses of mass and angular momentum, it was found that a serious difficulty exists in the scenarios which involve tidal captures of a normal star (a main sequence star or a red giant) by a neutron star. This difficulty can be avoided if a red giant star is captured by a massive white dwarf (M is approx. greater than 1.2 solar masses), which becomes a neutron star through the accretion induced collapse.

INTRINSIC COLORS, TEMPERATURES, AND BOLOMETRIC CORRECTIONS OF PRE-MAIN-SEQUENCE STARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pecaut, Mark J.; Mamajek, Eric E.

2013-09-01

We present an analysis of the intrinsic colors and temperatures of 5-30 Myr old pre-main-sequence (pre-MS) stars using the F0- through M9-type members of nearby, negligibly reddened groups: the η Cha cluster, the TW Hydra Association, the β Pic Moving Group, and the Tucana-Horologium Association. To check the consistency of spectral types from the literature, we estimate new spectral types for 52 nearby pre-MS stars with spectral types F3 through M4 using optical spectra taken with the SMARTS 1.5 m telescope. Combining these new types with published spectral types and photometry from the literature (Johnson-Cousins BVI{sub C} , 2MASS JHK{submore » S} and WISE W1, W2, W3, and W4), we derive a new empirical spectral type-color sequence for 5-30 Myr old pre-MS stars. Colors for pre-MS stars match dwarf colors for some spectral types and colors, but for other spectral types and colors, deviations can exceed 0.3 mag. We estimate effective temperatures (T {sub eff}) and bolometric corrections (BCs) for our pre-MS star sample through comparing their photometry to synthetic photometry generated using the BT-Settl grid of model atmosphere spectra. We derive a new T {sub eff} and BC scale for pre-MS stars, which should be a more appropriate match for T Tauri stars than often-adopted dwarf star scales. While our new T {sub eff} scale for pre-MS stars is within ≅100 K of dwarfs at a given spectral type for stars« less

On the formation of TW Crv optical radiation

NASA Astrophysics Data System (ADS)

Shimansky, V. V.; Mitrofanova, A. A.; Borisov, N. V.; Fabrika, S. N.; Galeev, A. I.

2016-10-01

We present the analysis of the optical radiation of the young pre-cataclysmic variable TW Crv. Spectroscopic and photometric observations were obtained at the SAO RAS 6-m BTA telescope and at the Russian-Turkish RTT-150 telescope. The light curves of the system posses nearly sinusoidal shapes with the amplitudes of Δ m > 0.m7, what is typical for young pre-cataclysmic variables with sdO-subdwarfs and orbit inclinations of less than 45◦. The optical spectrum contains dominant radiation of the hot subdwarf with the HI and He II absorption lines and strong emission lines, which are formed in the atmosphere of the secondary owing to the reflection effects. Radial velocities of the cool star were measured by analyzing the λλ 4630-4650 Å Bowen blend, which for the first time allowed to determine the component masses. A numerical simulation of the light curves and spectra of TW Crv, obtaining a complete set of systems fundamental parameters was carried out. The hot star parameters prompt its belonging to the sdOsubdwarf class at the stage of transition to the cooling white dwarf sequence. The absence of its observable planetary nebula is caused by a long-lasting evolution of the system after the common envelope state. The secondary component has a luminosity excess, which is typical for other young sdO-subdwarf precataclysmic variables. Its position on the " age-luminosity excess" diagram points at the accuracy of the obtained set of TW Crv fundamental parameters and at the similarity of its evolutionary and physical conditions with that of other BE UMa-type objects.

THE COLOR-PERIOD DIAGRAM AND STELLAR ROTATIONAL EVOLUTION-NEW ROTATION PERIOD MEASUREMENTS IN THE OPEN CLUSTER M34

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meibom, Soeren; Saar, Steven H.; Mathieu, Robert D.

2011-06-01

We present the results of a 5 month photometric time-series survey for stellar rotation periods combined with a 4 year radial-velocity survey for membership and binarity in the 220 Myr open cluster M34. We report surface rotation periods for 120 stars, 83 of which are kinematic and photometric late-type cluster members. A comparison to previous work serves to illustrate the importance of high-cadence long baseline photometric observations and membership information. The new M34 periods are less biased against slow rotation and cleaned for non-members. The rotation periods of the cluster members span over more than an order of magnitude frommore » 0.5 days up to 11.5 days, and trace two distinct rotational sequences-fast (C) and moderate-to-slow (I)-in the color-period diagram. The sequences represent two different states (fast and slow) in the rotational evolution of the late-type cluster members. We use the color-period diagrams for M34 and for younger and older clusters to estimate the timescale for the transition from the C to the I sequence and find {approx}<150 Myr, {approx}150-300 Myr, and {approx}300-600 Myr for G, early-mid K, and late K dwarfs, respectively. The small number of stars in the gap between C and I suggests a quick transition. We estimate a lower limit on the maximum spin-down rate (dP/dt) during this transition to be {approx}0.06 days Myr{sup -1} and {approx}0.08 days Myr{sup -1} for early and late K dwarfs, respectively. We compare the I sequence rotation periods in M34 and the Hyades for G and K dwarfs and find that K dwarfs spin down slower than the Skumanich {radical}t rate. We determine a gyrochronology age of 240 Myr for M34. The gyro-age has a small formal uncertainty of 2% which reflects the tight I sequence in the M34 color-period diagram. We measure the effect of cluster age uncertainties on the gyrochronology age for M34 and find the resulting error on the gyro-age to be consistent with the {approx}15% error estimate for the technique in general. We use the M34 I sequence to redetermine the coefficients in the expression for rotational dependence on color used in gyrochronology. Finally, we propose that stability in the phase, shape, and amplitude of the photometric variability for the 120 rotators over the {approx}5 month duration of our survey is due to spot generation at active stellar longitudes.« less

The Rotation Period and Magnetic Field of the T Dwarf 2MASSI J1047539+212423 Measured from Periodic Radio Bursts

NASA Astrophysics Data System (ADS)

Williams, P. K. G.; Berger, E.

