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1

Magnetic activity in low mass stars.  

National Technical Information Service (NTIS)

The manifestations of magnetic activity in low mass stars, particularly M dwarfs, can be used as a tool to study their evolution, the operation of the interior dynamo with changing interior conditions, and the structure of their outer atmospheres. Extensi...

S. L. Hawley

1992-01-01

2

Debris Disks around Low-Mass Stars  

Microsoft Academic Search

Surprisingly, mature low-mass stars do not seem to harbor debris disks. With the exception of a few stars in young clusters (e.g. AU Mic), no stars below ~0.75 solar masses have been identified as having infrared excess. This is in strong contrast with solar-type stars, which frequently have detectable dust emission even at ages of many Gyr. However, relatively few

George Rieke; Charles Beichman; Geoffrey Bryden; Thomas N. Gautier; Peter Plavchan; Karl Stapelfeldt; Angelle Tanner; David Trilling

2007-01-01

3

Gravitational Waves from Low Mass Neutron Stars  

NASA Astrophysics Data System (ADS)

Recently, using large scale molecular dynamics simulations, we determined that neutron star crust is very strong, some 10 billion times stronger than steel [1]. This makes star crust the strongest material known and it can support relatively large ``mountains''. These bumps on rapidly rotating neutron stars can radiate strong gravitational waves (GW). Therefore, we strongly encourage ongoing and future searches for continuous GW. In the present paper, we speculate that low mass neutron stars, although they may be difficult to produce, could be even stronger GW sources. We find that the crust can support very large ellipticities (fractional differences in moments of inertia) of 0.001 or even larger in low mass neutron stars. This is because a larger fraction of a low mass neutron star is solid crust compared to a 1.4 solar mass star and because the weaker gravity allows the crust to support even larger mountains. Therefore, if low mass neutron stars can be produced, for example via fragmentation during a neutron star merger, then they could produce very strong continuous gravitational waves. [4pt] [1] C. J. Horowitz and K. Kadau, Phys. Rev. Lett. 102:191102,2009. )

Horowitz, C. J.

2010-02-01

4

Protoclusters Forming Low Mass Stars  

NASA Astrophysics Data System (ADS)

While most stars are believed to form in clusters, our current understanding of the star formation process is largely limited to isolated cloud cores and single protostars. To make progress, detailed observational studies of the genesis and evolution of prestellar condensations in cluster-forming cloud cores are of prime importance. Recent wide-field (sub)millimeter continuum imaging of nearby protoclusters with the IRAM 30 m and JCMT telescopes (e.g. Motte, André & Neri 1998), as well as with the OVRO interferometer (e.g. Testi & Sargent 1998), has made possible the identification of several dozens of cold, gravitationally-bound starless condensations in, e.g., rho Oph and Serpens. Remarkably, the mass spectrum of these pre-stellar condensations resembles the shape of the stellar initial mass function (IMF), suggesting the IMF is at least partly determined by fragmentation at the pre-collapse stage of star formation. With present (sub)millimeter instrumentation, however, the dynamical properties of these protocluster condensations are difficult to assess, and only the nearest protoclusters are accessible. If ALMA can routinely mosaic fields up to or > 0.1 deg2, its high resolution and sensitivity in both continuum and lines will allow a complete census of prestellar condensations and their properties to be taken in the major protoclusters of the Galaxy. This will greatly help develop a satisfactory theory of cloud fragmentation and star cluster formation.

André, Philippe

1999-10-01

5

Debris Disks around Low-Mass Stars  

NASA Astrophysics Data System (ADS)

Surprisingly, mature low-mass stars do not seem to harbor debris disks. With the exception of a few stars in young clusters (e.g. AU Mic), no stars below ~0.75 solar masses have been identified as having infrared excess. This is in strong contrast with solar-type stars, which frequently have detectable dust emission even at ages of many Gyr. However, relatively few low-mass stars have been targeted (just 20 M stars with S/N > 3 at 70um, c.f. many 100's of F and G stars), giving considerable uncertainty to the strength of the trend, the stellar mass where its starts, and how sharp a cutoff might exist. We propose to observe a sample of 29 bright nearby M stars, more than doubling the current sample, in order to confirm and further quantify the apparent lack of dusty debris around these stars. The lack of IR excess around low mass stars, if confirmed, has important implications for understanding the formation and evolution debris disks. Among possible explanations for the observed trend are that 1) late-type stars simply do not have any colliding belts of planetesimals, 2) they lack gas giant planets that may be necessary to stir up these belts, or 3) low mass stars have strong stellar winds that efficiently remove the dust. Meanwhile other theories of debris disk evolution that are not strongly correlated with spectral type (e.g. planetesimal collisions stimulated by a passing field star) can potentially be ruled out. Given the correlation between planets and debris disks in many of these theories, providing constraints on the origin of IR excess emission will aid in our understanding of planet formation and, by linking theory with spectral type, may assist in future efforts to detect planets.

Rieke, George; Beichman, Charles; Bryden, Geoffrey; Gautier, Thomas N.; Plavchan, Peter; Stapelfeldt, Karl; Tanner, Angelle; Trilling, David

2007-05-01

6

Pulsation in extremely low mass helium stars  

NASA Astrophysics Data System (ADS)

Following the discovery of short-period oscillations in the low-mass pre-white-dwarf component of an eclipsing binary, we have explored the radial (p-mode) stability of extremely low mass stars across a range of composition, effective temperature and luminosity. We have identified the instability boundaries associated with low- to high-order radial oscillations (0 ? n ? 13) and show that these are a strong function of both composition and radial order (n). The blue edge shifts to higher effective temperature and luminosity with decreasing hydrogen abundance. In addition, high-order modes are more easily excited, and small islands of high-radial-order instability develop, some of which may correspond to real stars. The excitation mechanism is discussed with reference to these instability islands. If the envelope of the low-mass pre-white dwarf 1SWASP J024743.37-251549.2 (J0247-25B) is depleted in hydrogen, it is unstable to high-order p modes. Driving is by the classical ? mechanism operating in the second helium-ionization zone, with some support from the first helium-ionization zone. The instability is very sensitive to composition, temperature and luminosity. The reported periods, temperature and luminosity of J0247-25B require the envelope hydrogen abundance to lie in the range 0.2 ? X ? 0.3, in agreement with current evolution models.

Jeffery, C. S.; Saio, H.

2013-10-01

7

Pseudocepheids. III - The low-mass stars  

NASA Astrophysics Data System (ADS)

Light and color curves in four-color, H-beta, and (RI) photometric systems are presented for 20 low-mass pseudocepheids. Members of the Wolf 630 group and the cluster M67 are used to establish the positions of both variable and nonvariable giants with near solar abundance in the luminosity-temperature plane for old disk population stars, while members of Omega Cen and of Kapteyn's Star Group are used for the low metal abundance halo giants. The low-mass pseudocepheids discussed are divided into two main categories, based on the amplitude of light variation. The smaller amplitude stars, characterized by R CrB and RY Sgr in the old disk population, show the R CrB syndrome of occasional deep light minima, as does UW Cen. The small amplitude variables in the halo population, BL Tel and LN Hya, do not show the R CrB syndrome and their periods are longer than those of old disk stars. Large amplitude variables, with periods ranging from 10 to 150 days, are all halo objects with stability of period and form of light curve an obvious function of the period. Cen and BL Tel are members of Kapteyn's Star Group, and the spectroscopic orbital elements of the latter indicate a mass near 0.5 solar mass for the pseudocepheid and 1 solar mass for the late-type giant companion. Far-infrared observations are important in exploring the correlations between the presence and character of circumstellar dust shells and other post-AGB star parameters.

Eggen, O. J.

1986-04-01

8

Habitable Zones Around Low-Mass Stars  

NASA Astrophysics Data System (ADS)

Classically, the circumstellar habitable zone (HZ) is defined as the region inside which a terrestrial mass planet, with adequate supplies of carbon, water, and internal heat, can sustain liquid water on its surface (Kasting et al. 1993). A conservative estimate for the width of the HZ in our Solar system is 0.93-1.48 AU, assuming that the inner edge is limited by water loss and the outer edge is determined by the maximum greenhouse limit for a dense CO2 atmosphere. These numbers are revisions of ones published by Kasting et al. (1993), based on new climate modeling results. Kasting et al. obtained HZ boundaries for stars with effective temperatures between 3700 K and 7200 K--limits that do not include main-sequence M-dwarfs. In this study we use an updated 1-D radiative-convective, cloud-free climate model to estimate the width of the HZ around these low mass stars. Significant improvements in our climate model include: (1) updated collision-induced absorption coefficients for CO2 (critical for dense CO2 atmospheres at the outer edge) and (2) a revised Rayleigh scattering coefficient for H2O (important for water loss at the inner edge). Assuming Earth-like planets with CO2/H2O/N2 atmospheres, the width of the HZ is 0.24-0.44 AU around an early M star (Teff = 3600 K) and 0.05-0.09 AU for a late M star (Teff = 2800 K). As our model does not include the radiative effects of clouds, the actual HZ boundaries may extend further in both directions than our conservative estimates. Nonetheless, current ground-based surveys (e.g., the MEARTH project) and future space-based characterization missions (e.g., JWST/TPF) may be able to use these HZ boundaries to help guide their efforts to find habitable planets around main-sequence stars. (We acknowledge funding from NASA Astrobiology Institute's Virtual Planetary Laboratory, supported by NASA under cooperative agreement NNH05ZDA001C.)

Kopparapu, Ravi Kumar; Kasting, J. F.; Ramirez, R.

2011-09-01

9

30 Doradus: The Low-Mass Stars  

NASA Astrophysics Data System (ADS)

We have obtained HST/NICMOS H-band images of the central 1'x1' field around the R136 starburst cluster in the 30 Doradus HII region, in an attempt to reveal the presence (or absence) of a low-mass stellar population (M < 1 Mo). We will discuss the fascinating prospect of 30 Dor/R136 being a proto-globular cluster and a template starburst unit. At the time of writing, we are still working to determine which method and photometry package is best suited to our 0.15" NICMOS images, which are characterised by extreme crowding in the cluster center and a peculiar and slightly undersampled NICMOS PSF. The main difficulty with the PSF is identifying the many "dots" that appear outside the Airy ring as PSF features and not as faint stars. Prelimininary analysis suggests that the H-band luminosity function rises at least until H = 20 (2 Mo). We have detected numerous stars with 20.0 < H < 22.5 (the latter corresponding to 0.4 Mo) beyond about 7" from the cluster centre, but we have not yet determined the completeness in that magnitude range, and we are not yet in a position to make a statement about the shape of the H-band luminosity function there. We have combined our infrared data with the optical WFPC2 images of Hunter et al. (1995) to produce a VIH 3-colour image of the central 30" x 30" area. The result clearly shows unexpected patches of extinction, with one patch only about 5" from the cluster core.

Zinnecker, H.; Brandl, B.; Brandner, W.; Moneti, A.; Hunter, D.

10

Production of low-mass stars. IV. Carbon stars  

SciTech Connect

Detailed stellar evolution calculations were carried out for a metal-poor case (Z = 0.001) for stars of initial masses 1.0, 1.2, 2.0, and 3.0 solar and for a metal-rich (Z = 0.02) for stars of initial masses 1.2 and 3.0 solar. The stars were evolved from the main sequence through all intermediate stages and finally through a number of helium shell flashes on the AGB. Classical third dredge-up and carbon star production are obtained in two cases, both having metallicity Z = 0.001. A value of the mixing length parameter of greater than about 1.5 appears to be a necessary condition for dredge-up in low-mass stars, and an increase in alpha leads to conditions more favorable to dredge-up. Other conditions tending to favor dredge-up are high flash strength, relatively large envelope mass, and low metallicity. 39 references.

Boothroyd, A.I.; Sackmann, I.J.

1988-05-01

11

Very Low-Mass Stars and Brown Dwarfs  

NASA Astrophysics Data System (ADS)

Part I. Searches in Clusters, Stellar Associations and the Field: 1. Open clusters after HIPPARCOS J. S. Mermilliod; 2. Proper motions of very low mass stars and brown dwarfs in open clusters N. C. Hambly; 3. Parallaxes for brown dwarfs in clusters C. G. Tinney; 4. Very low mass stars and brown dwarfs in the Belt of Orion S. J. Wolk and F. M. Walter; 5. Photometric surveys in open clusters M. R. Zapatero Osorio; 6. The mass function of the Pleiades R. F. Jameson et al.; 7. Brown dwarfs and the low-mass initial mass function in young clusters K. L. Luhman; 8. Very low mass stars in globular clusters I. R. King and G. Piotto; 9. The DENIS very low mass star and brown dwarf results X. Delfosse and T. Forveille; 10. Preliminary results from the 2MASS core project J. Liebert et al.; Part II. Spectroscopic Properties, Fundamental Parameters and Modelling: 11. Properties of M dwarfs in clusters and the field S. L. Hawley et al.; 12. Spectroscopy of very low mass stars and brown dwarfs in young clusters E. L. Martin; 13. High resolution spectra of L type stars and brown dwarfs G. Basri et al.; 14. Modelling very low mass stars and brown dwarf atmospheres F. Allard; 15. Dust in very cool dwarfs T. Tsuji; 16. On the interpretation of the optical spectra of very cool dwarfs Ya. V. Pavlenko; 17. Absolute dimensions for M type dwarfs A. Gimenez; 18. Theory of very low mass stars and brown dwarfs I. Baraffe; Part III. Convection, Rotation and Acitivity: 19. Convection in low mass stars F. D'Antona; 20. Rotation law and magnetic field in M dwarf models G. Rudiger and M. Kuker; 21. Doppler imaging of cool dwarf stars K. G. Strassmeier; 22. X-ray Emission from cool dwarfs in clusters S. Randich; 23. X-ray variability for dM stars G. Micela and A. Marino; 24. The coronae of AD Leo and EV Lac S. Sciortino et al.; 25. Prospects of vuture X-ray missions for low mass stars and cluster stars R. Pallavicini.

Rebolo, Rafael; Rosa Zapatero-Osorio, Maria

2001-02-01

12

Low Mass Star Formation in the Norma Cloud  

Microsoft Academic Search

A small filamentary cloud in Norma hosts a number of young low-mass stars in various stages of evolution, from visible Halpha emission stars to embedded sources detected only in the sub-millimeter regime. The best known source is V346 Nor, an FU Orionis star that brightened in the early 1980s. The morphology of the cloud complex and an apparent age gradient

B. Reipurth; M. Nielbock

2008-01-01

13

Magnetic fields of low-mass stars & protostars. Observations & results  

NASA Astrophysics Data System (ADS)

Magnetic field are ubiquitous to young and mature low-mass stars, and can potentially impact their formation, their evolution and their internal structure; yet the physical processes that succeed at amplifying and sustaining these fields (called dynamo processes), like those capable of changing the fate of the host stars (and in particular their rotation rates), are still somewhat enigmatic. Although theoretical modelling and numerical simulations (e.g., of stellar dynamo action and magnetospheric accretion processes) showed breathtaking progress in the last decade, they are not yet in the state of accurately predicting the various magnetic topologies that different low-mass stars can generate nor the impact such fields can have on stellar formation. Thanks to the advent of new-generation instruments, spectropolarimetric observations coupled to tomographic techniques can now reveal the large-scale magnetic topologies of both young and mature low-mass stars, and in particular their poloidal and toroidal components. More specifically, one can now investigate magnetic topologies of cool dwarfs, all the way from the brown dwarf threshold (spectral type M8) where stars are fully convective up to the limit beyond which outer convective zones get vanishingly small (spectral type F5); one can also explore the magnetic topologies of young low-mass stars that are still accreting mass from their circumstellar disc (i.e., the classical T Tauri stars) and study how such fields can impact mass accretion processes from the surrounding discs. We review herein the latest observational advances in this field, showing in particular that large-scale magnetic topologies of low-mass stars and protostars can drastically vary with mass and rotation rate, and discuss their implications for our understanding of dynamo processes, stellar formation and stellar evolution.

Donati, J.-F.

2013-09-01

14

Young stars of low mass in the Gum nebula  

SciTech Connect

Observations are presented for four recently formed stars in the vicinity of the Gum nebula which are heavily obscured by surrounding dust and are associated with small reflection nebulae. HH46 is the only currently active star of the sample, and it is found to have a spectral type in the range of late G-early K, with superimposed emission lines of H-alpha, Ca II, Fe I, Fe II, and weak He I at near zero velocities. It is suggested that the observed scenario of low-mass stars in an older massive star environment may be analogous to the circumstances surrounding the birth of the sun. 53 refs.

Graham, J.A.; Heyer, M.H. (Carnegie Institution of Washington, Washington, DC (USA))

1989-06-01

15

Old star clusters: Bench tests of low mass stellar models  

NASA Astrophysics Data System (ADS)

Old star clusters in the Milky Way and external galaxies have been (and still are) traditionally used to constrain the age of the universe and the timescales of galaxy formation. A parallel avenue of old star cluster research considers these objects as bench tests of low-mass stellar models. This short review will highlight some recent tests of stellar evolution models that make use of photometric and spectroscopic observations of resolved old star clusters. In some cases these tests have pointed to additional physical processes efficient in low-mass stars, that are not routinely included in model computations. Moreover, recent results from the Kepler mission about the old open cluster NGC6791 are adding new tight constraints to the models.

Salaris, M.

2013-03-01

16

Evolution, nucleosynthesis and yields of low mass AGB stars  

Microsoft Academic Search

The envelope of thermally pulsing AGB stars undergoing periodic third\\u000adredge-up episodes is enriched in both light and heavy elements, the ashes of a\\u000acomplex internal nucleosynthesis involving p, alpha and n captures over\\u000ahundreds of stable and unstable isotopes. In this paper, new models of low-mass\\u000aAGB stars (2 Msun), with metallicity ranging between Z=0.0138 (the solar one)\\u000aand

S. Cristallo; O. Straniero; R. Gallino; L. Piersanti; I. Dominguez; M. T. Lederer

2009-01-01

17

The Evolution of Low Mass Stars in Close Binary Systems  

Microsoft Academic Search

We report on our extensive investigation of the evolution of low mass stars in close binary systems with white dwarfs. Cataclysmic variables (CVs), which are the most numerous UV and X-ray sources in the Galaxy, and Type Ia supernovae, which are standard candles for cosmology, are believed to be the end products of these close binary systems, but little is

N. M. Silvestri; S. L. Hawley; P. Szkody; J. J. Bochanski; A. A. West; O. J. Fraser; K. R. Covey; M. A. Wolfe; K. M. Vanlandingham; L. C. Dang

2004-01-01

18

The ejection of low mass clumps during star formation  

NASA Astrophysics Data System (ADS)

Modeling of the self-consistent formation and evolution of disks as a result of prestellar core collapse reveals an intense early phase of recurrent gravitational instability and clump formation. These clumps generally migrate inward due to gravitational interaction with trailing spiral arms, and can be absorbed into the central object. However, in situations of multiple clump formation, gravitational scattering of clumps can result in the ejection of a low mass clump. These clumps can then give rise to free-floating low mass stars, brown dwarfs, or even giant planets. Detailed modeling of this process in the context of present-day star formation reveals that these clumps start out essentially as Larson first cores and grow subsequently by accretion. In the context of Pop III star formation, preliminary indications are that the disk clumps may also be of low mass. This mechanism of clump formation and possible ejection provides a channel for the formation of low mass objects in the first generation of stars.

Basu, Shantanu; Vorobyov, Eduard I.; DeSouza, Alexander L.

2012-09-01

19

Why Do Low-Mass Stars Become Red Giants?  

NASA Astrophysics Data System (ADS)

We revisit the problem of why stars become red giants. We modify the physics of a standard stellar evolution code in order to determine what does and what does not contribute to a star becoming a red giant. In particular, we have run tests to try to separate the effects of changes in the mean molecular weight and in the energy generation. The implications for why stars become red giants are discussed. We find that while a change in the mean molecular weight is necessary (but not sufficient) for a 1-Msolar star to become a red giant, this is not the case in a star of 5 Msolar. It therefore seems that there may be more than one way to make a giant.

Stancliffe, Richard J.; Chieffi, Alessandro; Lattanzio, John C.; Church, Ross P.

2009-09-01

20

High-resolution Spectra of Very Low-Mass Stars  

Microsoft Academic Search

We present the results of high-resolution (1-0.4A) optical spectroscopy of a\\u000asample of very low-mass stars. These data are used to examine the kinematics of\\u000athe stars at the bottom of the hydrogen-burning main sequence. No evidence is\\u000afound for a significant difference between the kinematics of the stars in our\\u000asample with I-K > 3.5 (MBol > 12.8) and

C. G. Tinney; I. N. Reid

1998-01-01

21

COUNTING LOW-MASS STARS IN INTEGRATED LIGHT  

SciTech Connect

Low-mass stars (M {approx}< 0.4 M{sub Sun }) are thought to comprise the bulk of the stellar mass of galaxies but they constitute only of order 1 percent of the bolometric luminosity of an old stellar population. Directly estimating the number of low-mass stars from integrated flux measurements of old stellar systems is therefore possible but very challenging, given the numerous variables that can affect the light at the percent level. Here we present a new population synthesis model created specifically for the purpose of measuring the low-mass initial mass function (IMF) down to {approx}0.1 M{sub Sun} for metal-rich stellar populations with ages in the range 3-13.5 Gyr. Our fiducial model is based on the synthesis of three separate isochrones, and a combination of optical and near-IR empirical stellar libraries in order to produce integrated light spectra over the wavelength interval 0.35 {mu}m < {lambda} < 2.4 {mu}m at a resolving power of R Almost-Equal-To 2000. New synthetic stellar atmospheres and spectra have been computed in order to model the spectral variations due to changes in individual elemental abundances including C, N, Na, Mg, Si, Ca, Ti, Fe, and generic {alpha} elements. We demonstrate the power of combining blue spectral features with surface gravity-sensitive near-IR features in order to simultaneously constrain the low-mass IMF, stellar population age, metallicity, and abundance pattern from integrated light measurements. Finally, we show that the shape of the low-mass IMF can also be directly constrained by employing a suite of surface gravity-sensitive spectral features, each of which is most sensitive to a particular mass interval.

Conroy, Charlie [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States); Van Dokkum, Pieter [Department of Astrophysical Sciences, Yale University, New Haven, CT (United States)

2012-03-01

22

Kepler observations of very low-mass stars  

NASA Astrophysics Data System (ADS)

Observations of very low-mass stars with Kepler represent an excellent opportunity to search for planetary transits and to characterize optical photometric variability at the cool end of the stellar mass distribution. In this paper, we present low-resolution red optical spectra that allow us to identify 18 very low-mass stars that have Kepler light curves available in the public archive. Spectral types of these targets are found to lie in the range dM4.5-dM8.5, implying spectrophotometric distances from 17 pc to 80 pc. Limits to the presence of transiting planets are set by modeling of the Kepler light curves. We find that the size of the planets detectable by Kepler around these small stars typically lies in the range 1 to 5 Earth radii within the habitable regions (P ? 10 days). We identify one candidate transit with a period of 1.26 days whose light curve resembles a planet slightly smaller than the Moon. However, our pixel by pixel analysis of the Kepler data shows that the signal most likely arises from a background contaminating eclipsing binary. For 11 of these objects reliable photometric periods shorter than 7 days are derived, and are interpreted as rotational modulation of magnetic cool spots. For 3 objects we find possible photometric periods longer than 50 days that require confirmation. The H? emission measurements and flare rates are used as proxies for chromospheric activity, and transversal velocities are used as an indicator of dynamical ages. These data allow us to discuss the relationship between magnetic activity and detectability of planetary transits around very low-mass stars. We show that super-Earth planets with sizes around 2 Earth radii are detectable with Kepler around about two thirds of the stars in our sample, independently of their level of chromospheric activity.

Martín, E. L.; Cabrera, J.; Martioli, E.; Solano, E.; Tata, R.

2013-07-01

23

High-resolution spectra of very low-mass stars  

NASA Astrophysics Data System (ADS)

We present the results of high-resolution (1-0.4Angstroms) optical spectroscopy of a sample of very low-mass stars. These data are used to examine the kinematics of the stars at the bottom of the hydrogen-burning main sequence. No evidence is found for a significant difference between the kinematics of the stars in our sample with I-K>3.5 (M_bol>~12.8) and those of more massive M dwarfs (M_bol~7-10). A spectral atlas at high (0.4-Angstroms) resolution for M8-M9+ stars is provided, and the equivalent widths of CsI, RbI and H? lines present in our spectra are examined. We analyse our data to search for the presence of rapid rotation, and find that the brown dwarf LP944-20 is a member of the class of `inactive, rapid rotators'. Such objects seem to be common at and below the hydrogen-burning main sequence. It seems that in low-mass/low-temperature dwarf objects either the mechanism that heats the chromosphere, or the mechanism that generates magnetic fields, is greatly suppressed.

Tinney, C. G.; Reid, I. N.

1998-12-01

24

Formation of Low-Mass Stars and Brown Dwarfs  

NASA Astrophysics Data System (ADS)

These lectures attempt to expose the most important ideas, which have been proposed to explain the formation of stars with particular emphasis on the formation of brown dwarfs and low-mass stars. We first describe the important physical processes which trigger the collapse of a self-gravitating piece of fluid and regulate the star formation rate in molecular clouds. Then we review the various theories which have been proposed along the years to explain the origin of the stellar initial mass function paying particular attention to four models, namely the competitive accretion and the theories based respectively on stopped accretion, MHD shocks and turbulent dispersion. As it is yet unsettled whether the brown dwarfs form as low-mass stars, we present the theory of brown dwarfs based on disk fragmentation stressing all the uncertainties due to the radiative feedback and magnetic field. Finally, we describe the results of large scale simulations performed to explain the collapse and fragmentation of molecular clouds.

Hennebelle, P.

2012-11-01

25

Efficiencies of Low-Mass Star and Star Cluster Formation  

Microsoft Academic Search

Using a quantitative model for bipolar outflows driven by hydromagnetic\\u000aprotostellar winds, we calculate the efficiency of star formation assuming that\\u000aavailable gas is either converted into stars or ejected in outflows. We\\u000aestimate the efficiency of a single star formation event in a protostellar\\u000acore, finding 25%-70% for cores with various possible degrees of flattening.\\u000aThe core mass function

Christopher D. Matzner; Christopher F. McKee

2000-01-01

26

Feedback Effects on Low-mass Star Formation  

NASA Astrophysics Data System (ADS)

Protostellar feedback, both radiation and bipolar outflows, dramatically affects the fragmentation and mass accretion from star-forming cores. We use ORION, an adaptive mesh refinement gravito-radiation-hydrodynamics code, to simulate low-mass star formation in a turbulent molecular cloud in the presence of protostellar feedback. We present results of the first simulations of a star-forming cluster that include both radiative transfer and protostellar outflows. We run four simulations to isolate the individual effects of radiation feedback and outflow feedback as well as the combination of the two. We find that outflows reduce protostellar masses and accretion rates each by a factor of three and therefore reduce protostellar luminosities by an order of magnitude. This means that, while radiation feedback suppresses fragmentation, outflows render protostellar radiation largely irrelevant for low-mass star formation above a mass scale of 0.05 M ?. We find initial fragmentation of our cloud at half the global Jeans length, around 0.1 pc. With insufficient protostellar radiation to stop it, these 0.1 pc cores fragment repeatedly, forming typically 10 stars each. The accretion rate in these stars scales with mass as predicted from core accretion models that include both thermal and turbulent motions; the accretion rate does not appear to be consistent with either competitive accretion or accretion from an isothermal sphere. We find that protostellar outflows do not significantly affect the overall cloud dynamics, in the absence of magnetic fields, due to their small opening angles and poor coupling to the dense gas. The outflows reduce the mass from the cores by 2/3, giving a core to star efficiency, epsiloncore ~= 1/3. The simulations are also able to reproduce many observation of local star-forming regions. Our simulation with radiation and outflows reproduces the observed protostellar luminosity function. All of the simulations can reproduce observed core mass functions, though we find they are sensitive to telescope resolution. We also reproduce the two-point correlation function of these observed cores. Lastly, we reproduce the initial mass function itself, including the low-mass end, when outflows are included.

Hansen, Charles E.; Klein, Richard I.; McKee, Christopher F.; Fisher, Robert T.

2012-03-01

27

Thermohaline mixing in evolved low-mass stars  

NASA Astrophysics Data System (ADS)

Context. Thermohaline mixing has recently been proposed to occur in low-mass red giants, with large consequence for the chemical yields of low-mass stars. Aims: We investigate the role of thermohaline mixing during the evolution of stars between 1 M_? and 3 M_?, in comparison with other mixing processes acting in these stars. Methods: We use a stellar evolution code which includes rotational mixing, internal magnetic fields and thermohaline mixing. Results: We confirm that during the red giant stage, thermohaline mixing has the potential to decrease the abundance of 3He, which is produced earlier on the main sequence. In our models we find that this process is working on the RGB only in stars with initial mass M ? 1.5 M_?. Moreover we report that thermohaline mixing is also present during core He-burning and beyond, and has the potential to change the surface abundances of AGB stars. While we find rotational and magnetic mixing to be negligible compared to the thermohaline mixing in the relevant layers, the interaction of thermohaline motions with the differential rotation may be essential to establish the timescale of thermohaline mixing in red giants. Conclusions: To explain the surface abundances observed at the bump in the luminosity function, the speed of the mixing process needs to be more than two orders of magnitude higher than in our models. However it is not clear if thermohaline mixing is the only physical process responsible for these surface-abundance anomalies. Therefore it is not possible at this stage to calibrate the efficiency of thermohaline mixing against the observations.

Cantiello, M.; Langer, N.

2010-10-01

28

Outer Atmospheres of Low Mass Stars — Flare Characteristics.  

NASA Astrophysics Data System (ADS)

We compare the coronal properties during flares on active low mass stars CN Leonis, AB Doradus A and Proxima Centauri observed with XMM-Newton. From the X-ray data we analyze the temporal evolution of temperature, emission measure and coronal abundance. The nature of these flares are with secondary events following the first flare peak in the light curve, raising the question regarding the involved magnetic structure. We infer from the plasma properties and the geometry of the flaring structure that the flare originates from a compact arcade rather than in a single loop.

Lalitha, S.; Schmitt, J. H. M. M.

2013-04-01

29

Surveying low mass stars with SALT: newborn and stillborn.  

NASA Astrophysics Data System (ADS)

The SALT/HET telescopes are unique for several reasons. One of them is the need for queue scheduling, given the visibility characteristics of targets. The author argues here that this can be viewed as a virtue, allowing exploration of the time domain in Astronomy. Traditional scheduling on very large telescopes has practically precluded such programs, giving SALT/HET a valuable niche to perform truly unique science. While there are many subjects which would greatly benefit from time coverage, the author concentrates here on the subject of low mass star formation. He shows that only through synoptic observations can one hope to gain an understanding of the crucial star-disk interface zone, where disk material is both loaded down onto the star and is flung out in bipolar outflows, solving and regulating the buildup of both mass and angular momentum in the new star. The author also discusses the use of SALT/HET in the new area of substellar objects, both brown dwarfs and extrasolar planets.

Basri, G.

30

Multiplicity among Young Brown Dwarfs and Very Low Mass Stars  

NASA Astrophysics Data System (ADS)

We report on a near-infrared adaptive optics imaging survey of 31 young brown dwarfs and very low mass (VLM) stars, 28 of which are in the Chamaeleon I star-forming region, using the ESO Very Large Telescope. We resolve the suspected 0.16'' (~26 AU) binary Cha H? 2 and present two new binaries, Hn 13 and CHXR 15, with separations of 0.13'' (~20 AU) and 0.30'' (~50 AU), respectively; the latter is one of the widest VLM systems known. We find a binary frequency of 11+9-6%, thus confirming the trend for a lower binary frequency with decreasing mass. By combining our work with previous surveys, we arrive at the largest sample of young VLM objects (72) with high angular resolution imaging to date. Its multiplicity fraction is in statistical agreement with that for VLM objects in the field. Furthermore, we note that many field stellar binaries with lower binding energies and/or wider cross sections have survived dynamical evolution and that statistical models suggest tidal disruption by passing stars is unlikely to affect the binary properties of our systems. Thus, we argue that there is no significant evolution of multiplicity with age among brown dwarfs and VLM stars in OB and T associations between a few megayears to several gigayears. Instead, the observations so far suggest that VLM objects are either less likely to be born in fragile multiple systems than solar-mass stars or such systems are disrupted very early. We dedicate this paper to the memory of our coauthor, Eduardo Delgado-Donate, who died in a hiking accident in Tenerife earlier this year.

Ahmic, Mirza; Jayawardhana, Ray; Brandeker, Alexis; Scholz, Alexander; van Kerkwijk, Marten H.; Delgado-Donate, Eduardo; Froebrich, Dirk

2007-12-01

31

Neutron star formation in theoretical supernovae. Low mass stars and white dwarfs  

SciTech Connect

The presupernova evolution of stars that form semi-degenerate or strongly degenerate O + Ne + Mg cores is discussed. For the 10 to 13 Msub solar stars, behavior of off-center neon flashes is crucial. The 8 to 10 m/sub solar stars do not ignite neon and eventually collapse due to electron captures. Properties of supernova explosions and neutron stars expected from these low mass progenitors are compared with the Crab nebula. The conditions for which neutron stars form from accretion-induced collapse of white dwarfs in clsoe binary systems is also examined.

Nomoto, K.

1986-01-01

32

Globular Clusters: Low Mass Stars, Still No Brown Dwarfs!  

NASA Astrophysics Data System (ADS)

In spite of all the attempts to find them, no one has yet detected any brown dwarf in a globular cluster. Although powerful instruments such as the VLT and Advanced Camera could further push the frontiers of this search, globular clusters will probably hold tight to their secrets for a while longer. Nonetheless, the search for very low mass stars in globular clusters has taught us a lot about their original mass distribution (IMF) and its evolution in time. I shall review the results of an investigation carried out over what is presently the largest, most homogeneous sample, and discuss the reasons suggesting that: 1. dynamical evolution (internal and external) has reshaped the cluster mass function over time, but the imprint of the IMF is still visible; 2. the IMF appears to vary very little from cluster to cluster; 3. the most likely functional form of the IMF is that of a power law that rises to a peak at ˜0.3 M? and tapers off at smaller masses.

de Marchi, Guido

2003-06-01

33

New Evolutionary Tracks for Very Low Mass Stars  

Microsoft Academic Search

We present new evolutionary calculations for low-mass and very low mass M dwarfs, for a metallicity range -2 <= [M\\/H] <= 0, down to the hydrogen-burning minimum mass (0.07 < M\\/Msun < 0.6). We use the most recent atmosphere models calculated by Allard & Hauschildt (1995), based on synthetic spectra at finite metallicity, and gray atmosphere models based on Alexander

I. Baraffe; G. Chabrier; F. Allard; P. H. Hauschildt

1995-01-01

34

Low-mass stars with mass loss and low-luminosity carbon star formation  

SciTech Connect

The effects of large carbon enrichments in static stellar envelopes were investigated, using new Los Alamos opacities (including low-temperature carbon and molecular opacities) and including carbon ionizations. To search for the production of low-mass,low-luminosity carbon stars, detailed stellar evolutionary computations were carried out for a grid of low-mass stars of two different metallicities. The stars were evolved from the main sequence through all intermediate stages and through helium-shell flashes on the asymptotic giant branch. The effects of the latest nuclear reaction rates, the new Los Alamos opacities, Reimers-type wind mass loss, and detailed treatment of convection and semi-convection were investigated. Two low-luminosity carbon stars were achieved, in excellent agreement with observations. Conditions favoring dredge-up (and thus carbon-star production) include a reasonably large convective mixing length, low metallicity, relatively large envelope mass, and high flash strength. Mass loss was of major importance, tending to oppose dredge-up; the total mass-loss amounts inferred from observations suffice to prevent formation of high-mass, high-luminosity carbon stars.

Boothroyd, A.I.

1987-01-01

35

Global Star Formation Revisited  

NASA Astrophysics Data System (ADS)

A general treatment of disk star formation is developed from a dissipative multiphase model, with the dominant dissipation due to cloud collisions. The Schmidt-Kennicutt (SK) law emerges naturally for star-forming disks and starbursts. We predict that there should be an inverse correlation between Tully-Fisher law and SK law residuals. The model is extended to include a multiphase treatment of supernova feedback that leads to a turbulent pressure-regulated generalization of the star formation law and is applicable to gas-rich starbursts. Enhanced pressure, as expected in merger-induced star formation, enhances star formation efficiency. An upper limit is derived for the disk star formation rate in starbursts that depends on the ratio of global ISM to cloud pressures. We extend these considerations to the case where the interstellar gas pressure in the inner galaxy is dominated by outflows from a central active galactic nucleus (AGN). During massive spheroid formation, AGN-driven winds trigger star formation, resulting in enhanced supernova feedback and outflows. The outflows are comparable to the AGN-boosted star formation rate and saturate in the super-Eddington limit. Downsizing of both SMBH and spheroids is a consequence of AGN-driven positive feedback. Bondi accretion feeds the central black hole with a specific accretion rate that is proportional to the black hole mass. AGN-enhanced star formation is mediated by turbulent pressure and relates spheroid star formation rate to black hole accretion rate. The relation between black hole mass and spheroid velocity dispersion has a coefficient (Salpeter time to gas consumption time ratio) that provides an arrow of time. Highly efficient, AGN-boosted star formation can occur at high redshift.

Silk, Joseph; Norman, Colin

2009-07-01

36

Lick adaptive optics survey searching for low-mass companions to young, nearby stars  

Microsoft Academic Search

Using the Shane 3 meter telescope at Lick Observatory, we surveyed 102 nearby young stars with the near-infrared adaptive optics system. Young stars were targetted in order to increase the sensitivity to low-mass companions. Of these 102 stars, 44 had at least one other source in the field of view with separations ranging from 0.4\\

Q. M. Konopacky; B. A. Macintosh; A. M. Ghez; B. Zuckerman; D. Kaisler; I. Song

2002-01-01

37

A Vanishing Star Revisited  

NASA Astrophysics Data System (ADS)

VLT Observations of an Unusual Stellar System Reinhold Häfner of the Munich University Observatory (Germany) is a happy astronomer. In 1988, when he was working at a telescope at the ESO La Silla observatory, he came across a strange star that suddenly vanished off the computer screen. He had to wait for more than a decade to get the full explanation of this unusual event. On June 10-11, 1999, he observed the same star with the first VLT 8.2-m Unit Telescope (ANTU) and the FORS1 astronomical instrument at Paranal [1]. With the vast power of this new research facility, he was now able to determine the physical properties of a very strange stellar system in which two planet-size stars orbit each other. One is an exceedingly hot white dwarf star , weighing half as much as the Sun, but only twice as big as the Earth. The other is a much cooler and less massive red dwarf star , one-and-a-half times the size of planet Jupiter. Once every three hours, the hot star disappears behind the other, as seen from the Earth. For a few minutes, the brightness of the system drops by a factor of more than 250 and it "vanishes" from view in telescopes smaller than the VLT. A variable star named NN Serpentis ESO PR Photo 30a/99 ESO PR Photo 30a/99 [Preview - JPEG: 400 x 468 pix - 152k] [Normal - JPEG: 800 x 936 pix - 576k] [High-Res - JPEG: 2304 x 2695 pix - 4.4M] Caption to ESO PR Photo 30a/99 : The sky field around the 17-mag variable stellar system NN Serpentis , as seen in a 5 sec exposure through a V(isual) filter with VLT ANTU and FORS1. It was obtained just before the observation of an eclipse of this unsual object and served to centre the telescope on the corresponding sky position. The field shown here measures 4.5 x 4.5 armin 2 (1365 x 1365 pix 2 ; 0.20 arcsec/pix). The field is somewhat larger than that shown in Photo 30b/99 and has the same orientation to allow comparison: North is about 20° anticlockwise from the top and East is 90° clockwise from that direction. The unsual star in question is designated NN Serpentis , or just NN Ser . As the name indicates, it is located in the constellation of Serpens (The Serpent), about 12° north of the celestial equator. A double letter, here "NN", is used to denote variable stars [2]. It is a rather faint object of magnitude 17, about 25,000 times fainter than what can be perceived with the unaided eye. The distance is about 600 light-years (180 pc). In July 1988, Reinhold Häfner performed observations of NN Ser (at that time still known by its earlier name PG 1550+131 ) with the Danish 1.54-m telescope at La Silla. He was surprised, but also very pleased to discover that it underwent a very deep eclipse every 187 minutes. Within less than 2 minutes, the brightness dropped by a factor of more than 100 (5 magnitudes). During the next 9 minutes, the star completely disappeared from view - it was too faint to be observed with this telescope. It then again reappeared and the entire event was over after just 11 minutes. Why eclipses are so important for stellar studies An eclipse occurs when one of the stars in a binary stellar system moves in front of the other, as seen by the observer. The effect is similar to what happens during a solar eclipse when the Moon moves in front of the Sun. In both cases, the eclipse may be partial or total , depending on whether or not the eclipsed star (or the Sun) is completely hidden from view. The occurence of eclipses in stellar systems, as seen from the Earth, depends on the spatial orientation of the orbital plane and the sizes of the two stars. Two eclipses take place during one orbital revolution, but they may not both be observable. The physical properties of the two stars in a binary system (e.g., the sizes of the stars, the size and shape of the orbit, the distribution of the light on the surfaces of the stars, their temperatures etc.) can be determined from the measured "light-curve" of the system (a plot of brightness vrs. time). The stars are always too close to each other to be seen as anything but a point of lig

1999-07-01

38

Quantitative Spectral Analysis of Evolved Low-Mass Stars  

NASA Astrophysics Data System (ADS)

The hydrogen-deficiency in extremely hot post-AGB stars of spectral class PG1159 is probably caused by a (very) late helium-shell flash or a AGB final thermal pulse that consumes the hydrogen envelope, exposing the usually-hidden intershell region. Thus, the photospheric element abundances of these stars allow us to draw conclusions about details of nuclear burning and mixing processes in the precursor AGB stars. We compare predicted element abundances to those determined by quantitative spectral analyses performed with advanced non-LTE model atmospheres. A good qualitative and quantitative agreement is found for many species (He, C, N, O, Ne, F, Si, Ar) but discrepancies for others (P, S, Fe) point at shortcomings in stellar evolution models for AGB stars. Almost all of the chemical trace elements in these hot stars can only be identified in the UV spectral range. The Far Ultraviolet Spectroscopic Explorer and the Hubble Space Telescope played a crucial role for this research.

Werner, Klaus; Rauch, Thomas; Kruk, Jeffrey W.

2009-09-01

39

Photometry of low-mass stars in Praesepe  

NASA Astrophysics Data System (ADS)

The results of a program of BVRI photometry of a set of relatively faint stars in the Praesepe cluster are reported. The program stars were selected to be high-probability members of the cluster based on a new proper-motion study by Jones and Cudworth (1982). Those membership identifications appear to have been quite accurate, since all but two of the stars observed have colors and magnitudes consistent with cluster membership. The new photometry, combined with previous data from Upgren, Weis, and DeLuca (1979) and Weis (1981) are used to show that the intrinsic width of the Praesepe main sequence remains quite narrow within 0.15 magnitude up to at least magnitude 10.5.

Stauffer, J.

1982-08-01

40

Completing A Near-Infrared Search for Very Low Mass Companions to Stars within 10 pc  

Microsoft Academic Search

We continue our survey of stars within 10 parsecs for brown dwarf and very low mass stellar {VLM} companions. The nearby star population is dominated by the red dwarfs {75%}, which contribute 40% of the stellar mass to the disk and cause the luminosity function to climb all the way to the terminus of the stellar main sequence {Henry and

Todd Henry

1997-01-01

41

The Nitrogen Constraint on Habitability of Planets around Low Mass M-stars  

NASA Astrophysics Data System (ADS)

The traditional habitable zones around stars are defined based on the stability of liquid water over geological timescales. Being too far away from the stars, the planet would be incapable of maintaining a warm surface and thus no liquid water. Being too close to the star, the planet would experience a 'runaway' greenhouse phase, during which its oceans could be lost quickly, and end up similar to our sister planet, Venus. The definition of tranditional habitable zones does not consider the availability of other elements important for life. All life as we know it needs nitrogen. Our calculations of upper planetary atmospheres show that nitrogen could be lost rapidly from planetary atmospheres with CO2 concentrations lower than certain threshold. This suggests that life on planets around low mass M-stars may be selflimiting, and planets of low mass M-stars are less favorable places to search for life than G- or K-type stars.

Tian, F.

2011-10-01

42

The Nitrogen Constraint on Habitability of Planets of Low Mass M-stars  

NASA Astrophysics Data System (ADS)

The traditional habitable zones around stars are defined based on the stability of liquid water over geological timescales. Being too far away from the stars, the planet would be incapable of maintaining a warm surface and thus no liquid water. Being too close to the star, the planet would experience a 'runaway' greenhouse phase, during which its oceans could be lost quickly, and end up similar to our sister planet, Venus. The definition of tranditional habitable zones does not consider the availability of other elements important for life. All life as we know it needs nitrogen. Our calculations of upper planetary atmospheres show that nitrogen could be lost rapidly from planetary atmospheres with CO2 concentrations lower than certain threshold. This suggests that life on planets around low mass M-stars may be selflimiting, and planets of low mass M-stars are less favorable places to search for life than G- or K-type stars.

Tian, F.

2011-12-01

43

X-ray and Optical Studies of Low--Mass Star Formation  

Microsoft Academic Search

Weak--line T Tauri stars (WTTS) are low--mass pre--main sequence (PMS) stars which lack both the strong emission lines and the infra--red (IR) excesses typical of classical T Tauri stars (CTTS). Most of them have been discovered on the basis of their solar--like X--ray emission. In this work, X--ray data from the ROSAT all-sky survey in the Chamaeleon (Cha) and the

J. M. Alcalá

1994-01-01

44

Chemical Enrichment of the Early IGM by Low-Mass Primordial Stars  

NASA Astrophysics Data System (ADS)

For now, primordial stars lie beyond the realm of direct observation, but indirect measures of their masses may be possible by analyzing their nucleosynthetic imprint on subsequent generations of low-mass long-lived stars, some of which may persist as extremely metal-poor (EMP) and hyper metal-poor (HMP) stars in the Galactic halo today. The absence of the "odd-even" abundance pattern of pair-instability SNe in metal-poor halo stars surveyed to date suggests that the early IGM was primarily enriched by low-mass stars. We present numerical simulations of spherically-symmetric core collapse SNe of 15 - 40 solar mass stars, surveying two progenitor rotation rates, three masses, two metallicities and three explosion energies, for a total of 36 models. We compare our nucleosynthetic yields to the chemical abundances of the three most iron-poor stars and match the abundance pattern of one, HE 0557-4840, with a zero-metallicity 15 solar mass, 2.4 Bethe explosion. A Salpeter IMF average of our yields for Z = 0 models with explosion energies of 2.4 Bethe or less is a good match to the abundances in the much larger sample of EMP stars. Since EMP stars likely carry the cumulative nucleosynthetic imprint of a few well-established populations of SNe progenitors, our findings suggest that low-mass SNe contributed the bulk of the metals to the early universe.

Whalen, Daniel J.; Joggerst, C.

2010-01-01

45

Connecting the Dots: Low-Mass Stars, Brown Dwarfs, and Planets  

NASA Astrophysics Data System (ADS)

The lowest mass object that Mother Nature makes through the process of ``star formation'' is currently unknown. While numerous very low-mass stars, brown dwarfs, and planets have been found, their relation to each other remains unclear. Here I describe how the study of brown dwarfs has the potential to help us understand both star and planet formation mechanisms. I describe the physical traits attributed to stars, brown dwarfs, and planets; compare the mass functions of brown dwarfs and planets; and discuss how studies of brown dwarfs in both young clusters and in the field can be used to challenge and constrain star and planet formation theories.

Cruz, K.

2008-08-01

46

RADIUS-DEPENDENT ANGULAR MOMENTUM EVOLUTION IN LOW-MASS STARS. I  

SciTech Connect

Angular momentum evolution in low-mass stars is determined by initial conditions during star formation, stellar structure evolution, and the behavior of stellar magnetic fields. Here we show that the empirical picture of angular momentum evolution arises naturally if rotation is related to magnetic field strength instead of to magnetic flux and formulate a corrected braking law based on this. Angular momentum evolution then becomes a strong function of stellar radius, explaining the main trends observed in open clusters and field stars at a few Gyr: the steep transition in rotation at the boundary to full convection arises primarily from the large change in radius across this boundary and does not require changes in dynamo mode or field topology. Additionally, the data suggest transient core-envelope decoupling among solar-type stars and field saturation at longer periods in very low mass stars. For solar-type stars, our model is also in good agreement with the empirical Skumanich law. Finally, in further support of the theory, we show that the predicted age at which low-mass stars spin down from the saturated to unsaturated field regimes in our model corresponds remarkably well to the observed lifetime of magnetic activity in these stars.

Reiners, Ansgar [Institut fuer Astrophysik, Georg-August-Universitaet, Friedrich-Hund-Platz 1, 37077 Goettingen (Germany); Mohanty, Subhanjoy, E-mail: Ansgar.Reiners@phys.uni-goettingen.de [Imperial College London, 1010 Blackett Laboratory, Prince Consort Road, London SW7 2AZ (United Kingdom)

2012-02-10

47

Revisiting XENON100's constraints (and signals?) for low-mass dark matter  

NASA Astrophysics Data System (ADS)

Although observations made with the CoGeNT and CDMS experiments have been interpreted as possible signals of low-mass ( ~ 7–10 GeV) dark matter particles, constraints from the XENON100 collaboration appear to be incompatible with this hypothesis, at least at face value. In this paper, we revisit XENON100's constraint on dark matter in this mass range, and consider how various uncertainties and assumptions made might alter this conclusion. We also note that while XENON100's two nuclear recoil candidates each exhibit very low ratios of ionization-to-scintillation signals, making them difficult to attribute to known electronic or neutron backgrounds, they are consistent with originating from dark matter particles in the mass range favored by CoGeNT and CDMS. We argue that with lower, but not implausible, values for the relative scintillation efficiency of liquid xenon (Leff), and the suppression of the scintillation signal in liquid xenon at XENON100's electric field (Snr), these two events could consistently arise from dark matter particles with a mass and cross section in the range favored by CoGeNT and CDMS. If this interpretation is correct, we predict that the LUX experiment, with a significantly higher light yield than XENON100, should observe dark matter induced events at an observable rate of ~ 3–24 per month.

Hooper, Dan

2013-09-01

48

Deep Imagery of NGC 3603: Low-Mass Star Formation in the Closest Starburst Region  

NASA Astrophysics Data System (ADS)

This proposal aims at studying the intermediate and low-mass stellar population in NGC 3603, the most luminous visible starburst region in the Galaxy, which more than rivals the dense core R136 of 30 Dor in the 7 times more distant LMC. Although the massive star content of this very dense cluster is now fairly well known, our knowledge of the medium- and low -mass part {1.5 - 10 M_odot} of the IMF in NGC 3603, not to mention more distant starbursts, is marginal at best. We therefore propose to obtain deep WFPC2 images of NGC 3603 that will allow us to probe its stellar content and IMF down to V=22.5 {M_v = +3.5; M 1.5 M_odot}. Questions such as a possible low-mass cutoff, variation of the IMF slope as a function of radius, and differential star formation will be addressed. In particular, we want to know if violent star formation of the most massive stars {and the subsequent strong ionization field and wind kinetic energy they generate} has prevented, or delayed, the formation of less massive stars in the very core of the cluster. Because of its proximity, NGC 3603 is the only truly dense starburst where we can directly observe whether or not violent, massive star formation efficiently quenches the formation of lower mass stars.

Drissen, Laurent

1996-07-01

49

The Sodium Doublets as Youth Indicators for Low-Mass Stars  

NASA Astrophysics Data System (ADS)

We investigate the use of the Na I doublets at 5890 and 5896 Å (the Fraunhofer D lines) and 8183 and 8195 Å as gravity indicators for stars of late K and M spectral type. As is well known, the equivalent widths (EWs) of these doublets increase with photospheric log(g). We show that the EWs of members of the ? Pictoris moving group (BPMG) (age 10-20 Myr) lie between the EWs of giants and main sequence stars based on the analysis of approx. 200 spectra collected with the MDM 1.3-meter McGraw-Hill telescope and the SMARTS 1.5-meter telescope. We find the Na D lines are useful age indicators for low mass BPMG candidates earlier than M2 and the 8200 Å doublet becomes useful for stars later than M4. The EWs of the Na doublets may therefore be used to establish low gravity, hence youth, among low mass stars in general.

Schlieder, J. E.; Fielding, D.; Lepine, S.; Rice, E.; Tomasino, R.; Simon, M.; Shara, M. M.

2011-12-01

50

Triple star evolution and the formation of short-period, low mass X-ray binaries  

NASA Astrophysics Data System (ADS)

To explain the presence of a relatively massive black hole in 2A0620-00 the authors propose a new evolutionary scenario for the formation of short-period, low-mass X-ray binaries. The progenitor in this scenario is a triple star in which a massive close binary is accompanied at large distance by a late dwarf. After the evolution of the close binary into an ordinary X-ray binary, the compact object is engulfed by its expanding massive companion, and spirals in to settle at its centre. The resulting Thorne-Zytkow supergiant gradually expands until it attains the size of the late-dwarf orbit. Then a second spiral-in phase ensues, leading to the formation of a low-mass close binary. Depending on the initial parameters of the massive binary, this close low-mass binary may contain either a black hole or a neutron star.

Eggleton, P. P.; Verbunt, F.

1986-05-01

51

Evolution, Nucleosynthesis, and Yields of Low-Mass Asymptotic Giant Branch Stars at Different Metallicities  

Microsoft Academic Search

The envelope of thermally pulsing asymptotic giant branch (TP-AGB) stars undergoing periodic third dredge-up (TDU) episodes is enriched in both light and heavy elements, the ashes of a complex internal nucleosynthesis involving p, alpha, and n captures over hundreds of stable and unstable isotopes. In this paper, new models of low-mass AGB stars (2 M sun), with metallicity ranging between

S. Cristallo; O. Straniero; R. Gallino; L. Piersanti; I. Domínguez; M. T. Lederer

2009-01-01

52

Planet formation around low mass stars: the moving snow line and super-Earths  

Microsoft Academic Search

We develop a semi-analytic model for planet formation during the pre-main\\u000asequence contraction phase of a low mass star. During this evolution, the\\u000astellar magnetosphere maintains a fixed ratio between the inner disk radius and\\u000athe stellar radius. As the star contracts at constant effective temperature,\\u000athe `snow line', which separates regions of rocky planet formation from regions\\u000aof icy

Grant M. Kennedy; Scott J. Kenyon; Benjamin C. Bromley

2006-01-01

53

On the Formation of Low-Mass Black Holes in Massive Binary Stars  

NASA Astrophysics Data System (ADS)

Recently, Brown & Bethe suggested that most stars with main-sequence mass in the range of ˜18-30 Msun explode, returning matter to the Galaxy, and then go into low-mass (? 1.5 Msun) black holes. Even more massive main-sequence stars would chiefly go into high-mass (˜10 Msun) black holes. The Brown-Bethe estimates gave ˜15 x 108 low-mass black holes in the Galaxy. We here address why none of these have been seen, with the possible exception of the compact objects in SN 1987A and 4U 1700-37. Our main point is that the primary star in a binary loses its hydrogen envelope by transfer of matter to the secondary and loss into space, and the resulting "naked" helium star evolves differently than a helium core, which is at least initially covered by the hydrogen envelope in a massive main-sequence star. We show that primary stars in binaries can end up as neutron stars even if their initial mass substantially exceeds the mass limit for neutron star formation from single stars (˜118 Msun). An example is 4U 1223-62, in which we suggest that the initial primary mass exceeded 35 Msun, yet X-ray pulsations show a neutron star to be present. We also discuss some individual systems and argue that 4U 1700-37, the only example of a well-studied high-mass X-ray binary that does not pulse, could well contain a low-mass black hole. The statistical composition of the X-ray binary population is consistent with our scenario, but due to the paucity of systems it is consistent with more traditional models as well.

Brown, G. E.; Weingartner, J. C.; Wijers, Ralph A. M. J.

1996-05-01

54

The Massive Neutron Star or Low-Mass Black Hole in 2S 0921-630  

NASA Astrophysics Data System (ADS)

We report on the optical spectroscopy of the eclipsing halo low-mass X-ray binary 2S 0921-630, which reveals the absorption-line radial velocity curve of the K0 III secondary star with a semiamplitude K2=92.89+/-3.84 km s-1, a systemic velocity ?=34.9+/-3.3 km s-1, and an orbital period Porb of 9.0035+/-0.0029 days (1 ?). Given the quality of the data, we find no evidence for the effects of X-ray irradiation. Using the previously determined rotational broadening of the mass donor and applying conservative limits on the orbital inclination, we constrain the compact object mass to be 2.0-4.3 Msolar (1 ?), ruling out a canonical neutron star at the 99% level. Since the nature of the compact object is unclear, this mass range implies that the compact object is either a low-mass black hole with a mass slightly higher than the maximum possible neutron star mass (2.9 Msolar) or a massive neutron star. If the compact object is a black hole, it confirms the prediction of the existence of low-mass black holes, while if the object is a massive neutron star, its high mass severely constrains the equation of state of nuclear matter.

Shahbaz, T.; Casares, J.; Watson, C. A.; Charles, P. A.; Hynes, R. I.; Shih, S. C.; Steeghs, D.

2004-12-01

55

The Importance of Episodic Accretion for Low-mass Star Formation  

NASA Astrophysics Data System (ADS)

A star acquires much of its mass by accreting material from a disk. Accretion is probably not continuous but episodic. We have developed a method to include the effects of episodic accretion in simulations of star formation. Episodic accretion results in bursts of radiative feedback, during which a protostar is very luminous, and its surrounding disk is heated and stabilized. These bursts typically last only a few hundred years. In contrast, the lulls between bursts may last a few thousand years; during these lulls the luminosity of the protostar is very low, and its disk cools and fragments. Thus, episodic accretion enables the formation of low-mass stars, brown dwarfs, and planetary-mass objects by disk fragmentation. If episodic accretion is a common phenomenon among young protostars, then the frequency and duration of accretion bursts may be critical in determining the low-mass end of the stellar initial mass function.

Stamatellos, Dimitris; Whitworth, Anthony P.; Hubber, David A.

2011-03-01

56

S-process in extremely metal-poor, low-mass stars  

NASA Astrophysics Data System (ADS)

Context. Extremely metal-poor (EMP), low-mass stars experience an ingestion of protons into the helium-rich layer during the core He-flash, resulting in the production of neutrons through the reactions 12C(p,?)13N(?)13C(?,n)16O. This is a potential site for the production of s-process elements in EMP stars, which does not occur in more metal-rich counterparts. The signatures of s-process elements in the two most iron deficient stars observed to date, HE1327-2326 & HE0107-5240, still await for an explanation. Aims: We investigate the possibility that low-mass EMP stars could be the source of s-process elements observed in extremely iron deficient stars, either as a result of self-enrichment or in a binary scenario as the consequence of a mass transfer episode. Methods: We present evolutionary and post-processing s-process calculations of a 1 M? stellar model with metallicities of Z = 0, 10-8, and 10-7. We assess the sensitivity of nucleosynthesis results to uncertainties in the input physics of the stellar models with particular regard to the details of convective mixing during the core He-flash. Results: Our models provide the possibility of explaining the C, O, Sr, and Ba abundance for the star HE0107-5240 as the result of mass-transfer from a low-mass EMP star. The drawback of our model is that nitrogen would be overproduced and the 12C/^{13C} abundance ratio would be underproduced in comparison to the observed values if mass would be transferred before the primary star enters the asymptotic giant branch phase. Conclusions: Our results show that low-mass EMP stars cannot be ruled out as companion stars that might have polluted HE1327-2326 and HE0107-5240 and produced the observed s-process pattern. However, more detailed studies of the core He-flash and the proton ingestion episode are needed to determine the robustness of our predictions.

Cruz, M. A.; Serenelli, A.; Weiss, A.

2013-11-01

57

THE EFFECTS OF RADIATIVE TRANSFER ON LOW-MASS STAR FORMATION  

SciTech Connect

Forming stars emit a substantial amount of radiation into their natal environment. We use ORION, an adaptive mesh refinement (AMR) three-dimensional gravito-radiation-hydrodyanics code, to simulate low-mass star formation in a turbulent molecular cloud. We compare the distributions of stellar masses, accretion rates, and temperatures in the cases with and without radiative transfer, and we demonstrate that radiative feedback has a profound effect on accretion, multiplicity, and mass by reducing the number of stars formed and the total rate at which gas turns into stars. We also show that once the star formation reaches a steady state, protostellar radiation is by far the dominant source of energy in the simulation, exceeding viscous dissipation and compressional heating by at least an order of magnitude. Calculations that omit radiative feedback from protstars significantly underestimate the gas temperature and the strength of this effect. Although heating from protostars is mainly confined to the protostellar cores, we find that it is sufficient to suppress disk fragmentation that would otherwise result in very low-mass companions or brown dwarfs. We demonstrate that the mean protostellar accretion rate increases with the final stellar mass so that the star formation time is only a weak function of mass.

Offner, Stella S. R. [Department of Physics, University of California, Berkeley, CA 94720 (United States); Klein, Richard I. [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); McKee, Christopher F. [Departments of Physics and Astronomy, University of California, Berkeley, CA 94720 (United States); Krumholz, Mark R., E-mail: soffner@berkeley.ed [Department of Astronomy, University of California, Santa Cruz, CA 95064 (United States)

2009-09-20

58

Investigating the Properties of Low-Mass Stars Using Spectra of Wide Binaries  

NASA Astrophysics Data System (ADS)

We present results from a study designed to characterize wide, low-mass (< 0.5 M_Sun) binaries identified in the Sloan Digital Sky Survey (SDSS). We examine the SDSS database level completeness (for identifying visual binaries) and analyze the pairs that both have individual SDSS spectra. A comprehensive by-eye examination reveals that a significant fraction of the sources within 1" of the primary stellar source are misclassified as duplicate detections and, hence, are omitted from the photometric primary catalog in the SDSS database. This discrepancy has a noticeable effect on estimates of the binary fraction, mass function, luminosity function, and other studies that rely on large, photometric samples of low-mass stars. Due to their coeval nature, binaries with at least one low-mass component are important for calibrating the age-activity relation and the relative metallicity scales. Better defined stellar ages and metallicities allow for a proper analysis of stellar and Galactic evolution using ubiquitous low-mass stars. We constructed a spectroscopic sample of wide binaries, for which there is at least one low-mass component and an individual spectrum for each star. Each binary was verified using measurements of their common proper motions and a chance alignment probability calculated from a six-dimensional model of the Milky Way. The orbital separation of the binary components provides an extra age constraint due to mechanisms that destroy wide binaries during thin-disk dynamical heating. We evaluate the behavior of the magnetic activity in coeval systems, with a specific focus on the dependence of activity on orbital separation and location in the Galactic disk. The preliminary results of our analysis will help calibrate the age-activity relation in M dwarfs. In addition, we calibrate the relative metallicity scale for metal poor K and M dwarfs using a modified index based on TiO and CaH molecular band features.

Schluns, Kyle; West, A. A.; Dhital, S.; Massey, A. P.

2013-01-01

59

A Hybrid Scenario for the Formation of Brown Dwarfs and Very Low Mass Stars  

NASA Astrophysics Data System (ADS)

We present a calculation of protostellar disk formation and evolution in which gaseous clumps (essentially, the first Larson cores formed via disk fragmentation) are ejected from the disk during the early stage of evolution. This is a universal process related to the phenomenon of ejection in multiple systems of point masses. However, it occurs in our model entirely due to the interaction of compact, gravitationally bound gaseous clumps and is free from the smoothing-length uncertainty that is characteristic of models using sink particles. Clumps that survive ejection span a mass range of 0.08-0.35 M ?, and have ejection velocities 0.8 ± 0.35 km s-1, which are several times greater than the escape speed. We suggest that, upon contraction, these clumps can form substellar or low-mass stellar objects with notable disks, or even close-separation very low mass binaries. In this hybrid scenario, allowing for ejection of clumps rather than finished protostars/proto-brown-dwarfs, disk formation and the low velocity dispersion of low-mass objects are naturally explained, while it is also consistent with the observation of isolated low-mass clumps that are ejection products. We conclude that clump ejection and the formation of isolated low-mass stellar and substellar objects is a common occurrence, with important implications for understanding the initial mass function, the brown dwarf desert, and the formation of stars in all environments and epochs.

Basu, Shantanu; Vorobyov, Eduard I.

2012-05-01

60

Brown dwarfs and very low mass stars in the Hyades cluster: a dynamically evolved mass function  

Microsoft Academic Search

Aims: We conducted a search for brown dwarfs (BDs) and very low mass (VLM) stars in the 625 Myr-old Hyades cluster in order to derive the cluster's mass function across the stellar-substellar boundary. Methods: We performed a deep (I=23, z=22.5) photometric survey over 16 deg2 around the cluster center and followed up with K-band photometry to measure the proper motion

J. Bouvier; T. T. Kendall; G. Meeus; L. Testi; E. Moraux; J. R. Stauffer; D. James; J.-C. Cuillandre; J. Irwin; M. J. McCaughrean; I. Baraffe; E. Bertin

2008-01-01

61

Evolutionary Models for Very Low-Mass Stars and Brown Dwarfs with Dusty Atmospheres  

Microsoft Academic Search

We present evolutionary calculations for very low-mass stars and brown dwarfs based on synthetic spectra and nongray atmosphere models which include dust formation and opacity, i.e., objects with Teff<~2800 K. The interior of the most massive brown dwarfs is shown to develop a conductive core after ~2 Gyr which slows down their cooling. Comparison is made in optical and infrared

G. Chabrier; I. Baraffe; F. Allard; P. Hauschildt

2000-01-01

62

An Equation of State for Low-Mass Stars and Giant Planets  

Microsoft Academic Search

We present new equations of state (EOS) for hydrogen and helium, intended for applications to low-mass stars (M < 1 Msun), brown dwarfs, and giant planets. They cover the range 2.10

D. Saumon; G. Chabrier; H. M. van Horn

1995-01-01

63

X-ray Spectroscopy of Neutron Star Low-Mass X-ray Binaries  

Microsoft Academic Search

In this thesis, I present work spanning a variety of topics relating to neutron star low-mass X-ray binaries (LMXBs) and utilize spectral information from X-ray observations to further our understanding of these sources. First, I give an overview of important X-ray astrophysics relevant to the work I present in subsequent chapters, as well as information about the X-ray observatories from

M. I. Krauss

2007-01-01

64

First INTEGRAL observations of eight persistent neutron star low mass X-ray binaries  

Microsoft Academic Search

Early results from the INTEGRAL Core Program, for a sample of eight persistently bright neutron star low mass X-ray binaries in the energy range from 5 keV to 200 keV, are presented. It is shown that INTEGRAL efficiently detects sources and that spectra may be obtained up to several hundreds of keV by combining data from three of the four

A. Paizis; V. Beckmann; T. J.-L. Courvoisier; O. Vilhu; A. Lutovinov; K. Ebisawa; D. Hannikainen; M. Chernyakova; J. A. Zurita Heras; J. Rodriguez; A. A. Zdziarski; A. Bazzano; E. Kuulkers; T. Oosterbroek; F. Frontera; A. Gimenez; P. Goldoni; A. Santangelo; G. G. C. Palumbo

2003-01-01

65

The Radius Discrepancy in Low-mass Stars: Single versus Binaries  

NASA Astrophysics Data System (ADS)

A long-standing issue in the theory of low-mass stars is the discrepancy between predicted and observed radii and effective temperatures. In spite of the increasing availability of very precise radius determinations from eclipsing binaries and interferometric measurements of radii of single stars, there is no unanimous consensus on the extent (or even the existence) of the discrepancy and on its connection with other stellar properties (e.g., metallicity, magnetic activity). We investigate the radius discrepancy phenomenon using the best data currently available (accuracy <~ 5%). We have constructed a grid of stellar models covering the entire range of low-mass stars (0.1-1.25 M ?) and various choices of the metallicity and mixing length parameter, ?. We used an improved version of the Yale Rotational stellar Evolution Code, implementing surface boundary conditions based on the most up-to-date PHOENIX atmosphere models. Our models are in good agreement with others in the literature and improve and extend the low mass end of the Yale-Yonsei isochrones. Our calculations include rotation-related quantities, such as moments of inertia and convective turnover timescales, useful in studies of magnetic activity and rotational evolution of solar-like stars. Consistent with previous works, we find that both binaries and single stars have radii inflated by about 3% with respect to the theoretical models; among binaries, the components of short orbital period systems are found to be the most deviant. We conclude that both binaries and single stars are comparably affected by the radius discrepancy phenomenon.

