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Sample records for age main sequence

  1. Main sequence mass loss and the ages of stars

    NASA Technical Reports Server (NTRS)

    Willson, L. A.

    1989-01-01

    The potentially observable consequences of the pulsation/rotation-induced mass loss from main-sequence A and F stars proposed by Willson et al. (1987) are discussed, reviewing the results of recent investigations. Particular attention is given to (1) evidence for a deficiency in A stars and an excess of F and G stars, as predicted by the theory, (2) cluster HR diagrams and age estimates, and (3) modifications to standard models of solar-system evolution. It is pointed out that the time scales and mass-loss rates required to explain the observed properties of clusters and field stars in this theory are the same as those needed to account for the early development of the solar system.

  2. Stellar evolution from the zero-age main sequence

    NASA Technical Reports Server (NTRS)

    Mengel, J. G.; Demarque, P.; Sweigart, A. V.; Gross, P. G.

    1979-01-01

    A consistent set of 247 evolutionary sequences extending from the ZAMS to the red-giant branch is presented for Y from 0.10 to 0.40, Z from 0.00001 to 0.10, and masses of 0.55 to 6.90 solar masses. Each sequence is started from a homogeneous ZAMS model, and almost all are evolved to the base of the red-giant branch. It is shown that: (1) the relative position of the main sequence can be determined as a function of composition; (2) theoretical luminosity functions can be derived from the relative evolutionary time scales; (3) a dip in luminosity sometimes occurs at the base of the red-giant branch and is most pronounced at larger Z values; (4) metal-poor stars evolve farther up along the main sequence before turning off toward the red-giant branch; and (5) the onset of helium burning halts the evolution across the Hertzsprung gap for the most massive and most metal-poor models, so that the star remains blue during its phase of core-helium burning.

  3. The ages of globular cluster stars - Effects of rotation on pre-main-sequence, main-sequence, and turnoff evolution

    NASA Technical Reports Server (NTRS)

    Deliyannis, Constantine P.; Demarque, Pierre; Pinsonneault, Marc H.

    1989-01-01

    Evolutionary sequences for low-metallicity stars (Z ranging from 0.001 to 0.0001) to study the effects of internal stellar rotation on the evolutionary time scales in the pre-main sequence, the main sequence (MS), and around the MS turnoff. Although a substantial amount of angular momentum remains in the interior, rotation is only a minor perturbation on the structure and ages of globular cluster stars. Even models with large initial angular momenta have MS lifetimes that are within 1 percent of those of standard models of the same mass and composition. Therefore, rotation does not affect age estimates of globular clusters from isochrone fitting. Furthermore, the models suggest that because rotation is not likely to affect horizontal-branch (HB) morphology, it does not affect significantly age estimates from the Delta-V method. Nevertheless, the internal angular momentum in the models is consistent with observations of surface rotational velocities on the HB, which require the preservation of a large reservoir of internal angular momentum.

  4. The Chromospheric Activity and Age Relation among Main Sequence Stars in Wide Binaries

    NASA Astrophysics Data System (ADS)

    Oswalt, Terry D.; Zhao, J.

    2011-05-01

    We present a study of the chromospheric activity levels in 36 wide binary systems. Thirty one of the binaries contain a white dwarf component. In such binaries the total age can be estimated by adding the cooling age of the white dwarf to an estimate of the progenitor's main sequence lifetime. To better understand how activity correlates to stellar age, 14 cluster member stars were also observed. Our observations confirm the expectation derived from studies of single main sequence stars that activity decays with age. However, for the first time we demonstrate that this relation extends from 50 Myr to at least 8 Gyr for stars with 1.0 < V-I < 2.4 color index. We also find that little change in activity occurs for stars with V-I < 1.0 and ages between 1 Gyr and 5 Gyr. The slope of constant age lines in the activity vs. V-I plane for young stars is relatively steep, while for old stars it appears to be flatter. In addition, our sample includes five wide binaries consisting of two main sequence stars. These pairs provide a useful reality check on our activity vs. age relation. Support for this project from NSF grant AST-0807919 to Florida Institute of Technology is gratefully acknowledged.

  5. The age rank of the nearest pre-main-sequence groups

    NASA Astrophysics Data System (ADS)

    Lawson, Warrick A.; Lyo, A.-Ran; Bessell, M. S.

    2009-11-01

    We address the age rank of the nearest pre-main-sequence (PMS) associations, using low-resolution spectrophotometry to measure gravity-sensitive indices in these stars. We compare spectral index-colour sequences for the PMS populations and rank them according to the strength of their gravity-sensitive features. The age rank using the gravity method is in general agreement with the ranking of these groups suggested by colour-magnitude (CM) diagram placement. Several of the groups have a kinematic origin in the Oph-Sco-Cen OB association. For three of them, their age rank is also in agreement with epochs resulting from a formation scenario for the OB association.

  6. Effects of main-sequence mass loss on the turnoff ages of globular clusters

    SciTech Connect

    Guzik, J.A.

    1989-01-01

    Willson, Bowen, and Struck-Marcell have proposed that globular cluster main-sequence turnoff ages can be reconciled with the lower ages of the Galaxy and universe deduced from other methods by incorporating an epoch of early main-sequence mass-loss by stars of spectral types A through early-F. The proposed mass loss is pulsation-driven, and facilitated by rapid rotation. This paper presents stellar evolution calculations of Pop. II (Z = 0.001) mass-losing stars of initial mass 0.8 to 1.6 M/sub /circle dot//, with exponentially-decreasing mass loss rates of e-folding times 0.5 to 2.0 Gyr, evolving to a final mass of 0.7 M/sub /circle dot//. The calculations indicate that a globular cluster with apparent turnoff age 18 Gyr could have an actual age as low as /approximately/12 Gyr. Observational implications that may help to verify the hypothesis, e.g. low C/N abundance ratios among red giants following first dredge-up, blue stragglers, red giant deficiencies, and signatures in cluster mass/luminosity functions, are also discussed.25 refs., 4 figs., 3 tabs.

  7. The Impact of Starspots on Mass and Age Estimates for Pre-main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Somers, Garrett; Pinsonneault, Marc H.

    2016-01-01

    We investigate the impact of starspots on the evolution of late-type stars during the pre-main sequence (pre-MS). We find that heavy spot coverage increases the radii of stars by 4-10%, consistent with inflation factors in eclipsing binary systems, and suppresses the rate of pre-MS lithium depletion, leading to a dispersion in zero-age MS Li abundance (comparable to observed spreads) if a range of spot properties exist within clusters from 3-10 Myr. This concordance with data implies that spots induce a range of radii at fixed mass during the pre-MS. These spots decrease the luminosity and T eff of stars, leading to a displacement on the HR diagram. This displacement causes isochrone derived masses and ages to be systematically under-estimated, and can lead to the spurious appearance of an age spread in a co-eval population.

  8. Age-rotation relationship for late-type main-sequence stars

    NASA Technical Reports Server (NTRS)

    Rengarajan, T. N.

    1984-01-01

    With advancing spectral type and increasing age, late main-sequence stars exhibit monotonic decrease in rotational velocity. It is of great interest to extend the rotation-age relationship to stars of later spectral type. In recent times it has become possible to measure directly the rotational periods from the photometric modulation by Ca II H and K line emission. There have also been successful attempts to relate the chromospheric activity as manifested through Ca II H and K lines to the rotation period, and it was shown that the fraction of total stellar luminosity in Ca II H and K lines, corrected for photospheric contribution, is a function of a single parameter related to P and B-V. In the present investigation, this rotation-activity relation is utilized to infer the rotation periods as a function of spectral type. The period versus B-V plot is employed as a basis to infer that the rotational period of main-sequence stars is a single-valued function of mass (B-V color) and age.

  9. ON THE MULTIPLICITY OF THE ZERO-AGE MAIN-SEQUENCE O STAR HERSCHEL 36

    SciTech Connect

    Arias, Julia I.; Barba, Rodolfo H.; Gamen, Roberto C.; Apellaniz, Jesus MaIz; Alfaro, Emilio J.; Sota, Alfredo; Bidin, Christian Moni

    2010-02-10

    We present the analysis of high-resolution optical spectroscopic observations of the zero-age main-sequence O star Herschel 36 spanning six years. This star is definitely a multiple system, with at least three components detected in its spectrum. Based on our radial-velocity (RV) study, we propose a picture of a close massive binary and a more distant companion, most probably in wide orbit about each other. The orbital solution for the binary, whose components we identify as O9 V and B0.5 V, is characterized by a period of 1.5415 {+-} 0.0006 days. With a spectral type O7.5 V, the third body is the most luminous component of the system and also presents RV variations with a period close to 498 days. Some possible hypotheses to explain the variability are briefly addressed and further observations are suggested.

  10. The evolution of angular momentum among zero-age main-sequence solar-type stars

    NASA Technical Reports Server (NTRS)

    Soderblom, David R.; Stauffer, John R.; Macgregor, Keith B.; Jones, Burton F.

    1993-01-01

    We consider a survey of rotation among F, G, and K dwarfs of the Pleiades in the context of other young clusters (Alpha Persei and the Hyades) and pre-main-sequence (PMS) stars (in Taurus-Auriga and Orion) in order to examine how the angular momentum of a star like the sun evolves during its early life on the main sequence. The rotation of PMS stars can be evolved into distributions like those seen in the young clusters if there is only modest, rotation-independent angular momentum loss prior to the ZAMS. Even then, the ultrafast rotators (UFRs, or ZAMS G and K dwarfs with v sin i equal to or greater than 30 km/s) must owe their extra angular momentum to their conditions of formation and to different angular momentum loss rates above a threshold velocity, for it is unlikely that these stars had angular momentum added as they neared the ZAMS, nor can a spread in ages within a cluster account for the range of rotation seen. Only a fraction of solar-type stars are thus capable of becoming UFRs, and it is not a phase that all stars experience. Simple scaling relations (like the Skumanich relation) applied to the observed surface rotation rates of young solar-type stars cannot reproduce the way in which the Pleiades evolve into the Hyades. We argue that invoking internal differential rotation in these ZAMS stars can explain several aspects of the observations and thus can provide a consistent picture of ZAMS angular momentum evolution.

  11. The age-metallicity relation in the solar neighbourhood from a pilot sample of white dwarf-main sequence binaries

    NASA Astrophysics Data System (ADS)

    Rebassa-Mansergas, A.; Anguiano, B.; García-Berro, E.; Freeman, K. C.; Cojocaru, R.; Manser, C. J.; Pala, A. F.; Gänsicke, B. T.; Liu, X.-W.

    2016-08-01

    The age-metallicity relation (AMR) is a fundamental observational constraint for understanding how the Galactic disc formed and evolved chemically in time. However, there is not yet an agreement on the observational properties of the AMR for the solar neighborhood, primarily due to the difficulty in obtaining accurate stellar ages for individual field stars. We have started an observational campaign for providing the much needed observational input by using wide white dwarf-main sequence (WDMS) binaries. White dwarfs are "natural" clocks and can be used to derive accurate ages. Metallicities can be obtained from the main sequence companions. Since the progenitors of white dwarfs and the main sequence stars were born at the same time, WDMS binaries provide a unique opportunity to observationally constrain in a robust way the properties of the AMR. In this work we present the AMR derived from analysing a pilot sample of 23 WDMS binaries and provide clear observational evidence for the lack of correlation between age and metallicity at young and intermediate ages (0-7 Gyrs).

  12. Rotating Stellar Models Can Account for the Extended Main-sequence Turnoffs in Intermediate-age Clusters

    NASA Astrophysics Data System (ADS)

    Brandt, Timothy D.; Huang, Chelsea X.

    2015-07-01

    We show that the extended main-sequence turnoffs seen in intermediate-age Large Magellanic Cloud (LMC) clusters, often attributed to age spreads of several 100 Myr, may be easily accounted for by variable stellar rotation in a coeval population. We compute synthetic photometry for grids of rotating stellar evolution models and interpolate them to produce isochrones at a variety of rotation rates and orientations. An extended main-sequence turnoff naturally appears in color-magnitude diagrams at ages just under 1 Gyr, peaks in extent between ˜1 and 1.5 Gyr, and gradually disappears by around 2 Gyr in age. We then fit our interpolated isochrones by eye to four LMC clusters with very extended main-sequence turnoffs: NGC 1783, 1806, 1846, and 1987. In each case, stellar populations with a single age and metallicity can comfortably account for the observed extent of the turnoff region. The new stellar models predict almost no correlation of turnoff color with rotational v{sin}i. The red part of the turnoff is populated by a combination of slow rotators and edge-on rapid rotators, while the blue part contains rapid rotators at lower inclinations.

  13. THE EFFECTS OF ROTATION ON THE MAIN-SEQUENCE TURNOFF OF INTERMEDIATE-AGE MASSIVE STAR CLUSTERS

    SciTech Connect

    Yang, Wuming; Bi, Shaolan; Liu, Zhie; Meng, Xiangcun E-mail: yangwuming@ynao.ac.cn

    2013-10-20

    The double or extended main-sequence turnoffs (MSTOs) in the color-magnitude diagram (CMD) of intermediate-age massive star clusters in the Large Magellanic Cloud are generally interpreted as age spreads of a few hundred Myr. However, such age spreads do not exist in younger clusters (i.e., 40-300 Myr), which challenges this interpretation. The effects of rotation on the MSTOs of star clusters have been studied in previous works, but the results obtained are conflicting. Compared with previous works, we consider the effects of rotation on the main-sequence lifetime of stars. Our calculations show that rotating models have a fainter and redder MSTO with respect to non-rotating counterparts with ages between about 0.8 and 2.2 Gyr, but have a brighter and bluer MSTO when age is larger than 2.4 Gyr. The spread of the MSTO caused by a typical rotation rate is equivalent to the effect of an age spread of about 200 Myr. Rotation could lead to the double or extended MSTOs in the CMD of the star clusters with ages between about 0.8 and 2.2 Gyr. However, the extension is not significant, and it does not even exist in younger clusters. If the efficiency of the mixing were high enough, the effects of the mixing would counteract the effect of the centrifugal support in the late stage of evolution, and the rotationally induced extension would disappear in the old intermediate-age star clusters, but younger clusters would have an extended MSTO. Moreover, the effects of rotation might aid in understanding the formation of some 'multiple populations' in globular clusters.

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  15. Lithium and age of pre-main sequence stars: the case of Parenago 1802

    NASA Astrophysics Data System (ADS)

    Giarrusso, M.; Tognelli, E.; Catanzaro, G.; Degl'Innocenti, S.; Dell'Omodarme, M.; Lamia, L.; Leone, F.; Pizzone, R. G.; Prada Moroni, P. G.; Romano, S.; Spitaleri, C.

    2016-04-01

    With the aim to test the present capability of the stellar surface lithium abundance in providing an estimation for the age of PMS stars, we analyze the case of the detached, double-lined, eclipsing binary system PAR 1802. For this system, the lithium age has been compared with the theoretical one, as estimated by applying a Bayesian analysis method on a large grid of stellar evolutionary models. The models have been computed for several values of chemical composition and mixing length, by means of the code FRANEC updated with the Trojan Horse reaction rates involving lithium burning.