2015-08-01

Periodic radio bursts from very low mass stars and brown dwarfs simultaneously probe their magnetic and rotational properties. The brown dwarf 2MASSI J1047539+212423 (2M 1047+21) is currently the only T dwarf (T6.5) detected at radio wavelengths. Previous observations of this source with the Arecibo observatory revealed intermittent, 100%-polarized radio pulses similar to those detected from other brown dwarfs, but were unable to constrain a pulse periodicity; previous Very Large Array (VLA) observations detected quiescent emission a factor of ∼100 times fainter than the Arecibo pulses but no additional events. Here we present 14 hr of VLA observations of this object that reveal a series of pulses at ∼6 GHz with highly variable profiles, showing that the pulsing behavior evolves on time scales that are both long and short compared to the rotation period. We measure a periodicity of ∼1.77 hr and identify it with the rotation period. This is just the sixth rotation period measurement in a late T dwarf, and the first obtained in the radio. We detect a pulse at 10 GHz as well, suggesting that the magnetic field strength of 2 M 1047+21 reaches at least 3.6 kG. Although this object is the coolest and most rapidly rotating radio-detected brown dwarf to date, its properties appear continuous with those of other such objects, suggesting that the generation of strong magnetic fields and radio emission may continue to even cooler objects. Further studies of this kind will help to clarify the relationships between mass, age, rotation, and magnetic activity at and beyond the end of the main sequence, where both theories and observational data are currently scarce.

Magnetic Inflation and Stellar Mass. II. On the Radii of Single, Rapidly Rotating, Fully Convective M-Dwarf Stars

NASA Astrophysics Data System (ADS)

Kesseli, Aurora Y.; Muirhead, Philip S.; Mann, Andrew W.; Mace, Greg

2018-06-01

Main-sequence, fully convective M dwarfs in eclipsing binaries are observed to be larger than stellar evolutionary models predict by as much as 10%–15%. A proposed explanation for this discrepancy involves effects from strong magnetic fields, induced by rapid rotation via the dynamo process. Although, a handful of single, slowly rotating M dwarfs with radius measurements from interferometry also appear to be larger than models predict, suggesting that rotation or binarity specifically may not be the sole cause of the discrepancy. We test whether single, rapidly rotating, fully convective stars are also larger than expected by measuring their R\\sin i distribution. We combine photometric rotation periods from the literature with rotational broadening (v\\sin i) measurements reported in this work for a sample of 88 rapidly rotating M dwarf stars. Using a Bayesian framework, we find that stellar evolutionary models underestimate the radii by 10 % {--}15{ % }-2.5+3, but that at higher masses (0.18 < M < 0.4 M Sun), the discrepancy is only about 6% and comparable to results from interferometry and eclipsing binaries. At the lowest masses (0.08 < M < 0.18 M Sun), we find that the discrepancy between observations and theory is 13%–18%, and we argue that the discrepancy is unlikely to be due to effects from age. Furthermore, we find no statistically significant radius discrepancy between our sample and the handful of M dwarfs with interferometric radii. We conclude that neither rotation nor binarity are responsible for the inflated radii of fully convective M dwarfs, and that all fully convective M dwarfs are larger than models predict.

Isolation and characterisation of a dwarf rice mutant exhibiting defective gibberellins biosynthesis.

PubMed

Ji, S H; Gururani, M A; Lee, J W; Ahn, B-O; Chun, S-C

2014-03-01

We have isolated a severe dwarf mutant derived from a Ds (Dissociation) insertion mutant rice (Oryza sativa var. japonica c.v. Dongjin). This severe dwarf phenotype, has short and dark green leaves, reduced shoot growth early in the seedling stage, and later severe dwarfism with failure to initiate flowering. When treated with bioactive GA3 , mutants are restored to the normal wild-type phenotype. Reverse transcription PCR analyses of 22 candidate genes related to the gibberellin (GA) biosynthesis pathway revealed that among 22 candidate genes tested, a dwarf mutant transcript was not expressed only in one OsKS2 gene. Genetic analysis revealed that the severe dwarf phenotype was controlled by recessive mutation of a single nuclear gene. The putative OsKS2 gene was a chromosome 4-located ent-kaurene synthase (KS), encoding the enzyme that catalyses an early step of the GA biosynthesis pathway. Sequence analysis revealed that osks2 carried a 1-bp deletion in the ORF region of OsKS2, which led to a loss-of-function mutation. The expression pattern of OsKS2 in wild-type cv Dongjin, showed that it is expressed in all organs, most prominently in the stem and floral organs. Morphological characteristics of the dwarf mutant showed dramatic modifications in internal structure and external morphology. We propose that dwarfism in this mutant is caused by a point mutation in OsKS2, which plays a significant role in growth and development of higher plants. Further investigation on OsKS2 and other OsKS-like proteins is underway and may yield better understanding of the putative role of OsKS in severe dwarf mutants. © 2013 German Botanical Society and The Royal Botanical Society of the Netherlands.