Spada, F.; Demarque, P.; Kim, Y.-C.; Sills, A.

2013-10-01

66

Constraints on the low-mass IMF in young super-star clusters in starburst galaxies  

NASA Astrophysics Data System (ADS)

As evidence for variations in the initial mass function (IMF) in nearby star forming regions remains elusive we are forced to expand our search to more extreme regions of star formation. Starburst galaxies, which contain massive young clusters have in the past been reported to have IMFs different than that characterizing the field star IMF. In this thesis we use high signal-to-noise near-infrared spectra to place constraints on the shape of the IMF in extreme regions of extragalactic star formation and also try to understand the star formation history in these regions. Through high signal-to-noise near-infrared spectra it is possible to directly detect low-mass PMS stars in unresolved young super-star clusters, using absorption features that trace cool stars. Combining Starburst99 and available PMS tracks it is then possible to constrain the IMF in young super-star clusters using a combination of absorption lines each tracing different ranges of stellar masses and comparing observed spectra to models. Our technique can provide a direct test of the universality of the IMF compared to the Milky Way. We have obtained high signal-to-noise H- and K-band spectra of two young super-star clusters in the starburst galaxies NGC 4039/39 and NGC 253 in order to constrain the low-mass IMF and star formation history in the clusters. The cluster in NGC 4038/39 shows signs of youth such as thermal radio emission and strong hydrogen emission lines as well as late-type absorption lines indicative of cool stars. The strength and ratio of these absorption lines cannot be reproduced through either late-type pre-main sequence stars or red supergiants alone. We interpret the spectrum as a superposition of two star clusters of different ages over the physical region of 90 pc our spectrum represents. One cluster is young (? 3 Myr) and is responsible for part of the late-type absorption features, which are due to PMS stars in the cluster, and the hydrogen emission lines. The second cluster is older (6 Myr - 18 Myr) and is needed to reproduce the overall depth of the late-type absorption features in the spectrum. While the superposition of clusters does not allow us to place stringent constraints on the IMF there is no evidence of a low-mass cutoff in the cluster and the IMF is consistent with a Chabrier and Kroupa IMF typical of the field. The cluster in NGC 253 shows the same signs of youth as the cluster in NGC 4038/39 and sits in front of a background population of older stars. The background population has an age of ? 12 Myr and thus contains red supergiants. After carefully subtracting this background we model the spectrum of the young cluster. We find that its IMF is consistent with a Chabrier and Kroupa IMF with a best-fit power-law slope of 1.0 in linear units. Slopes of 0.0 - 1.5 are also formally consistent with the cluster spectrum. We conclude that there is no strong evidence for an unusual IMF or a lack of low-mass stars (? 1 M? ) in either of these galaxies.

Greissl, Julia Jennifer

2010-12-01

67

Accurate masses of very low mass stars. III. 16 new or improved masses  

NASA Astrophysics Data System (ADS)

We have obtained adaptive optics images and accurate radial velocities for 7 very low mass objects, In the course of a long term effort to determine accurate masses for very low mass stars (M<0.6 M_sun). We use the new data, together with measurements from the litterature for some stars, to determine new or improved orbits for these 7 systems. They provide masses for 16 very low mass stars with accuracies that range between 0.2% and 5%, and in some cases a very accurate distance as well. This information is used in a companion paper to discuss the Mass-Luminosity relation for the V, J, H and K photometric bands. Observations collected at the European Southern Observatory -- ESO, Chile, Laboratório Nacional de Astrofísica -- LNA, Brazil and Observatoire de Haute Provence -- OHP, France Table 7 is available only in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strsbg.fr/Abstract.html

Ségransan, D.; Delfosse, X.; Forveille, T.; Beuzit, J.-L.; Udry, S.; Perrier, C.; Mayor, M.

2000-12-01

68

Volatiles in Terrestrial Planets Orbiting Within Habitable Zones of Low-Mass Stars  

NASA Astrophysics Data System (ADS)

Dynamical considerations derived from analytic calculations and numerical experiments imply that Earth-mass planets that accrete in regions that become habitable zones of M dwarf stars form within several million years. Temperatures in these regions during planetary accretion are higher than those encountered by the material that formed the Earth. Collision velocities during and after the prime planetary accretionary epoch are larger than for Earth. These factors suggest that planets orbiting low mass main sequence stars are likely to be either too distant (and thus too cold) for carbon/water based life on their surfaces or have abundances of the volatiles required life that are substantially less than those of Earth.

Lissauer, J. J.

2009-12-01

69

Protoplanetary disks and planet formation around brown dwarfs and very low-mass stars  

NASA Astrophysics Data System (ADS)

Brown dwarfs and very low-mass stars are very common in the Galaxy, yet we know little about the planetary systems they may host. Here we review observational evidence emerging from comparative studies of disks around brown dwarfs and sun-like stars. These studies show that very young brown dwarfs and very low mass stars have disks as frequently as sun-like stars do, arguing for the same formation processes. There are indications, but no conclusive evidence yet, for a longer disk lifetime around the lowest-mass stars and brown dwarfs. At the same time, evidence for faster dust processing and more strongly reduced disk scale heights is found, demonstrating that the first steps of planet formation also take place around brown dwarfs. With increasingly sensitive infrared instruments a new window is opening on gas-phase chemistry in these disks and the first surveys indicate a different gas-phase chemistry and, perhaps, a suppressed nitrogen chemistry. Sub-millimeter surveys reveal disk masses of a few Jupiter mass, which core accretion models show is enough to form few Earth-mass and smaller planets, but not gas giant planets.

Apai, D.

2013-02-01

70

Star formation in BOK globules and low-mass clouds. V - H-alpha emission stars near SA 101, CG13 and CG22  

Microsoft Academic Search

We have surveyed five fields in the Gum Nebula containing cometary globules, in a search for new regions of low-mass star formation. Seven H-alpha emission stars were found in association with the CG4\\/CG6\\/Sa101 cloud complex, and one in association with the CG13 globule. All eight stars are late-type emission line stars, and appear to be low-mass pre-main sequence stars. Low

Bo Reipurth; Bertil Pettersson

1993-01-01

71

Current Advances in the Computational Simulation of the Formation of Low-Mass Stars  

SciTech Connect

Developing a theory of low-mass star formation ({approx} 0.1 to 3 M{sub {circle_dot}}) remains one of the most elusive and important goals of theoretical astrophysics. The star-formation process is the outcome of the complex dynamics of interstellar gas involving non-linear interactions of turbulence, gravity, magnetic field and radiation. The evolution of protostellar condensations, from the moment they are assembled by turbulent flows to the time they reach stellar densities, spans an enormous range of scales, resulting in a major computational challenge for simulations. Since the previous Protostars and Planets conference, dramatic advances in the development of new numerical algorithmic techniques have been successfully implemented on large scale parallel supercomputers. Among such techniques, Adaptive Mesh Refinement and Smooth Particle Hydrodynamics have provided frameworks to simulate the process of low-mass star formation with a very large dynamic range. It is now feasible to explore the turbulent fragmentation of molecular clouds and the gravitational collapse of cores into stars self-consistently within the same calculation. The increased sophistication of these powerful methods comes with substantial caveats associated with the use of the techniques and the interpretation of the numerical results. In this review, we examine what has been accomplished in the field and present a critique of both numerical methods and scientific results. We stress that computational simulations should obey the available observational constraints and demonstrate numerical convergence. Failing this, results of large scale simulations do not advance our understanding of low-mass star formation.

Klein, R I; Inutsuka, S; Padoan, P; Tomisaka, K

2005-10-24

72

Discovery of an outflow of the very low-mass star ISO 143  

NASA Astrophysics Data System (ADS)

We discover that the very young very low-mass star ISO 143 (M5) is driving an outflow based on spectro-astrometry of forbidden [S II] emission lines at 6716 Å and 6731 Å observed in UVES/VLT spectra. This adds another object to the handful of brown dwarfs and very low-mass stars (M5-M8) for which an outflow has been confirmed and which show that the T Tauri phase continues at very low masses. We find the outflow of ISO 143 to be intrinsically asymmetric and the accretion disk to not obscure the outflow, as only the red outflow component is visible in the [S II] lines. ISO 143 is only the third T Tauri object showing a stronger red outflow component in spectro-astrometry, after RW Aur (G5) and ISO 217 (M6.25). We show here that, including ISO 143, two out of seven outflows confirmed in the very low-mass regime (M5-M8) are intrinsically asymmetric. We measure a spatial extension of the outflow in [S II] of up to 200-300 mas (about 30-50 AU) and velocities of up to 50-70 km s-1. We furthermore detect line emission of ISO 143 in Ca II (8498 Å), O I (8446 Å), He I (7065 Å), and weakly in [Fe II] (7155 Å). Based on a line profile analysis and decomposition we demonstrate that (i) the Ca II emission can be attributed to chromospheric activity, a variable wind, and the magnetospheric infall zone, (ii) the O I emission mainly to accretion-related processes but also a wind, and (iii) the He I emission to chromospheric or coronal activity. We estimate a mass outflow rate of ISO 143 of ~10-10 M? yr-1 and a mass accretion rate in the range of ~10-8 to ~10-9 M? yr-1. These values are consistent with those of other brown dwarfs and very low-mass stars. The derived ?out/?acc ratio of 1-20% does not support previous findings of this number being very large (>40%) for very low-mass objects. Based on observations obtained at the Very Large Telescope of the European Southern Observatory at Paranal, Chile in program 080.C- 0904(A) 082.C-0023(A+B).

Joergens, V.; Kopytova, T.; Pohl, A.

2012-12-01

73

Mass-Radius Relation for Low Mass White Dwarf Stars with Kepler  

NASA Astrophysics Data System (ADS)

We present initial results from a new survey for low mass white dwarf stars in binaries with FGK type main-sequence stars using Kepler data. These objects will provide the first direct measurement of the masses and radii of low mass white dwarf stars. We search Kepler data for stars showing both transits and occultations. The relative depths of these events can be explained by either a cool, dark companion (where the transit is the deeper event), or a hot dark companion (where the occultation is the deeper event). We measure the relative radii and the temperature ratios using the relative depths of the two events. We select objects where the derived temperature and radii are consistent with hot white dwarf companions and inconsistent with cool main-sequence companions. We then plan to measure the white dwarf mass with follow-up radial velocity measurements. This work includes data collected by the Kepler mission. Funding for the Kepler mission is provided by the NASA Science Mission directorate.

Mullally, Fergal; Shah, Y.; Thompson, S. E.; Barclay, T.

2013-01-01

74

KOI-126: A Triply Eclipsing Hierarchical Triple with Two Low-Mass Stars  

NASA Astrophysics Data System (ADS)

The Kepler spacecraft has been monitoring the light from 150,000 stars in its primary quest to detect transiting exoplanets. Here, we report on the detection of an eclipsing stellar hierarchical triple, identified in the Kepler photometry. KOI-126 [A, (B, C)], is composed of a low-mass binary [masses MB = 0.2413 ± 0.0030 solar mass (M?), MC = 0.2127 ± 0.0026 M?; radii RB = 0.2543 ± 0.0014 solar radius (R?), RC = 0.2318 ± 0.0013 R?; orbital period P1 = 1.76713 ± 0.00019 days] on an eccentric orbit about a third star (mass MA = 1.347 ± 0.032 M?; radius RA = 2.0254 ± 0.0098 R?; period of orbit around the low-mass binary P2 = 33.9214 ± 0.0013 days; eccentricity of that orbit e2 = 0.3043 ± 0.0024). The low-mass pair probe the poorly sampled fully convective stellar domain offering a crucial benchmark for theoretical stellar models.

Carter, Joshua A.; Fabrycky, Daniel C.; Ragozzine, Darin; Holman, Matthew J.; Quinn, Samuel N.; Latham, David W.; Buchhave, Lars A.; Van Cleve, Jeffrey; Cochran, William D.; Cote, Miles T.; Endl, Michael; Ford, Eric B.; Haas, Michael R.; Jenkins, Jon M.; Koch, David G.; Li, Jie; Lissauer, Jack J.; MacQueen, Phillip J.; Middour, Christopher K.; Orosz, Jerome A.; Rowe, Jason F.; Steffen, Jason H.; Welsh, William F.

2011-02-01

75

Optical spectroscopy of low-mass stars and brown dwarfs in the Pleiades  

NASA Astrophysics Data System (ADS)

We present low-resolution spectra in the range 4600-9700 A of a sample of low-mass stars and brown dwarf candidates in the Pleiades. We order the spectra into a temperature sequence, using a least-squares minimization procedure, and assign spectral types. The effectiveness of various proposed spectroscopic and photometric temperature indicators for low-mass stars is investigated. We find that the most effective spectroscopic temperature indicators are those based on molecular bands, especially TiO, rather than atomic transitions. We also find that the Pleiades objects may have surface gravities slightly lower than main-sequence objects of the same temperature, supporting their identification as pre-main-sequence cluster members. We investigate the effect of unresolved binarity on the temperature indicators, and conclude that ~46 per cent of low-mass sytems in the Pleiades are multiple. Finally, we discuss how these results affect the status of our brown dwarf candidates, revising the number to 11 systems containing such candidates, of which three are single and the remainder binary.

Steele, I. A.; Jameson, R. F.

1995-02-01

76

The outburst and nature of young eruptive low mass stars in dark clouds  

NASA Astrophysics Data System (ADS)

The FU Orionis (FUor) or EX Orionis (EXor) phenomenon has attracted increasing attention in recent years and is now accepted as a crucial element in the early evolution of low-mass stars. FUor and EXor eruptions of young stellar objects (YSOs) are caused by strongly enhanced accretion from the surrounding disk. FUors display optical outbursts of ˜ 4 mag or more and last for several decades, whereas EXors show smaller outbursts (?m ˜ 2 - 3 mag) that last from a few months to a few years and may occur repeatedly. Therefore, FUor/EXor eruptions represent a rare but very important phenomenon in early stellar evolution, during which a young low-mass YSO brightens by up to several optical magnitudes. Hence, long-term observations of this class of eruptive variables are important to design theoretical models of low-mass star formation. In this paper, we present recent results from our long-term monitoring observations of three rare types of eruptive young variables with the 2-m Himalayan Chandra Telescope (HCT) and the 2-m IUCAA Girawali Observatory (IGO) telescope.

Ninan, J. P.; Ojha, D. K.; Bhatt, B. C.; Mallick, K. K.; Tej, A.; Sahu, D. K.; Ghosh, S. K.; Mohan, V.

77

KOI-126: a triply eclipsing hierarchical triple with two low-mass stars.  

PubMed

The Kepler spacecraft has been monitoring the light from 150,000 stars in its primary quest to detect transiting exoplanets. Here, we report on the detection of an eclipsing stellar hierarchical triple, identified in the Kepler photometry. KOI-126 [A, (B, C)], is composed of a low-mass binary [masses M(B) = 0.2413 ± 0.0030 solar mass (M(?)), M(C) = 0.2127 ± 0.0026 M(?); radii R(B) = 0.2543 ± 0.0014 solar radius (R(?)), R(C) = 0.2318 ± 0.0013 R(?); orbital period P(1) = 1.76713 ± 0.00019 days] on an eccentric orbit about a third star (mass M(A) = 1.347 ± 0.032 M(?); radius R(A) = 2.0254 ± 0.0098 R(?); period of orbit around the low-mass binary P(2) = 33.9214 ± 0.0013 days; eccentricity of that orbit e(2) = 0.3043 ± 0.0024). The low-mass pair probe the poorly sampled fully convective stellar domain offering a crucial benchmark for theoretical stellar models. PMID:21224439

Carter, Joshua A; Fabrycky, Daniel C; Ragozzine, Darin; Holman, Matthew J; Quinn, Samuel N; Latham, David W; Buchhave, Lars A; Van Cleve, Jeffrey; Cochran, William D; Cote, Miles T; Endl, Michael; Ford, Eric B; Haas, Michael R; Jenkins, Jon M; Koch, David G; Li, Jie; Lissauer, Jack J; MacQueen, Phillip J; Middour, Christopher K; Orosz, Jerome A; Rowe, Jason F; Steffen, Jason H; Welsh, William F

2011-01-11

78

Carbon star formation and neutron-rich isotope formation in low-mass asymptotic giant branch stars  

SciTech Connect

A preliminary analysis of the results of a very time-consuming program for the determination of dredge-up properties of thermally pulsing asymptotic giant branch (AGB) stars of low mass shows that: the dredge up to the surface of freshly made isotopes such as /sup 12/C does not continue throughout a star's AGB lifetime, but has a beginning and an end; only in stars of small initial metallicity and of sufficiently small mass does semicondvection play a role in the production of /sup 13/C, which can act as a source of neutrons for s-process-like isotope production; the primary reason for dredge-up properties of low-mass stars is the fact that the strength of thermal pulses reaches values that are an order of magnitude larger than in high-mass AGB stars; the minimum core mass when dredge up first begins increases with increasing metallicity and with decreasing total stellar mass; only above the critical value of mixing length over scale height does dredge up occur at all; although model stars of larger than solar metallicity can dredge up carbon, they probably do not become carbon stars, in agreement with the known lack of carbon stars in regions of high metallicity such as the galactic bulge. It is postulated that, in stars of moderate initial mass which can survive wind mass loss long enough to develop a core mass larger than those studied here, a second dredge-up phase may occur, and this may account for the abundances of Nb and Tc in stars such as R CMi and CY Cyg.

Iben, I. Jr.

1983-12-15

79

Stochastic Star Formation in Low Mass Galaxies: A case study of DDO 210  

NASA Astrophysics Data System (ADS)

To address the longstanding question of whether dwarf galaxies have bursty star formation histories requires a large sample of dwarf galaxies and an accurate tracer of star formation. Here we explore the utility of using two common tracers, H-alpha and the ultraviolet (UV). H-alpha and UV photons are primarily produced by massive stars, so stochastic effects come into play when the star formation rate (SFR) is so low that the upper mass end of the initial mass function (IMF) is not fully populated. We use Monte-Carlo simulations to explore these effects at a range of SFRs for a standard Chabrier IMF. We do not impose the restriction that stars form primarily in low mass clusters as explored by Kroupa and Weidner. Here we simply consider Poisson fluctuations in the number of massive stars when star formation occurs at a constant low rate. We find that above SFRs of 0.001 Msun/yr both the far-UV and H-alpha are reliable tracers of SFR. Below this value both indicators begin to show deviations, with H-alpha being more strongly affected. We explore the implications of these findings for the 11 Mpc H-alpha UV Galaxy Survey (11HUGS), a GALEX Legacy program designed to characterize the star formation properties of a local volume-limited sample. We highlight the dwarf galaxy DDO 210, which has a UV luminosity of 270 L_sun, but no nebular H-alpha emission. While we cannot rule out a truncated star formation history for this galaxy, our simulations demonstrate that this H-alpha deficient galaxy could be forming stars at a constant rate of 0.0001 Msun/yr.

Tremonti, Christina A.; Lee, J. C.; van Zee, L.; Kennicutt, R. C.; Gil de Paz, A.; Sakai, S.; Funes, J.; Akiyama, S.

2007-12-01

80

Cyg X-3: a low-mass black hole or a neutron star  

NASA Astrophysics Data System (ADS)

Cyg X-3 is a highly interesting accreting X-ray binary, emitting from the radio to high-energy gamma-rays. It consists of a compact object wind-fed by a Wolf-Rayet (WR) star, but the masses of the components and the mass-loss rate have been a subject of controversies. Here, we determine its masses, inclination and the mass-loss rate using our derived relationship between the mass-loss rate and the mass for WR stars of the WN type, published infrared and X-ray data, and a relation between the mass-loss rate and the binary period derivative (observed to be >0 in Cyg X-3). Our obtained mass-loss rate is almost identical to that from two independent estimates and consistent with other ones, which strongly supports the validity of this solution. The found WR and compact-object masses are 10.3+ 3.9- 2.8 and 2.4+ 2.1- 1.1 M?, respectively. Thus, our solution still allows for the presence of either a neutron star or a black hole, but the latter only with a low mass. However, the radio, infrared and X-ray properties of the system suggest that the compact object is a black hole. Such a low-mass black hole could be formed via accretion-induced collapse or directly from a supernova.

Zdziarski, Andrzej A.; Miko?ajewska, Joanna; Belczy?ski, Krzysztof

2013-02-01

81

Disk structure and planet formation around young low-mass stars and brown dwarfs  

NASA Astrophysics Data System (ADS)

We propose to obtain IRS complete (5-40 micron) low-resolution spectra of a sample of 41 young low-mass stars and brown dwarfs, to study the characteristics of their disks and to search for evidence of ongoing planet formation. We also propose to use IRAC to observe an additional 43 newly-identified brown dwarfs in Taurus and Chamaeleon, for future IRS spectroscopic followup. This guaranteed-time observing program has a total of 50.1 hours, with 14 hours provided by IRAC PI Giovanni Fazio, and 36.1 hours by IRS PI Jim Houck.

Houck, James R.; Luhman, Kevin; Allen, Lori; Calvet, Nuria; Chen, Christine; Fazio, Giovanni; Forrest, Bill; Furlan, Elise; Hartmann, Lee; Jura, Mike; Keller, Luke; Mainzer, Amy; Markwick-Kemper, Ciska; Marley, Mark; Megeath, Tom; Muzerolle, James; Najita, Joan; Roellig, Tom; Sloan, Greg; Uchida, Keven; Watson, Dan; D'Alessio, Paola

2006-05-01

82

Photospheric abundance analysis of low-mass pre-main sequence stars  

NASA Astrophysics Data System (ADS)

This thesis investigation uses photospheric abundance analysis techniques to determine metal abundances both for individual weakly active T Tauri stars and the molecular clouds with which these stars are associated. Using the high resolution echelle spectrographs of the Palomar 1.5m and the Las Campanas Observatory 2.5m telescopes, high signal-to-noise ratio spectra have been obtained for 53 low pre-main sequence stars in six major northern and southern hemisphere star formation regions. Spectra were also taken of 14 main sequence stars with known effective temperatures and metallicity to serve as spectral standards. Equivalent widths of a large number of Fe I absorption lines have been measured, as well as lines of Ca I, Al I, V I, Ni I, Ti I, K I, and Li I. Temperature-sensitive line ratios of neutral iron and vanadium calibrated against the spectral standards are used to derive effective temperatures for 30 weak-line T Tauri stars, which are much improved over the low resolution spectral classifications found for these objects in the literature. Microturbulent velocities have also been found for 16 of the pre-main sequence stars in the sample. Several stars with abnormally high microturbulences for their spectral type have been found. Using these improved stellar parameters, metallicities of a large number of T Tauri stars have been determined for the first time. Abundance analyses of iron, aluminum, calcium, nickel, and titanium are performed on 30 low masses, pre-main sequence stars. In the star-formation regions of Taurus-Auriga, Orion, Chamaeleon, and Ophiuchus, which each contributed five or more association members to the young star survey, bulk metallicities have been determined. The results indicate that the current metal abundances in these clouds are near or slightly above solar values. Cloud material metallicities are then used to calibrate ultraviolet line-of-sight metal depletion studies for the Orion and rho Ophiuchi clouds. The final chapter of this work is a lithium abundance analysis for the entire sample of 53 pre-main sequence stars.

Padgett, Deborah Lynne

1992-06-01

83

IDENTIFYING THE YOUNG LOW-MASS STARS WITHIN 25 pc. II. DISTANCES, KINEMATICS, AND GROUP MEMBERSHIP  

SciTech Connect

We have conducted a kinematic study of 165 young M dwarfs with ages of {approx}<300 Myr. Our sample is composed of stars and brown dwarfs with spectral types ranging from K7 to L0, detected by ROSAT and with photometric distances of {approx}<25 pc assuming that the stars are single and on the main sequence. In order to find stars kinematically linked to known young moving groups (YMGs), we measured radial velocities for the complete sample with Keck and CFHT optical spectroscopy and trigonometric parallaxes for 75 of the M dwarfs with the CAPSCam instrument on the du Pont 2.5 m Telescope. Due to their youthful overluminosity and unresolved binarity, the original photometric distances for our sample underestimated the distances by 70% on average, excluding two extremely young ({approx}<3 Myr) objects found to have distances beyond a few hundred parsecs. We searched for kinematic matches to 14 reported YMGs and identified 10 new members of the AB Dor YMG and 2 of the Ursa Majoris group. Additional possible candidates include six Castor, four Ursa Majoris, two AB Dor members, and one member each of the Her-Lyr and {beta} Pic groups. Our sample also contains 27 young low-mass stars and 4 brown dwarfs with ages {approx}<150 Myr that are not associated with any known YMG. We identified an additional 15 stars that are kinematic matches to one of the YMGs, but the ages from spectroscopic diagnostics and/or the positions on the sky do not match. These warn against grouping stars together based only on kinematics and that a confluence of evidence is required to claim that a group of stars originated from the same star-forming event.

Shkolnik, Evgenya L. [Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ 86001 (United States); Anglada-Escude, Guillem [Institut fuer Astrophysik, Universitaet Goettingen, Friedrich-Hund-Platz 1, D-37077 Goettingen (Germany); Liu, Michael C.; Bowler, Brendan P. [Institute for Astronomy, University of Hawaii at Manoa 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Weinberger, Alycia J.; Boss, Alan P. [Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Road, NW, Washington, DC 20015 (United States); Reid, I. Neill [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Tamura, Motohide, E-mail: shkolnik@lowell.edu [National Astronomical Observatory of Japan, Tokyo (Japan)

2012-10-10

84

Very low mass M dwarfs--stars or brown dwarfs in disguise?  

NASA Astrophysics Data System (ADS)

We have used radial velocity and proper motion observations to determine the space motions of a sample of 25 low-luminosity M dwarfs. We find that the solar motion and velocity dispersions of these stars are similar to the kinematics of a sample of more luminous, earlier type M dwarfs. However, there is evidence to indicate that when objects selected by photometric criteria alone are considered, the kinematics are more characteristic of an approximately 3 X 108 year old population. This suggest that the faintest known stars may be younger on average than the local M dwarfs in the Galactic disk, indicating the possible presence of a number of brown dwarfs or transition objects in our sample of very low-mass objects.

Reid, Neill; Tinney, C. G.; Mould, Jeremy

1994-10-01

85

Models of very-low-mass stars, brown dwarfs and exoplanets.  

PubMed

Within the next few years, GAIA and several instruments aiming to image extrasolar planets will be ready. In parallel, low-mass planets are being sought around red dwarfs, which offer more favourable conditions, for both radial velocity detection and transit studies, than solar-type stars. In this paper, the authors of a model atmosphere code that has allowed the detection of water vapour in the atmosphere of hot Jupiters review recent advances in modelling the stellar to substellar transition. The revised solar oxygen abundances and cloud model allow the photometric and spectroscopic properties of this transition to be reproduced for the first time. Also presented are highlight results of a model atmosphere grid for stars, brown dwarfs and extrasolar planets. PMID:22547243

Allard, F; Homeier, D; Freytag, B

2012-06-13

86

High and Low Metallicity Models of Extremely Low-Mass Stars and Brown Dwarfs  

NASA Astrophysics Data System (ADS)

We present our latest generation of evolutionary models for very low-luminosity stars (near the ends of their respective Main Sequences) and for Brown Dwarfs. These results have been computed for a wide range of metallicities which includes extremely old subdwarfs (0.0001 < Z < 0.02). Using sophisticated atmospheric models from the Allard-Hauschildt library, we precompute an extensive grid of outer boundary conditions and then interpolate this grid as the models are being calculated. Using very sophisticated input physics such as the OPAL opacities, the Alexander and Ferguson low-temperature opacities, and our own equation of state which is largely derived from that of the SCVH low-temperature EOS, we have calculated the evolution of low-mass stars and Brown Dwarfs ranging from 0.001 to 0.5 solar masses. The physical properties of these models will be presented and the observational implications will be discussed briefly.

Nelson, Lorne A.

2011-05-01

87

A spectral differential approach to characterizing low-mass companions to late-type stars  

NASA Astrophysics Data System (ADS)

In this paper, we develop a spectral differential technique with which the dynamical mass of low-mass companions can be found. This method aims at discovering close companions to late-type stars by removing the stellar spectrum through a subtraction of spectra obtained at different orbital phases and discovering the companion spectrum in the difference spectrum in which the companion lines appear twice (positive and negative signal). The resulting radial velocity difference of these two signals provides the true mass of the companion, if the orbital solution for the radial velocities of the primary is known. We select the CO line region in the K band for our study, because it provides a favourable star-to-companion brightness ratio for our test case GJ 1046, an M2V dwarf with a low-mass companion that most likely is a brown dwarf. Furthermore, these lines remain largely unblended in the difference spectrum so that the radial velocity amplitude of the companion can be measured directly. Only if the companion rotates rapidly and has a small radial velocity due to a high mass, does blending occur for all lines so that our approach fails. We also consider activity of the host star, and show that the companion difference flux can be expected to have larger amplitude than the residual signal from the active star so that stellar activity does not inhibit the determination of the companion mass. In addition to determining the companion mass, we restore the single companion spectrum from the difference spectrum using singular value decomposition.

Kostogryz, N. M.; Kürster, M.; Yakobchuk, T. M.; Lyubchik, Y.; Kuznetsov, M. K.

88

Effects of Cosmions upon the structure and evolution of very low mass stars  

SciTech Connect

A number of recent studies have suggested that cosmions, or WIMPS, may play an important role in the energetics of the solar interior; in particular, it has been argued that these hypothetical particles may transport sufficient energy within the nuclear-burning solar core so as to depress the solar core temperature to the point of resolving the solar neutrino problem. Solutions to the solar neutrino problem have proven themselves to be quite nonunique, so that it is of some interest whether the cosmion solution can be tested in some independent manner. It is argued that if cosmions solve the solar neutrino problem, then they must also play an important role in the evolution of low mass main sequence stars; and, second, that if they do so, then a simple (long mean free path) model for the interaction of cosmions with baryons leads to changes in the structure of the nuclear-burning core which may be in principal observable. Such changes include suppression of a fully-convective core in very low mass main sequence stars; and a possible thermal runaway in the core of the nuclear burning region. Some of these changes may be directly observable, and hence may provide independent constraints on the properties of the cosmions required to solve the solar neutrino problem, perhaps even ruling them out.

Deluca, E.E.; Griest, K.; Rosner, R.; Wang, J.

1989-02-01

89

Near Infrared Photometric and Optical Spectroscopic Study of 22 Low Mass Star Clusters embedded in Nebulae  

NASA Astrophysics Data System (ADS)

Among the star clusters in the Galaxy, those embedded in nebulae represent the youngest group that has only recently been explored. The analysis of a sample of 22 candidate embedded stellar systems in reflection nebulae and/or HII environments is presented. We employed optical spectroscopic observations of stars in the directions of the clusters together with near infrared photometry from the 2MASS catalogue. Our analysis is based on source surface density, colour-colour diagram and on theoretical pre-main sequence isochrones. We take into account the field star contamination by carrying out a statistical subtraction. The studied objects have the characteristics of low mass systems. We derive their fundamental parameters. Most of the cluster ages turned out to be younger than 2 Myr. The studied embedded stellar systems in reflection nebulae and/or HII region complexes do not have stars of spectral types earlier than B. The total stellar masses locked in the clusters are in the range 20-220 solar masses. They are found to be gravitationally unstable and are expected to dissolve in a timescale of a few Myr (Soares et al. 2008, A&A, 478, 419).

Soares, J. B.; Bica, E.; Ahumada, A. V.; Clariá, J. J.

2009-05-01

90

Photometric and spectroscopic study of low mass embedded star clusters in reflection nebulae  

NASA Astrophysics Data System (ADS)

An analysis of the candidate embedded stellar systems in the reflection nebulae vdBH-RN 26, vdBH-RN} 38, vdBH-RN} 53a, GGD 20, ESO 95-RN 18 and NGC 6595 is presented. Optical spectroscopic data from CASLEO (Argentina) in conjunction with near infrared photometry from the 2MASS Point Source Catalogue were employed. The analysis is based on source surface density, colour-colour and colour-magnitude diagrams together with theoretical pre-main sequence isochrones. We take into account the field population affecting the analysis by carrying out a statistical subtraction. The fundamental parameters for the stellar systems were derived. The resulting ages are in the range 1-4 Myr and the objects are dominated by pre-main sequence stars. The observed masses locked in the clusters are less than 25 M?. The studied systems have no stars of spectral types earlier than B, indicating that star clusters do not necessarily evolve through an HII region phase. The relatively small locked mass combined with the fact that they are not numerous in catalogues suggests that these low mass clusters are not important donors of stars to the field populations. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina.

Soares, J. B.; Bica, E.; Ahumada, A. V.; Clariá, J. J.

2005-02-01

91

Near infrared photometric and optical spectroscopic study of 22 low mass star clusters embedded in nebulae  

NASA Astrophysics Data System (ADS)

Aims:Among the star clusters in the Galaxy, those embedded in nebulae represent the youngest group, which has only recently been explored. The analysis of a sample of 22 candidate embedded stellar systems in reflection nebulae and/or HII environments is presented. Methods: We employed optical spectroscopic observations of stars in the directions of the clusters carried out at CASLEO (Argentina) together with near infrared photometry from the 2MASS catalogue. Our analysis is based on source surface density, colour-colour diagrams and on theoretical pre-main sequence isochrones. We take into account the field star contamination by carrying out a statistical subtraction. Results: The studied objects have the characteristics of low mass systems. We derive their fundamental parameters. Most of the cluster ages are younger than 2 Myr. The studied embedded stellar systems in reflection nebulae and/or HII region complexes do not have stars of spectral types earlier than B. The total stellar masses locked in the clusters are in the range 20-220 M?. They are found to be gravitationally unstable and are expected to dissolve in a timescale of a few Myr. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina.

Soares, J. B.; Bica, E.; Ahumada, A. V.; Clariá, J. J.

2008-02-01

92

Constraining the neutron star equation of state using quiescent low-mass X-ray binaries  

SciTech Connect

Chandra or XMM-Newton observations of quiescent low-mass X-ray binaries can provide important constraints on the equation of state of neutron stars. The mass and radius of the neutron star can potentially be determined from fitting a neutron star atmosphere model to the observed X-ray spectrum. For a radius measurement it is of critical importance that the distance to the source is well constrained since the fractional uncertainty in the radius is at least as large as the fractional uncertainty in the distance. Uncertainties in modelling the neutron star atmosphere remain. At this stage it is not yet clear if the soft thermal component in the spectra of many quiescent X-ray binaries is variable on timescales too short to be accommodated by the cooling neutron star scenario. This can be tested with a long XMM-Newton observation of the neutron star X-ray transient Cen X-4 in quiescence. With such an observation one can use the Reflection Grating Spectrometer spectrum to constrain the interstellar extinction to the source. This removes this parameter from the X-ray spectral fitting of the EPIC pn and MOS spectra and allows one to investigate whether the variability observed in the quiescent X-ray spectrum of this source is due to variations in the soft thermal spectral component or variations in the power law spectral component coupled with variations in N{sub H}. This will test whether the soft thermal component can indeed be due to the hot thermal glow of the neutron star. Irrespective of the outcome of such a study, the observed cooling in quiescence in sources for which the crust is significantly out of thermal equilibrium with the core due to a prolonged outburst, such as KS 1731-260, seem excellent candidates for mass and radius determinations through modelling the observed X-rays with a neutron star atmosphere model (the caveats about the source distance and atmosphere modelling do also apply here obviously and presently prevent one from obtaining such constraints). Finally, the fact that the soft thermal glow in sources such as SAX J1808.4-3658 and 1H 1905+000 has not been detected in quiescence means that the neutron star cores of these sources must be cold. The most plausible explanation seems to be that the neutron stars are more massive than 1.4 M{sub {center_dot}} and cool via the direct URCA process.

Jonker, P. G. [SRON, Netherlands Institute for Space Research, 3584 CA, Utrecht (Netherlands); Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, Massachusetts (United States); Astronomical Institute, Utrecht University, 3508 TA, Utrecht (Netherlands)

2008-02-27

93

Constraining the neutron star equation of state using quiescent low-mass X-ray binaries  

NASA Astrophysics Data System (ADS)

Chandra or XMM-Newton observations of quiescent low-mass X-ray binaries can provide important constraints on the equation of state of neutron stars. The mass and radius of the neutron star can potentially be determined from fitting a neutron star atmosphere model to the observed X-ray spectrum. For a radius measurement it is of critical importance that the distance to the source is well constrained since the fractional uncertainty in the radius is at least as large as the fractional uncertainty in the distance. Uncertainties in modelling the neutron star atmosphere remain. At this stage it is not yet clear if the soft thermal component in the spectra of many quiescent X-ray binaries is variable on timescales too short to be accommodated by the cooling neutron star scenario. This can be tested with a long XMM-Newton observation of the neutron star X-ray transient Cen X-4 in quiescence. With such an observation one can use the Reflection Grating Spectrometer spectrum to constrain the interstellar extinction to the source. This removes this parameter from the X-ray spectral fitting of the EPIC pn and MOS spectra and allows one to investigate whether the variability observed in the quiescent X-ray spectrum of this source is due to variations in the soft thermal spectral component or variations in the power law spectral component coupled with variations in NH. This will test whether the soft thermal component can indeed be due to the hot thermal glow of the neutron star. Irrespective of the outcome of such a study, the observed cooling in quiescence in sources for which the crust is significantly out of thermal equilibrium with the core due to a prolonged outburst, such as KS 1731-260, seem excellent candidates for mass and radius determinations through modelling the observed X-rays with a neutron star atmosphere model (the caveats about the source distance and atmosphere modelling do also apply here obviously and presently prevent one from obtaining such constraints). Finally, the fact that the soft thermal glow in sources such as SAX J1808.4-3658 and 1H 1905+000 has not been detected in quiescence means that the neutron star cores of these sources must be cold. The most plausible explanation seems to be that the neutron stars are more massive than 1.4 Msolar and cool via the direct URCA process.

Jonker, P. G.

2008-02-01

94

Low-Mass Star Formation and the Initial Mass Function in IC 348  

NASA Astrophysics Data System (ADS)

We have performed deep infrared and optical spectroscopy of virtually the entire stellar population within the 5' x 5' core of IC 348, measuring K (2.2 ?m) band and optical spectral types that are in good agreement. We have also identified several sources that may be substellar depending on the choice of temperature scales and evolutionary tracks, with three particularly late-type objects (M7.5-M8) that are likely bonafide brown dwarfs. In conjunction with the theoretical evolutionary tracks of D'Antona & Mazzitelli, the H-R diagram indicates a spread in ages from 0.5 to 10 Myr, with most of the core star formation occurring in the last 3 Myr. Using K-band imaging to provide a completeness correction to the spectroscopic sample, we arrive at an initial mass function (IMF) that matches that of Miller & Scalo from 0.25 to 3 M_?. The IMF appears to fall slowly from 0.25 M_? to the hydrogen burning limit, slightly below the IMF of Miller & Scalo, which is flat in logarithmic units (as compared to slopes of ~1.35 and -2.6 for Salpeter and Scalo). Correction for unresolved binary systems could steepen the slope of the low-mass IMF by about 0.5, which implies a single-star IMF that is roughly flat below 0.25 M_?. The low-mass IMF in IC 348 is similar to that derived in studies of most other young clusters, implying that the IMF does not vary dramatically among clusters of differing environments; however, the derived IMF is dependent on the evolutionary tracks and the detailed shape of the IMF should be viewed with caution until these models are tested against observations, particularly at low masses (<0.3 M_?) and young ages (<10 Myr). H? and Brgamma emission strengths are consistent with predictions of magnetospheric accretion models of Muzerolle, Calvet, & Hartmann for accretion rates of 10^-9-10^-8 M_? yr^-1. Combining our data with the H? measurements of Herbig, we find that ~25% of stars within the core of IC 348 and younger than 3 Myr exhibit signatures of disks in the form of strong H? (>10 Å) or Brgamma (>1 Å) emission or K-band continuum veiling (r_K >= 0.5). Since no sources older than 3 Myr show evidence for massive disks, disk lifetimes in the core of IC 348 appear to be shorter than those observed in Taurus or in the outer regions of IC 348.

Luhman, K. L.; Rieke, G. H.; Lada, C. J.; Lada, E. A.

1998-11-01

95

A HERSCHEL SURVEY OF COLD DUST IN DISKS AROUND BROWN DWARFS AND LOW-MASS STARS  

SciTech Connect

We report the complete photometric results from our Herschel study which is the first comprehensive program to search for far-infrared emission from cold dust around young brown dwarfs (BDs). We surveyed 50 fields containing 51 known or suspected BDs and very low mass stars that have evidence of circumstellar disks based on Spitzer photometry and/or spectroscopy. The objects with known spectral types range from M3 to M9.5. Four of the candidates were subsequently identified as extragalactic objects. Of the remaining 47 we have successfully detected 36 at 70 {mu}m and 14 at 160 {mu}m with signal-to-noise ratio (S/N) greater than 3, as well as several additional possible detections with low S/N. The objects exhibit a range of [24]-[70] {mu}m colors suggesting a range in mass and/or structure of the outer disk. We present modeling of the spectral energy distributions of the sample and discuss trends visible in the data. Using two Monte Carlo radiative transfer codes we investigate disk masses and geometry. We find a very wide range in modeled total disk masses from less than 10{sup -6} M{sub Sun} up to 10{sup -3} M{sub Sun} with a median disk mass of the order of 3 Multiplication-Sign 10{sup -5} M{sub Sun }, suggesting that the median ratio of disk mass to central object mass may be lower than for T Tauri stars. The disk scale heights and flaring angles, however, cover a range consistent with those seen around T Tauri stars. The host clouds in which the young BDs and low-mass stars are located span a range in estimated age from {approx}1-3 Myr to {approx}10 Myr and represent a variety of star-forming environments. No obvious dependence on cloud location or age is seen in the disk properties, though the statistical significance of this conclusion is not strong.

Harvey, Paul M.; Evans, Neal J. II [Astronomy Department, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712-0259 (United States); Henning, Thomas [Max Planck Institut for Astronomy, Koenigstuhl 17, 69117 Heidelberg (Germany); Liu Yao; Wolf, Sebastian [Institute of Theoretical Physics and Astrophysics, University of Kiel, Leibnizstr. 15, 24098 Kiel (Germany); Menard, Francois; Pinte, Christophe [UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d'Astrophysique (IPAG) UMR 5274, BP 53, 38041 Grenoble cedex 9 (France); Cieza, Lucas A. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Pascucci, Ilaria, E-mail: pmh@astro.as.utexas.edu, E-mail: nje@astro.as.utexas.edu, E-mail: henning@mpia.de, E-mail: wolf@astrophysik.uni-kiel.de, E-mail: yliu@pmo.ac.cn, E-mail: yliu@pmo.ac.cn, E-mail: menard@obs.ujf-grenoble.fr, E-mail: christophe.pinte@obs.ujf-grenoble.fr, E-mail: lcieza@ifa.hawaii.edu, E-mail: pascucci@lpl.arizona.edu [Lunar and Planetary Laboratory, Department of Planetary Sciences, University of Arizona, 1629 E. University Boulevard, Tucson, AZ 85721 (United States)

2012-08-10

96

THE SEARCH FOR LOW-MASS COMPANIONS OF B STARS IN THE CARINA NEBULA CLUSTER TRUMPLER 16  

SciTech Connect

We have developed lists of likely B3-A0 stars (called 'late B' stars) in the young cluster Trumpler 16. The following criteria were used: location within 3' of {eta} Car, an appropriate V and B - V combination, and proper motion (where available). Color and magnitude cuts have been made assuming an E(B - V) = 0.55 mag {+-} 0.1, which is a good approximation close to the center of Trumpler 16. These lists have been cross-correlated with X-ray sources found in the Chandra Carina Complex Project. Previous studies have shown that only very rarely (if at all) do late main-sequence B stars produce X-rays. We present evidence that the X-ray-detected sources are binaries with low-mass companions, since stars less massive than 1.4 M{sub sun} are strong X-ray sources at the age of the cluster. Both the median X-ray energies and X-ray luminosities of these sources are in good agreement with values for typical low-mass coronal X-ray sources. We find that 39% of the late B stars based on a list with proper motions have low-mass companions. Similarly, 32% of a sample without proper motions have low-mass companions. We discuss the X-ray detection completeness. These results on low-mass companions of intermediate-mass stars are complementary to spectroscopic and interferometric results and probe new parameter space of low-mass companions at all separations. They do not support a steeply rising distribution of mass ratios to low masses for intermediate-mass (5 M{sub sun}) primaries, such as would be found by random pairing from the initial mass function.

Remage Evans, Nancy [Smithsonian Astrophysical Observatory, MS 4, 60 Garden Street, Cambridge, MA 02138 (United States); DeGioia-Eastwood, Kathleen [Department of Physics and Astronomy, Northern Arizona University, Box 6010, Flagstaff, AZ 86011-6010 (United States); Gagne, Marc [Department of Geology and Astronomy, West Chester University, West Chester, PA 19883 (United States); Townsley, Leisa; Broos, Patrick [Department of Astronomy and Astrophysics, 525 Davey Laboratory, Pennsylvania State University, University Park, PA 16802 (United States); Wolk, Scott [Smithsonian Astrophysical Observatory, MS 70, 60 Garden Street, Cambridge, MA 02138 (United States); Naze, Yael [GAPHE Departement AGO, Universite de Liege, Allee du 6 Aout 17, Bat. B5C, B4000-Liege (Belgium); Corcoran, Michael [NASA's Goddard Space Flight Center, Code 662, Greenbelt, MD 20771 (United States); Oskinova, Lida [Institute for Physics and Astronomy, University Potsdam, 14476 Potsdam (Germany); Moffat, Anthony F. J. [Dept. de Physique, Univ. de Montreal, CP 6128 Succ. A. Centre-Ville, Montreal, QC H3C 3J7 (Canada); Wang Junfeng [Smithsonian Astrophysical Observatory, MS 06, 60 Garden Street, Cambridge, MA 02138 (United States); Walborn, Nolan R., E-mail: nevans@cfa.harvard.edu [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2011-05-01

97

Completing A Near-Infrared Search for Very Low Mass Companions to Stars within 10 pc  

NASA Astrophysics Data System (ADS)

We continue our survey of stars within 10 parsecs for brown dwarf and very low mass stellar {VLM} companions. The nearby star population is dominated by the red dwarfs {75%}, which contribute 40% of the stellar mass to the disk and cause the luminosity function to climb all the way to the terminus of the stellar main sequence {Henry and McCarthy 1990}. But what happens to the LF past the end of the main sequence, in the realm of brown dwarfs? With a 10sigma detection limit of M_J 22 at 10 pc, our survey can reveal companions between 0.5" and 10" that are 11 mag fainter than the empirical end of the main sequence {M_J = 11}, and 6.5 mag fainter than the brown dwarf Gl 229B {M_J = 15.5}. This search will therefore be the largest, most sensitive, volume-limited search for VLM companions ever undertaken. In addition to the increased probability of finding brown dwarfs, this program provides fundamental ``spinoff'' science, including an improved determination of the LF for the nearby stars and characterization of all companions with separations 10-100 AU, similar to the scale of our solar system.

Henry, Todd

1997-12-01

98

A New Twist in the Evolution of Low-mass Stars  

NASA Astrophysics Data System (ADS)

We show that the evolutionary track of a low-mass red giant should make an extended zigzag on the Hertzsprung-Russel diagram just after the bump luminosity if fast internal rotation and enhanced extra mixing in the radiative zone bring the temperature gradient close to the adiabatic one. This can explain both the location and peculiar surface chemical composition of Li-rich K giants studied by Kumar et al. We also discuss a striking resemblance between the photometric and composition peculiarities of these stars and giant components of RS CVn binaries. We demonstrate that the observationally constrained values of the temperature gradient in the Li-rich K giants agree with the required rate of extra mixing only if the turbulence that is believed to be responsible for this extra mixing is highly anisotropic, with its associated transport coefficients in the horizontal direction strongly dominating over those in the vertical direction.

Denissenkov, Pavel A.

2012-07-01

99

Energy generation in convective shells of low mass, low metallicity stars  

SciTech Connect

We report on the non-negligible energy generation from the {sup 13}C neutron source and neutron capture reactions in low mass, low metallicity AGB stars. About 10{sup 4} L{sub {circle dot}} are generated within the thermal pulse convective shell by the combination of the {sup 13}C({alpha}, n){sup 16}O rate and the sum of the Y(Z,A)(n,{gamma})Y(Z,A + 1) reactions and beta decays. The inclusion of this energy source in an AGB thermal pulse evolution is shown to alter the evolution of the convective shell boundaries, and, hence, how the {sup 13}C is ingested into the convective shell. Also, the duration of the pulse itself is reduced by the additional energy input. The nucleosynthetic consequences are discussed for these evolutionary changes. 17 refs., 5 figs.

Bazan, G. (Illinois Univ., Urbana, IL (USA). Dept. of Astronomy); Lattanzio, J.C. (Lawrence Livermore National Lab., CA (USA))

1989-11-10

100

Quest for quiescent neutron star low mass x-ray binaries in the Small Magellanic Cloud  

NASA Astrophysics Data System (ADS)

We present the first spectral search for neutron stars (NSs) in low-mass X-ray binaries (LMXBs) between outbursts in the Small Magellanic Cloud (SMC). We identify and discuss candidate LMXBs in quiescence in the SMC using deep Chandra X-ray observations of two portions of the SMC. We produce X-ray color-magnitude-diagrams of XRSs of these two fields and identify 10 candidates for quiescent NS LMXBs. Spectral fitting and searches for optical counterparts rule out five, leaving five candidate quiescent NS LMXBs. We estimate that we are sensitive to ˜ 10% of quiescent NS LMXBs in our fields. Our fields include 4.4 × 10^7 M? of stellar mass, giving an upper limit of 10^-6 LMXBs per M? in the SMC. We place a lower limit on the average duty cycle of NS LMXBs as ˜ 0.003.

Chowdhury, Mizanul Huq

101

Multi-fibre optical spectroscopy of low-mass stars and brown dwarfs in Upper Scorpius  

NASA Astrophysics Data System (ADS)

Context. Knowledge of the mass function in open clusters constitutes one way to critically examine the formation mechanisms proposed to explain the existence of low-mass stars and brown dwarfs. Aims: The aim of the project is to determine as accurately as possible the shape of the mass function across the stellar/substellar boundary in the young (5 Myr) and nearby (d = 145 pc) Upper Sco association. Methods: We have obtained multi-fibre intermediate-resolution (R ~ 1100) optical (~5750-8800 Å) spectroscopy of 94 photometric and proper motion selected low-mass star and brown dwarf candidates in Upper Sco with the AAOmega spectrograph on the Anglo-Australian Telescope. Results: We have estimated the spectral types and measured the equivalent widths of youth (H?) and gravity (Na I and K I) diagnostic features to confirm the spectroscopic membership of about 95% of the photometric and proper motion candidates extracted from 6.5 square degrees surveyed in Upper Sco by the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Clusters Survey (GCS). We also detect lithium in the spectra with the highest signal-to-noise, consolidating our conclusions about their youth. Furthermore, we derive an estimate of the efficiency of the photometric and proper motion selections used in our earlier studies using spectroscopic data obtained for a large number of stars falling into the instrument's field-of-view. We have estimated the effective temperatures and masses for each new spectroscopic member using the latest evolutionary models available for low-mass stars and brown dwarfs. Combining the current optical spectroscopy presented here with near-infrared spectroscopy obtained for the faintest photometric candidates, we confirm the shape and slope of our earlier photometric mass function. The luminosity function drawn from the spectroscopic sample of 113 USco members peaks at around M6 and is flat at later spectral type. We may detect the presence of the M7/M8 gap in the luminosity function as a result of the dust properties in substellar atmospheres. The mass function may peak at 0.2 M? and is quite flat in the substellar regime. We observe a possible excess of cool low-mass brown dwarfs compared to IC 348 and the extrapolation of the field mass functions, supporting the original hypothesis that Upper Sco may possess an excess of brown dwarfs compared to other young regions. Conclusions: This result shows that the selection of photometric candidates based on five band photometry available from the UKIDSS GCS and complemented partially by proper motions can lead to a good representation of the spectroscopic mass function. Based on observations obtained with the AAOmega spectrograph at the Anglo-Australian Observatory.Appendices are only available in electronic form at http://www.aanda.orgFull Table B.1 and optical spectra are only available in electronic form 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/527/A24

Lodieu, N.; Dobbie, P. D.; Hambly, N. C.

2011-03-01

102

Using Proxy Stars to Reduce Radius and Temperature Estimates for Low-Mass Kepler Objects of Interest  

NASA Astrophysics Data System (ADS)

The number of exoplanets being found around low-mass stars continues to increase, but study of these planets is complicated by the difficulty of characterizing their host stars. While empirical metrics and synthetic spectra enable stellar characterization for cooler and hotter stellar types, respectively, stars in the range between M1 and K5 are especially challenging. Since nearly all exoplanets are discovered indirectly by the effect they produce on their host stars, the errors in these stellar parameters for low-mass stars result in correspondingly large errors in the size and temperature of the planets around them. For planets near their stellar habitable zones, this uncertainty is especially salient. We improve this accuracy for a sample of planet candidates discovered by the Kepler Space Telescope by assigning the temperatures and radii of nearby "proxy" stars, which have had their radii measured directly, to our target stars. We identify these proxy stars by using spectral typing software to compare the spectra of planet hosting stars to the spectra of similar nearby stars. By assigning them the parameters of the proxy stars, we reduce the uncertainties in size and temperature for the planet hosting stars. This also reduces the uncertainties in the size and temperature of the exoplanets, and thus allows us to better characterize their habitability.

Brown, Justin; Ballard, S.

2013-06-01

103

Sloan Low-mass Wide Pairs of Kinematically Equivalent Stars (SLoWPoKES): A Catalog of Very Wide, Low-mass Pairs  

NASA Astrophysics Data System (ADS)

We present the Sloan Low-mass Wide Pairs of Kinematically Equivalent Stars (SLoWPoKES), a catalog of 1342 very-wide (projected separation gsim500 AU), low-mass (at least one mid-K to mid-M dwarf component) common proper motion pairs identified from astrometry, photometry, and proper motions in the Sloan Digital Sky Survey. A Monte Carlo-based Galactic model is constructed to assess the probability of chance alignment for each pair; only pairs with a probability of chance alignment <=0.05 are included in the catalog. The overall fidelity of the catalog is expected to be 98.35%. The selection algorithm is purposely exclusive to ensure that the resulting catalog is efficient for follow-up studies of low-mass pairs. The SLoWPoKES catalog is the largest sample of wide, low-mass pairs to date and is intended as an ongoing community resource for detailed study of bona fide systems. Here, we summarize the general characteristics of the SLoWPoKES sample and present preliminary results describing the properties of wide, low-mass pairs. While the majority of the identified pairs are disk dwarfs, there are 70 halo subdwarf (SD) pairs and 21 white dwarf-disk dwarf pairs, as well as four triples. Most SLoWPoKES pairs violate the previously defined empirical limits for maximum angular separation or binding energies. However, they are well within the theoretical limits and should prove very useful in putting firm constraints on the maximum size of binary systems and on different formation scenarios. We find a lower limit to the wide binary frequency (WBF) for the mid-K to mid-M spectral types that constitute our sample to be 1.1%. This frequency decreases as a function of Galactic height, indicating a time evolution of the WBF. In addition, the semi-major axes of the SLoWPoKES systems exhibit a distinctly bimodal distribution, with a break at separations around 0.1 pc that is also manifested in the system binding energy. Compared with theoretical predictions for the disruption of binary systems with time, we conclude that the SLoWPoKES sample comprises two populations of wide binaries: an "old" population of tightly bound systems, and a "young" population of weakly bound systems that will not survive more than a few Gyr. The SLoWPoKES catalog and future ancillary data are publicly available on the Internet for utilization by the astronomy community.

Dhital, Saurav; West, Andrew A.; Stassun, Keivan G.; Bochanski, John J.

2010-06-01

104

Class I methanol masers in low-mass star-forming regions  

NASA Astrophysics Data System (ADS)

Results of observations of Class I methanol masers in regions of low-mass star formation (MMIL) are summarized and analyzed. Four masers were detected at 44, 84, and 95 GHz towards "chemically active" bipolar outflows in the low-mass star-forming regions NGC1333 I4A, NGC 1333 I2A, HH 25, and L1157. Another maser was found at 36 GHz towards a similar outflow in NGC 2023. Thus, all the detected MMILs are associated with chemically active outflows. The brightness temperatures of the strongest 44-GHz maser spots in NGC 1333 I4A, HH 25, and L1157 exceed 2000 K, whereas the brightness temperature in NGC 1333 I2A is only 176 K, although a rotational-diagram analysis shows that this last source is also amaser. The flux densities of the newly detectedmasers are no higher than 18 Jy, and are much lower than those of strong masers in regions of high-mass star formation (MMIH). The MMIL luminosities match the maser luminosity-protostar luminosity relation established earlier for MMIHs. No MMIL variability was detected in 2004-2011. The radial velocities of the newly detected masers are close to the systemic velocities of the associated regions, except for NGC 2023, where the maser radial velocity is lower than the systemic velocity by approximately 3.5 km/s. Thus, the main MMILproperties are similar to those of MMIHs. MMILs are likely to be an extension of the MMIH population toward lower luminosities of both the masers and the associated young stellar objects. The results of VLA observations of MMILs can be explained using a turbulent-cloud model, which predicts that compact maser spots can arise in extended sources because the coherence lengths along some directions randomly appear to be longer than the mean coherence length in a turbulent velocity field. However, one must assume that the column density of methanol towardM1, the strongest maser in L1157, is appreciably higher than the mean column density of the clump B0a where the maser arises. The shape of the maser lines in L1157, forming double profiles with a red asymmetry, may indicate that the masers arise in collapsing clumps. However, although this model may be correct for L1157, it is specific to this source, since none of the other masers observed exhibited a double profile.

Kalenskii, S. V.; Kurtz, S.; Bergman, P.

2013-02-01

105

The Low-mass Interacting Binary System OO Aql Revisited: A New Quadruple System  

NASA Astrophysics Data System (ADS)

In this study we present photometric and spectroscopic variation analysis and an orbital period study of a low-mass interacting system OO Aql. Simultaneous solution of the light and radial velocity curves provides us with the determination of a new set of stellar physical parameters for the primary and the secondary companion, M 1 = 1.05(2) M ?, M 2 = 0.89(2) M ?, R 1 = 1.38(2) R ?, R 2 = 1.28(2) R ?, log (L 1/L ?) = 0.258, and log (L 2/L ?) = 0.117, and the separation of the components was determined to be a = 3.333(16) R ?. Newly obtained parameters yield the distance of the system as 136(8) pc. Analyses of the mid-eclipse times indicate a period increase of ({P}/{\\dot{P}})=4\\times 10^{7} yr that can be interpreted in terms of the mass transfer (dM/dt) = 5 × 10–8 M ? yr–1 from the less massive component to the more massive component. Our new solution confirmed that OO Aql is a multiple system in the form of AB + C + D. We found initial astrophysical parameters for the component of the system and its current age to be 8.6 Gyr using a non-conservative stellar evolution model (EV-TWIN code).

?çli, T.; Koçak, D.; Boz, G. Ç.; Yakut, K.

2013-05-01

106

On the detection of (habitable) super-Earths around low-mass stars using Kepler and transit timing variation method  

Microsoft Academic Search

We present the results of an extensive study of the detectability of Earth-sized planets and super-Earths in the habitable\\u000a zones of cool and low-mass stars using transit timing variation method. We have considered a system consisting of a star,\\u000a a transiting giant planet, and a terrestrial-class perturber, and calculated TTVs for different values of the parameters of\\u000a the system. To

Nader Haghighipour; Sabrina Kirste

2011-01-01

107

Multiplicity among Very-Low Mass Stars and Brown Dwarfs in Alpha Persei and the Pleiades  

NASA Astrophysics Data System (ADS)

Open clusters provide excellent hunting grounds for brown dwarf {BD} searches. The AlphaPer and Pleiades clusters are young {80-120 Myr}, nearby {120-175 pc}, and have low extinction. They are cosidered to be the best-suited places to study the Substellar Mass Function {SMF}. A dozen of cool faint AlphaPer and Pleiades members have been confirmed as ``bona-fide'' BDs with the lithium test. By comparison with those, about 60 very good cluster BD candiates are currently known. The Pleiades SMF obtained using the most recent deep large CCD surveys indicates that BDs are quite numerous but do not make a significant contribution to the total cluster mass. One of the main uncertainties of the SMF is the effect of binary corrections. We propose a WFPC2 search for faint companions to very low-mass cluster stars and BDs. We will use any identified companions to provide empirical constraints on BD evolutionary models, to test our ideas about fragmentation in molecular clouds, and to correct the SMF. The sensitivity of WFPC2 shows that we can readily detect secondaries with masses of about 25 Jupiters orbiting at about 40 AU from our targets. Companions with masses of about 15 Jupiters can be detected at separations of 80 AU.

Martin, Eduardo

2000-07-01

108

An IR search for faint companions to Pleiades very low-mass stars and brown dwarfs  

NASA Astrophysics Data System (ADS)

The Pleiades has been the best site for brown dwarf {BD} searches, with half of the presently "confirmed" BDs being Pleiades members. It is also the only cluster or star-forming region where it is currently possible to estimate the IMF to below the hydrogen burning mass limit with any confidence. We propose to obtain NICMOS images of a set of highly probable very low-mass Pleiades members to search for lower mass companions. We will use any identified companions to provide empirical constraints on BD models and to improve the IMF. In the mass range of interest, Pleiades age BD's are expected to range in temperature from about 2500 to 900 K, and thus are predicted to have a large range in molecular band properties and predicted colors {e.g., within this temperature range one should see the effects of both grain formation and methane formation}. Our choice of NICMOS filters will provide key information on the surface temperature of any detected companion. NICMOS PSF simulations show that we can detect secondaries with masses of about 25 Jupiters orbiting at about 10.3 AU from our targets. Companions with masses about 10 Jupiters can be detected at separations of 35 AU. Therefore, we will explore deeper into the substellar domain of the Pleiades than any previous survey.

Martin, Eduardo

1997-12-01

109

Near-infrared spectroscopy of low mass stars and brown dwarfs  

NASA Astrophysics Data System (ADS)

Motivated by the potential identification by the near- infrared survey 2MASS of a few 103 candidate L and T-dwarfs in the northern sky, an efficient NIR spectrograph, the Cornell Massachusetts Slit Spectrograph (CorMASS), was built specifically for the confirmation and classification of low-mass object candidates. In its first two years of use on the 60-inch telescope at Palomar Observatory, CorMASS has observed over 150 new field late-M and L-dwarf candidates for inclusion in a magnitude-limited spectroscopic survey to improve the statistics of the luminosity function across the stellar—sub-stellar boundary in the solar neighborhood. While many of the observations remain to be reduced and new observations are continuing, 25 new late- M and L-dwarf have been confirmed. In collaboration with other workers, CorMASS has also been used for the confirmation of the brightest known T-dwarf and three wide-separation L-dwarf companions to nearby stars. CorMASS is a compact, low-resolution (R ˜ 300), double-pass prism cross-dispersed near- infrared (NIR) spectrograph. Its 2-dimensional spectral format provides simultaneous coverage from ? ˜ 0.75?m to ? ˜ 2.5?m (z'JHK bands). A remotely operated cold flip mirror permits its NICMOS 3 detector to function as a Ks slit viewer to assist object placement into the 2? x 15? slit.

Wilson, John Christian

2002-06-01

110

NUMERICAL SIMULATIONS OF THERMOHALINE CONVECTION: IMPLICATIONS FOR EXTRA-MIXING IN LOW-MASS RGB STARS  

SciTech Connect

Low-mass stars are known to experience extra-mixing in their radiative zones on the red giant branch (RGB) above the bump luminosity. To determine if the salt-fingering transport of chemical composition driven by {sup 3}He burning is efficient enough to produce RGB extra-mixing, two-dimensional numerical simulations of thermohaline convection for physical conditions corresponding to the RGB case have been carried out. We have found that the effective ratio of a salt finger's length to its diameter a{sub eff} {approx}< 0.5 is more than 10 times smaller than the value needed to reproduce observations (a{sub obs} {approx}> 7). On the other hand, using the thermohaline diffusion coefficient from linear stability analysis together with a = a{sub obs} is able to describe the RGB extra-mixing at all metallicities so well that it is tempting to believe that it may represent the true mechanism. In view of these results, follow-up three-dimensional numerical simulations of thermohaline convection for the RGB case are clearly needed.

Denissenkov, Pavel A., E-mail: pavel.denisenkov@gmail.co [Department of Physics and Astronomy, University of Victoria, P.O. Box 3055, Victoria, B.C., V8W 3P6 (Canada)

2010-11-01

111

The Na 8200 Å Doublet as an Age Indicator in Low-mass Stars  

NASA Astrophysics Data System (ADS)

We investigate the use of the gravity sensitive neutral sodium (Na I) doublet at 8183 Å and 8195 Å (Na 8200 Å doublet) as an age indicator for M dwarfs. We measured the Na doublet equivalent width (EW) in giants, old dwarfs, young dwarfs, and candidate members of the ? Pic moving group using medium-resolution spectra. Our Na 8200 Å doublet EW analysis shows that the feature is useful as an approximate age indicator in M-type dwarfs with (V - K s ) >= 5.0, reliably distinguishing stars older and younger than 100 Myr. A simple derivation of the dependence of the Na EW on temperature and gravity supports the observational results. An analysis of the effects of metallicity shows that this youth indicator is best used on samples with similar metallicity. The age estimation technique presented here becomes useful in a mass regime where traditional youth indicators are increasingly less reliable, is applicable to other alkali lines, and will help identify new low-mass members in other young clusters and associations.