  16. STELLAR AGES AND CONVECTIVE CORES IN FIELD MAIN-SEQUENCE STARS: FIRST ASTEROSEISMIC APPLICATION TO TWO KEPLER TARGETS

    SciTech Connect

    Silva Aguirre, V.; Christensen-Dalsgaard, J.; Chaplin, W. J.; Basu, S.; Deheuvels, S.; Brandao, I. M.; Cunha, M. S.; Sousa, S. G.; Dogan, G.; Metcalfe, T. S.; Serenelli, A. M.; Garcia, R. A.; Ballot, J.; Weiss, A.; Appourchaux, T.; Casagrande, L.; Cassisi, S.; Creevey, O. L.; Lebreton, Y.; Noels, A.; and others

    2013-06-01

    Using asteroseismic data and stellar evolution models we obtain the first detection of a convective core in a Kepler field main-sequence star, putting a stringent constraint on the total size of the mixed zone and showing that extra mixing beyond the formal convective boundary exists. In a slightly less massive target the presence of a convective core cannot be conclusively discarded, and thus its remaining main-sequence lifetime is uncertain. Our results reveal that best-fit models found solely by matching individual frequencies of oscillations corrected for surface effects do not always properly reproduce frequency combinations. Moreover, slightly different criteria to define what the best-fit model is can lead to solutions with similar global properties but very different interior structures. We argue that the use of frequency ratios is a more reliable way to obtain accurate stellar parameters, and show that our analysis in field main-sequence stars can yield an overall precision of 1.5%, 4%, and 10% in radius, mass, and age, respectively. We compare our results with those obtained from global oscillation properties, and discuss the possible sources of uncertainties in asteroseismic stellar modeling where further studies are still needed.

  17. Extended main sequence turnoffs in intermediate-age star clusters: a correlation between turnoff width and early escape velocity

    SciTech Connect

    Goudfrooij, Paul; Kozhurina-Platais, Vera; Kalirai, Jason S.; Correnti, Matteo E-mail: verap@stsci.edu E-mail: correnti@stsci.edu; and others

    2014-12-10

    We present a color-magnitude diagram analysis of deep Hubble Space Telescope imaging of a mass-limited sample of 18 intermediate-age (1-2 Gyr old) star clusters in the Magellanic Clouds, including eight clusters for which new data were obtained. We find that all star clusters in our sample feature extended main-sequence turnoff (eMSTO) regions that are wider than can be accounted for by a simple stellar population (including unresolved binary stars). FWHM widths of the MSTOs indicate age spreads of 200-550 Myr. We evaluate the dynamical evolution of clusters with and without initial mass segregation. Our main results are (1) the fraction of red clump (RC) stars in secondary RCs in eMSTO clusters scales with the fraction of MSTO stars having pseudo-ages of ≲1.35 Gyr; (2) the width of the pseudo-age distributions of eMSTO clusters is correlated with their central escape velocity v {sub esc}, both currently and at an age of 10 Myr. We find that these two results are unlikely to be reproduced by the effects of interactive binary stars or a range of stellar rotation velocities. We therefore argue that the eMSTO phenomenon is mainly caused by extended star formation within the clusters; and (3) we find that v {sub esc} ≥ 15 km s{sup –1} out to ages of at least 100 Myr for all clusters featuring eMSTOs, and v {sub esc} ≤ 12 km s{sup –1} at all ages for two lower-mass clusters in the same age range that do not show eMSTOs. We argue that eMSTOs only occur for clusters whose early escape velocities are higher than the wind velocities of stars that provide material from which second-generation stars can form. The threshold of 12-15 km s{sup –1} is consistent with wind velocities of intermediate-mass asymptotic giant branch stars and massive binary stars in the literature.

  18. ADIABATIC MASS LOSS IN BINARY STARS. II. FROM ZERO-AGE MAIN SEQUENCE TO THE BASE OF THE GIANT BRANCH

    SciTech Connect

    Ge, Hongwei; Chen, Xuefei; Han, Zhanwen; Webbink, Ronald F. E-mail: rwebbink@illinois.edu

    2015-10-10

    In the limit of extremely rapid mass transfer, the response of a donor star in an interacting binary becomes asymptotically one of adiabatic expansion. We survey here adiabatic mass loss from Population I stars (Z = 0.02) of mass 0.10 M{sub ⊙}–100 M{sub ⊙} from the zero-age main sequence to the base of the giant branch, or to central hydrogen exhaustion for lower main sequence stars. The logarithmic derivatives of radius with respect to mass along adiabatic mass-loss sequences translate into critical mass ratios for runaway (dynamical timescale) mass transfer, evaluated here under the assumption of conservative mass transfer. For intermediate- and high-mass stars, dynamical mass transfer is preceded by an extended phase of thermal timescale mass transfer as the star is stripped of most of its envelope mass. The critical mass ratio q{sub ad} (throughout this paper, we follow the convention of defining the binary mass ratio as q ≡ M{sub donor}/M{sub accretor}) above which this delayed dynamical instability occurs increases with advancing evolutionary age of the donor star, by ever-increasing factors for more massive donors. Most intermediate- or high-mass binaries with nondegenerate accretors probably evolve into contact before manifesting this instability. As they approach the base of the giant branch, however, and begin developing a convective envelope, q{sub ad} plummets dramatically among intermediate-mass stars, to values of order unity, and a prompt dynamical instability occurs. Among low-mass stars, the prompt instability prevails throughout main sequence evolution, with q{sub ad} declining with decreasing mass, and asymptotically approaching q{sub ad} = 2/3, appropriate to a classical isentropic n = 3/2 polytrope. Our calculated q{sub ad} values agree well with the behavior of time-dependent models by Chen and Han of intermediate-mass stars initiating mass transfer in the Hertzsprung gap. Application of our results to cataclysmic variables, as systems

  19. Core-Halo Structure of a Chemically Homogeneous Massive Star and Bending of the Zero-Age Main Sequence

    NASA Astrophysics Data System (ADS)

    Ishii, Mie; Ueno, Munetaka; Kato, Mariko

    1999-08-01

    We have recalculated the interior structure of very massive stars of uniform chemical composition with the OPAL opacity. Very massive stars are found to develop a core-halo structure with an extended radiative-envelope. With the core-halo structure, because a more massive star has a more extended envelope, the track of the upper zero-age main-sequence (ZAMS) curves redward in the H-R diagram at > 100 MO (Z=0.02), >70 MO (Z=0.05), and > 15 MO for helium ZAMS (X=0, Z=0.02). Therefore, the effective temperatures of very massive ZAMS stars are rather low: e.g., for a 200 MO star, log T_eff=4.75 (Z=0.004), 4.60 (Z=0.02), 4.46 (Z=0.05), and 4.32 (Z=0.10). The effective temperatures of very luminous stars (> 120 MO ) found in the LMC, the SMC, and the Galaxy are discussed in relation to this metal dependence of a curving upper main-sequence.

  20. Controversial age spreads from the main sequence turn-off and red clump in intermediate-age clusters in the LMC

    NASA Astrophysics Data System (ADS)

    Niederhofer, F.; Bastian, N.; Kozhurina-Platais, V.; Hilker, M.; de Mink, S. E.; Cabrera-Ziri, I.; Li, C.; Ercolano, B.

    2016-02-01

    Most star clusters at an intermediate age (1-2 Gyr) in the Large and Small Magellanic Clouds show a puzzling feature in their color-magnitude diagrams (CMD) that is not in agreement with a simple stellar population. The main sequence turn-off of these clusters is much broader than expected from photometric uncertainties. One interpretation of this feature is that age spreads of the order of 200-500 Myr exist within individual clusters, although this interpretation is highly debated. Such large age spreads should affect other parts of the CMD, which are sensitive to age, as well. In this study, we analyze the CMDs of a sample of 12 intermediate-age clusters in the Large Magellanic Cloud that all show an extended turn-off using archival optical data taken with the Hubble Space Telescope. We fit the star formation history of the turn-off region and the red clump region independently. We find that in most cases, the age spreads inferred from the red clumps are smaller than those that result from the turn-off region. However, the age ranges that result from the red clump region are broader than expected for a single age. Only two out of 12 clusters in our sample show a red clump which seems to be consistent with a single age. As our results are ambiguous, by fitting the star formation histories to the red clump regions, we cannot ultimately tell if the extended main sequence turn-off feature is the result of an age spread or not. However, we do find that the width of the extended main sequence turn-off feature is correlated with the age of the clusters in a way which would be unexplained in the so-called age spread interpretation, but which may be expected if stellar rotation is the cause of the spread at the turn-off. Based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST

  1. Older and colder: The impact of starspots on stellar masses, ages, and lithium during the pre-main sequence

    NASA Astrophysics Data System (ADS)

    Somers, Garrett

    2016-01-01

    Starspots are ubiquitously found on young, active stars on the pre-main sequence (pre-MS), and may cover up to ~50% of their surfaces, but their effects on early stellar evolution have never been fully explored. I study the impact of such extreme spot coverage on pre-MS stellar evolution by modifying an existing stellar evolution code to account for spot effects on both the surface boundary conditions and the transport of energy in the interior. I show that heavy spot coverage systematically increases the radii of young stars, while reducing their luminosity and average surface temperature. Such increased radii may underlie the well-known radius inflation of some young, active stars, while the decreased luminosity and effective temperature displace stars on the HR diagram, leading to systematic under-estimation of stellar masses by up to 2x, and of stellar ages by up to 10x, if spotted stars are interpreted with un-spotted isochrones. The inhomogeneous surfaces of spotted stars also distort the emission spectrum, and can thus explain the anomalous colors of the rapidly rotating K dwarfs of the Pleiades, a young open cluster. I further find that spots reduce the central temperature of stars, leading to a suppression of lithium burning during the pre-MS. As a result, pre-MS stars of equal mass but differing spot properties reach the zero-age main sequence with different surface lithium abundances. I show that this effect can account for the previously unexplained lithium abundance dispersions observed at fixed Teff in the Pleiades, and other young clusters.Synthesizing these results, I argue that the inclusion of spots, a prominent phenomenon on the pre-MS, can explain several outstanding mysteries associated with young stars: inflated radii, age spreads in young clusters, the anomalous colors of rapid rotators, and the lithium abundance dispersions in young star clusters. I discuss implications of under-estimated masses and ages for measuring age spreads in young

  2. On the interpretation of sub-giant branch morphologies of intermediate-age star clusters with extended main sequence turnoffs

    NASA Astrophysics Data System (ADS)

    Goudfrooij, Paul; Girardi, Léo; Rosenfield, Philip; Bressan, Alessandro; Marigo, Paola; Correnti, Matteo; Puzia, Thomas H.

    2015-06-01

    High-quality photometry of many star clusters in the Magellanic Clouds with ages of 1-2 Gyr revealed main sequence turnoffs (MSTOs) that are significantly wider than can be accounted for by a simple stellar population (SSP). Such extended MSTOs (eMSTOs) are often interpreted in terms of an age spread of several 108 yr, challenging the traditional view of star clusters as being formed in a single star formation episode. Li et al. and Bastian & Niederhofer recently investigated the sub-giant branches (SGBs) of NGC 1651, NGC 1806, and NGC 1846, three star clusters in the Large Magellanic Cloud (LMC) that exhibit an eMSTO. They argued that the SGB of these star clusters can be explained only by an SSP. We study these and two other similar star clusters in the LMC, using extensive simulations of SSPs including unresolved binaries. We find that the shapes of the cross-SGB profiles of all star clusters in our sample are in fact consistent with their cross-MSTO profiles when the latter are interpreted as age distributions. Conversely, SGB morphologies of star clusters with eMSTOs are found to be inconsistent with those of simulated SSPs. Finally, we create PARSEC isochrones from tracks featuring a grid of convective overshoot levels and a very fine grid of stellar masses. A comparison of the observed photometry with these isochrones shows that the morphology of the red clump (RC) of such star clusters is also consistent with that implied by their MSTO in the age spread scenario. We conclude that the SGB and RC morphologies of star clusters featuring eMSTOs are consistent with the scenario in which the eMSTOs are caused by a distribution of stellar ages.

  3. Evidence for a Significant Intermediate-Age Population in the M31 Halo from Main Sequence Photometry

    NASA Technical Reports Server (NTRS)

    Brown, Thomas M.; Ferguson, Henry C.; Smith, Ed; Kimble, Randy A.; Sweigart, Allen V.; Renzini, Alvio; Rich, R. Michael; Vandenberg, Don A.

    2003-01-01

    We present a color-magnitude diagram (CMD) for a minor-axis field in the halo of the Andromeda galaxy (M3l), 51 arcmin (11 kpc) from the nucleus. These observations, taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope, are the deepest optical images yet obtained, attaining 50% completeness at m(sub v) = 30.7 mag. The CMD, constructed from approx. 3 x 10(exp 5) stars, reaches more than 1.5 mag fainter than the old main-sequence turnoff. Our analysis is based on direct comparisons to ACS observations of four globular clusters through the same filters, as well as chi square fitting to a finely-spaced grid of calibrated stellar-population models. We find that the M31 halo contains a major (approx. 30% by mass) intermediate-age (6-8 Gyr) metal-rich ([Fe/H] greater than -0.5) population, as well as a significant globular-cluster age (11-13.5 Gyr) metal-poor population. These findings support the idea that galaxy mergers played an important role in the formation of the M31 halo.

  4. THE CONTRIBUTIONS OF INTERACTIVE BINARY STARS TO DOUBLE MAIN-SEQUENCE TURNOFFS AND DUAL RED CLUMP OF INTERMEDIATE-AGE STAR CLUSTERS

    SciTech Connect

    Yang Wuming; Bi Shaolan; Tian Zhijia; Li Tanda; Liu Kang; Meng Xiangcun E-mail: woomyang@gmail.com

    2011-04-20

    Double or extended main-sequence turnoffs (DMSTOs) and dual red clump (RC) were observed in intermediate-age clusters, such as in NGC 1846 and 419. The DMSTOs are interpreted as that the cluster has two distinct stellar populations with differences in age of about 200-300 Myr but with the same metallicity. The dual RC is interpreted as a result of a prolonged star formation. Using a stellar population-synthesis method, we calculated the evolution of a binary-star stellar population. We found that binary interactions and merging can reproduce the dual RC in the color-magnitude diagrams of an intermediate-age cluster, whereas in actuality only a single population exists. Moreover, the binary interactions can lead to an extended main-sequence turnoff (MSTO) rather than DMSTOs. However, the rest of the main sequence, subgiant branch, and first giant branch are hardly spread by the binary interactions. Part of the observed dual RC and extended MSTO may be the results of binary interactions and mergers.

  5. New clues to the cause of extended main-sequence turnoffs in intermediate-age star clusters in the Magellanic Clouds

    SciTech Connect

    Correnti, Matteo; Goudfrooij, Paul; Kalirai, Jason S.; Girardi, Leo; Puzia, Thomas H.; Kerber, Leandro E-mail: goudfroo@stsci.edu E-mail: leo.girardi@oapd.inaf.it E-mail: lkerber@gmail.com

    2014-10-01

    We use the Wide Field Camera 3 on board the Hubble Space Telescope (HST) to obtain deep, high-resolution images of two intermediate-age star clusters in the Large Magellanic Cloud of relatively low mass (≈10{sup 4} M {sub ☉}) and significantly different core radii, namely NGC 2209 and NGC 2249. For comparison purposes, we also reanalyzed archival HST images of NGC 1795 and IC 2146, two other relatively low-mass star clusters. From the comparison of the observed color-magnitude diagrams with Monte Carlo simulations, we find that the main-sequence turnoff (MSTO) regions in NGC 2209 and NGC 2249 are significantly wider than that derived from simulations of simple stellar populations, while those in NGC 1795 and IC 2146 are not. We determine the evolution of the clusters' masses and escape velocities from an age of 10 Myr to the present age. We find that differences among these clusters can be explained by dynamical evolution arguments if the currently extended clusters (NGC 2209 and IC 2146) experienced stronger levels of initial mass segregation than the currently compact ones (NGC 2249 and NGC 1795). Under this assumption, we find that NGC 2209 and NGC 2249 have estimated escape velocities, V {sub esc} ≳ 15 km s{sup –1} at an age of 10 Myr, large enough to retain material ejected by slow winds of first-generation stars, while the two clusters that do not feature extended MSTOs have V {sub esc} ≲ 12 km s{sup –1} at that age. These results suggest that the extended MSTO phenomenon can be better explained by a range of stellar ages rather than a range of stellar rotation velocities or interacting binaries.

  6. Evaluating gyrochronology on the zero-age-main-sequence: rotation periods in the southern open cluster Blanco 1 from the Kelt-South survey

    SciTech Connect

    Cargile, P. A.; Pepper, J.; Siverd, R.; Stassun, K. G.; James, D. J.; Kuhn, R. B.

    2014-02-10

    We report periods for 33 members of Blanco 1 as measured from Kilodegree Extremely Little Telescope-South light curves, the first reported rotation periods for this benchmark zero-age-main-sequence open cluster. The distribution of these stars spans from late-A or early-F dwarfs to mid-K with periods ranging from less than a day to ∼8 days. The rotation period distribution has a morphology similar to the coeval Pleiades cluster, suggesting the universal nature of stellar rotation distributions. Employing two different gyrochronology methods, we find an age of 146{sub −14}{sup +13} Myr for the cluster. Using the same techniques, we infer an age of 134{sub −10}{sup +9} Myr for the Pleiades measured from existing literature rotation periods. These rotation-derived ages agree with independently determined cluster ages based on the lithium depletion boundary technique. Additionally, we evaluate different gyrochronology models and quantify levels of agreement between the models and the Blanco 1/Pleiades rotation period distributions, including incorporating the rotation distributions of clusters at ages up to 1.1 Gyr. We find the Skumanich-like spin-down rate sufficiently describes the rotation evolution of stars hotter than the Sun; however, we find cooler stars rotating faster than predicted by a Skumanich law, suggesting a mass dependence in the efficiency of stellar angular momentum loss rate. Finally, we compare the Blanco 1 and Pleiades rotation period distributions to available nonlinear angular momentum evolution models. We find they require a significant mass dependence on the initial rotation rate of solar-type stars to reproduce the observed range of rotation periods at a given stellar mass and are furthermore unable to predict the observed over-density of stars along the upper envelope of the clusters' rotation distributions.

  7. A Systematic Study of Effects of Stellar Rotation, Age Spread, and Binaries on Color-Magnitude Diagrams with Extended Main-sequence Turnoffs

    NASA Astrophysics Data System (ADS)

    Li, Zhongmu; Mao, Caiyan; Zhang, Liyun; Zhang, Xi; Chen, Li

    2016-07-01

    Stellar rotation, age spread, and binary stars are thought to be the three most possible causes of the peculiar color-magnitude diagrams (CMDs) of some star clusters, which exhibit extended main-sequence turnoffs (eMSTOs). The answer is far from clear. This paper studies the effects of the three above causes on the CMDs of star clusters systematically. A rapid stellar evolutionary code and a recently published database of rotational effects of single stars have been used, via an advanced stellar population synthesis technique. As a result, we find a similar result for rotation to recent works, which suggests that rotation is able to explain, at least partially, the eMSTOs of clusters, if clusters are not too old (<2.0 Gyr). In addition, an age spread of 200-500 Myr reproduces extended turnoffs for all clusters younger than 2.5 Gyr, in particular, for those younger than 2.2 Gyr. Age spread also results in extended red clumps (eRCs) for clusters younger than 0.5 Gyr. The younger the clusters, the clearer the eRC structures. Moreover, it is shown that binaries (including interactive binaries) affect the spread of MSTOs slightly for old clusters, but they can contribute to the eMSTOs of clusters younger than 0.5 Gyr. Our result suggests a possible way to disentangle the roles of stellar rotation and age spread, i.e., checking the existence of CMDs with both eMSTOs and eRCs in clusters younger than 0.5 Gyr.

  8. Age-dependent metallicity gradients of the MilkyWay disk from main sequence turn-off stars in LSS-GAC

    NASA Astrophysics Data System (ADS)

    Xiang, Maosheng; Liu, Xiaowei

    2015-08-01

    The stellar metallicity gradient plays an important role on constraining the formation and assemblage history of the Galactic disk. We use 297, 042 main sequence turn-off stars from LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC) to study the radial metallicity gradient, [Fe/H]/R, and the vertical metallicity gradient, [Fe/H]/|Z|, of the Galactic disk in the anti-center direction. We carry out age determination for these turnoff stars via isochrone fitting and study the age-dependent metallicity gradients. We have implemented a detailed analysis on the sample selection effect to account for the target selection in the color - magnitude diagram (CMD) and the potential bias on metallicity gradients of a magnitude limited sample. Our results show that both the radial and vertical gradients have strong spatial and temporal evolution. The radial gradients of the oldest (age > 11Gyr) stars are almost zero at all heights above the Galactic disk plane, while those of the younger stars are always negative. The vertical gradients of the oldest stars are negative and show very weak evolution with the Galactocentric distance in the disk plane, R, while those of the younger stars show strong evolution with R. At the early epoch, the radial gradient steepens as the age becomes younger, with a maximum occurs at 7 - 8Gyr, after then it becomes flatter. Similar trend with age is also presented in the vertical gradients. We infer that the formation of the Galactic disk has experienced at least two phases. The earlier phase is probably a slow, pressure-supported collapse of gas, where the gas settle down to the disk from the vertical direction. In the later phase, there is significant radial flow of gas. Transition of the gas behaviors between the two phases occurs between 8 and 11Gyr. The two phases are responsible for the formation of the Galactic thick and thin disks, respectively, and consequently, we recommend that the age is a natural, physical criterion to

  9. Atomic diffusion in metal poor stars. The influence on the Main Sequence fitting distance scale, subdwarfs ages and the value of Delta Y/ Delta Z

    NASA Astrophysics Data System (ADS)

    Salaris, M.; Groenewegen, M. A. T.; Weiss, A.

    2000-03-01

    The effect of atomic diffusion on the Main Sequence (MS) of metal-poor low mass stars is investigated. Since diffusion alters the stellar surface chemical abundances with respect to their initial values, one must ensure - by calibrating the initial chemical composition of the theoretical models - that the surface abundances of the models match the observed ones of the stellar population under scrutiny. When properly calibrated, our models with diffusion reproduce well within the errors the Hertzsprung-Russell diagram of Hipparcos subdwarfs with empirically determined T_eff values and high resolution spectroscopical [Fe/H] determinations. Since the observed surface abundances of subdwarfs are different from the initial ones due to the effect of diffusion, while the globular clusters stellar abundances are measured in Red Giants, which have practically recovered their initial abundances after the dredge-up, the isochrones to be employed for studying globular clusters and Halo subdwarfs with the same observational value of [Fe/H] are different and do not coincide. This is at odds with the basic assumption of the MS-fitting technique for distance determinations. However, the use of the rather large sample of Hipparcos lower MS subdwarfs with accurate parallaxes keeps at minimum the effect of these differences, for two reasons. First, it is possible to use subdwarfs with observed [Fe/H] values close to the cluster one; this minimizes the colour corrections (which are derived from the isochrones) needed to reduce all the subdwarfs to a mono-metallicity sequence having the same [Fe/H] than the cluster. Second, one can employ objects sufficiently faint so that the differences between the subdwarfs and cluster MS with the same observed value of [Fe/H] are small (they increase for increasing luminosity). We find therefore that the distances based on standard isochrones are basically unaltered when diffusion is taken properly into account. On the other hand, the absolute ages

  10. Population Parameters of Intermediate-age Star Clusters in the Large Magellanic Cloud. III. Dynamical Evidence for a Range of Ages Being Responsible for Extended Main-sequence Turnoffs

    NASA Astrophysics Data System (ADS)

    Goudfrooij, Paul; Puzia, Thomas H.; Chandar, Rupali; Kozhurina-Platais, Vera

    2011-08-01

    We present a new analysis of 11 intermediate-age (1-2 Gyr) star clusters in the Large Magellanic Cloud based on Hubble Space Telescope imaging data. Seven of the clusters feature main-sequence turnoff (MSTO) regions that are wider than can be accounted for by a simple stellar population, whereas their red giant branches (RGBs) indicate a single value of [Fe/H]. The star clusters cover a range in present-day mass from about 1 × 104 M sun to 2 × 105 M sun. We compare radial distributions of stars in the upper and lower parts of the MSTO region, and calculate cluster masses and escape velocities from the present time back to a cluster age of 10 Myr. Our main result is that for all clusters in our sample with estimated escape velocities v esc >~ 15 km s-1 at an age of 10 Myr, the stars in the brightest half of the MSTO region are significantly more centrally concentrated than the stars in the faintest half and more massive RGB and asymptotic giant branch stars. This is not the case for clusters with v esc <~ 10 km s-1 at an age of 10 Myr. We argue that the wide MSTO region of such clusters is caused mainly by a ~200-500 Myr range in the ages of cluster stars due to extended star formation within the cluster from material shed by first-generation stars featuring slow stellar winds. Dilution of this enriched material by accretion of ambient interstellar matter is deemed plausible if the spread of [Fe/H] in this ambient gas was very small when the second-generation stars were formed in the cluster. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

  11. Habitable zones around main sequence stars.

    PubMed

    Kasting, J F; Whitmire, D P; Reynolds, R T

    1993-01-01

    A one-dimensional climate model is used to estimate the width of the habitable zone (HZ) around our Sun and around other main sequence stars. Our basic premise is that we are dealing with Earth-like planets with CO2/H2O/N2 atmospheres and that habitability requires the presence of liquid water on the planet's surface. The inner edge of the HZ is determined in our model by loss of water via photolysis and hydrogen escape. The outer edge of the HZ is determined by the formation of CO2 clouds, which cool a planet's surface by increasing its albedo and by lowering the convective lapse rate. Conservative estimates for these distances in our own Solar System are 0.95 and 1.37 AU, respectively; the actual width of the present HZ could be much greater. Between these two limits, climate stability is ensured by a feedback mechanism in which atmospheric CO2 concentrations vary inversely with planetary surface temperature. The width of the HZ is slightly greater for planets that are larger than Earth and for planets which have higher N2 partial pressures. The HZ evolves outward in time because the Sun increases in luminosity as it ages. A conservative estimate for the width of the 4.6-Gyr continuously habitable zone (CHZ) is 0.95 to 1.15 AU. Stars later than F0 have main sequence lifetimes exceeding 2 Gyr and, so, are also potential candidates for harboring habitable planets. The HZ around an F star is larger and occurs farther out than for our Sun; the HZ around K and M stars is smaller and occurs farther in. Nevertheless, the widths of all of these HZs are approximately the same if distance is expressed on a logarithmic scale. A log distance scale is probably the appropriate scale for this problem because the planets in our own Solar System are spaced logarithmically and because the distance at which another star would be expected to form planets should be related to the star's mass. The width of the CHZ around other stars depends on the time that a planet is required to

  12. Post-main-sequence planetary system evolution.

    PubMed

    Veras, Dimitri

    2016-02-01

    The fates of planetary systems provide unassailable insights into their formation and represent rich cross-disciplinary dynamical laboratories. Mounting observations of post-main-sequence planetary systems necessitate a complementary level of theoretical scrutiny. Here, I review the diverse dynamical processes which affect planets, asteroids, comets and pebbles as their parent stars evolve into giant branch, white dwarf and neutron stars. This reference provides a foundation for the interpretation and modelling of currently known systems and upcoming discoveries. PMID:26998326

  13. Post-main-sequence planetary system evolution

    PubMed Central

    Veras, Dimitri

    2016-01-01

    The fates of planetary systems provide unassailable insights into their formation and represent rich cross-disciplinary dynamical laboratories. Mounting observations of post-main-sequence planetary systems necessitate a complementary level of theoretical scrutiny. Here, I review the diverse dynamical processes which affect planets, asteroids, comets and pebbles as their parent stars evolve into giant branch, white dwarf and neutron stars. This reference provides a foundation for the interpretation and modelling of currently known systems and upcoming discoveries. PMID:26998326

  14. Post-main-sequence planetary system evolution.

    PubMed

    Veras, Dimitri

    2016-02-01

    The fates of planetary systems provide unassailable insights into their formation and represent rich cross-disciplinary dynamical laboratories. Mounting observations of post-main-sequence planetary systems necessitate a complementary level of theoretical scrutiny. Here, I review the diverse dynamical processes which affect planets, asteroids, comets and pebbles as their parent stars evolve into giant branch, white dwarf and neutron stars. This reference provides a foundation for the interpretation and modelling of currently known systems and upcoming discoveries.

  15. Comparison of Tertiary depositional sequences, age of bounding unconformities, and coastal onlap patterns in Baltimore Canyon Trough, offshore New Jersey, and Main Pass, offshore Alabama

    SciTech Connect

    Greenlee, S.M.

    1987-05-01

    Interpretation of high-quality seismic reflection profiles tied to well bores has delineated the Tertiary geologic history of the Baltimore Canyon Trough and the Main Pass area. During the Tertiary both areas subsided slowly, were in comparable paleographic position, and were the focus of primarily siliciclastic, progradational sedimentation. Because these areas are so similar geologically and have extensive seismic, log, and paleontologic data, they provide a unique opportunity to compare the character, timing, and extent of depositional sequences found on two different portions of the North American continental margin. The Cretaceous-Tertiary boundary is characterized by an erosional unconformity which is downlapped by overlying Paleocene clinoforms. This downlap surface is interpreted to be a result of the rapid rise in sea level in the late Maastrichtian and early Paleocene. Both areas remained in deep water throughout the Paleocene and Eocene and record second-order (5-10 m.y.) eustatic cycles. Following a major basinward shift of coastal onlap in the Oligocene, thick progradational deltaic wedges are found within the study areas which record the effects of third-order (approx. 1 m.y.) eustatic cycles. These depositional sequences may be grouped into second-order eustatic cycles recognized by major downward shifts in coastal onlap in the Oligocene, lower Miocene, and at the end of the middle Miocene. Landward and basinward shifts in coastal onlap patterns show a high degree of similarity among the study areas and with the global coastal onlap chart. A departure in the middle Miocene is attributed to differing subsidence histories of the two margins.

  16. Are Post-Main Sequence Planets Doomed?

    NASA Astrophysics Data System (ADS)

    Villaver, E.

    2014-04-01

    Post-main sequence evolution directly affects the survival of planetary and sub-planetary mass bodies. Planets orbiting evolved stars undergo orbital evolution under the influence of tides and mass-loss, can be ejected, evaporated, and suffer multiple-body instabilities. The conditions on the planet surface are expected to be modified as well as the result of the evolution of the star. I will discuss the new limits that the theoretical studies allow us to set on the survival and habitability of planets as the star runs out of its hydrogen fuel.

  17. Main sequence stars with asymmetric dark matter.

    PubMed

    Iocco, Fabio; Taoso, Marco; Leclercq, Florent; Meynet, Georges

    2012-02-10

    We study the effects of feebly or nonannihilating weakly interacting dark matter (DM) particles on stars that live in DM environments denser than that of our Sun. We find that the energy transport mechanism induced by DM particles can produce unusual conditions in the cores of main sequence stars, with effects which can potentially be used to probe DM properties. We find that solar mass stars placed in DM densities of ρ(χ)≥10(2) GeV/cm(3) are sensitive to spin-dependent scattering cross section σ(SD)≥10(-37) cm(2) and a DM particle mass as low as m(χ)=5 GeV, accessing a parameter range weakly constrained by current direct detection experiments.

  18. Main-sequence mass loss and the lithium dip

    NASA Technical Reports Server (NTRS)

    Schramm, David N.; Steigman, Gary; Dearborn, David S. P.

    1990-01-01

    The significant dip in observed lithium abundances for Population I stars near M about 1.3 solar mass is discussed. It is noted that this dip occurs near where the instability strip crosses the main sequence on the lower edge of the Delta Scuti stars and that stellar pulsations are expected to give rise to mass loss. A total mass loss of 0.05 solar mass over the main-sequence lifetime of these stars would be sufficient to explain the observations of lithium depletion. The absence of a dip in the Pleiades and of significant depletion of beryllium in the Hyades places tight constraints on the rate of mass loss. These constraints make unlikely the high main-sequence mass-loss rates which would significantly affect globular cluster ages.