Schlieder, Joshua E.; Lépine, Sébastien; Rice, Emily; Simon, Michal; Fielding, Drummond; Tomasino, Rachael

2012-05-01

112

THE Na 8200 Angstrom-Sign DOUBLET AS AN AGE INDICATOR IN LOW-MASS STARS  

SciTech Connect

We investigate the use of the gravity sensitive neutral sodium (Na I) doublet at 8183 Angstrom-Sign and 8195 Angstrom-Sign (Na 8200 Angstrom-Sign doublet) as an age indicator for M dwarfs. We measured the Na doublet equivalent width (EW) in giants, old dwarfs, young dwarfs, and candidate members of the {beta} Pic moving group using medium-resolution spectra. Our Na 8200 A doublet EW analysis shows that the feature is useful as an approximate age indicator in M-type dwarfs with (V - K{sub s}) {>=} 5.0, reliably distinguishing stars older and younger than 100 Myr. A simple derivation of the dependence of the Na EW on temperature and gravity supports the observational results. An analysis of the effects of metallicity shows that this youth indicator is best used on samples with similar metallicity. The age estimation technique presented here becomes useful in a mass regime where traditional youth indicators are increasingly less reliable, is applicable to other alkali lines, and will help identify new low-mass members in other young clusters and associations.

Schlieder, Joshua E.; Simon, Michal [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794 (United States); Lepine, Sebastien; Rice, Emily [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States); Fielding, Drummond [Department of Physics and Astronomy, Johns Hopkins University, 366 Bloomberg Center, 3400 North Charles Street, Baltimore, MD 21218 (United States); Tomasino, Rachael, E-mail: michal.simon@stonybrook.edu, E-mail: schlieder@mpia-hd.mpg.de, E-mail: lepine@amnh.org, E-mail: erice@amnh.org, E-mail: dfieldi1@jhu.edu, E-mail: tomas1r@cmich.edu [Department of Physics, Central Michigan University, Mount Pleasant, MI 48859 (United States)

2012-05-15

113

Optical and Infrared Constraints on the Evolutionary States of Low Mass X-Ray Binary Stars  

NASA Astrophysics Data System (ADS)

The most luminous stellar X-ray sources are interacting binaries in which matter from a 'normal' star is transferred to either a neutron star (NS) or black hole. Two groups of X-ray binaries are generally distinguished base the nature of the mass donating star, the high mass X-ray binaries and the low mass X-ray binaries (LMXBs). The X-ray brightest LMXBs fall into two classes characterized by their X-ray time and spectral variability. They are termed Z sources and Atoll sources according to the pattern they trace in the X-ray color-color diagram. The Z sources are believed to have both higher accretion rates and stronger NS magnetic fields than the Atoll sources. It has been suggested that this difference has its origin in evolutionary histories that lead to evolved companions for Z and dwarf companions for Atoll sources. Longer orbital periods are consequently expected for Z sources when compared to Atoll sources. The orbital period distribution of sources observed seemed to support this scenario, although only a small number of periods were known. We obtained observations of several additional Atoll and Z sources in an effort to determine their orbital periods and? uncover other clues that would indicate the evolutionary state of the mass donor in each system. We determined the orbital period of the Z source GX 349+2 to be 22.5 hours, in line with expectations. Our observations of four Atoll sources, however, fail to confirm the expected correlation between dwarf secondaries and Atoll sources. While V801 Ara is found to be similar to other short period Atoll sources, strong evidence points towards a long orbital period in GX 13+1. For X0614+091 and X1608-52, both long and short orbital periods are compatible with the observed photometric and spectroscopic behavior. As more detailed studies of Z and Atoll sources become available, it appears increasingly difficult to unite all observed characteristics under one consistent model. The exact appearance of an Atoll or Z source might depend on the interplay of very subtle variations of many factors, such as NS properties, mass accretion rate, inclination, and evolutionary history.

Wachter, Stefanie

114

INTERACTIONS BETWEEN FORMING STARS AND DENSE GAS IN THE SMALL LOW-MASS CLUSTER CEDERBLAD 110  

SciTech Connect

We present observations of dense gas and outflow activity in the Cederblad 110 region of the Chamaeleon I dark cloud complex. The region contains nine forming low-mass stars in evolutionary stages ranging from Class 0 to Class II/III crowded into a 0.2 pc region with high surface density ({Sigma}{sub YSO} {approx} 150 pc{sup -2}). The analysis of our N{sub 2}H{sup +} (J = 1{yields}0) maps indicates the presence of 13 {+-} 3 solar masses of dense (n {approx} 10{sup 5} cm{sup -3}) gas in this region, much of which is unstable against gravitational collapse. The most unstable material is located near the Class 0 source MMS-1, which is almost certainly actively accreting material from its dense core. Smaller column densities of more stable dense gas are found toward the region's Class I sources, IRS 4, 11, and 6. Little or no dense gas is colocated with the Class II and III sources in the region. The outflow from IRS 4 is interacting with the dense core associated with MMS-1. The molecular component of the outflow, measured in the (J = 1{yields}0) line of {sup 12}CO, appears to be deflected by the densest part of the core, after which it appears to plow through some of the lower column density portions of the core. The working surface between the head of the outflow lobe and the dense core material can be seen in the enhanced velocity dispersion of the dense gas. IRS 2, the Class III source that produces the optical reflection nebula that gives the Cederblad 110 region its name, may also be influencing the dense gas in the region. A dust temperature gradient across the MMS-1 dense core is consistent with warming from IRS 2, and a sharp gradient in dense gas column density may be caused by winds from this source. Taken together, our data indicate that this region has been producing several young stars in the recent past, and that sources which began forming first are interacting with the remaining dense gas in the region, thereby influencing current and future star formation activity.

Ladd, E. F. [Department of Physics and Astronomy, Bucknell University, Lewisburg, PA 17837 (United States); Wong, T. [Department of Astronomy, University of Illinois, Urbana, IL 61801 (United States); Bourke, T. L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Thompson, K. L., E-mail: ladd@bucknell.edu [Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506 (United States)

2011-12-20

115

The joint evolution of normal and compact magnetized stars in low-mass binary systems - The analytical description of degenerate component evolution  

NASA Astrophysics Data System (ADS)

The evolution of the magnetized degenerate component (white dwarf, neutron star) in a low-mass binary system is described. The possible evolutionary paths of such stars in the lg P - lg (M/?2) diagram are considered qualitatively.

Lipunov, V. M.; Postnov, K. A.

1987-08-01

116

Spatially resolved H2 emission from a very low-mass star  

NASA Astrophysics Data System (ADS)

Context. Molecular outflows from very low-mass stars (VLMSs) and brown dwarfs have been studied very little. So far, only a few CO outflows have been observed, allowing us to map the immediate circumstellar environment. Aims: We present the first spatially resolved H2 emission around IRS54 (YLW 52), a ~0.1-0.2 M? Class I source. Methods: By means of VLT SINFONI K-band observations, we probed the H2 emission down to the first ~50 AU from the source. Results: The molecular emission shows a complex structure delineating a large outflow cavity and an asymmetric molecular jet. Thanks to the detection of several H2 transitions, we are able to estimate average values along the jet-like structure (from source position to knot D) of AV ~ 28 mag, T ~ 2000-3000 K, and H2 column density N(H2) ~ 1.7 × 1017 cm-2. This allows us to estimate a mass loss rate of ~2 × 10-10 M? yr-1 for the warm H2 component. In addition, from the total flux of the Br ? line, we infer an accretion luminosity and mass accretion rate of 0.64 L? and ~3 × 10-7M? yr-1, respectively. The outflow structure is similar to those found in low-mass Class I and CTTS. However, the Lacc/Lbol ratio is very high (~80%), and the mass accretion rate is about one order of magnitude higher when compared to objects of roughly the same mass, pointing to the young nature of the investigated source. Based on observations collected at the European Southern Observatory Paranal, Chile (ESO programme 385.C-0893(A)).Appendices are available in electronic form at http://www.aanda.orgThe reduced datacube 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/552/L2

Garcia Lopez, R.; Caratti o Garatti, A.; Weigelt, G.; Nisini, B.; Antoniucci, S.

2013-04-01

117

Forecasting life: a study of activity cycles in low-mass stars: lessons from long-term stellar light curves.  

PubMed

Magnetic activity cycles are indirect traces of magnetic fields and can provide an insight on the nature and action of stellar dynamos and stellar magnetic activity. This, in turn, can determine local space weather and activity effects on stellar habitable zones. Using photometric monitoring of low-mass stars, we study the presence and properties of their magnetic activity cycles. We introduce long-term light curves of our sample stars, and discuss the properties of the observed trends, especially at spectral types where stars are fully convective (later than M3). PMID:22729352

Kafka, Stella

2012-06-23

118

THE LUMINOSITY AND MASS FUNCTIONS OF LOW-MASS STARS IN THE GALACTIC DISK. II. THE FIELD  

SciTech Connect

We report on new measurements of the luminosity function (LF) and mass function (MF) of field low-mass dwarfs derived from Sloan Digital Sky Survey Data Release 6 photometry. The analysis incorporates {approx}15 million low-mass stars (0.1 M{sub sun}< M < 0.8 M{sub sun}), spread over 8400 deg{sup 2}. Stellar distances are estimated using new photometric parallax relations, constructed from ugriz photometry of nearby low-mass stars with trigonometric parallaxes. We use a technique that simultaneously measures Galactic structure and the stellar LF from 7 < M{sub r} < 16. We compare the LF to previous studies and convert to an MF using the mass-luminosity relations of Delfosse et al. The system MF, measured over -1.0< log M/M{sub sun} <-0.1, is well described by a lognormal distribution with M{sub o} = 0.25 M{sub sun}. We stress that our results should not be extrapolated to other mass regimes. Our work generally agrees with prior low-mass stellar MFs and places strong constraints on future theoretical star formation studies.

Bochanski, John J.; Hawley, Suzanne L.; Ivezic, Zeljko [Astronomy Department, University of Washington, P.O. Box 351580, Seattle, WA 98195 (United States); Covey, Kevin R. [Department of Astronomy, Cornell University, 226 Space Sciences Building, Ithaca, NY 14853 (United States); West, Andrew A. [Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Building 37, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Reid, I. Neill; Golimowski, David A., E-mail: jjb@mit.ed [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2010-06-15

119

The Interior Structure Constants as an Age Diagnostic for Low-mass, Pre-main-sequence Detached Eclipsing Binary Stars  

NASA Astrophysics Data System (ADS)

We propose a novel method for determining the ages of low-mass, pre-main-sequence stellar systems using the apsidal motion of low-mass detached eclipsing binaries. The apsidal motion of a binary system with an eccentric orbit provides information regarding the interior structure constants of the individual stars. These constants are related to the normalized stellar interior density distribution and can be extracted from the predictions of stellar evolution models. We demonstrate that low-mass, pre-main-sequence stars undergoing radiative core contraction display rapidly changing interior structure constants (greater than 5% per 10 Myr) that, when combined with observational determinations of the interior structure constants (with 5%-10% precision), allow for a robust age estimate. This age estimate, unlike those based on surface quantities, is largely insensitive to the surface layer where effects of magnetic activity are likely to be most pronounced. On the main sequence, where age sensitivity is minimal, the interior structure constants provide a valuable test of the physics used in stellar structure models of low-mass stars. There are currently no known systems where this technique is applicable. Nevertheless, the emphasis on time domain astronomy with current missions, such as Kepler, and future missions, such as LSST, has the potential to discover systems where the proposed method will be observationally feasible.

Feiden, Gregory A.; Dotter, Aaron

2013-03-01

120

EVOLUTION, NUCLEOSYNTHESIS, AND YIELDS OF LOW-MASS ASYMPTOTIC GIANT BRANCH STARS AT DIFFERENT METALLICITIES  

SciTech Connect

The envelope of thermally pulsing asymptotic giant branch (TP-AGB) stars undergoing periodic third dredge-up (TDU) episodes is enriched in both light and heavy elements, the ashes of a complex internal nucleosynthesis involving p, {alpha}, and n captures over hundreds of stable and unstable isotopes. In this paper, new models of low-mass AGB stars (2 M {sub sun}), with metallicity ranging between Z = 0.0138 (the solar one) and Z = 0.0001, are presented. Main features are (1) a full nuclear network (from H to Bi) coupled to the stellar evolution code, (2) a mass loss-period-luminosity relation, based on available data for long-period variables, and (3) molecular and atomic opacities for C- and/or N-enhanced mixtures, appropriate for the chemical modifications of the envelope caused by the TDU. For each model, a detailed description of the physical and chemical evolutions is presented; moreover, we present a uniform set of yields, comprehensive of all chemical species (from hydrogen to bismuth). The main nucleosynthesis site is the thin {sup 13}C pocket, which forms in the core-envelope transition region after each TDU episode. The formation of this {sup 13}C pocket is the principal by-product of the introduction of a new algorithm, which shapes the velocity profile of convective elements at the inner border of the convective envelope: both the physical grounds and the calibration of the algorithm are discussed in detail. We find that the pockets shrink (in mass) as the star climbs the AGB, so that the first pockets, the largest ones, leave the major imprint on the overall nucleosynthesis. Neutrons are released by the {sup 13}C({alpha}, n){sup 16}O reaction during the interpulse phase in radiative conditions, when temperatures within the pockets attain T {approx} 1.0 x 10{sup 8} K, with typical densities of (10{sup 6}-10{sup 7}) neutrons cm{sup -3}. Exceptions are found, as in the case of the first pocket of the metal-rich models (Z = 0.0138, Z = 0.006 and Z = 0.003), where the {sup 13}C is only partially burned during the interpulse: the surviving part is ingested in the convective zone generated by the subsequent thermal pulse (TP) and then burned at T {approx} 1.5 x 10{sup 8} K, thus producing larger neutron densities (up to 10{sup 11} neutrons cm{sup -3}). An additional neutron exposure, caused by the {sup 22}Ne({alpha}, n){sup 25}Mg during the TPs, is marginally activated at large Z, but becomes an important nucleosynthesis source at low Z, when most of the {sup 22}Ne is primary. The final surface compositions of the various models reflect the differences in the initial iron-seed content and in the physical structure of AGB stars belonging to different stellar populations. Thus, at large metallicities the nucleosynthesis of light s-elements (Sr, Y, Zr) is favored, whilst, decreasing the iron content, the overproduction of heavy s-elements (Ba, La, Ce, Nd, Sm) and lead becomes progressively more important. At low metallicities (Z = 0.0001) the main product is lead. The agreement with the observed [hs/ls] index observed in intrinsic C stars at different [Fe/H] is generally good. For the solar metallicity model, we found an interesting overproduction of some radioactive isotopes, like {sup 60}Fe, as a consequence of the anomalous first {sup 13}C pocket. Finally, light elements (C, F, Ne, and Na) are enhanced at any metallicity.

Cristallo, S.; Straniero, O.; Piersanti, L. [INAF-Osservatorio Astronomico di Collurania, 64100 Teramo (Italy); Gallino, R. [Dipartimento di Fisica Generale, Universita di Torino, 10125 Torino (Italy); DomInguez, I. [Departamento de Fisica Teorica y del Cosmos, Universidad de Granada, 18071 Granada (Spain); Lederer, M. T. [Institut fuer Astronomie, Tuerkenschanzstrasse 17, A-1180 Wien (Austria)

2009-05-01

121

Evolution, Nucleosynthesis, and Yields of Low-Mass Asymptotic Giant Branch Stars at Different Metallicities  

NASA Astrophysics Data System (ADS)

The envelope of thermally pulsing asymptotic giant branch (TP-AGB) stars undergoing periodic third dredge-up (TDU) episodes is enriched in both light and heavy elements, the ashes of a complex internal nucleosynthesis involving p, ?, and n captures over hundreds of stable and unstable isotopes. In this paper, new models of low-mass AGB stars (2 M sun), with metallicity ranging between Z = 0.0138 (the solar one) and Z = 0.0001, are presented. Main features are (1) a full nuclear network (from H to Bi) coupled to the stellar evolution code, (2) a mass loss-period-luminosity relation, based on available data for long-period variables, and (3) molecular and atomic opacities for C- and/or N-enhanced mixtures, appropriate for the chemical modifications of the envelope caused by the TDU. For each model, a detailed description of the physical and chemical evolutions is presented; moreover, we present a uniform set of yields, comprehensive of all chemical species (from hydrogen to bismuth). The main nucleosynthesis site is the thin 13C pocket, which forms in the core-envelope transition region after each TDU episode. The formation of this 13C pocket is the principal by-product of the introduction of a new algorithm, which shapes the velocity profile of convective elements at the inner border of the convective envelope: both the physical grounds and the calibration of the algorithm are discussed in detail. We find that the pockets shrink (in mass) as the star climbs the AGB, so that the first pockets, the largest ones, leave the major imprint on the overall nucleosynthesis. Neutrons are released by the 13C(?, n)16O reaction during the interpulse phase in radiative conditions, when temperatures within the pockets attain T ~ 1.0 × 108 K, with typical densities of (106-107) neutrons cm-3. Exceptions are found, as in the case of the first pocket of the metal-rich models (Z = 0.0138, Z = 0.006 and Z = 0.003), where the 13C is only partially burned during the interpulse: the surviving part is ingested in the convective zone generated by the subsequent thermal pulse (TP) and then burned at T ~ 1.5 × 108 K, thus producing larger neutron densities (up to 1011 neutrons cm-3). An additional neutron exposure, caused by the 22Ne(?, n)25Mg during the TPs, is marginally activated at large Z, but becomes an important nucleosynthesis source at low Z, when most of the 22Ne is primary. The final surface compositions of the various models reflect the differences in the initial iron-seed content and in the physical structure of AGB stars belonging to different stellar populations. Thus, at large metallicities the nucleosynthesis of light s-elements (Sr, Y, Zr) is favored, whilst, decreasing the iron content, the overproduction of heavy s-elements (Ba, La, Ce, Nd, Sm) and lead becomes progressively more important. At low metallicities (Z = 0.0001) the main product is lead. The agreement with the observed [hs/ls] index observed in intrinsic C stars at different [Fe/H] is generally good. For the solar metallicity model, we found an interesting overproduction of some radioactive isotopes, like 60Fe, as a consequence of the anomalous first 13C pocket. Finally, light elements (C, F, Ne, and Na) are enhanced at any metallicity.

Cristallo, S.; Straniero, O.; Gallino, R.; Piersanti, L.; Domínguez, I.; Lederer, M. T.

2009-05-01

122

A Search for Low Mass Stars and Substellar Companions and A Study of Circumbinary Gas and Dust Disks  

NASA Astrophysics Data System (ADS)

We have searched for nearby low-mass stars and brown dwarfs and have studied the planet-forming environment of binary stars. We have carried out a search for young, low-mass stars in nearby stellar associations using X-ray and UV source catalogs. We discovered a new technique to identify 10-100 Myr-old low-mass stars within 100 pc of the Earth using GALEX-optical/near-IR data. We present candidate young stars found by applying this new method in the 10 Myr old TW Hydrae and Scorpius-Centaurus associations. In addition, we have searched for the coolest brown dwarf class: Y-dwarfs, expected to appear at temperatures <500 K. Using wide-field near infrared imaging with ground (CTIO, Palomar, KPNO) and space (Spitzer, AKARI) observatories, we have looked for companions to nearby, old (2 Gyr or older), high proper motion white dwarfs. We present results for Southern Hemisphere white dwarfs. Additionally, we have characterized how likely planet formation occurs in binary star systems. While 20% of planets have been discovered around one member of a binary system, these binaries have semi-major axes larger than 20 AU. We have performed an AO and spectroscopic search for binary stars among a sample of known debris disk stars, which allows us to indirectly study planet formation and evolution in binary systems. As a case study, we examined the gas and dust present in the circumbinary disk around V4046 Sagittarii, a 2.4-day spectroscopic binary. Our results demonstrate it is unlikely that planets can form in binaries with stellar semi-major axes of 10s of AU. This research has been funded by a NASA ADA grant to UCLA and RIT.

Rodriguez, David R.

2011-01-01

123

The joint evolution of normal and compact magnetized stars in low-mass binary systems - The analytical description of normal component evolution  

NASA Astrophysics Data System (ADS)

The evolution of low-mass binaries is studied with allowance for the spin evolution of the magnetized compact stars within them (white dwarfs, neutron stars). A classification scheme for the evolutionary states of low-mass binary systems is presented together with an analytical description of normal component evolution. The Monte Carlo method was used to construct the present model.

Lipunov, V. M.; Postnov, K. A.

1987-06-01

124

Planets around Low-mass Stars (PALMS). II. A Low-mass Companion to the Young M Dwarf GJ 3629 Separated by 0.2"  

NASA Astrophysics Data System (ADS)

We present the discovery of a 0.2" companion to the young M dwarf GJ 3629 as part of our high-contrast adaptive optics imaging search for giant planets around low-mass stars with the Keck-II and Subaru telescopes. Two epochs of imaging confirm that the pair is comoving and reveal signs of orbital motion. The primary exhibits saturated X-ray emission which, together with its UV photometry from GALEX, points to an age younger than ~300 Myr. At these ages the companion lies below the hydrogen burning limit with a model-dependent mass of 46 ± 16 M Jup based on the system's photometric distance of 22 ± 3 pc. Resolved YJHK photometry of the pair indicates a spectral type of M7 ± 2 for GJ 3629 B. With a projected separation of 4.4 ± 0.6 AU and an estimated orbital period of 21 ± 5 yr, GJ 3629 AB is likely to yield a dynamical mass in the next several years, making it one of only a handful of brown dwarfs to have a measured mass and an age constrained from the stellar primary. Some of the 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.

Bowler, Brendan P.; Liu, Michael C.; Shkolnik, Evgenya L.; Tamura, Motohide

2012-09-01

125

PLANETS AROUND LOW-MASS STARS (PALMS). II. A LOW-MASS COMPANION TO THE YOUNG M DWARF GJ 3629 SEPARATED BY 0.''2  

SciTech Connect

We present the discovery of a 0.''2 companion to the young M dwarf GJ 3629 as part of our high-contrast adaptive optics imaging search for giant planets around low-mass stars with the Keck-II and Subaru telescopes. Two epochs of imaging confirm that the pair is comoving and reveal signs of orbital motion. The primary exhibits saturated X-ray emission which, together with its UV photometry from GALEX, points to an age younger than {approx}300 Myr. At these ages the companion lies below the hydrogen burning limit with a model-dependent mass of 46 {+-} 16 M{sub Jup} based on the system's photometric distance of 22 {+-} 3 pc. Resolved YJHK photometry of the pair indicates a spectral type of M7 {+-} 2 for GJ 3629 B. With a projected separation of 4.4 {+-} 0.6 AU and an estimated orbital period of 21 {+-} 5 yr, GJ 3629 AB is likely to yield a dynamical mass in the next several years, making it one of only a handful of brown dwarfs to have a measured mass and an age constrained from the stellar primary.

Bowler, Brendan P.; Liu, Michael C. [Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Shkolnik, Evgenya L. [Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ 86001 (United States); Tamura, Motohide, E-mail: bpbowler@ifa.hawaii.edu [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)

2012-09-01

126

KIC 1571511B: A Benchmark Low-Mass Star In An Eclipsing Binary System In The Kepler Field  

Microsoft Academic Search

KIC 1571511 is a 14d eclipsing binary (EB) in the Kepler dataset. The secondary of this EB is a very low mass star with a mass of 0.14136 +\\/- 0.00036 M_sun and a radius of 0.17831 +0.00051\\/-0.00062 R_sun (statistical errors only). The overall system parameters make KIC 1571511B an ideal \\

Aviv Ofir; Davide Gandolfi; Lars Buchhave; Claud H. S. Lacy; Artie P. Hatzes; Malcolm Fridlund

2011-01-01

127

The T Tauri Phase Down to Nearly Planetary Masses: Echelle Spectra of 82 Very Low Mass Stars and Brown Dwarfs  

NASA Astrophysics Data System (ADS)

Using the largest high-resolution spectroscopic sample to date of young, very low mass stars and brown dwarfs, we investigate disk accretion in objects ranging from just above the hydrogen-burning limit all the way to nearly planetary masses. Our 82 targets span spectral types from M5 to M9.5, or masses from 0.15 Msolar down to about 15 jupiters. They are confirmed members of the ? Ophiuchus, Taurus, Chamaeleon I, IC 348, R Coronae Australis, Upper Scorpius, and TW Hydrae star-forming regions and young clusters, with ages from <1 to ~10 Myr. The sample contains 41 brown dwarfs (spectral types >=M6.5). We have previously presented high-resolution optical spectra for roughly half the sample; the rest are new. This is a close to complete survey of all confirmed brown dwarfs known so far in the regions examined, except in ? Oph and IC 348 (where we are limited by a combination of extinction and distance). We find that (1) classical T Tauri-like disk accretion persists in the substellar domain down to nearly the deuterium-burning limit; (2) while an H? 10% width >~200 km s-1 is our prime accretion diagnostic (following our previous work), permitted emission lines of Ca II, O I, and He I are also good accretion indicators, just as in classical T Tauri stars (we caution against a blind use of H? width alone, since inclination and rotation effects on the line are especially important at the low accretion rates in very low mass objects); (3) the Ca II ?8662 line flux is an excellent quantitative measure of the accretion rate in very low mass stars and brown dwarfs (as in higher mass classical T Tauri Stars), correlating remarkably well with the M? obtained from veiling and H? modeling; (4) the accretion rate diminishes rapidly with mass-our measurements support previous suggestions that M?~M2* (albeit with considerable scatter) and extend this correlation to the entire range of substellar masses; (5) the fraction of very low mass stellar and substellar accretors decreases substantially with age, as in higher mass stars; (6) at any given age, the fraction of very low mass stellar and substellar accretors is comparable to the accretor fraction in higher mass stars; and (7) a number of our sources with infrared excesses arising from dusty disks do not evince measurable accretion signatures, with the incidence of such a mismatch increasing with age: this implies that disks in the low-mass regime can persist beyond the main accretion phase and parallels the transition from the classical to post-T Tauri stage in more massive stars. These strong similarities at young ages, between higher mass stars on the one hand and low-mass bodies close to and below the hydrogen-burning limit on the other, are consistent with a common formation mechanism in the two mass regimes.

Mohanty, Subhanjoy; Jayawardhana, Ray; Basri, Gibor

2005-06-01

128

Cumulative physical uncertainty in modern stellar models. I. The case of low-mass stars  

NASA Astrophysics Data System (ADS)

Context. Theoretical stellar evolutionary models are still affected by not negligible uncertainties due to the errors in the adopted physical inputs. Aims: In this paper, using our updated stellar evolutionary code, we quantitatively evaluate the effects of the uncertainties in the main physical inputs on the evolutionary characteristics of low mass stars, and thus of old stellar clusters, from the main sequence to the zero age horizontal branch (ZAHB). To this aim we calculated more than 3000 stellar tracks and isochrones, with updated solar mixture, by changing the following physical inputs within their current range of uncertainty: 1H(p, ?e+)2H, 14N(p,?)15O, and triple-? reaction rates, radiative and conductive opacities, neutrino energy losses, and microscopic diffusion velocities. Methods: The analysis was conducted performing a systematic variation on a fixed grid, in a way to obtain a full crossing of the perturbed input values. The effect of the variations of the chosen physical inputs on relevant stellar evolutionary features, such as the turn-off luminosity, the central hydrogen exhaustion time, the red-giant branch tip luminosity, the helium core mass, and the ZAHB luminosity in the RR Lyrae region are analyzed in a statistical way. Results: We find that, for a 0.9 M? model, the cumulative uncertainty on the turn-off, the red-giant branch tip, and the ZAHB luminosities accounts for ±0.02 dex, ±0.03 dex, and ±0.045 dex respectively, while the central hydrogen exhaustion time varies of about ±0.7 Gyr. For all examined features the most relevant effect is due to the radiative opacities uncertainty; for the later evolutionary stages the second most important effect is due to the triple-? reaction rate uncertainty. For an isochrone of 12 Gyr, we find that the isochrone turn-off log luminosity varies of ±0.013 dex, the mass at the isochrone turn-off varies of ±0.015 M?, and the difference between ZAHB and turn-off log-luminosity varies of ±0.05 dex. The effect of the physical uncertainty affecting the age inferred from turn-off luminosity and from the vertical method are of ±0.375 Gyr and ±1.25 Gyr, respectively. Appendices are available in electronic form at http://www.aanda.org

Valle, G.; Dell'Omodarme, M.; Prada Moroni, P. G.; Degl'Innocenti, S.

2013-01-01

129

Vaporizing neutron stars in low-mass x-ray binaries and the statistics of millisecond pulsars  

SciTech Connect

Recent data on low-mass X-ray binaries (LMXBs) and msec pulsars (MSPs) pose a challenge to evolutionary which neglect the effects of disk and companion irradiation. Here we discuss the main features of a radiation-driven (RD) evolutionary model that may be applicable to several LMXBs. According to this model, irradiation from the accreting compact star LMXBs vaporizes'' the accretion disk and the companion star by driving a self-sustained mass loss until a sudden accretion-turn of occurs. The main characteristics of the RD-evolution are: (1) the lifetime of RD-LMXB's is of order 10{sup 7} years or less: (2) both the orbital period gap and the X-ray luminosity may be consequences of RD-evolution of LMXB's containing lower main sequence and degenerate companion stars; (3) the companion star may transfer mass to the primary even if it underfills its Roche lobe; (4) the recycled msec pulsar can continue to vaporize the low-mass companion star even after the accretion turn-off produced by a strong pulsar wind; (5) the RD-evolutionary model resolves the apparent statistical discrepancy between the number of MSP's and their LMXB progenitors. 14 refs., 1 fig., 1 tab.

Tavani, M. (California Univ., Livermore, CA (United States). Inst. of Geophysics and Planetary Physics)

1991-08-08

130

Photometric monitoring of open clusters: Low-mass eclipsing binary stars and the stellar mass-luminosity-radius relation  

NASA Astrophysics Data System (ADS)

This thesis describes a photometric monitoring survey of Galactic star clusters designed to detect low-mass eclipsing binary star systems through variations in their relative lightcurves. The aim is to use cluster eclipsing binaries to measure the masses and radii of M-dwarf stars with ages and metallicities known from studies of brighter cluster stars. This information will provide an improved calibration of the mass-luminosity-radius relation for low-mass stars, be used to test stellar structure and evolution models, and help quantify the contribution of low-mass stars to the global mass census in the Galaxy. The survey is designed to detect eclipse events in stars of ~0.3 M_sun and consists of 600 Gbytes of raw imaging data on six open clusters with a range of ages (~ 0.15 - 4 Gyr) and metallicites (~ -0.2 - 0.0 dex). The clusters NGC 1647 and M 35 contain excellent candidate systems showing eclipse like variations in brightness and photometry consistent with cluster membership. The analysis of these clusters and the eclipsing M-dwarf stars detected in them are presented. Analysis of the candidate system in NGC 1647 confirms the object as a newly discovered M-dwarf eclipsing binary in the cluster with compenent masses of M 1 = 0.47 ± 0.05[Special characters omitted.] and M 2 = 0.19 ± 0.02[Special characters omitted.] . The small mass ratio ( M 2 / M 1 ) and low secondary mass of this object provide an unprecedented opportunity to test stellar models. We find that no stellar evolution models are consistent with all the properties of both M-dwarf stars in the eclipsing binary. The candidate in M 35 has been confirmed as an M-dwarf eclipsing binary, and the masses of the individual components are estimated to be M 1 ~ 0.25 M_sun and M 2 ~ 0.15 M_sun . Additional high resolution spectroscopic and photometric observations, for which we have applied and been awarded time, are necessary to accurately derive the intrinsic properties of the individual stellar components. The completion of our analysis will yield values for the intrinsic properties of four M-dwarf stars of known age and metallicity with masses of ~ 0.5 - 0.1 M_sun.

Hebb, Leslie

2006-06-01

131

THE FORMATION AND EVOLUTION OF YOUNG LOW-MASS STARS WITHIN HALOS WITH HIGH CONCENTRATION OF DARK MATTER PARTICLES  

SciTech Connect

The formation and evolution of low-mass stars within dense halos of dark matter (DM) leads to evolution scenarios quite different from the classical stellar evolution. As a result of our detailed numerical work, we describe these new scenarios for a range of DM densities on the host halo, for a range of scattering cross sections of the DM particles considered, and for stellar masses from 0.7 to 3 M {sub sun}. For the first time, we also computed the evolution of young low-mass stars in their Hayashi track in the pre-main-sequence phase and found that, for high DM densities, these stars stop their gravitational collapse before reaching the main sequence, in agreement with similar studies on first stars. Such stars remain indefinitely in an equilibrium state with lower effective temperatures (|DELTAT{sub eff}|>10{sup 3} K for a star of one solar mass), the annihilation of captured DM particles in their core being the only source of energy. In the case of lower DM densities, these protostars continue their collapse and progress through the main-sequence burning hydrogen at a lower rate. A star of 1 M{sub sun} will spend a time period greater than the current age of the universe consuming all the hydrogen in its core if it evolves in a halo with DM density rho{sub c}hi = 10{sup 9} GeV cm{sup -3}. We also show the strong dependence of the effective temperature and luminosity of these stars on the characteristics of the DM particles and how this can be used as an alternative method for DM research.

Casanellas, Jordi; Lopes, IlIDio, E-mail: jordicasanellas@ist.utl.p, E-mail: ilidio.lopes@ist.utl.p [Centro Multidisciplinar de Astrofisica, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal)

2009-11-01

132

On the detection of (habitable) super-Earths around low-mass stars using Kepler and transit timing variation method  

NASA Astrophysics Data System (ADS)

We present the results of an extensive study of the detectability of Earth-sized planets and super-Earths in the habitable zones of cool and low-mass stars using transit timing variation method. We have considered a system consisting of a star, a transiting giant planet, and a terrestrial-class perturber, and calculated TTVs for different values of the parameters of the system. To identify ranges of the parameters for which these variations would be detectable by Kepler, we considered the analysis presented by Ford et al. (Transit timing observations from Kepler: I. Statistical analysis of the first four months. ArXiv:1102.0544, 2011) and assumed that a peak-to-peak variation of 20 s would be within the range of the photometric sensitivity of this telescope. We carried out simulations for resonant and non-resonant orbits, and identified ranges of the semimajor axes and eccentricities of the transiting and perturbing bodies for which an Earth-sized planet or a super-Earth in the habitable zone of a low-mass star would produce such TTVs. Results of our simulations indicate that in general, outer perturbers near first- and second-order resonances show a higher prospect for detection. Inner perturbers are potentially detectable only when near 1:2 and 1:3 mean-motion resonances. For a typical M star with a Jupiter-mass transiting planet, for instance, an Earth-mass perturber in the habitable zone can produce detectable TTVs when the orbit of the transiting planet is between 15 and 80 days. We present the details of our simulations and discuss the implication of the results for the detection of terrestrial planets around different low-mass stars.

Haghighipour, Nader; Kirste, Sabrina

2011-10-01

133

RADIO INTERFEROMETRIC PLANET SEARCH. I. FIRST CONSTRAINTS ON PLANETARY COMPANIONS FOR NEARBY, LOW-MASS STARS FROM RADIO ASTROMETRY  

SciTech Connect

Radio astrometry of nearby, low-mass stars has the potential to be a powerful tool for the discovery and characterization of planetary companions. We present a Very Large Array survey of 172 active M dwarfs at distances of less than 10 pc. Twenty-nine stars were detected with flux densities greater than 100 {mu}Jy. We observed seven of these stars with the Very Long Baseline Array at milliarcsecond resolution in three separate epochs. With a detection threshold of 500 {mu}Jy in images of sensitivity 1{sigma} {approx} 100 {mu}Jy, we detected three stars three times (GJ 65B, GJ 896A, GJ 4247), one star twice (GJ 285), and one star once (GJ 803). Two stars were undetected (GJ 412B and GJ 1224). For the four stars detected in multiple epochs, residuals from the optically determined apparent motions have an root-mean-square deviation of {approx}0.2 milliarcseconds, consistent with statistical noise limits. Combined with previous optical astrometry, these residuals provide acceleration upper limits that allow us to exclude planetary companions more massive than 3-6 M{sub Jup} at a distance of {approx}1 AU with a 99% confidence level.

Bower, Geoffrey C.; Bolatto, Alberto; Ford, Eric B.; Kalas, Paul [Astronomy Department and Radio Astronomy Laboratory, University of California, Berkeley, CA 94720 (United States)], E-mail: gbower@astro.berkeley.edu

2009-08-20

134

The Specific Star Formation Rate and Stellar Mass Fraction of Low-mass Central Galaxies in Cosmological Simulations  

NASA Astrophysics Data System (ADS)

By means of cosmological N-body + hydrodynamics simulations of galaxies in the context of the ? cold dark matter (?CDM) scenario we explore the specific star formation rates (SSFR = SFR/Ms , Ms is the stellar mass) and stellar mass fractions (Fs ? Ms /Mh , Mh is the halo mass) for sub-M* field galaxies at different redshifts (0 <~ z <~ 1.5). Distinct low-mass halos (2.5 <~ Mh /1010 M sun <~ 50 at z = 0) were selected for the high-resolution re-simulations. The Hydrodynamics Adaptive Refinement Tree (ART) code was used and some variations of the sub-grid parameters were explored. Most simulated galaxies, specially those with the highest resolutions, have significant disk components and their structural and dynamical properties are in reasonable agreement with observations of sub-M* field galaxies. However, the SSFRs are 5-10 times smaller than the averages of several (compiled and homogenized here) observational determinations for field blue/star-forming galaxies at z < 0.3 (at low masses, most observed field galaxies are actually blue/star forming). This inconsistency seems to remain even at z ~ 1-1.5, although it is less drastic. The Fs of simulated galaxies increases with Mh as semi-empirical inferences show. However, the values of Fs at z ? 0 are ~5-10 times larger in the simulations than in the inferences; these differences increases probably to larger factors at z ~ 1-1.5. The inconsistencies reported here imply that simulated low-mass galaxies (0.2 <~ Ms /109 M sun <~ 30 at z = 0) assembled their stellar masses much earlier than observations suggest. Our results confirm the predictions found by means of ?CDM-based models of disk galaxy formation and evolution for isolated low-mass galaxies, and highlight that our understanding and implementation of astrophysics into simulations and models are still lacking vital ingredients.

Avila-Reese, V.; Colín, P.; González-Samaniego, A.; Valenzuela, O.; Firmani, C.; Velázquez, H.; Ceverino, D.

2011-08-01

135

DISCOVERY OF A LOW-MASS COMPANION TO A METAL-RICH F STAR WITH THE MARVELS PILOT PROJECT  

SciTech Connect

We report the discovery of a low-mass companion orbiting the metal-rich, main sequence F star TYC 2949-00557-1 during the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS) pilot project. The host star has an effective temperature T{sub eff} = 6135 {+-} 40 K, logg = 4.4 {+-} 0.1, and [Fe/H] = 0.32 {+-} 0.01, indicating a mass of M = 1.25 {+-} 0.09 M{sub sun} and R = 1.15 {+-} 0.15 R{sub sun}. The companion has an orbital period of 5.69449 {+-} 0.00023 days and straddles the hydrogen burning limit with a minimum mass of 64 M{sub J} , and thus may be an example of the rare class of brown dwarfs orbiting at distances comparable to those of 'Hot Jupiters'. We present relative photometry that demonstrates that the host star is photometrically stable at the few millimagnitude level on time scales of hours to years, and rules out transits for a companion of radius {approx}>0.8 R{sub J} at the 95% confidence level. Tidal analysis of the system suggests that the star and companion are likely in a double synchronous state where both rotational and orbital synchronization have been achieved. This is the first low-mass companion detected with a multi-object, dispersed, fixed-delay interferometer.

Fleming, Scott W.; Ge Jian; Mahadevan, Suvrath; Lee, Brian; Cuong Nguyen, Duy; Morehead, Robert C.; Wan Xiaoke; Zhao Bo; Liu Jian; Guo Pengcheng; Kane, Stephen R. [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 326711-2055 (United States); Eastman, Jason D.; Siverd, Robert J.; Scott Gaudi, B. [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Niedzielski, Andrzej [Torun Center for Astronomy, Nicolaus Copernicus University, ul. Gagarina 11, 87-100, Torun (Poland); Sivarani, Thirupathi [Indian Institute of Astrophysics, Bangalore 560034 (India); Stassun, Keivan G.; Gary, Bruce [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Wolszczan, Alex [Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States); Barnes, Rory, E-mail: scfleming@astro.ufl.ed [Department of Astronomy, University of Washington, P.O. Box 351580, Seattle, WA 98195 (United States)

2010-08-01

136

Stochastic Star Formation in Low Mass Galaxies: A case study of DDO 210  

Microsoft Academic Search

To address the longstanding question of whether dwarf galaxies have bursty star formation histories requires a large sample of dwarf galaxies and an accurate tracer of star formation. Here we explore the utility of using two common tracers, H-alpha and the ultraviolet (UV). H-alpha and UV photons are primarily produced by massive stars, so stochastic effects come into play when

Christina A. Tremonti; J. C. Lee; L. van Zee; R. C. Kennicutt; A. Gil de Paz; S. Sakai; J. Funes; S. Akiyama

2007-01-01

137

Star Formation History of a Young Super-Star Cluster in NGC 4038/39: Direct Detection of Low-Mass Pre-Main Sequence Stars  

NASA Astrophysics Data System (ADS)

We present an analysis of the near-infrared spectrum of a young massive star cluster in the overlap region of the interacting galaxies NGC 4038/39 using population synthesis models. Our goal is to model the cluster population as well as provide rough constraints on its initial mass function (IMF). The cluster shows signs of youth, such as thermal radio emission and strong hydrogen emission lines in the near-infrared. Late-type absorption lines are also present which are indicative of late-type stars in the cluster. The strength and ratio of these absorption lines cannot be reproduced through either late-type pre-main sequence (PMS) stars or red supergiants alone. Thus, we interpret the spectrum as a superposition of two star clusters of different ages, which is feasible since the 1'' spectrum encompasses a physical region of ?90 pc and radii of super-star clusters (SSCs) are generally measured to be a few parsecs. One cluster is young (<= 3 Myr) and is responsible for part of the late-type absorption features, which are due to PMS stars in the cluster, and the hydrogen emission lines. The second cluster is older (6 Myr-18 Myr) and is needed to reproduce the overall depth of the late-type absorption features in the spectrum. Both are required to accurately reproduce the near-infrared spectrum of the object. Thus, we have directly detected PMS objects in an unresolved SSC for the first time using a combination of population synthesis models and PMS tracks. This analysis serves as a testbed of our technique to constrain the low-mass IMF in young SSCs as well as an exploration of the star formation history of young UC H II regions.

Greissl, Julia; Meyer, Michael R.; Christopher, Micol H.; Scoville, Nick Z.

2010-02-01

138

Impact of internal gravity waves on the rotation profile inside pre-main sequence low-mass stars  

NASA Astrophysics Data System (ADS)

Aims: We study the impact of internal gravity waves (IGW), meridional circulation, shear turbulence, and stellar contraction on the internal rotation profile and surface velocity evolution of solar metallicity low-mass pre-main sequence stars. Methods: We compute a grid of rotating stellar evolution models with masses between 0.6 and 2.0 M? taking these processes into account for the transport of angular momentum, as soon as the radiative core appears and assuming no more disk-locking from that moment on. IGW generation along the PMS is computed taking Reynolds-stress and buoyancy into account in the bulk of the stellar convective envelope and convective core (when present). Redistribution of angular momentum within the radiative layers accounts for damping of prograde and retrograde IGW by thermal diffusivity and viscosity in corotation resonance. Results: Over the whole mass range considered, IGW are found to be efficiently generated by the convective envelope and to slow down the stellar core early on the PMS. In stars more massive than ~1.6 M?, IGW produced by the convective core also contribute to angular momentum redistribution close to the ZAMS. Conclusions: Overall, IGW are found to significantly change the internal rotation profile of PMS low-mass stars.

Charbonnel, C.; Decressin, T.; Amard, L.; Palacios, A.; Talon, S.

2013-06-01

139

KIC 1571511B: a benchmark low-mass star in an eclipsing binary system in the Kepler field  

NASA Astrophysics Data System (ADS)