  19. Accretion onto Pre-Main-Sequence Stars

    NASA Astrophysics Data System (ADS)

    Hartmann, Lee; Herczeg, Gregory; Calvet, Nuria

    2016-09-01

    Accretion through circumstellar disks plays an important role in star formation and in establishing the properties of the regions in which planets form and migrate. The mechanisms by which protostellar and protoplanetary disks accrete onto low-mass stars are not clear; angular momentum transport by magnetic fields is thought to be involved, but the low-ionization conditions in major regions of protoplanetary disks lead to a variety of complex nonideal magnetohydrodynamic effects whose implications are not fully understood. Accretion in pre-main-sequence stars of masses ≲1M⊙ (and in at least some 2–3-M⊙ systems) is generally funneled by the stellar magnetic field, which disrupts the disk at scales typically of order a few stellar radii. Matter moving at near free-fall velocities shocks at the stellar surface; the resulting accretion luminosities from the dissipation of kinetic energy indicate that mass addition during the T Tauri phase over the typical disk lifetime ˜3 Myr is modest in terms of stellar evolution, but is comparable to total disk reservoirs as estimated from millimeter-wave dust emission (˜10‑2 M⊙). Pre-main-sequence accretion is not steady, encompassing timescales ranging from approximately hours to a century, with longer-timescale variations tending to be the largest. Accretion during the protostellar phase—while the protostellar envelope is still falling onto the disk—is much less well understood, mostly because the properties of the central obscured protostar are difficult to estimate. Kinematic measurements of protostellar masses with new interfometric facilities should improve estimates of accretion rates during the earliest phases of star formation.

  20. Submillimeter studies of main-sequence stars

    NASA Technical Reports Server (NTRS)

    Zuckerman, B.; Becklin, E. E.

    1993-01-01

    JCMT maps of the 800-micron emission from Vega, Fomalhaut, and Beta Pictoris are interpreted to indicate that they are not ringed by large reservoirs of distant orbiting dust particles that are too cold to have been detected by IRAS. A search for 800-micron emission from stars in the Pleiades and Ursa Majoris open clusters is reported. In comparison with the mass of dust particles near T Tauri and Herbig Ae stars, the JCMT data indicate a decline in dust mass during the initial 3 x 10 exp 8 yr that a star spends on the main sequence that is at least as rapid as (time) exp -2. It is estimated that in the Kuiper belt the ratio of total mass carried by small particles to that carried by comets is orders of magnitude smaller than this ratio is 1 AU from the sun. If 800-micron opacities calculated by Pollack et al. (1993) are correct, then the particles with radii less than 100 microns that dominate the FIR fluxes measured by IRAS cannot entirely account for the measured 800-micron fluxes at Vega, Beta Pic, and Fomalhaut; larger particles must be present as well.

  1. Blue supergiants as descendants of magnetic main sequence stars

    NASA Astrophysics Data System (ADS)

    Petermann, I.; Langer, N.; Castro, N.; Fossati, L.

    2015-12-01

    About 10% of the massive main sequence stars have recently been found to host a strong, large scale magnetic field. Both, the origin and the evolutionary consequences of these fields are largely unknown. We argue that these fields may be sufficiently strong in the deep interior of the stars to suppress convection near the outer edge of their convective core. We performed parametrised stellar evolution calculations and assumed a reduced size of the convective core for stars in the mass range 16M⊙ to 28M⊙ from the zero age main sequence until core carbon depletion. We find that such models avoid the coolest part of the main sequence band, which is usually filled by evolutionary models that include convective core overshooting. Furthermore, our "magnetic" models populate the blue supergiant region during core helium burning, i.e., the post-main sequence gap left by ordinary single star models, and some of them end their life in a position near that of the progenitor of Supernova 1987A in the Hertzsprung-Russell diagram. Further effects include a strongly reduced luminosity during the red supergiant stage, and downward shift of the limiting initial mass for white dwarf and neutron star formation.

  2. Dusty debris clouds around main sequence and post-main sequence stars

    NASA Technical Reports Server (NTRS)

    Zuckerman, B.

    1993-01-01

    During the past decade, infrared observations by IRAS and from the ground have revealed that many stars are orbited by dusty debris disks. Somewhat more indirect arguments indicate that many of these systems also contain asteroids, comets, and/or planets, thereby suggesting that planetary systems may be quite common in the Milky Way. Dust clouds at the main sequence K5 star HD 98800 and the white dwarf Giclas 29-38 are particularly noteworthy and mysterious.

  3. Pulsating pre-main sequence stars as possible Eddington targets

    NASA Astrophysics Data System (ADS)

    Zwintz, K.; Weiss, W. W.

    2004-01-01

    PMS stars lie between the birthline and the zero-age main sequence (ZAMS) in the Hertzsprung-Russell (HR) diagram. They show photometric and spectroscopic variability on time scales of minutes to years, indicating that photospheric activity begins in the earliest phases of stellar evolution. The fact that they move across the instability region during their evolution to the main sequence suggests that at least part of their activity is due to stellar pulsations. δ Scuti-like PMS stars are ideal targets for the Eddington mission. First, their location in open clusters provides the simultaneous observations of numerous objects as a photometric reference. Second, the PMS variables lie in a magnitude range between V = 8 and V = 15, which meets the requirements of the mission. Third, the analysis of these stars by means of asteroseismological methods provides the unique chance to distinguish between young and evolved stars and hence leads to a better fundamental understanding of stellar structure and evolution.

  4. Main sequence models for massive zero-metal stars

    NASA Technical Reports Server (NTRS)

    Cary, N.

    1974-01-01

    Zero-age main-sequence models for stars of 20, 10, 5, and 2 solar masses with no heavy elements are constructed for three different possible primordial helium abundances: Y=0.00, Y=0.23, and Y=0.30. The latter two values of Y bracket the range of primordial helium abundances cited by Wagoner. With the exceptions of the two 20 solar mass models that contain helium, these models are found to be self-consistent in the sense that the formation of carbon through the triple-alpha process during premain sequence contraction is not sufficient to bring the CN cycle into competition with the proton-proton chain on the ZAMS. The zero-metal models of the present study have higher surface and central temperatures, higher central densities, smaller radii, and smaller convective cores than do the population I models with the same masses.

  5. MAIN-SEQUENCE STAR POPULATIONS IN THE VIRGO OVERDENSITY REGION

    SciTech Connect

    Jerjen, H.; Da Costa, G. S.; Tisserand, P.; Willman, B.; Arimoto, N.; Okamoto, S.; Mateo, M.; Saviane, I.; Walsh, S.; Geha, M.; Jordan, A.; Zoccali, M.; Olszewski, E.; Walker, M.; Kroupa, P.

    2013-05-20

    We present deep color-magnitude diagrams (CMDs) for two Subaru Suprime-Cam fields in the Virgo Stellar Stream (VSS)/Virgo Overdensity (VOD) and compare them to a field centered on the highest concentration of Sagittarius (Sgr) Tidal Stream stars in the leading arm, Branch A of the bifurcation. A prominent population of main-sequence stars is detected in all three fields and can be traced as faint as g Almost-Equal-To 24 mag. Using theoretical isochrone fitting, we derive an age of 9.1{sup +1.0}{sub -1.1} Gyr, a median abundance of [Fe/H] = -0.70{sup +0.15}{sub -0.20} dex, and a heliocentric distance of 30.9 {+-} 3.0 kpc for the main sequence of the Sgr Stream Branch A. The dominant main-sequence populations in the two VSS/VOD fields ({Lambda}{sub Sun} Almost-Equal-To 265 Degree-Sign , B{sub Sun} Almost-Equal-To 13 Degree-Sign ) are located at a mean distance of 23.3 {+-} 1.6 kpc and have an age of {approx}8.2 Gyr, and an abundance of [Fe/H] = -0.67{sup +0.16}{sub -0.12} dex, similar to the Sgr Stream stars. These statistically robust parameters, derived from the photometry of 260 main-sequence stars, are also in good agreement with the age of the main population in the Sgr dwarf galaxy (8.0 {+-} 1.5 Gyr). They also agree with the peak in the metallicity distribution of 2-3 Gyr old M giants, [Fe/H] Almost-Equal-To -0.6 dex, in the Sgr north leading arm. We then compare the results from the VSS/VOD fields with the Sgr Tidal Stream model by Law and Majewski based on a triaxial Galactic halo shape that is empirically calibrated with Sloan Digital Sky Survey Sgr A-branch and Two Micron All Sky Survey M-giant stars. We find that the most prominent feature in the CMDs, the main-sequence population at 23 kpc, is not explained by the model. Instead the model predicts in these directions a low-density filamentary structure of Sgr debris stars at {approx}9 kpc and a slightly higher concentration of Sgr stars spread over a heliocentric distance range of 42-53 kpc. At best

  6. Reinterpretation of age and correlation between tectonostratigraphic units, southwestern Maine

    SciTech Connect

    Hussey, A.M. . Geology Dept.); Aleinikoff, J. ); Marvinney, R. )

    1993-03-01

    Tectonostratigraphic sequence within the Coastal Lithotectonic Belt of southwestern Maine include the Merrimack Group (MG), Casco Bay Group (CBG), Falmouth-Brunswick sequence (FBS), and Central Maine sequence (CMS). Formations of FBS (Nehumkeag Pond, Mt. Ararat, Torrey Hill, and Richmond Corner), all west of the Norumbega Fault Zone, constitute a separate sequence unrelated to the Casco Bay Group east of the Fault. The age of these rocks is uncertain. The Mt. Ararat and Nehumkeag Pond Fms. are tentatively correlated with lithically similar parts of the Massabesic Gneiss in New Hampshire, and with the Monson Gneiss in Massachusetts. The Mt. Ararat and Nehumkeag Pond Formations, now no longer correlated with the Cushing Fm. may form a basement to the CMS. The CBG, a package of metamorphosed volcanic and pelitic rocks crops out only east of the Norumbega Fault. Felsic metavolcanic rocks of the Cushing Fm. at the base of the CBG give a 471[+-]3 MA U/Pb age on zircons, indicating a Middle Ordovician age for the base of the CBG. The Sebascodegan Fm., an easterly felspathic and calcareous volcaniclastic facies of the upper part of the Cushing Fm., is correlated with the Bucksport Fm. of southeastern coastal Maine, suggesting a Middle Ordovician age for that formation. The Sebascodegan Fm may be equivalent to the Kittery Formation of the MG. The Macworth Fm. of the CBG is equivalent to the Elliot Fm. of the MG, and the Cape Elizabeth Fm. stratigraphically above the Cushing Fm in the CBG, may be equivalent in part to the Elliot Fm. Units of the CBG above the Cape Elizabeth Fm. are not present to the south in the MG due either to faulting or stratigraphic pinchout.

  7. Pre- and main-sequence evolution of solar activity

    NASA Technical Reports Server (NTRS)

    Walter, Frederick M.; Barry, Don C.

    1991-01-01

    The magnetic activity on single solarlike stars declines with stellar age. This has important consequences for the influence of the sun on the early solar system. What is meant by stellar activity, and how it is measured, is reviewed. Stellar activity on the premain-sequence phase of evolution is discussed; the classical T Tauri stars do not exhibit solarlike activity, while the naked T Tauri stars do. The emission surface fluxes of the naked T Tauri stars are similar to those of the youngest main-sequence G stars. The best representation for solarlike stars is a decay proportional to exp(A x t exp 0.5), where A is a function of line excitation temperature. From these decay laws, one can determine the interdependences of the activity, age, and rotation periods. The fluxes of ionizing photons at the earth early in its history are discussed; there was sufficient fluence to account for the observed isotopic ratios of the noble gases.

  8. Infrared Mapping of the Dust Around Main Sequence Stars

    NASA Technical Reports Server (NTRS)

    Heinrichsen, I.; Walker, H.; Klaas, U.; Sylvester, R.

    1998-01-01

    The photopolarimeter on ISO (ISOPHOT) has been used to investigate the dust discs around the four prototype Vega-like stars and several main sequence stars with excess infrared emission from IRAS data.

  9. THE HABITABLE ZONES OF PRE-MAIN-SEQUENCE STARS

    SciTech Connect

    Ramirez, Ramses M.; Kaltenegger, Lisa

    2014-12-20

    We calculate the pre-main-sequence habitable zone (HZ) for stars of spectral classes F-M. The spatial distribution of liquid water and its change during the pre-main-sequence phase of protoplanetary systems is important for understanding how planets become habitable. Such worlds are interesting targets for future missions because the coolest stars could provide habitable conditions for up to 2.5 billion years post-accretion. Moreover, for a given star type, planetary systems are more easily resolved because of higher pre-main-sequence stellar luminosities, resulting in larger planet-star separation for cool stars than is the case for the traditional main-sequence (MS) HZ. We use one-dimensional radiative-convective climate and stellar evolutionary models to calculate pre-main-sequence HZ distances for F1-M8 stellar types. We also show that accreting planets that are later located in the traditional MS HZ orbiting stars cooler than a K5 (including the full range of M stars) receive stellar fluxes that exceed the runaway greenhouse threshold, and thus may lose substantial amounts of water initially delivered to them. We predict that M-star planets need to initially accrete more water than Earth did, or, alternatively, have additional water delivered later during the long pre-MS phase to remain habitable. Our findings are also consistent with recent claims that Venus lost its water during accretion.

  10. Quenching star formation: insights from the local main sequence

    NASA Astrophysics Data System (ADS)

    Leslie, S. K.; Kewley, L. J.; Sanders, D. B.; Lee, N.

    2016-01-01

    The so-called star-forming main sequence of galaxies is the apparent tight relationship between the star formation rate and stellar mass of a galaxy. Many studies exclude galaxies which are not strictly `star forming' from the main sequence, because they do not lie on the same tight relation. Using local galaxies in the Sloan Digital Sky Survey, we have classified galaxies according to their emission line ratios, and studied their location on the star formation rate-stellar mass plane. We find that galaxies form a sequence from the `blue cloud' galaxies which are actively forming stars, through a combination of composite, Seyfert, and low-ionization nuclear emission-line region galaxies, ending as `red-and-dead' galaxies. The sequence supports an evolutionary pathway for galaxies in which star formation quenching by active galactic nuclei plays a key role.

  11. COMMON WARM DUST TEMPERATURES AROUND MAIN-SEQUENCE STARS

    SciTech Connect

    Morales, Farisa Y.; Werner, M. W.; Bryden, G.; Stapelfeldt, K. R.; Rieke, G. H.; Su, K. Y. L.

    2011-04-01

    We compare the properties of warm dust emission from a sample of main-sequence A-type stars (B8-A7) to those of dust around solar-type stars (F5-K0) with similar Spitzer Space Telescope Infrared Spectrograph/MIPS data and similar ages. Both samples include stars with sources with infrared spectral energy distributions that show evidence of multiple components. Over the range of stellar types considered, we obtain nearly the same characteristic dust temperatures ({approx}190 K and {approx}60 K for the inner and outer dust components, respectively)-slightly above the ice evaporation temperature for the inner belts. The warm inner dust temperature is readily explained if populations of small grains are being released by sublimation of ice from icy planetesimals. Evaporation of low-eccentricity icy bodies at {approx}150 K can deposit particles into an inner/warm belt, where the small grains are heated to T{sub dust} {approx} 190 K. Alternatively, enhanced collisional processing of an asteroid belt-like system of parent planetesimals just interior to the snow line may account for the observed uniformity in dust temperature. The similarity in temperature of the warmer dust across our B8-K0 stellar sample strongly suggests that dust-producing planetesimals are not found at similar radial locations around all stars, but that dust production is favored at a characteristic temperature horizon.

  12. Magnetic main sequence stars as progenitors of blue supergiants

    NASA Astrophysics Data System (ADS)

    Petermann, I.; Castro, N.; Langer, N.

    2015-01-01

    Blue supergiants (BSGs) to the right the main sequence band in the HR diagram can not be reproduced by standard stellar evolution calculations. We investigate whether a reduced convective core mass due to strong internal magnetic fields during the main sequence might be able to recover this population of stars. We perform calculations with a reduced mass of the hydrogen burning convective core of stars in the mass range 3-30 M ⊙ in a parametric way, which indeed lead to BSGs. It is expected that these BSGs would still show large scale magnetic fields in the order of 10 G.

  13. Distributions of Quasar Hosts on the Galaxy Main Sequence Plane

    NASA Astrophysics Data System (ADS)

    Zhang, Zhoujian; Shi, Yong; Rieke, George H.; Xia, Xiaoyang; Wang, Yikang; Sun, Bingqing; Wan, Linfeng

    2016-03-01

    The relation between star formation rates (SFRs) and stellar masses, i.e., the galaxy main sequence, is a useful diagnostic of galaxy evolution. We present the distributions relative to the main sequence of 55 optically selected PG and 12 near-IR-selected Two Micron All Sky Survey (2MASS) quasars at z ≤ 0.5. We estimate the quasar host stellar masses from Hubble Space Telescope or ground-based AO photometry, and the SFRs through the mid-infrared aromatic features and far-IR photometry. We find that PG quasar hosts more or less follow the main sequence defined by normal star-forming galaxies while 2MASS quasar hosts lie systematically above the main sequence. PG and 2MASS quasars with higher nuclear luminosities seem to have higher specific SFRs (sSFRs), although there is a large scatter. No trends are seen between sSFRs and SMBH masses, Eddington ratios, or even morphology types (ellipticals, spirals, and mergers). Our results could be placed in an evolutionary scenario with quasars emerging during the transition from ULIRGs/mergers to ellipticals. However, combined with results at higher redshift, they suggest that quasars can be widely triggered in normal galaxies as long as they contain abundant gas and have ongoing star formation.

  14. Binary interactions with high accretion rates onto main sequence stars

    NASA Astrophysics Data System (ADS)

    Shiber, Sagiv; Schreier, Ron; Soker, Noam

    2016-07-01

    Energetic outflows from main sequence stars accreting mass at very high rates might account for the powering of some eruptive objects, such as merging main sequence stars, major eruptions of luminous blue variables, e.g., the Great Eruption of Eta Carinae, and other intermediate luminosity optical transients (ILOTs; red novae; red transients). These powerful outflows could potentially also supply the extra energy required in the common envelope process and in the grazing envelope evolution of binary systems. We propose that a massive outflow/jets mediated by magnetic fields might remove energy and angular momentum from the accretion disk to allow such high accretion rate flows. By examining the possible activity of the magnetic fields of accretion disks, we conclude that indeed main sequence stars might accrete mass at very high rates, up to ≈ 10‑2 M ⊙ yr‑1 for solar type stars, and up to ≈ 1 M ⊙ yr‑1 for very massive stars. We speculate that magnetic fields amplified in such extreme conditions might lead to the formation of massive bipolar outflows that can remove most of the disk's energy and angular momentum. It is this energy and angular momentum removal that allows the very high mass accretion rate onto main sequence stars.

  15. Binary interactions with high accretion rates onto main sequence stars

    NASA Astrophysics Data System (ADS)

    Shiber, Sagiv; Schreier, Ron; Soker, Noam

    2016-07-01

    Energetic outflows from main sequence stars accreting mass at very high rates might account for the powering of some eruptive objects, such as merging main sequence stars, major eruptions of luminous blue variables, e.g., the Great Eruption of Eta Carinae, and other intermediate luminosity optical transients (ILOTs; red novae; red transients). These powerful outflows could potentially also supply the extra energy required in the common envelope process and in the grazing envelope evolution of binary systems. We propose that a massive outflow/jets mediated by magnetic fields might remove energy and angular momentum from the accretion disk to allow such high accretion rate flows. By examining the possible activity of the magnetic fields of accretion disks, we conclude that indeed main sequence stars might accrete mass at very high rates, up to ≈ 10-2 M ⊙ yr-1 for solar type stars, and up to ≈ 1 M ⊙ yr-1 for very massive stars. We speculate that magnetic fields amplified in such extreme conditions might lead to the formation of massive bipolar outflows that can remove most of the disk's energy and angular momentum. It is this energy and angular momentum removal that allows the very high mass accretion rate onto main sequence stars.

  16. A DOUBLE MAIN SEQUENCE IN THE GLOBULAR CLUSTER NGC 6397

    SciTech Connect

    Milone, A. P.; Aparicio, A.; Marino, A. F.; Piotto, G.; Bedin, L. R.; Anderson, J.; Cassisi, S.; Rich, R. M. E-mail: aparicio@iac.es E-mail: giampaolo.piotto@unipd.it E-mail: bedin@stsci.edu E-mail: rmr@astro.ucla.edu

    2012-01-20

    High-precision multi-band Hubble Space Telescope (HST) photometry reveals that the main sequence of the globular cluster NGC 6397 splits into two components, containing {approx}30% and {approx}70% of the stars. This double sequence is consistent with the idea that the cluster hosts two stellar populations: (1) a primordial population that has a composition similar to field stars, containing {approx}30% of the stars, and (2) a second generation with enhanced sodium and nitrogen, depleted carbon and oxygen, and a slightly enhanced helium abundance ({Delta}Y {approx} 0.01). We examine the color difference between the two sequences across a variety of color baselines and find that the second sequence is anomalously faint in m{sub F336W}. Theoretical isochrones indicate that this could be due to NH depletion.

  17. The evolution of massive stars and their spectra. I. A non-rotating 60 M⊙ star from the zero-age main sequence to the pre-supernova stage

    NASA Astrophysics Data System (ADS)

    Groh, Jose H.; Meynet, Georges; Ekström, Sylvia; Georgy, Cyril

    2014-04-01

    For the first time, the interior and spectroscopic evolution of a massive star is analyzed from the zero-age main sequence (ZAMS) to the pre-supernova (SN) stage. For this purpose, we combined stellar evolution models using the Geneva code and stellar atmospheric/wind models using CMFGEN. With our approach, we were able to produce observables, such as a synthetic high-resolution spectrum and photometry, thereby aiding the comparison between evolution models and observed data. Here we analyze the evolution of a non-rotating 60 M⊙ star and its spectrum throughout its lifetime. Interestingly, the star has a supergiant appearance (luminosity class I) even at the ZAMS. We find the following evolutionary sequence of spectral types: O3 I (at the ZAMS), O4 I (middle of the H-core burning phase), B supergiant (BSG), B hypergiant (BHG), hot luminous blue variable (LBV; end of H-core burning), cool LBV (H-shell burning through the beginning of the He-core burning phase), rapid evolution through late WN and early WN, early WC (middle of He-core burning), and WO (end of He-core burning until core collapse). We find the following spectroscopic phase lifetimes: 3.22 × 106 yr for the O-type, 0.34 × 105 yr (BSG), 0.79 × 105 yr (BHG), 2.35 × 105 yr (LBV), 1.05 × 105 yr (WN), 2.57 × 105 yr (WC), and 3.80 × 104 yr (WO). Compared to previous studies, we find a much longer (shorter) duration for the early WN (late WN) phase, as well as a long-lived LBV phase. We show that LBVs arise naturally in single-star evolution models at the end of the MS when the mass-loss rate increases as a consequence of crossing the bistability limit. We discuss the evolution of the spectra, magnitudes, colors, and ionizing flux across the star's lifetime, and the way they are related to the evolution of the interior. We find that the absolute magnitude of the star typically changes by ~6 mag in optical filters across the evolution, with the star becoming significantly fainter in optical filters at

  18. Pre-main-sequence isochrones - II. Revising star and planet formation time-scales

    NASA Astrophysics Data System (ADS)

    Bell, Cameron P. M.; Naylor, Tim; Mayne, N. J.; Jeffries, R. D.; Littlefair, S. P.

    2013-09-01

    We have derived ages for 13 young (<30 Myr) star-forming regions and find that they are up to a factor of 2 older than the ages typically adopted in the literature. This result has wide-ranging implications, including that circumstellar discs survive longer (≃ 10-12 Myr) and that the average Class I lifetime is greater (≃1 Myr) than currently believed. For each star-forming region, we derived two ages from colour-magnitude diagrams. First, we fitted models of the evolution between the zero-age main sequence and terminal-age main sequence to derive a homogeneous set of main-sequence ages, distances and reddenings with statistically meaningful uncertainties. Our second age for each star-forming region was derived by fitting pre-main-sequence stars to new semi-empirical model isochrones. For the first time (for a set of clusters younger than 50 Myr), we find broad agreement between these two ages, and since these are derived from two distinct mass regimes that rely on different aspects of stellar physics, it gives us confidence in the new age scale. This agreement is largely due to our adoption of empirical colour-Teff relations and bolometric corrections for pre-main-sequence stars cooler than 4000 K. The revised ages for the star-forming regions in our sample are: ˜2 Myr for NGC 6611 (Eagle Nebula; M 16), IC 5146 (Cocoon Nebula), NGC 6530 (Lagoon Nebula; M 8) and NGC 2244 (Rosette Nebula); ˜6 Myr for σ Ori, Cep OB3b and IC 348; ≃10 Myr for λ Ori (Collinder 69); ≃11 Myr for NGC 2169; ≃12 Myr for NGC 2362; ≃13 Myr for NGC 7160; ≃14 Myr for χ Per (NGC 884); and ≃20 Myr for NGC 1960 (M 36).

  19. Finding the Onset of Convection in Main Sequence Stars

    NASA Technical Reports Server (NTRS)

    Simon, Theodore

    2003-01-01

    The primary goal of the work performed under this grant was to locate, if possible, the onset of subphotospheric convection zones in normal main sequence stars by using the presence of emission in high temperature lines in far ultraviolet spectra from the FUSE spacecraft as a proxy for convection. The change in stellar structure represented by this boundary between radiative and convective stars has always been difficult to find by other empirical means. A search was conducted through observations of a sample of A-type stars, which were somewhat hotter and more massive than the Sun, and which were carefully chosen to bridge the theoretically expected radiative/convective boundary line along the main sequence.

  20. Are blue supergiants descendants of magnetic main sequence stars?

    NASA Astrophysics Data System (ADS)

    Petermann, Ilka; Langer, Norbert

    2013-06-01

    Red and blue supergiants are, together with luminous blue variables and Wolf-Rayet stars, evolved phases of massive (OB) stars. The position of blue supergiants (BSG) near the main sequence band cannot be reproduced by standard stellar evolution calculations. However, the assumption of a reduced convective core mass during the main sequence (MS) due to strong internal magnetic fields, established in roughly 10% of all stars on the upper MS, can recover this BSG population. For our calculations of the (non-rotating) massive stars at solar metallicity we used the 1D stellar evolution code MESA and compare their evolutionary tracks with positions from stars obtained from the VLT Flames survey of massive stars.

  1. An observational approach to convection in main sequence stars

    NASA Astrophysics Data System (ADS)

    Régulo, C.; Vázquez Ramió, H.; Roca Cortés, T.

    2005-12-01

    Observational results concerning possible changes in the granulation of Main Sequence stars were found by analysing their seismic power spectra obtained from photometric microvariability. We analysed as many as 178 stars with spectral types F, G, K, and M observed for 54 days. We present evidence of changes in the lifetime and contrast of the granulation, which both increase from F to M stars, although within the limit of resolution.

  2. Nearby main sequence stars with cool circumstellar material

    NASA Technical Reports Server (NTRS)

    Backman, Dana E.; Paresce, Francesco

    1991-01-01

    The discovery of the so-called Vega phenomenon was one of the most important and unexpected results of the IRAS mission. Several nearby main sequence stars were found to possess clouds of solid grains emitting strongly in the far-IR. Three of these objects were marginally resolved by IRAS. This phenomenon appears to be widespread and not limited to proto-planetary epochs. Possible connection of this phenomenon to the existing of planets is discussed.

  3. On the POST main sequence expansion of low mass stars

    NASA Astrophysics Data System (ADS)

    Deinzer, W.

    1999-02-01

    The post main sequence expansion of stars is investigated by means of a simple composite configuration: an isothermal He-core (allowing for non-relativistic electron degeneracy) is surrounded by a H-envelope of constant density (polytrope \\(n=0 \\)). Solving the equations of hydrostatic equilibrium for fixed values of total mass and temperature at the interface a one dimensional sequence of models is obtained with the mass of the core as parameter. As soon as the main part of the core becomes fully degenerate, the model stars expand rapidly. This behaviour is in good agreement with that of models obtained by numerical simulations. The expansion is caused by an intermediate non-degenerate layer of large extension (but of very small mass content) just below the interface. It shifts the envelope to larger distances from the center and thus reduces the gravitational pull on it due to the highly contracted part of the core. Without this layer the thermal forces of the envelope - determined by the hydrogen burning temperatures at the interface - would be much too small to balance gravity. Such a loosely bound envelope extends to the large radii in question. Hence, the model suggests the fixed temperature required by hydrogen burning to be the ultimate reason for the post main sequence expansion.

  4. Ultraviolet emission from main-sequence companions of AGB stars

    NASA Astrophysics Data System (ADS)

    Ortiz, Roberto; Guerrero, Martín A.

    2016-09-01

    Although the majority of known binary asymptotic giant branch (AGB) stars are symbiotic systems (i.e. with a white dwarf as a secondary star), main-sequence companions of AGB stars can be more numerous, even though they are more difficult to find because the primary high luminosity hampers the detection of the companion at visual wavelengths. However, in the ultraviolet the flux emitted by a secondary with Teff > 5500 ˜ 6000 K may prevail over that of the primary, and then it can be used to search for candidates to binary AGB stars. In this work, theoretical atmosphere models are used to calculate the UV excess in the GALEX near- and far-UV bands due to a main-sequence companion. After analysing a sample of confirmed binary AGB stars, we propose as a criterium for binarity: (1) the detection of the AGB star in the GALEX far-UV band and/or (2) a GALEX near-UV observed-to-predicted flux ratio >20. These criteria have been applied to a volume-limited sample of AGB stars within 500 pc of the Sun; 34 out of the sample of 58 AGB stars (˜60 per cent) fulfill them, implying to have a main-sequence companion of spectral type earlier than K0. The excess in the GALEX near- and far-UV bands cannot be attributed to a single temperature companion star, thus suggesting that the UV emission of the secondary might be absorbed by the extended atmosphere and circumstellar envelope of the primary or that UV emission is produced in accretion flows.

  5. Stochastically excited oscillations in the upper main sequence

    NASA Astrophysics Data System (ADS)

    Antoci, Victoria

    2014-02-01

    Convective envelopes in stars on the main sequence are usually connected only with stars of spectral types F5 or later. However, observations as well as theory indicate that the convective outer layers in hotter stars, despite being shallow, are still effective and turbulent enough to stochastically excite oscillations. Because of the low amplitudes, exploring stochastically excited pulsations became possible only with space missions such as Kepler and CoRoT. Here I review the recent results and discuss among others, pulsators such as δ Scuti, γ Doradus, roAp, β Cephei, Slowly Pulsating B and Be stars, all in the context of solar-like oscillations.

  6. Evolution of Pre-Main Sequence Accretion Disks

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee W.

    2003-01-01

    The aim of this project is to develop a comprehensive global picture of the physical conditions in, and evolutionary timescales of, pre-main sequence accretion disks. The results of this work will help constrain the initial conditions for planet formation. To this end we are developing much larger samples of 3-10 Myr-old stars to provide better empirical constraints on protoplanetary disk evolution; measuring disk accretion rates in these systems; and constructing detailed model disk structures consistent with observations to infer physical conditions such as grain growth in protoplanetary disks.

  7. Environmental impact analysis for the main accidental sequences of ignitor

    SciTech Connect

    Carpignano, A.; Francabandiera, S.; Vella, R.; Zucchetti, M.

    1996-12-31

    A safety analysis study has been applied to the Ignitor machine using Probabilistic Safety Assessment. The main initiating events have been identified, and accident sequences have been studied by means of traditional methods such as Failure Mode and Effect Analysis (FMEA), Fault Trees (FT) and Event Trees (ET). The consequences of the radioactive environmental releases have been assessed in terms of Effective Dose Equivalent (EDEs) to the Most Exposed Individuals (MEI) of the chosen site, by means of a population dose code. Results point out the low enviromental impact of the machine. 13 refs., 1 fig., 3 tabs.