KIC 1571511 is a 14-d eclipsing binary (EB) in the Kepler data set. The secondary of this EB is a very low mass star with a mass of ? and a radius of ? (statistical errors only). The overall system parameters make KIC 1571511B an ideal 'benchmark object': among the smallest, lightest and best-described stars known, smaller even than some known exoplanet. Currently available photometry encompasses only a small part of the total: future Kepler data releases promise to constrain many of the properties of KIC 1571511B to unprecedented level. However, as in many spectroscopic single-lined systems, the current error budget is dominated by the modelling errors of the primary and not by the above statistical errors. We conclude that detecting the RV signal of the secondary component is crucial to achieving the full potential of this possible benchmark object for the study of low-mass stars. Footnotes<label>1</label>Kepler Data Processing Handbook section 9.3, document number KSCI-19081-001 of 2011 April 1.<label>2</label>See Kepler Instrument Handbook, document KSCI-19033, for full description.</p> <div class="credits"> <p class="dwt_author">Ofir, A.; Gandolfi, D.; Buchhave, Lars; Lacy, C. H. S.; Hatzes, A. P.; Fridlund, Malcolm</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">140</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012EPJWC..1902009C"> <span id="translatedtitle">S-process in <span class="hlt">low-mass</span> extremely metal-poor <span class="hlt">stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present post-processing s-process calculations for the core He-flash of a 1M? <span class="hlt">star</span> with and Z = 10-8. Our model shows neutron densities larger than 1014cm-3, resulting in the production of s-process elements. The model reproduces the C, O, Sr, and Ba abundances of the <span class="hlt">star</span> hyper metal-poor <span class="hlt">star</span> HE0107-5240 within a factor of 4.</p> <div class="credits"> <p class="dwt_author">Cruz, M. A.; Serenelli, A.; Weiss, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-02-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_6");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return 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onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_9");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">141</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.hq.eso.org/public/archives/releases/sciencepapers/eso0950/eso0950.pdf"> <span id="translatedtitle">A super-Earth transiting a nearby <span class="hlt">low-mass</span> <span class="hlt">star</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A decade ago, the detection of the first transiting extrasolar planet provided a direct constraint on its composition and opened the door to spectroscopic investigations of extrasolar planetary atmospheres. Because such characterization studies are feasible only for transiting systems that are both nearby and for which the planet-to-<span class="hlt">star</span> radius ratio is relatively large, nearby small <span class="hlt">stars</span> have been surveyed intensively.</p> <div class="credits"> <p class="dwt_author">David Charbonneau; Zachory K. Berta; Jonathan Irwin; Christopher J. Burke; Philip Nutzman; Lars A. Buchhave; Christophe Lovis; Xavier Bonfils; David W. Latham; Stéphane Udry; Ruth A. Murray-Clay; Matthew J. Holman; Emilio E. Falco; Joshua N. Winn; Didier Queloz; Francesco Pepe; Michel Mayor; Xavier Delfosse; Thierry Forveille</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">142</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/200777"> <span id="translatedtitle">HABITABLE ZONES AROUND <span class="hlt">LOW</span> <span class="hlt">MASS</span> <span class="hlt">STARS</span> AND THE SEARCH FOR EXTRATERRESTRIAL LIFE</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">. Habitable planets are likely to exist around <span class="hlt">stars</span> not too different from the Sun ifcurrent theories about terrestrial climate evolution are correct. Some of these planets may haveevolved life, and some of the inhabited planets may have evolved O 2 -rich atmospheres. Suchatmospheres could be detected spectroscopically on planets around nearby <span class="hlt">stars</span> using a spacebasedinterferometer to search for the</p> <div class="credits"> <p class="dwt_author">James F. Kasting</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">143</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/53396063"> <span id="translatedtitle">Triggered Collapse, Magnetic Fields, and Very <span class="hlt">Low</span> <span class="hlt">Mass</span> <span class="hlt">Star</span> Formation (Invited Review)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Protostellar collapse calculations traditionally ignore the effects of nearby <span class="hlt">stars</span> and of magnetic fields. Including these effects can help answer several questions, such as the origin of the Solar System and of free-floating planetary mass objects. Shock waves derived from massive <span class="hlt">stars</span> can trigger the collapse of an otherwise stable dense cloud core, leading to the formation of single or</p> <div class="credits"> <p class="dwt_author">A. P. Boss</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">144</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/9150578"> <span id="translatedtitle">Habitable zones around <span class="hlt">low</span> <span class="hlt">mass</span> <span class="hlt">stars</span> and the search for extraterrestrial life.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Habitable planets are likely to exist around <span class="hlt">stars</span> not too different from the Sun if current theories about terrestrial climate evolution are correct. Some of these planets may have evolved life, and some of the inhabited planets may have evolved O2-rich atmospheres. Such atmospheres could be detected spectroscopically on planets around nearby <span class="hlt">stars</span> using a space-based interferometer to search for the 9.6 micron band of O3. Planets with O2-rich atmospheres that lie within the habitable zone around their parent <span class="hlt">star</span> are, in all probability, inhabited. PMID:9150578</p> <div class="credits"> <p class="dwt_author">Kasting, J F</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">145</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21578203"> <span id="translatedtitle">THE SPECIFIC <span class="hlt">STAR</span> FORMATION RATE AND STELLAR MASS FRACTION OF <span class="hlt">LOW-MASS</span> CENTRAL GALAXIES IN COSMOLOGICAL SIMULATIONS</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">By means of cosmological N-body + hydrodynamics simulations of galaxies in the context of the {Lambda} cold dark matter ({Lambda}CDM) scenario we explore the specific <span class="hlt">star</span> formation rates (SSFR = SFR/M{sub s} , M{sub s} is the stellar mass) and stellar mass fractions (F{sub s} {identical_to} M{sub s} /M{sub h} , M{sub h} is the halo mass) for sub-M* field galaxies at different redshifts (0 {approx}< z {approx}< 1.5). Distinct <span class="hlt">low-mass</span> halos (2.5 {approx}< M{sub h} /10{sup 10} M{sub sun} {approx}< 50 at z = 0) were selected for the high-resolution re-simulations. The Hydrodynamics Adaptive Refinement Tree (ART) code was used and some variations of the sub-grid parameters were explored. Most simulated galaxies, specially those with the highest resolutions, have significant disk components and their structural and dynamical properties are in reasonable agreement with observations of sub-M* field galaxies. However, the SSFRs are 5-10 times smaller than the averages of several (compiled and homogenized here) observational determinations for field blue/<span class="hlt">star</span>-forming galaxies at z < 0.3 (at <span class="hlt">low</span> <span class="hlt">masses</span>, most observed field galaxies are actually blue/<span class="hlt">star</span> forming). This inconsistency seems to remain even at z {approx} 1-1.5, although it is less drastic. The F{sub s} of simulated galaxies increases with M{sub h} as semi-empirical inferences show. However, the values of F{sub s} at z {approx} 0 are {approx}5-10 times larger in the simulations than in the inferences; these differences increases probably to larger factors at z {approx} 1-1.5. The inconsistencies reported here imply that simulated <span class="hlt">low-mass</span> galaxies (0.2 {approx}< M{sub s} /10{sup 9} M{sub sun} {approx}< 30 at z = 0) assembled their stellar masses much earlier than observations suggest. Our results confirm the predictions found by means of {Lambda}CDM-based models of disk galaxy formation and evolution for isolated <span class="hlt">low-mass</span> galaxies, and highlight that our understanding and implementation of astrophysics into simulations and models are still lacking vital ingredients.</p> <div class="credits"> <p class="dwt_author">Avila-Reese, V.; Gonzalez-Samaniego, A.; Valenzuela, O.; Firmani, C. [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, A. P. 70-264, 04510, Mexico, D. F. (Mexico); ColIn, P. [Centro de Radioastronomia y Astrofisica, Universidad Nacional Autonoma de Mexico, A. P. 72-3 (Xangari), Morelia, Michoacan 58089 (Mexico); Velazquez, H. [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, A. P. 877, Ensenada BC 22800 (Mexico); Ceverino, D. [Racah Institute of Physics, The Hebrew University, Jerusalem 91904 (Israel)</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">146</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22047681"> <span id="translatedtitle">A LIKELY CLOSE-IN <span class="hlt">LOW-MASS</span> STELLAR COMPANION TO THE TRANSITIONAL DISK <span class="hlt">STAR</span> HD 142527</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">With the uniquely high contrast within 0.''1 ({Delta}mag(L') = 5-6.5 mag) available using Sparse Aperture Masking with NACO at Very Large Telescope, we detected asymmetry in the flux from the Herbig Fe <span class="hlt">star</span> HD 142527 with a barycenter emission situated at a projected separation of 88 {+-} 5 mas (12.8 {+-} 1.5 AU at 145 pc) and flux ratios in H, K, and L' of 0.016 {+-} 0.007, 0.012 {+-} 0.008, and 0.0086 {+-} 0.0011, respectively (3{sigma} errors), relative to the primary <span class="hlt">star</span> and disk. After extensive closure-phase modeling, we interpret this detection as a close-in, <span class="hlt">low-mass</span> stellar companion with an estimated mass of {approx}0.1-0.4 M{sub Sun }. HD 142527 has a complex disk structure, with an inner gap imaged in both the near and mid-IR as well as a spiral feature in the outer disk in the near-IR. This newly detected <span class="hlt">low-mass</span> stellar companion may provide a critical explanation of the observed disk structure.</p> <div class="credits"> <p class="dwt_author">Biller, Beth; Benisty, Myriam; Chauvin, Gael; Olofsson, Johan; Pott, Joerg-Uwe; Mueller, Andre; Bonnefoy, Mickaeel; Henning, Thomas [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg (Germany); Lacour, Sylvestre; Thebault, Philippe [LESIA, CNRS/UMR-8109, Observatoire de Paris, UPMC, Universite Paris Diderot, 5 place Jules Janssen, 92195 Meudon (France); Juhasz, Attila [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Sicilia-Aguilar, Aurora [Departamento de Fisica Teorica, Facultad de Ciencias, Universidad Autonoma de Madrid, 28049 Cantoblanco, Madrid (Spain); Tuthill, Peter [School of Physics, University of Sydney, NSW 2006 (Australia); Crida, Aurelien, E-mail: biller@mpia.de [Universite de Nice - Sophia antipolis/C.N.R.S./Observatoire de la Cote d'Azur, Laboratoire Lagrange (UMR 7293), Boulevard de l'Observatoire, B.P. 4229 06304 NICE cedex 04 (France)</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-07-10</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">147</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21301428"> <span id="translatedtitle">PHYSICAL PROPERTIES OF YOUNG BROWN DWARFS AND VERY <span class="hlt">LOW</span> <span class="hlt">MASS</span> <span class="hlt">STARS</span> INFERRED FROM HIGH-RESOLUTION MODEL SPECTRA</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">By comparing near-infrared spectra with atmospheric models, we infer the effective temperature, surface gravity, projected rotational velocity, and radial velocity for 21 very <span class="hlt">low</span> <span class="hlt">mass</span> <span class="hlt">stars</span> and brown dwarfs. The unique sample consists of two sequences in spectral type from M6-M9, one of 5-10 Myr objects and one of >1 Gyr field objects. A third sequence is comprised of only {approx}M6 objects with ages ranging from <1 Myr to >1 Gyr. Spectra were obtained in the J band at medium (R {approx} 2000) and high (R {approx} 20,000) resolutions with NIRSPEC on the Keck II telescope. Synthetic spectra were generated from atmospheric structures calculated with the PHOENIX model atmosphere code. Using multi-dimensional least-squares fitting and Monte Carlo routines we determine the best-fit model parameters for each observed spectrum and note which spectral regions provide consistent results. We identify successes in the reproduction of observed features by atmospheric models, including pressure-broadened K I lines, and investigate deficiencies in the models, particularly missing FeH opacity, that will need to be addressed in order to extend our analysis to cooler objects. The precision that can be obtained for each parameter using medium- and high-resolution near-infrared spectra is estimated and the implications for future studies of very <span class="hlt">low</span> <span class="hlt">mass</span> <span class="hlt">stars</span> and brown dwarfs are discussed.</p> <div class="credits"> <p class="dwt_author">Rice, Emily L.; Mclean, Ian S. [Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1562 (United States); Barman, T.; Prato, L. [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Kirkpatrick, J. Davy [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States)], E-mail: erice@amnh.org</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">148</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012AIPC.1480..397N"> <span id="translatedtitle">Long duration X-ray flash from <span class="hlt">low</span> <span class="hlt">mass</span> population III <span class="hlt">stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Recent numerical simulations suggest that the typical mass of a Population III (Pop III) <span class="hlt">star</span> become ~ 40Msolar. We investigate if a Pop III <span class="hlt">star</span> can raise a gamma ray burst (GRB) by considering the jet propagation in the stellar envelope for a 40Msolar Pop III model. We find that a relativistic jet launched from the central black hole pierces the stellar envelope, although a Pop III <span class="hlt">star</span> has a large envelope since the mass loss is not expected for zero metallicity <span class="hlt">stars</span>. Thus, a Pop III <span class="hlt">star</span> can be the progenitor of a GRB. We predict that GRBs from 40Msolar Pop III progenitors have much longer duration ~ 105 sec, slightly lower luminosity ~6×1050 erg/sec and much softer spectrum peak energy ~ 5 keV than the local long GRBs. Therefore, observationally, we regard a Pop III GRB as a long duration X-ray flash. We can observe such Pop III GRBs using the future detector Lobster.</p> <div class="credits"> <p class="dwt_author">Nakauchi, Daisuke; Suwa, Yudai; Kashiyama, Kazumi; Nakamura, Takashi</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">149</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1998A%26A...335..959T"> <span id="translatedtitle">The Li dip: a probe of angular momentum transport in <span class="hlt">low</span> <span class="hlt">mass</span> <span class="hlt">stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We use the measures of Li and rotational velocities in F Hyades <span class="hlt">stars</span> to assess the role of the wind-driven meridian circulation and of shear turbulence in the transport of angular momentum in <span class="hlt">stars</span> of different masses. Our models include both element segregation and rotation-induced mixing, and we treat simultaneously the transport of matter and angular momentum as described by Zahn (1992) and Maeder (1995). We show that the hot side of the Li dip in the Hyades is well explained within this framework, which was also successfully used to reproduce the C and N anomalies in B type <span class="hlt">stars</span> (Talon et al. 1997). On the cool side of the dip, another mechanism must participate in the transport of angular momentum; its efficiency is linked to the depth of the surface convection zone. That mechanism should also be responsible for the Sun's flat rotation profile.</p> <div class="credits"> <p class="dwt_author">Talon, Suzanne; Charbonnel, Corinne</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">150</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012cosp...39.1947T"> <span id="translatedtitle">Neutron <span class="hlt">star</span> <span class="hlt">low</span> <span class="hlt">mass</span> X-ray binaries monitoring with INTEGRAL</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have been monitoring since 2003 with INTEGRAL a sample of persistent and variable sources of Atoll type, as part of a long time study of X-ray bursters <span class="hlt">Low</span> <span class="hlt">Mass</span> X-ray Binaries to discern their hard X-ray characteristics up to 200-300 keV. By the light curves in different energy bands, by the hardness-intensity diagrams and by the detailed spectral states analysis, we discuss the physical parameters dominating the spectral states variations. Then, we compare the results between the sources themselves, evidencing and confirming a wide variability in this field, not only within the different sources but also within the same source, as evidenced in the last studied case of 4U 1722-30 which showed different type of outbursts with different spectral changes.</p> <div class="credits"> <p class="dwt_author">Tarana, Antonella</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">151</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013ASPC..470..263C"> <span id="translatedtitle">Detecting donor <span class="hlt">star</span> signatures in <span class="hlt">low</span> <span class="hlt">mass</span> X-ray binaries</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Here I present an overview of the Bowen survey of <span class="hlt">low</span> <span class="hlt">mass</span> X-ray binaries (LMXBs). The Bowen fluorescence technique uses the fact that narrow emission lines arise on the surface of the irradiated donor of LMXBs, making possible to derive a radial velocity curve and thereby constrain the mass of the compact object. I will concentrate on the main results of the last ?4 years, and provide an example that illustrates the validity of the technique (EXO 0748-676). Furthermore I will also illustrate where the results were limited (SAX J1808.4-3658) or did not work. Finally, now that the Bowen fluorescence technique has been applied to most of the optically bright X-ray binaries I will point out several new paths to pursue in the future.</p> <div class="credits"> <p class="dwt_author">Cornelisse, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">152</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008yCat..83852210M"> <span id="translatedtitle">lam Ori and sig Ori <span class="hlt">low-mass</span> <span class="hlt">stars</span> spectroscopy (Maxted+, 2008)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Radial velocities and spectral indices for 218 <span class="hlt">stars</span> and brown dwarfs around {sigma} and {lambda} Orionis. Observations were obtained with the FLAMES/GIRAFFE multi-object spectrograph on ESO's VLT UT2 (Kueyen) telescope (programme ID 076.C_145). The equivalent width of the NaI 8200{AA} and the strength of the TiO 8442{AA} spectral features were measured from the median average spectrum. Radial velocities were measured by cross-correlation against a template spectrum of the brown dwarf <span class="hlt">star</span> USco CTIO 055 at multiple epochs. (3 data files).</p> <div class="credits"> <p class="dwt_author">Maxted, P. F. L.; Jeffries, R. D.; Oliveira, J. M.; Naylor, T.; Jackson, R. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">153</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/970021"> <span id="translatedtitle">Radiative feedback by <span class="hlt">low-mass</span> <span class="hlt">stars</span> in the first generation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The survival of cosmological minihalos in both ionizing and Lyman-Werner (LW) UV fields from nearby and distant sources has attracted recent attention for its role in regulating the rise of stellar populations at high red-shifts. Numerical models suggest that the first <span class="hlt">stars</span> form in isolation in small dark matter halos of {approx} 10{sup 5}-10{sup 7} M{sub {circle_dot}} at z {approx} 20-30 and that they are very massive, 25-500 M{sub {circle_dot}}. These <span class="hlt">stars</span> form large H II regions 2.5-5 kpc in radius capable of engulfing nearby halos. With the rise of Population III <span class="hlt">stars</span> throughout the cosmos also comes a global LW background that sterilizes mini-halos of H{sub 2}, delaying or preventing new <span class="hlt">star</span> formation in them. At high redshifts, ionizaing radiation is therefore relatively local while LW photons can originate from many megaparsects away because their energies lie below the ionization limit of H.</p> <div class="credits"> <p class="dwt_author">Whalen, Daniel James [Los Alamos National Laboratory; Hueckstaedt, Robert [Los Alamos National Laboratory; Mcconkie, Thomas [Los Alamos National Laboratory</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">154</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009Natur.462..891C"> <span id="translatedtitle">A super-Earth transiting a nearby <span class="hlt">low-mass</span> <span class="hlt">star</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A decade ago, the detection of the first transiting extrasolar planet provided a direct constraint on its composition and opened the door to spectroscopic investigations of extrasolar planetary atmospheres. Because such characterization studies are feasible only for transiting systems that are both nearby and for which the planet-to-<span class="hlt">star</span> radius ratio is relatively large, nearby small <span class="hlt">stars</span> have been surveyed intensively. Doppler studies and microlensing have uncovered a population of planets with minimum masses of 1.9-10 times the Earth's mass (M?), called super-Earths. The first constraint on the bulk composition of this novel class of planets was afforded by CoRoT-7b (refs 8, 9), but the distance and size of its <span class="hlt">star</span> preclude atmospheric studies in the foreseeable future. Here we report observations of the transiting planet GJ1214b, which has a mass of 6.55M? and a radius 2.68 times Earth's radius (R?), indicating that it is intermediate in stature between Earth and the ice giants of the Solar System. We find that the planetary mass and radius are consistent with a composition of primarily water enshrouded by a hydrogen-helium envelope that is only 0.05% of the mass of the planet. The atmosphere is probably escaping hydrodynamically, indicating that it has undergone significant evolution during its history. The <span class="hlt">star</span> is small and only 13parsecs away, so the planetary atmosphere is amenable to study with current observatories.</p> <div class="credits"> <p class="dwt_author">Charbonneau, David; Berta, Zachory K.; Irwin, Jonathan; Burke, Christopher J.; Nutzman, Philip; Buchhave, Lars A.; Lovis, Christophe; Bonfils, Xavier; Latham, David W.; Udry, Stéphane; Murray-Clay, Ruth A.; Holman, Matthew J.; Falco, Emilio E.; Winn, Joshua N.; Queloz, Didier; Pepe, Francesco; Mayor, Michel; Delfosse, Xavier; Forveille, Thierry</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">155</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009ApJ...698.1068P"> <span id="translatedtitle">New Debris Disks Around Young, <span class="hlt">Low-Mass</span> <span class="hlt">Stars</span> Discovered with the Spitzer Space Telescope</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present 24 ?m and 70 ?m Multiband Imaging Photometer for Spitzer (MIPS) observations of 70 A through M-type dwarfs with estimated ages from 8 Myr to 1.1 Gyr, as part of a Spitzer guaranteed time program, including a re-analysis of some previously published source photometry. Our sample is selected from <span class="hlt">stars</span> with common youth indicators such as lithium abundance, X-ray activity, chromospheric activity, and rapid rotation. We compare our MIPS observations to empirically derived Ks -[24] colors as a function of the stellar effective temperature to identify 24 ?m and 70 ?m excesses. We place constraints or upper limits on dust temperatures and fractional infrared luminosities with a simple blackbody dust model. We confirm the previously published 70 ?m excesses for HD 92945, HD 112429, and AU Mic, and provide updated flux density measurements for these sources. We present the discovery of 70 ?m excesses for five <span class="hlt">stars</span>: HD 7590, HD 10008, HD 59967, HD 73350, and HD 135599. HD 135599 is also a known Spitzer IRS (InfraRed Spectrograph) excess source, and we confirm the excess at 24 ?m. We also present the detection of 24 ?m excesses for 10 <span class="hlt">stars</span>: HD 10008, GJ 3400A, HD 73350, HD 112429, HD 123998, HD 175742, AT Mic, BO Mic, HD 358623 and Gl 907.1. We find that large 70 ?m excesses are less common around <span class="hlt">stars</span> with effective temperatures of less than 5000 K (3.7+7.6 -1.1%) than around <span class="hlt">stars</span> with effective temperatures between 5000 K and 6000 K (21.4+9.5 -5.7%), despite the cooler <span class="hlt">stars</span> having a younger median age in our sample (12 Myr vs. 340 Myr). We find that the previously reported excess for TWA 13A at 70 ?m is due to a nearby background galaxy, and the previously reported excess for HD 177724 is due to saturation of the near-infrared photometry used to predict the mid-infrared stellar flux contribution. In the Appendix, we present an updated analysis of dust grain removal timescales due to grain-grain collisions and radiation pressure, Poynting-Robertson (P-R) drag, stellar wind drag, and planet-dust dynamical interaction. We find that drag forces can be important for disk dynamics relative to grain-grain collisions for L IR/L * < 10-4, and that stellar wind drag is more important than P-R drag for K and M dwarfs, and possibly for young (<1 Gyr) G dwarfs as well.</p> <div class="credits"> <p class="dwt_author">Plavchan, Peter; Werner, M. W.; Chen, C. H.; Stapelfeldt, K. R.; Su, K. Y. L.; Stauffer, J. R.; Song, I.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">156</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/4557464"> <span id="translatedtitle"><span class="hlt">Low-Mass</span> Normal-Matter Atmospheres of Strange <span class="hlt">Stars</span> and Their Radiation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The quark surface of a strange <span class="hlt">star</span> has a very low emissivity for X-ray photons. I find that a small amount of normal matter at the quark surface with temperature in the range 107 K <~ TS << mc2\\/k ~= 6 x 109 K is enough to produce X-rays with high luminosity LX ~= (1032--1034)[ Delta M\\/(10-22 Msolar)]2 ergs s-1.</p> <div class="credits"> <p class="dwt_author">Vladimir V. Usov</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">157</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/56036410"> <span id="translatedtitle">New Debris Disks Around Young, <span class="hlt">Low-Mass</span> <span class="hlt">Stars</span> Discovered with the Spitzer Space Telescope</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We present 24 mum and 70 mum Multiband Imaging Photometer for Spitzer (MIPS) observations of 70 A through M-type dwarfs with estimated ages from 8 Myr to 1.1 Gyr, as part of a Spitzer guaranteed time program, including a re-analysis of some previously published source photometry. Our sample is selected from <span class="hlt">stars</span> with common youth indicators such as lithium abundance,</p> <div class="credits"> <p class="dwt_author">Peter Plavchan; M. W. Werner; C. H. Chen; K. R. Stapelfeldt; K. Y. L. Su; J. R. Stauffer; I. Song</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">158</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/52195939"> <span id="translatedtitle">A study of circumstellar disk properties in <span class="hlt">low-mass</span> <span class="hlt">stars</span> and brown dwarfs</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We present Spitzer Space Telescope IRAC and MIPS observations for a sample of eight M dwarfs: six dMe, one dM, and one sdMe <span class="hlt">star</span>. All of our targets are found to have Spectral Energy Distributions (SEDs) which are fitted within the error bars by a purely photospheric spectrum out to 24m m . The estimated ages for all are >10</p> <div class="credits"> <p class="dwt_author">Basmah Riaz</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">159</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010yCat..35279024L"> <span id="translatedtitle">Spectra of <span class="hlt">low-mass</span> <span class="hlt">stars</span> in Upper Sco (Lodieu+, 2011)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Coordinates (J2000), ZYJHK photometry from the UKIDSS Galactic Clusters Survey, and proper motions derived from the UKIDSS/2MASS cross-match (in arcsec/yr) of <span class="hlt">stars</span> in the AAOmega field-of-view ordered by increasing Z magnitude. The last column provides a tentative estimate of the spectral type. Data obtained with the AAOmega spectrograph on the Anglo-Australian telescope in May 2007. (4 data files).</p> <div class="credits"> <p class="dwt_author">Lodieu, N.; Dobbie, P. D.; Hambly, N. C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">160</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011RMxAC..40..118F"> <span id="translatedtitle">Ionization of the diffuse gas in galaxies: Hot <span class="hlt">low-mass</span> evolved <span class="hlt">stars</span> at work</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Diffuse Ionized Medium (DIG) is visible through its faint optical line emission outside classical HII regions (Reynolds 1971) and turns out to be a major component of the interstellar medium in galaxies. OB <span class="hlt">stars</span> in galaxies likely represent the main source of ionizing photons for the DIG. However, an additional source is needed to explain the increase of [NII]/H?, [SII]/H? with galactic height.</p> <div class="credits"> <p class="dwt_author">Flores-Fajardo, N.; Morisset, C.; Stasinska, G.; Binette, L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-10-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_7");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> 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showDiv("page_10");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">161</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013ApJ...768..108S"> <span id="translatedtitle">The Galactic Center Cloud G2—a Young <span class="hlt">Low-mass</span> <span class="hlt">Star</span> with a Stellar Wind</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We explore the possibility that the G2 gas cloud falling in toward SgrA* is the mass-loss envelope of a young T Tauri <span class="hlt">star</span>. As the <span class="hlt">star</span> plunges to smaller radius at 1000-6000 km s-1, a strong bow shock forms where the stellar wind is impacted by the hot X-ray emitting gas in the vicinity of SgrA*. For a stellar mass-loss rate of 4 × 10-8 M ? yr-1 and wind velocity 100 km s-1, the bow shock will have an emission measure (EM = n 2 vol) at a distance ~1016 cm, similar to that inferred from the IR emission lines. The ionization of the dense bow shock gas is potentially provided by collisional ionization at the shock front and cooling radiation (X-ray and UV) from the post shock gas. The former would predict a constant line flux as a function of distance from SgrA*, while the latter will have increasing emission at lesser distances. In this model, the <span class="hlt">star</span> and its mass-loss wind should survive pericenter passage since the wind is likely launched at 0.2 AU and this is much less than the Roche radius at pericenter (~3 AU for a stellar mass of 2 M ?). In this model, the emission cloud will probably survive pericenter passage, discriminating this scenario from others.</p> <div class="credits"> <p class="dwt_author">Scoville, N.; Burkert, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">162</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6438116"> <span id="translatedtitle">Role of <span class="hlt">low-mass</span> asymptotic giant branch <span class="hlt">stars</span> in producing a solar system distribution of s-process isotopes</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The production of s-isotopes due to the operation of the reaction C-13(alpha, n)O-16 in <span class="hlt">low-mass</span> <span class="hlt">stars</span> during asymptotic giant branch phases is investigated. The time evolution of the thermal pulses, the temperature, and the density stratification within the convective shells is followed in detail, taking into account the effect of the neutron recycling by C-12. The resulting average neutron density reaches a maximum of about 5 x to the 9th/cu cm and then decreases smoothly. Strong overabundances for all s-isotopes with A larger than 80 are obtained in a solar system distribution. The process appears suitable for reproducing many observed details concerning isotopic ratios. Contrary to previous estimates, an anomalous overproduction of Zr-96 is not obtained. 33 references.</p> <div class="credits"> <p class="dwt_author">Gallino, R.; Busso, M.; Picchio, G.; Raiteri, C.M.; Renzini, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1988-11-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">163</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012AIPC.1480..367H"> <span id="translatedtitle">Three-dimensional modelling of proton ingestion episodes in <span class="hlt">low-mass</span> <span class="hlt">stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have modelled a dual shell flash (DSF) in a low-metallicity 1.5Msolar AGB <span class="hlt">star</span> using the 3-dimensional hydrodynamic program "Djehuty", observing how the evolution of these events compares to 1-dimensional models, which are hypothesised to be inaccurate due to the simplifications in the treatment of convective processes. In particular, the stability of the separated convective structure following hydrogen ignition is investigated. In both models constructed, the split convective zone structure was found to be unstable, with the velocities within the inner convective zone increasing until material breaks through the gap and recombines the two regions into a large single convective region.</p> <div class="credits"> <p class="dwt_author">Heap, Stuart A.; Stancliffe, Richard J.; Lattanzio, John C.; Dearborn, David S. P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">164</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1992ApJ...400L..39R"> <span id="translatedtitle">Nonequilibrium iron oxide formation in some <span class="hlt">low-mass</span> post-asymptotic giant branch <span class="hlt">stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Using experimental evidence that under highly oxidizing conditions gamma-Fe2O3 (maghemite) and Fe3O4 display refractory behavior, it is proposed that very low C/O ratios, that could be unique to evolving AGB <span class="hlt">stars</span>, induce nonequilibrium formation of ferromagnetic iron oxide grains along with chondritic dust. The oxides are preferentially fractionated from chondritic dust in the stellar magnetic field which could account for the observed extreme iron underabundance in their photosphere. A search for the 1-2.5-micron IR absorption feature, or for diagnostic magnetite and maghemite IR absorption features, could show the validity of the model proposed.</p> <div class="credits"> <p class="dwt_author">Rietmeijer, Frans J. M.</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-11-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">165</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5663177"> <span id="translatedtitle">Water masers associated with <span class="hlt">low-mass</span> <span class="hlt">stars</span> - a survey of the Rho Ophiuchi infrared cluster</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The detection of H2O masers toward two extremely young premain-sequence objects embedded in the nearby Rho Ophiuchi molecular cloud complex is reported. These embedded sources are among the lowest luminosity objects known to be associated with maser emission. Their proximity presents possibilities for high spatial resolution studies of masers and the near-stellar environment of <span class="hlt">stars</span> in their earliest stage of evolution; using aperture synthesis techniques with VLBI and/or VLBA will result in an unsurpassed resolution of better than 0.2 A.U. The mechanisms resulting in the maser activity of the objects are discussed. 31 references.</p> <div class="credits"> <p class="dwt_author">Wilking, B.A.; Claussen, M.J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">166</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011PhRvD..83f3521L"> <span id="translatedtitle">The capture of dark matter particles through the evolution of <span class="hlt">low-mass</span> <span class="hlt">stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We studied the rate at which <span class="hlt">stars</span> capture dark matter (DM) particles, considering different assumptions regarding the DM characteristics and, in particular, investigating how the stellar physics influences the capture rate. Two scenarios were considered: first, we assumed the maximal values for the spin-dependent and spin-independent DM particle-nucleon scattering cross sections allowed by the limits from direct detection experiments. Second, we considered that both scattering cross sections are of the same order, with the aim of studying the dependencies of the capture rate on stellar elements other than hydrogen. We found that the characteristics of the capture rate are very different in the two scenarios. Furthermore, we quantified the uncertainties on the computed capture rate (C?) and on the ratio between the luminosities from DM annihilations and thermonuclear reactions (L?/Lnuc) derived from an imprecise knowledge of the stellar structure and DM parameters. For instance, while an uncertainty of 10% on the typical DM velocity leads to similar errors on the computed C? and L?/Lnuc, the same uncertainty on the stellar mass becomes more relevant and duplicates the errors. Our results may be used to evaluate the reliability of the computed capture rate for the hypothetical use of <span class="hlt">stars</span> other than the Sun as DM probes.</p> <div class="credits"> <p class="dwt_author">Lopes, Ilídio; Casanellas, Jordi; Eugénio, Daniel</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">167</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21537514"> <span id="translatedtitle">The capture of dark matter particles through the evolution of <span class="hlt">low-mass</span> <span class="hlt">stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We studied the rate at which <span class="hlt">stars</span> capture dark matter (DM) particles, considering different assumptions regarding the DM characteristics and, in particular, investigating how the stellar physics influences the capture rate. Two scenarios were considered: first, we assumed the maximal values for the spin-dependent and spin-independent DM particle-nucleon scattering cross sections allowed by the limits from direct detection experiments. Second, we considered that both scattering cross sections are of the same order, with the aim of studying the dependencies of the capture rate on stellar elements other than hydrogen. We found that the characteristics of the capture rate are very different in the two scenarios. Furthermore, we quantified the uncertainties on the computed capture rate (C{sub {chi}}) and on the ratio between the luminosities from DM annihilations and thermonuclear reactions (L{sub {chi}}/L{sub nuc}) derived from an imprecise knowledge of the stellar structure and DM parameters. For instance, while an uncertainty of 10% on the typical DM velocity leads to similar errors on the computed C{sub {chi}} and L{sub {chi}}/L{sub nuc}, the same uncertainty on the stellar mass becomes more relevant and duplicates the errors. Our results may be used to evaluate the reliability of the computed capture rate for the hypothetical use of <span class="hlt">stars</span> other than the Sun as DM probes.</p> <div class="credits"> <p class="dwt_author">Lopes, Ilidio; Casanellas, Jordi; Eugenio, Daniel [Departamento de Fisica, Universidade de Evora, Portugal and CENTRA, Instituto Superior Tecnico, Lisboa (Portugal); CENTRA, Instituto Superior Tecnico, Lisboa (Portugal)</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-03-15</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">168</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2003A%26A...399..603P"> <span id="translatedtitle">Rotational mixing in <span class="hlt">low-mass</span> <span class="hlt">stars</span>. I Effect of the mu-gradients in main sequence and subgiant Pop I <span class="hlt">stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present a first set of results concerning stellar evolution of rotating <span class="hlt">low-mass</span> <span class="hlt">stars</span>. Our models include fully consistent transport of angular momentum and chemicals due to the combined action of rotation induced mixing (according to Maeder & Zahn \\cite{Maeder98}) and element segregation. The analysis of the effects of local variations of molecular weight due to the meridional circulation on the transport of angular momentum and chemicals are under the scope of this study. We apply this mechanism to <span class="hlt">low</span> <span class="hlt">mass</span> main sequence and subgiant <span class="hlt">stars</span> of population I. We show that the so-called mu -currents are of major importance in setting the shape of the rotation profile, specially near the core. Furthermore, as shown by Talon & Charbonnel (\\cite{Talon98}) and Charbonnel & Talon (\\cite{Charbonnel99}) using models without mu -currents, we confirm that rotation-induced mixing in <span class="hlt">stars</span> braked via magnetic torquing can explain the blue side of the Li dip, as well as the low Li abundances observed in subgiants even when mu -currents are taken into account. We emphasize that mu variations are not to be neglected when treating rotation-induced mixing, and that they could be of great importance for latter evolutionary stages.</p> <div class="credits"> <p class="dwt_author">Palacios, A.; Talon, S.; Charbonnel, C.; Forestini, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">169</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008PhDT.........9R"> <span id="translatedtitle">A study of circumstellar disk properties in <span class="hlt">low-mass</span> <span class="hlt">stars</span> and brown dwarfs</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present Spitzer Space Telescope IRAC and MIPS observations for a sample of eight M dwarfs: six dMe, one dM, and one sdMe <span class="hlt">star</span>. All of our targets are found to have Spectral Energy Distributions (SEDs) which are fitted within the error bars by a purely photospheric spectrum out to 24m m . The estimated ages for all are >10 Myr, suggesting that enough disk dissipation has occurred within the inner several AU of the <span class="hlt">star</span>. Scaling from Houdebine's model of the AU Mic chromosphere, we have computed the free-free infrared excesses for a range of densities. Our Spitzer 24m m data shows that the chromospheres in two of our targets are less dense than in AU Mic by a factor of 10 or more. Our models also indicate that the chromospheric contribution to the observed AU Mic emission at submillimeter wavelengths is only about 2%. We present Spitzer IRAC, MIPS and IRS observations for three sub-stellar members of the TW Hydrae Association (TWA): 2MASSW J1207334-393254 (2M1207), SSSPM J1102-3431 (SSSPM 1102), and 2MASS J1139511-315921 (2M1139). The near- to mid-infrared SEDs indicate the presence of flat optically thick disks around 2M1207 and SSSPM 1102, and a transition disk around 2M1139. 2M1207 shows absorption in the 10 m m silicate feature, with a peak near 11.3 m m due to crystalline forsterite. The absorption can be attributed to a close to edge-on disk. No silicate absorption/emission is observed towards SSSPM 1102. We have performed detailed modeling of these two brown dwarf disks. The best-fits have been obtained using a flat disk of mass 10 -4 [Special characters omitted.] , M of 10 -10 [Special characters omitted.] /yr, and an inclination angle of 75=B0 for 2M1207, whereas a disk mass of 10 -5 [Special characters omitted.] , M of 10 -11 [Special characters omitted.] /yr, and an inclination angle of 63° provides a good fit to SSSPM 1102. Modeling of the 10 m m silicate feature requires the presence of large (>50 m m ) grains in the disk midplane, which indicates substantial grain growth and dust settling in both brown dwarf disks. Our analysis of the stellar and sub-stellar members of the TWA indicates that while only 6 out of 25 stellar members show excess emission at these mid- infrared wavelengths, all of the TWA brown dwarfs that have been observed so far with Spitzer show signs of disks around them, resulting in a disk fraction of at least 60%. A comparison with younger clusters indicates that by the age of the TWA (~10 Myr), the disk fraction for brown dwarfs has not decreased, whereas it drops by a factor of ~2 for the higher mass <span class="hlt">stars</span>. This suggests longer disk decay time scales for brown dwarfs compared to higher mass <span class="hlt">stars</span>.</p> <div class="credits"> <p class="dwt_author">Riaz, Basmah</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">170</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21454915"> <span id="translatedtitle">THE RELATIONSHIP BETWEEN MOLECULAR GAS AND <span class="hlt">STAR</span> FORMATION IN <span class="hlt">LOW-MASS</span> E/S0 GALAXIES</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We consider the relationship between molecular gas and <span class="hlt">star</span> formation surface densities in 19 morphologically defined E/S0s with stellar mass {approx}<4 x 10{sup 10} M{sub sun}, paying particular attention to those found on the blue sequence in color versus stellar mass parameter space, where spiral galaxies typically reside. While some blue-sequence E/S0s must be young major-merger remnants, many <span class="hlt">low-mass</span> blue-sequence E/S0s appear much less disturbed and may be experiencing the milder starbursts associated with inner-disk building as spirals (re)grow. For a sample of eight E/S0s (four blue, two mid, and two red sequence) whose CARMA CO(1-0), Spitzer MIPS 24 {mu}m, and GALEX FUV emission distributions are spatially resolved on a 750 pc scale, we find roughly linear relationships between molecular gas and <span class="hlt">star</span> formation surface densities within all galaxies, with power-law indices N = 0.6-1.9 (median 1.2). Adding 11 more blue-sequence E/S0s whose CO(1-0) emission is not as well resolved, we find that most of our E/S0s have global 1-8 kpc aperture-averaged molecular gas surface densities overlapping the range spanned by the disks and centers of spiral galaxies. While many of our E/S0s fall on the same Schmidt-Kennicutt relation as local spirals, {approx}80% (predominantly on the blue sequence) are offset toward apparently higher molecular gas <span class="hlt">star</span> formation efficiency (i.e., shorter molecular gas depletion time). Possible interpretations of the elevated efficiencies include bursty <span class="hlt">star</span> formation similar to that in local dwarf galaxies, H{sub 2} depletion in advanced starbursts, or simply a failure of the CO(1-0) emission to trace all of the molecular gas.</p> <div class="credits"> <p class="dwt_author">Wei, Lisa H.; Vogel, Stuart N. [Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States); Kannappan, Sheila J.; Stark, David V. [Department of Physics and Astronomy, University of North Carolina, Phillips Hall CB 3255, Chapel Hill, NC 27599-3255 (United States); Baker, Andrew J. [Department of Physics and Astronomy, Rutgers, the State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854-8019 (United States); Laine, Seppo [Spitzer Science Center, California Institute of Technology, MS 220-6, Pasadena, CA 91125 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-12-10</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">171</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011ApJ...740..110A"> <span id="translatedtitle">The Factory and the Beehive. I. Rotation Periods for <span class="hlt">Low-mass</span> <span class="hlt">Stars</span> in Praesepe</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Stellar rotation periods measured from single-age populations are critical for investigating how stellar angular momentum content evolves over time, how that evolution depends on mass, and how rotation influences the stellar dynamo and the magnetically heated chromosphere and corona. We report rotation periods for 40 late-K to mid-M <span class="hlt">star</span> members of the nearby, rich, intermediate-age (~600 Myr) open cluster Praesepe. These rotation periods were derived from ~200 observations taken by the Palomar Transient Factory of four cluster fields from 2010 February to May. Our measurements indicate that Praesepe's mass-period relation transitions from a well-defined singular relation to a more scattered distribution of both fast and slow rotators at ~0.6 M sun. The location of this transition is broadly consistent with expectations based on observations of younger clusters and the assumption that stellar spin-down is the dominant mechanism influencing angular momentum evolution at 600 Myr. However, a comparison to data recently published for the Hyades, assumed to be coeval to Praesepe, indicates that the divergence from a singular mass-period relation occurs at different characteristic masses, strengthening the finding that Praesepe is the younger of the two clusters. We also use previously published relations describing the evolution of rotation periods as a function of color and mass to evolve the sample of Praesepe periods in time. Comparing the resulting predictions to periods measured in M35 and NGC 2516 (~150 Myr) and for kinematically selected young and old field <span class="hlt">star</span> populations suggests that stellar spin-down may progress more slowly than described by these relations.</p> <div class="credits"> <p class="dwt_author">Agüeros, Marcel A.; Covey, Kevin R.; Lemonias, Jenna J.; Law, Nicholas M.; Kraus, Adam; Batalha, Natasha; Bloom, Joshua S.; Cenko, S. Bradley; Kasliwal, Mansi M.; Kulkarni, Shrinivas R.; Nugent, Peter E.; Ofek, Eran O.; Poznanski, Dovi; Quimby, Robert M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">172</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012A%26A...546A..63V"> <span id="translatedtitle">Astrometric confirmation of young <span class="hlt">low-mass</span> binaries and multiple systems in the Chamaeleon <span class="hlt">star</span>-forming regions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Context. The <span class="hlt">star</span>-forming regions in Chamaeleon (Cha) are one of the nearest (distance ~ 165 pc) and youngest (age ~ 2 Myr) conglomerates of recently formed <span class="hlt">stars</span> and the ideal target for population studies of <span class="hlt">star</span> formation. Aims: We investigate a total of 16 Cha targets that have been suggested, but not confirmed, to be binaries or multiple systems in previous literature. Methods: We used the adaptive optics instrument Naos-Conica (NACO) at the Very Large Telescope Unit Telescope (UT) 4 / YEPUN of the Paranal Observatory, at 2-5 different epochs, in order to obtain relative and absolute astrometric measurements, as well as differential photometry in the J, H, and K band. On the basis of known proper motions and these observations, we analyse the astrometric results in our proper motion diagram (PMD: angular separation / position angle versus time), to eliminate possible (non-moving) background <span class="hlt">stars</span>, establish co-moving binaries and multiples, and search for curvature as indications for orbital motion. Results: All previously suggested close components are co-moving and no background <span class="hlt">stars</span> are found. The angular separations range between 0.07 and 9 arcsec, corresponding to projected distances between the components of 6-845 AU. Thirteen <span class="hlt">stars</span> are at least binaries and the remaining three (RX J0919.4-7738, RX J0952.7-7933, VW Cha) are confirmed high-order multiple systems with up to four components. In 13 cases, we found significant slopes in the PMDs, which are compatible with orbital motion whose periods (estimated from the observed gradients in the position angles) range from 60 to 550 years. However, in only four cases there are indications of a curved orbit, the ultimate proof of a gravitational bond. Conclusions: A statistical study based on the 2MASS catalogue confirms the high probability of all 16 stellar systems being gravitationally bound. Most of the secondary components are well above the mass limit of hydrogen burning <span class="hlt">stars</span> (0.08 M?), and have masses twice as high as this value or more. Massive primary components appear to avoid the simultaneous formation of equal-mass secondary components, while extremely <span class="hlt">low-mass</span> secondary components are hard to find for both high and <span class="hlt">low</span> <span class="hlt">mass</span> primaries owing to the much higher dynamic range and the faintness of the secondaries. Based on observations made with ESO telescopes at the Paranal Observatory under program IDs 076.C-0292(A), 078.C-0535(A), 080.C-0424(A), 082.C-0489(A), 084.C-0364(B), 086.C-0638(A) & 086.C-0600(B), the Hubble Space Telescope under program ID GO-8716 and data obtained from the ESO/ST-ECF Science Archive Facility from the Paranal Observatory under program IDs 075.C-0042(A), 076.C-0579(A), 278.C-5070(A) and from the Hubble Space Telescope under programme IDs SNAP-7387, GO-11164. Appendix A is available in electronic form at http://www.aanda.org</p> <div class="credits"> <p class="dwt_author">Vogt, N.; Schmidt, T. O. B.; Neuhäuser, R.; Bedalov, A.; Roell, T.; Seifahrt, A.; Mugrauer, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">173</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2002MNRAS.336..797V"> <span id="translatedtitle">Enhanced molecular abundances in <span class="hlt">low-mass</span> <span class="hlt">star</span>-forming cores</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The outflow from a young stellar object interacts with the dense core in which it is embedded to create anomalously high abundances of HCO+ that under high resolution show a `butterfly' morphology. It has been suggested that the high HCO+ abundance and its morphology arose in a photochemistry induced in the highly turbulent interface induced between the outflow and the core. In this paper we use a very large chemical network to explore the molecular nature of this interface, and demonstrate that, beside HCO+, many other molecular tracers should be anomalously enhanced in this interface and should under high resolution show the same morphology as HCO+. We predict that particularly abundant species should include H2S, CS, H2CS, SO, SO2, CH3OH, and recommend that a study for these species and their morphologies be made in <span class="hlt">star</span>-forming cores. Such observations should help to define the fluid interaction in the interface. The range of molecules predicted here should more generally represent a chemical signature of energetic turbulent mixing of hot and cold interstellar fluids, and our models developed may be able to interpret observations to determine the nature of the fluids and their interaction.</p> <div class="credits"> <p class="dwt_author">Viti, Serena; Natarajan, Sukina; Williams, David A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">174</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21371914"> <span id="translatedtitle">DIAGNOSTIC LINE EMISSION FROM EXTREME ULTRAVIOLET AND X-RAY-ILLUMINATED DISKS AND SHOCKS AROUND <span class="hlt">LOW-MASS</span> <span class="hlt">STARS</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Extreme ultraviolet (EUV; 13.6 eV <h{nu} {approx}< 100 eV) and X-rays in the 0.1-2 keV band can heat the surfaces of disks around young, <span class="hlt">low-mass</span> <span class="hlt">stars</span> to thousands of degrees and ionize species with ionization potentials greater than 13.6 eV. Shocks generated by protostellar winds can also heat and ionize the same species close to the <span class="hlt">star</span>/disk system. These processes produce diagnostic lines (e.g., [Ne II] 12.8 {mu}m and [O I] 6300 A) that we model as functions of key parameters such as EUV luminosity and spectral shape, X-ray luminosity and spectral shape, and wind mass loss rate and shock speed. Comparing our models with observations, we conclude that either internal shocks in the winds or X-rays incident on the disk surfaces often produce the observed [Ne II] line, although there are cases where EUV may dominate. Shocks created by the oblique interaction of winds with disks are unlikely [Ne II] sources because these shocks are too weak to ionize Ne. Even if [Ne II] is mainly produced by X-rays or internal wind shocks, the neon observations typically place upper limits of {approx}<10{sup 42} s{sup -1} on the EUV photon luminosity of these young <span class="hlt">low-mass</span> <span class="hlt">stars</span>. The observed [O I] 6300 A line has both a low velocity component (LVC) and a high velocity component. The latter likely arises in internal wind shocks. For the former we find that X-rays likely produce more [O I] luminosity than either the EUV layer, the transition layer between the EUV and X-ray layer, or the shear layer where the protostellar wind shocks and entrains disk material in a radial flow across the surface of the disk. Our soft X-ray models produce [O I] LVCs with luminosities up to 10{sup -4} L{sub sun}, but may not be able to explain the most luminous LVCs.</p> <div class="credits"> <p class="dwt_author">Hollenbach, David; Gorti, U. [SETI Institute, 515 North Whisman Road, Mountain View, CA 94043 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">175</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22034318"> <span id="translatedtitle">KEPLER CYCLE 1 OBSERVATIONS OF <span class="hlt">LOW-MASS</span> <span class="hlt">STARS</span>: NEW ECLIPSING BINARIES, SINGLE <span class="hlt">STAR</span> ROTATION RATES, AND THE NATURE AND FREQUENCY OF STARSPOTS</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We have analyzed Kepler light curves for 849 <span class="hlt">stars</span> with T{sub eff} {<=} 5200 K from our Cycle 1 Guest Observer program. We identify six new eclipsing binaries, one of which has an orbital period of 29.91 days and two of which are probably W UMa variables. In addition, we identify a candidate 'warm Jupiter' exoplanet. We further examine a subset of 670 sources for variability. Of these objects, 265 <span class="hlt">stars</span> clearly show periodic variability that we assign to rotation of the <span class="hlt">low-mass</span> <span class="hlt">star</span>. At the photometric precision level provided by Kepler, 251 of our objects showed no evidence for variability. We were unable to determine periods for 154 variable objects. We find that 79% of <span class="hlt">stars</span> with T{sub eff} {<=} 5200 K are variable. The rotation periods we derive for the periodic variables span the range 0.31 days {<=} P{sub rot} {<=} 126.5 days. A considerable number of <span class="hlt">stars</span> with rotation periods similar to the solar value show activity levels that are 100 times higher than the Sun. This is consistent with results for solar-like field <span class="hlt">stars</span>. As has been found in previous studies, <span class="hlt">stars</span> with shorter rotation periods generally exhibit larger modulations. This trend flattens beyond P{sub rot} = 25 days, demonstrating that even long-period binaries may still have components with high levels of activity and investigating whether the masses and radii of the stellar components in these systems are consistent with stellar models could remain problematic. Surprisingly, our modeling of the light curves suggests that the active regions on these cool <span class="hlt">stars</span> are either preferentially located near the rotational poles, or that there are two spot groups located at lower latitudes, but in opposing hemispheres.</p> <div class="credits"> <p class="dwt_author">Harrison, T. E.; Coughlin, J. L.; Ule, N. M. [Department of Astronomy, New Mexico State University, Box 30001, MSC 4500, Las Cruces, NM 88003-8001 (United States); Lopez-Morales, M., E-mail: tharriso@nmsu.edu, E-mail: jlcough@nmsu.edu, E-mail: nmule@nmsu.edu, E-mail: mlopez@ieec.uab.es [Institut de Ciencies de L'Espai (CSIC-IEEC), Campus UAB, Fac. Ciencies. Torre C5 parell 2, 08193 Bellaterra, Barcelona (Spain)</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-15</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">176</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013ApJ...771...99T"> <span id="translatedtitle">The Relationship between ? max and Age t from ZAMS to RGB-Tip for <span class="hlt">Low-mass</span> <span class="hlt">Stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Stellar age is an important quantity in astrophysics, which is useful for many fields both in the universe and galaxies. It cannot be determined by direct measurements, but can only be estimated or inferred. We attempt to find a useful indicator of stellar age, which is accurate from the zero-age main sequence to the tip of red giant branch for <span class="hlt">low-mass</span> <span class="hlt">stars</span>. Using the Yale Rotation and Evolution Code (YREC), a grid of stellar models has been constructed. Meanwhile, the frequency of maximum oscillations' power ?max and the large frequency separation ?? are calculated using the scaling relations. For the <span class="hlt">stars</span>, the masses of which are from 0.8 M ? to 2.8 M ?, we can obtain the ?max and stellar age by combing the scaling relations with the four sets of grid models (YREC, Dotter et al., Marigo et al., and YY isochrones). We find that ?max is tightly correlated and decreases monotonically with the age of the <span class="hlt">star</span> from the main sequence to the red giant evolutionary stages. Moreover, we find that the line shapes of the curves in the Age versus ?max diagram, which is plotted by the four sets of grid models, are consistent for red giants with masses from 1.1 M ? to 2.8 M ?. For red giants, the differences of correlation coefficients between Age and ?max for different grid models are minor and can be ignored. Interestingly, we find two peaks that correspond to the subgiants and bump of red giants in the Age versus ?max diagram. By general linear least-squares, we make the polynomial fitting and deduce the relationship between log(Age) and log(?max) in red giants' evolutionary state.</p> <div class="credits"> <p class="dwt_author">Tang, Y. K.; Gai, N.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">177</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013MNRAS.431.1883J"> <span id="translatedtitle">On the relationship between the size and surface coverage of starspots on magnetically active <span class="hlt">low-mass</span> <span class="hlt">stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present a model that predicts the light-curve amplitude distribution for an ensemble of <span class="hlt">low-mass</span> magnetically active <span class="hlt">stars</span>, under the assumptions that stellar spin axes are randomly orientated and that cool starspots have a characteristic scalelength and are randomly distributed across the stellar surfaces. The model is compared with observational data for highly magnetically active M-dwarfs in the young cluster NGC 2516. We find that the best-fitting starspot scalelength is not constrained by these data alone, but requires assumptions about the overall starspot-filling factor and starspot temperature. Assuming a spot coverage fraction of 0.4 ± 0.1 and a starspot to unspotted photosphere temperature ratio of 0.7 ± 0.05, as suggested by the inflated radii of these <span class="hlt">stars</span> compared to evolutionary model predictions and by TiO band measurements on other active cool <span class="hlt">stars</span> of earlier spectral type, the best-fitting starspot angular scalelength is 3.5+ 2- 1 degrees, or a linear scalelength of ˜25 000 km. This linear scalelength is similar to large sunspot groups, but two to five times smaller than the starspots recently deduced on an active G-dwarf using eclipse mapping by a transiting exoplanet. However, the best-fitting spot scalelength in the NGC 2516 M-dwarfs increases with the assumed spot temperature ratio and with the inverse square root of the assumed spot-filling factor. Hence, the light-curve amplitude distribution might equally well be described by these larger spot scalelengths if the spot-filling factors are <0.1 or the spot temperature ratio is >0.9.</p> <div class="credits"> <p class="dwt_author">Jackson, R. J.; Jeffries, R. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">178</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012AJ....143..107W"> <span id="translatedtitle">Very <span class="hlt">Low</span> <span class="hlt">Mass</span> Stellar and Substellar Companions to Solar-like <span class="hlt">Stars</span> from MARVELS. I. A <span class="hlt">Low-mass</span> Ratio Stellar Companion to TYC 4110-01037-1 in a 79 Day Orbit</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">TYC 4110-01037-1 has a <span class="hlt">low-mass</span> stellar companion, whose small mass ratio and short orbital period are atypical among binary systems with solar-like (T eff <~ 6000 K) primary <span class="hlt">stars</span>. Our analysis of TYC 4110-01037-1 reveals it to be a moderately aged (lsim5 Gyr) solar-like <span class="hlt">star</span> having a mass of 1.07 ± 0.08 M ? and radius of 0.99 ± 0.18 R ?. We analyze 32 radial velocity (RV) measurements from the SDSS-III MARVELS survey as well as 6 supporting RV measurements from the SARG spectrograph on the 3.6 m Telescopio Nazionale Galileo telescope obtained over a period of ~2 years. The best Keplerian orbital fit parameters were found to have a period of 78.994 ± 0.012 days, an eccentricity of 0.1095 ± 0.0023, and a semi-amplitude of 4199 ± 11 m s-1. We determine the minimum companion mass (if sin i = 1) to be 97.7 ± 5.8 M Jup. The system's companion to host <span class="hlt">star</span> mass ratio, >=0.087 ± 0.003, places it at the lowest end of observed values for short period stellar companions to solar-like (T eff <~ 6000 K) <span class="hlt">stars</span>. One possible way to create such a system would be if a triple-component stellar multiple broke up into a short period, low q binary during the cluster dispersal phase of its lifetime. A candidate tertiary body has been identified in the system via single-epoch, high contrast imagery. If this object is confirmed to be comoving, we estimate it would be a dM4 <span class="hlt">star</span>. We present these results in the context of our larger-scale effort to constrain the statistics of <span class="hlt">low-mass</span> stellar and brown dwarf companions to FGK-type <span class="hlt">stars</span> via the MARVELS survey.</p> <div class="credits"> <p class="dwt_author">Wisniewski, John P.; Ge, Jian; Crepp, Justin R.; De Lee, Nathan; Eastman, Jason; Esposito, Massimiliano; Fleming, Scott W.; Gaudi, B. Scott; Ghezzi, Luan; Gonzalez Hernandez, Jonay I.; Lee, Brian L.; Stassun, Keivan G.; Agol, Eric; Allende Prieto, Carlos; Barnes, Rory; Bizyaev, Dmitry; Cargile, Phillip; Chang, Liang; Da Costa, Luiz N.; Porto De Mello, G. F.; Femenía, Bruno; Ferreira, Leticia D.; Gary, Bruce; Hebb, Leslie; Holtzman, Jon; Liu, Jian; Ma, Bo; Mack, Claude E.; Mahadevan, Suvrath; Maia, Marcio A. G.; Nguyen, Duy Cuong; Ogando, Ricardo L. C.; Oravetz, Daniel J.; Paegert, Martin; Pan, Kaike; Pepper, Joshua; Rebolo, Rafael; Santiago, Basilio; Schneider, Donald P.; Shelden, Alaina C.; Simmons, Audrey; Tofflemire, Benjamin M.; Wan, Xiaoke; Wang, Ji; Zhao, Bo</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">179</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21301447"> <span id="translatedtitle">THE BROWN DWARF KINEMATICS PROJECT. II. DETAILS ON NINE WIDE COMMON PROPER MOTION VERY <span class="hlt">LOW</span> <span class="hlt">MASS</span> COMPANIONS TO NEARBY <span class="hlt">STARS</span> ,</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We report on nine wide common proper motion systems containing late-type M, L, or T companions. We confirm six previously reported companions, and identify three new systems. The ages of these systems are determined using diagnostics for both stellar primaries and <span class="hlt">low-mass</span> secondaries and masses for the secondaries are inferred using evolutionary models. Of our three new discoveries, the M3+T6.5 pair G 204-39 and SDSS J1758+4633 has an age constrained to 0.5-1.5 Gyr making the secondary a potentially useful brown dwarf benchmark. The G5+L4 pair G 200-28 and SDSS J1416+5006 has a projected separation of {approx}25,000 AU making it one of the widest and lowest binding energy systems known to date. The system containing NLTT 2274 and SDSS J0041+1341 is an older M4+L0 (>4.5 Gyr) pair which shows H{alpha} activity in the secondary but not the primary making it a useful tracer of age/mass/activity trends. Two of the nine systems have discrepant component ages that emerge from stellar or ultracool diagnostics indicating possible shortcomings in our understanding of the age diagnostics of <span class="hlt">stars</span> and brown dwarfs. We find a resolved binary frequency for widely separated (>100 AU) <span class="hlt">low-mass</span> companions (i.e., at least a triple system) which is at least twice the frequency found for the field ultracool dwarf population. The ratio of triples to binaries and quadruples to binaries is also high for this sample: 3:5 and 1:4, respectively, compared to 8 pc sample values of 1:4 and 1:26. The additional components in these wide companion systems indicates a formation mechanism that requires a third or fourth component to maintain gravitational stability or facilitate the exchange of angular momentum. The binding energies for the nine multiples discussed in this text are among the lowest known for wide <span class="hlt">low-mass</span> systems, suggesting that weakly bound, low-to-intermediate mass (0.2 M {sub sun} < M {sub tot}< 1.0 M {sub sun}) multiples can form and survive to exist in the field (1-8 Gyr)</p> <div class="credits"> <p class="dwt_author">Faherty, Jacqueline K.; Shara, Michael M. [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10034 (United States); Burgasser, Adam J.; West, Andrew A.; Bochanski, John J. [Massachusetts Institute of Technology, Kavli Institute for Astrophysics and Space Research, Building 37, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Cruz, Kelle L. [Astronomy Department, California Institute of Technology, Pasadena, CA 91125 (United States); Walter, Frederick M. [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800 (United States)], E-mail: jfaherty@amnh.org</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-15</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">180</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22078549"> <span id="translatedtitle">CAN THE GROWTH OF DUST GRAINS IN LOW-METALLICITY <span class="hlt">STAR</span>-FORMING CLOUDS AFFECT THE FORMATION OF METAL-POOR <span class="hlt">LOW-MASS</span> <span class="hlt">STARS</span>?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The discovery of a <span class="hlt">low-mass</span> <span class="hlt">star</span> with such a low metallicity as {<=}4.5 Multiplication-Sign 10{sup -5} Z{sub Sun} reveals the critical role of dust in the formation of extremely metal-poor <span class="hlt">stars</span>. In this Letter, we explore the effect of the growth of dust grains through accretion of gaseous refractory elements in very low metallicity pre-stellar cores on cloud fragmentation induced by dust emission cooling. Employing a simple model of grain growth in a gravitationally collapsing gas, we show that Fe and Si grains can grow efficiently at hydrogen densities of {approx_equal} 10{sup 10}-10{sup 14} cm{sup -3} in the clouds with metal abundances of -5 {approx}< [Fe, Si/H] {approx}< -3. The critical metal number abundances, above which the grain growth could induce the fragmentation of the gas clouds, are estimated to be A{sub crit} {approx_equal} 10{sup -9}-10{sup -8}, unless the initial grain radius is too large ({approx}>1 {mu}m) or the sticking probability is too small ({approx}<0.01). We find that even if the initial dust-to-gas mass ratio is well below the minimum value required for the dust-induced fragmentation, the grain growth increases the dust mass high enough to cause the gas to fragment into sub-solar mass clumps. We suggest that as long as the critical metal abundance is satisfied, grain growth could play an important role in the formation of <span class="hlt">low-mass</span> <span class="hlt">stars</span> with metallicity as low as 10{sup -5} Z{sub Sun }.</p> <div class="credits"> <p class="dwt_author">Nozawa, Takaya; Nomoto, Ken'ichi [Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, University of Tokyo, Kashiwa, Chiba 277-8583 (Japan); Kozasa, Takashi, E-mail: takaya.nozawa@ipmu.jp [Department of Cosmosciences, Graduate School of Science, Hokkaido University, Sapporo 060-0810 (Japan)</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-09-10</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" 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<div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012A%26A...542L..27P"> <span id="translatedtitle">A relativistic iron emission line from the neutron <span class="hlt">star</span> <span class="hlt">low-mass</span> X-ray binary GX 3+1</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present the results of a spectroscopic study of the Fe K? emission of the persistent neutron-<span class="hlt">star</span> atoll <span class="hlt">low-mass</span> X-ray binary and type I X-ray burster GX 3+1 with the EPIC-PN on board XMM-Newton. The source shows a flux modulation over several years and we observed it during its fainter phase, which corresponds to an X-ray luminosity of LX ~ 1037 erg s-1. When fitted with a two-component model, the X-ray spectrum shows broad residuals at ~6-7 keV that can be ascribed to an iron K? fluorescence line. In addition, lower energy features are observed at ~3.3 keV, ~3.9 keV and might originate from Ar XVIII and Ca XIX. The broad iron line feature is well fitted with a relativistically smeared profile. This result is robust against possible systematics caused by instrumental pile-up effects. Assuming that the line is produced by reflection from the inner accretion disk, we infer an inner disk radius of ~25Rg and a disk inclination of 35° < i < 44°.</p> <div class="credits"> <p class="dwt_author">Piraino, S.; Santangelo, A.; Kaaret, P.; Mück, B.; D'Aì, A.; Di Salvo, T.; Iaria, R.; Robba, N.; Burderi, L.; Egron, E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">182</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004PhDT........19C"> <span id="translatedtitle">A 0.6 to 4.1 mum spectroscopic study of very <span class="hlt">low-mass</span> <span class="hlt">stars</span> and brown dwarfs</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present the results of a 0.6 to 4.1 ?m spectroscopic survey of a sample of very <span class="hlt">low-mass</span> <span class="hlt">stars</span> and brown dwarfs with spectral types ranging from M0 V to T5 V. The survey was conducted with SpeX, a 0.8 to 5.5 ?m, medium-resolution spectrograph and imager on the NASA Infrared Telescope Facility. We developed a data reduction package for SpeX called Spextool which performs all the steps necessary to produce fully reduced spectra including preparation of calibration frames, processing and spectral extraction of science frames, wavelength calibration of spectra, and flux calibration of spectra. We have identified the most prominate atomic and molecular absorption features including ˜100 new FeH features, ˜30 new CH4 features, a new band of VO, and ˜80 atomic features. We have also derived the bolometric luminosities and effective temperatures of the dwarfs. Finally, by comparing the dwarf spectra to synthetic spectra computed from model atmospheres we show, for the first time, spectroscopic evidence for the prescence of condenstate clouds in the atmospheres of brown dwarfs.</p> <div class="credits"> <p class="dwt_author">Cushing, Michael C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">183</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010ApJ...716.1060V"> <span id="translatedtitle">Atmospheric Chemistry in Giant Planets, Brown Dwarfs, and <span class="hlt">Low-mass</span> Dwarf <span class="hlt">Stars</span>. III. Iron, Magnesium, and Silicon</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We use thermochemical equilibrium calculations to model iron, magnesium, and silicon chemistry in the atmospheres of giant planets, brown dwarfs, extrasolar giant planets (EGPs), and <span class="hlt">low-mass</span> <span class="hlt">stars</span>. The behavior of individual Fe-, Mg-, and Si-bearing gases and condensates is determined as a function of temperature, pressure, and metallicity. Our equilibrium results are thus independent of any particular model atmosphere. The condensation of Fe metal strongly affects iron chemistry by efficiently removing Fe-bearing species from the gas phase. Monatomic Fe is the most abundant Fe-bearing gas throughout the atmospheres of EGPs and L dwarfs, and in the deep atmospheres of giant planets and T dwarfs. Mg- and Si-bearing gases are effectively removed from the atmosphere by forsterite (Mg2SiO4) and enstatite (MgSiO3) cloud formation. Monatomic Mg is the dominant magnesium gas throughout the atmospheres of EGPs and L dwarfs and in the deep atmospheres of giant planets and T dwarfs. Silicon monoxide (SiO) is the most abundant Si-bearing gas in the deep atmospheres of brown dwarfs and EGPs, whereas SiH4 is dominant in the deep atmosphere of Jupiter and other gas giant planets. Several other Fe-, Mg-, and Si-bearing gases become increasingly important with decreasing effective temperature. In principle, a number of Fe, Mg, and Si gases are potential tracers of weather or diagnostic of temperature in substellar atmospheres.</p> <div class="credits"> <p class="dwt_author">Visscher, Channon; Lodders, Katharina; Fegley, Bruce, Jr.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">184</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21452943"> <span id="translatedtitle">ATMOSPHERIC CHEMISTRY IN GIANT PLANETS, BROWN DWARFS, AND <span class="hlt">LOW-MASS</span> DWARF <span class="hlt">STARS</span>. III. IRON, MAGNESIUM, AND SILICON</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We use thermochemical equilibrium calculations to model iron, magnesium, and silicon chemistry in the atmospheres of giant planets, brown dwarfs, extrasolar giant planets (EGPs), and <span class="hlt">low-mass</span> <span class="hlt">stars</span>. The behavior of individual Fe-, Mg-, and Si-bearing gases and condensates is determined as a function of temperature, pressure, and metallicity. Our equilibrium results are thus independent of any particular model atmosphere. The condensation of Fe metal strongly affects iron chemistry by efficiently removing Fe-bearing species from the gas phase. Monatomic Fe is the most abundant Fe-bearing gas throughout the atmospheres of EGPs and L dwarfs, and in the deep atmospheres of giant planets and T dwarfs. Mg- and Si-bearing gases are effectively removed from the atmosphere by forsterite (Mg{sub 2}SiO{sub 4}) and enstatite (MgSiO{sub 3}) cloud formation. Monatomic Mg is the dominant magnesium gas throughout the atmospheres of EGPs and L dwarfs and in the deep atmospheres of giant planets and T dwarfs. Silicon monoxide (SiO) is the most abundant Si-bearing gas in the deep atmospheres of brown dwarfs and EGPs, whereas SiH{sub 4} is dominant in the deep atmosphere of Jupiter and other gas giant planets. Several other Fe-, Mg-, and Si-bearing gases become increasingly important with decreasing effective temperature. In principle, a number of Fe, Mg, and Si gases are potential tracers of weather or diagnostic of temperature in substellar atmospheres.</p> <div class="credits"> <p class="dwt_author">Visscher, Channon [Current address: Lunar and Planetary Institute, USRA, Houston, TX 77058-1113 (United States); Lodders, Katharina; Fegley, Bruce, E-mail: visscher@lpi.usra.ed, E-mail: lodders@wustl.ed, E-mail: bfegley@wustl.ed [Planetary Chemistry Laboratory, Department of Earth and Planetary Sciences, McDonnell Center for the Space Sciences, Washington University, St. Louis, MO 63130-4899 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-06-20</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">185</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AAS...22125042K"> <span id="translatedtitle">Centaurus <span class="hlt">Star</span>-Forming Field <span class="hlt">Revisited</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We analyze the structure of the <span class="hlt">star</span>-forming field in Centaurus based on intermediate-band uvby? photometry of a large sample of O-B9 -<span class="hlt">stars</span>. The derived precise homogeneous photometric distances and color excesses allow us to reveal spatially coherent groups and layers and to revise the membership and distance of the Cen OB1 association. In particular, we are seeking a correlation between the distribution of the massive OB-<span class="hlt">stars</span> and that of ionized and neutral interstellar material that would allow a better understanding of the interactions among various ISM components in the Galactic <span class="hlt">stars</span>-forming fields. For the purpose we combine the photometric findings with several multi-wavelength surveys (Wisconsin H-Alpha Mapper Northern Sky Survey, Southern H-Alpha Sky Survey Atlas, MSX Galactic Plane Survey, WISE All-Sky Data Release, CO survey of the Milky Way, and Southern Galactic Plane Survey). This allows us to map the OB-<span class="hlt">star</span> distribution together with the super-shells of neutral and ionized material located toward Centaurus. Acknowledgments. This work was supported by NSF grant AST-0708950.</p> <div class="credits"> <p class="dwt_author">Kaltcheva, Nadia; Golev, V.; Moran, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">186</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013MNRAS.431.2612H"> <span id="translatedtitle"><span class="hlt">Revisiting</span> binary <span class="hlt">stars</span> in population synthesis models</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We report results of a population synthesis model that follows the evolution of single and binary <span class="hlt">stars</span>. In this model, we include the two He white dwarfs merger channel, suggested by Han et al., for the formation of extreme horizontal branch (EHB) <span class="hlt">stars</span>. The physical parameters of the resulting EHB <span class="hlt">stars</span> are derived from the Bag of Stellar Tracks and Isochrones data base by Pietrinferni et al., and are thus realistic and observationally supported. The predictions of this model are in good agreement with traditional population synthesis models, except when the spectrum of the stellar population is dominated by binary <span class="hlt">stars</span> or their products, e.g., EHB <span class="hlt">stars</span> in the ultraviolet (UV) of early-type galaxies (ETGs). We reproduce successfully the observed colour-magnitude diagram and spectral energy distribution of the metal-rich open cluster NGC 6791. The stellar population in this cluster may be archetypal of the stellar population in ETGs that show the UV excess phenomenon. Our models should be appropriate to study the UV upturn in ETGs.</p> <div class="credits"> <p class="dwt_author">Hernández-Pérez, Fabiola; Bruzual, Gustavo</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">187</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AN....334...14D"> <span id="translatedtitle">The SLoWPoKES catalog of <span class="hlt">low-mass</span> ultra-wide binaries: A cool <span class="hlt">stars</span> resource for testing fundamental properties and for constraining binary formation theory</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present results from the Sloan <span class="hlt">Low-mass</span> Wide Pairs of Kinematically Equivalent <span class="hlt">Stars</span> (SLoWPoKES) catalog of ultra-wide (103-105.5 AU), <span class="hlt">low-mass</span> (K5-M7) common proper motion binaries. We constructed a Galactic model, based on empirical stellar number density and 3D velocity distributions, to select bona fide pairs with probability of chance alignment < 5 %, making SLoWPoKES an efficient sample for followup observations. Our initial catalog contains 1342 disk dwarf, subdwarf, and white dwarf-red dwarf systems and is the largest collection of <span class="hlt">low-mass</span>, wide binaries ever assembled. The diversity - in mass, metallicity, age, and evolutionary states - of SLoWPoKES pairs makes it a valuable resource of coeval laboratories to examine and constrain the physical properties of <span class="hlt">low-mass</span> <span class="hlt">stars</span>. SLoWPoKES pairs show signatures of two (or more) formation modes in the distribution of the physical separation and higher-order multiplicity. Neither dynamical dissipation of primordial triples/quadruples or dynamical capture of ejected <span class="hlt">stars</span> can explain the observed populations by itself. We use follow-up spectroscopic observations to recalibrate the metallicity-sensitive ?{TiO/CaH} index by assuming that both members of the binary system have the same composition. Our new formulation is a significantly better tracer of absolute metallicity, particularly for the early-type M dwarfs. The catalogs are publicly available on a custom data visualization portal.</p> <div class="credits"> <p class="dwt_author">Dhital, S.; West, A. A.; Stassun, K. G.; Law, N. M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">188</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22034651"> <span id="translatedtitle">VERY <span class="hlt">LOW</span> <span class="hlt">MASS</span> STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE <span class="hlt">STARS</span> FROM MARVELS. I. A <span class="hlt">LOW-MASS</span> RATIO STELLAR COMPANION TO TYC 4110-01037-1 IN A 79 DAY ORBIT</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">TYC 4110-01037-1 has a <span class="hlt">low-mass</span> stellar companion, whose small mass ratio and short orbital period are atypical among binary systems with solar-like (T{sub eff} {approx}< 6000 K) primary <span class="hlt">stars</span>. Our analysis of TYC 4110-01037-1 reveals it to be a moderately aged ({approx}<5 Gyr) solar-like <span class="hlt">star</span> having a mass of 1.07 {+-} 0.08 M{sub Sun} and radius of 0.99 {+-} 0.18 R{sub Sun }. We analyze 32 radial velocity (RV) measurements from the SDSS-III MARVELS survey as well as 6 supporting RV measurements from the SARG spectrograph on the 3.6 m Telescopio Nazionale Galileo telescope obtained over a period of {approx}2 years. The best Keplerian orbital fit parameters were found to have a period of 78.994 {+-} 0.012 days, an eccentricity of 0.1095 {+-} 0.0023, and a semi-amplitude of 4199 {+-} 11 m s{sup -1}. We determine the minimum companion mass (if sin i = 1) to be 97.7 {+-} 5.8 M{sub Jup}. The system's companion to host <span class="hlt">star</span> mass ratio, {>=}0.087 {+-} 0.003, places it at the lowest end of observed values for short period stellar companions to solar-like (T{sub eff} {approx}< 6000 K) <span class="hlt">stars</span>. One possible way to create such a system would be if a triple-component stellar multiple broke up into a short period, low q binary during the cluster dispersal phase of its lifetime. A candidate tertiary body has been identified in the system via single-epoch, high contrast imagery. If this object is confirmed to be comoving, we estimate it would be a dM4 <span class="hlt">star</span>. We present these results in the context of our larger-scale effort to constrain the statistics of <span class="hlt">low-mass</span> stellar and brown dwarf companions to FGK-type <span class="hlt">stars</span> via the MARVELS survey.</p> <div class="credits"> <p class="dwt_author">Wisniewski, John P.; Agol, Eric; Barnes, Rory [Astronomy Department, University of Washington, Box 351580, Seattle, WA 98195 (United States); Ge, Jian; De Lee, Nathan; Fleming, Scott W.; Lee, Brian L.; Chang, Liang [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611-2055 (United States); Crepp, Justin R. [Department of Astrophysics, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Eastman, Jason; Gaudi, B. Scott [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Esposito, Massimiliano; Gonzalez Hernandez, Jonay I.; Prieto, Carlos Allende [Instituto de Astrofisica de Canarias (IAC), E-38205 La Laguna, Tenerife (Spain); Ghezzi, Luan; Da Costa, Luiz N.; Porto De Mello, G. F. [Laboratorio Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro, RJ 20921-400 (Brazil); Stassun, Keivan G.; Cargile, Phillip [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Bizyaev, Dmitry, E-mail: jwisnie@u.washington.edu [Apache Point Observatory, P.O. Box 59, Sunspot, NM 88349-0059 (United States); and others</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-05-15</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">189</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21576879"> <span id="translatedtitle">NEUTRON <span class="hlt">STAR</span> RADIUS MEASUREMENT WITH THE QUIESCENT <span class="hlt">LOW-MASS</span> X-RAY BINARY U24 IN NGC 6397</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">This paper reports the spectral and timing analyses of the quiescent <span class="hlt">low-mass</span> X-ray binary (qLMXB) U24 observed during five archived Chandra/ACIS exposures of the nearby globular cluster NGC 6397, for a total of 350 ks. We find that the X-ray flux and the parameters of the hydrogen atmosphere spectral model are consistent with those previously published for this source. On short timescales, we find no evidence of aperiodic intensity variability, with 90% confidence upper limits during five observations ranging between <8.6% rms and <19% rms, in the 0.0001-0.1 Hz frequency range (0.5-8.0 keV); and no evidence of periodic variability, with maximum observed powers in this frequency range having a chance probability of occurrence from a Poisson-deviated light curve in excess of 10%. We also report the improved neutron <span class="hlt">star</span> (NS) physical radius measurement, with statistical accuracy of the order of {approx}10%: R{sub NS} = 8.9{sup +0.9}{sub -0.6} km for M{sub NS} = 1.4 M{sub sun}. Alternatively, we provide the confidence regions in mass-radius space as well as the best-fit projected radius R{sub {infinity}} = 11.9{sup +1.0}{sub -0.8} km, as seen by an observer at infinity. The best-fit effective temperature, kT{sub eff} = 80{sup +4}{sub -5} eV, is used to estimate the NS core temperature which falls in the range T{sub core} = (3.0-9.8) x 10{sup 7} K, depending on the atmosphere model considered. This makes U24 the third most precisely measured NS radius among qLMXBs, after those in {omega} Cen and M13.</p> <div class="credits"> <p class="dwt_author">Guillot, Sebastien; Rutledge, Robert E. [Department of Physics, McGill University, 3600 rue University, Montreal, QC H3A-2T8 (Canada); Brown, Edward F., E-mail: guillots@physics.mcgill.ca, E-mail: rutledge@physics.mcgill.ca [Department of Physics and Astronomy, Michigan State University, 3250 Biomedical Physical Science Building, East Lansing, MI 48824-2320 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-05-10</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">190</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/27665372"> <span id="translatedtitle">Spherically Symmetric Model Atmospheres for <span class="hlt">Low-Mass</span> Pre-Main-Sequence <span class="hlt">Stars</span> with Effective Temperatures between 2000 and 6800 K</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We present a grid of spherically symmetric model atmospheres for young pre-MS <span class="hlt">stars</span>. This grid spans the parameter range 2000 K<=Teff<=6800 K and 2.0<=logg<=3.5 for M=0.1 Msolar, appropriate for <span class="hlt">low-mass</span> <span class="hlt">stars</span> and brown dwarfs. A major improvement is the replacement of TiO and H2O line lists with the newer line list, calculated by the NASA-Ames group, for TiO (about 175</p> <div class="credits"> <p class="dwt_author">France Allard; Peter H. Hauschildt; Andreas Schweitzer</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">191</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/52534015"> <span id="translatedtitle">Seismic study of stellar convective regions: the base of the convective envelope in <span class="hlt">low-mass</span> <span class="hlt">stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The possibility of observing solar-type oscillations on other <span class="hlt">stars</span> is of great relevance to investigating the uncertain aspects of the internal structure of <span class="hlt">stars</span>. One of these aspects is the convective overshoot that takes place at the borders of the envelopes of <span class="hlt">stars</span> of mass similar to, or lower than, the Sun. It affects the temperature stratification, mixing, rotation and</p> <div class="credits"> <p class="dwt_author">Jørgen Christensen-Dalsgaard; Michael J. Thompson</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">192</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012ApJ...748....5O"> <span id="translatedtitle">The Mass and Radius of the Neutron <span class="hlt">Star</span> in the Bulge <span class="hlt">Low-mass</span> X-Ray Binary KS 1731-260</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Measurements of neutron <span class="hlt">star</span> masses and radii are instrumental in determining the equation of state of their interiors, understanding the dividing line between neutron <span class="hlt">stars</span> and black holes, and obtaining accurate statistics of source populations in the Galaxy. We report here on the measurement of the mass and radius of the neutron <span class="hlt">star</span> in the <span class="hlt">low-mass</span> X-ray binary KS 1731-260. The analysis of the spectroscopic data on multiple thermonuclear bursts yields well-constrained values for the apparent angular area and the Eddington flux of the source, both of which depend in a distinct way on the mass and radius of the neutron <span class="hlt">star</span>. The binary KS 1731-260 is in the direction of the Galactic bulge, allowing a distance estimate based on the density of <span class="hlt">stars</span> in that direction. Making use of the Han & Gould model, we determine the probability distribution over the distance to the source, which is approximately flat between 7 and 9 kpc. Combining these measurements, we place a strong upper bound on the radius of the neutron <span class="hlt">star</span>, R <= 12.5 km, while confining its mass to M <= 2.1 M ?.</p> <div class="credits"> <p class="dwt_author">Özel, Feryal; Gould, Andrew; Güver, Tolga</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">193</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009ApJ...692...73H"> <span id="translatedtitle">A Variable Near-Infrared Counterpart to the Neutron-<span class="hlt">Star</span> <span class="hlt">Low-Mass</span> X-Ray Binary 4U 1705 - 440</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We report the discovery of a near-infrared (NIR) counterpart to the persistent neutron-<span class="hlt">star</span> <span class="hlt">low-mass</span> X-ray binary 4U 1705 - 440, at a location consistent with its recently determined Chandra X-ray position. The NIR source is highly variable, with Ks -band magnitudes varying between 15.2 and 17.3 and additional J- and H-band observations revealing color variations. A comparison with contemporaneous X-ray monitoring observations shows that the NIR brightness correlates well with X-ray flux and X-ray spectral state. We also find possible indications of a change in the slope of the NIR/X-ray flux relation among different X-ray states. We discuss and test various proposed mechanisms for the NIR emission from neutron-<span class="hlt">star</span> <span class="hlt">low-mass</span> X-ray binaries and conclude that the NIR emission in 4U 1705 - 440 is most likely dominated by X-ray heating of the outer accretion disk and the secondary <span class="hlt">star</span>. This paper includes data gathered with the 6.5 m Magellan Baade Telescope, located at Las Campanas Observatory, Chile, and the 4 m Blanco Telescope, located at CTIO, Chile.</p> <div class="credits"> <p class="dwt_author">Homan, Jeroen; Kaplan, David L.; van den Berg, Maureen; Young, Andrew J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">194</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AAS...21330304L"> <span id="translatedtitle">Cool Subdwarfs As Tracers Of The Galactic Halo: A Massive Spectroscopic Survey Of <span class="hlt">Low-mass</span>, Metal-poor <span class="hlt">Stars</span> In Sdss And Segue.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present the spectroscopic identification of an unprecedented 6,900 cool subdwarfs (sdM/esdM/usdM) from the Sloan Digital Sky Survey (SDSS) and Sloan Extension for Galactic Understanding and Exploration (SEGUE). The census provides the most detailed picture to date of the local population of old, <span class="hlt">low-mass</span> <span class="hlt">stars</span>, including abundances and kinematics. New high signal-to-noise classification templates are generated for each ot the subdwarf (sdM), extreme subdwarf (esdM) and ultrasubdwarf (usdM) metallicity classes. The high sucess rate in the SEGUE target selection algorithm confirms that cool subdwarfs can be very efficiently identified based on color and proper motion alone. We further confirm the earlier assumption that M subdwarfs are segregated according to metallicity in the g-r/r-i color-color diagram, making it possible to identify <span class="hlt">low-mass</span> metal poor <span class="hlt">stars</span> with minimal kinematic bias. Kinematics of our sample shows a distribution consistent with a sizable population of metal-poor <span class="hlt">stars</span> on eccentric Galactic orbits, part of a flattened and co-rotating "inner halo".</p> <div class="credits"> <p class="dwt_author">Lepine, Sebastien; Lee, Y. S.; Yanni, B.; SEGUE Collaboration</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">195</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/56304175"> <span id="translatedtitle">Bounds on Compactness for <span class="hlt">Low-Mass</span> X-Ray Binary Neutron <span class="hlt">Stars</span> from X-Ray Burst Oscillations</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We have modeled X-ray burst oscillations observed with the Rossi X-Ray Timing Explorer from two <span class="hlt">low-mass</span> X-ray binaries (LMXB): 4U 1636-53 with a frequency of 580 Hz and 4U 1728-34 at a frequency of 363 Hz. We have computed least-squares fits to the oscillations observed during the rising phase of bursts using a model that includes emission from either a</p> <div class="credits"> <p class="dwt_author">Nitya R. Nath; Tod E. Strohmayer; Jean H. Swank</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">196</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012A%26A...545A..19S"> <span id="translatedtitle">Empirical near-infrared colors for <span class="hlt">low-mass</span> <span class="hlt">stars</span> and brown dwarfs in the Orion Nebula Cluster. An empirical near-infrared isochrone at ~1 Myr</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Context. Current atmospheric and evolutionary models for <span class="hlt">low-mass</span> <span class="hlt">stars</span> and brown dwarfs rely on approximate assumptions on the physics of the stellar structure and the atmospheric radiative transfer. This leads to biased theoretical predictions on the photospheric spectral energy distributions of these system, especially when applied to low surface gravity objects such as pre-main sequence (PMS) <span class="hlt">stars</span>, and affects the derivation of stellar parameters from photometric data. Aims: Our main goal is to correct the biases present in the theoretical predictions for the near-IR photometry of <span class="hlt">low-mass</span> PMS <span class="hlt">stars</span>. Using empirical intrinsic IR colors, we assess the accuracy of current synthetic spectral libraries and evolutionary models. We investigate how the uncertainty in the intrinsic colors associated with different PMS models affect the derivation of the initial mass function of young clusters from near-IR photometry. Methods: We consider a sample of ~300 PMS <span class="hlt">stars</span> in the Orion Nebula Cluster (age ? 1 Myr) with well measured luminosities, temperatures and photospheric JHKS photometry. This sample is used as a benchmark for testing both atmospheric and evolutionary theoretical models. Results: By analyzing the photospheric colors of our sample of young <span class="hlt">stars</span>, we find that the synthetic JHKS photometry provided by theoretical spectral templates for late spectral types (>K6) are accurate at the level of ~0.2 mag, while colors are accurate at ? 0.1 mag. We tabulate the intrinsic photospheric colors, appropriate for the Orion Nebula Cluster, in the range K6-M8.5. They can be conveniently used as templates for the intrinsic colors of other young (age ? 5 Myr) stellar clusters. Conclusions: The theoretically-predicted JHKS magnitudes of young late type <span class="hlt">stars</span> do not accurately reproduce the intrinsic ones of the Orion Nebula Cluster members. An empirical correction of the atmospheric templates can fix the discrepancies between expected and observed colors. Still, other biases in the evolutionary models prevent a more robust comparison between observations and theoretical absolute magnitudes. In particular, PMS evolutionary models seem to consistently underestimate the intrinsic near-infrared flux at the very late spectral types, and this may introduce spurious features in the <span class="hlt">low-mass</span> end of the photometrically-determined initial mass function of young clusters.</p> <div class="credits"> <p class="dwt_author">Scandariato, G.; Da Rio, N.; Robberto, M.; Pagano, I.; Stassun, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">197</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011A%26A...531A...7G"> <span id="translatedtitle">Time evolution of high-energy emissions of <span class="hlt">low-mass</span> <span class="hlt">stars</span>. I. Age determination using stellar chronology with white dwarfs in wide binaries</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Context. Stellar ages are extremely difficult to determine and often subject to large uncertainties, especially for field <span class="hlt">low-mass</span> <span class="hlt">stars</span>. We plan to carry out a calibration of the decrease in high-energy emissions of <span class="hlt">low-mass</span> GKM <span class="hlt">stars</span> with time, and therefore precise age determination is a key ingredient. The overall goal of our research is to study the time evolution of these high-energy emissions as an essential input to studying exoplanetary atmospheres. Aims: We propose to determine stellar ages with a methodology based on wide binaries. We are interested in systems composed of a <span class="hlt">low-mass</span> <span class="hlt">star</span> and a white dwarf (WD), where the latter serves as a stellar chronometer for the system. We aim at obtaining reliable ages for a sample of late-type <span class="hlt">stars</span> older than 1 Gyr. Methods: We selected a sample of wide binaries composed by a DA type WD and a GKM companion. High signal-to-noise, low-resolution spectroscopic observations were obtained for most of the WD members of the sample. Atmospheric parameters were determined by fitting the spectroscopic data to appropiate WD models. The total ages of the systems were derived by using cooling sequences, an initial-final mass relationship and evolutionary tracks, to account for the progenitor life. Results: The spectroscopic observations have allowed us to determine ages for the binary systems using WDs as cosmochronometers. We obtained reliable ages for 27 <span class="hlt">stars</span> between 1 and 5 Gyr, which is a range where age determination becomes difficult for field objects. Roughly half of these systems have cooling ages that contribute at least 30% the total age. We select those for further study since their age estimate should be less prone to systematic errors coming from the initial-final mass relationship. Conclusions: We have determined robust ages for a sizeable sample of GKM <span class="hlt">stars</span> that can be subsequently used to study the time evolution of their emissions associated to stellar magnetic activity. 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).Based on observations made with the WHT (William Herschel Telescope) operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.</p> <div class="credits"> <p class="dwt_author">Garcés, A.; Catalán, S.; Ribas, I.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">198</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/12533372"> <span id="translatedtitle">Innermost stable circular orbits around strange <span class="hlt">stars</span> and kHz QPOs in <span class="hlt">low-mass</span> X-ray binaries</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Exact calculations of innermost stable circular orbit (ISCO) around rotating strange <span class="hlt">stars</span> are performed within the framework of general relativity. Equations of state (EOS) of strange quark matter based on the MIT Bag Model with massive strange quarks and lowest order QCD interactions, are used. The presence of a solid crust of normal matter on rotating, mass accreting strange <span class="hlt">stars</span></p> <div class="credits"> <p class="dwt_author">J. L. Zdunik; P. Haensel; D. Gondek-Rosinska; E. Gourgoulhon</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">199</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012ApJS..201...20D"> <span id="translatedtitle">Short-duration Lensing Events. I. Wide-orbit Planets? Free-floating <span class="hlt">Low-mass</span> Objects? Or High-velocity <span class="hlt">Stars</span>?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Short-duration lensing events tend to be generated by <span class="hlt">low-mass</span> lenses or by lenses with high transverse velocities. Furthermore, for any given lens mass and speed, events of short duration are preferentially caused by nearby lenses (mesolenses) that can be studied in detail, or else by lenses so close to the source <span class="hlt">star</span> that finite-source-size effects may be detected, yielding information about both the Einstein ring radius and the surface of the lensed <span class="hlt">star</span>. Planets causing short-duration events may be in orbits with any orientation, and may have semimajor axes smaller than 1 AU, or they may reach the outer limits of their planetary systems, in the region corresponding to the solar system's Oort Cloud. They can have masses larger than Jupiter's or smaller than Pluto's. Lensing therefore has a unique potential to expand our understanding of planetary systems. A particular advantage of lensing is that it can provide precision measurements of system parameters, including the masses of and projected separation between <span class="hlt">star</span> and planet. We demonstrate how the parameters can be extracted and show that a great deal can be learned. For example, it is remarkable that the gravitational mass of nearby free-floating planet-mass lenses can be measured by complementing observations of a photometric event with deep images that detect the planet itself. A fraction of short events may be caused by high-velocity <span class="hlt">stars</span> located within a kiloparsec. Many high-velocity lenses are likely to be neutron <span class="hlt">stars</span> that received large natal kicks. Other high-speed <span class="hlt">stars</span> may be members of the halo population. Still others may be hypervelocity <span class="hlt">stars</span> that have been ejected from the Galactic center, or runaway <span class="hlt">stars</span> escaped from close binaries, possibly including the progenitor binaries of Type Ia supernovae.</p> <div class="credits"> <p class="dwt_author">Di Stefano, Rosanne</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">200</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22047665"> <span id="translatedtitle">SHORT-DURATION LENSING EVENTS. I. WIDE-ORBIT PLANETS? FREE-FLOATING <span class="hlt">LOW-MASS</span> OBJECTS? OR HIGH-VELOCITY <span class="hlt">STARS</span>?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Short-duration lensing events tend to be generated by <span class="hlt">low-mass</span> lenses or by lenses with high transverse velocities. Furthermore, for any given lens mass and speed, events of short duration are preferentially caused by nearby lenses (mesolenses) that can be studied in detail, or else by lenses so close to the source <span class="hlt">star</span> that finite-source-size effects may be detected, yielding information about both the Einstein ring radius and the surface of the lensed <span class="hlt">star</span>. Planets causing short-duration events may be in orbits with any orientation, and may have semimajor axes smaller than 1 AU, or they may reach the outer limits of their planetary systems, in the region corresponding to the solar system's Oort Cloud. They can have masses larger than Jupiter's or smaller than Pluto's. Lensing therefore has a unique potential to expand our understanding of planetary systems. A particular advantage of lensing is that it can provide precision measurements of system parameters, including the masses of and projected separation between <span class="hlt">star</span> and planet. We demonstrate how the parameters can be extracted and show that a great deal can be learned. For example, it is remarkable that the gravitational mass of nearby free-floating planet-mass lenses can be measured by complementing observations of a photometric event with deep images that detect the planet itself. A fraction of short events may be caused by high-velocity <span class="hlt">stars</span> located within a kiloparsec. Many high-velocity lenses are likely to be neutron <span class="hlt">stars</span> that received large natal kicks. Other high-speed <span class="hlt">stars</span> may be members of the halo population. Still others may be hypervelocity <span class="hlt">stars</span> that have been ejected from the Galactic center, or runaway <span class="hlt">stars</span> escaped from close binaries, possibly including the progenitor binaries of Type Ia supernovae.</p> <div class="credits"> <p class="dwt_author">Di Stefano, Rosanne [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-08-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_9");' href="#" 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onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_12");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">201</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2003ApJ...587..407C"> <span id="translatedtitle">Detection of Nine M8.0-L0.5 Binaries: The Very <span class="hlt">Low</span> <span class="hlt">Mass</span> Binary Population and Its Implications for Brown Dwarf and Very <span class="hlt">Low</span> <span class="hlt">Mass</span> <span class="hlt">Star</span> Formation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Use of the highly sensitive Hokupa'a/Gemini curvature wave front sensor has allowed direct adaptive optics (AO) guiding on very <span class="hlt">low</span> <span class="hlt">mass</span> (VLM) <span class="hlt">stars</span> with SpT = M8.0-L0.5. A survey of 39 such objects detected nine VLM binaries (seven of which were discovered for the first time to be binaries). Most of these systems are tight (separation <5 AU) and have similar masses (?Ks<0.8 mag; 0.85<q<1.0). However, two systems (LHS 2397a and 2M 2331016-040618) have large ?Ks>2.4 mag and consist of a VLM <span class="hlt">star</span> orbited by a much cooler L7-L8 brown dwarf companion. On the basis of this flux-limited (Ks<12 mag) survey of 39 M8.0-L0.5 <span class="hlt">stars</span> (mainly from the 2MASS sample of Gizis et al.), we find a sensitivity-corrected binary fraction in the range 15%+/-7% for M8.0-L0.5 <span class="hlt">stars</span> with separations greater than 2.6 AU. This is less than the 32%+/-9% measured for more massive M0-M4 dwarfs over the same separation range. It appears M8.0-L0.5 binaries (as well as L and T dwarf binaries) have a much smaller semimajor axis distribution peak (~4 AU) compared to more massive M and G dwarfs, which have a broad peak at larger ~30 AU separations. We also find no VLM binary systems (defined here as systems with Mtot<0.185Msolar) with separations greater than 15 AU. We briefly explore possible reasons why VLM binaries are slightly less common, nearly equal in mass, and much more tightly bound compared to more massive binaries. We investigate the hypothesis that the lack of wide (a>20 AU) VLM/brown dwarf binaries may be explained if the binary components were given a significant differential velocity kick. Such a velocity kick is predicted by current ``ejection'' theories, where brown dwarfs are formed because they are ejected from their embryonic minicluster and therefore starved of accretion material. We find that a kick from a close triple or quadruple encounter (imparting a differential kick of ~3 km s-1 between the members of an escaping binary) could reproduce the observed cutoff in the semimajor axis distribution at ~20 AU. However, the estimated binarity (<~5%) produced by such ejection scenarios is below the 15%+/-7% observed. Similarly, VLM binaries could be the final hardened binaries produced when a minicluster decays. However, the models of Sterzik & Durisen and Durisen, Sterzik, & Pickett also could not produce a VLM binary fraction of 15% and a G <span class="hlt">star</span> binary fraction of 57%. The observed VLM binary frequency could possibly be produced by cloud core fragmentation. However, our estimate of a fragmentation-produced VLM binary semimajor axis distribution contains a significant fraction of ``wide'' VLM binaries with a>20 AU in contrast to observation. In summary, more detailed theoretical work will be needed to explain these interesting results that show VLM binaries to be a significantly different population from more massive M & G dwarf binaries.</p> <div class="credits"> <p class="dwt_author">Close, Laird M.; Siegler, Nick; Freed, Melanie; Biller, Beth</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">202</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013ApJ...775...85N"> <span id="translatedtitle">A Survey of H2O, CO2, and CO Ice Features toward Background <span class="hlt">Stars</span> and <span class="hlt">low-mass</span> Young Stellar Objects Using AKARI</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present near-infrared spectroscopic observations of 19 molecular clouds made using the AKARI satellite, and the data reduction pipeline written to analyze those observations. The 2.5-5 ?m spectra of 30 objects—22 field <span class="hlt">stars</span> behind quiescent molecular clouds and 8 <span class="hlt">low-mass</span> young stellar objects in cores—were successfully extracted using the pipeline. Those spectra are further analyzed to calculate the column densities of key solid phase molecular species, including H2O, CO2, CO, and OCN–. The profile of the H2O ice band is seen to vary across the objects observed and we suggest that the extended red wing may be an evolutionary indicator of both dust and ice mantle properties. The observation of 22 spectra with fluxes as low as < 5 mJy toward background <span class="hlt">stars</span>, including 15 where the column densities of H2O, CO, and CO2 were calculated, provides valuable data that could help to benchmark the initial conditions in <span class="hlt">star</span>-forming regions prior to the onset of <span class="hlt">star</span> formation. Based on observations with AKARI, a JAXA project with the participation of ESA.</p> <div class="credits"> <p class="dwt_author">Noble, J. A.; Fraser, H. J.; Aikawa, Y.; Pontoppidan, K. M.; Sakon, I.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">203</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1986ApJ...307..415S"> <span id="translatedtitle">Self-regulated cooling flows in elliptical galaxies and in cluster cores - Is exclusively <span class="hlt">low</span> <span class="hlt">mass</span> <span class="hlt">star</span> formation really necessary?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A self-consistent treatment of the heating by supernovae associated with <span class="hlt">star</span> formation in a spherically symmetric cooling flow in a cluster core or elliptical galaxy is presented. An initial stellar mass function similar to that in the solar neighborhood is adopted. Inferred <span class="hlt">star</span>-formation rates, within the cooling region - typically the inner 100 kpc around dominant galaxies at the centers of cooling flows in XD clusters - are reduced by about a factor of 2, relative to rates inferred when the heat input from <span class="hlt">star</span> formation is ignored. Truncated initial mass functions (IMFs) are also considered, in which massive <span class="hlt">star</span> formation is suppressed in accordance with previous treatments, and colors are predicted for <span class="hlt">star</span> formation in cooling flows associated with central dominant elliptical galaxies and with isolated elliptical galaxies surrounded by gaseous coronae. The low inferred cooling-flow rates around isolated elliptical galaxies are found to be insensitive to the upper mass cutoff in the IMF, provided that the upper mass cutoff exceeds 2 M solar mass. Comparison with observed colors favors a cutoff in the IMF above 1 M solar mass in at least two well-studied cluster cooling flows, but a normal IMF cannot be excluded definitively. Models for NGC 1275 support a young (less than about 3 Gyr) cooling flow. As for the isolated elliptical galaxies, the spread in colors is consistent with a normal IMF. A definitive test of the IMF arising via <span class="hlt">star</span> formation in cooling flows requires either UV spectral data or supernova searches in the cooling-flow-centered galaxies.</p> <div class="credits"> <p class="dwt_author">Silk, J.; Djorgovski, S.; Wyse, R. F. G.; Bruzual A., G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">204</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/27681405"> <span id="translatedtitle">HIGH AND <span class="hlt">LOW-MASS</span> <span class="hlt">STAR</span>-FORMING REGIONS FROM HIERARCHICAL GRAVITATIONAL FRAGMENTATION. HIGH LOCAL <span class="hlt">STAR</span> FORMATION RATES WITH LOW GLOBAL EFFICIENCIES</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We investigate the properties of '<span class="hlt">star</span>-forming regions' in a previously published numerical simulation of molecular cloud formation out of compressive motions in the warm neutral atomic interstellar medium, neglecting magnetic fields and stellar feedback. We study the properties (density, total gas + <span class="hlt">stars</span> mass, stellar mass, velocity dispersion, and <span class="hlt">star</span> formation rate (SFR)) of the cloud hosting the first local,</p> <div class="credits"> <p class="dwt_author">Enrique Vazquez-Semadeni; Gilberto C. Gomez; Javier Ballesteros-Paredes; A.-Katharina Jappsen; Ralf S. Klessen</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">205</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012ApJ...759..128N"> <span id="translatedtitle">Long-duration X-Ray Flash and X-Ray-rich Gamma-Ray Bursts from <span class="hlt">Low-mass</span> Population III <span class="hlt">Stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Recent numerical simulations suggest that Population III (Pop III) <span class="hlt">stars</span> were born with masses not larger than ~100 M ? and typically ~40 M ?. By self-consistently considering the jet generation and propagation in the envelope of these <span class="hlt">low-mass</span> Pop III <span class="hlt">stars</span>, we find that a Pop III blue supergiant <span class="hlt">star</span> has the possibility of giving rise to a gamma-ray burst (GRB) even though it keeps a massive hydrogen envelope. We evaluate observational characteristics of Pop III GRBs and predict that Pop III GRBs have a duration of ~105 s in the observer frame and a peak luminosity of ~5 × 1050 erg s-1. Assuming that the E p-L p (or E p-E ?, iso) correlation holds for Pop III GRBs, we find that the spectrum peak energy falls at approximately a few keV (or ~100 keV) in the observer frame. We discuss the detectability of Pop III GRBs by future satellite missions such as EXIST and Lobster. If the E p-E ?, iso correlation holds, we have the possibility to detect Pop III GRBs at z ~ 9 as long-duration X-ray-rich GRBs by EXIST. Conversely, if the E p-L p correlation holds, we have the possibility to detect Pop III GRBs up to z ~ 19 as long-duration X-ray flashes by Lobster.</p> <div class="credits"> <p class="dwt_author">Nakauchi, Daisuke; Suwa, Yudai; Sakamoto, Takanori; Kashiyama, Kazumi; Nakamura, Takashi</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">206</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/43181564"> <span id="translatedtitle">Coronal Mass Ejection (CME) Activity of <span class="hlt">Low</span> <span class="hlt">Mass</span> M <span class="hlt">Stars</span> as An Important Factor for The Habitability of Terrestrial Exoplanets. I. CME Impact on Expected Magnetospheres of Earth-Like Exoplanets in Close-In Habitable Zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary"><span class="hlt">Low</span> <span class="hlt">mass</span> M- and K-type <span class="hlt">stars</span> are much more numerous in the solar neighborhood than solar-like G-type <span class="hlt">stars</span>. Therefore, some of them may appear as interesting candidates for the target <span class="hlt">star</span> lists of terrestrial exoplanet (i.e., planets with mass, radius, and internal parameters identical to Earth) search programs like Darwin (ESA) or the Terrestrial Planet Finder Coronagraph\\/Inferometer (NASA). The higher</p> <div class="credits"> <p class="dwt_author">Maxim L. Khodachenko; Ignasi Ribas; Helmut Lammer; Jean-Mathias Grießmeier; Martin Leitner; Franck Selsis; Carlos Eiroa; Arnold Hanslmeier; Helfried K. Biernat; Charles J. Farrugia; Helmut O. Rucker</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">207</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21583051"> <span id="translatedtitle">INFRARED AND OPTICAL POLARIMETRY AROUND THE <span class="hlt">LOW-MASS</span> <span class="hlt">STAR</span>-FORMING REGION NGC 1333 IRAS 4A</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We performed J- and R-band linear polarimetry with the 4.2 m William Herschel Telescope at the Observatorio del Roque de los Muchachos and with the 1.6 m telescope at the Observatorio do Pico dos Dias, respectively, to derive the magnetic field geometry of the diffuse molecular cloud surrounding the embedded protostellar system NGC 1333 IRAS 4A. We obtained interstellar polarization data for about three dozen <span class="hlt">stars</span>. The distribution of polarization position angles has low dispersion and suggests the existence of an ordered magnetic field component at physical scales larger than the protostar. Some of the observed <span class="hlt">stars</span> present intrinsic polarization and evidence of being young stellar objects. The estimated mean orientation of the interstellar magnetic field as derived from these data is almost perpendicular to the main direction of the magnetic field associated with the dense molecular envelope around IRAS 4A. Since the distribution of the CO emission in NGC 1333 indicates that the diffuse molecular gas has a multi-layered structure, we suggest that the observed polarization position angles are caused by the superposed projection of different magnetic field components along the line of sight.</p> <div class="credits"> <p class="dwt_author">Alves, Felipe O.; Girart, Josep M. [Institut de Ciencies de l'Espai (IEEC-CSIC), Campus UAB, Facultat de Ciencies, 08193 Bellaterra, Catalunya (Spain); Acosta-Pulido, Jose A. [Instituto de Astrofisica de Canarias, E-38200 La Laguna, Tenerife (Spain); Franco, Gabriel A. P. [Departamento de Fisica-ICEx-UFMG, 30.123-970 Belo Horizonte (Brazil); Lopez, Rosario, E-mail: oliveira@ice.cat, E-mail: girart@ice.cat, E-mail: jap@iac.es, E-mail: franco@fisica.ufmg.br, E-mail: rosario@am.ub.es, E-mail: falves@astro.uni-bonn.de [Departament d'Astronomia i Meteorologia (IEEC-UB), Institut de Ciencies del Cosmos, Universitat de Barcelona, MartI i Franques 1, E-08028 Barcelona (Spain)</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-07-15</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">208</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013ApJ...767...31B"> <span id="translatedtitle">A Thermal Infrared Imaging Study of Very <span class="hlt">Low</span> <span class="hlt">Mass</span>, Wide-separation Brown Dwarf Companions to Upper Scorpius <span class="hlt">Stars</span>: Constraining Circumstellar Environments</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present a 3-5 ?m LBT/MMT adaptive optics imaging study of three Upper Scorpius <span class="hlt">stars</span> with brown dwarf (BD) companions with very <span class="hlt">low</span> <span class="hlt">masses</span>/mass ratios (M BD <25 M Jup; M BD/M sstarf ? 1%-2%) and wide separations (300-700 AU): GSC 06214, 1RXS 1609, and HIP 78530. We combine these new thermal IR data with existing 1-4 ?m and 24 ?m photometry to constrain the properties of the BDs and identify evidence for circumprimary/circumsecondary disks in these unusual systems. We confirm that GSC 06214B is surrounded by a disk, further showing that this disk produces a broadband IR excess due to small dust near the dust sublimation radius. An unresolved 24 ?m excess in the system may be explained by the contribution from this disk. 1RXS 1609B exhibits no 3-4 ?m excess, nor does its primary; however, the system as a whole has a modest 24 ?m excess, which may come from warm dust around the primary and/or BD. Neither object in the HIP 78530 system exhibits near- to mid-IR excesses. We additionally find that the 1-4 ?m colors of HIP 78530B match a spectral type of M3 ± 2, inconsistent with the M8 spectral type assigned based on its near-IR spectrum, indicating that it may be a <span class="hlt">low-mass</span> <span class="hlt">star</span> rather than a BD. We present new upper limits on additional <span class="hlt">low-mass</span> companions in the system (<5 M Jup beyond 175 AU). Finally, we examine the utility of circumsecondary disks as probes of the formation histories of wide BD companions, finding that the presence of a disk may disfavor BD formation near the primary with subsequent outward scattering. Observations reported here were obtained at the LBT and MMT Observatories. The MMT Observatory is a joint facility of the University of Arizona and the Smithsonian Institution. The LBT is an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University; and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University of Virginia.</p> <div class="credits"> <p class="dwt_author">Bailey, Vanessa; Hinz, Philip M.; Currie, Thayne; Su, Kate Y. L.; Esposito, Simone; Hill, John M.; Hoffmann, William F.; Jones, Terry; Kim, Jihun; Leisenring, Jarron; Meyer, Michael; Murray-Clay, Ruth; Nelson, Matthew J.; Pinna, Enrico; Puglisi, Alfio; Rieke, George; Rodigas, Timothy; Skemer, Andrew; Skrutskie, Michael F.; Vaitheeswaran, Vidhya; Wilson, John C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">209</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011ASPC..447..107P"> <span id="translatedtitle">Simulations of the Common Envelope Interaction Between a Red Giant Branch <span class="hlt">Star</span> and <span class="hlt">Low-Mass</span> Companions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present three-dimensional hydrodynamical simulations of the fast in-spiral phase of the common envelope interaction between a red giant <span class="hlt">star</span> and a range of companions with different masses. In order to verify the reliability of the numerics we use two different approaches. The code-to-code comparison shows consistent results. We then compare the outcomes of our simulations to post common envelope systems. At the end of the simulations, most of the envelope of the progenitor is still bound to the system and the orbital separations are systematically larger than those observed. We explain what the reasons for this discrepancy might be and how we will proceed with our investigation.</p> <div class="credits"> <p class="dwt_author">Passy, J.-C.; De Marco, O.; Fryer, C. L.; Herwig, F.; Diehl, S.; Oishi, J. S.; Mac Low, M.-M.; Bryan, G. L.; Rockefeller, G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">210</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21583009"> <span id="translatedtitle">SPECTRAL ENERGY DISTRIBUTIONS OF YOUNG <span class="hlt">STARS</span> IN IC 348: THE ROLE OF DISKS IN ANGULAR MOMENTUM EVOLUTION OF YOUNG, <span class="hlt">LOW-MASS</span> <span class="hlt">STARS</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Theoretical work suggests that a young <span class="hlt">star</span>'s angular momentum content and rotation rate may be strongly influenced by magnetic interactions with its circumstellar disk. A generic prediction of these 'disk-locking' theories is that a disk-locked <span class="hlt">star</span> will be forced to co-rotate with the Keplerian angular velocity of the inner edge of the disk; that is, the disk's inner-truncation radius should equal its co-rotation radius. These theories have also been interpreted to suggest a gross correlation between young <span class="hlt">stars</span>' rotation periods and the structural properties of their circumstellar disks, such that slowly rotating <span class="hlt">stars</span> possess close-in disks that enforce the <span class="hlt">star</span>'s slow rotation, whereas rapidly rotating <span class="hlt">stars</span> possess anemic or evacuated inner disks that are unable to brake the <span class="hlt">stars</span> and instead the <span class="hlt">stars</span> spin up as they contract. To test these expectations, we model the spectral energy distributions (SEDs) of 33 young <span class="hlt">stars</span> in IC 348 with known rotation periods and infrared excesses indicating the presence of circumstellar disks. For each <span class="hlt">star</span>, we match the observed SED, typically sampling 0.6-8.0 {mu}m, to a grid of 200,000 pre-computed <span class="hlt">star</span>+disk radiative transfer models, from which we infer the disk's inner-truncation radius. We then compare this truncation radius to the disk's co-rotation radius, calculated from the <span class="hlt">star</span>'s measured rotation period. We do not find obvious differences in the disk truncation radii of slow rotators versus rapid rotators. This holds true both at the level of whether close-in disk material is present at all, and in analyzing the precise location of the inner disk edge relative to the co-rotation radius among the subset of <span class="hlt">stars</span> with close-in disk material. One interpretation is that disk locking is unimportant for the IC 348 <span class="hlt">stars</span> in our sample. Alternatively, if disk locking does operate, then it must operate on both the slow and rapid rotators, potentially producing both spin-up and spin-down torques, and the transition from the disk-locked state to the disk-released state must occur more rapidly than the stellar contraction timescale.</p> <div class="credits"> <p class="dwt_author">Le Blanc, Thompson S.; Stassun, Keivan G. [Department of Physics and Astronomy, Vanderbilt University, 6301 Stevenson Center, Nashville, TN 37235 (United States); Covey, Kevin R. [Department of Astronomy, Cornell University, 226 Space Sciences Building, Ithaca, NY 14853 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-08-15</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">211</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AJ....142...55L"> <span id="translatedtitle">Spectral Energy Distributions of Young <span class="hlt">Stars</span> in IC 348: The Role of Disks in Angular Momentum Evolution of Young, <span class="hlt">Low-mass</span> <span class="hlt">Stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Theoretical work suggests that a young <span class="hlt">star</span>'s angular momentum content and rotation rate may be strongly influenced by magnetic interactions with its circumstellar disk. A generic prediction of these "disk-locking" theories is that a disk-locked <span class="hlt">star</span> will be forced to co-rotate with the Keplerian angular velocity of the inner edge of the disk; that is, the disk's inner-truncation radius should equal its co-rotation radius. These theories have also been interpreted to suggest a gross correlation between young <span class="hlt">stars</span>' rotation periods and the structural properties of their circumstellar disks, such that slowly rotating <span class="hlt">stars</span> possess close-in disks that enforce the <span class="hlt">star</span>'s slow rotation, whereas rapidly rotating <span class="hlt">stars</span> possess anemic or evacuated inner disks that are unable to brake the <span class="hlt">stars</span> and instead the <span class="hlt">stars</span> spin up as they contract. To test these expectations, we model the spectral energy distributions (SEDs) of 33 young <span class="hlt">stars</span> in IC 348 with known rotation periods and infrared excesses indicating the presence of circumstellar disks. For each <span class="hlt">star</span>, we match the observed SED, typically sampling 0.6-8.0 ?m, to a grid of 200,000 pre-computed <span class="hlt">star</span>+disk radiative transfer models, from which we infer the disk's inner-truncation radius. We then compare this truncation radius to the disk's co-rotation radius, calculated from the <span class="hlt">star</span>'s measured rotation period. We do not find obvious differences in the disk truncation radii of slow rotators versus rapid rotators. This holds true both at the level of whether close-in disk material is present at all, and in analyzing the precise location of the inner disk edge relative to the co-rotation radius among the subset of <span class="hlt">stars</span> with close-in disk material. One interpretation is that disk locking is unimportant for the IC 348 <span class="hlt">stars</span> in our sample. Alternatively, if disk locking does operate, then it must operate on both the slow and rapid rotators, potentially producing both spin-up and spin-down torques, and the transition from the disk-locked state to the disk-released state must occur more rapidly than the stellar contraction timescale.</p> <div class="credits"> <p class="dwt_author">Le Blanc, Thompson S.; Covey, Kevin R.; Stassun, Keivan G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">212</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013A%26A...554A..17J"> <span id="translatedtitle">The influence of turbulence during magnetized core collapse and its consequences on <span class="hlt">low-mass</span> <span class="hlt">star</span> formation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Context. Theoretical and numerical studies of <span class="hlt">star</span> formation have shown that a magnetic field can greatly influence both disk formation and its fragmentation, with even relatively low magnetic field strengths being able to prevent these processes. However, very few studies have investigated the combined effects of magnetic field and turbulence. Aims: We study the collapse of turbulent, magnetized prestellar cores, focusing on the effects of magnetic diffusion, and misalignment between rotation axis and magnetic field, on the formation of disks, fragmentation, and the generation of outflows. Methods: We performed three-dimensional, adaptive-mesh, numerical simulations of magnetically super-critical collapsing dense cores of 5 M? using the magneto-hydrodynamic code Ramses. A turbulent velocity field is imposed as initial conditions, characterized by a Kolmogorov power spectrum. Different levels of turbulence (a laminar case, as well as subsonic and supersonic cases) and magnetization (from weak to strong magnetization) are investigated, as are three realizations for the turbulent velocity field. Results: The turbulent velocity field imposed as initial conditions contains a non-zero angular momentum, which is responsible for a misalignment of the rotation axis with respect to the initial magnetic field, and an effective turbulent diffusivity in the vicinity of the core. Both effects are responsible for a significant decrease in the magnetic braking, and they facilitate the formation of early massive disks. These disks can fragment even with ? ~ 5 at late times, in contrast to simulations of 1 M? cores, where fragmentation is prevented for these values of ?. Slow asymmetric outflows are always launched, and they carry a mass comparable to that of the adiabatic first core. Conclusions: Because of turbulence-induced misalignment and magnetic diffusivity, massive disk formation is possible; nevertheless, their mass and size are much more reduced than for disks formed in unmagnetized collapsing cores. We find that for ? ? 5 fragmentation can occur.</p> <div class="credits"> <p class="dwt_author">Joos, M.; Hennebelle, P.; Ciardi, A.; Fromang, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">213</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22086363"> <span id="translatedtitle">LONG-DURATION X-RAY FLASH AND X-RAY-RICH GAMMA-RAY BURSTS FROM <span class="hlt">LOW-MASS</span> POPULATION III <span class="hlt">STARS</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Recent numerical simulations suggest that Population III (Pop III) <span class="hlt">stars</span> were born with masses not larger than {approx}100 M {sub Sun} and typically {approx}40 M {sub Sun }. By self-consistently considering the jet generation and propagation in the envelope of these <span class="hlt">low-mass</span> Pop III <span class="hlt">stars</span>, we find that a Pop III blue supergiant <span class="hlt">star</span> has the possibility of giving rise to a gamma-ray burst (GRB) even though it keeps a massive hydrogen envelope. We evaluate observational characteristics of Pop III GRBs and predict that Pop III GRBs have a duration of {approx}10{sup 5} s in the observer frame and a peak luminosity of {approx}5 Multiplication-Sign 10{sup 50} erg s{sup -1}. Assuming that the E {sub p}-L {sub p} (or E {sub p}-E {sub {gamma},iso}) correlation holds for Pop III GRBs, we find that the spectrum peak energy falls at approximately a few keV (or {approx}100 keV) in the observer frame. We discuss the detectability of Pop III GRBs by future satellite missions such as EXIST and Lobster. If the E {sub p}-E {sub {gamma},iso} correlation holds, we have the possibility to detect Pop III GRBs at z {approx} 9 as long-duration X-ray-rich GRBs by EXIST. Conversely, if the E {sub p}-L {sub p} correlation holds, we have the possibility to detect Pop III GRBs up to z {approx} 19 as long-duration X-ray flashes by Lobster.</p> <div class="credits"> <p class="dwt_author">Nakauchi, Daisuke; Kashiyama, Kazumi; Nakamura, Takashi [Department of Physics, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502 (Japan); Suwa, Yudai [Yukawa Institute for Theoretical Physics, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502 (Japan); Sakamoto, Takanori [Center for Research and Exploration in Space Science and Technology (CRESST), NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-11-10</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">214</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010HEAD...11.4307H"> <span id="translatedtitle">New Insights Into The Relation Between Mass Accretion Rate And The X-ray Properties Of Neutron-<span class="hlt">star</span> <span class="hlt">Low-mass</span> X-ray Binaries</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The relation between mass accretion rate and the X-ray properties of neutron-<span class="hlt">star</span> <span class="hlt">low-mass</span> X-ray binaries (NS-LMXBs) remains poorly understood. One of the major questions is whether differences in accretion rate alone are enough to account for the various (Z and atoll) sub-classes. Here I report on observations of the unique, super-Eddington neutron-<span class="hlt">star</span> transient XTE J1701-462 that answer this question unambiguously. During its 20 month outburst, which was followed in unprecedented detail with RXTE, this source evolved through various NS-LMXBs sub-classes. This evolution primarily manifested itself as a change in the shape of the tracks in X-ray color-color and hardness-intensity diagrams, and was accompanied by changes in the kHz quasi-periodic oscillations, broad-band variability, burst behavior, and X-ray spectra. The observations strongly suggest that the wide variety in behavior observed in NS-LMXBs with different luminosities can be linked through changes in a single variable parameter, namely the mass accretion rate, without the need for additional differences in neutron <span class="hlt">star</span> spin/magnetic field, or viewing angle, as was long believed. I will also discuss the implications of these findings for the nature of the spectral evolution in individual NS-LMXBs accreting at near-Eddington luminosities. I suggest that, contrary to the low-luminosity NS-LNMBs, motion along the color-color tracks of these sources is most likely not caused by changes in the mass accretion rate, but rather is the result of instabilities in the accretion flow.</p> <div class="credits"> <p class="dwt_author">Homan, Jeroen</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">215</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012A%26G....53a...6."> <span id="translatedtitle">News and Views: <span class="hlt">Low-mass</span> <span class="hlt">stars</span> pull weight in globular clusters; Red dwarf planets are common, too; More planets than <span class="hlt">stars</span> in the Milky Way? After Bullet comes Musket Ball; Planets survive red giant phase</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Gravitational microlensing techniques have uncovered the first <span class="hlt">low-mass</span> <span class="hlt">star</span> found in a globular cluster, suggesting that previously undetectable <span class="hlt">stars</span> may contribute to cluster masses, meaning that there is less dark matter to find. Data from NASA's Kepler mission suggest that small rocky planets may be common orbiting red dwarf <span class="hlt">stars</span> - and because red dwarfs are common types of <span class="hlt">star</span>, this means that rocky planets may be commonplace in the Milky Way. A survey using gravitational microlensing suggest that exoplanets are the exception rather than the rule in the Milky Way - and that small planets like Earth are more common than gas and ice giants. The Bullet Cluster famously allows mapping of the dark matter distribution during the merger of two clusters. Now a merging cluster named the Musket Ball shows a later stage in the process. Planets are not necessarily vaporized when a red giant <span class="hlt">star</span> expands; the cores of gas giants may survive, but they would not be pleasant places to live. Data from NASA's Kepler mission has revealed two small planets orbiting a <span class="hlt">star</span> after its red giant phase.</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">2012-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">216</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22039388"> <span id="translatedtitle">PLANETS AROUND <span class="hlt">LOW-MASS</span> <span class="hlt">STARS</span> (PALMS). I. A SUBSTELLAR COMPANION TO THE YOUNG M DWARF 1RXS J235133.3+312720</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We report the discovery of a brown dwarf companion to the young M dwarf 1RXS J235133.3+312720 as part of a high contrast imaging search for planets around nearby young <span class="hlt">low-mass</span> <span class="hlt">stars</span> with Keck-II/NIRC2 and Subaru/HiCIAO. The 2.''4 ({approx}120 AU) pair is confirmed to be comoving from two epochs of high-resolution imaging. Follow-up low- and moderate-resolution near-infrared spectroscopy of 1RXS J2351+3127 B with IRTF/SpeX and Keck-II/OSIRIS reveals a spectral type of L0{sup +2}{sub -1}. The M2 primary <span class="hlt">star</span> 1RXS J2351+3127 A exhibits X-ray and UV activity levels comparable to young moving group members with ages of {approx}10-100 Myr. UVW kinematics based the measured radial velocity of the primary and the system's photometric distance (50 {+-} 10 pc) indicate it is likely a member of the {approx}50-150 Myr AB Dor moving group. The near-infrared spectrum of 1RXS J2351+3127 B does not exhibit obvious signs of youth, but its H-band morphology shows subtle hints of intermediate surface gravity. The spectrum is also an excellent match to the {approx}200 Myr M9 brown dwarf LP 944-20. Assuming an age of 50-150 Myr, evolutionary models imply a mass of 32 {+-} 6 M{sub Jup} for the companion, making 1RXS J2351+3127 B the second lowest-mass member of the AB Dor moving group after the L4 companion CD-35 2722 B and one of the few benchmark brown dwarfs known at young ages.</p> <div class="credits"> <p class="dwt_author">Bowler, Brendan P.; Liu, Michael C.; Cieza, Lucas A.; Kraus, Adam L. [Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Shkolnik, Evgenya L. [Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ 86001 (United States); Dupuy, Trent J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Tamura, Motohide, E-mail: bpbowler@ifa.hawaii.edu [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-07-10</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">217</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013ApJ...767...28P"> <span id="translatedtitle">Using High-resolution Optical Spectra to Measure Intrinsic Properties of <span class="hlt">Low-mass</span> <span class="hlt">Stars</span>: New Properties for KOI-314 and GJ 3470</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We construct high signal-to-noise "template" spectra by co-adding hundreds of spectra of nearby dwarfs spanning K7 to M4, taken with Keck/HIRES as part of the California Planet Search. We identify several spectral regions in the visible (370-800 nm) that are sensitive to the stellar luminosity and metallicity. We use these regions to develop a spectral calibration method to measure the mass, metallicity, and distance of <span class="hlt">low-mass</span> <span class="hlt">stars</span>, without the requirement of geometric parallaxes. Testing our method on a sample of nearby M dwarfs, we show that we can reproduce stellar masses to about 8%-10%, metallicity to ~0.15 dex, and distance to 11%. We were able to make use of HIRES spectra obtained as part of the radial velocity monitoring of the <span class="hlt">star</span> KOI-314 to derive a new mass estimate of 0.57 ± 0.05 M ?, a radius of 0.54 ± 0.05 R ?, a metallicity, [Fe/H], of -0.28 ± 0.10, and a distance of 66.5 ± 7.3 pc. Using HARPS archival data and combining our spectral method with constraints from transit observations, we are also able to derive the stellar properties of GJ 3470, a transiting planet hosting M dwarf. We estimate a mass of 0.53 ± 0.05 M ?, a radius of 0.50 ± 0.05 R ?, a metallicity, [Fe/H], of 0.12 ± 0.12, and a distance of 29.9+/- _{3.4}^{3.7} pc.</p> <div class="credits"> <p class="dwt_author">Pineda, J. Sebastian; Bottom, Michael; Johnson, John A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">218</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013prpl.conf1K072T"> <span id="translatedtitle">Observation vs. theory: testing the synthetic IR colours of young very <span class="hlt">low</span> <span class="hlt">mass</span> <span class="hlt">stars</span>/brown dwarfs using the evolutionary tracks</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Our ability to accurately derive stellar properties from spectral energy distributions (SEDs) depends on how well they can be fit with atmospheric models. The AMES-Dusty synthetic spectra (Allard et al., 2001), which incorporate dust grains suspended in the stellar atmosphere, are commonly used to fit SEDs of very <span class="hlt">low</span> <span class="hlt">mass</span> <span class="hlt">stars</span> (VLMS) and brown dwarfs (BDs). Recently, the same group has produced an updated model named BT-Settl (Allard et al., 2012) that allow these grains to gradually settle out of the atmosphere at cooler temperatures. Using these models it is now possible to produce the NIR colours across the main sequence from spectral types M to T. However, one significant area in which these Dusty and Settl models have not been thoroughly tested is in PMS VLMS/BDs. We use empirical IR colours of PMS M-dwarfs to show that both of these models show significant discrepancies with observations. We find that the synthetic spectra imply a temperature up to 500K cooler than expected for these objects from the theoretical evolutionary tracks for their estimated ages. We postulate that the problem lies mainly with the spectra; and if so, we conjecture that an incorrect H2O opacity may be to blame, aided by additional dust effects.</p> <div class="credits"> <p class="dwt_author">Tottle, Jonathan; Mohanty, Subhanjoy</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">219</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/17407406"> <span id="translatedtitle">Coronal mass ejection (CME) activity of <span class="hlt">low</span> <span class="hlt">mass</span> M <span class="hlt">stars</span> as an important factor for the habitability of terrestrial exoplanets. I. CME impact on expected magnetospheres of Earth-like exoplanets in close-in habitable zones.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary"><span class="hlt">Low</span> <span class="hlt">mass</span> M- and K-type <span class="hlt">stars</span> are much more numerous in the solar neighborhood than solar-like G-type <span class="hlt">stars</span>. Therefore, some of them may appear as interesting candidates for the target <span class="hlt">star</span> lists of terrestrial exoplanet (i.e., planets with mass, radius, and internal parameters identical to Earth) search programs like Darwin (ESA) or the Terrestrial Planet Finder Coronagraph/Inferometer (NASA). The higher level of stellar activity of <span class="hlt">low</span> <span class="hlt">mass</span> M <span class="hlt">stars</span>, as compared to solar-like G <span class="hlt">stars</span>, as well as the closer orbital distances of their habitable zones (HZs), means that terrestrial-type exoplanets within HZs of these <span class="hlt">stars</span> are more influenced by stellar activity than one would expect for a planet in an HZ of a solar-like <span class="hlt">star</span>. Here we examine the influences of stellar coronal mass ejection (CME) activity on planetary environments and the role CMEs may play in the definition of habitability criterion for the terrestrial type exoplanets near M <span class="hlt">stars</span>. We pay attention to the fact that exoplanets within HZs that are in close proximity to <span class="hlt">low</span> <span class="hlt">mass</span> M <span class="hlt">stars</span> may become tidally locked, which, in turn, can result in relatively weak intrinsic planetary magnetic moments. Taking into account existing observational data and models that involve the Sun and related hypothetical parameters of extrasolar CMEs (density, velocity, size, and occurrence rate), we show that Earth-like exoplanets within close-in HZs should experience a continuous CME exposure over long periods of time. This fact, together with small magnetic moments of tidally locked exoplanets, may result in little or no magnetospheric protection of planetary atmospheres from a dense flow of CME plasma. Magnetospheric standoff distances of weakly magnetized Earth-like exoplanets at orbital distances <or=0.1 AU can be shrunk, under the action of CMEs, to altitudes of about 1,000 km above the planetary surface. Such compressed magnetospheres may have crucial consequences for atmospheric erosion processes. PMID:17407406</p> <div class="credits"> <p class="dwt_author">Khodachenko, Maxim L; Ribas, Ignasi; Lammer, Helmut; Griessmeier, Jean-Mathias; Leitner, Martin; Selsis, Franck; Eiroa, Carlos; Hanslmeier, Arnold; Biernat, Helfried K; Farrugia, Charles J; Rucker, Helmut O</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">220</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013MNRAS.tmp.2427B"> <span id="translatedtitle">Daily multiwavelength Swift monitoring of the neutron <span class="hlt">star</span> <span class="hlt">low-mass</span> X-ray binary Cen X-4: evidence for accretion and reprocessing during quiescence</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We conducted the first long-term (60 d), multiwavelength (optical, ultraviolet, UV, and X-ray) simultaneous monitoring of Cen X-4 with daily Swift observations from 2012 June to August, with the goal of understanding variability in the <span class="hlt">low-mass</span> X-ray binary Cen X-4 during quiescence. We found Cen X-4 to be highly variable in all energy bands on time-scales from days to months, with the strongest quiescent variability a factor of 22 drop in the X-ray count rate in only 4 d. The X-ray, UV and optical (V band) emission are correlated on time-scales down to less than 110 s. The shape of the correlation is a power law with index ? about 0.2-0.6. The X-ray spectrum is well fitted by a hydrogen neutron <span class="hlt">star</span> (NS) atmosphere (kT = 59-80 eV) and a power law (with spectral index ? = 1.4-2.0), with the spectral shape remaining constant as the flux varies. Both components vary in tandem, with each responsible for about 50 per cent of the total X-ray flux, implying that they are physically linked. We conclude that the X-rays are likely generated by matter accreting down to the NS surface. Moreover, based on the short time-scale of the correlation, we also unambiguously demonstrate that the UV emission cannot be due to either thermal emission from the stream impact point, or a standard optically thick, geometrically thin disc. The spectral energy distribution shows a small UV emitting region, too hot to arise from the accretion disc, that we identified as a hotspot on the companion <span class="hlt">star</span>. Therefore, the UV emission is most likely produced by reprocessing from the companion <span class="hlt">star</span>, indeed the vertical size of the disc is small and can only reprocess a marginal fraction of the X-ray emission. We also found the accretion disc in quiescence to likely be UV faint, with a minimal contribution to the whole UV flux.</p> <div class="credits"> <p class="dwt_author">Bernardini, F.; Cackett, E. M.; Brown, E. F.; D'Angelo, C.; Degenaar, N.; Miller, J. M.; Reynolds, M.; Wijnands, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-10-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_10");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return 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href="#">11</a> <a style="font-weight: bold;">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_13");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">221</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21319535"> <span id="translatedtitle">THE FREQUENCY OF <span class="hlt">LOW-MASS</span> EXOPLANETS</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We report first results from the Anglo-Australian Telescope Rocky Planet Search-an intensive, high-precision Doppler planet search targeting <span class="hlt">low-mass</span> exoplanets in contiguous 48 night observing blocks. On this run, we targeted 24 bright, nearby and intrinsically stable Sun-like <span class="hlt">stars</span> selected from the Anglo-Australian Planet Search's main sample. These observations have already detected one <span class="hlt">low-mass</span> planet reported elsewhere (HD 16417b), and here we reconfirm the detection of HD 4308b. Further, we have Monte Carlo simulated data from this run on a <span class="hlt">star-by-star</span> basis to produce robust detection constraints. These simulations demonstrate clear differences in the exoplanet detectability functions from <span class="hlt">star</span> to <span class="hlt">star</span> due to differences in sampling, data quality and intrinsic stellar stability. They reinforce the importance of <span class="hlt">star-by-star</span> simulation when interpreting the data from Doppler planet searches. These simulations indicate that for some of our target <span class="hlt">stars</span> we are sensitive to close-orbiting planets as small as a few Earth masses. The two <span class="hlt">low-mass</span> planets present in our 24-<span class="hlt">star</span> sample indicate that the exoplanet minimum mass function at <span class="hlt">low</span> <span class="hlt">masses</span> is likely to be a flat {alpha} {approx} -1 (for dN/dM {proportional_to} M {sup {alpha}}) and that between 15% {+-} 10% (at {alpha} = -0.3) and 48% {+-} 34% (at {alpha} = -1.3) of <span class="hlt">stars</span> host planets with orbital periods of less than 16 days and minimum masses greater than 3 M {sub +}.</p> <div class="credits"> <p class="dwt_author">O'Toole, S. J. [Anglo-Australian Observatory, P.O. Box 296, Epping 1710 (Australia); Jones, H. R. A. [Centre for Astrophysics Research, University of Hertfordshire, Hatfield, AL 10 9AB (United Kingdom); Tinney, C. G.; Bailey, J.; Wittenmyer, R. A. [Department of Astrophysics, School of Physics, University of NSW, 2052 (Australia); Butler, R. P. [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington DC 20015-1305 (United States); Marcy, G. W. [Department of Astronomy, University of California, Berkeley, CA 94720 (United States); Carter, B. [Faculty of Sciences, University of Southern Queensland, Toowoomba, Queensland 4350 (Australia)], E-mail: otoole@aao.gov.au</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-08-20</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">222</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012ApJ...753..142B"> <span id="translatedtitle">Planets around <span class="hlt">Low-mass</span> <span class="hlt">Stars</span> (PALMS). I. A Substellar Companion to the Young M Dwarf 1RXS J235133.3+312720</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We report the discovery of a brown dwarf companion to the young M dwarf 1RXS J235133.3+312720 as part of a high contrast imaging search for planets around nearby young <span class="hlt">low-mass</span> <span class="hlt">stars</span> with Keck-II/NIRC2 and Subaru/HiCIAO. The 2farcs4 (~120 AU) pair is confirmed to be comoving from two epochs of high-resolution imaging. Follow-up low- and moderate-resolution near-infrared spectroscopy of 1RXS J2351+3127 B with IRTF/SpeX and Keck-II/OSIRIS reveals a spectral type of L0+2 -1. The M2 primary <span class="hlt">star</span> 1RXS J2351+3127 A exhibits X-ray and UV activity levels comparable to young moving group members with ages of ~10-100 Myr. UVW kinematics based the measured radial velocity of the primary and the system's photometric distance (50 ± 10 pc) indicate it is likely a member of the ~50-150 Myr AB Dor moving group. The near-infrared spectrum of 1RXS J2351+3127 B does not exhibit obvious signs of youth, but its H-band morphology shows subtle hints of intermediate surface gravity. The spectrum is also an excellent match to the ~200 Myr M9 brown dwarf LP 944-20. Assuming an age of 50-150 Myr, evolutionary models imply a mass of 32 ± 6 M Jup for the companion, making 1RXS J2351+3127 B the second lowest-mass member of the AB Dor moving group after the L4 companion CD-35 2722 B and one of the few benchmark brown dwarfs known at young ages. Some of the 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.</p> <div class="credits"> <p class="dwt_author">Bowler, Brendan P.; Liu, Michael C.; Shkolnik, Evgenya L.; Dupuy, Trent J.; Cieza, Lucas A.; Kraus, Adam L.; Tamura, Motohide</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">223</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AAS...22112903M"> <span id="translatedtitle"><span class="hlt">Revisiting</span> The First Galaxies: The Epoch of Population III <span class="hlt">Stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We study the formation of the first galaxies using new hydrodynamic cosmological simulations with the ART code. Our simulations feature a recently developed model for dust-based formation of molecular gas. Here, we develop and implement a new recipe for the formation of metal-free Pop III <span class="hlt">stars</span>. We reach a spatial resolution of 2 pc at z=10 and resolve <span class="hlt">star</span>-forming galaxies with the masses above 10^6 solar masses. We find the epoch during which Pop III <span class="hlt">stars</span> dominate the energy and metal budget of the universe to be short-lived. While these <span class="hlt">stars</span> seed their host galaxies with metals, they cannot drive significant outflows to enrich the IGM in our simulations. Feedback from pair instability supernovae causes Pop III <span class="hlt">star</span> formation to self-terminate within their host galaxies, but is not strong enough to suppress <span class="hlt">star</span> formation in external galaxies. Within any individual galaxy, Pop II <span class="hlt">stars</span> overtake Pop III <span class="hlt">stars</span> within ~50-150 Myr. A threshold of M = 3 * 10^6 solar masses separates galaxies that lose a significant fraction of their baryons due to Pop III feedback from those that do not. Understanding the nature of the transition between Pop III and Pop II <span class="hlt">star</span> formation is of key importance for studying the dawn of galaxy formation.</p> <div class="credits"> <p class="dwt_author">Muratov, Alexander; Gnedin, O. Y.; Gnedin, N. Y.; Zemp, M. K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">224</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008AJ....136.1921K"> <span id="translatedtitle">The Variable <span class="hlt">Stars</span> of the Draco Dwarf Spheroidal Galaxy: <span class="hlt">Revisited</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present a CCD survey of variable <span class="hlt">stars</span> in the Draco dwarf spheroidal galaxy. This survey, which has the largest areal coverage since the original variable <span class="hlt">star</span> survey by Baade & Swope, includes photometry for 270 RR Lyrae (RRL) <span class="hlt">stars</span>, 9 anomalous Cepheids (ACs), 2 eclipsing binaries, and 12 slow, irregular red variables, as well as 30 background QSOs. Twenty-six probable double-mode RRL <span class="hlt">stars</span> were identified. Observed parameters, including mean V and I magnitudes, V amplitudes, and periods, have been derived. Photometric metallicities of the ab-type RRL <span class="hlt">stars</span> were calculated according to the method of Jurcsik & Kovacs, yielding a mean metallicity of lang[Fe/H]rang = -2.19 ± 0.03. The well-known Oosterhoff intermediate nature of the RRL <span class="hlt">stars</span> in Draco is reconfirmed, although the double-mode RRL <span class="hlt">stars</span>, with one exception, have properties similar to those found in Oosterhoff type II globular clusters. The period-luminosity relation of the ACs is rediscussed with the addition of the new Draco ACs.</p> <div class="credits"> <p class="dwt_author">Kinemuchi, K.; Harris, H. C.; Smith, Horace A.; Silbermann, N. A.; Snyder, L. A.; La Cluyzé, A. P.; Clark, C. L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-11-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">225</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21394263"> <span id="translatedtitle">HIGH-RESOLUTION OBSERVATIONS OF DUST CONTINUUM EMISSION AT 340 GHz FROM THE <span class="hlt">LOW-MASS</span> T TAURI <span class="hlt">STAR</span> FN TAURI</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">FN Tau is a rare example of a very <span class="hlt">low-mass</span> T Tauri <span class="hlt">star</span> that exhibits a spatially resolved nebulosity in near-infrared scattering light. To directly derive the parameters of a circumstellar disk around FN Tau, observations of dust continuum emission at 340 GHz are carried out with the Submillimeter Array (SMA). A point-like dust continuum emission was detected with a synthesized beam of {approx}0.''7 in FWHM. From the analysis of the visibility plot, the radius of the emission is estimated to be <=0.''29, corresponding to 41 AU. This is much smaller than the radius of the nebulosity, 1.''85 for its brighter part at 1.6 {mu}m. The 340 GHz continuum emission observed with the SMA and the photometric data at lambda <= 70 {mu}m are explained by a power-law disk model whose outer radius and mass are 41 AU and (0.24-5.9) x 10{sup -3} M{sub sun}, respectively, if the exponent of dust mass opacity (beta) is assumed to be 0-2. The disk model cannot fully reproduce the flux density at 230 GHz obtained with the IRAM 30 m telescope, suggesting that there is another extended 'halo' component that is missed in the SMA observations. By requiring the halo not to be detected with the SMA, the lower limit to the size of the halo is evaluated to be between 174 AU and 574 AU, depending on the assumed beta value. This size is comparable to the near-infrared nebulosity, implying that the halo unseen with the SMA corresponds to the origin of the near-infrared nebulosity. The halo can contain mass comparable to or at most 8 times greater than that of the inner power-law disk, but its surface density should be lower than that at the outer edge of the power-law disk by more than 1 order of magnitude. The physical nature of the halo is unclear, but it may be the periphery of a flared circumstellar disk that is not described well in terms of a power-law disk model, or a remnant of a protostellar envelope having flattened structure.</p> <div class="credits"> <p class="dwt_author">Momose, Munetake [College of Science, Ibaraki University, Bunkyo 2-1-1, Mito, Ibaraki 310-8512 (Japan); Ohashi, Nagayoshi [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan (China); Kudo, Tomoyuki; Tamura, Motohide [National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588 (Japan); Kitamura, Yoshimi, E-mail: momose@mx.ibaraki.ac.j [Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510 (Japan)</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-03-20</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">226</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009IAUS..256..311D"> <span id="translatedtitle"><span class="hlt">Star</span> cluster evolution in the Magellanic Clouds <span class="hlt">revisited</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The evolution of <span class="hlt">star</span> clusters in the Magellanic Clouds has been the subject of significant recent controversy, particularly regarding the importance and length of the earliest, largely mass-independent disruption phase (referred to as “infant mortality”). Here, we take a fresh approach to the problem, using a large, independent, and homogeneous data set of UBVR imaging observations, from which we obtain the cluster age and mass distributions in both the Large and Small Magellanic Clouds (LMC, SMC) in a self-consistent manner. We conclude that the (optically selected) SMC <span class="hlt">star</span> cluster population has undergone at most ~30% (1?) infant mortality between the age range from about 3-10 Myr, to that of approximately 40-160 Myr. We rule out a 90% cluster mortality rate per decade of age (for the full age range up to 109 yr) at a > 6? level. Using a simple approach, we derive a “characteristic” cluster disruption time-scale for the cluster population in the LMC that implies that we are observing the initial cluster mass function (CMF). Preliminary results suggest that the LMC cluster population may be affected by <10% infant mortality.