  8. Cool circumstellar matter around nearby main-sequence stars

    NASA Technical Reports Server (NTRS)

    Walker, H. J.; Wolstencroft, R. D.

    1988-01-01

    Stars are presented which have characteristics similar to Vega and other main-sequence stars with cool dust disks, based on the IRAS Point Source Catalog fluxes. The objects are selected to have a 60-micron/100-micron ratio similar to Vega, Beta Pic, Alpha PsA, and Epsilon Eri, and they are also required to show evidence of extension in the IRAS Working Survey Database. The fluxes are modeled using a blackbody energy distribution. The temperatures derived range from 50 to 650 K. The diameters of the dust disks observed by IRAS are estimated.

  9. Spatially Resolved Star Formation Main Sequence of Galaxies

    NASA Astrophysics Data System (ADS)

    Cano-Díaz, M.; Sánchez, S. F.; Zibetti, S.; Ascaribar, Y.; Bland-Hawthorn, J.; Ziegler, B.; González-Delgado, R. M.; Walcher, C. J.; García-Benito, R.; Mast, D.; Mendoza-Pérez, M. A.; Falcón-Barroso, J.; Galbany, L.; Husemann, B.; Kehring, C.; Marino, R. A.; Sánchez-Blázquez, P.; López-Cobá, C.; López-Sánchez, A. R.; Vilchez, J. M.

    2016-06-01

    The relation known as Star Formation Main Sequence (SFMS) of galaxies is defined in terms of stellar mass and star formation rate. This approximately linear relation has been proven to be tight and holds for several star formation indicators at local and at high redshifts. In this talk I will show recent results about our first attempts to study the Spatially Resolved SFMS, using integral field spectroscopic data, coming primarily from the CALIFA survey. I will present as a main result that a local SFMS is found with a slope and zero point of 0.72 +/ 0.04, and -7.95 +/ 0.29 respectively. I will also discuss the influence of characteristics such as environment and morphology in the relation. Finally I will present some extensions of these results for data com in from the MaNGA survey.

  10. Dissecting the Quasar Main Sequence: Insight from Host Galaxy Properties

    NASA Astrophysics Data System (ADS)

    Sun, Jiayi; Shen, Yue

    2015-05-01

    The diverse properties of broad-line quasars appear to follow a well-defined main sequence along which the optical Fe ii strength increases. It has been suggested that this sequence is mainly driven by the Eddington ratio (L/LEdd) of the black hole (BH) accretion. Shen & Ho demonstrated with quasar clustering analysis that the average BH mass decreases with increasing Fe ii strength when quasar luminosity is fixed, consistent with this suggestion. Here we perform an independent test by measuring the stellar velocity dispersion σ* (hence, the BH mass via the M-σ* relation) from decomposed host spectra in low-redshift Sloan Digital Sky Survey quasars. We found that at fixed quasar luminosity, σ* systematically decreases with increasing Fe ii strength, confirming that the Eddington ratio increases with Fe ii strength. We also found that at fixed luminosity and Fe ii strength, there is little dependence of σ* on the broad Hβ FWHM. These new results reinforce the framework that the Eddington ratio and orientation govern most of the diversity seen in broad-line quasar properties.

  11. DISSECTING THE QUASAR MAIN SEQUENCE: INSIGHT FROM HOST GALAXY PROPERTIES

    SciTech Connect

    Sun, Jiayi; Shen, Yue

    2015-05-01

    The diverse properties of broad-line quasars appear to follow a well-defined main sequence along which the optical Fe ii strength increases. It has been suggested that this sequence is mainly driven by the Eddington ratio (L/L{sub Edd}) of the black hole (BH) accretion. Shen and Ho demonstrated with quasar clustering analysis that the average BH mass decreases with increasing Fe ii strength when quasar luminosity is fixed, consistent with this suggestion. Here we perform an independent test by measuring the stellar velocity dispersion σ{sub *} (hence, the BH mass via the M–σ{sub *} relation) from decomposed host spectra in low-redshift Sloan Digital Sky Survey quasars. We found that at fixed quasar luminosity, σ{sub *} systematically decreases with increasing Fe ii strength, confirming that the Eddington ratio increases with Fe ii strength. We also found that at fixed luminosity and Fe ii strength, there is little dependence of σ{sub *} on the broad Hβ FWHM. These new results reinforce the framework that the Eddington ratio and orientation govern most of the diversity seen in broad-line quasar properties.

  12. Orbital motion in pre-main sequence binaries

    SciTech Connect

    Schaefer, G. H.; Prato, L.; Simon, M.; Patience, J.

    2014-06-01

    We present results from our ongoing program to map the visual orbits of pre-main sequence (PMS) binaries in the Taurus star forming region using adaptive optics imaging at the Keck Observatory. We combine our results with measurements reported in the literature to analyze the orbital motion for each binary. We present preliminary orbits for DF Tau, T Tau S, ZZ Tau, and the Pleiades binary HBC 351. Seven additional binaries show curvature in their relative motion. Currently, we can place lower limits on the orbital periods for these systems; full solutions will be possible with more orbital coverage. Five other binaries show motion that is indistinguishable from linear motion. We suspect that these systems are bound and might show curvature with additional measurements in the future. The observations reported herein lay critical groundwork toward the goal of measuring precise masses for low-mass PMS stars.

  13. ON THE DIFFERENTIAL ROTATION OF MASSIVE MAIN-SEQUENCE STARS

    SciTech Connect

    Rogers, T. M.

    2015-12-20

    To date, asteroseismology has provided core-to-surface differential rotation measurements in eight main-sequence stars. These stars, ranging in mass from ∼1.5–9 M{sub ⊙}, show rotation profiles ranging from uniform to counter-rotation. Although they have a variety of masses, these stars all have convective cores and overlying radiative regions, conducive to angular momentum transport by internal gravity waves (IGWs). Using two-dimensional numerical simulations, we show that angular momentum transport by IGWs can explain all of these rotation profiles. We further predict that, should high mass, faster rotating stars be observed, the core-to-envelope differential rotation will be positive, but less than one.

  14. Condition for Convective Cores in Main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Monteiro, M. J. P. F. G.

    1990-09-01

    The aim of this work is to find the condition for the existence of convective cores in homogenous main sequence stars where the opacity per unit mass is $k=k_0ρα T-β and the energy generation rate per unit mass is ɛ=ɛ0ρ Tη (ρ and T being the density and the temperature, respectively). Numerical models of stars with different values of α, β and η are constructed and the condition for the existence of a convective core in terms of the relation between α, β and η determined. Forty points η=η(α,β) are determined for αin[0,2] and βin[0,4] and the condition is found to be η = - 3.3294; α + 2.0243; β + 1.8393

  15. The circumstellar environments of intermediate mass main sequence stars

    NASA Technical Reports Server (NTRS)

    Grady, Carol A.

    1993-01-01

    Analysis of archival Infrared Astronomy Satellite (IRAS) and International Ultraviolet Explorer (IUE) data resulted in identification of accreting gas toward a 2.8 Myr post-Herbig Be star in the R CrA star formation region, and identification of accreting gas toward HD 93563, previously identified as a classical Be star. Accreting gas was also detected toward two B(e) stars of previously controversial evolutionary state, resulting in identification of these systems as pre-Main Sequence Herbig Be stars viewed edge-on to their circumstellar disks. In parallel with this effort, accreting gas was detected toward the Herbig Ae star HR 5999, resulting in development of identification criteria for edge-on PMS proto-planetary disk systems. The work on individual stars is described.

  16. An Assessment of Dynamical Mass Constraints on Pre-Main-Sequence Evolutionary Tracks

    NASA Astrophysics Data System (ADS)

    Hillenbrand, Lynne A.; White, Russel J.

    2004-04-01

    , but the case for this is not compelling, given the similar warm offset at older ages between most sets of tracks and the empirical main sequence. Over all age ranges, the systematic discrepancies between track-predicted and dynamically determined masses appear to be dominated by inaccuracies in the treatment of convection and in the adopted opacities.

  17. Massive main-sequence stars evolving at the Eddington limit

    NASA Astrophysics Data System (ADS)

    Sanyal, D.; Grassitelli, L.; Langer, N.; Bestenlehner, J. M.

    2015-08-01

    Context. Massive stars play a vital role in the Universe, however, their evolution even on the main-sequence is not yet well understood. Aims: Because of the steep mass-luminosity relation, massive main-sequence stars become extremely luminous. This brings their envelopes very close to the Eddington limit. We analyse stellar evolutionary models in which the Eddington limit is reached and exceeded, explore the rich diversity of physical phenomena that take place in their envelopes, and investigate their observational consequences. Methods: We use published grids of detailed stellar models, computed with a state-of-the-art, one-dimensional hydrodynamic stellar evolution code using LMC composition, to investigate the envelope properties of core hydrogen burning massive stars. Results: We find that the Eddington limit is almost never reached at the stellar surface, even for stars up to 500 M⊙. When we define an appropriate Eddington limit locally in the stellar envelope, we can show that most stars more massive than ~40 M⊙ actually exceed this limit, in particular, in the partial ionisation zones of iron, helium, or hydrogen. While most models adjust their structure such that the local Eddington limit is exceeded at most by a few per cent, our most extreme models do so by a factor of more than seven. We find that the local violation of the Eddington limit has severe consequences for the envelope structure, as it leads to envelope inflation, convection, density inversions, and, possibly to, pulsations. We find that all models with luminosities higher than 4 × 105L⊙, i.e. stars above ~40 M⊙ show inflation, with a radius increase of up to a factor of about 40. We find that the hot edge of the S Dor variability region coincides with a line beyond which our models are inflated by more than a factor of two, indicating a possible connection between S Dor variability and inflation. Furthermore, our coolest models show highly inflated envelopes with masses of up to

  18. Constraints on pre-main-sequence evolution from stellar pulsations

    NASA Astrophysics Data System (ADS)

    Casey, M. P.; Zwintz, K.; Guenther, D. B.

    2014-02-01

    Pulsating pre-main-sequence (PMS) stars afford the earliest opportunity in the lifetime of a star to which the concepts of asteroseismology can be applied. PMS stars should be structurally simpler than their evolved counterparts, thus (hopefully!) making any asteroseismic analysis relatively easier. Unfortunately, this isn't necessarily the case. The majority of these stars (around 80) are δ Scuti pulsators, with a couple of γ Doradus, γ Doradus - δ Scuti hybrids, and slowly pulsating B stars thrown into the mix. The majority of these stars have only been discovered within the last ten years, with the community still uncovering the richness of phenomena associated with these stars, many of which defy traditional asteroseismic analysis. A systematic asteroseismic analysis of all of the δ Scuti PMS stars was performed in order to get a better handle on the properties of these stars as a group. Some strange results have been found, including one star pulsating up to the theoretical acoustic cut-off frequency of the star, and a number of stars in which the most basic asteroseismic analysis suggests problems with the stars' positions in the Hertzsprung-Russell diagram. From this we get an idea of the\\break constraints - or lack thereof - that these results can put on PMS stellar evolution.

  19. Planetary Systems Associated with Main-Sequence Stars.

    PubMed

    Brown, H

    1964-09-11

    The luminosity function is used to estimate the number of invisible planet-like objects in the neighborhood of the sun, taking into account the likely chemical composition of planets in relation to the composition of main-sequence stars. There may be about 60 objects more massive than Mars for every visible star. An attempt is made to estimate the distribution of these planet-like cold bodies in relation to stars. It is suggested that stars, together with cold objects, were formed in clusters of bodies of random size distribution. Clusters averaging about 50 bodies each account for the observed distribution of frequencies of double and triple star systems relative to single stars. On this basis, virtually every star should have a planetary system associated with it. As a corollary, systems of cold bodies in which there are no luminous stars should be abundant. The possible distribution of planets around such stars has been studied, making use of the observed orbital characteristics of double star systems. It is concluded that favorable conditions for life processes may be far more abundant than has generally been thought possible.

  20. Planetary Systems Associated with Main-Sequence Stars.

    PubMed

    Brown, H

    1964-09-11

    The luminosity function is used to estimate the number of invisible planet-like objects in the neighborhood of the sun, taking into account the likely chemical composition of planets in relation to the composition of main-sequence stars. There may be about 60 objects more massive than Mars for every visible star. An attempt is made to estimate the distribution of these planet-like cold bodies in relation to stars. It is suggested that stars, together with cold objects, were formed in clusters of bodies of random size distribution. Clusters averaging about 50 bodies each account for the observed distribution of frequencies of double and triple star systems relative to single stars. On this basis, virtually every star should have a planetary system associated with it. As a corollary, systems of cold bodies in which there are no luminous stars should be abundant. The possible distribution of planets around such stars has been studied, making use of the observed orbital characteristics of double star systems. It is concluded that favorable conditions for life processes may be far more abundant than has generally been thought possible. PMID:17743661

  1. Habitable Zones of Post-Main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Ramirez, Ramses M.; Kaltenegger, Lisa

    2016-05-01

    Once a star leaves the main sequence and becomes a red giant, its Habitable Zone (HZ) moves outward, promoting detectable habitable conditions at larger orbital distances. We use a one-dimensional radiative-convective climate and stellar evolutionary models to calculate post-MS HZ distances for a grid of stars from 3700 to 10,000 K (˜M1 to A5 stellar types) for different stellar metallicities. The post-MS HZ limits are comparable to the distances of known directly imaged planets. We model the stellar as well as planetary atmospheric mass loss during the Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) phases for super-Moons to super-Earths. A planet can stay between 200 million years up to 9 Gyr in the post-MS HZ for our hottest and coldest grid stars, respectively, assuming solar metallicity. These numbers increase for increased stellar metallicity. Total atmospheric erosion only occurs for planets in close-in orbits. The post-MS HZ orbital distances are within detection capabilities of direct imaging techniques.

  2. Submillimeter Imaging of Dust Around Main Sequence Stars

    NASA Technical Reports Server (NTRS)

    Jewitt, David

    1998-01-01

    This grant was to image circumstellar dust disks surrounding main-sequence stars. The delivery of the SCUBA detector we had planned to use for this work was delayed repeatedly, leading us to undertake a majority of the observations with the UKT14 submillimeter detector at the JCMT (James Clerk Maxwell Telescope) and optical imagers and a coronagraph at the University of Hawaii 2.2-m telescope. Major findings under this grant include: (1) We discovered 5 asymmetries in the beta Pictoris regenerated dust disk. The discovery of these asymmetries was a surprise, since smearing due to Keplerian shear should eliminate most such features on timescales of a few thousand years. One exception is the "wing tilt" asymmetry, which we interpret as due to the scattering phase function of dust disk particles. From the wing tilt and a model of the phase function, we find a disk plane inclination to the line of sight of < 5 degrees. Other asymmetries (e.g. the butterfly asymmetry) suggest a disk that has been recently disturbed. We searched for possible nearby perturbers but found no clear candidates. Low mass stars (M dwarfs) and brown dwarfs would have fallen beneath the sensitivity threshhold of our survey, however. (2) We calculated a set of disk models to assess the detectability of dust disks around stars as a function of (a) distance, (b) disk, inclination (c) dust optical depth/mass, and (d) imaging resolution. These models guided our observational strategy on Mauna Kea. (3) We performed a coronagraphic survey of approx. 100 main-sequence stars in search of additional examples of circumstellar disks. The best new candidate disk, around the 5 M(sun) star BD+31deg.643, is distinguished by its large extent (few x 10( exp 3) AU). This disk, if real, cannot be rotationally supported. We suggest that the dust particles are ejected from a smaller, unseen disk (Kuiper Belt?) by strong radiation pressure forces due to the high luminosity central star. (4) SCUBA images of

  3. Evidence of magnetic field decay in massive main-sequence stars

    NASA Astrophysics Data System (ADS)

    Fossati, L.; Schneider, F. R. N.; Castro, N.; Langer, N.; Simón-Díaz, S.; Müller, A.; de Koter, A.; Morel, T.; Petit, V.; Sana, H.; Wade, G. A.