</p> <div class="credits"> <p class="dwt_author">de Grijs, Richard; Goodwin, Simon P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">227</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/12490001"> <span id="translatedtitle">THE FORMATION OF <span class="hlt">LOW-MASS</span> TRANSIENT</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We consider constraints on the formation of <span class="hlt">low-mass</span> X-ray binaries containing neutron <span class="hlt">stars</span> (NLMXBs) arising from the presence of soft X-ray transients among these systems. For a neutron <span class="hlt">star</span> mass M1 ? 1.4M? at formation, we show that in short- period (? < 1 ? 2 d) systems driven by angular momentum loss these constraints require the secondary at the</p> <div class="credits"> <p class="dwt_author">A. R. King; U. Kolb</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">228</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007ApJ...669.1235L"> <span id="translatedtitle">Revised Metallicity Classes for <span class="hlt">Low-Mass</span> <span class="hlt">Stars</span>: Dwarfs (dM), Subdwarfs (sdM), Extreme Subdwarfs (esdM), and Ultrasubdwarfs (usdM)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The current classification system of M <span class="hlt">stars</span> on the main sequence distinguishes three metallicity classes (dwarfs: dM; subdwarfs: sdM; and extreme subdwarfs: esdM). The spectroscopic definition of these classes is based on the relative strength of prominent CaH and TiO molecular absorption bands near 7000 Å, as quantified by three spectroscopic indices (CaH2, CaH3, and TiO5). The boundaries between the metallicity classes were initially defined from a relatively small sample of only 79 metal-poor <span class="hlt">stars</span> (subdwarfs and extreme subdwarfs). We re-examine this classification system in light of our ongoing spectroscopic survey of <span class="hlt">stars</span> with proper motion ?>0.45'' yr-1, which has increased the census of spectroscopically identified metal-poor M <span class="hlt">stars</span> to over 400 objects. Kinematic separation of disk dwarfs and halo subdwarfs suggest deficiencies in the current classification system. Observations of common proper motion doubles indicates that the current dM/sdM and sdM/esdM boundaries in the [TiO5, CaH2+CaH3] index plane do not follow isometallicity contours, leaving some binaries inappropriately classified as dM+sdM or sdM+esdM. We propose a revision of the classification system based on an empirical calibration of the TiO/CaH ratio for <span class="hlt">stars</span> of near solar metallicity. We introduce the parameter ?TiO/CaH, which quantifies the weakening of the TiO band strength due to metallicity effect, with values ranging from ?TiO/CaH=1 for <span class="hlt">stars</span> of near-solar metallicity to ?TiO/CaH~=0 for the most metal-poor (and TiO depleted) subdwarfs. We redefine the metallicity classes based on the value of the parameter ?TiO/CaH and refine the scheme by introducing an additional class of ultrasubdwarfs (usdM). We introduce sequences of sdM, esdM, and usdM <span class="hlt">stars</span> to be used as formal classification standards. Based on observations conducted at the MDM observatory, operated jointly by the University of Michigan, Dartmouth College, Ohio State University, Columbia University, and the University of Ohio. Based on observations conducted at the Lick Observatory, operated by the University of California system.</p> <div class="credits"> <p class="dwt_author">Lépine, Sébastien; Rich, R. Michael; Shara, Michael M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-11-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">229</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012ApJ...755...95C"> <span id="translatedtitle">Effects of Rotationally Induced Mixing in Compact Binary Systems with <span class="hlt">Low-mass</span> Secondaries and in Single Solar-type <span class="hlt">Stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Many population synthesis and stellar evolution studies have addressed the evolution of close binary systems in which the primary is a compact remnant and the secondary is filling its Roche lobe, thus triggering mass transfer. Although tidal locking is expected in such systems, most studies have neglected the rotationally induced mixing that may occur. Here we study the possible effects of mixing in mass-losing <span class="hlt">stars</span> for a range of secondary <span class="hlt">star</span> masses and metallicities. We find that tidal locking can induce rotational mixing prior to contact and thus affect the evolution of the secondary <span class="hlt">star</span> if the effects of the Spruit-Tayler dynamo are included both for angular momentum and chemical transport. Once contact is made, the effect of mass transfer tends to be more rapid than the evolutionary timescale, so the effects of mixing are no longer directly important, but the mass-transfer strips matter to inner layers that may have been affected by the mixing. These effects are enhanced for secondaries of 1-1.2 M ? and for lower metallicities. We discuss the possible implications for the paucity of carbon in the secondaries of the cataclysmic variable SS Cyg and the black hole candidate XTE J1118+480 and for the progenitor evolution of Type Ia supernovae. We also address the issue of the origin of blue straggler <span class="hlt">stars</span> in globular and open clusters. We find that for models that include rotation consistent with that observed for some blue straggler <span class="hlt">stars</span>, evolution is chemically homogeneous. This leads to tracks in the H-R diagram that are brighter and bluer than the non-rotating main-sequence turn-off point. Rotational mixing could thus be one of the factors that contribute to the formation of blue stragglers.</p> <div class="credits"> <p class="dwt_author">Chatzopoulos, E.; Robinson, Edward L.; Wheeler, J. Craig</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">230</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012ApJ...748...58D"> <span id="translatedtitle">Multi-wavelength Characterization of Stellar Flares on <span class="hlt">Low-mass</span> <span class="hlt">Stars</span> Using SDSS and 2MASS Time-domain Surveys</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present the first rates of flares from M dwarf <span class="hlt">stars</span> in both red optical and near-infrared (NIR) filters. We have studied ~50,000 M dwarfs from the Sloan Digital Sky Survey (SDSS) Stripe 82 area and 1321 M dwarfs from the Two Micron All Sky Survey (2MASS) Calibration Scan Point Source Working Database that overlap SDSS imaging fields. We assign photometric spectral types from M0 to M6 using (r - i) and (i - z) colors for every <span class="hlt">star</span> in our sample. Stripe 82 <span class="hlt">stars</span> each have 50-100 epochs of data, while 2MASS Calibration <span class="hlt">stars</span> have ~1900 epochs. From these data we estimate the observed rates and theoretical detection thresholds for flares in eight photometric bands as a function of spectral type. Optical flare rates are found to be in agreement with previous studies, while the frequency per hour of NIR flare detections is found to be more than two orders of magnitude lower. An excess of small-amplitude flux increases in all bands exhibits a power-law distribution, which we interpret as the result of flares below our detection thresholds. In order to investigate the recovery efficiency for flares in each filter, we extend a two-component flare model into the NIR. Quiescent M0-M6 spectral templates were used with the model to predict the photometric response of flares from u to Ks . We determine that red optical filters are sensitive to flares with u-band amplitudes gsim2 mag, and NIR filters to flares with ?u gsim 4.5 mag. Our model predicts that M0 <span class="hlt">stars</span> have the best color contrast for J-band detections, but M4-M6 <span class="hlt">stars</span> should yield the highest rate of NIR flares with amplitudes of ?J >= 0.01 mag. Characterizing flare rates and photometric variations at longer wavelengths is important for predicting the signatures of M dwarf variability in next-generation surveys, and we discuss their impact on surveys such as the Large Synoptic Survey Telescope.</p> <div class="credits"> <p class="dwt_author">Davenport, James R. A.; Becker, Andrew C.; Kowalski, Adam F.; Hawley, Suzanne L.; Schmidt, Sarah J.; Hilton, Eric J.; Sesar, Branimir; Cutri, Roc</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">231</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22016140"> <span id="translatedtitle">MULTI-WAVELENGTH CHARACTERIZATION OF STELLAR FLARES ON <span class="hlt">LOW-MASS</span> <span class="hlt">STARS</span> USING SDSS AND 2MASS TIME-DOMAIN SURVEYS</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We present the first rates of flares from M dwarf <span class="hlt">stars</span> in both red optical and near-infrared (NIR) filters. We have studied {approx}50,000 M dwarfs from the Sloan Digital Sky Survey (SDSS) Stripe 82 area and 1321 M dwarfs from the Two Micron All Sky Survey (2MASS) Calibration Scan Point Source Working Database that overlap SDSS imaging fields. We assign photometric spectral types from M0 to M6 using (r - i) and (i - z) colors for every <span class="hlt">star</span> in our sample. Stripe 82 <span class="hlt">stars</span> each have 50-100 epochs of data, while 2MASS Calibration <span class="hlt">stars</span> have {approx}1900 epochs. From these data we estimate the observed rates and theoretical detection thresholds for flares in eight photometric bands as a function of spectral type. Optical flare rates are found to be in agreement with previous studies, while the frequency per hour of NIR flare detections is found to be more than two orders of magnitude lower. An excess of small-amplitude flux increases in all bands exhibits a power-law distribution, which we interpret as the result of flares below our detection thresholds. In order to investigate the recovery efficiency for flares in each filter, we extend a two-component flare model into the NIR. Quiescent M0-M6 spectral templates were used with the model to predict the photometric response of flares from u to K{sub s} . We determine that red optical filters are sensitive to flares with u-band amplitudes {approx}>2 mag, and NIR filters to flares with {Delta}u {approx}> 4.5 mag. Our model predicts that M0 <span class="hlt">stars</span> have the best color contrast for J-band detections, but M4-M6 <span class="hlt">stars</span> should yield the highest rate of NIR flares with amplitudes of {Delta}J {>=} 0.01 mag. Characterizing flare rates and photometric variations at longer wavelengths is important for predicting the signatures of M dwarf variability in next-generation surveys, and we discuss their impact on surveys such as the Large Synoptic Survey Telescope.</p> <div class="credits"> <p class="dwt_author">Davenport, James R. A.; Becker, Andrew C.; Kowalski, Adam F.; Hawley, Suzanne L.; Schmidt, Sarah J.; Hilton, Eric J. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Sesar, Branimir [Division of Physics, Mathematics and Astronomy, Caltech, Pasadena, CA 91125 (United States); Cutri, Roc, E-mail: jrad@astro.washington.edu [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-03-20</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">232</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/53765846"> <span id="translatedtitle">The Habitable Zone Planet Finder Project: A Proposed High Resolution NIR Spectrograph for the Hobby Eberly Telescope (HET) to Discover <span class="hlt">Low</span> <span class="hlt">Mass</span> Exoplanets around M <span class="hlt">Stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Radial velocity precision in the NIR is now approaching the level necessary to detect exoplanets around mid-late M <span class="hlt">stars</span> that are very faint in the optical and emit most of their flux in the NIR. The Penn State Pathfinder prototype instrument has already demonstrated 7-10 ms-1 precision on sunlight, and similar precision has been reported at the Pathways conference using</p> <div class="credits"> <p class="dwt_author">S. Mahadevan; L. Ramsey; S. Redman; S. Zonak; J. Wright; A. Wolszczan; M. Endl; B. Zhao</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">233</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012ApJ...750L..37M"> <span id="translatedtitle">Characterizing the Cool Kepler Objects of Interests. New Effective Temperatures, Metallicities, Masses, and Radii of <span class="hlt">Low-mass</span> Kepler Planet-candidate Host <span class="hlt">Stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We report stellar parameters for late-K and M-type planet-candidate host <span class="hlt">stars</span> announced by the Kepler Mission. We obtained medium-resolution, K-band spectra of 84 cool (T eff <~ 4400 K) Kepler Objects of Interest (KOIs) from Borucki et al. We identified one object as a giant (KOI 977); for the remaining dwarfs, we measured effective temperatures (T eff) and metallicities [M/H] using the K-band spectral indices of Rojas-Ayala et al. We determine the masses (M sstarf) and radii (R sstarf) of the cool KOIs by interpolation onto the Dartmouth evolutionary isochrones. The resultant stellar radii are significantly less than the values reported in the Kepler Input Catalog and, by construction, correlate better with T eff. Applying the published KOI transit parameters to our stellar radius measurements, we report new physical radii for the planet candidates. Recalculating the equilibrium temperatures of the planet-candidates assuming Earth's albedo and re-radiation fraction, we find that three of the planet-candidates are terrestrial sized with orbital semimajor axes that lie within the habitable zones of their host <span class="hlt">stars</span> (KOI 463.01, KOI 812.03, and KOI 854.01). The stellar parameters presented in this Letter serve as a resource for prioritization of future follow-up efforts to validate and characterize the cool KOI planet candidates.</p> <div class="credits"> <p class="dwt_author">Muirhead, Philip S.; Hamren, Katherine; Schlawin, Everett; Rojas-Ayala, Bárbara; Covey, Kevin R.; Lloyd, James P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">234</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22047634"> <span id="translatedtitle">THE INFRARED EYE OF THE WIDE-FIELD CAMERA 3 ON THE HUBBLE SPACE TELESCOPE REVEALS MULTIPLE MAIN SEQUENCES OF VERY <span class="hlt">LOW</span> <span class="hlt">MASS</span> <span class="hlt">STARS</span> IN NGC 2808</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We use images taken with the infrared channel of the Wide Field Camera 3 on the Hubble Space Telescope to study the multiple main sequences (MSs) of NGC 2808. Below the turnoff, the red, the middle, and the blue MS, previously detected from visual-band photometry, are visible over an interval of about 3.5 F160W magnitudes. The three MSs merge together at the level of the MS bend. At fainter magnitudes, the MS again splits into two components containing {approx}65% and {approx}35% of <span class="hlt">stars</span>, with the most-populated MS being the bluest one. Theoretical isochrones suggest that the latter is connected to the red MS discovered in the optical color-magnitude diagram (CMD) and hence corresponds to the first stellar generation, having primordial helium and enhanced carbon and oxygen abundances. The less-populated MS in the faint part of the near-IR CMD is helium-rich and poor in carbon and oxygen, and it can be associated with the middle and the blue MS of the optical CMD. The finding that the photometric signature of abundance anti-correlation is also present in fully convective MS <span class="hlt">stars</span> reinforces the inference that they have a primordial origin.</p> <div class="credits"> <p class="dwt_author">Milone, A. P.; Aparicio, A.; Monelli, M., E-mail: milone@iac.es, E-mail: aparicio@iac.es, E-mail: monelli@iac.es [Instituto de Astrofisica de Canarias, E-38200 La Laguna, Tenerife, Canary Islands (Spain); and others</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-08-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">235</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013ApJ...776...47D"> <span id="translatedtitle">Black Hole-Neutron <span class="hlt">Star</span> Mergers with a Hot Nuclear Equation of State: Outflow and Neutrino-cooled Disk for a <span class="hlt">Low-mass</span>, High-spin Case</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Neutrino emission significantly affects the evolution of the accretion tori formed in black hole-neutron <span class="hlt">star</span> mergers. It removes energy from the disk, alters its composition, and provides a potential power source for a gamma-ray burst. To study these effects, simulations in general relativity with a hot microphysical equation of state (EOS) and neutrino feedback are needed. We present the first such simulation, using a neutrino leakage scheme for cooling to capture the most essential effects and considering a moderate mass (1.4 M ? neutron <span class="hlt">star</span>, 5.6 M ? black hole), high-spin (black hole J/M 2 = 0.9) system with the K 0 = 220 MeV Lattimer-Swesty EOS. We find that about 0.08 M ? of nuclear matter is ejected from the system, while another 0.3 M ? forms a hot, compact accretion disk. The primary effects of the escaping neutrinos are (1) to make the disk much denser and more compact, (2) to cause the average electron fraction Ye of the disk to rise to about 0.2 and then gradually decrease again, and (3) to gradually cool the disk. The disk is initially hot (T ~ 6 MeV) and luminous in neutrinos (L ? ~ 1054 erg s–1), but the neutrino luminosity decreases by an order of magnitude over 50 ms of post-merger evolution.</p> <div class="credits"> <p class="dwt_author">Deaton, M. Brett; Duez, Matthew D.; Foucart, Francois; O'Connor, Evan; Ott, Christian D.; Kidder, Lawrence E.; Muhlberger, Curran D.; Scheel, Mark A.; Szilagyi, Bela</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">236</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009ApJ...692..778R"> <span id="translatedtitle">A Steep Faint-End Slope of the UV Luminosity Function at z ~ 2-3: Implications for the Global Stellar Mass Density and <span class="hlt">Star</span> Formation in <span class="hlt">Low-Mass</span> Halos</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We use the deep ground-based optical photometry of the Lyman Break Galaxy (LBG) Survey to derive robust measurements of the faint-end slope (?) of the UV luminosity function (LF) at redshifts 1.9 <= z <= 3.4. Our sample includes >2000 spectroscopic redshifts and ?31000 LBGs in 31 spatially independent fields over a total area of 3261 arcmin2. These data allow us to select galaxies to 0.07L* and 0.10L* at z ~ 2 and z ~ 3, respectively. A maximum-likelihood analysis indicates steep values of ?(z = 2) = -1.73 ± 0.07 and ?(z = 3) = -1.73 ± 0.13. This result is robust to luminosity-dependent systematics in the Ly? equivalent width and reddening distributions, and is similar to the steep values advocated at z gsim 4, and implies that ?93% of the unobscured UV luminosity density at z ~ 2-3 arises from sub-L* galaxies. With a realistic luminosity-dependent reddening distribution, faint to moderately luminous galaxies account for gsim70% and gsim25% of the bolometric luminosity density and present-day stellar mass density, respectively, when integrated over 1.9 <= z < 3.4. We find a factor of 8-9 increase in the <span class="hlt">star</span>-formation rate density between z ~ 6 and z ~ 2, due to both a brightening of L* and an increasing dust correction proceeding to lower redshifts. Combining the UV LF with stellar mass estimates suggests a relatively steep <span class="hlt">low-mass</span> slope of the stellar mass function at high redshift. The previously observed discrepancy between the integral of the <span class="hlt">star</span>-formation history and stellar mass density measurements at z ~ 2 may be reconciled by invoking a luminosity-dependent reddening correction to the <span class="hlt">star</span>-formation history combined with an accounting for the stellar mass contributed by UV-faint galaxies. The steep and relatively constant faint-end slope of the UV LF at z gsim 2 contrasts with the shallower slope inferred locally, suggesting that the evolution in the faint-end slope may be dictated simply by the availability of <span class="hlt">low-mass</span> halos capable of supporting <span class="hlt">star</span> formation at z lsim 2. Based, in part, on data 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 NASA, and was made possible by the generous financial support of the W. M. Keck Foundation.</p> <div class="credits"> <p class="dwt_author">Reddy, Naveen A.; Steidel, Charles C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">237</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/53822951"> <span id="translatedtitle">The rotation of very <span class="hlt">low</span> <span class="hlt">mass</span> objects</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">This dissertation contains an investigation of the rotation of very <span class="hlt">low</span> <span class="hlt">mass</span> objects, i.e. Brown Dwarfs and <span class="hlt">stars</span> with masses <0.4 MS. Today, it is well-established that there are large populations of such VLM objects in open clusters and in the field, but our knowledge about their physical properties and evolution is still very limited. Contrary to their solar-mass siblings,</p> <div class="credits"> <p class="dwt_author">Alexander Scholz</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">238</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/55011971"> <span id="translatedtitle">Canonical Extra Mixing in <span class="hlt">Low-Mass</span> Red Giants</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We have used the latest observational data on the evolutionary variations of the surface chemical composition in <span class="hlt">low-mass</span> metal-poor <span class="hlt">stars</span>, both in the field and in globular clusters, to constrain the basic properties of extra mixing in upper red giant branch (RGB) <span class="hlt">stars</span>. Two different models of extra mixing have been incorporated into a stellar evolution code: a parametrical diffusion</p> <div class="credits"> <p class="dwt_author">Pavel A. Denissenkov; Don A. VandenBerg</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">239</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/55959615"> <span id="translatedtitle">The Eta-Earth Survey for <span class="hlt">Low-Mass</span> Exoplanets</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The NASA-UC Eta-Earth Survey by the California Planet Search (CPS) group is a systematic search for <span class="hlt">low-mass</span> planets ( 3-30 Earth masses) orbiting the nearest 230 GKM <span class="hlt">stars</span> suitable for high-precision Doppler observations at Keck Observatory. These 1 m\\/s measurements of a well-defined sample of nearby <span class="hlt">stars</span> will provide one of the first estimates of the fraction of <span class="hlt">stars</span> with</p> <div class="credits"> <p class="dwt_author">Andrew Howard; G. Marcy; D. Fischer; J. Johnson; J. Wright; J. Valenti; J. Anderson; N. Piskunov; H. Isaacson; J. Brewer; K. Clubb; D. Lin; S. Ida</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">240</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21574882"> <span id="translatedtitle">THE BINARY FRACTION OF <span class="hlt">LOW-MASS</span> WHITE DWARFS</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We describe spectroscopic observations of 21 <span class="hlt">low-mass</span> ({<=}0.45 M{sub sun}) white dwarfs (WDs) from the Palomar-Green survey obtained over four years. We use both radial velocities and infrared photometry to identify binary systems, and find that the fraction of single, <span class="hlt">low-mass</span> WDs is {<=}30%. We discuss the potential formation channels for these single <span class="hlt">stars</span> including binary mergers of lower-mass objects. However, binary mergers are not likely to explain the observed number of single <span class="hlt">low-mass</span> WDs. Thus, additional formation channels, such as enhanced mass loss due to winds or interactions with substellar companions, are likely.</p> <div class="credits"> <p class="dwt_author">Brown, Justin M. [Franklin and Marshall College, 415 Harrisburg Avenue, Lancaster, PA 17604 (United States); Kilic, Mukremin; Brown, Warren R.; Kenyon, Scott J., E-mail: brown.justin.michael@gmail.com [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-04-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_11");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" 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showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_14");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">241</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/27646474"> <span id="translatedtitle">OGLE2005-BLG-153: Microlensing Discovery and Characterization of a Very <span class="hlt">Low</span> <span class="hlt">Mass</span> Binary</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The mass function and statistics of binaries provide important diagnostics of the <span class="hlt">star</span> formation process. Despite this importance, the mass function at <span class="hlt">low</span> <span class="hlt">masses</span> remains poorly known due to observational difficulties caused by the faintness of the objects. Here we report the microlensing discovery and characterization of a binary lens composed of very <span class="hlt">low</span> <span class="hlt">mass</span> <span class="hlt">stars</span> just above the hydrogen-burning</p> <div class="credits"> <p class="dwt_author">K.-H. Hwang; A. Udalski; C. Han; Y.-H. Ryu; I. A. Bond; J.-P. Beaulieu; M. Dominik; K. Horne; A. Gould; B. S. Gaudi; M. Kubiak; M. K. Szymanski; G. Pietrzynski; I. Soszynski; O. Szewczyk; K. Ulaczyk; L. Wyrzykowski; F. Abe; C. S. Botzler; J. B. Hearnshaw; Y. Itow; K. Kamiya; P. M. Kilmartin; K. Masuda; Y. Matsubara; M. Motomura; Y. Muraki; S. Nakamura; K. Ohnishi; C. Okada; N. Rattenbury; To. Saito; T. Sako; M. Sasaki; D. J. Sullivan; T. Sumi; P. J. Tristram; J. N. Wood; P. C. M. Yock; T. Yoshioka; M. Albrow; D. P. Bennett; D. M. Bramich; S. Brillant; J. A. R. Caldwell; J. J. Calitz; A. Cassan; K. H. Cook; E. Corrales; C. Coutures; M. Desort; S. Dieters; D. Dominis; J. Donatowicz; P. Fouqué; J. Greenhill; K. Harpsøe; K. Hill; M. Hoffman; U. G. Jørgensen; S. Kane; D. Kubas; R. Martin; J.-B. Marquette; P. Meintjes; J. Menzies; K. Pollard; K. Sahu; I. Steele; C. Vinter; J. Wambsganss; A. Williams; K. Woller; M. Burgdorf; C. Snodgrass; M. Bode; D. L. Depoy; C.-U. Lee; B.-G. Park; R. W. Pogge</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">242</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012AAS...21933004M"> <span id="translatedtitle">Accurate Stellar Parameters of <span class="hlt">Low-Mass</span> Kepler Planet Hosts</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We report stellar parameters for <span class="hlt">low-mass</span> planet-candidate host <span class="hlt">stars</span> recently announced by the Kepler Mission. We obtained medium-resolution, K-band spectra of 84 <span class="hlt">low-mass</span> Kepler Objects of Interest (KOIs). We identified one KOI as a giant; for the remaining dwarfs, we estimated effective temperatures by comparing measurements of K-band regions dominated by H2O opacity with predictions of synthetic spectra for <span class="hlt">low-mass</span> <span class="hlt">stars</span>. We measured overall metallicities ([M/H]) using the equivalent widths of Na I and Ca I absorption features and an empirical metallicity relation calibrated with nearby <span class="hlt">stars</span>. With effective temperatures and metallicities, we estimate the masses and radii of the <span class="hlt">low-mass</span> KOIs by interpolation onto two sets of evolutionary isochrones. The resultant stellar radii are significantly less than the values reported in the Kepler Input Catalogue and, by construction, correlate better with effective temperature. Using either set of isochrones, our results significantly reduce the sizes of the corresponding planet candidates, with many less than 1 Earth radius. We report recalculated equilibrium temperatures for the planet-candidates and the implications for Kepler's yield of terrestrial exoplanets in the habitable zones of their host <span class="hlt">stars</span>.</p> <div class="credits"> <p class="dwt_author">Muirhead, Philip; Hamren, K.; Schlawin, E.; Rojas-Ayala, B.; Covey, K.; Lloyd, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">243</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/52795695"> <span id="translatedtitle">Nitrogen line spectroscopy of O-<span class="hlt">stars</span>. I. Nitrogen III emission line formation <span class="hlt">revisited</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Context. Evolutionary models of massive <span class="hlt">stars</span> predict a surface enrichment of nitrogen, due to rotational mixing. Recent studies within the VLT-FLAMES survey of massive <span class="hlt">stars</span> have challenged (part of) these predictions. Such systematic determinations of nitrogen abundances, however, have been mostly performed only for cooler (B-type) objects. For the most massive and hottest <span class="hlt">stars</span>, corresponding results are scarce. Aims: This</p> <div class="credits"> <p class="dwt_author">J. G. Rivero González; J. Puls; F. Najarro</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">244</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004IAUS..219..275B"> <span id="translatedtitle">Magnetic Activity at Very <span class="hlt">Low</span> <span class="hlt">Masses</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The rotation-activity paradigm has proven very effective in solar-type <span class="hlt">stars</span> explaining both their activity and rotational histories. The basic ingredients are rotationally-driven dynamos and conversion of magnetic energy into heating. Things change near the bottom of the main sequence. A saturation velocity persists cooler than M3 suggesting that the remaining dynamo is not purely turbulent (even though the <span class="hlt">stars</span> are fully convective and cannot support a solar-type dynamo). At M9 the levels of stellar activity plummet. This is probably due to a decoupling of the field from atmospheric motions given extreme neutrality of the atmospheres. It is no longer forced into dissipative configurations and quiescent chromospheres and coronae disappear. The lack of magnetic braking leaves these stellar and substellar objects very rapid rotators. Thus the rotation-activity relation is REVERSED at the <span class="hlt">low</span> <span class="hlt">mass</span> limit. Flaring persists in very cool objects suggesting some field is still present. We don't know how these flares are generated (they exhibit odd ratios of X-ray to radio flux). A further mystery is the elevated activity of very young cool objects. Clearly we still have much to learn in this area.</p> <div class="credits"> <p class="dwt_author">Basri, G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">245</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004ApJ...613.1213S"> <span id="translatedtitle">The Secular Bar-Mode Instability in Rapidly Rotating <span class="hlt">Stars</span> <span class="hlt">Revisited</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Uniformly rotating, homogeneous, incompressible Maclaurin spheroids that spin sufficiently rapidly are secularly unstable to nonaxisymmetric, bar-mode perturbations when viscosity is present. The intuitive explanation is that energy dissipation by viscosity can drive an unstable spheroid to a stable, triaxial configuration of lower energy-a Jacobi ellipsoid. But what about rapidly rotating compressible <span class="hlt">stars</span>? Unlike incompressible <span class="hlt">stars</span>, which contain no internal energy and therefore immediately liberate all the energy dissipated by viscosity, compressible <span class="hlt">stars</span> have internal energy and can retain the dissipated energy as internal heat. Now compressible <span class="hlt">stars</span> that rotate sufficiently rapidly and also manage to liberate this dissipated energy very quickly are known to be unstable to bar-mode perturbations, like their incompressible counterparts. But what is the situation for rapidly rotating compressible <span class="hlt">stars</span> that have very long cooling timescales, so that all the energy dissipated by viscosity is retained as heat, and the total energy of the <span class="hlt">star</span> remains constant on a secular (viscous) evolution timescale? Are such <span class="hlt">stars</span> also unstable to the nonlinear growth of bar modes, or is the viscous heating sufficient to cause them to expand, drive down the ratio of rotational kinetic to gravitational potential energy T/|W|~R-1eq, where Req is the equatorial radius, and turn off the instability before it gets underway? Alternatively, if the instability still arises in such <span class="hlt">stars</span>, at what rotation rate do they become unstable, and to what final state do they evolve? We provide definitive answers to these questions in the context of the compressible ellipsoid model for rotating <span class="hlt">stars</span>. The results should serve as useful guides for numerical simulations that solve the exact Navier-Stokes equations in 3+1 dimensions for rotating <span class="hlt">stars</span> containing viscosity.</p> <div class="credits"> <p class="dwt_author">Shapiro, Stuart L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">246</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AN....334...93B"> <span id="translatedtitle">The kinematics of very <span class="hlt">low</span> <span class="hlt">mass</span> dwarfs: Splinter session summary</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Kinematic investigations are being increasingly deployed in studies of the lowest mass <span class="hlt">stars</span> and brown dwarfs to investigate their origins, characterize their atmospheres, and examine the evolution of their physical parameters. This article summarizes the contributions made at the ``Kinematics of Very <span class="hlt">Low</span> <span class="hlt">Mass</span> Dwarfs'' splinter session. Results discussed include analysis of kinematic distributions of M, L, and T dwarfs; theoretical tools for interpreting these distributions; identifications of very <span class="hlt">low</span> <span class="hlt">mass</span> halo dwarfs and wide companions to nearby <span class="hlt">stars</span>; radial velocity variability among young and very cool brown dwarfs; and the search and identification of M dwarfs in young moving groups. A summary of discussion points at the conclusion of the splinter sesseion is also presented.</p> <div class="credits"> <p class="dwt_author">Burgasser, A. J.; Faherty, J. K.; Schmidt, S.; West, A. A.; Zapatero Osorio, M. R.; Pineda, J. S.; Burningham, B.; Nicholls, C.; Sanderson, R.; Shkolnik, E.; Rodriguez, D.; Riedel, A.; Joergens, V.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">247</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/54392984"> <span id="translatedtitle">A population synthesis study of <span class="hlt">low-mass</span> X-ray binary systems</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The origin of <span class="hlt">low-mass</span> X-ray binary systems from the helium <span class="hlt">star</span>-main-sequence binary remnants of a common-envelope phase is studied. Using a statistical Monte Carlo approach, the evolution of an initial distribution of zero-age binaries is followed from the main sequence through a phase of common-envelope evolution and subsequent supernova explosion of the helium <span class="hlt">star</span>. The resultant population of <span class="hlt">low-mass</span> main-sequence</p> <div class="credits"> <p class="dwt_author">James L. Terman; Ronald E. Taam; Craig O. Savage</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">248</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/43181565"> <span id="translatedtitle">Coronal Mass Ejection (CME) Activity of <span class="hlt">Low</span> <span class="hlt">Mass</span> M <span class="hlt">Stars</span> as An Important Factor for The Habitability of Terrestrial Exoplanets. II. CME-Induced Ion Pick Up of Earth-like Exoplanets in Close-In Habitable Zones</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Atmospheric erosion of CO2 -rich Earth-size exoplanets due to coronal mass ejection (CME)-induced ion pick up within close-in habitable zones of active M-type dwarf <span class="hlt">stars</span> is investigated. Since M <span class="hlt">stars</span> are active at the X-ray and extreme ultraviolet radiation (XUV) wave-lengths over long periods of time, we have applied a thermal balance model at various XUV flux input values for</p> <div class="credits"> <p class="dwt_author">Helmut Lammer; Herbert I. M. Lichtenegger; Yuri N. Kulikov; Jean-Mathias Grießmeier; N. Terada; Nikolai V. Erkaev; Helfried K. Biernat; Maxim L. Khodachenko; Ignasi Ribas; Thomas Penz; Franck Selsis</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">249</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2004AAS...205.2308S"> <span id="translatedtitle">Blue Stragglers in <span class="hlt">Low-Mass</span> Globular Clusters</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present a tabulation of over 200 blue straggler <span class="hlt">stars</span> for 11 <span class="hlt">low-mass</span> (MV,total > -6) Milky Way globular clusters that extends the results of Piotto et al. (2004) for massive clusters. The relative frequencies of blue stragglers (FBSS = NBSS / NHB) appears to continue to increase with decreasing cluster luminosity down to the least luminous clusters in the Milky Way. For the faintest clusters in the sample, the relative frequency is approximately equal to that for field <span class="hlt">stars</span>. We will also discuss the luminosity function of the total straggler sample for these clusters. This work has been funded through grant AST 00-98696 from the National Science Foundation.</p> <div class="credits"> <p class="dwt_author">Sandquist, E. L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">250</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/12303516"> <span id="translatedtitle">Metallic Fingers and Metallicity Excess in Exoplanets' Host <span class="hlt">Stars</span>: The Accretion Hypothesis <span class="hlt">Revisited</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">While the metallicity excess observed in the central <span class="hlt">stars</span> of planetary systems is confirmed by all recent observations, the reason for this excess is still a subject of debate: is it primordial, or the result of accretion, or both? The basic argument against an accretion origin is related to the mass of the outer convective zones, which varies by more</p> <div class="credits"> <p class="dwt_author">Sylvie Vauclair</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">251</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1991BAICz..42....1H"> <span id="translatedtitle">Properties and nature of Be <span class="hlt">stars</span>. XV - Light variations of LQ And and its check <span class="hlt">stars</span> <span class="hlt">revisited</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Results of an analysis of 624 UBV observations of LQ And made at six observatories between 1980 and 1988 have been used to find a period of 0.30952 or 0.61904 days, with a full amplitude of about 0.025 m. No evidence of multiperiodicity is found, and the only variation other than the periodic one at 0.6 or 0.3 days is the suspected decline in brightness between 1951 and 1988, probably connected with physical changes in the Be envelope. A new period of 3.5112 days is derived for LQ And light and color variations, and it is suggested that this hot CP <span class="hlt">star</span> is an oblique rotator.</p> <div class="credits"> <p class="dwt_author">Harmanec, P.; Matthews, J. M.; Bozic, H.; Pavlovski, K.; Huang, L.; Guo, Z.-H.; Percy, J. R.; Plume, R.; Ruzic, Z.; Wehlau, W. H.; Bohlender, D. A.; Horn, J.; Koubsky, P.; Walker, G. A. H.; Yang, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">252</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1999A%26AS..137..273G"> <span id="translatedtitle">Search for reference A0 dwarf <span class="hlt">stars</span>: Masses and luminosities <span class="hlt">revisited</span> with HIPPARCOS parallaxes</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Hipparcos data for 71 nearby dwarf A0 <span class="hlt">stars</span> were combined with other data, in particular with high resolution spectra to establish the HR diagram in this temperature range. Almost 30% of unknown binaries were detected and discarded before establishing the cal M-L relation for bright A0 V field <span class="hlt">stars</span>. The relationship derived for these single <span class="hlt">stars</span> is compared to the classical diagram derived from eclipsing binaries. The scatter of the latter is examined and the role of gravity is discussed. A good agreement is found between the evolution-based surface gravity log g_ev and the value of log g_ph obtained from photometric data. Based on observations collected at the European Southern Observatory (ESO), La Silla, Chile in the framework of the Key Programme 5-004-43K and on data from the ESA Hipparcos astrometry satellite. The Tables 1-4 are also available electronically via anonymous ftp 130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html</p> <div class="credits"> <p class="dwt_author">Gerbaldi, M.; Faraggiana, R.; Burnage, R.; Delmas, F.; Gómez, A. E.; Grenier, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">253</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011MPLA...26.2029J"> <span id="translatedtitle"><span class="hlt">Low-Mass</span> Diffraction at the Lhc</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The expected resonance structure for <span class="hlt">low-mass</span> single diffractive states is predicted from a Regge-dual model elaborated earlier by the present authors. Estimates for the observable <span class="hlt">low-mass</span> single diffraction dissociation (SDD) cross-sections and efficiencies for single diffractive events simulated by PYTHIA 6.2 as a function of the diffractive mass are given.</p> <div class="credits"> <p class="dwt_author">Jenkovszky, L. L.; Kuprash, O. E.; Lämsä, J. W.; Orava, R.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">254</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AJ....145...20M"> <span id="translatedtitle">Very-<span class="hlt">low-mass</span> Stellar and Substellar Companions to Solar-like <span class="hlt">Stars</span> from Marvels. III. A Short-period Brown Dwarf Candidate around an Active G0IV Subgiant</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present an eccentric, short-period brown dwarf candidate orbiting the active, slightly evolved subgiant <span class="hlt">star</span> TYC 2087-00255-1, which has effective temperature T eff = 5903 ± 42 K, surface gravity log (g) = 4.07 ± 0.16 (cgs), and metallicity [Fe/H] = -0.23 ± 0.07. This candidate was discovered using data from the first two years of the Multi-object APO Radial Velocity Exoplanets Large-area Survey, which is part of the third phase of Sloan Digital Sky Survey. From our 38 radial velocity measurements spread over a two-year time baseline, we derive a Keplerian orbital fit with semi-amplitude K = 3.571 ± 0.041 km s-1, period P = 9.0090 ± 0.0004 days, and eccentricity e = 0.226 ± 0.011. Adopting a mass of 1.16 ± 0.11 M ? for the subgiant host <span class="hlt">star</span>, we infer that the companion has a minimum mass of 40.0 ± 2.5 M Jup. Assuming an edge-on orbit, the semimajor axis is 0.090 ± 0.003 AU. The host <span class="hlt">star</span> is photometrically variable at the ~1% level with a period of ~13.16 ± 0.01 days, indicating that the host <span class="hlt">star</span> spin and companion orbit are not synchronized. Through adaptive optics imaging we also found a point source 643 ± 10 mas away from TYC 2087-00255-1, which would have a mass of 0.13 M ? if it is physically associated with TYC 2087-00255-1 and has the same age. Future proper motion observation should be able to resolve if this tertiary object is physically associated with TYC 2087-00255-1 and make TYC 2087-00255-1 a triple body system. Core Ca II H and K line emission indicate that the host is chromospherically active, at a level that is consistent with the inferred spin period and measured v rotsin i, but unusual for a subgiant of this T eff. This activity could be explained by ongoing tidal spin-up of the host <span class="hlt">star</span> by the companion.</p> <div class="credits"> <p class="dwt_author">Ma, Bo; Ge, Jian; Barnes, Rory; Crepp, Justin R.; De Lee, Nathan; Dutra-Ferreira, Leticia; Esposito, Massimiliano; Femenia, Bruno; Fleming, Scott W.; Gaudi, B. Scott; Ghezzi, Luan; Hebb, Leslie; Gonzalez Hernandez, Jonay I.; Lee, Brian L.; Porto de Mello, G. F.; Stassun, Keivan G.; Wang, Ji; Wisniewski, John P.; Agol, Eric; Bizyaev, Dmitry; Cargile, Phillip; Chang, Liang; Nicolaci da Costa, Luiz; Eastman, Jason D.; Gary, Bruce; Jiang, Peng; Kane, Stephen R.; Li, Rui; Liu, Jian; Mahadevan, Suvrath; Maia, Marcio A. G.; Muna, Demitri; Nguyen, Duy Cuong; Ogando, Ricardo L. C.; Oravetz, Daniel; Pepper, Joshua; Paegert, Martin; Allende Prieto, Carlos; Rebolo, Rafael; Santiago, Basilio X.; Schneider, Donald P.; Shelden, Alaina; Simmons, Audrey; Sivarani, Thirupathi; van Eyken, J. C.; Wan, Xiaoke; Weaver, Benjamin A.; Zhao, Bo</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">255</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22089722"> <span id="translatedtitle">VERY-<span class="hlt">LOW-MASS</span> STELLAR AND SUBSTELLAR COMPANIONS TO SOLAR-LIKE <span class="hlt">STARS</span> FROM MARVELS. III. A SHORT-PERIOD BROWN DWARF CANDIDATE AROUND AN ACTIVE G0IV SUBGIANT</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We present an eccentric, short-period brown dwarf candidate orbiting the active, slightly evolved subgiant <span class="hlt">star</span> TYC 2087-00255-1, which has effective temperature T{sub eff} = 5903 {+-} 42 K, surface gravity log (g) = 4.07 {+-} 0.16 (cgs), and metallicity [Fe/H] = -0.23 {+-} 0.07. This candidate was discovered using data from the first two years of the Multi-object APO Radial Velocity Exoplanets Large-area Survey, which is part of the third phase of Sloan Digital Sky Survey. From our 38 radial velocity measurements spread over a two-year time baseline, we derive a Keplerian orbital fit with semi-amplitude K = 3.571 {+-} 0.041 km s{sup -1}, period P = 9.0090 {+-} 0.0004 days, and eccentricity e = 0.226 {+-} 0.011. Adopting a mass of 1.16 {+-} 0.11 M{sub Sun} for the subgiant host <span class="hlt">star</span>, we infer that the companion has a minimum mass of 40.0 {+-} 2.5 M{sub Jup}. Assuming an edge-on orbit, the semimajor axis is 0.090 {+-} 0.003 AU. The host <span class="hlt">star</span> is photometrically variable at the {approx}1% level with a period of {approx}13.16 {+-} 0.01 days, indicating that the host <span class="hlt">star</span> spin and companion orbit are not synchronized. Through adaptive optics imaging we also found a point source 643 {+-} 10 mas away from TYC 2087-00255-1, which would have a mass of 0.13 M{sub Sun} if it is physically associated with TYC 2087-00255-1 and has the same age. Future proper motion observation should be able to resolve if this tertiary object is physically associated with TYC 2087-00255-1 and make TYC 2087-00255-1 a triple body system. Core Ca II H and K line emission indicate that the host is chromospherically active, at a level that is consistent with the inferred spin period and measured v{sub rot}sin i, but unusual for a subgiant of this T{sub eff}. This activity could be explained by ongoing tidal spin-up of the host <span class="hlt">star</span> by the companion.</p> <div class="credits"> <p class="dwt_author">Ma Bo; Ge Jian; De Lee, Nathan; Fleming, Scott W.; Lee, Brian L.; Wang Ji [Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611-2055 (United States); Barnes, Rory; Agol, Eric [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195-1580 (United States); Crepp, Justin R. [Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); Dutra-Ferreira, Leticia; Porto de Mello, G. F. [Observatorio do Valongo, Universidade Federal do Rio de Janeiro, Ladeira do Pedro Antonio, 43, CEP: 20080-090, Rio de Janeiro, RJ (Brazil); Esposito, Massimiliano; Femenia, Bruno; Gonzalez Hernandez, Jonay I. [Instituto de Astrofisica de Canarias, C/Via Lctea S/N, E-38200 La Laguna (Spain); Gaudi, B. Scott [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Ghezzi, Luan [Laboratorio Interinstitucional de e-Astronomia (LIneA), Rio de Janeiro, RJ 20921-400 (Brazil); Hebb, Leslie; Stassun, Keivan G. [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Wisniewski, John P. [Homer L Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W Brooks St, Norman, OK 73019 (United States); Bizyaev, Dmitry, E-mail: boma@astro.ufl.edu [Apache Point Observatory, P.O. Box 59, Sunspot, NM 88349-0059 (United States); and others</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">256</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1989A%26A...223..241B"> <span id="translatedtitle">Activity in late-type <span class="hlt">stars</span>. IV - The 1980 August 20 flare on Proxima Centauri <span class="hlt">revisited</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">This paper presents a reanalysis of simultaneous ultraviolet and soft X-ray observations of a flare on the dMe <span class="hlt">star</span>, Proxima Centauri. Using an emission measure analysis, as well as density sensitive line ratios, the electron density and the total emitting volume of the flare plasma which is at midtransition region temperatures are derived. These, and the corresponding parameters derived from the previously published X-ray light curve, are compared in the framework of a simple loop model of the flare. This analysis suggests that the coronal X-rays and the transition-region UV line emission arose in volumes of comparable extent. The combined L-alpha and total transition region line losses are found to be comparable to the estimated total coronal losses during the flare. This latter conclusion disagrees with the original deduction of Haisch et al. (1983) that the transition region losses are unimportant compared with the coronal losses.</p> <div class="credits"> <p class="dwt_author">Byrne, P. B.; McKay, D.</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">257</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/17407407"> <span id="translatedtitle">Coronal mass ejection (CME) activity of <span class="hlt">low</span> <span class="hlt">mass</span> M <span class="hlt">stars</span> as an important factor for the habitability of terrestrial exoplanets. II. CME-induced ion pick up of Earth-like exoplanets in close-in habitable zones.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Atmospheric erosion of CO2-rich Earth-size exoplanets due to coronal mass ejection (CME)-induced ion pick up within close-in habitable zones of active M-type dwarf <span class="hlt">stars</span> is investigated. Since M <span class="hlt">stars</span> are active at the X-ray and extreme ultraviolet radiation (XUV) wave-lengths over long periods of time, we have applied a thermal balance model at various XUV flux input values for simulating the thermospheric heating by photodissociation and ionization processes due to exothermic chemical reactions and cooling by the CO2 infrared radiation in the 15 microm band. Our study shows that intense XUV radiation of active M <span class="hlt">stars</span> results in atmospheric expansion and extended exospheres. Using thermospheric neutral and ion densities calculated for various XUV fluxes, we applied a numerical test particle model for simulation of atmospheric ion pick up loss from an extended exosphere arising from its interaction with expected minimum and maximum CME plasma flows. Our results indicate that the Earth-like exoplanets that have no, or weak, magnetic moments may lose tens to hundreds of bars of atmospheric pressure, or even their whole atmospheres due to the CME-induced O ion pick up at orbital distances <or=0.2 astronomical units. We have found that, when exposed to intense XUV fluxes, atmospheres with CO2/N2 mixing ratios lower than 96% will show an increase in exospheric temperatures and expanded thermosphere-exosphere environments. Hence, they suffer stronger atmospheric erosion, which can result in the total loss of several hundred bars even if an exoplanet is protected by a "magnetic shield" with its boundary located at 1 Earth radius above the surface. Furthermore, our study indicates that magnetic moments of tidally locked Earth-like exoplanets are essential for protecting their expanded upper atmospheres because of intense XUV radiation against CME plasma erosion. Therefore, we suggest that larger and more massive terrestrial-type exoplanets may better protect their atmospheres against CMEs, because the larger cores of such exoplanets would generate stronger magnetic moments and their higher gravitational acceleration would constrain the expansion of their thermosphere-exosphere regions and reduce atmospheric escape. PMID:17407407</p> <div class="credits"> <p class="dwt_author">Lammer, Helmut; Lichtenegger, Herbert I M; Kulikov, Yuri N; Griessmeier, Jean-Mathias; Terada, N; Erkaev, Nikolai V; Biernat, Helfried K; Khodachenko, Maxim L; Ribas, Ignasi; Penz, Thomas; Selsis, Franck</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">258</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AJ....140..242M"> <span id="translatedtitle">Binary <span class="hlt">Star</span> Orbits. III. <span class="hlt">Revisiting</span> the Remarkable Case of Tweedledum and Tweedledee</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Two of the most challenging objects for optical interferometry in the middle of the last century were the close components (FIN 332) of the wide visual binary STF2375 (= WDS 18455+0530 = HIP 92027 = ADS 11640). Each component of the wide pair was found to have subcomponents of approximately the same magnitude, position angle, and separation and, hence, were designated by the tongue-in-cheek monikers "Tweedledum and Tweedledee" by the great visual interferometrist William S. Finsen in 1953. They were later included in a list of "Double <span class="hlt">Stars</span> that Vex the Observer" by W.H. van den Bos in 1958. While speckle interferometry has reaped a rich harvest investigating the close inteferometric binaries of Finsen, the "Tweedles" have continued to both fascinate and exasperate due to both the great similarity of the close pairs and the inherent 180° ambiguity associated with interferometry. Detailed analysis of all published observations of the system has revealed several errors which are here corrected, allowing for determination of these orbital elements which resolve the quadrant ambiguity. A unique software filter was developed which allowed subarrays from archival ICCD speckle data from 1982 to be re-reduced. Those data, combined with new and unpublished observations obtained in 2001-2009 from NOAO 4 m telescopes, the Mount Wilson 100 inch telescope and the Naval Observatory Flagstaff Station 61 inch telescope as well as high-quality unresolved measures all allow for the correct orbits to be determined. Co-planarity of the multiple system is also investigated.</p> <div class="credits"> <p class="dwt_author">Mason, Brian D.; Hartkopf, William I.; McAlister, Harold A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">259</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21443285"> <span id="translatedtitle">BINARY <span class="hlt">STAR</span> ORBITS. III. <span class="hlt">REVISITING</span> THE REMARKABLE CASE OF TWEEDLEDUM AND TWEEDLEDEE</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Two of the most challenging objects for optical interferometry in the middle of the last century were the close components (FIN 332) of the wide visual binary STF2375 (= WDS 18455+0530 = HIP 92027 = ADS 11640). Each component of the wide pair was found to have subcomponents of approximately the same magnitude, position angle, and separation and, hence, were designated by the tongue-in-cheek monikers 'Tweedledum and Tweedledee' by the great visual interferometrist William S. Finsen in 1953. They were later included in a list of 'Double <span class="hlt">Stars</span> that Vex the Observer' by W.H. van den Bos in 1958. While speckle interferometry has reaped a rich harvest investigating the close inteferometric binaries of Finsen, the 'Tweedles' have continued to both fascinate and exasperate due to both the great similarity of the close pairs and the inherent 180{sup 0} ambiguity associated with interferometry. Detailed analysis of all published observations of the system has revealed several errors which are here corrected, allowing for determination of these orbital elements which resolve the quadrant ambiguity. A unique software filter was developed which allowed subarrays from archival ICCD speckle data from 1982 to be re-reduced. Those data, combined with new and unpublished observations obtained in 2001-2009 from NOAO 4 m telescopes, the Mount Wilson 100 inch telescope and the Naval Observatory Flagstaff Station 61 inch telescope as well as high-quality unresolved measures all allow for the correct orbits to be determined. Co-planarity of the multiple system is also investigated.</p> <div class="credits"> <p class="dwt_author">Mason, Brian D.; Hartkopf, William I. [U.S. Naval Observatory, 3450 Massachusetts Avenue, NW, Washington, DC, 20392-5420 (United States); McAlister, Harold A., E-mail: bdm@usno.navy.mi, E-mail: wih@usno.navy.mi, E-mail: hal@chara.gsu.ed [Center for High Angular Resolution Astronomy, Georgia State University, Atlanta, GA 30303 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-07-15</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">260</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/12485380"> <span id="translatedtitle">On the detection of pre-<span class="hlt">low-mass</span> X-ray binaries</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We explore the population of candidate pre-<span class="hlt">low-mass</span> X-ray binaries in which a neutron <span class="hlt">star</span> accretes mass from the wind of a <span class="hlt">low-mass</span> companion (mass <=2 Msolar) in the framework of a binary population synthesis study. The simulated accretion-luminosity distribution shows a primary peak close to 1031 erg s-1 and a secondary peak near 1028 erg s-1. The relative contribution of</p> <div class="credits"> <p class="dwt_author">B. Willems; U. Kolb</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_12");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">261</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EPJWC..4713003K"> <span id="translatedtitle">A spectral differential characterization of <span class="hlt">low-mass</span> companions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present a new approach with which the dynamical mass of <span class="hlt">low-mass</span> companions around cool <span class="hlt">stars</span> can be found. In order to discover companions to late-type <span class="hlt">stars</span> the stellar spectrum is removed. For this we substract two spectra obtained at different orbital phases from each other in order to discover the companion spectrum in the difference spectrum in which the companion lines appear twice (positive and negative signal). The resulting radial velocity difference of these two signals provides the true mass of the companion. For our test case GJ1046, an M2V dwarf with a <span class="hlt">low-mass</span> companion that most likely is a brown dwarf we select the CO line region in the K-band. We show that the dynamical mass of a faint companion to an M dwarf can be determined using our spectral differential technique. Only if the companion rotates rapidly and has a small radial velocity amplitude due to a high mass, does blending occur for all lines so that our approach fails. In addition to determining the companion mass, we restore the single companion spectrum from the difference spectrum using singular value decomposition.</p> <div class="credits"> <p class="dwt_author">Kostogryz, N.; Kürster, M.; Yakobchuk, T.; Lyubchik, Y.; Kuznetsov, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">262</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21432358"> <span id="translatedtitle">Effect of <span class="hlt">low</span> <span class="hlt">mass</span> dark matter particles on the Sun</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We study the effect of dark matter (DM) particles in the Sun, focusing, in particular, on the possible reduction of the solar neutrinos flux due to the energy carried away by DM particles from the innermost regions of the Sun, and to the consequent reduction of the temperature of the solar core. We find that in the very <span class="hlt">low-mass</span> range between 4 and 10 GeV, recently advocated to explain the findings of the DAMA and CoGent experiments, the effects on neutrino fluxes are detectable only for DM models with a very small, or vanishing, self-annihilation cross section, such as the so-called asymmetric DM models, and we study the combination of DM masses and spin-dependent cross sections which can be excluded with current solar neutrino data. Finally, we <span class="hlt">revisit</span> the recent claim that DM models with large self-interacting cross sections can lead to a modification of the position of the convective zone, alleviating or solving the solar composition problem. We show that when the 'geometric' upper limit on the capture rate is correctly taken into account, the effects of DM are reduced by orders of magnitude, and the position of the convective zone remains unchanged.</p> <div class="credits"> <p class="dwt_author">Taoso, Marco [IFIC-CSIC-Universitat de Valencia, Ed. Instituts, Apt. 22085, 46071 Valencia (Spain); Iocco, Fabio [Institut d'Astrophysique de Paris, UMR 7095-CNRS, Universite Pierre et Marie Curie, 98 bis Boulevard Arago 75014, Paris (France); Meynet, Georges; Eggenberger, Patrick [Geneva Observatory, University of Geneva, Maillettes 51, 1290 Sauverny (Switzerland); Bertone, Gianfranco [Institut d'Astrophysique de Paris, UMR 7095-CNRS, Universite Pierre et Marie Curie, 98 bis Boulevard Arago 75014, Paris (France); Institute fuer Theoretische Physik, Universitaet Zuerich, Winterthurerstrasse 190, CH-8057 Zuerich (Switzerland)</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-10-15</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">263</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21467163"> <span id="translatedtitle">OGLE-2005-BLG-153: MICROLENSING DISCOVERY AND CHARACTERIZATION OF A VERY <span class="hlt">LOW</span> <span class="hlt">MASS</span> BINARY</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The mass function and statistics of binaries provide important diagnostics of the <span class="hlt">star</span> formation process. Despite this importance, the mass function at <span class="hlt">low</span> <span class="hlt">masses</span> remains poorly known due to observational difficulties caused by the faintness of the objects. Here we report the microlensing discovery and characterization of a binary lens composed of very <span class="hlt">low</span> <span class="hlt">mass</span> <span class="hlt">stars</span> just above the hydrogen-burning limit. From the combined measurements of the Einstein radius and microlens parallax, we measure the masses of the binary components of 0.10 {+-} 0.01 M{sub sun} and 0.09 {+-} 0.01 M{sub sun}. This discovery demonstrates that microlensing will provide a method to measure the mass function of all Galactic populations of very <span class="hlt">low</span> <span class="hlt">mass</span> binaries that is independent of the biases caused by the luminosity of the population.</p> <div class="credits"> <p class="dwt_author">Hwang, K.-H.; Han, C.; Ryu, Y.-H. [Department of Physics, Chungbuk National University, Cheongju 361-763 (Korea, Republic of); Udalski, A.; Kubiak, M.; Szymanski, M. K.; Pietrzynski, G.; Soszynski, I.; Szewczyk, O.; Ulaczyk, K.; Wyrzykowski, L. [Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa (Poland); Bond, I. A. [Institute of Information and Mathematical Sciences, Massey University, Private Bag 102-904, North Shore Mail Centre, Auckland (New Zealand); Beaulieu, J.-P. [Institut d'Astrophysique de Paris, CNRS, Universite Pierre et Marie Curie UMR7095, 98bis Boulevard Arago, 75014 Paris (France); Dominik, M.; Horne, K. [Scottish Universities Physics Alliance, University of St. Andrews, School of Physics and Astronomy, North Haugh, St. Andrews KY16 9SS (United Kingdom); Gould, A.; Gaudi, B. S. [Department of Astronomy, Ohio State University, 140 W. 18th Ave., Columbus, OH 43210 (United States); Abe, F. [Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601 (Japan); Botzler, C. S. [Department of Physics, University of Auckland, Private Bag 92019, Auckland (New Zealand); Hearnshaw, J. B. [Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch 8020 (New Zealand)</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">264</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/27715630"> <span id="translatedtitle">The Formation of <span class="hlt">Low-Mass</span> Transient X-Ray Binaries</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We consider constraints on the formation of <span class="hlt">low-mass</span> X-ray binaries containing neutron <span class="hlt">stars</span> (NLMXBs) arising from the presence of soft X-ray transients among these systems. For a neutron <span class="hlt">star</span> of mass M1 ~= 1.4 M&sun; at formation, we show that in short-period (<~1--2 day) systems driven by angular momentum loss these constraints require the secondary at the beginning of mass</p> <div class="credits"> <p class="dwt_author">A. R. King; U. Kolb</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">265</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013ASPC..476..321Y"> <span id="translatedtitle">Shock Chemistry in <span class="hlt">Low-Mass</span> <span class="hlt">Star</span>-Forming Regions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have conducted spectral line surveys in the 3 mm band with the 45 m telescope of the Nobeyama Radio Observatory toward the L1157 B1 and L1448 B1/R1 shocked regions. L1157 B1 is a famous shocked region formed by the interaction between the outflow from the protostar IRAS 20386+6751 and the ambient gas, while L1448 B1/R1 are formed from internal bow shocks within the extremely energetic jet from the protostar L1448 mm. As a result, we found a grate difference of the chemical composition between the two shocked regions.</p> <div class="credits"> <p class="dwt_author">Yamaguchi, T.; Takano, S.; Sakai, N.; Watanabe, Y.; Yamamoto, S.; NRO Line Survey Team Members</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">266</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22016292"> <span id="translatedtitle">RESOLVING THE LUMINOSITY PROBLEM IN <span class="hlt">LOW-MASS</span> <span class="hlt">STAR</span> FORMATION</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We determine the observational signatures of protostellar cores by coupling two-dimensional radiative transfer calculations with numerical hydrodynamical simulations that predict accretion rates that both decline with time and feature short-term variability and episodic bursts caused by disk gravitational instability and fragmentation. We calculate the radiative transfer of the collapsing cores throughout the full duration of the collapse, using as inputs the core, disk, protostellar masses, radii, and mass accretion rates predicted by the hydrodynamical simulations. From the resulting spectral energy distributions, we calculate standard observational signatures (L{sub bol}, T{sub bol}, L{sub bol}/L{sub smm}) to directly compare to observations. We show that the accretion process predicted by these models reproduces the full spread of observed protostars in both L{sub bol}-T{sub bol} and L{sub bol}-M{sub core} space, including very low luminosity objects, provides a reasonable match to the observed protostellar luminosity distribution, and resolves the long-standing luminosity problem. These models predict an embedded phase duration shorter than recent observationally determined estimates (0.12 Myr versus 0.44 Myr), and a fraction of total time spent in Stage 0 of 23%, consistent with the range of values determined by observations. On average, the models spend 1.3% of their total time in accretion bursts, during which 5.3% of the final stellar mass accretes, with maximum values being 11.8% and 35.5% for the total time and accreted stellar mass, respectively. Time-averaged models that filter out the accretion variability and bursts do not provide as good of a match to the observed luminosity problem, suggesting that the bursts are required.</p> <div class="credits"> <p class="dwt_author">Dunham, Michael M. [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520 (United States); Vorobyov, Eduard I., E-mail: michael.dunham@yale.edu, E-mail: eduard.vorobiev@univie.ac.at [Institute of Astronomy, University of Vienna, Vienna 1180 (Austria)</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">267</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AAS...21723205W"> <span id="translatedtitle"><span class="hlt">Low</span> <span class="hlt">Mass</span> <span class="hlt">Star</span> L1551 IRS 5 Jets</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">L1551 IRS5 is a multiple protostellar system showing two nearly parallel jets of ionized gas. The southern jet shows a peculiar bend at about 0.6? to the southwest of its driving source. One hypothesis to explain the bend jet is interaction of the two jets. In order to test the hypothesis, we compared the maps of the jet in 3 different epochs comprising 1994, 2002 and 2003. The 3.5cm continuum maps observed by Very Large Array with the Pie Town antenna reveal the intensity of the Southwest part of the southern jet increase from 1994 to 2002. Comparing epoch 2002 to 2003, the southwest part of the Southern jet keeps changing in intensity. Furthermore, an intensity change is found close to or at the location where jet bends. We don't see change anywhere even close to the source where the emission is strongest and any change easiest to detect. The position of the bending jet shows an increase in intensity, but the spatial position is the same. We are looking at different models for what could cause the observed changes.</p> <div class="credits"> <p class="dwt_author">Wing, Leung Ka; Lim, J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">268</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/11560604"> <span id="translatedtitle">Asymmetric supernova explosions and the formation of short period <span class="hlt">low-mass</span> X-ray binaries</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We consider the formation of short period <span class="hlt">low-mass</span> X-ray binaries using standard evolutionary scenario which involves a common envelope phase and a supernova explosion. We consider three models of systems and assume several values of the efficiency factor for the common envelope evolution (alpha_ {CE). In most cases the systems can only be formed if the neutron <span class="hlt">stars</span> in the</p> <div class="credits"> <p class="dwt_author">W. Sutantyo</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">269</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013MmSAI..84..117B"> <span id="translatedtitle">On <span class="hlt">low</span> <span class="hlt">mass</span> X-ray binaries and millisecond pulsar</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The detection, in 1998, of the first Accreting Millisecond Pulsar, started an exiciting season of continuing discoveries in the fashinating field of compact binary systems harbouring a neutron <span class="hlt">star</span>. Indeed, in these last three lustres, thanks to the extraordinary performances of astronomical detectors, on ground as well as on board of satellites, mainly in the radio, optical, x-ray, and gamma-ray bands, astrophysicists had the opportunity to thoroughly investigate the so-called Recycling Scenario: the evolutionary path leading to the formation of a Millisecond Radio Pulsar. The most intriguing phase is certainly the spin-up stage during which, because of the accretion of matter and angular momentum, the neutron <span class="hlt">star</span> accumulates an extraordinary amount of mechanical rotational energy, up to 1% of its whole rest-mass energy. These millisecond spinning neutron <span class="hlt">stars</span> are truly extreme physical objects: General and Special Relativity are fully in action, since their surfaces, attaining speeds close to one fifth of the speed of light, are located just beyond their Schwartzscild Radius, and electrodynamical forces, caused by the presence of huge surface magnetic fields of several hundred million Gauss, display their spectacular properties accelerating electrons up to such energies to promote pair creation in a cascade process responsible for the emission in Radio and Gamma-ray. The rotational energy is swiftly converted and released into electromagnetic power which, in some cases, causes the neutron <span class="hlt">star</span> to outshine with a luminosity of one hundred suns. Along these fifteen years, a fruitful collaboration was established, at the Rome Astronomical Observatory, between my group and Franca D'Antona: her profound knowledge of the complex phases of stellar evolution, in particular of <span class="hlt">low-mass</span> <span class="hlt">stars</span> in close binary systems, was the key ingredient which boosted our theoretical and experimental studies of different evolutionary stages of these intriguing and fashinating systems. In this paper I will review some of the most recent discoveries on (accreting) millisecond pulsars, highlighting the role played by our proficuous collaboration.</p> <div class="credits"> <p class="dwt_author">Burderi, L.; Di Salvo, T.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">270</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AAS...22231412W"> <span id="translatedtitle">Kinematic Analysis of Nine <span class="hlt">Low</span> <span class="hlt">Mass</span> Gas-rich Galaxies</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present results from an optical, near-IR, and neutral gas study of a sample of 9 nearby gas-rich <span class="hlt">low</span> <span class="hlt">mass</span> galaxies. Half of the galaxies in this sample were previously known to host unusually extended gaseous disks (D_HI > 5xD_25). We trace the stellar distribution using new deep, wide field-of-view Spitzer 3.6micron images and use archival data from the VLA to trace the gas distribution and kinematics. Rotation curves have been derived by interactively fitting tilted-ring models to observed velocity fields from the neutral hydrogen synthesis observations. We derive a dark matter halo profile by fitting the observed rotation curve to the sum in quadrature of the baryonic components (<span class="hlt">stars</span> and gas) and an isothermal dark matter halo. The stellar mass-to-light ratio is calculated for each galaxy in both the optical and near-IR. As is typical for <span class="hlt">low</span> <span class="hlt">mass</span> galaxies, these systems appear to be dark matter dominated throughout their stellar disk. We discuss the extent of their neutral gas disk, stellar distribution, and dark matter fraction in the context of galaxy formation and evolution.</p> <div class="credits"> <p class="dwt_author">Wavle, Daniel; van Zee, L.; Richards, E. E.; Barnes, K. L.; Staudaher, S.; Dale, D. A.; Calzetti, D.; Dalcanton, J.; Bullock, J.; Chandar, R.; Hinz, J. L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">271</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/54190050"> <span id="translatedtitle">Extreme Starbursts and the <span class="hlt">Low</span> <span class="hlt">Mass</span> IMF</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The temperatures and densities of the interstellar medium (ISM) in starburst galaxies are greatly elevated compared to those in <span class="hlt">star</span> forming giant molecular clouds (GMCs) in normal galaxies. I review the observed ISM properties in the prototype starburst Arp 200 and then discuss considerations for <span class="hlt">star</span> formation in such starburst galaxy nuclei. We have also found a previously unrecognized observational</p> <div class="credits"> <p class="dwt_author">N. Scoville; G. Li</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">272</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://sunshine.chpc.utah.edu/labs/star_life/starlife_end.html"> <span id="translatedtitle"><span class="hlt">Stars</span> : the end of a <span class="hlt">star</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">What happens during the death of a <span class="hlt">star</span>? This activity page, part of an interactive laboratory series for grades 8-12, introduces students to the final processes of <span class="hlt">stars</span>. Here students read about <span class="hlt">low-mass</span>, medium-mass, and massive <span class="hlt">stars</span>. <span class="hlt">Low-mass</span> <span class="hlt">stars</span> produce white dwarfs. A pop-up window describes how white dwarfs form. Medium-mass <span class="hlt">stars</span> produce neutron <span class="hlt">stars</span> and supernova. Pop-up information explains the supernova process. Massive <span class="hlt">stars</span> undergo carbon burning. An interactive lab activity presents students the opportunity to predict temperature, pressure, and gravity changes that occur during carbon fusion. In a final lab activity, students compare initial <span class="hlt">star</span> size with the type of death that occurs. Activity questions about <span class="hlt">star</span> death are provided for each <span class="hlt">star</span> size and are recordable and printable. Copyright 2005 Eisenhower National Clearinghouse</p> <div class="credits"> <p class="dwt_author">University of Utah. Astrophysics Science Project Integrating Research and Education (ASPIRE)</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">273</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2007A%26A...475..667J"> <span id="translatedtitle">Lithium abundances of very <span class="hlt">low</span> <span class="hlt">mass</span> members of Chamaeleon I</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Aims:We present the first study of the lithium abundances of very <span class="hlt">low</span> <span class="hlt">mass</span> objects in Chamaeleon I close to the hydrogen burning mass limit based on atmospheric models and high-resolution spectroscopic observations. The studied objects, Cha H? 2, 3, 4, 5, 6 and 8, are very young brown dwarf candidates and very <span class="hlt">low</span> <span class="hlt">mass</span> <span class="hlt">stars</span> on the verge of lithium depletion. Methods: For this analysis, we have computed a new “GAIA-cond” class model grid over effective temperatures from 2600 K to 3100 K, surface gravities from log(g) = 3.5 to 5.5, and lithium abundances from log? = 0.0 to 3.7, for two different line profile setups introduced in previous work. Calculated synthetic spectra are compared with high-resolution UVES / VLT echelle spectra of the objects. Results: We find good descriptions of the lithium resonance doublet lines at 6708 Å and of the surrounding pseudo-continuum and determine a consistent set of lithium abundances (log(?) = 1.55). However, the derived lithium abundances are lower than the meteoritic one (log(?) = 3.31) and that of higher mass <span class="hlt">stars</span> in Cha I (log(?) = 3.1/3.4 for LTE-/non-LTE-calculations). By modeling the TiO-line, we demonstrate that veiling does not make the lithium lines appear weaker. We can also rule out that the results are spoiled by the presence of spots. Conclusions: A possible explanation for these results would be that the objects are either more massive, or much older, than previously thought, so that the lithium depletion has already started. Although the uncertainties of the masses and ages are large, they are not large enough as to explain the observed lithium depletion. Therefore, the most likely explanation is either a lack of understanding of the details of the formation of the lithium line, or a lack of understanding of the internal structure of the very young <span class="hlt">low-mass</span> objects. Based on observations obtained at the European Southern Observatory at Paranal, Chile in program 65.L-0629(A,B) and 65.I-0011(A).</p> <div class="credits"> <p class="dwt_author">Johnas, C. M. S.; Guenther, E. W.; Joergens, V.; Schweitzer, A.; Hauschildt, P. H.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">274</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1999AIPC..488....9D"> <span id="translatedtitle">Closing the <span class="hlt">low-mass</span> axigluon window</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In this report, I will present the current status of the <span class="hlt">low-mass</span> axigluon. The axigluon is a massive, color octet, axial vector boson, predicted in, e.g., chiral color models and some technicolor models, with a mass of order the electroweak scale. Axigluons with a mass larger than about 125 GeV to nearly 1 TeV can be eliminated by di-jet production at hadron colliders like the TEVATRON, but a <span class="hlt">low-mass</span> window exists that the di-jet search can not probe. ? decays can rule out axigluons with a mass up to 25 GeV, and low energy e+e- (PEP and PETRA) can rule out axigluons with a mass up to 50 GeV using a measurement of R. Top production at the TEVATRON disfavors a light axigluon. A measurement of R at LEP strongly disfavors a light axigluon, and rules out an axigluon with mass <365 GeV.</p> <div class="credits"> <p class="dwt_author">Doncheski, Michael A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">275</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21583234"> <span id="translatedtitle"><span class="hlt">LOW-MASS</span> VISUAL COMPANIONS TO NEARBY G-DWARFS</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">A complete census of wide visual companions to nearby G-dwarf <span class="hlt">stars</span> can be achieved by selecting candidates from the Two Micron All Sky Survey (2MASS) Point-Source Catalog and checking their status by second-epoch imaging. Such data are obtained for 124 candidates with separations up to 20'', 47 of which are shown to be new physical <span class="hlt">low-mass</span> stellar companions. A list of visual binaries with G-dwarf primaries is produced by combining newly found companions with historical data. Maximum likelihood analysis leads to a companion frequency of 0.13 {+-} 0.015 per decade of separation. The mass ratio is distributed almost uniformly, with a power-law index between -0.4 and 0. The remaining uncertainty in the index is related to modeling of the companion detection threshold in 2MASS. These findings are confirmed by an alternative analysis of wider companions in 2MASS, removing the contamination by background <span class="hlt">stars</span> statistically. Extension of this work will lead to a complete detection of visual companions-a necessary step toward reaching unbiased multiplicity statistics over the full range of orbital periods and, eventually, understanding the origin of multiple systems.