    2016-08-01

    A significant fraction of massive main-sequence stars show strong, large-scale magnetic fields. The origin of these fields, their lifetimes, and their role in shaping the characteristics and evolution of massive stars are currently not well understood. We compile a catalogue of 389 massive main-sequence stars, 61 of which are magnetic, and derive their fundamental parameters and ages. The two samples contain stars brighter than magnitude 9 in the V-band and range in mass between 5 and 100 M⊙. We find that the fractional main-sequence age distribution of all considered stars follows what is expected for a magnitude limited sample, while that of magnetic stars shows a clear decrease towards the end of the main sequence. This dearth of old magnetic stars is independent of the choice of adopted stellar evolution tracks, and appears to become more prominent when considering only the most massive stars. We show that the decreasing trend in the distribution is significantly stronger than expected from magnetic flux conservation. We also find that binary rejuvenation and magnetic suppression of core convection are unlikely to be responsible for the observed lack of older magnetic massive stars, and conclude that its most probable cause is the decay of the magnetic field, over a time span longer than the stellar lifetime for the lowest considered masses, and shorter for the highest masses. We then investigate the spin-down ages of the slowly rotating magnetic massive stars and find them to exceed the stellar ages by far in many cases. The high fraction of very slowly rotating magnetic stars thus provides an independent argument for a decay of the magnetic fields.

  4. Dust around main-sequence and supergiant stars

    NASA Astrophysics Data System (ADS)

    Sylvester, Roger James

    This thesis is a study of the properties of the dust around two rather different types of star. The first part is concerned with the mid-infrared emission from a sample of 16 M-type supergiants. As well as silicate emission features, seven of the stars showed the UIR (unidentified infrared) emission bands, associated with carbonaceous material. According to standard theory, all the carbon in the outflows from these oxygen-rich stars should be bound up in CO molecules, preventing the formation of carbonaceous dust. The results were interpreted in terms of a non-equilibrium chemical model, which invoked chromospheric UV photons to dissociate CO, allowing carbonaceous material to form, and to excite the observed UIR-band emission. The larger part of the thesis considers Vega-excess stars - main sequence stars with excess infrared emission from circumstellar dust discs. Photometric and spectroscopic observations were carried out. A number of the stars displayed excess near-IR emission, indicating the presence of hot material. Mid-infrared spectroscopy enabled the grain composition to be identified: both silicates and carbonaceous species were detected. Millimetre and submillimetre photometry indicated that large grains are present around many of our sources, implying that significant grain coagulation has occurred. Most of the sources were modelled using a radiative transfer code, with disc geometry and multiple grain sizes. Two grain materials, astronomical silicate and amorphous carbon, were considered. Successful fits to the spectral energy distributions at mid-IR and longer wavelengths were found. The temperatures needed to produce near-IR excess emission were too high for grains in thermal equilibrium to survive. A model was therefore developed with very small grains undergoing thermal spiking due to single-photon absorption, which provided satisfactory fits for the hottest stars; the others had insufficient UV flux to excite the small grains.

  5. On the Eccentricity Excitation in Post-main-sequence Binaries

    NASA Astrophysics Data System (ADS)

    Rafikov, Roman R.

    2016-10-01

    Several classes of stellar binaries with post-main-sequence (post-MS) components—millisecond pulsars with the white dwarf companions (MSP+WD) and periods of {P}b∼ 30 days, binaries hosting post-asymptotic giant branch stars, or barium stars with {P}b ∼ several years—feature high eccentricities (up to 0.4) despite the expectation of their efficient tidal circularization during their post-MS evolution. It was suggested that the eccentricities of these binaries can be naturally excited by their tidal coupling to the circumbinary disk, formed by the material ejected from the binary. Here we critically reassess this idea using simple arguments rooted in the global angular momentum conservation of the disk+binary system. Compared to previous studies, we (1) fully account for the viscous spreading of the circumbinary disk, (2) consider the possibility of reaccretion from the disk onto the binary (in agreement with simulations and empirical evidence), and (3) allow for the reduced viscosity after the disk expands, cools, and forms dust. These ingredients conspire to significantly lower the efficiency of eccentricity excitation by the disk tides. We find that explaining eccentricities of the post-MS binaries is difficult and requires massive (≳ {10}-2 {M}ȯ ), long-lived (≳ {10}5 years) circumbinary disks that do not reaccrete. While disk tides may account for the eccentricities of the MSP+WD binaries, we show reaccretion to also be detrimental for these systems. Reduced efficiency of the disk-driven excitation motivates the study of alternative mechanisms for producing the peculiar eccentricities of the post-MS binaries.

  6. Habitable zone lifetimes of exoplanets around main sequence stars.

    PubMed

    Rushby, Andrew J; Claire, Mark W; Osborn, Hugh; Watson, Andrew J

    2013-09-01

    The potential habitability of newly discovered exoplanets is initially assessed by determining whether their orbits fall within the circumstellar habitable zone of their star. However, the habitable zone (HZ) is not static in time or space, and its boundaries migrate outward at a rate proportional to the increase in luminosity of a star undergoing stellar evolution, possibly including or excluding planets over the course of the star's main sequence lifetime. We describe the time that a planet spends within the HZ as its "habitable zone lifetime." The HZ lifetime of a planet has strong astrobiological implications and is especially important when considering the evolution of complex life, which is likely to require a longer residence time within the HZ. Here, we present results from a simple model built to investigate the evolution of the "classic" HZ over time, while also providing estimates for the evolution of stellar luminosity over time in order to develop a "hybrid" HZ model. These models return estimates for the HZ lifetimes of Earth and 7 confirmed HZ exoplanets and 27 unconfirmed Kepler candidates. The HZ lifetime for Earth ranges between 6.29 and 7.79×10⁹ years (Gyr). The 7 exoplanets fall in a range between ∼1 and 54.72 Gyr, while the 27 Kepler candidate planets' HZ lifetimes range between 0.43 and 18.8 Gyr. Our results show that exoplanet HD 85512b is no longer within the HZ, assuming it has an Earth analog atmosphere. The HZ lifetime should be considered in future models of planetary habitability as setting an upper limit on the lifetime of any potential exoplanetary biosphere, and also for identifying planets of high astrobiological potential for continued observational or modeling campaigns.

  7. Habitable zone lifetimes of exoplanets around main sequence stars.

    PubMed

    Rushby, Andrew J; Claire, Mark W; Osborn, Hugh; Watson, Andrew J

    2013-09-01

    The potential habitability of newly discovered exoplanets is initially assessed by determining whether their orbits fall within the circumstellar habitable zone of their star. However, the habitable zone (HZ) is not static in time or space, and its boundaries migrate outward at a rate proportional to the increase in luminosity of a star undergoing stellar evolution, possibly including or excluding planets over the course of the star's main sequence lifetime. We describe the time that a planet spends within the HZ as its "habitable zone lifetime." The HZ lifetime of a planet has strong astrobiological implications and is especially important when considering the evolution of complex life, which is likely to require a longer residence time within the HZ. Here, we present results from a simple model built to investigate the evolution of the "classic" HZ over time, while also providing estimates for the evolution of stellar luminosity over time in order to develop a "hybrid" HZ model. These models return estimates for the HZ lifetimes of Earth and 7 confirmed HZ exoplanets and 27 unconfirmed Kepler candidates. The HZ lifetime for Earth ranges between 6.29 and 7.79×10⁹ years (Gyr). The 7 exoplanets fall in a range between ∼1 and 54.72 Gyr, while the 27 Kepler candidate planets' HZ lifetimes range between 0.43 and 18.8 Gyr. Our results show that exoplanet HD 85512b is no longer within the HZ, assuming it has an Earth analog atmosphere. The HZ lifetime should be considered in future models of planetary habitability as setting an upper limit on the lifetime of any potential exoplanetary biosphere, and also for identifying planets of high astrobiological potential for continued observational or modeling campaigns. PMID:24047111

  8. Stellar winds on the main-sequence. I. Wind model

    NASA Astrophysics Data System (ADS)

    Johnstone, C. P.; Güdel, M.; Lüftinger, T.; Toth, G.; Brott, I.

    2015-05-01

    Aims: We develop a method for estimating the properties of stellar winds for low-mass main-sequence stars between masses of 0.4 M⊙ and 1.1 M⊙ at a range of distances from the star. Methods: We use 1D thermal pressure driven hydrodynamic wind models run using the Versatile Advection Code. Using in situ measurements of the solar wind, we produce models for the slow and fast components of the solar wind. We consider two radically different methods for scaling the base temperature of the wind to other stars: in Model A, we assume that wind temperatures are fundamentally linked to coronal temperatures, and in Model B, we assume that the sound speed at the base of the wind is a fixed fraction of the escape velocity. In Paper II of this series, we use observationally constrained rotational evolution models to derive wind mass loss rates. Results: Our model for the solar wind provides an excellent description of the real solar wind far from the solar surface, but is unrealistic within the solar corona. We run a grid of 1200 wind models to derive relations for the wind properties as a function of stellar mass, radius, and wind temperature. Using these results, we explore how wind properties depend on stellar mass and rotation. Conclusions: Based on our two assumptions about the scaling of the wind temperature, we argue that there is still significant uncertainty in how these properties should be determined. Resolution of this uncertainty will probably require both the application of solar wind physics to other stars and detailed observational constraints on the properties of stellar winds. In the final section of this paper, we give step by step instructions for how to apply our results to calculate the stellar wind conditions far from the stellar surface.

  9. BVI CCD photometry of the broad main-sequence globular cluster NGC 1851

    SciTech Connect

    Alcaino, G.; Liller, W.; Alvarado, F.; Wenderoth, E. )

    1990-03-01

    Three-color CCD C-M diagrams are presented for the globular cluster NGC 1851, showing an extreme breadth of the main-sequence, similar to that of Omega Centauri. It is found that the main-sequence turnoff points are located at V(TO) = 19.44 + or - 0.10, with colors at B-V = 0.54 + or - 0.02, V-I = 0.61 + or - 0.02, and B-I = 1.15 + or - 0.03. The best fit to the VandenBerg and Bell (1985) isochrones is shown to be all C-M diagrams with Y = 0.20, Fe/H abundance ratio = -1.27, and (m-M)v = 15.45. It is concluded that NGC 1851 has a Delta V(TO - HB) = 3.34 + or - 0.10 and an age of 16 + or - 2 Gyr. 29 refs.

  10. Spectral class distribution of circumstellar material in main-sequence stars

    NASA Technical Reports Server (NTRS)

    Aumann, H. H.

    1988-01-01

    A detailed statistical evaluation of IRAS survey data of main-sequence stars within 25 pc indicates that the presence of cool shells around A, F, and G main-sequence stars is the rule, rather than the exception. While luminosity bias favors A and F stars, the typical G star still appears to have almost three orders of magnitude more excess than the excess of the solar system due to known zodiacal dust and all planets combined. The Vega effect is thus not restricted to stars of particularly young age. The finding that the 'archetypical' solar system appears to have much less far-IR excess than the majority of G stars supports a speculation that the sun could have a cloud of cold particles beyond the outer planets, undetected by IRAS viewing from earth.

  11. Accreting pre-main-sequence models and abundance anomalies in globular clusters

    NASA Astrophysics Data System (ADS)

    Tognelli, E.; Prada Moroni, P. G.; Degl'Innocenti, S.

    2015-12-01

    We investigated the possibility of producing helium-enhanced stars in globular clusters by accreting polluted matter during the pre-main-sequence phase. We followed the evolution of two different classes of pre-main-sequence accreting models, one which neglects and the other that takes into account the protostellar evolution. We analysed the dependence of the final central helium abundance, of the tracks position in the HR diagram and of the surface lithium abundance evolution on the age at which the accretion of polluted material begins and on the main physical parameters that govern the protostellar evolution. The later is the beginning of the late accretion and the lower are both the central helium and the surface lithium abundances at the end of the accretion phase and in Zero Age Main Sequence (ZAMS). In order to produce a relevant increase of the central helium content the accretion of polluted matter should start at ages lower than 1 Myr. The inclusion of the protostellar evolution has a strong impact on the ZAMS models too. The adoption of a very low seed mass (i.e. 0.001 M⊙) results in models with the lowest central helium and surface lithium abundances. The higher is the accretion rate and the lower is the final helium content in the core and the residual surface lithium. In the worst case - i.e. seed mass 0.001 M⊙ and accretion rate ≥10-5 M⊙ yr-1 - the central helium is not increased at all and the surface lithium is fully depleted in the first few million years.

  12. The mosaic multiple stellar populations in ω Centauri: the horizontal branch and the main sequence

    NASA Astrophysics Data System (ADS)

    Tailo, M.; Di Criscienzo, M.; D'Antona, F.; Caloi, V.; Ventura, P.

    2016-04-01

    We interpret the stellar population of ω Centauri by means of a population synthesis analysis, following the most recent observational guidelines for input metallicities, helium and [(C+N+O)/Fe] contents. We deal at the same time with the main sequences, sub-giant and horizontal branch (HB) data. The reproduction of the observed colour-magnitude features is very satisfying and bears interesting hints concerning the evolutionary history of this peculiar stellar ensemble. Our main results are: (1) no significant spread in age is required to fit the colour-magnitude diagram. Indeed, we can use coeval isochrones for the synthetic populations, and we estimate that the ages fall within a ˜0.5 Gyr time interval; in particular the most metal-rich population can be coeval (in the above meaning) with the others, if its stars are very helium-rich (Y ˜ 0.37) and with the observed CNO enhancement ([(C+N+O)/Fe] = +0.7); (2) a satisfactory fit of the whole HB is obtained, consistent with the choice of the populations providing a good reproduction of the main sequence and sub-giant data; (3) the split in magnitude observed in the red HB is well reproduced assuming the presence of two stellar populations in the two different sequences observed: a metal-poor population made of stars evolving from the blue side (luminous branch) and a metal richer one whose stars are in a stage closer to the zero age HB (dimmer branch). This modelization also fits satisfactorily the period and the [Fe/H] distribution of the RR Lyrae stars.

  13. Can rotation explain the multiple main-sequence turn-offs of Magellanic Cloud star clusters?

    NASA Astrophysics Data System (ADS)

    Girardi, Léo; Eggenberger, Patrick; Miglio, Andrea

    2011-03-01

    Many intermediate-age star clusters in the Magellanic Clouds present multiple main-sequence turn-offs (MMSTOs), which challenge the classical idea that star formation in such objects took place over short time-scales. It has been recently suggested that the presence of fast rotators among main-sequence stars could be the cause of such features, hence relaxing the need for extended periods of star formation. In this Letter, we compute evolutionary tracks and isochrones of models with and without rotation. We find that, for the same age and input physics, both kinds of models present turn-offs with an almost identical position in the colour-magnitude diagrams (CMDs). As a consequence, a dispersion of rotational velocities in coeval ensembles of stars could not explain the presence of MMSTOs. We construct several synthetic CMDs for the different kinds of tracks and combinations of them. The models that best reproduce the morphology of observed MMSTOs are clearly those assuming a significant spread in the stellar ages - as long as ˜400 Myr - added to a moderate amount of convective core overshooting. Only these models produce the detailed ‘golf club’ shape of observed MMSTOs. A spread in rotational velocities alone cannot do anything similar. We also discuss models involving a mixture of stars with and without overshooting, as an additional scenario to producing MMSTOs with coeval populations. We find that they produce turn-offs with a varying extension in the CMD direction perpendicular to the lower main sequence, which are clearly not present in observed MMSTOs.