</p> <div class="credits"> <p class="dwt_author">Tokovinin, Andrei, E-mail: atokovinin@ctio.noao.edu [Cerro Tololo Inter-American Observatory, Casilla 603, La Serena (Chile)</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-02-15</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">276</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011IAUS..270.....A"> <span id="translatedtitle">Computational <span class="hlt">Star</span> Formation (IAU S270)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">1. Historical introduction; 2. Individual <span class="hlt">star</span> formation: observations; 3. <span class="hlt">Low-mass</span> <span class="hlt">star</span> formation: observations; 4. Individual <span class="hlt">star</span> formation: theory; 5. Formation of clusters: observations; 6. Formation of clusters: theory; 7. Numerical methods: MHD; 8. Numerical methods: radiative dynamics; 9. Local <span class="hlt">star</span> formation processes; 10. <span class="hlt">Star</span> formation feedback; 11. <span class="hlt">Star</span> formation on galactic scales; 12. Special purpose hardware; 13. Computational methods; 14. Radiation diagnostics of <span class="hlt">star</span> formation; 15. Large scale <span class="hlt">star</span> formation; 16. Cosmological <span class="hlt">star</span> formation; 17. Computational <span class="hlt">star</span> formation: Summary; Index.</p> <div class="credits"> <p class="dwt_author">Alves, João.; Elmegreen, Bruce G.; Girart, Josep M.; Trimble, Virginia</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">277</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012AcA....62..153S"> <span id="translatedtitle">Evolution of <span class="hlt">Low</span> <span class="hlt">Mass</span> Contact Binaries</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">VFTS 682, a very massive and very hot Wolf-Rayet (WR) <span class="hlt">star</span> recently discovered in the Large Magellanic Cloud near the famous <span class="hlt">star</span> cluster R136, might be providing us with a glimpse of a missing link in our understanding of Long Gamma-Ray Bursts (LGRBs), including dark GRBs. It is likely its properties result from chemically homogeneous evolution (CHE), believed to be a key process for a massive <span class="hlt">star</span> to become a GRB. It is also heavily obscured by dust extinction, which could make it a dark GRB upon explosion. Using Spitzer data we investigate the properties of interstellar dust in the vicinity of R136, and argue that its high obscuration is not unusual for its environment and that it could indeed be a slow runaway (``walkaway'') from R136. Unfortunately, based on its current mass loss rate, VFTS 682 is unlikely to become a GRB, because it will lose too much angular momentum at its death. If it were to become a GRB, it probably would also not be dark, either escaping or destroying its surrounding dusty region. Nevertheless, it is a very interesting <span class="hlt">star</span>, deserving further studies, and being one of only three presently identified WR <span class="hlt">stars</span> (two others in the Small Magellanic Cloud) that seems to be undergoing CHE.</p> <div class="credits"> <p class="dwt_author">St?pie?, K.; Gazeas, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">278</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22034561"> <span id="translatedtitle">ROTATIONAL VELOCITIES OF INDIVIDUAL COMPONENTS IN VERY <span class="hlt">LOW</span> <span class="hlt">MASS</span> BINARIES</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We present rotational velocities for individual components of 11 very <span class="hlt">low</span> <span class="hlt">mass</span> (VLM) binaries with spectral types between M7 and L7.5. These results are based on observations taken with the near-infrared spectrograph, NIRSPEC, and the Keck II laser guide <span class="hlt">star</span> adaptive optics system. We find that the observed sources tend to be rapid rotators (v sin i > 10 km s{sup -1}), consistent with previous seeing-limited measurements of VLM objects. The two sources with the largest v sin i, LP 349-25B and HD 130948C, are rotating at {approx}30% of their break-up speed, and are among the most rapidly rotating VLM objects known. Furthermore, five binary systems, all with orbital semimajor axes {approx}<3.5 AU, have component v sin i values that differ by greater than 3{sigma}. To bring the binary components with discrepant rotational velocities into agreement would require the rotational axes to be inclined with respect to each other, and that at least one component is inclined with respect to the orbital plane. Alternatively, each component could be rotating at a different rate, even though they have similar spectral types. Both differing rotational velocities and inclinations have implications for binary <span class="hlt">star</span> formation and evolution. We also investigate possible dynamical evolution in the triple system HD 130948A-BC. The close binary brown dwarfs B and C have significantly different v sin i values. We demonstrate that components B and C could have been torqued into misalignment by the primary <span class="hlt">star</span>, A, via orbital precession. Such a scenario can also be applied to another triple system in our sample, GJ 569A-Bab. Interactions such as these may play an important role in the dynamical evolution of VLM binaries. Finally, we note that two of the binaries with large differences in component v sin i, LP 349-25AB and 2MASS 0746+20AB, are also known radio sources.</p> <div class="credits"> <p class="dwt_author">Konopacky, Q. M.; Macintosh, B. A. [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 (United States); Ghez, A. M. [UCLA Division of Astronomy and Astrophysics, Los Angeles, CA 90095-1562 (United States); Fabrycky, D. C. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); White, R. J. [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303 (United States); Barman, T. S. [Lowell Observatory, 1400 W. Mars Hill Rd., Flagstaff, AZ 86001 (United States); Rice, E. L. [American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024-5192 (United States); Hallinan, G. [Department of Astrophysics, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States); Duchene, G., E-mail: macintosh1@llnl.gov, E-mail: konopacky@di.utoronto.ca, E-mail: ghez@astro.ucla.edu, E-mail: fabrycky@ucolick.org, E-mail: white@chara.gsu.edu, E-mail: barman@lowell.edu, E-mail: erice@amnh.org, E-mail: gh@astro.caltech.edu, E-mail: gduchene@berkeley.edu [Astronomy Department, University of California, Berkeley, Hearst Field Annex B-20, CA 94720-3411 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">279</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/5167865"> <span id="translatedtitle">SP-100 <span class="hlt">low</span> <span class="hlt">mass</span> shield design</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The shielding considerations for an unmanned space reactor system are somewhat different from those for a terrestrial reactor. An unmanned operation in space implies that only a shadow shield, rather than a 4..pi.. one, is required to protect payload hardware that typically can tolerate 10/sup 4/ to 10/sup 6/ times more radiation than can a human crew. On the other hand, the system mass, of which the radiation shield can be a significant fraction, is a severe constraint for space reactors and not normally a problem with terrestrial ones. The object of this paper is to briefly summarize advancements made on various aspects of <span class="hlt">low</span> <span class="hlt">mass</span> shield design for space reactors, including materials and their arrangements, geometric factors and their potential impact on system design optimization, and proposed new configuration concepts for further mass reduction.</p> <div class="credits"> <p class="dwt_author">Carlson, D.E.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">280</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.windows2universe.org/the_universe/Stars.html"> <span id="translatedtitle"><span class="hlt">Stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">This section of the Windows to the Universe web site provides information and images about <span class="hlt">stars</span> including <span class="hlt">star</span> statistics, and a <span class="hlt">star</span> gallery. Windows to the Universe is a user-friendly learning system pertaining to the Earth and Space sciences. The objective of this project is to develop an innovative and engaging web site that spans the Earth and Space sciences and includes a rich array of documents, including images, movies, animations, and data sets that explore the Earth and Space sciences and the historical and cultural ties between science, exploration and the human experience. Links at the top of each page allow users to navigate between beginner, intermediate and advanced levels.</p> <div class="credits"> <p class="dwt_author">Johnson, Roberta</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-07-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_13");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' 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showDiv("page_16");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">281</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/27692646"> <span id="translatedtitle">Superbursts from Strange <span class="hlt">Stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Recent models of carbon ignition on accreting neutron <span class="hlt">stars</span> predict superburst ignition depths that are an order of magnitude larger than those observed. We explore a possible solution to this problem, that the compact <span class="hlt">stars</span> in <span class="hlt">low-mass</span> X-ray binaries that have shown superbursts are in fact strange <span class="hlt">stars</span> with a crust of normal matter. We calculate the properties of superbursts</p> <div class="credits"> <p class="dwt_author">Dany Page; Andrew Cumming</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">282</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/55438539"> <span id="translatedtitle">X-ray spectroscopy of <span class="hlt">low-mass</span> X-ray binaries</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">I present high-resolution X-ray grating spectroscopy of neutron <span class="hlt">stars</span> in <span class="hlt">low-mass</span> X-ray binaries (LMXBs) using instruments onboard the Chandra X-ray Observatory and the X-ray Multi-Mirror Mission (XMM-Newton). The first part of this thesis concentrates on results from the subset of LMXBs with orbital periods less than an hour, known as ultracompact binaries. Previous low- resolution X-ray spectra of four systems</p> <div class="credits"> <p class="dwt_author">Adrienne Marie Juett</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">283</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/12286331"> <span id="translatedtitle">Formation of <span class="hlt">Low-Mass</span> X-ray Binaries. III. A New Formation Mechanism: Direct Supernova</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We propose a new formation mechanism (direct-supernova) for <span class="hlt">low-mass</span> X-ray binaries (LMXBs) that does not involve any prior phase of mass transfer. Survival through the supernova (SN) explosion and shrinkage of the orbit is achieved by a kick velocity of appropriate magnitude and direction imparted to the neutron <span class="hlt">star</span> at its birth. We present analytical population synthesis calculations of LMXBs</p> <div class="credits"> <p class="dwt_author">Vassiliki Kalogera</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">284</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/43144282"> <span id="translatedtitle">Formation of <span class="hlt">Low-Mass</span> X-Ray Binaries. III. A New Formation Mechanism: Direct Supernova</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">We propose a new formation mechanism (direct-supernova) for <span class="hlt">low-mass</span> X-ray binaries (LMXBs) that does not involve any prior phase of mass transfer. Survival through the supernova (SN) explosion and shrinkage of the orbit is achieved by a kick velocity of appropriate magnitude and direction imparted to the neutron <span class="hlt">star</span> at its birth. We present analytical population synthesis calculations of LMXBs</p> <div class="credits"> <p class="dwt_author">Vassiliki Kalogera</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">285</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010AJ....139.1968E"> <span id="translatedtitle">Chandra Observation of Polaris: Census of <span class="hlt">Low-mass</span> Companions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have observed Cepheid Polaris (? UMi A: F7 Ib [Aa] + F6 V [Ab]) with Chandra ACIS-I for 10 ks. An X-ray source was found at the location of Polaris with log LX = 28.89 erg s-1 (0.3-8 keV) and kT = 0.6 keV. A spectrum this soft could come from either the supergiant or the dwarf, as shown by comparable coronal <span class="hlt">stars</span>. Two resolved <span class="hlt">low-mass</span> visual companions, "C" and "D," are not physical members of the system based on the lack of X-rays (indicating an age older than the Cepheid) and inconsistent proper motions. Polaris B is not an X-ray source, consistent with its early F spectral type, and probably does not have a lower mass companion itself. A possible more distant member is identified, and an additional less plausible one. This provides a complete census of companions out to 0.1 pc covering a mass ratio range of an order of magnitude and a ?V of nearly 15 mag. Based on observations made with the NASA Chandra Satellite.</p> <div class="credits"> <p class="dwt_author">Evans, Nancy Remage; Guinan, Edward; Engle, Scott; Wolk, Scott J.; Schlegel, Eric; Mason, Brian D.; Karovska, Margarita; Spitzbart, Bradley</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">286</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009cfdd.confE..96E"> <span id="translatedtitle">Chandra Observation of Polaris: Census of <span class="hlt">Low-Mass</span> Companions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have observed Polaris = HD 8890 with Chandra ACIS-I for 10 ksec and found an X-ray source at the location of the Cepheid Polaris A = Aa + Ab with log L_X = 28.89 ergs s^{-1} and a kT = 0.6 keV. Either the F7 Ib supergiant or the F6 V spectroscopic companion could produce a spectrum this soft. Polaris B is not an X-ray source, which is consistent with its early F spectral type. However, this shows that it does not itself have a lower mass companion. Two resolved <span class="hlt">low</span> <span class="hlt">mass</span> <span class="hlt">stars</span> ``C and D" are not physical companions based on the lack of X-rays (indicating an older age than the Cepheid) and inconsistent motion. In addition, a possible more distant companion is identified, and also less plausible one. Thus, this observation provides a complete census of companions down to masses as small as an order of magnitude less than the Cepheid and nearly 15 mag fainter within the surrounding 0.1 pc.Funding for this work was provided by Chandra grant GO6-7011A Chandra X-ray Center NASA Contract NAS8-39073</p> <div class="credits"> <p class="dwt_author">Evans, Nancy Remage; Wolk, Scott; Guinan, Edward; Engle, Scott; Schlegel, Eric; Mason, Brian; Karovska, Margarita; Spitzbart, Bradley</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">287</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21443110"> <span id="translatedtitle">CHANDRA OBSERVATION OF POLARIS: CENSUS OF <span class="hlt">LOW-MASS</span> COMPANIONS</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We have observed Cepheid Polaris ({alpha} UMi A: F7 Ib [Aa] + F6 V [Ab]) with Chandra ACIS-I for 10 ks. An X-ray source was found at the location of Polaris with log L{sub X} = 28.89 erg s{sup -1} (0.3-8 keV) and kT = 0.6 keV. A spectrum this soft could come from either the supergiant or the dwarf, as shown by comparable coronal <span class="hlt">stars</span>. Two resolved <span class="hlt">low-mass</span> visual companions, 'C' and 'D', are not physical members of the system based on the lack of X-rays (indicating an age older than the Cepheid) and inconsistent proper motions. Polaris B is not an X-ray source, consistent with its early F spectral type, and probably does not have a lower mass companion itself. A possible more distant member is identified, and an additional less plausible one. This provides a complete census of companions out to 0.1 pc covering a mass ratio range of an order of magnitude and a {Delta}V of nearly 15 mag.</p> <div class="credits"> <p class="dwt_author">Remage Evans, Nancy; Wolk, Scott J.; Karovska, Margarita; Spitzbart, Bradley [Smithsonian Astrophysical Observatory, MS 4, 60 Garden Street, Cambridge, MA 02138 (United States); Guinan, Edward; Engle, Scott [Department of Astronomy, Villanova University, Villanova, PA 19085 (United States); Schlegel, Eric [Department of Physics and Astronomy, University of Texas, San Antonio, 1 UTSA Circle, San Antonio, TX 78249-0697 (United States); Mason, Brian D., E-mail: nevans@cfa.harvard.ed [US Naval Observatory, 3450 Massachusetts Avenue, NW, Washington, DC 20392-5420 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-05-15</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">288</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2006Ap%26SS.304...25Q"> <span id="translatedtitle">Photometric Studies of Twelve Deep, <span class="hlt">Low-mass</span> Ratio Overcontact Binary Systems</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The formations of the blue straggler <span class="hlt">stars</span> and the FK Com-type <span class="hlt">stars</span> are unsolved problems in stellar astrophysics. One of the possibilities for their formations is from the coalescence of W UMa-type overcontact binary systems. Therefore, deep (f > 50%), <span class="hlt">low-mass</span> ratio (q < 0.25) overcontact binary <span class="hlt">stars</span> are a very important source to understand the phenomena of Blue Straggler/FK Com-type <span class="hlt">stars</span>. Recently, 12 W UMa-type binary <span class="hlt">stars</span>, FG Hya, GR Vir, IK Per, TV Mus, CU Tau, V857 Her, V410 Aur, XY Boo, SX CrV, QX And, GSC 619-232, and AH Cnc, were investigated photometrically. Apart from TV Mus, XY boo, and GSC 619-232, new observations of the other 9 binaries were obtained. Complete light curves of the 10 systems, FG Hya, GR Vir, IK Per, TV Mus, CU Tau, V857 Her, GSC 619-232, V410 Aur, XY Boo, and AH Cnc, were analyzed with the 2003 version of the W-D code. It is shown that all of those systems are deep (f > 50%), <span class="hlt">low-mass</span> ratio (q < 0.25) overcontact binary <span class="hlt">stars</span>. We found that the system GSC 619-232 has the highest degree of overcontact (f = 93.4%). The derived photometric mass ratio of V857 Her, q = 0.0653, indicates that it is the lowest-mass ratio system among W UMa-type binaries. Of the 12 sample <span class="hlt">stars</span>, long-term period changes of 11 systems were found. About 58% (seven) of the sample binaries show cyclic period oscillation. No cyclic period changes were discovered for the other 5 systems, which may be caused by the short observational time interval or by insufficient observations. Therefore, we think that all W UMa-type binary <span class="hlt">stars</span> may contain cyclic period variations. By considering the long-term period changes (both increase and decrease) of those binary <span class="hlt">stars</span>, we proposed two evolutionary scenarios evolving from deep, <span class="hlt">low-mass</span> ratio overcontact binaries into Blue Straggler/FK Com-type <span class="hlt">stars</span>.</p> <div class="credits"> <p class="dwt_author">Qian, Shengbang; Yang, Yuangui; Zhu, Liying; He, Jiajia; Yuan, Jingzhao</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-08-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">289</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21565456"> <span id="translatedtitle">THE SURVEY OF H I IN EXTREMELY <span class="hlt">LOW-MASS</span> DWARFS (SHIELD)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We present first results from the Survey of H I in Extremely <span class="hlt">Low-mass</span> Dwarfs (SHIELD), a multi-configuration Expanded Very Large Array (EVLA) study of the neutral gas contents and dynamics of galaxies with H I masses in the 10{sup 6}-10{sup 7} M{sub sun} range detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey. We describe the survey motivation and concept demonstration using Very Large Array imaging of six <span class="hlt">low-mass</span> galaxies detected in early ALFALFA data products. We then describe the primary scientific goals of SHIELD and present preliminary EVLA and WIYN 3.5 m imaging of the 12 SHIELD galaxies. With only a few exceptions, the neutral gas distributions of these extremely <span class="hlt">low-mass</span> galaxies are centrally concentrated. In only one system have we detected H I column densities higher than 10{sup 21} cm{sup -2}. Despite this, the stellar populations of all of these systems are dominated by blue <span class="hlt">stars</span>. Further, we find ongoing <span class="hlt">star</span> formation as traced by H{alpha} emission in 10 of the 11 galaxies with H{alpha} imaging obtained to date. Taken together these results suggest that extremely <span class="hlt">low-mass</span> galaxies are forming <span class="hlt">stars</span> in conditions different from those found in more massive systems. While detailed dynamical analysis requires the completion of data acquisition, the most well-resolved system is amenable to meaningful position-velocity analysis. For AGC 749237, we find well-ordered rotation of 30 km s{sup -1} at {approx}40'' distance from the dynamical center. At the adopted distance of 3.2 Mpc, this implies the presence of a {approx}>1 x 10{sup 8} M{sub sun} dark matter halo and a baryon fraction {approx}<0.1.</p> <div class="credits"> <p class="dwt_author">Cannon, John M.; Engstrom, Eric; Allan, John; Erny, Grace; Fliss, Palmer; Smith, AnnaLeigh [Department of Physics and Astronomy, Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-09-20</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">290</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005nfcd.conf..409S"> <span id="translatedtitle">Globular clusters in <span class="hlt">low</span> <span class="hlt">mass</span> galaxies</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We study properties of globular cluster candidates (GCCs) and the diffuse stellar populations in nearby low surface brightness dwarf galaxies, using HST WFPC2 photometry in the V and I bands. Our sample consists of 18 dwarf spheroidal (dSph), 36 dwarf irregular (dIrr), and 3 transition-type galaxies, with projected linear diameters less than 3.5 kpc and mean blue surface brightness >23 mag/arcsec2 situated at the distance 2-6 Mpc in the field and in nearby groups. Our sample dwarf spheroidal galaxies were not detected in HI and are located at the distances of up to ˜1 Mpc away from a nearby bright galaxy. Transition-type galaxies, which are distributed like dSph galaxies, form a very rare class of galaxies. dIrr galaxies show a weaker concentration to the nearest massive neighbors than dSph and transition-type galaxies. At a given surface brightness and luminosity, they exhibit lower mean metallicities than dSphs. In contrast to dIrr galaxies, the majority of dSph galaxies at a similar mean surface brightness contains GCCs. The percentage of GCCs located near the centers of dSph galaxies is much higher than that for dIrr galaxies. The composite population of GCCs in dSphs is spatially more concentrated than in dIrr galaxies. The color distributions of GCCs in dSph and dIrr galaxies show major differences. While the latter shows obvious bimodality with the peaks near (V-I)0 ˜ 0.5 and ˜1.0 mag, the GCC color distribution in dSph galaxies shows only one peak with a mean color (V-I)0 ˜ 1.0 mag. There is a tendency of increasing half-light radii with increasing projected galactocentric distances for a large number of GCCs in dSph galaxies, which is also observed in the Galactic globular cluster system. We embarked on a spectroscopic survey of GCCs in <span class="hlt">low-mass</span> galaxies to obtain their chemical compositions and relative ages.</p> <div class="credits"> <p class="dwt_author">Sharina, Margarita E.; Puzia, T. H.; Afanasiev, V. L.; Makarov, D. I.; Dolphin, A. E.; Karataeva, G. M.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">291</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012A%26A...545A..12C"> <span id="translatedtitle">The inner wind of IRC+10216 <span class="hlt">revisited</span>: new exotic chemistry and diagnostic for dust condensation in carbon <span class="hlt">stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Aims: We model the chemistry of the inner wind of the carbon <span class="hlt">star</span> IRC+10216 and consider the effects of periodic shocks induced by the stellar pulsation on the gas to follow the non-equilibrium chemistry in the shocked gas layers. We consider a very complete set of chemical families, including hydrocarbons and aromatics, hydrides, halogens, and phosphorous-bearing species. Our derived abundances are compared to those for the latest observational data from large surveys and the Herschel telescope. Methods: A semi-analytical formalism based on parameterised fluid equations is used to describe the gas density, velocity, and temperature from 1 R? to 5 R?. The chemistry is described using a chemical kinetic network of reactions and a set of stiff, ordinary, coupled differential equations is solved. Results: The shocks induce an active non-equilibrium chemistry in the dust formation zone of IRC+10216 where the collision destruction of CO in the post-shock gas triggers the formation of O-bearing species such as H2O and SiO. Most of the modelled molecular abundances agree very well with the latest values derived from Herschel data on IRC+10216. The hydrides form a family of abundant species that are expelled into the intermediate envelope. In particular, HF traps all the atomic fluorine in the dust formation zone. The halogens are also abundant and their chemistry is independent of the C/O ratio of the <span class="hlt">star</span>. Therefore, HCl and other Cl-bearing species should also be present in the inner wind of O-rich AGB or supergiant <span class="hlt">stars</span>. We identify a specific region ranging from 2.5 R? to 4 R?, where polycyclic aromatic hydrocarbons form and grow. The estimated carbon dust-to-gas mass ratio derived from the mass of aromatics formed ranges from 1.2 × 10-3 to 5.8 × 10-3 and agrees well with existing values deduced from observations. This aromatic formation region is situated outside hot layers where SiC2 is produced as a bi-product of silicon carbide dust synthesis. The MgS grains can form from the gas phase but in lower quantities than those necessary to reproduce the strength of the 30 ?m emission band. Finally, we predict that some molecular lines will show a flux variation with pulsation phase and time (e.g., H2O), while other species will not (e.g., CO). These variations merely reflect the non-equilibrium chemistry that destroys and reforms molecules over a pulsation period in the shocked gas of the dust formation zone. Full Table A.1 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/545/A12</p> <div class="credits"> <p class="dwt_author">Cherchneff, I.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">292</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EPJWC..4705004B"> <span id="translatedtitle">Prized results from HARPS. <span class="hlt">Low-mass</span>/habitable/transiting planets orbiting M dwarfs</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Searching for planets around <span class="hlt">stars</span> with different masses probes the outcome of planetary formation for different initial conditions. The <span class="hlt">low-mass</span> M dwarfs are also the most frequent <span class="hlt">stars</span> in our Galaxy and potentially therefore, the most frequent planet hosts. This has motivated our search for planets around M dwarfs with HARPS. That observing program has now run for almost a decade and detected most of the known <span class="hlt">low-mass</span> planets orbiting M dwarfs (m sin i < 20 M?), including the least massive (GJ581e, msini = 1.9 M?) and the first potentially habitable planets (GJ581c&d GJ667Cc, GJ163c). This proceeding shortly reviews the detections made with HARPS, reports on the occurrence of planets around M dwarfs and how they mesh up with planet formation theory. It also highlights our sensitivity to <span class="hlt">low-mass</span> habitable planets, the first direct measure of ??, and the recent detection of a transiting planet the size of Uranus.</p> <div class="credits"> <p class="dwt_author">Bonfils, Xavier; Bouchy, François; Delfosse, X.; Forveille, T.; Gillon, M.; Lovis, C.; Mayor, M.; Neves, V.; Pepe, F.; Perrier, C.; Queloz, D.; Santos, N.; Ségransan, D.; Udry, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">293</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013ASPC..469...57H"> <span id="translatedtitle">Discovery of Pulsations in He-core, Extremely <span class="hlt">Low</span> <span class="hlt">Mass</span> White Dwarfs</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">After an extensive search, we announce the discovery of the first three extremely <span class="hlt">low</span> <span class="hlt">mass</span> (ELM, ? 0.25 M?), putatively He-core pulsating white dwarfs (WDs). The objects are by far the coolest and the lowest-mass pulsating WD known. The first to be published, SDSS J1840+6423 (Hermes et al. 2012), has Teff = 9140±170 K and log g = 6.22±0.06, which corresponds to a mass of ˜ 0.17 M?. The second and third pulsating ELM WDs have similarly <span class="hlt">low</span> <span class="hlt">masses</span>. SDSS J1112+1117 has Teff = 9400±490 K and a log g = 5.99±0.12. SDSS J1518+0658 has Teff = 9810±320 K and a log g = 6.66±0.06. These <span class="hlt">low-mass</span> pulsating WDs greatly extend the DAV (or ZZ Ceti) instability strip, and begin to bridge the gap in surface gravity between WDs and main-sequence <span class="hlt">stars</span>. Consistent with the expectation that these ELM WDs are the product of binary evolution, all three of these <span class="hlt">stars</span> have an unseen binary companion, with 4.2-14.6 hr orbital periods, in each case most likely another WD.</p> <div class="credits"> <p class="dwt_author">Hermes, J. J.; Montgomery, M. H.; Winget, D. E.; Brown, W. R.; Kilic, M.; Kenyon, S. J.; Harrold, S. T.; Bell, K.; Pelletier, J.; Rostopchina, A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">294</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005MNRAS.359..734L"> <span id="translatedtitle">The role of general relativity in the evolution of <span class="hlt">low-mass</span> X-ray binaries</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We study the evolution of <span class="hlt">low-mass</span> X-ray binaries hosting a neutron <span class="hlt">star</span> and of millisecond binary radio pulsars using numerical simulations that take into account the detailed evolution of the companion <span class="hlt">star</span>, of the binary system, and of the neutron <span class="hlt">star</span>. According to general relativity, when energy is released during accretion or due to magnetodipole radiation during the pulsar phase, the system loses gravitational mass. Moreover, the neutron <span class="hlt">star</span> can collapse to a black hole if its mass exceeds a critical limit, which depends on the equation of state of ultradense matter and is typically ~2Msolar. These facts have some interesting consequences. (i) In a millisecond radio pulsar the mass-energy is lost with a specific angular momentum that is smaller than the specific angular momentum of the system, resulting in a positive contribution to the orbital period derivative. If this contribution is dominant and can be measured, we can extract information about the moment of inertia of the neutron <span class="hlt">star</span>, since the energy loss rate depends on it. Such a measurement can help to put constraints on the equation of state of ultradense matter. (ii) In <span class="hlt">low-mass</span> X-ray binaries below the bifurcation period (~18 h), the neutron <span class="hlt">star</span> survives the `period gap' only if its mass is smaller than the maximum non-rotating mass when the companion becomes fully convective and accretion pauses. Since in such evolutions ~0.8Msolar can be accreted on to the neutron <span class="hlt">star</span>, short-period (P<= 2 h) millisecond X-ray pulsars such as SAX J1808.4-3658 can be formed only if either a large part of the accreting matter has been ejected from the system, or the equation of state of ultradense matter is very stiff. (iii) In <span class="hlt">low-mass</span> X-ray binaries above the bifurcation period, the mass-energy loss lowers the mass transfer rate. As a side effect, the inner core of the companion <span class="hlt">star</span> becomes ~1 per cent bigger than in a system with a non-collapsed primary. As a result of this difference, the final orbital period of the system is 20 per cent longer than if the mass-energy loss effect is not taken into account.</p> <div class="credits"> <p class="dwt_author">Lavagetto, G.; Burderi, L.; D'Antona, F.; di Salvo, T.; Iaria, R.; Robba, N. R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">295</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AAS...22144317Z"> <span id="translatedtitle">A New Method to Search for Quiescent <span class="hlt">Low-Mass</span> X-ray Binary</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We explore a new method in searching for quiescent <span class="hlt">Low-Mass</span> X-ray Binary (qLMXB). To date, almost all the accretion-powered BH-LMXBs, which stay in their quiescent state most of the time, were only found during their X-ray outburst. Our method explores a new way to find accretion binaries in their quiescent states. We search objects with spectral types earlier than K and M_V more than 2-? brighter than that expected for a main-sequence <span class="hlt">star</span>, then look for <span class="hlt">stars</span> in the above sample with log(F_X/F_R) (0.5-2. keV) more than 2-? greater than that seen in typical subgiant <span class="hlt">stars</span>. Most likely there is an accretion disk responsible for the extra X-ray emission. We show one example target of this study, with its X-ray and optical data.</p> <div class="credits"> <p class="dwt_author">Zhao, Ping; Grindlay, J. E.; Hong, J.; Servillat, M.; Van Den Berg, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">296</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013MNRAS.431.1719M"> <span id="translatedtitle">Evolution of protostellar outflow around <span class="hlt">low-mass</span> protostar</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The evolution of protostellar outflow is investigated with resistive magneto-hydrodynamic nested-grid simulations that cover a wide range of spatial scales (˜1 au-1 pc). We follow cloud evolution from the pre-stellar core stage until the infalling envelope dissipates long after the protostar formation. We also calculate protostellar evolution to derive protostellar luminosity with time-dependent mass accretion through a circumstellar disc. The protostellar outflow is driven by the first core prior to protostar formation and is directly driven by the circumstellar disc after protostar formation. The opening angle of the outflow is large in the Class 0 stage. A large fraction of the cloud mass is ejected in this stage, which reduces the <span class="hlt">star</span> formation efficiency to ˜50 per cent. After the outflow breaks out from the natal cloud, the outflow collimation is gradually improved in the Class I stage. The head of the outflow travels more than ˜105 au in ˜105 yr. The outflow momentum, energy and mass derived in our calculations agree well with observations. In addition, our simulations show the same correlations among outflow momentum flux, protostellar luminosity and envelope mass as those in observations. These correlations differ between Class 0 and I stages, which are explained by different evolutionary stages of the outflow; in the Class 0 stage, the outflow is powered by the accreting mass and acquires its momentum from the infalling envelope; in the Class I stage, the outflow enters the momentum-driven snow-plough phase. Our results suggest that protostellar outflow should determine the final stellar mass and significantly affect the early evolution of <span class="hlt">low-mass</span> protostars.</p> <div class="credits"> <p class="dwt_author">Machida, Masahiro N.; Hosokawa, Takashi</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">297</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22020415"> <span id="translatedtitle">ENVIRONMENTAL EFFECTS ON THE METAL ENRICHMENT OF <span class="hlt">LOW-MASS</span> GALAXIES IN NEARBY CLUSTERS</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">In this paper, we study the chemical history of <span class="hlt">low-mass</span> <span class="hlt">star</span>-forming (SF) galaxies in the local universe clusters Coma, A1367, A779, and A634. The aim of this work is to search for the imprint of the environment on the chemical evolution of these galaxies. Galaxy chemical evolution is linked to the <span class="hlt">star</span> formation history, as well as to the gas interchange with the environment, and <span class="hlt">low-mass</span> galaxies are well known to be vulnerable systems to environmental processes affecting both these parameters. For our study we have used spectra from the SDSS-III DR8. We have examined the spectroscopic properties of SF galaxies of stellar masses 10{sup 8}-10{sup 10} M{sub Sun }, located from the core to the cluster's outskirts. The gas-phase O/H and N/O chemical abundances have been derived using the latest empirical calibrations. We have examined the mass-metallicity relation of cluster galaxies, finding well-defined sequences. The slope of these sequences, for galaxies in <span class="hlt">low-mass</span> clusters and galaxies at large cluster-centric distances, follows the predictions of recent hydrodynamic models. A flattening of this slope has been observed for galaxies located in the core of the two more massive clusters of the sample, principally in Coma, suggesting that the imprint of the cluster environment on the chemical evolution of SF galaxies should be sensitive to both the galaxy mass and the host cluster mass. The H I gas content of Coma and A1367 galaxies indicates that <span class="hlt">low-mass</span> SF galaxies, located at the core of these clusters, have been severely affected by ram-pressure stripping (RPS). The observed mass-dependent enhancement of the metal content of <span class="hlt">low-mass</span> galaxies in dense environments seems plausible, according to hydrodynamic simulations. This enhanced metal enrichment could be produced by the combination of effects such as wind reaccretion, due to pressure confinement by the intracluster medium (ICM), and the truncation of gas infall, as a result of the RPS. Thus, the properties of the ICM should play an important role in the chemical evolution of <span class="hlt">low-mass</span> galaxies in clusters.</p> <div class="credits"> <p class="dwt_author">Petropoulou, V.; Vilchez, J.; Iglesias-Paramo, J. [Instituto de Astrofisica de Andalucia-C.S.I.C., Glorieta de la Astronomia, 18008 Granada (Spain)</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-04-20</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">298</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AAS...22125025H"> <span id="translatedtitle">Evidence for Past Mass Loss from the <span class="hlt">Low-Mass</span> Halo Clusters AM-4 and Palomar 13</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Mass loss has been suggested to play a significant role in the evolution of <span class="hlt">low-mass</span> globular clusters (GCs). Some of the Milky Way's halo <span class="hlt">stars</span> are thought to have been ejected from GCs, and mass loss could explain the form of the Milky Way GC luminosity function’s faint end. In addition, it could explain how <span class="hlt">low-mass</span> GCs could have been massive enough to self-enrich - and generate multiple stellar populations - before evolving into the lower-mass systems we see today. Palomar 5 was the first M < 10^4 Msolar GC in which mass loss through stellar evaporation or tidal disruption was observed. It displays a tell-tale tidal tail as well as a main sequence luminosity function (MSLF) depleted of <span class="hlt">low-mass</span> <span class="hlt">stars</span>. To determine whether Pal 5 is typical of most <span class="hlt">low-mass</span> GCs we used HST data to determine the MSLFs of two even lower-mass GCs: Palomar 13 and AM-4. We find that in both cases, the luminosity function dN/dMv is flat or declining with increasing magnitude. These MSLFs coupled with the large fraction of binary <span class="hlt">stars</span> in each cluster indicate significant past mass loss.</p> <div class="credits"> <p class="dwt_author">Hamren, Katherine; Smith, G. H.; Guhathakurta, P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">299</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009MNRAS.392.1034O"> <span id="translatedtitle">The <span class="hlt">low-mass</span> initial mass function in the young cluster NGC6611</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">NGC6611 is the massive young cluster (2-3Myr) that ionizes the Eagle Nebula. We present very deep photometric observations of the central region of NGC6611 obtained with the Hubble Space Telescope and the following filters: ACS/WFC F775W and F850LP and NIC2 F110W and F160W, loosely equivalent to ground-based IZJH filters. This survey reaches down to I ~ 26mag. We construct the initial mass function (IMF) from ~1.5Msolar well into the brown dwarf regime (down to ~0.02Msolar). We have detected 30-35 brown dwarf candidates in this sample. The <span class="hlt">low-mass</span> IMF is combined with a higher-mass IMF constructed from the ground-based catalogue from Oliveira et al. We compare the final IMF with those of well-studied <span class="hlt">star</span>-forming regions: we find that the IMF of NGC6611 more closely resembles that of the <span class="hlt">low-mass</span> <span class="hlt">star</span>-forming region in Taurus than that of the more massive Orion Nebula Cluster. We conclude that there seems to be no severe environmental effect in the IMF due to the proximity of the massive <span class="hlt">stars</span> in NGC6611.</p> <div class="credits"> <p class="dwt_author">Oliveira, J. M.; Jeffries, R. D.; van Loon, J. Th.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">300</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21582921"> <span id="translatedtitle">THE FREQUENCY OF <span class="hlt">LOW-MASS</span> EXOPLANETS. III. TOWARD {eta}{sub +} AT SHORT PERIODS</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Determining the occurrence rate of 'super-Earth' planets (m sin i < 10 M{sub +}) is a critically important step on the path toward determining the frequency of Earth-like planets ({eta}{sub +}), and hence the uniqueness of our solar system. Current radial-velocity surveys, achieving precisions of 1 m s{sup -1}, are now able to detect super-Earths and provide meaningful estimates of their occurrence rate. We present an analysis of 67 solar-type <span class="hlt">stars</span> from the Anglo-Australian Planet Search specifically targeted for very high precision observations. When corrected for incompleteness, we find that the planet occurrence rate increases sharply with decreasing planetary mass. Our results are consistent with those from other surveys: in periods shorter than 50 days, we find that 3.0% of <span class="hlt">stars</span> host a giant (msin i > 100 M{sub +}) planet, and that 17.4% of <span class="hlt">stars</span> host a planet with msin i < 10 M{sub +}. The preponderance of <span class="hlt">low-mass</span> planets in short-period orbits is in conflict with formation simulations in which the majority of super-Earths reside at larger orbital distances. This work gives a hint as to the size of {eta}{sub +}, but to make meaningful predictions on the frequency of terrestrial planets in longer, potentially habitable orbits, <span class="hlt">low-mass</span> terrestrial planet searches at periods of 100-200 days must be made an urgent priority for ground-based Doppler planet searches in the years ahead.</p> <div class="credits"> <p class="dwt_author">Wittenmyer, Robert A.; Tinney, C. G.; Bailey, J.; Horner, J. [Department of Astrophysics, School of Physics, University of NSW, NSW 2052 (Australia); Butler, R. P. [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington DC 20015-1305 (United States); O'Toole, Simon J. [Australian Astronomical Observatory, P.O. Box 296, Epping, NSW 1710 (Australia); Jones, H. R. A. [Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Herts, AL10 9AB (United Kingdom); Carter, B. D., E-mail: rob@phys.unsw.edu.au [Faculty of Sciences, University of Southern Queensland, Toowoomba, Queensland 4350 (Australia)</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-09-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_14");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return 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title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">301</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/946860"> <span id="translatedtitle">M dwarfs in the Local Milky Way: The Field <span class="hlt">Low-Mass</span> Stellar Luminosity and Mass Functions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Modern sky surveys, such as the Sloan Digital Sky Survey (SDSS) and the Two-Micron All Sky Survey, have revolutionized how Astronomy is done. With millions of photometric and spectroscopic observations, global observational properties can be studied with unprecedented statistical significance. <span class="hlt">Low-mass</span> <span class="hlt">stars</span> dominate the local Milky Way, with tens of millions observed by SDSS within a few kpc. Thus, they make ideal tracers of the Galactic potential, and the thin and thick disks. In this thesis dissertation, I present my efforts to characterize the local <span class="hlt">low-mass</span> stellar population, using a collection of observations from the Sloan Digital Sky Survey (SDSS). First, <span class="hlt">low-mass</span> stellar template spectra were constructed from the co-addition of thousands of SDSS spectroscopic observations. These template spectra were used to quantify the observable changes introduced by chromospheric activity and metallicity. Furthermore, the average ugriz colors were measured as a function of spectral type. Next, the local kinematic structure of the Milky Way was quantified, using a special set of SDSS spectroscopic observations. Combining proper motions and radial velocities (measured using the spectral templates), along with distances, the full UVW space motions of over 7000 <span class="hlt">low-mass</span> <span class="hlt">stars</span> along one line of sight were computed. These <span class="hlt">stars</span> were also separated kinematically to investigate other observational differences between the thin and thick disks. Finally, this dissertation details a project designed to measure the luminosity and mass functions of <span class="hlt">low-mass</span> <span class="hlt">stars</span>. Using a new technique optimized for large surveys, the field luminosity function (LF) and local stellar density profile are measured simultaneously. The sample size used to estimate the LF is nearly three orders of magnitude larger than any previous study, offering a definitive measurement of this quantity. The observed LF is transformed into a mass function (MF) and compared to previous studies.</p> <div class="credits"> <p class="dwt_author">Bochanski, John J., Jr.; /Washington U., Seattle, Astron. Dept.</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">302</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012MNRAS.427.1503Z"> <span id="translatedtitle">The growth of galactic bulges through mergers in ? CDM haloes <span class="hlt">revisited</span> - I. Present-day properties</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We use the combined data sets of the Millennium I and II cosmological simulations to <span class="hlt">revisit</span> the impact of mergers in the growth of bulges in central galaxies in the ? cold dark matter (?CDM) scenario. We seed galaxies within the growing CDM haloes using semi-empirical relations to assign stellar and gaseous masses, and an analytic treatment to estimate the transfer of stellar mass to the bulge of the remnant after a galaxy merger. We find that this model roughly reproduces the observed correlation between the bulge-to-total mass (B/T) ratio and stellar mass (M*) in present-day central galaxies as well as their observed demographics, although <span class="hlt">low-mass</span> B/T < 0.1 (bulgeless) galaxies might be scarce relative to the observed abundance. In our merger-driven scenario, bulges have a composite stellar population made of (i) <span class="hlt">stars</span> acquired from infalling satellites, (ii) <span class="hlt">stars</span> transferred from the primary disc due to merger-induced perturbations and (iii) newly formed <span class="hlt">stars</span> in starbursts triggered by mergers. We find that the first two are the main channels of mass assembly, with the first one being dominant for massive galaxies, creating large bulges with different stellar populations than those of the inner discs, while the second is dominant for intermediate/<span class="hlt">low-mass</span> galaxies and creates small bulges with similar stellar populations to the inner discs. We associate the dominion of the first (second) channel to classical (pseudo) bulges, and compare the predicted fractions to observations. We emphasize that our treatment does not include other mechanisms of bulge growth such as intrinsic secular processes in the disc or misaligned gas accretion. Interestingly, we find that the evolution of the stellar and gaseous contents of the satellite as it spirals towards the central galaxy is a key ingredient in setting the morphology of the remnant galaxy, and that a good match to the observed bulge demographics occurs when this evolution proceeds closely to that of the central galaxy.</p> <div class="credits"> <p class="dwt_author">Zavala, Jesus; Avila-Reese, Vladimir; Firmani, Claudio; Boylan-Kolchin, Michael</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">303</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/51823607"> <span id="translatedtitle">Initial Conditions for <span class="hlt">Star</span> Formation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Recent studies have provided important information on the initial conditions for the formation of <span class="hlt">low</span> <span class="hlt">mass</span> <span class="hlt">stars</span>. These studies, using submillimeter continuum and line observations, have identified objects in the earliest stages of <span class="hlt">star</span> formation as cold, dense cores in which most molecules are frozen onto dust grains. We are placing constraints on different theories of <span class="hlt">star</span> formation with these</p> <div class="credits"> <p class="dwt_author">N. J. Evans</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">304</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.astro.keele.ac.uk/workx/starlife/StarpageS_26M.html"> <span id="translatedtitle">The Life of a <span class="hlt">Star</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">This website provides an introduction to what a <span class="hlt">star</span> is and the evolution of high and <span class="hlt">low</span> <span class="hlt">mass</span> <span class="hlt">stars</span>. It details the life of a <span class="hlt">star</span> that is one solar mass and over ten solar masses. Pictures, graphs, and links are also provided for the user within the site.</p> <div class="credits"> <p class="dwt_author"></p> <p class="dwt_publisher"></p> <p class="publishDate">2004-12-18</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">305</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AAS...22131205C"> <span id="translatedtitle">Magnetic Field Alignment With The Inner Envelope Of <span class="hlt">Low-mass</span> Cores</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present 350 ?m SHARP/CSO polarization results on seven <span class="hlt">low-mass</span> cores with class 0 protostars. These cores are part of a larger program to test magnetically regulated <span class="hlt">star</span> formation models. One key prediction of these models is that the magnetic field symmetry axis in a core is aligned with the symmetry axis of the flattened YSO inner envelope (aka pseudodisk). The inclination angle of a YSO can alter the projected degree of alignment. After taking the inclination angle into account, we find evidence for an alignment between the magnetic field and pseudodisk symmetry axes. This work is funded by NSF grant AST-0909030.</p> <div class="credits"> <p class="dwt_author">Chapman, Nicholas L.; Novak, G.; Davidson, J.; Matthews, T.; Matthews, B. C.; Goldsmith, P.; Volgenau, N. H.; Vaillancourt, J. E.; Looney, L.; Kwon, W.; Houde, M.; Peng, R.; Li, Z.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">306</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013prpl.conf2B060K"> <span id="translatedtitle">Radial velocity variations in EX Lup: hints for a <span class="hlt">low-mass</span> close companion</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">EXors are <span class="hlt">low-mass</span> pre-main sequence objects producing repetitive optical outbursts attributed to highly enhanced accretion from the circumstellar disk onto the <span class="hlt">star</span>. One type of outburst theories requires a close stellar or sub-stellar companion that perturbs the inner part of the disk and triggers the onset of the enhanced accretion. Here, we look for a possible companion to EX Lup, the prototype of the EXor class, using radial velocity (RV) observations. The RVs show large periodic variations that can be explained by the presence of a close companion in the brown dwarf mass range. Chromospheric activity or starspots are less likely to explain the observed RV curve.</p> <div class="credits"> <p class="dwt_author">Kóspál, Ágnes; Mohler-Fischer, Maren; Sicilia-Aguilar, Aurora; Ábrahám, Péter; Curé, Michel; Henning, Thomas; Kiss, Csaba; Launhardt, Ralf; Moór, Attila; Müller, André</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">307</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013ApJ...775..138S"> <span id="translatedtitle">Substellar Objects in Nearby Young Clusters. VII. The Substellar Mass Function <span class="hlt">Revisited</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The abundance of brown dwarfs (BDs) in young clusters is a diagnostic of <span class="hlt">star</span> formation theory. Here we <span class="hlt">revisit</span> the issue of determining the substellar initial mass function (IMF) based on a comparison between NGC 1333 and IC348, two clusters in the Perseus <span class="hlt">star</span>-forming region. We derive their mass distributions for a range of model isochrones, varying distances, extinction laws, and ages with comprehensive assessments of the uncertainties. We find that the choice of isochrone and other parameters have significant effects on the results, thus we caution against comparing IMFs obtained using different approaches. For NGC 1333, we find that the <span class="hlt">star</span>/BD ratio R is between 1.9 and 2.4 for all plausible scenarios, consistent with our previous work. For IC348, R is found to be between 2.9 and 4.0, suggesting that previous studies have overestimated this value. Thus the <span class="hlt">star</span>-forming process generates about 2.5-5 substellar objects per 10 <span class="hlt">stars</span>. The derived <span class="hlt">star</span>/BD ratios correspond to a slope of the power-law mass function of ? = 0.7-1.0 for the 0.03-1.0 M ? mass range. The median mass in these clusters—the typical stellar mass—is between 0.13 and 0.30 M ?. Assuming that NGC 1333 is at a shorter distance than IC348, we find a significant difference in the cumulative distribution of masses between the two clusters, resulting from an overabundance of very <span class="hlt">low</span> <span class="hlt">mass</span> objects in NGC 1333. Gaia astrometry will constrain the cluster distances better and will lead to a more definitive conclusion. Furthermore, the <span class="hlt">star</span>/BD ratio is somewhat larger in IC348 compared with NGC 1333, although this difference is still within the margins of error. Our results indicate that environments with higher object density may produce a larger fraction of very <span class="hlt">low</span> <span class="hlt">mass</span> objects, in line with predictions for BD formation through gravitational fragmentation of filaments falling into a cluster potential.</p> <div class="credits"> <p class="dwt_author">Scholz, Alexander; Geers, Vincent; Clark, Paul; Jayawardhana, Ray; Muzic, Koraljka</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">308</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005AAS...207.7415B"> <span id="translatedtitle">Discovery of a <span class="hlt">Low</span> <span class="hlt">Mass</span> Bipolar Molecular Outflow from L1014-IRS with the Submillimeter Array</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">With the discovery of the faint embedded source L1014-IRS, the Spitzer Space Telescope has opened a new window for the study of very <span class="hlt">low</span> <span class="hlt">mass</span> objects and the formation of brown dwarfs. Using the Submillimeter Array we report the discovery of a compact <span class="hlt">low</span> <span class="hlt">mass</span> bipolar molecular outflow from L1014-IRS and confirm its association with the L1014 dense core at 200 pc. Consequently, L1014-IRS is the lowest luminosity (L ˜ 0.09 L?) and perhaps the lowest mass source known to be driving a bipolar molecular outflow, which is one of the smallest known in size ( ˜500 AU), mass (< 10-4 M?), and energetics (e.g., with a force < 10-7 M? km s-1 yr-1). These results suggest that L1014-IRS is either a very young protostar yet to accrete a significant fraction of its final mass, or will remain substellar, which would suggest that brown dwarfs can form in a manner broadly similiar to <span class="hlt">low</span> <span class="hlt">mass</span> <span class="hlt">stars</span>. T.L.B. acknowledges support from the Submillimeter Array Fellowship Program. The work of A.C. was supported by a Smithsonian Predoctoral Fellowship at the Smithsonian Astrophysical Observatory. P.C.M. acknowledges support from NASA Origins of Solar Systems Program Grant NAG 5-13050.</p> <div class="credits"> <p class="dwt_author">Bourke, T. L.; Crapsi, A.; Myers, P. C.; Evans, N. J., II; Wilner, D. J.; Huard, T. L.; Jorgensen, J. K.; Young, C. H.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">309</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013prpl.conf2S008R"> <span id="translatedtitle">DN Tau - a young <span class="hlt">low-mass</span> CTTS in X-rays</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present a deep XMM-Newton observation of DN Tau, a M0 type classical T Tauri <span class="hlt">star</span> (CTTS) and extend the sample of young accreting <span class="hlt">stars</span> studied with high-resolution X-ray spectroscopy to lower masses. We detect X-ray emission from magnetic activity and accretion shocks. DN Tau's X-ray properties link it to more massive and older CTTS. The strong hot corona makes DN Tau one of the X-ray brightest CTTS in its mass range, while the <span class="hlt">low</span> <span class="hlt">mass</span> and large radius result in a very cool accretion component and thus reduces its imprint in the observed X-ray spectrum and emission line diagnostics.</p> <div class="credits"> <p class="dwt_author">Robrade, Jan; Guedel, Manuel; Guenther, Moritz; Schmitt, Juergen</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">310</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008ApJ...676..594K"> <span id="translatedtitle">The Initial-Final Mass Relation: Direct Constraints at the <span class="hlt">Low-Mass</span> End</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The initial-final mass relation represents a mapping between the mass of a white dwarf remnant and the mass that the hydrogen-burning main-sequence <span class="hlt">star</span> that created it once had. The empirical relation thus far has been constrained using a sample of ~40 <span class="hlt">stars</span> in young open clusters, ranging in initial mass from ~2.75 to 7 Msolar, and shows a general trend that connects higher mass main-sequence <span class="hlt">stars</span> with higher mass white dwarfs. In this paper, we present CFHT CFH12K photometric and Keck LRIS multiobject spectroscopic observations of a sample of 22 white dwarfs in two older open clusters, NGC 7789 (t=1.4 Gyr) and NGC 6819 (t=2.5 Gyr). We measure masses for the highest signal-to-noise ratio spectra by fitting the Balmer lines to atmosphere models and place the first direct constraints on the <span class="hlt">low-mass</span> end of the initial-final mass relation. Our results indicate that the observed general trend at higher masses continues down to <span class="hlt">low</span> <span class="hlt">masses</span>, with Minitial=1.6 Msolar main-sequence <span class="hlt">stars</span> forming Mfinal=0.54 Msolar white dwarfs. When added to our new data from the very old cluster NGC 6791, the relation is extended down to Minitial=1.16 Msolar (corresponding to Mfinal=0.53 Msolar). This extension of the relation represents a fourfold increase in the total number of hydrogen-burning <span class="hlt">stars</span> for which the integrated mass loss can now be calculated from empirical data, assuming a Salpeter initial mass function. The new leverage at the <span class="hlt">low-mass</span> end is used to derive a purely empirical initial-final mass relation. The sample of white dwarfs in these clusters also shows several interesting systems that we discuss further: a DB (helium) white dwarf, a magnetic white dwarf, a DAB (mixed hydrogen/helium atmosphere or a double degenerate DA+DB) white dwarf(s), and two possible equal-mass DA double degenerate binary systems. 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.</p> <div class="credits"> <p class="dwt_author">Kalirai, Jasonjot S.; Hansen, Brad M. S.; Kelson, Daniel D.; Reitzel, David B.; Rich, R. Michael; Richer, Harvey B.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">311</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012MNRAS.426.2797W"> <span id="translatedtitle">A fundamental problem in our understanding of <span class="hlt">low-mass</span> galaxy evolution</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Recent studies have found a dramatic difference between the observed number density evolution of <span class="hlt">low-mass</span> galaxies and that predicted by semi-analytic models. Whilst models accurately reproduce the z = 0 number density, they require that the evolution occurs rapidly at early times, which is incompatible with the strong late evolution found in observational results. We report here the same discrepancy in two state-of-the-art cosmological hydrodynamical simulations, which is evidence that the problem is fundamental. We search for the underlying cause of this problem using two complementary methods. First, we consider a narrow range in stellar mass of log (Mstar/(h-2 M?)) = 9-9.5 and look for evidence of a different history of today's <span class="hlt">low-mass</span> galaxies in models and observations. We find that the exclusion of satellite galaxies from the analysis brings the median ages and <span class="hlt">star</span> formation rates of galaxies into reasonable agreement. However, the models yield too few young, strongly <span class="hlt">star</span>-forming galaxies. Secondly, we construct a toy model to link the observed evolution of specific <span class="hlt">star</span> formation rates with the evolution of the galaxy stellar mass function. We infer from this model that a key problem in both semi-analytic and hydrodynamical models is the presence of a positive instead of a negative correlation between specific <span class="hlt">star</span> formation rate and stellar mass. A similar positive correlation is found between the specific dark matter halo accretion rate and the halo mass, indicating that model galaxies are growing in a way that follows the growth of their host haloes too closely. It therefore appears necessary to find a mechanism that decouples the growth of <span class="hlt">low-mass</span> galaxies, which occurs primarily at late times, from the growth of their host haloes, which occurs primarily at early times. We argue that the current form of <span class="hlt">star</span> formation-driven feedback implemented in most galaxy formation models is unlikely to achieve this goal, owing to its fundamental dependence on host halo mass and time.</p> <div class="credits"> <p class="dwt_author">Weinmann, Simone M.; Pasquali, Anna; Oppenheimer, Benjamin D.; Finlator, Kristian; Mendel, J. Trevor; Crain, Robert A.; Macciò, Andrea V.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">312</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008AAS...21116209J"> <span id="translatedtitle">The Evolution of Matter in the Embedded Stages of <span class="hlt">Low-Mass</span> Protostars</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">One of the most important questions about <span class="hlt">low-mass</span> <span class="hlt">star</span> formation is how circumstellar disks form and evolve through the embedded protostellar stages. We present the results of high angular resolution (1-2"; 200-400 AU) observations from a large program, PROSAC, studying embedded <span class="hlt">low-mass</span> protostars (Class 0 and I objects) with the Submillimeter Array. In total 17 sources have been observed in a variety of lines of common molecular species together with continuum at (sub)millimeter wavelengths. The continuum observations reveal the presence of compact emission on the smallest scales in all sources which can best be attributed to thermal emission from dust in the circumstellar disks. The inferred masses of the central disks are comparable for both Class 0 and I objects suggesting that disks are formed and rapidly grow in size early in the evolution of the protostars. Line observations of the more evolved Class I systems reveal rotational signatures which in turn constrain the central stellar masses. Together with single-dish continuum data, these observations for the first time allow us to trace evolution of the mass of the <span class="hlt">stars</span>, disks and envelopes through these pivotal stages.</p> <div class="credits"> <p class="dwt_author">Jorgensen, Jes; Lommen, D.; Bourke, T. L.; van Dishoeck, E. F.; Wilner, D.; PROSAC Team</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-03-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">313</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008PhDT.........9B"> <span id="translatedtitle">Milliarcsecond resolution infrared observations of the recurrent nova RS Ophiuchi and <span class="hlt">low</span> <span class="hlt">mass</span> stellar systems</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We introduce the method of long-baseline stellar interferometry starting with the fundamental combination of electric fields. We describe beam combination techniques and how they are realized at the observatories used in the conduct of this research. We subsequently give a mathematical description of the Keck Interferometer Nuller and describe our pathfinder effort to produce the first science with this instrument. We present the results of a 2.5 year observing campaign using four different observatories; the Spitzer Space Telescope , the Infrared and Optical Telescope Array on Mt. Hopkins, Arizona, the Palomar Testbed Interferometer on Mt. Palomar, California, and the Keck Interferometer on Mauna Kea, Hawaii. We describe our observations of a broad array of <span class="hlt">low-mass</span> binary <span class="hlt">stars</span> and the recurrent nova RS Ophiuchi in outburst--a candidate Type Ia supernova progenitor. We present calculations that suggest a new paradigm for dust creation in recurrent novae. We explore this paradigm through analysis of line and continuum emission from near peak brightness to quiescence. We report radial velocity and astrometric model fitting on the <span class="hlt">low-mass</span> M-dwarf binary Gliese 268. We derive masses of the constituent <span class="hlt">stars</span> with 0.5% uncertainty.</p> <div class="credits"> <p class="dwt_author">Barry, Richard Keith, Jr.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">314</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008ApJ...685.1039A"> <span id="translatedtitle">Submillimeter Observations of the Young <span class="hlt">Low-Mass</span> Object IRAS 04158+2805</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present high spatial resolution Submillimeter Array observations and supplementary single-dish photometry of the molecular gas and dust around IRAS 04158+2805, a young source with spectral type M5-M6 in the Taurus <span class="hlt">star</span>-forming region. A bright, highly elongated dust structure that extends 8" (~1120 AU) in diameter is revealed in a 883 ?m thermal continuum image. This emission geometry is in good agreement with optical observations that show a similar structure in absorption, aligned perpendicular to bipolar scattered light nebulae. However, the interferometric data also clearly demonstrate that the submillimeter continuum emission is not centrally concentrated, but rather appears to have a toroidal geometry with substantially lower intensities inside a radius of ~250-300 AU. Spatially resolved emission from the CO J=3-2 transition exhibits a velocity gradient along the major axis of the dust structure. If this kinematic pattern is interpreted as the signature of rotation around a central object, then a relatively <span class="hlt">low</span> <span class="hlt">mass</span> is inferred (M*~0.3 Msolar, with a ~50% uncertainty). We discuss several possible explanations for the observed gas and dust environment around IRAS 04158+2805, including a flattened envelope with an outflow cavity and a large circumbinary ring. This source offers unique views of the gas and dust environment surrounding a young <span class="hlt">low-mass</span> stellar system. Its properties are generally not commensurate with formation scenarios for such <span class="hlt">low-mass</span> objects that rely on dynamical ejection, but rather confirms that a single mechanism-molecular cloud core collapse and fragmentation-can produce <span class="hlt">stars</span> over a wide range of stellar masses (at least an order of magnitude).</p> <div class="credits"> <p class="dwt_author">Andrews, Sean M.; Liu, Michael C.; Williams, Jonathan P.; Allers, K. N.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">315</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008PhDT........12W"> <span id="translatedtitle">Understanding the <span class="hlt">star</span>-forming environment in stellar clusters</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The main goal of this thesis is to investigate the physical conditions of the <span class="hlt">star</span>-forming environment in stellar clusters, especially for the formation of <span class="hlt">low-mass</span> cluster members. Embedded, young, and intermediate-mass stellar clusters around Herbig Ae/Be <span class="hlt">stars</span> are sampled. Mid- and near-infrared observations identifying young <span class="hlt">stars</span> and millimeter interferometric observations probing dense molecular gas and dust continuum are presented. These observations are used to reveal the large-scale young stellar population around the vicinity where the sampled clusters form, probe the physical conditions of dense molecular clumps which are capable of forming individual <span class="hlt">low-mass</span> cluster members, and examine the influence of the most massive <span class="hlt">star</span> in the cluster on its siblings and natal cluster-forming cloud. This study shows that <span class="hlt">stars</span> within the cluster tend to seem younger than those outside the cluster, suggesting a higher and continuous <span class="hlt">star</span>-forming rate within the cluster than outside, or massive <span class="hlt">stars</span> are initiated later than <span class="hlt">low-mass</span> <span class="hlt">stars</span> within the same cloud. A thorough investigation of young <span class="hlt">stars</span> and dense gas toward the MWC 1080 cluster further suggests a domination of the most massive <span class="hlt">star</span> in the cluster on both the natal cloud dispersal and its <span class="hlt">low-mass</span> cluster members. As active outflows and winds from the Herbig Ae/Be <span class="hlt">stars</span> increase the non-thermal motion in the cloud, <span class="hlt">low-mass</span> cluster members are formed within denser and more turbulent cores, than isolated <span class="hlt">low-mass</span> <span class="hlt">star</span>-forming cores. In addition, the strong gas dispersal from the Herbig Ae/Be <span class="hlt">stars</span> also helps the removal of the circumstellar material around nearby <span class="hlt">low-mass</span> <span class="hlt">stars</span>. This makes these <span class="hlt">low-mass</span> cluster members appear older. In summary, this thesis provides the observational evidence showing how the most massive <span class="hlt">star</span> in the cluster affects the formation and evolution of <span class="hlt">low-mass</span> cluster members and the physical conditions of <span class="hlt">star</span> formation in the cluster.</p> <div class="credits"> <p class="dwt_author">Wang, Shiya</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">316</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2006AIPC..813..631Q"> <span id="translatedtitle"><span class="hlt">Low-Mass</span> Stirling Convertor Assembly Progress Update</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Infinia is developing the next generation of space-ready Stirling Convertor Assemblies. Infinia has previously proposed a <span class="hlt">Low-Mass</span> Stirling Convertor Assembly (SCA) design employing a flux-concentrating, moving-iron linear alternator. This paper describes further development of that proposed machine, including additional improvements and advancements. One significant change is a new, lighter-weight moving-magnet alternator design. Infinia has shown progress in the <span class="hlt">low</span> <span class="hlt">mass</span> design's development and testing: namely in the area of flexure spring rates, welding techniques on the flange, and a change to the alternator configuration. Progress has been made with the flat-top heater head design and its capabilities, as well. The changes described in this paper will significantly reduce the mass and increase the power density of the <span class="hlt">low-mass</span> design.</p> <div class="credits"> <p class="dwt_author">Qiu, Songgang; Augenblick, John E.; Redinger, Darin L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">317</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21583272"> <span id="translatedtitle">ORBITAL SOLUTIONS FOR TWO YOUNG, <span class="hlt">LOW-MASS</span> SPECTROSCOPIC BINARIES IN OPHIUCHUS</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We report the orbital parameters for ROXR1 14 and RX J1622.7-2325Nw, two young, <span class="hlt">low-mass</span>, and double-lined spectroscopic binaries recently discovered in the Ophiuchus <span class="hlt">star</span>-forming region. Accurate orbital solutions were determined from over a dozen high-resolution spectra taken with the Keck II and Gemini South telescopes. These objects are T Tauri <span class="hlt">stars</span> with mass ratios close to unity and periods of {approx}5 and {approx}3 days, respectively. In particular, RX J1622.7-2325Nw shows a non-circularized orbit with an eccentricity of 0.30, higher than any other short-period pre-main-sequence (PMS) spectroscopic binary known to date. We speculate that the orbit of RX J1622.7-2325Nw has not yet circularized because of the perturbing action of a {approx}1'' companion, itself a close visual pair. A comparison of known young spectroscopic binaries (SBs) and main-sequence (MS) SBs in the eccentricity-period plane shows an indistinguishable distribution of the two populations, implying that orbital circularization occurs in the first 1 Myr of a <span class="hlt">star</span>'s lifetime. With the results presented in this paper we increase by {approx}4% the small sample of PMS spectroscopic binary <span class="hlt">stars</span> with known orbital elements.</p> <div class="credits"> <p class="dwt_author">Rosero, V.; Prato, L.; Wasserman, L. H. [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Rodgers, B., E-mail: viviana@lowell.edu, E-mail: lprato@lowell.edu, E-mail: lhw@lowell.edu, E-mail: brodgers@gemini.edu [Gemini Observatory, Gemini South, AURA/Chile, P.O. Box 26732, Tucson, AZ 85726 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-15</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">318</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012ApJ...756L..19W"> <span id="translatedtitle">The Formation of Supermassive Black Holes from <span class="hlt">Low-mass</span> Pop III Seeds</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The existence of 109 M ? black holes (BHs) in massive galaxies by z ~ 7 is one of the great unsolved mysteries in cosmological structure formation. One theory argues that they originate from the BHs of Pop III <span class="hlt">stars</span> at z ~ 20 and then accrete at the Eddington limit down to the epoch of reionization, which requires that they have constant access to rich supplies of fuel. Because early numerical simulations suggested that Pop III <span class="hlt">stars</span> were gsim100 M ?, the supermassive black hole (SMBH) seeds considered up to now were 100-300 M ?. However, there is a growing numerical and observational consensus that some Pop III <span class="hlt">stars</span> were tens of solar masses, not hundreds, and that 20-40 M ? BHs may have been much more plentiful at high redshift. However, we find that natal kicks imparted to 20-40 M ? Pop III BHs during formation eject them from their halos and hence their fuel supply, precluding them from Eddington-limit growth. Consequently, SMBHs are far less likely to form from <span class="hlt">low-mass</span> Pop III <span class="hlt">stars</span> than from very massive ones.</p> <div class="credits"> <p class="dwt_author">Whalen, Daniel J.; Fryer, Chris L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">319</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22078568"> <span id="translatedtitle">THE FORMATION OF SUPERMASSIVE BLACK HOLES FROM <span class="hlt">LOW-MASS</span> POP III SEEDS</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The existence of 10{sup 9} M{sub Sun} black holes (BHs) in massive galaxies by z {approx} 7 is one of the great unsolved mysteries in cosmological structure formation. One theory argues that they originate from the BHs of Pop III <span class="hlt">stars</span> at z {approx} 20 and then accrete at the Eddington limit down to the epoch of reionization, which requires that they have constant access to rich supplies of fuel. Because early numerical simulations suggested that Pop III <span class="hlt">stars</span> were {approx}>100 M{sub Sun }, the supermassive black hole (SMBH) seeds considered up to now were 100-300 M{sub Sun }. However, there is a growing numerical and observational consensus that some Pop III <span class="hlt">stars</span> were tens of solar masses, not hundreds, and that 20-40 M{sub Sun} BHs may have been much more plentiful at high redshift. However, we find that natal kicks imparted to 20-40 M{sub Sun} Pop III BHs during formation eject them from their halos and hence their fuel supply, precluding them from Eddington-limit growth. Consequently, SMBHs are far less likely to form from <span class="hlt">low-mass</span> Pop III <span class="hlt">stars</span> than from very massive ones.</p> <div class="credits"> <p class="dwt_author">Whalen, Daniel J. [Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213 (United States); Fryer, Chris L. [CCS-2, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">320</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012A%26A...537A..97C"> <span id="translatedtitle">Discarded candidate companions to <span class="hlt">low-mass</span> members of Chamaeleon I</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Context. Direct detections of brown dwarfs and planetary-mass companions to members of nearby <span class="hlt">star</span>-forming regions provide important clues about the process of <span class="hlt">star</span> formation, core fragmentation, and protoplanetary disk evolution. Aims: We study two faint objects at a very small angular distance from the <span class="hlt">low-mass</span> <span class="hlt">star</span> ESO-H?-558 and the possible massive brown dwarf ESO-H?-566, both of which are members of the Chamaeleon I <span class="hlt">star</span>-forming region, to establish whether they are physical companions to those sources. If they are, their low luminosities should imply L or T spectral types, which have clearly detectable spectral features. Methods: Adaptive optics-assisted imaging and spectroscopy of both faint candidate companions has been obtained with the NACO instrument at the Very Large Telescope (VLT). Results: Photometry shows that the colors of both objects are compatible with them being moderately reddened, normal <span class="hlt">stars</span> in the background of the Chamaeleon I clouds. This interpretation is confirmed spectroscopically, as the spectrum between 1.4 and 2.4 ?m of both objects has a featureless, monotonic slope lacking the strong H2O absorption features that dominate cool stellar and substellar spectra in that domain. Conclusions: We demonstrate that the two faint sources seen very close to ESO-H?-558 and ESO-H?-566 are unrelated background <span class="hlt">stars</span>, instead of giant planetary-mass companions as might be expected based on their faintness and angular proximity. Based on observations collected with the Very Large Telescope (VLT) at the European Southern Observatory, Paranal, Chile, under observing programmes 075.C-0809(B) and 078.C-0429(C).</p> <div class="credits"> <p class="dwt_author">Comerón, F.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_15");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" 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onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a style="font-weight: bold;">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_18");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">321</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/21825/1/97-0226.pdf"> <span id="translatedtitle">Electroactive polymers (EAP) <span class="hlt">low-mass</span> muscle actuators</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Actuation devices are used for many space applications with an increasing need to reduce their size, mass, and power consumption as well as cut their cost. Existing transducing actuators, such as piezoceramics, induce limited displacement levels. Potentially, electroactive polymers (EAP) have the potential for <span class="hlt">low-mass</span>, low-power, inexpensive miniature muscle actuators that are superior to the widely used actuators. Under electrical</p> <div class="credits"> <p class="dwt_author">Yoseph Bar-Cohen; T. Xue; Benjamin Joffe; Shyh-Shiuh Lih; Mohsen Shahinpoor; Jaycelyn O. Simpson; J. Smith; P. Willis</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">322</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/147876"> <span id="translatedtitle">Enhancement of <span class="hlt">low-mass</span> dileptons in heavy ion collisions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Using a relativistic transport model for the expansion stage of S+Au collisions at 200 GeV/nucleon, we show that the recently observed enhancement of <span class="hlt">low-mass</span> dileptons by the CERES Collaboration can be explained by the decrease of vector meson masses in hot and dense hadronic matter. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.</p> <div class="credits"> <p class="dwt_author">Li, G.Q.; Ko, C.M.; Brown, G.E. [Cyclotron Institute and Physics Department, Texas A& M University, College Station, Texas 77843 (United States)]|[Department of Physics, State University of New York, Stony Brook, New York 11794 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-11-27</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">323</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008galx.prop....2H"> <span id="translatedtitle">The Role of Environment in the Evolution of <span class="hlt">Low</span> <span class="hlt">Mass</span> Alfalfa Galaxies</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We propose to obtain 1.5 ksec GALEX observations of a set of nearby, <span class="hlt">low</span> <span class="hlt">mass</span> galaxies detected in the HI line by the currently ongoing Arecibo Legacy Fast ALFA (ALFALFA) survey found in diverse environments: the Leo Group of galaxies and very local density regions. The targets are among the lowest HI mass ALFALFA detections, and their narrow line widths imply low dynamical masses. The proposed observations complement on-going Cycle 3 (GI3-84) and Cycle 4 (GI4-42) SNAP observations of ALFALFA objects selected from earlier versions of the ALFALFA catalog and are specifically designed to probe the extremes of intergalactic environment. As members of the ALFALFA team, we are undertaking a multiwavelength study of the lowest mass ALFALFA detections to determine the cosmic abundance of <span class="hlt">low</span> <span class="hlt">mass</span> gas-rich systems, their distribution and their characteristics as a galaxy population. In combination with optical broad band and H-alpha imaging, NIR/FIR and radio continuum fluxes, and HI line measures (fluxes, redshifts and widths), GALEX UV observations will yield <span class="hlt">star</span> formation rates and ages and trace the sites of the youngest stellar populations, even in systems where the current/past <span class="hlt">star</span> formation activity has been very low. In combination with GALEX archive observations of the Virgo Cluster region, the proposed program will yield a sample of sufficient size to allow the identification of trends in <span class="hlt">star</span> formation within the Virgo Cluster and Leo Group environments and will explore a set of objects which may not have experienced interactions with other galaxies over the Hubble time.</p> <div class="credits"> <p class="dwt_author">Haynes, Martha</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">324</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/54745103"> <span id="translatedtitle">X-ray emission of young solar type <span class="hlt">stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">T Tauri <span class="hlt">Stars</span> (TTS) are young (<= 107 yrs) <span class="hlt">low</span> <span class="hlt">mass</span> (<= 2 Modot) <span class="hlt">stars</span>. They have been originally characterized by strong emission lines (CTTS), and by IR excesses interpreted in terms of circumstellar disks. Ten years ago, the ``Einstein\\</p> <div class="credits"> <p class="dwt_author">Sophie Casanova</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">325</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009A%26A...508.1301B"> <span id="translatedtitle">Evidence of early disk-locking among <span class="hlt">low-mass</span> members of the Orion Nebula Cluster</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Context: We present new high-resolution spectroscopic observations for 91 pre-main sequence <span class="hlt">stars</span> in the Orion Nebular Cluster (ONC) with masses in the range 0.10-0.25~M_? carried out with the multi-fiber spectrograph flames attached to the UT2 at the Paranal Observatory. Aims: Our aim is to better understand the disk-locking scenario in very <span class="hlt">low-mass</span> <span class="hlt">stars</span>. Methods: We have derived radial velocities, projected rotational velocities, and full width at 10% of the H? emission peak. Using published measurements of infrared excess (?(I_C-K)), as disk tracer and equivalent width of the nead-infrared Ca II line ?8542, mid-infrared difference [3.6]-[8.0] ?m derived by Spitzer data, and 10% H? width as diagnostic of the level of accretion, we looked for any correlation between projected angular rotational velocity divided by the radius (v sin i/R) and presence of disk and accretion. Results: For 4 <span class="hlt">low-mass</span> <span class="hlt">stars</span>, the cross-correlation function is clearly double-lined, indicating that the <span class="hlt">stars</span> are SB2 systems. The distribution of rotation periods derived from our v sin i measurements is unimodal with a peak of a few days, in agreement with previous results for M<0.25~M_?. The photometric periods were combined with our v sin i to derive the equatorial velocity and the distribution of rotational axes. Our < sin i> is lower than the one expected for a random distribution, as previously found. We find no evidence of a population of fast rotators close to the break-up velocity. A clear correlation between v sin i/R and ?(I_C-K) has been found. While a spread in the rotation rates is seen for <span class="hlt">stars</span> with no circumstellar disk (?(I_C-K)<0.3), <span class="hlt">stars</span> with a circumstellar disk (?(I_C-K)>0.3) show an abrupt drop in their rotation rates by a factor of ~5. On the other hand, only a partial correlation between v sin i and accretion is observed when other indicators are used. The X-ray coronal activity level (log L_X/L_bol) shows no dependence on v sin i/R, suggesting that all <span class="hlt">stars</span> are in a saturated regime limit. The critical velocity is probably below our v sin i detection limit of 9 km s-1. Conclusions: The ONC <span class="hlt">low-mass</span> <span class="hlt">stars</span> in our sample, close to the hydrogen burning limit, at present do not seem to be locked, but the clear correlation we find between rotation and infrared color excess suggests that they were locked once. In addition, the percentage of accretors seems to scale inversely to the stellar mass. Based on the flames Science Verification proposal 60.A-9145(A) and the flames proposal 76.C-0524(A). Table [see full textsee full textsee full textsee full text] is only available in electronic form at http://www.aanda.org</p> <div class="credits"> <p class="dwt_author">Biazzo, K.; Melo, C. H. F.; Pasquini, L.; Randich, S.; Bouvier, J.; Delfosse, X.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">326</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013ApJ...769..148H"> <span id="translatedtitle">The Metallicity Evolution of <span class="hlt">Low-mass</span> Galaxies: New Constraints at Intermediate Redshift</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present abundance measurements from 26 emission-line-selected galaxies at z ~ 0.6-0.7. By reaching stellar masses as low as 108 M ?, these observations provide the first measurement of the intermediate-redshift mass-metallicity (MZ) relation below 109 M ?. For the portion of our sample above M > 109 M ? (8/26 galaxies), we find good agreement with previous measurements of the intermediate-redshift MZ relation. Compared to the local relation, we measure an evolution that corresponds to a 0.12 dex decrease in oxygen abundances at intermediate redshifts. This result confirms the trend that metallicity evolution becomes more significant toward lower stellar masses, in keeping with a downsizing scenario where <span class="hlt">low-mass</span> galaxies evolve onto the local MZ relation at later cosmic times. We show that these galaxies follow the local fundamental metallicity relation, where objects with higher specific (mass-normalized) <span class="hlt">star</span> formation rates (SFRs) have lower metallicities. Furthermore, we show that the galaxies in our sample lie on an extrapolation of the SFR-M * relation (the <span class="hlt">star</span>-forming main sequence). Leveraging the MZ relation and <span class="hlt">star</span>-forming main sequence (and combining our data with higher-mass measurements from the literature), we test models that assume an equilibrium between mass inflow, outflow, and <span class="hlt">star</span> formation. We find that outflows are required to describe the data. By comparing different outflow prescriptions, we show that momentum, driven winds can describe the MZ relation; however, this model underpredicts the amount of <span class="hlt">star</span> formation in <span class="hlt">low-mass</span> galaxies. This disagreement may indicate that preventive feedback from gas heating has been overestimated, or it may signify a more fundamental deviation from the equilibrium assumption. Some of the 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.</p> <div class="credits"> <p class="dwt_author">Henry, Alaina; Martin, Crystal L.; Finlator, Kristian; Dressler, Alan</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">327</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2006A%26A...447..185S"> <span id="translatedtitle">Stellar populations in the CFHTLS. I. New constraints on the IMF at <span class="hlt">low</span> <span class="hlt">mass</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present a stellar populations analysis of the first release of the CFHTLS (Canada-France-Hawai Telescope Legacy Survey) data. A detailed comparison between the Besançon model of the Galaxy and the first data release of the CFHTLS-Deep survey is performed by implementing the MEGACAM photometric system in this model using stellar atmosphere model libraries. The reliability of the theoretical libraries to reproduce the observed colours in the MEGACAM system is investigated. The locations of various stellar species like subdwarfs, white dwarfs, late-type and brown dwarfs, binary systems are identified. The contamination of the stellar sample by quasars and compact galaxies is quantified using spectroscopic data from the VIMOS-VLT Deep Survey (VVDS) as a function of i' magnitude and r'-i' colour. A comparison between simulated counts using the standard IMF at <span class="hlt">low</span> <span class="hlt">masses</span> show that the number of very <span class="hlt">low</span> <span class="hlt">mass</span> dwarfs may have been underestimated in previous studies. These observations favour a power law IMF following d(n)/dm propto m-? with ?=2.5 for m < 0.25 M? or ?=3.0 for m < 0.2 M? for single <span class="hlt">stars</span>. The resulting LF is in agreement with the local LF as measured from the 5 or 25 pc samples. It is in strong disagreement with the Zheng et al. (2001) LF measured from deep HST data. We show that this discrepancy can be understood as an indication of a different IMF at <span class="hlt">low</span> <span class="hlt">masses</span> at early epochs of the Galaxy compared to the local thin disc IMF.</p> <div class="credits"> <p class="dwt_author">Schultheis, M.; Robin, A. C.; Reylé, C.; McCracken, H. J.; Bertin, E.; Mellier, Y.; Le Fèvre, O.</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">328</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21583218"> <span id="translatedtitle"><span class="hlt">LOW-MASS</span> ECLIPSING BINARIES IN THE INITIAL KEPLER DATA RELEASE</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We identify 231 objects in the newly released Cycle 0 data set from the Kepler Mission as double-eclipse, detached eclipsing binary systems with T{sub eff} < 5500 K and orbital periods shorter than {approx}32 days. We model each light curve using the JKTEBOP code with a genetic algorithm to obtain precise values for each system. We identify 95 new systems with both components below 1.0 M{sub sun} and eclipses of at least 0.1 mag, suitable for ground-based follow-up. Of these, 14 have periods less than 1.0 day, 52 have periods between 1.0 and 10.0 days, and 29 have periods greater than 10.0 days. This new sample of main-sequence, <span class="hlt">low-mass</span>, double-eclipse, detached eclipsing binary candidates more than doubles the number of previously known systems and extends the sample into the completely heretofore unexplored P > 10.0 day period regime. We find preliminary evidence from these systems that the radii of <span class="hlt">low-mass</span> <span class="hlt">stars</span> in binary systems decrease with period. This supports the theory that binary spin-up is the primary cause of inflated radii in <span class="hlt">low-mass</span> binary systems, although a full analysis of each system with radial-velocity and multi-color light curves is needed to fully explore this hypothesis. Also, we present seven new transiting planet candidates that do not appear among the list of 706 candidates recently released by the Kepler team, or in the Kepler False Positive Catalog, along with several other new and interesting systems. We also present novel techniques for the identification, period analysis, and modeling of eclipsing binaries.</p> <div class="credits"> <p class="dwt_author">Coughlin, J. L.; Harrison, T. E.; Ule, N. [Department of Astronomy, New Mexico State University, P.O. Box 30001, MSC 4500, Las Cruces, NM 88003-8001 (United States); Lopez-Morales, M. [Carnegie Institution of Washington, Department of Terrestrial Magnetism, 5241 Broad Branch Road NW, Washington, DC 20015 (United States); Hoffman, D. I., E-mail: jlcough@nmsu.edu [California Institute of Technology, MC 249-17, 1200 East California Boulevard, Pasadena, CA 91125 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-03-15</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">329</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/5225871"> <span id="translatedtitle">Radiation-driven evolution of <span class="hlt">low-mass</span> x-ray binaries and the formation of millisecond pulsars</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Recent data on <span class="hlt">low-mass</span> X-ray binaries (LMXBs) and millisecond pulsars (MSPs) pose a challenge to evolutionary theories which neglect the effects of disk and comparison irradiation. Here we discuss the main features of a radiation-driven (RD) evolutionary model that may be applicable to several LMXBs. According to this model, radiation from the accreting compact <span class="hlt">star</span> in LMXBs vaporizes'' the accretion disk and the companion <span class="hlt">star</span> by driving a self-sustained mass loss until a sudden accretion-turn off occurs. The main characteristics of the RD-evolution are: (1) lifetime of RD-LMXB's is of order 10{sup 7} years or less; (2) both the orbital period gap and the X-ray luminosity may be consequences of RD-evolution of LMXB's containing lower main sequence and degeneration companion <span class="hlt">stars</span>; (3) the companion <span class="hlt">star</span> may transfer mass to the primary even if it underfills its Roche lobe; (4) a class of recycled MSPs can continue to vaporize the <span class="hlt">low-mass</span> companions by a strong pulsar wind even after the accretion turn-off; (5) the RD-evolutionary model resolves the apparent statistical descrepancy between the number of MSPs and their LMXB progenitors in the Galaxy. We discuss the implications of the discovery of single MSPs in low-density globular clusters and the recent measurements of short orbital timescales of four LMXBs. 34 refs., 3 figs., 2 tabs.</p> <div class="credits"> <p class="dwt_author">Tavani, M. (Lawrence Livermore National Lab., CA (United States) California Univ., Berkeley, CA (United States). Dept. of Astronomy)</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-08-08</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">330</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1998AAS...193.3708C"> <span id="translatedtitle">Cataclysmic Variables and Possible <span class="hlt">Low-Mass</span> White Dwarfs in the Globular Cluster NGC 6397</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present photometric and spectroscopic HST observations of cataclysmic variables and a new class of faint ultraviolet (UV) <span class="hlt">stars</span> in the collapsed-core globular cluster NGC 6397. Color-magnitude diagrams constructed from UBVI images obtained with the WFPC2 reveal seven UV-bright <span class="hlt">stars</span> that lie between the main sequence and the white dwarf sequence in a U vs. U-B CMD. Four of these are cataclysmic variables (CVs), whose spectra show the emission lines and whose lightcurves show the "flicker" characteristic of accreting binaries. All four have quite faint disks as compared to field CVs, which may imply low accretion rates. Unlike the CVs, the other three UV-bright <span class="hlt">stars</span> show no photometric variability and have broad-band colors characteristic of B <span class="hlt">stars</span>. An FOS spectrum we have obtained of one of these non-flickering (NF) <span class="hlt">stars</span> reveals a broad H-beta line in absorption. Detailed comparisons with stellar atmosphere models yield log g = 6.25 +/- 1.0 and an effective temperature of 17,500 +/- 5,000 K. Using these line parameters and the luminosity of the NF we show that the spectrum is consistent with a helium white dwarf with a mass of about 0.25 solar masses and an age of 0.1-0.5 Gyr. The NF spectrum is significantly Doppler shifted from the expected wavelength, which may imply the presence of a dark, massive companion. We suggest that such <span class="hlt">low-mass</span> He WDs could be formed when the evolution of a red giant is interrupted, due either to Roche-lobe overflow onto a binary companion, or to envelope ejection following a common-envelope phase in a tidal-capture binary. Both the CVs and the possible He WDs are strongly concentrated toward the cluster center, to the extent that mass segregation from 2-body relaxation alone may be unable to explain their distribution.</p> <div class="credits"> <p class="dwt_author">Cool, A. M.; Edmonds, P. D.; Grindlay, J. E.</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">331</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013HEAD...1312638Z"> <span id="translatedtitle">A New Method to Search for Quiescent <span class="hlt">Low-Mass</span> X-ray Binary</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We explore a new method in searching for quiescent <span class="hlt">Low-Mass</span> X-ray Binaries (qLMXBs). To date, almost all the accretion-powered BH-LMXBs, which stay in their quiescent state most of the time, were only found during their X-ray outburst. Our method explores a new way to find accretion binaries in their quiescent states. We search objects with spectral types earlier than K and M$_V$ more than 2-$\\sigma$ brighter than that expected for a main-sequence <span class="hlt">star</span>, then look for <span class="hlt">stars</span> in the above sample with $log(F_X/F_R)$ (0.5-2. keV) more than 2-$\\sigma$ greater than that seen in typical subgiant <span class="hlt">stars</span>. Most likely there is an accretion disk responsible for the extra X-ray emission. We show one example target of this study, with its X-ray and optical data. This approach opens a new way to search for accretion binaries hidden in the Galactic plane.</p> <div class="credits"> <p class="dwt_author">Zhao, Ping; Grindlay, J. E.; Hong, J.; Servillat, M.; Van Den Berg, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">332</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2001ARep...45..620K"> <span id="translatedtitle">Formation of <span class="hlt">Low-Mass</span> X-Ray Novae with Black Holes from Triple Systems</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We apply a population synthesis technique to study the formation and evolution of <span class="hlt">low-mass</span> X-ray binaries with black holes, observed as X-ray novae, from hierarchical triple systems. A scenario is suggested in which an inner close binary system evolves into an X-ray system with a large mass ratio. The high rate of accretion onto the neutron <span class="hlt">star</span> leads to a common envelope stage, which may result in the formation of a Thorne-Zytkow (TZ) object. During its evolution, the envelope of the TZ object expands, encompassing the third <span class="hlt">star</span>. The recurrent common-envelope stage decreases the size of the orbit of the third <span class="hlt">star</span>, leading to the formation of a lowmass X-ray nova with a black hole. The dynamical stability of triple systems automatically ensures that only lowmass X-ray novae form. We also consider the possible formation of an X-ray nova from a binary in the case of asymmetrical core collapse during a supernova explosion.</p> <div class="credits"> <p class="dwt_author">Kuranov, A. G.; Postnov, K. A.; Prokhorov, M. E.</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-08-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">333</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012sptz.prop90236B"> <span id="translatedtitle">Infrared Monitoring of the Nearest <span class="hlt">Low-Mass</span> T Tauri Binary: TWA 30AB</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The T Tauri phase of young stellar evolution is known to exist down to substellar masses. However, the intrinsic faintness of these objects and distances to <span class="hlt">star</span> forming regions has limited detailed study of this critical phase. We propose monitoring observations of the nearest pair of <span class="hlt">low-mass</span> T Tauri accretors, TWA 30A and B. Both of these 8 Myr sources exhibit spectroscopic signatures indicating actively accreting, nearly edge-on disks with jets and stellar outflows. However, their time-dependent behavior at optical and near-infrared wavelengths are distinct, suggesting differing geometries and differing sources for the observed emission. We propose to test these models through short-term (continuous over 6 hr) and medium-term (daily for 40 days) IRAC monitoring of both <span class="hlt">stars</span>. These observations will allow us to simultaneously probe variations in the accretion on and warping of the outer disk of TWA 30A, and coherent scaleheight and opacity variations in the disk around TWA 30B in the region where planets may be forming. Combined with coincident ground-based follow-up, our program will provide the most detailed picture of disk evolution during the planet-building phase of the lowest-mass <span class="hlt">stars</span>.</p> <div class="credits"> <p class="dwt_author">Burgasser, Adam; Faherty, Jacqueline; Mohanty, Subhanjoy; Gizis, John; Melis, Carl; Bochanski, John; Drake, Andrew; Looper, Dagny</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">334</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/14865830"> <span id="translatedtitle">A possible <span class="hlt">low-mass</span> type Ia supernova</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">IN the standard model for type Ia supernovae1, a massive white dwarf in a binary system accretes matter from the companion <span class="hlt">star</span> until it reaches the Chandrasekhar mass (the stability limit for degenerate-electron <span class="hlt">stars</span>, corresponding to ~1.4 solar masses), and a runaway thermonuclear explosion ensues. In a popular variant of this model2, the companion <span class="hlt">star</span> is also a white dwarf.</p> <div class="credits"> <p class="dwt_author">Pilar Ruiz-Lapuente; David J. Jeffery; Peter M. Challis; Alexei V. Filippenko; Robert P. Kirshner; Luis C. Ho; Brian P. Schmidt; Francisco Sánchez; Ramon Canal</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">335</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013ASPC..476..353W"> <span id="translatedtitle">The 0.8 mm Spectral Line Survey toward <span class="hlt">Low-Mass</span> Protostellar Cores with ASTE</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have conducted spectral line surveys in the 345 GHz band with Atacama Submillimeter Telescope Experiment (ASTE) 10 m dish toward two <span class="hlt">low</span> <span class="hlt">mass</span> class 0 protostars R CrA IRS7B and Serpens SMM4. For R CrA IRS7B, 16 molecular species and 16 isotopologues are identified. Strong emission of CN and CCH is observed, whereas complex organic molecules and long carbon-chain molecules are not detected. This result indicates that the hot corino activity as well as the WCCC activity is weak in R CrA IRS7B. Lindberg & Jørgensen (2012) suggested that UV radiation from the Herbig Be <span class="hlt">star</span> R CrA significantly affects the chemical composition in R CrA IRS7B. Our results also support their conclusion. For Serpens SMM4, we identified 12 normal molecular species and 8 isotopologues. The chemical composition in Serpens SMM4 is similar to that found in hot corinos, although sulfur bearing species seem slightly deficient. These results illustrates the further chemical diversity in <span class="hlt">low-mass</span> protostars.</p> <div class="credits"> <p class="dwt_author">Watanabe, Y.; Sakai, N.; Lindberg, J.; Jørgensen, J.; Bisschop, S.; Yamamoto, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">336</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21300575"> <span id="translatedtitle">A RADIO SEARCH FOR PULSAR COMPANIONS TO SLOAN DIGITAL SKY SURVEY <span class="hlt">LOW-MASS</span> WHITE DWARFS</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We have conducted a search for pulsar companions to 15 <span class="hlt">low-mass</span> white dwarfs (LMWDs; M <0.4 M {sub sun}) at 820 MHz with the NRAO Green Bank Telescope (GBT). These LMWDs were spectroscopically identified in the Sloan Digital Sky Survey (SDSS), and do not show the photometric excess or spectroscopic signature associated with a companion in their discovery data. However, LMWDs are believed to evolve in binary systems and to have either a more massive white dwarf (WD) or a neutron <span class="hlt">star</span> (NS) as a companion. Indeed, evolutionary models of <span class="hlt">low-mass</span> X-ray binaries, the precursors of millisecond pulsars (MSPs), produce significant numbers of LMWDs, suggesting that the SDSS LMWDs may have NS companions. No convincing pulsar signal is detected in our data. This is consistent with the findings of van Leeuwen et al., who conducted a GBT search for radio pulsations at 340 MHz from unseen companions to eight SDSS WDs (five are still considered LMWDs; the three others are now classified as 'ordinary' WDs). We discuss the constraints our nondetections place on the probability P {sub MSP} that the companion to a given LMWD is a radio pulsar in the context of the luminosity and acceleration limits of our search; we find that P {sub MSP} < 10{sup +4} {sub -2}%.</p> <div class="credits"> <p class="dwt_author">Agueeros, Marcel A.; Camilo, Fernando [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States); Silvestri, Nicole M.; Anderson, Scott F. [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States); Kleinman, S. J. [Gemini Observatory, Northern Operations Center, Hilo, HI 96720 (United States); Liebert, James W. [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)], E-mail: marcel@astro.columbia.edu</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-05-20</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">337</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011ApJ...740...14O"> <span id="translatedtitle">Complex Molecules toward <span class="hlt">Low-mass</span> Protostars: The Serpens Core</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Gas-phase complex organic molecules are commonly detected toward high-mass protostellar hot cores. Detections toward <span class="hlt">low-mass</span> protostars and outflows are comparatively rare, and a larger sample is the key to investigate how the chemistry responds to its environment. Guided by the prediction that complex organic molecules form in CH3OH-rich ices and thermally or non-thermally evaporate with CH3OH, we have identified three sight lines in the Serpens core—SMM1, SMM4, and SMM4-W—which are likely to be rich in complex organics. Using the IRAM 30 m telescope, narrow lines (FWHM of 1-2 km s-1) of CH3CHO and CH3OCH3 are detected toward all sources, HCOOCH3 toward SMM1 and SMM4-W, and C2H5OH not at all. Beam-averaged abundances of individual complex organics range between 0.6% and 10% with respect to CH3OH when the CH3OH rotational temperature is applied. The summed complex organic abundances also vary by an order of magnitude, with the richest chemistry toward the most luminous protostar SMM1. The range of abundances compare well with other beam-averaged observations of <span class="hlt">low-mass</span> sources. Complex organic abundances are of the same order of magnitude toward <span class="hlt">low-mass</span> protostars and high-mass hot cores, but HCOOCH3 is relatively more important toward <span class="hlt">low-mass</span> protostars. This is consistent with a sequential ice photochemistry, dominated by CHO-containing products at low temperatures and early times. Based on observations carried out with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).</p> <div class="credits"> <p class="dwt_author">Öberg, Karin I.; van der Marel, Nienke; Kristensen, Lars E.; van Dishoeck, Ewine F.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">338</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013ApJ...768...70B"> <span id="translatedtitle"><span class="hlt">Low-mass</span> Suppression of the Satellite Luminosity Function Due to the Supersonic Baryon-Cold-dark-matter Relative Velocity</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We study the effect of the supersonic baryon-cold-dark-matter (CDM) flow, which has recently been shown to have a large effect on structure formation during the dark ages 10 <~ z <~ 1000, on the abundance of luminous, <span class="hlt">low-mass</span> satellite galaxies around galaxies like the Milky Way. As the supersonic baryon-CDM flow significantly suppresses both the number of halos formed and the amount of baryons accreted onto such halos of masses 106 < M halo/M ? < 108 at z >~ 10, a large effect results on the stellar luminosity function before reionization. As halos of these masses are believed to have very little <span class="hlt">star</span> formation after reionization due to the effects of photoheating by the ultraviolet background, this effect persists to the present day. We calculate that the number of <span class="hlt">low-mass</span> 106 < M halo/M ? < 5 × 107 halos that host luminous satellite galaxies today is typically suppressed by 50%, with values ranging up to 90% in regions where the initial supersonic velocity is high. We show that this previously ignored cosmological effect resolves some of the tension between the observed and predicted number of <span class="hlt">low-mass</span> satellites in the Milky Way, reducing the need for other mass-dependent <span class="hlt">star</span>-formation suppression before reionization.</p> <div class="credits"> <p class="dwt_author">Bovy, Jo; Dvorkin, Cora</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">339</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012APS..TSS.C2001P"> <span id="translatedtitle">Constraints on <span class="hlt">Low-Mass</span> WIMP signals from CDMS</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Dark Matter constitutes more than 80% of matter content in known universe. A major candidate to Dark Matter is Weakly Interacting Masive Particle (WIMP). The Cryogenic Dark Matter Search (CDMS) experiment uses cryogenically cooled Germanium detectors to look for recoil signals with the slow moving WIMPs in our galaxy. The most recent results optimized for high mass WIMPs yielded 2 possible candidates, which were statistically consistent with expected background. An updated analysis optimized for <span class="hlt">low</span> <span class="hlt">mass</span> WIMP search showed no evidence of <span class="hlt">low</span> <span class="hlt">mass</span> WIMPs and disfavors an explanation for the DAMA/LIBRA and CoGeNT signals in terms of spin-independent elastic scattering of <span class="hlt">low-mass</span> WIMP. Search for annual modulation of our data shows no strong evidence of possible WIMP signature, and rejects the observation of similar phenomenon in CoGeNT at more than 95% confidence level. The next generation SuperCDMS experiment utilizing more advanced detector technology is expected to have much higher sensitivity for WIMP search with very little expected background.</p> <div class="credits"> <p class="dwt_author">Prasad, Kunj</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-03-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">340</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013ASPC..476..343N"> <span id="translatedtitle">Observations of Deuterated Species toward <span class="hlt">Low-Mass</span> Prestellar and Protostellar Cores</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We have conducted observations of the ground-state transition lines (J = 1-0) of the fundamental deuterated species DCO+, DNC, DCN, CCD and N2D+ as well as those of H13CO+, HN13C, H13CN, CCH and N2H+ with the Nobeyama 45 m telescope. The target sources are the cold starless cores, TMC-1 and Lupus-1A, and the <span class="hlt">low-mass</span> <span class="hlt">star</span> forming cores, L1527 and IRAS15398-3359. The excitation temperatures derived from intensities of resolved hyperfine components are systematically different between DNC and HN13C. On the other hand, the excitation temperatures of DCN and H13CN are comparable to each other. Although the origin of these results is puzzling, the present result indicates that accurate evaluation of the excitation temperature is essential for deriving deuterium fractionation ratios accurately.</p> <div class="credits"> <p class="dwt_author">Nishimura, Y.; Sakai, N.; Watanabe, Y.; Sakai, T.; Hirota, T.; Yamamoto, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-10-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_16");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" 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<a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a style="font-weight: bold;">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_19");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">341</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010MNRAS.401..355D"> <span id="translatedtitle">Decade time-scale modulation of <span class="hlt">low-mass</span> X-ray binaries</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Regular observations by the All-Sky Monitor aboard the Rossi X-ray Timing Explorer satellite have yielded well-sampled light curves with a time baseline of over 10 years. We find that up to eight of the 16 brightest persistent <span class="hlt">low-mass</span> X-ray binaries (LMXBs) show significant, possible sinusoidal, variations with periods of the order of 10 years. We speculate on its possible origin and prevalence in the population of LMXBs, and we find the presence of a third object in the system, or long-period variability intrinsic to the donor <span class="hlt">star</span>, as being attractive origins for the X-ray flux modulation we detect. For some of the objects in which we do not detect a signal, there is substantial short-term variation which may hide modest modulation on long time-scales. Decade time-scale modulations may thus be even more common.</p> <div class="credits"> <p class="dwt_author">Durant, Martin; Cornelisse, Remon; Remillard, Ron; Levine, Alan</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">342</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/52970935"> <span id="translatedtitle">What Drives <span class="hlt">Star</span> Formation?</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Current theoretical models for what drives <span class="hlt">star</span> formation (especially <span class="hlt">low-mass</span> <span class="hlt">star</span> formation) are: (1) magnetic support of self-gravitating clouds with ambipolar diffusion removing support in cores and triggering collapse, and (2) compressible turbulence forming self-gravitating clumps that collapse as soon as the turbulent cascade produces insufficient turbulent support. A crucial observational difference between the two models is the mass to</p> <div class="credits"> <p class="dwt_author">R. M. Crutcher</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">343</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22139933"> <span id="translatedtitle">KEPLER STUDIES OF <span class="hlt">LOW-MASS</span> ECLIPSING BINARIES. I. PARAMETERS OF THE LONG-PERIOD BINARY KIC 6131659</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">KIC 6131659 is a long-period (17.5 days) eclipsing binary discovered by the Kepler mission. We analyzed six quarters of Kepler data along with supporting ground-based photometric and spectroscopic data to obtain accurate values for the mass and radius of both <span class="hlt">stars</span>, namely, M{sub 1} = 0.922 {+-} 0.007 M{sub Sun }, R{sub 1} = 0.8800 {+-} 0.0028 R{sub Sun }, and M{sub 2} = 0.685 {+-} 0.005 M{sub Sun }, R{sub 2} = 0.6395 {+-} 0.0061 R{sub Sun }. There is a well-known issue with <span class="hlt">low-mass</span> (M {approx}< 0.8 M{sub Sun }) <span class="hlt">stars</span> (in cases where the mass and radius measurement uncertainties are smaller than 2% or 3%) where the measured radii are almost always 5% to 15% larger than expected from evolutionary models, i.e., the measured radii are all above the model isochrones in a mass-radius plane. In contrast, the two <span class="hlt">stars</span> in KIC 6131659 were found to sit on the same theoretical isochrone in the mass-radius plane. Until recently, all of the well-studied eclipsing binaries with <span class="hlt">low-mass</span> <span class="hlt">stars</span> had periods of less than about three days. The <span class="hlt">stars</span> in such systems may have been inflated by high levels of stellar activity induced by tidal effects in these close binaries. KIC 6131659 shows essentially no evidence of enhanced stellar activity, and our measurements support the hypothesis that the unusual mass-radius relationship observed in most <span class="hlt">low-mass</span> <span class="hlt">stars</span> is influenced by strong magnetic activity created by the rapid rotation of the <span class="hlt">stars</span> in tidally locked, short-period systems. Finally, using short cadence data, we show that KIC 6131657 has one of the smallest measured non-zero eccentricities of a binary with two main-sequence <span class="hlt">stars</span>, where ecos {omega} (4.57 {+-} 0.02) Multiplication-Sign 10{sup -5}.</p> <div class="credits"> <p class="dwt_author">Bass, Gideon; Orosz, Jerome A.; Welsh, William F.; Windmiller, Gur; Gregg, Trevor Ames; Fetherolf, Tara [Department of Astronomy, San Diego State University, 5500 Campanile Dr., San Diego, CA 92182 (United States); Wade, Richard A. [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Lab, University Park, PA 16802 (United States); Quinn, Samuel N. [Department of Physics and Astronomy, Georgia State University, P.O. Box 4106, Atlanta, GA 30302 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-20</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">344</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/5112626"> <span id="translatedtitle">Evolution of variable <span class="hlt">stars</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Throughout the domain of the H R diagram lie groupings of <span class="hlt">stars</span> whose luminosity varies with time. These variable <span class="hlt">stars</span> can be classified based on their observed properties into distinct types such as ..beta.. Cephei <span class="hlt">stars</span>, delta Cephei <span class="hlt">stars</span>, and Miras, as well as many other categories. The underlying mechanism for the variability is generally felt to be due to four different causes: geometric effects, rotation, eruptive processes, and pulsation. In this review the focus will be on pulsation variables and how the theory of stellar evolution can be used to explain how the various regions of variability on the H R diagram are populated. To this end a generalized discussion of the evolutionary behavior of a massive <span class="hlt">star</span>, an intermediate mass <span class="hlt">star</span>, and a <span class="hlt">low</span> <span class="hlt">mass</span> <span class="hlt">star</span> will be presented. 19 refs., 1 fig., 1 tab.</p> <div class="credits"> <p class="dwt_author">Becker, S.A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-08-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">345</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012A%26A...542L...5P"> <span id="translatedtitle">Detection of OD towards the <span class="hlt">low-mass</span> protostar IRAS 16293-2422</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Context. Although water is an essential and widespread molecule in <span class="hlt">star</span>-forming regions, its chemical formation pathways are still not very well constrained. Observing the level of deuterium fractionation of OH, a radical involved in the water chemical network, is a promising way to infer its chemical origin. Aims: We aim at understanding the formation mechanisms of water by investigating the origin of its deuterium fractionation. This can be achieved by observing the abundance of OD towards the <span class="hlt">low-mass</span> protostar IRAS 16293-2422, where the HDO distribution is already known. Methods: Using the GREAT receiver on board SOFIA, we observed the ground-state OD transition at 1391.5 GHz towards the <span class="hlt">low-mass</span> protostar IRAS 16293-2422. We also present the detection of the HDO 111-000 line using the APEX telescope. We compare the OD/HDO abundance ratio inferred from these observations with the predictions of chemical models. Results: The OD line is detected in absorption towards the source continuum. This is the first detection of OD outside the solar system. The SOFIA observation, coupled to the observation of the HDO 111-000 line, provides an estimate of the abundance ratio OD/HDO ~ 17-90 in the gas where the absorption takes place. This value is fairly high compared with model predictions. This may be reconciled if reprocessing in the gas by means of the dissociative recombination of H2DO+ further fractionates OH with respect to water. Conclusions: The present observation demonstrates the capability of the SOFIA/GREAT instrument to detect the ground transition of OD towards <span class="hlt">star</span>-forming regions in a frequency range that was not accessible before. Dissociative recombination of H2DO+ may play an important role in setting a high OD abundance. Measuring the branching ratios of this reaction in the laboratory will be of great value for chemical models. Figure 5 is available in electronic form at http://www.aanda.org</p> <div class="credits"> <p class="dwt_author">Parise, B.; Du, F.; Liu, F.-C.; Belloche, A.; Wiesemeyer, H.; Güsten, R.; Menten, K. M.; Hübers, H.-W.; Klein, B.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">346</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21301672"> <span id="translatedtitle">DEEP, <span class="hlt">LOW</span> <span class="hlt">MASS</span> RATIO OVERCONTACT BINARY SYSTEMS. IX. V345 GEMINORUM WITH A BRIGHT VISUAL PAIR</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">CCD photometric observations of the visual binary, V345 Geminorum, obtained from 2007 January 24 to 2009 March 22, are presented. When comparing the light curves in 2007 and 2008, it is found that there appears to be an O'Connell effect in the light curves of 2008. From those observations, two sets of photometric solutions were deduced using the 2003 version of the W-D program. The results indicated that V345 Gem is a <span class="hlt">low</span> <span class="hlt">mass</span> ratio overcontact binary with f = 72.9%({+-}3.1%). The asymmetric light curves in 2008 may be attributed to the activity of starspot, whose area is up to 1.55% of the area of the more massive component. The contributions of the third light to the total light are approximately 20% in the BVR bands. The absolute physical parameters for V345 Gem were obtained first. From the log L-log M diagram of the binary-<span class="hlt">star</span> evolution, the primary component is an evolved <span class="hlt">star</span>. From the O-C curve for V345 Gem, it is discovered that there exists a long-term period increase with a cyclic variation. The period and amplitude of the cyclic variation are P {sub 3} = 646.7({+-}0.7) day and A = 0fd0019({+-}0fd0002), which may be caused by the light-time effect via the assumed third body. If it is true, the visual binary V345 Gem may be a quadruple <span class="hlt">star</span>. The kind of additional component may remove angular momentum from the central system, which may play an important role for the formation and evolution of the binary. The secular period increases at a rate of dP/dt = +5.88 x 10{sup -8} d yr{sup -1}, indicating that the mass transfers from the less massive component to the more massive component. With mass transferring, the orbital angular momentum decreases while the spin angular momentum increases. When J {sub spin}/J {sub orb} > 1/3, this kind of deep, <span class="hlt">low</span> <span class="hlt">mass</span> ratio overcontact binary with secular period increase may evolve into a rapid-rotating single <span class="hlt">star</span>.</p> <div class="credits"> <p class="dwt_author">Yang, Y.-G. [School of Physics and Electric Information, Huaibei Coal Industry Teachers College, 235000 Huaibei, Anhui Province (China); Qian, S.-B.; Zhu, L.-Y.; He, J.-J. [National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, 650011 Kunming (China)], E-mail: yygcn@163.com</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-08-15</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">347</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011AJ....142..124Z"> <span id="translatedtitle">Deep, <span class="hlt">Low</span> <span class="hlt">Mass</span> Ratio Overcontact Binary Systems. XI. V1191 Cygni</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Complete CCD photometric light curves in BV(RI) c bands obtained on one night in 2009 for the short-period close-binary system V1191 Cygni are presented. A new photometric analysis with the 2003 version of the Wilson-Van Hamme code shows that V1191 Cyg is a W-type overcontact binary system and suggests that it has a high degree of overcontact (f = 68.6%) with very <span class="hlt">low</span> <span class="hlt">mass</span> ratio, implying that it is at the late stage of overcontact evolution. The absolute parameters of V1191 Cyg are derived using spectroscopic and photometric solutions. Combining new determined times of light minimum with others published in the literature, the period change of the binary <span class="hlt">star</span> is investigated. A periodic variation, with a period of 26.7 years and an amplitude of 0.023 days, was discovered to be superimposed on a long-term period increase (dP/dt = +4.5(± 0.1) × 10-7 days yr-1). The cyclic period oscillation may be caused by the magnetic activity cycles of either of the components or the light-time effect due to the presence of a third body with a mass of m 3 = 0.77 M sun and an orbital radius of a 3 = 7.6 AU, when this body is coplanar to the orbit of the eclipsing pair. The secular orbital period increase can be interpreted as a mass transfer from the less massive component to the more massive one. With the period increases, V1191 Cyg will evolve from its present <span class="hlt">low</span> <span class="hlt">mass</span> ratio, high filled overcontact state to a rapidly rotating single <span class="hlt">star</span> when its orbital angular momentum is less than three times the total spin angular momentum. V1191 Cyg is too blue for its orbital period and it is an unusual W-type overcontact system with such a <span class="hlt">low</span> <span class="hlt">mass</span> ratio and high fill-out overcontact configuration, which is worth monitoring continuously in the future.</p> <div class="credits"> <p class="dwt_author">Zhu, L. Y.; Qian, S. B.; Soonthornthum, B.; He, J. J.; Liu, L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">348</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012APS..TSF.B4004S"> <span id="translatedtitle"><span class="hlt">Low</span> <span class="hlt">Mass</span> WIMP Search Using High Pressure Xenon Gas</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Several groups around the globe employ unique detector technologies in the direct search for dark matter weakly interacting massive particles (WIMPs). One of the leading technologies uses scintillation and ionization signals produced when WIMPs scatter off xenon nuclei. Recent compelling results hint at the possibility of a less massive WIMP (7 -- 10 GeV/c^2), than was previously thought. A plan will be presented for a <span class="hlt">low</span> <span class="hlt">mass</span> WIMP search using high pressure xenon, and possibly neon gas. The design, calibration, and expected results will be discussed.</p> <div class="credits"> <p class="dwt_author">Sofka, Clement</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">349</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008ApJ...688..377S"> <span id="translatedtitle">A Large-Area Search for <span class="hlt">Low-Mass</span> Objects in Upper Scorpius. II. Age and Mass Distributions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We present continued results from a wide-field, ~150 deg2, optical photometric and spectroscopic survey of the northern part of the ~5 Myr old Upper Scorpius OB association. Photometry and spectral types were used to derive effective temperatures and luminosities and place newly identified association members onto a theoretical Hertzsprung-Russell diagram. From our survey, we have discovered 145 new <span class="hlt">low-mass</span> members of the association and determined ~10% of these objects to be actively accreting material from a surrounding circumstellar disk. Based on comparison of the spatial distributions of low- and high-mass association members, we find no evidence for spatial segregation by mass within the northern portion of the association. Measured data are combined with pre-main-sequence evolutionary models to derive a mass and age for each <span class="hlt">star</span>. Using Monte Carlo simulations, we show that, taking into account known observational uncertainties, the observed age dispersion for the <span class="hlt">low-mass</span> population in USco is consistent with all <span class="hlt">stars</span> forming in a single burst ~5 Myr ago, and we place an upper limit of +/-3 Myr on the age spread if the <span class="hlt">star</span> formation rate has been constant in time. We derive the first spectroscopic mass function for USco that extends into the substellar regime and compare these results to those for three other young clusters and associations.</p> <div class="credits"> <p class="dwt_author">Slesnick, Catherine L.; Hillenbrand, Lynne A.; Carpenter, John M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">350</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AAS...22114225G"> <span id="translatedtitle">The Case for a <span class="hlt">Low</span> <span class="hlt">Mass</span> Black Hole in the LMXB V1408 Aquilae (= 4U 1957+115)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The optical light curve of the persistent <span class="hlt">low-mass</span> X-ray binary V1408 Aquilae (= 4U 1957+115) has a sinusoidal modulation at the system's 9.33 h orbital period. We obtained new broadband high-speed optical photometry of V1408 Aql on five successive nights in 2012 July and another four nights in 2012 August. Its brightness varied from night to night by almost a factor of two in both months, obscuring the orbital modulation. After these long-term variations were removed, the July photometry showed the orbital sinusoidal modulation clearly. We used the July data to refine the orbital period. We have previously shown that the orbital modulation is caused by the varying aspect of the heated face of the secondary <span class="hlt">star</span>. This model requires a mass ratio not far from unity, suggesting that the compact object in the system is a neutron <span class="hlt">star</span>. However, the X-ray spectrum of V1408 Aql suggests that its compact object is a black hole. The optical and X-ray data can be reconciled if the compact <span class="hlt">star</span> is a black hole with a <span class="hlt">low</span> <span class="hlt">mass</span>, possibly less than 4 solar masses.</p> <div class="credits"> <p class="dwt_author">Gomez, Sebastian; Mason, P. A.; Robinson, E. L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">351</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/940503"> <span id="translatedtitle">Compulsory Deep Mixing of 3He and CNO Isotopes in the Envelopes of <span class="hlt">low-mass</span> Red Giants</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Three-dimensional stellar modeling has enabled us to identify a deep-mixing mechanism that must operate in all <span class="hlt">low</span> <span class="hlt">mass</span> giants. This mixing process is not optional, and is driven by a molecular weight inversion created by the {sup 3}He({sup 3}He,2p){sup 4}He reaction. In this paper we characterize the behavior of this mixing, and study its impact on the envelope abundances. It not only eliminates the problem of {sup 3}He overproduction, reconciling stellar and big bang nucleosynthesis with observations, but solves the discrepancy between observed and calculated CNO isotope ratios in <span class="hlt">low</span> <span class="hlt">mass</span> giants, a problem of more than 3 decades standing. This mixing mechanism operates rapidly once the hydrogen burning shell approaches the material homogenized by the surface convection zone. In agreement with observations, Pop I <span class="hlt">stars</span> between 0.8 and 2.0 M{sub {circle_dot}} develop {sup 12}C/{sup 13}C ratios of 14.5 {+-} 1.5, while Pop II <span class="hlt">stars</span> process the carbon to ratios of 4.0 {+-} 0.5. In <span class="hlt">stars</span> less than 1.25 M{sub {circle_dot}}, this mechanism also destroys 90% to 95% of the {sup 3}He produced on the main sequence.</p> <div class="credits"> <p class="dwt_author">Eggleton, P P; Dearborn, D P; Lattanzio, J C</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-03-20</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">352</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009AIPC.1094.....S"> <span id="translatedtitle">Cool <span class="hlt">Stars</span>, Stellar Systems and the Sun.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The series of 'Cool <span class="hlt">Star</span>' meetings concentrates on the astrophysics of <span class="hlt">low-mass</span> <span class="hlt">stars</span> (with masses similar to that of the Sun and lower), including the Sun. The meeting in St. Andrews, Scotland, was the 15th in this series, and focused in particular on the origin of <span class="hlt">low-mass</span> <span class="hlt">stars</span> and their planets, as well as the properties of their atmospheres. This volume provides a comprehensive overview of the science presented by the 350 participants of this meeting. The book is suitable for researchers and graduate students interested in the astrophysics of cool <span class="hlt">stars</span> and the Sun.</p> <div class="credits"> <p class="dwt_author">Stempels, Eric</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">353</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013prpl.conf1B070P"> <span id="translatedtitle">Water D/H Ratio In <span class="hlt">Low-Mass</span> Protostars</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Water is an important molecule for our life on Earth, but its way from formation on the surfaces of dust grains to planets and the accompanying chemical processing are not well understood. Through evaporation in the warm inner regions of protostars, water brings complex organics and other species previously locked up in the ice into the gas phase. The water deuterium fractionation (HDO/H2O abundance ratio) has traditionally been used to infer the amount of water that was brought to the Earth by comets. Deducing this ratio in the warm gas of deeply-embedded <span class="hlt">low-mass</span> protostars allows to extend the discussion of the origin of Earth's water to earlier evolutionary stages. This poster present high-angular resolution, ground based interferometric observations of both HDO and H2(18)O water isotopologues toward several Class~0 <span class="hlt">low-mass</span> protostars. The emission is compact, and stems from the inner few 100 AU in all sources. The derived amount of deuterium fractionation in water, obtained assuming LTE and optically thin emission, is the same within the uncertainties in all sources and shows only small enhancements compared with Earth's oceans and solar system's comets.</p> <div class="credits"> <p class="dwt_author">Persson, Magnus V.; Jørgensen, Jes K.; van Dishoeck, Ewine F.; Harsono, Daniel</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">354</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013ApJ...769L...9B"> <span id="translatedtitle">Mass-Radius Relationships for Very <span class="hlt">Low</span> <span class="hlt">Mass</span> Gaseous Planets</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Recently, the Kepler spacecraft has detected a sizable aggregate of objects, characterized by giant-planet-like radii and modest levels of stellar irradiation. With the exception of a handful of objects, the physical nature, and specifically the average densities, of these bodies remain unknown. Here, we propose that the detected giant planet radii may partially belong to planets somewhat less massive than Uranus and Neptune. Accordingly, in this work, we seek to identify a physically sound upper limit to planetary radii at <span class="hlt">low</span> <span class="hlt">masses</span> and moderate equilibrium temperatures. As a guiding example, we analyze the interior structure of the Neptune-mass planet Kepler-30d and show that it is acutely deficient in heavy elements, especially compared with its solar system counterparts. Subsequently, we perform numerical simulations of planetary thermal evolution and in agreement with previous studies, show that generally, 10-20 M ?, multi-billion year old planets, composed of high density cores and extended H/He envelopes can have radii that firmly reside in the giant planet range. We subject our results to stability criteria based on extreme ultraviolet radiation, as well as Roche-lobe overflow driven mass-loss and construct mass-radius relationships for the considered objects. We conclude by discussing observational avenues that may be used to confirm or repudiate the existence of putative <span class="hlt">low</span> <span class="hlt">mass</span>, gas-dominated planets.</p> <div class="credits"> <p class="dwt_author">Batygin, Konstantin; Stevenson, David J.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">355</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21499359"> <span id="translatedtitle"><span class="hlt">Low-mass</span> dilepton rate from the deconfined phase</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We discuss <span class="hlt">low-mass</span> dilepton rates ({<=}1 GeV) from the deconfined phase of QCD using both perturbative and nonperturbative models and compare them with those from lattice gauge theory and in-medium hadron gas. Our analysis suggests that the rate at very low invariant mass (M{<=}200 MeV) using the nonperturbative gluon condensate in a semiempirical way within the Green function approach dominates over the Born rate, independent of any uncertainty associated with the choice of the strong coupling in perturbation theory. On the other hand, the rate from {rho}-q interaction in the deconfined phase is important at 200 MeV {<=}M{<=} 1 GeV as it is almost of same order as the Born rate as well as the in-medium hadron gas rate. Also, the higher order perturbative rate, leaving aside its various uncertainties, from the hard-thermal-loop approximation becomes reliable at M{>=}200 MeV and also becomes comparable with the Born rate and the lattice rate for M{>=}500 MeV, constraining on the broad resonance structures in the dilepton rate at large invariant mass. We also discuss the lattice constraints on the <span class="hlt">low-mass</span> dilepton rate. Furthermore, we discuss a realistic way to advocate the quark-hadron duality hypothesis based on the dilepton rates from quark-gluon plasma and hadron gas.</p> <div class="credits"> <p class="dwt_author">Greiner, Carsten [Institut fuer Theoretische Physik, Johann Wolfgang Goethe University, Max-von-Laue-Strasse 1, D-60438 Frankfurt (Germany); Haque, Najmul [Theory Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700 064 (India); Mustafa, Munshi G. [Institut fuer Theoretische Physik, Johann Wolfgang Goethe University, Max-von-Laue-Strasse 1, D-60438 Frankfurt (Germany); Theory Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700 064 (India); Thoma, Markus H. [Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstrasse, 85748 Garching (Germany)</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-15</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">356</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/374932"> <span id="translatedtitle"><span class="hlt">Low</span> <span class="hlt">mass</span> large aperture vacuum window development at CEBAF</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Large aperture <span class="hlt">low</span> <span class="hlt">mass</span> vacuum windows are being developed for the HMS (High Momentum Spectrometer) and SOS (Short Orbit Spectrometer) spectrometers in Hall C at CEBAF. Because multiple scattering degrades the performance of a spectrometer it is important that the volume be evacuated and that the entrance and exit windows be as <span class="hlt">low</span> <span class="hlt">mass</span> as possible. The material used for such windows must be thin and light enough so as to have minimum effect of the beam, and at the same time, be thick and strong enough to operate reliably and safely. To achieve these goals, composite vacuum windows have been constructed of a thin sheet of Mylar with a reinforcing fabric. Reinforcing fabrics such as Kevlar and Spectra are available with tensile strengths significantly greater than that of Mylar. A thin layer of Myler remains necessary since the fabrics cannot achieve any sort of vacuum seal. The design, fabrication, testing, and operating experience with such composite windows for the Hall C spectrometers will be discussed.</p> <div class="credits"> <p class="dwt_author">Keppel, C.</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">357</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013MNRAS.435.2048H"> <span id="translatedtitle">Planetary nebulae after common-envelope phases initiated by <span class="hlt">low-mass</span> red giants</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">It is likely that at least some planetary nebulae are composed of matter which was ejected from a binary <span class="hlt">star</span> system during common-envelope (CE) evolution. For these planetary nebulae the ionizing component is the hot and luminous remnant of a giant which had its envelope ejected by a companion in the process of spiralling-in to its current short-period orbit. A large fraction of CE phases which end with ejection of the envelope are thought to be initiated by <span class="hlt">low-mass</span> red giants, giants with inert, degenerate helium cores. We discuss the possible end-of-CE structures of such <span class="hlt">stars</span> and their subsequent evolution to investigate for which structures planetary nebulae are formed. We assume that a planetary nebula forms if the remnant reaches an effective temperature greater than 30 kK within 104 yr of ejecting its envelope. We assume that the composition profile is unchanged during the CE phase so that possible remnant structures are parametrized by the end-of-CE core mass, envelope mass and entropy profile. We find that planetary nebulae are expected in post-CE systems with core masses greater than about 0.3 M? if remnants end the CE phase in thermal equilibrium. We show that whether the remnant undergoes a pre-white dwarf plateau phase depends on the prescribed end-of-CE envelope mass. Thus, observing a young post-CE system would constrain the end-of-CE envelope mass and post-CE evolution.</p> <div class="credits"> <p class="dwt_author">Hall, Philip D.; Tout, Christopher A.; Izzard, Robert G.; Keller, Denise</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">358</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012sptz.prop90230C"> <span id="translatedtitle"><span class="hlt">Low</span> <span class="hlt">Mass</span> Galaxy Evolution In The WFC3 Infrared Spectroscopic Parallels Survey</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The WFC3 Infrared Spectroscopic Parallel (WISP) Survey uses nearly 1000 HST orbits to study the epoch of peak <span class="hlt">star</span> formation. Its slitless grism spectroscopy over a wide, continuous spectral range (0.8-1.7 micron) provides an unbiased selection of thousands of emission line galaxies over 0.5 < z < 2.5. Hundreds of these galaxies are detected in multiple emission lines, allowing for important diagnostics of metallicity and dust extinction. We propose deep 3.6 micron imaging (5 sigma, 0.9 micro-Jy) of 39 of the deepest WISP fields observed with the combination of G102+G141 grisms, in order to detect emission-line galaxies down to 0.1 L*. Combined with our HST optical and near-IR photometry, these IRAC data will be critical to determining accurate stellar masses for both passive and active galaxies in our survey. We will determine the evolution of the faint end slope of the stellar mass function and the mass-metallicity relation down to <span class="hlt">low-mass</span> galaxies, including measurement of a possible mass-metallicity-SFR fundamental plane. The addition of the IRAC photometry will also provide much stronger constraints on dust extinction and <span class="hlt">star</span> formation history, especially when combined with information available from the emission lines themselves.</p> <div class="credits"> <p class="dwt_author">Colbert, James; Teplitz, Harry; Scarlata, Claudia; Siana, Brian; Malkan, Matt; McCarthy, Patrick; Henry, Alaina; Atek, Hakim; Fosbury, Robert; Ross, Nathanial; Hathi, Nimish; Bridge, Carrie; Bunker, Andrew; Dressler, Alan; Shim, Hyunjin; Bedregal, Alejandro; Dominguez, Alberto; Rafelski, Marc; Masters, Dan</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">359</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013DPS....4510503M"> <span id="translatedtitle">Clouds in <span class="hlt">Low-mass</span>, Low-density Planets</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The Kepler Space Telescope has revealed huge populations of <span class="hlt">low-mass</span>, low-density planets, but their compositions remain elusive. For example, the density of GJ 1214b is consistent with either a water-world with a water atmosphere or a rock-iron core with a H/He envelope. Other super-Earths must contain hydrogen and helium to match their observed masses and radii. To understand this population of objects, we must be able to characterize their compositions through spectroscopy. The formation of clouds in exoplanet atmospheres significantly changes their observable spectra. For exoplanets, the opacity of hazes or clouds has been invoked as a possible explanation for the observed flat transmission spectrum of transiting super-Earth GJ 1214b as well as for the strong Rayleigh scattering feature in HD 189733b, the best-studied hot Jupiter. Here, we examine the effect of clouds on <span class="hlt">low-mass</span>, low-density exoplanet spectra. We include the condensates that are present in chemical equilibrium for objects at these temperatures (500-900 K) which include minerals like sulfides and alkali salts. The most important of these clouds are sodium sulfide, potassium chloride, and zinc sulfide. These clouds should be most prominent at low surface gravity, strongly super-solar atmospheric abundances, and at the slant viewing geometry appropriate for transits. Hence they could be quite important for affecting the transmission spectra of cool low density super-Earth and Neptune-class planets. Another class of clouds may also dramatically alter the spectra of irradiated planets: photochemical hazes. We additionally include a hydrocarbon haze layer similar to the tholin haze in Titan’s atmosphere. We calculate the location and density of the haze layer using photochemical models from Kempton et al. 2012. We present new results that show that for enhanced metallicity atmospheres, either the clouds that form in equilibrium or a hydrocarbon haze layer could become sufficiently optically thick to reproduce the observations of GJ 1214b. We also present predictions for other <span class="hlt">low-mass</span>, low-density exoplanets which will be targets of future observational campaigns: HD 97658b and GJ 3470b.</p> <div class="credits"> <p class="dwt_author">Morley, Caroline; Fortney, J.; Marley, M.; Kempton, E.; Visscher, C.; Zahnle, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">360</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008A%26A...479..177K"> <span id="translatedtitle">First superburst from a classical <span class="hlt">low-mass</span> X-ray binary transient</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We report the analysis of the first superburst from a transiently accreting neutron <span class="hlt">star</span> system with the All-Sky Monitor (ASM) on the Rossi X-ray Timing Explorer. The superburst occurred 55 days after the onset of an accretion outburst in 4U 1608-522. During that time interval, the accretion rate was at least 7% of the Eddington limit. The peak flux of the superburst is 22 to 45% of the Eddington limit, and its radiation energy output is between 4× 1041 and 9× 1041 erg for a distance of 3.2 kpc. Fits of cooling models to the superburst light curve indicate an ignition column depth between 1.5× 1012 and 4.1× 1012 g cm-2. Extrapolating the accretion history observed by the ASM, we derive that this column was accreted over a period of 26 to 72. The superburst characteristics are consistent with those seen in other superbursting <span class="hlt">low-mass</span> X-ray binaries. However, the transient nature of the hosting binary presents significant challenges for superburst theory, requiring additional ingredients for the models. The carbon that fuels the superburst is thought to be produced mostly during the accretion outbursts and destroyed in the frequent type-I X-ray bursts. Mixing and sedimentation of the elements in the neutron <span class="hlt">star</span> envelope may significantly influence the balance between the creation and destruction of carbon. Furthermore, predictions for the temperature of the neutron <span class="hlt">star</span> crust fail to reach the values required for the ignition of carbon at the inferred column depth.</p> <div class="credits"> <p class="dwt_author">Keek, L.; in't Zand, J. J. M.; Kuulkers, E.; Cumming, A.; Brown, E. F.; Suzuki, M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-02-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_17");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a onClick='return showDiv("page_14");' href="#">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a style="font-weight: bold;">19</a> <a onClick='return showDiv("page_20");' href="#">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_20");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">361</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21464574"> <span id="translatedtitle">THE FREQUENCY OF <span class="hlt">LOW-MASS</span> EXOPLANETS. II. THE 'PERIOD VALLEY'</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Radial-velocity planet search campaigns are now beginning to detect <span class="hlt">low-mass</span> 'Super-Earth' planets, with minimum masses M sin i{approx}< 10 M{sub +}. Using two independently developed methods, we have derived detection limits from nearly four years of the highest-precision data on 24 bright, stable <span class="hlt">stars</span> from the Anglo-Australian Planet Search. Both methods are more conservative than a human analyzing an individual observed data set, as is demonstrated by the fact that both techniques would detect the radial-velocity signals announced as exoplanets for the 61 Vir system in 50% of trials. There are modest differences between the methods which can be recognized as arising from particular criteria that they adopt. What both processes deliver is a quantitative selection process such that one can use them to draw quantitative conclusions about planetary frequency and orbital parameter distribution from a given data set. Averaging over all 24 <span class="hlt">stars</span>, in the period range P< 300 days and the eccentricity range 0.0 < e < 0.6, we could detect 99% of planets with velocity amplitudes K{approx}> 7.1 m s{sup -1}. For the best <span class="hlt">stars</span> in the sample, we are able to detect or exclude planets with K{approx}> 3 m s{sup -1}, corresponding to minimum masses of 8 M{sub +} (P = 5 days) or 17 M{sub +} (P = 50 days). Our results indicate that the observed 'period valley', a lack of giant planets (M > 100 M{sub +}) with periods between 10 and 100 days, is indeed real. However, for planets in the mass range 10-100 M{sub +}, our results suggest that the deficit of such planets may be a result of selection effects.</p> <div class="credits"> <p class="dwt_author">Wittenmyer, Robert A.; Tinney, C. G.; Bailey, J. [Department of Astrophysics, School of Physics, University of NSW, 2052 (Australia); O'Toole, Simon J. [Anglo-Australian Observatory, P.O. Box 296, Epping, 1710 (Australia); Jones, H. R. A. [Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, Herts AL10 9AB (United Kingdom); Butler, R. P. [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015-1305 (United States); Carter, B. D., E-mail: rob@phys.unsw.edu.a [Faculty of Sciences, University of Southern Queensland, Toowoomba, Queensland 4350 (Australia)</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-10-20</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">362</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008ASPC..398..529M"> <span id="translatedtitle">Inflated Planets and Their <span class="hlt">Low-Mass</span> Companions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Various mechanisms have been proposed to explain the inflated size of HD 209458b after it became clear that it has no companions capable of producing a stellar reflex velocity greater than around 5 m s-1. Had there been such a companion, the hypothesis that it forces the eccentricity of the inflated planet thereby tidally heating it may have been readily accepted. Here we summarize a paper by the author which shows that companion planets with masses as low as a fraction of an Earth mass are capable of sustaining a non-zero eccentricity in the observed planet for at least the age of the system. While such companions produce stellar reflex velocities which are fractions of a meter per second and hence are below the stellar jitter limit, they are consistent with recent theoretical work which suggests that the planet migration process often produces <span class="hlt">low-mass</span> companions to short-period giants.</p> <div class="credits"> <p class="dwt_author">Mardling, R. A.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">363</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6252801"> <span id="translatedtitle">Design of large aperture, <span class="hlt">low</span> <span class="hlt">mass</span> vacuum windows</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Large aperture, <span class="hlt">low</span> <span class="hlt">mass</span>, thin vacuum windows are required to minimize beam loss in the beam lines of particle accelerators as the products of nuclear collisions move from upstream targets to downstream detectors. This article describes the design, fabrication, testing, and operating experience of a large rectangular vacuum window, 122 cm[times]61 cm, and two circular windows of 91.4 and 96.5 cm diam. These window designs utilize a composite Kevlar 29 fabric and Mylar laminate as a window material with a typical combined thickness of 0.35 mm. Data for several material thicknesses are also presented. The windows are usually designed to withstand a pressure differential of two to three atmospheres to achieve the required factor of safety. These windows are typically used in the medium vacuum range of 10[sup [minus]4] Torr. The equations used to predict the behavior of the window material will also be discussed.</p> <div class="credits"> <p class="dwt_author">Mapes, M.; Leonhardt, W.J. (Brookhaven National Laboratory, Upton, New York 11973 (United States))</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">364</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/21128073"> <span id="translatedtitle"><span class="hlt">Low</span> <span class="hlt">Mass</span> Dimuons Produced in Relativistic Nuclear Collisions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The NA60 experiment has measured <span class="hlt">low</span> <span class="hlt">mass</span> muon pair production in In-In collisions at 158A GeV with unprecedented precision. We show that these data are reproduced very well by a dynamical model with parameters scaled from fits to measurements of hadronic transverse mass spectra and Hanbury Brown-Twiss correlations in Pb-Pb and Pb-Au collisions at the same energy. The data are consistent with in-medium properties of {rho} and {omega} mesons at finite temperature and density as deduced from empirical forward-scattering amplitudes. Inclusion of the vacuum decay of the {rho} meson after freeze-out is necessary for an understanding of the mass and transverse momentum spectrum of dimuons with M < or approx. 0.9 GeV/c{sup 2}.</p> <div class="credits"> <p class="dwt_author">Ruppert, Joerg; Gale, Charles [Department of Physics, McGill University, 3600 University Street, Montreal, QC, H3A 2T8 Canada (Canada); Renk, Thorsten [Department of Physics, PO Box 35 FIN-40014, University of Jyvaeskylae, Finland and Helsinki Institute of Physics, PO Box 64 FIN-00014, University of Helsinki (Finland); Lichard, Peter [Institute of Physics, Silesian University in Opava, Bezrucovo nam. 13, 746 01 Opava, Czech Republic and Institute of Experimental and Applied Physics, Czech Technical University, Horska 3, 12800 Prague (Czech Republic); Kapusta, Joseph I. [School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455 (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-04-25</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">365</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009A%26A...506.1183B"> <span id="translatedtitle"><span class="hlt">Low-mass</span> protostars and dense cores in different evolutionary stages in IRAS 00213+6530</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Aims: The aim of this paper is to study with high angular resolution a dense core associated with a low-luminosity IRAS source, IRAS 00213+6530, in order to investigate whether <span class="hlt">low</span> <span class="hlt">mass</span> <span class="hlt">star</span> formation is taking place in isolation. Methods: We carried out observations at 1.2 mm with the IRAM 30 m telescope, and VLA observations in the continuum mode at 6 cm, 3.6 cm, 1.3 cm and 7 mm, together with H2O maser and NH3 lines toward IRAS 00213+6530. Additionally, we observed the CCS J_N=2_1-10 transition, and H2O maser emission using the NASA 70 m antenna at Robledo de Chavela, Spain. We studied the nature of the centimeter and millimeter emission of the young stellar objects (YSOs) found in the region, and the physical properties of the dense gas and dust emission. Results: The centimeter and millimeter continuum emission, together with the near infrared data from 2MASS allowed us to identify three YSOs, IRS 1, VLA 8A, and VLA 8B, with different radio and infrared properties, and which seem to be in different evolutionary stages. IRS 1, detected only in the infrared, is in the more advanced stage. On the other hand, VLA 8A, bright at centimeter and millimeter wavelengths, coincides with a near infrared 2MASS source, whereas VLA 8B has no infrared emission associated with it and is in the earliest evolutionary stage. The overall structure of the NH3 emission consists of three clouds. Two of these, MM1 and MM2, are associated with dust emission at millimeter wavelengths, while the southern cloud is only detected in NH3. The YSOs are embedded in MM1, where we found evidence of line broadening and temperature enhancements. On the other hand, the southern cloud and MM2 appear to be quiescent and starless. Concerning the 1.2 mm dust emission, we modeled the radial intensity profile of MM1. The model fits the data reasonably well, but it underestimates the intensity at small projected distances from the 1.2 mm peak, probably due to the presence of multiple YSOs embedded in the dusty envelope. There is a strong differentiation in the relative NH3 abundance with low values of ~2×10-8 toward MM1, which harbors the YSOs, and high values, up to 10-6, toward the southern cloud and MM2, suggesting that these clouds could be in a young evolutionary stage. Conclusions: IRAS 00213+6530 harbors a multiple system of <span class="hlt">low-mass</span> protostars, indicating that <span class="hlt">star</span> formation in this cloud is taking place in groups or clusters, rather than in isolation. The <span class="hlt">low-mass</span> YSOs found in IRAS 00213+6530 are in different evolutionary stages, suggesting that <span class="hlt">star</span> formation takes place in different episodes.</p> <div class="credits"> <p class="dwt_author">Busquet, G.; Palau, Aina; Estalella, R.; Girart, J. M.; Anglada, G.; Sepúlveda, I.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">366</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013ApJ...765..102H"> <span id="translatedtitle">Discovery of Pulsations, Including Possible Pressure Modes, in Two New Extremely <span class="hlt">Low</span> <span class="hlt">Mass</span>, He-core White Dwarfs</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We report the discovery of the second and third pulsating extremely <span class="hlt">low</span> <span class="hlt">mass</span> (ELM) white dwarfs (WDs), SDSS J111215.82+111745.0 (hereafter J1112) and SDSS J151826.68+065813.2 (hereafter J1518). Both have masses < 0.25 M ? and effective temperatures below 10, 000 K, establishing these putatively He-core WDs as a cooler class of pulsating hydrogen-atmosphere WDs (DAVs, or ZZ Ceti <span class="hlt">stars</span>). The short-period pulsations evidenced in the light curve of J1112 may also represent the first observation of acoustic (p-mode) pulsations in any WD, which provide an exciting opportunity to probe this WD in a complimentary way compared to the long-period g-modes that are also present. J1112 is a T eff =9590 ± 140 K and log g =6.36 ± 0.06 WD. The <span class="hlt">star</span> displays sinusoidal variability at five distinct periodicities between 1792 and 2855 s. In this <span class="hlt">star</span>, we also see short-period variability, strongest at 134.3 s, well short of the expected g-modes for such a <span class="hlt">low-mass</span> WD. The other new pulsating WD, J1518, is a T eff =9900 ± 140 K and log g =6.80 ± 0.05 WD. The light curve of J1518 is highly non-sinusoidal, with at least seven significant periods between 1335 and 3848 s. Consistent with the expectation that ELM WDs must be formed in binaries, these two new pulsating He-core WDs, in addition to the prototype SDSS J184037.78+642312.3, have close companions. However, the observed variability is inconsistent with tidally induced pulsations and is so far best explained by the same hydrogen partial-ionization driving mechanism at work in classic C/O-core ZZ Ceti <span class="hlt">stars</span>.</p> <div class="credits"> <p class="dwt_author">Hermes, J. J.; Montgomery, M. H.; Winget, D. E.; Brown, Warren R.; Gianninas, A.; Kilic, Mukremin; Ken