  14. Magnetic Activity of Pre-main Sequence Stars near the Stellar-Substellar Boundary

    NASA Astrophysics Data System (ADS)

    Principe, David; Kastner, Joel. H.; Rodriguez, David

    2016-01-01

    X-ray observations of pre-main sequence (pre-MS) stars of M-type probe coronal emission and offer a means to investigate magnetic activity at the stellar-substellar boundary. Recent observations of main sequence (MS) stars at this boundary display a decrease in fractional X-ray luminosity (L X /L bol ) by almost two orders of magnitude for spectral types M7 and later. We investigate magnetic activity and search for a decrease in X-ray emission in the pre-MS progenitors of these MS stars. We present XMM-Newton X-ray observations and preliminary results for ~10 nearby (30-70 pc), very low mass pre-MS stars in the relatively unexplored age range of 10-30 Myr. We compare the fractional X-ray luminosities of these 10-30 Myr old stars to younger (1-3 Myr) pre-MS brown dwarfs and find no dependence on spectral type or age suggesting that X-ray activity declines at an age later than ~30 Myr in these very low-mass stars.

  15. Main-sequence stars with circumstellar solid material - The Vega phenomenon

    NASA Technical Reports Server (NTRS)

    Backman, Dana E.; Paresce, Francesco

    1993-01-01

    The detection of solid grains with temperatures of 50 to 125 K and fractional bolometric luminosities in the range 10 exp -5 to 10 exp -3 early in the IRAS mission around three nearby A main-sequence stars, Alpha Lyrae (Vega), Alpha Piscis Austrinus (Fomalhaut), and Beta Pictoris, is discussed. Spatial resolution of the emission indicates that: the grains are larger than interstellar grains, the material probably lies in disks in the stellar equatorial planes, the disks extend to distances of 100 to 1000 AU from the stars, and zones a few tens of AU in radius around the central stars are relatively empty. Subsequent surveys of IRAS data reveal more than 100 main-sequence stars of all spectral classes having unresolved excesses with similar temperatures and fractional luminosities to the three prototypes. Some stars with excesses have estimated ages of 1 to 5 Gyr. Thus, main-sequence FIR excesses appear to be widespread and are present in systems old enough to be probably past the stage of active planet formation.

  16. AGeS: A Software System for Microbial Genome Sequence Annotation

    PubMed Central

    Kumar, Kamal; Desai, Valmik; Cheng, Li; Khitrov, Maxim; Grover, Deepak; Satya, Ravi Vijaya; Yu, Chenggang; Zavaljevski, Nela; Reifman, Jaques

    2011-01-01

    Background The annotation of genomes from next-generation sequencing platforms needs to be rapid, high-throughput, and fully integrated and automated. Although a few Web-based annotation services have recently become available, they may not be the best solution for researchers that need to annotate a large number of genomes, possibly including proprietary data, and store them locally for further analysis. To address this need, we developed a standalone software application, the Annotation of microbial Genome Sequences (AGeS) system, which incorporates publicly available and in-house-developed bioinformatics tools and databases, many of which are parallelized for high-throughput performance. Methodology The AGeS system supports three main capabilities. The first is the storage of input contig sequences and the resulting annotation data in a central, customized database. The second is the annotation of microbial genomes using an integrated software pipeline, which first analyzes contigs from high-throughput sequencing by locating genomic regions that code for proteins, RNA, and other genomic elements through the Do-It-Yourself Annotation (DIYA) framework. The identified protein-coding regions are then functionally annotated using the in-house-developed Pipeline for Protein Annotation (PIPA). The third capability is the visualization of annotated sequences using GBrowse. To date, we have implemented these capabilities for bacterial genomes. AGeS was evaluated by comparing its genome annotations with those provided by three other methods. Our results indicate that the software tools integrated into AGeS provide annotations that are in general agreement with those provided by the compared methods. This is demonstrated by a >94% overlap in the number of identified genes, a significant number of identical annotated features, and a >90% agreement in enzyme function predictions. PMID:21408217

  17. Primordial stellar evolution - The pre-main-sequence phase

    NASA Technical Reports Server (NTRS)

    Stahler, S. W.; Palla, F.; Salpeter, E. E.

    1986-01-01

    The quasi-static contraction of primordial stars composed of pure hydrogen and helium gas is studied by following numerically the evolution of a star of five solar masses from the end of protostellar accretion to the onset of hydrogen burning. Although the protostellar core of this mass is radiatively stable and undergoing nonhomologous contraction, its large surface area and luminosity force the star to a partially convective, homologously contracting state within only 100 yr. Deuterium later ignites at an off-center temperature maximum but fails to produce interior convection. The star follows a conventional premain sequence track in the HR diagram, reaching the ZAMS after 1.2 million yr, with a luminosity of 880 solar luminosities and a radius of 1.2 solar radii.

  18. Possible evidence for metal accretion onto the surfaces of metal-poor main-sequence stars

    SciTech Connect

    Hattori, Kohei; Yoshii, Yuzuru; Beers, Timothy C.; Carollo, Daniela; Lee, Young Sun

    2014-04-01

    The entire evolution of the Milky Way, including its mass-assembly and star-formation history, is imprinted onto the chemo-dynamical distribution function of its member stars, f(x, v, [X/H]), in the multi-dimensional phase space spanned by position, velocity, and elemental abundance ratios. In particular, the chemo-dynamical distribution functions for low-mass stars (e.g., G- or K-type dwarfs) are precious tracers of the earliest stages of the Milky Way's formation, since their main-sequence lifetimes approach or exceed the age of the universe. A basic tenet of essentially all previous analyses is that the stellar metallicity, usually parameterized as [Fe/H], is conserved over time for main-sequence stars (at least those that have not been polluted due to mass transfer from binary companions). If this holds true, any correlations between metallicity and kinematics for long-lived main-sequence stars of different masses, effective temperatures, or spectral types must strictly be the same, since they reflect the same mass-assembly and star-formation histories. By analyzing a sample of nearby metal-poor halo and thick-disk stars on the main sequence, taken from Data Release 8 of the Sloan Digital Sky Survey, we find that the median metallicity of G-type dwarfs is systematically higher (by about 0.2 dex) than that of K-type dwarfs having the same median rotational velocity about the Galactic center. If it can be confirmed, this finding may invalidate the long-accepted assumption that the atmospheric metallicities of long-lived stars are conserved over time.

  19. Absolute Properties of the Pre-main-sequence Eclipsing Binary Star NP Persei

    NASA Astrophysics Data System (ADS)

    Lacy, Claud H. Sandberg; Fekel, Francis C.; Pavlovski, Krešimir; Torres, Guillermo; Muterspaugh, Matthew W.

    2016-07-01

    NP Per is a well-detached, 2.2 day eclipsing binary whose components are both pre-main-sequence stars that are still contracting toward the main-sequence phase of evolution. We report extensive photometric and spectroscopic observations with which we have determined their properties accurately. Their surface temperatures are quite different: 6420 ± 90 K for the larger F5 primary star and 4540 ± 160 K for the smaller K5e star. Their masses and radii are 1.3207 ± 0.0087 solar masses and 1.372 ± 0.013 solar radii for the primary, and 1.0456 ± 0.0046 solar masses and 1.229 ± 0.013 solar radii for the secondary. The orbital period is variable over long periods of time. A comparison of the observations with current stellar evolution models from MESA indicates that the stars cannot be fit at a single age: the secondary appears significantly younger than the primary. If the stars are assumed to be coeval and to have the age of the primary (17 Myr), then the secondary is larger and cooler than predicted by current models. The Hα spectral line of the secondary component is completely filled by, presumably, chromospheric emission due to a magnetic activity cycle.

  20. NEW X-RAY-SELECTED PRE-MAIN-SEQUENCE MEMBERS OF THE SERPENS MOLECULAR CLOUD

    SciTech Connect

    Oliveira, Isa; Van der Laan, Margriet; Brown, Joanna M.

    2013-11-01

    The study of young stars no longer surrounded by disks can greatly add to our understanding of how protoplanetary disks evolve and planets form. We have used VLT/FLAMES optical spectroscopy to confirm the youth and membership of 19 new young diskless stars in the Serpens Molecular Cloud, identified at X-ray wavelengths. Spectral types, effective temperatures, and stellar luminosities were determined using optical spectra and optical/near-infrared photometry. Stellar masses and ages were derived based on pre-main-sequence evolutionary tracks. The results yield remarkable similarities for age and mass distribution between the diskless and disk-bearing stellar populations in Serpens. We discuss the important implications these similarities may have on the standard picture of disk evolution.

  1. A New Semi-Empirical Technique For Computing Effective Temperatures For Main Sequence Stars From Their Mass And Radii

    NASA Astrophysics Data System (ADS)

    Aslan, Gürkan; Soydugan, Faruk; Eker, Zeki; Bilir, Selçuk; Bakış, Volkan

    2016-07-01

    A semi-empirical technique of improving effective temperature for main sequence stars from their observed mass and radius based on the Stefan-Boltzmann law, was introduced and applied to 450 main-sequence stars with accurate parameters. The method requires a mass-luminosity relation (MLR) and theoretical predictions of radius and effective temperature for stars at zero age main-sequence and at terminal age main-sequence. The MLRs, which act as if a catalyst, are necessary but have no effect on the final result. The present sample of main-sequence stars, which are members of the detached double-lined eclipsing binaries in the solar neighborhood chosen from Eker et al. (2014), have an error histogram for the observed effective temperatures with a peak at 2-3%. Errors of refined effective temperatures by the present method are the propagated errors of the observed masses and radii, that is, the refined temperatures and associated errors are independent of the observational temperatures and their associated errors. The histogram of the refined temperature errors shows a peak at less than 1%. A refined sample of stars (270 out of 450) with masses and radii accurate up to 3% and their refined effective temperatures has been used in this study to improve the classical MLRs. One may prefer, however, to use improved classical MLRs, which allows one to compute effective temperatures as accurate as 3.5%.

  2. New pre-main-sequence stars in the Upper Scorpius subgroup of Sco-Cen

    NASA Astrophysics Data System (ADS)

    Rizzuto, A. C.; Ireland, M. J.; Kraus, A. L.

    2015-04-01

    We present 237 new spectroscopically confirmed pre-main-sequence K- and M-type stars in the young Upper Scorpius subgroup of the Sco-Cen association, the nearest region of recent massive star formation. Using the Wide-Field Spectrograph at the Australian National University 2.3 m telescope at Siding Spring, we observed 397 kinematically and photometrically selected candidate members of Upper Scorpius, and identified new members by the presence of lithium absorption. The HR-diagram of the new members shows a spread of ages, ranging from ˜3 to 20 Myr, which broadly agrees with the current age estimates of ˜5-10 Myr. We find a significant range of Li 6708 equivalent widths among the members, and a minor dependence of HR-diagram position on the measured equivalent width of the Li 6708 Å line, with members that appear younger having more lithium. This could indicate the presence of either populations of different age, or a spread of ages in Upper Scorpius. We also use Wide-Field Infrared Survey Explorer data to infer circumstellar disc presence in 25 of the members on the basis of infrared excesses, including two candidate transition discs. We find that 11.2 ± 3.4 per cent of the M0-M2 spectral type (0.4-0.8 M⊙) Upper Sco stars display an excess that indicates the presence of a gaseous disc.

  3. The effect of starspots on the radii of low-mass pre-main-sequence stars

    NASA Astrophysics Data System (ADS)

    Jackson, R. J.; Jeffries, R. D.

    2014-07-01

    A polytropic model is used to investigate the effects of dark photospheric spots on the evolution and radii of magnetically active, low-mass (M < 0.5 M⊙), pre-main-sequence (PMS) stars. Spots slow the contraction along Hayashi tracks and inflate the radii of PMS stars by a factor of (1 - β)-N compared to unspotted stars of the same luminosity, where β is the equivalent covering fraction of dark starspots and N ≃ 0.45 ± 0.05. This is a much stronger inflation than predicted by Spruit & Weiss for main-sequence stars with the same β, where N ˜ 0.2-0.3. These models have been compared to radii determined for very magnetically active K- and M-dwarfs in the young Pleiades and NGC 2516 clusters, and the radii of tidally locked, low-mass eclipsing binary components. The binary components and zero-age main-sequence K-dwarfs have radii inflated by ˜10 per cent compared to an empirical radius-luminosity relation that is defined by magnetically inactive field dwarfs with interferometrically measured radii; low-mass M-type PMS stars, that are still on their Hayashi tracks, are inflated by up to ˜40 per cent. If this were attributable to starspots alone, we estimate that an effective spot coverage of 0.35 < β < 0.51 is required. Alternatively, global inhibition of convective flux transport by dynamo-generated fields may play a role. However, we find greater consistency with the starspot models when comparing the loci of active young stars and inactive field stars in colour-magnitude diagrams, particularly for the highly inflated PMS stars, where the large, uniform temperature reduction required in globally inhibited convection models would cause the stars to be much redder than observed.

  4. BVRI main-sequence photometry of the globular cluster M4

    SciTech Connect

    Alcaino, G.; Liller, W.

    1984-09-01

    We present BV and RI photographic photometry of 1421 and 189 stars, respectively, in the intermediate metallicity globular cluster M4 (NGC 6121). This investigation includes the first results of RI main-sequence photometry of a globular cluster. The use of longer wavelengths and longer color baselines provides the potential of improved isochrone fittings and underscores the urgent need for calculations of RI synthetic isochrones to be compared with observations. The Pickering-Racine wedge was used with the ESO 3.6 m telescope, the Las Campanas 2.5 m du Pont telescope, and the CTIO 1 m Yale telescope to extend the photoelectric limit from Vroughly-equal16.1 to Vroughly-equal19.1. We have determined the position of the main-sequence turnoff to lie at V = 16.6 +- 0.2 (m.e.) and B-V = 0.80 +- 0.03 (m.e.). A comparison of our BV observations with the CCD data of Richer and Fahlman shows excellent agreement: the two fifucial main sequences agree at all points to within 0.025 mag and, on average, to 0.013 mag. For the cluster we derive a distance modulus (m-M)/sub V/ = 12.52 +- 0.2 and reddening E(B-V) = 0.44 +- 0.03, results which confirm that at a distance of 2 kpc, M4 is the closest globular clusters to the Sun. Using the isochrones of VandenBerg, we deduce an age 13 +- 2 Gyr. As noted in several other investigations, there is a striking deficiency of stars in certain parts of the color-magnitude diagram; in M4 we find a pronounced gap over approx.0.6 mag at the base of the subgiant branch.

  5. Pre-main-sequence isochrones - III. The Cluster Collaboration isochrone server

    NASA Astrophysics Data System (ADS)

    Bell, Cameron P. M.; Rees, Jon M.; Naylor, Tim; Mayne, N. J.; Jeffries, R. D.; Mamajek, Eric E.; Rowe, John

    2014-12-01

    We present an isochrone server for semi-empirical pre-main-sequence model isochrones in the following systems: Johnson-Cousins, Sloan Digital Sky Survey, Two-Micron All-Sky Survey, Isaac Newton Telescope (INT) Wide-Field Camera and INT Photometric Hα Survey (IPHAS)/UV-Excess Survey (UVEX). The server can be accessed via the Cluster Collaboration webpage http://www.astro.ex.ac.uk/people/timn/isochrones/. To achieve this, we have used the observed colours of member stars in young clusters with well-established age, distance and reddening to create fiducial loci in the colour-magnitude diagram. These empirical sequences have been used to quantify the discrepancy between the models and data arising from uncertainties in both the interior and atmospheric models, resulting in tables of semi-empirical bolometric corrections (BCs) in the various photometric systems. The model isochrones made available through the server are based on existing stellar interior models coupled with our newly derived semi-empirical BCs. As part of this analysis, we also present new cluster parameters for both the Pleiades and Praesepe, yielding ages of 135^{+20}_{-11} and 665^{+14}_{-7} {Myr} as well as distances of 132 ± 2 and 184 ± 2 pc, respectively (statistical uncertainty only).

  6. Pre-main-sequence stars in the young cluster IC 2391

    NASA Technical Reports Server (NTRS)

    Stauffer, John; Hartmann, Lee W.; Jones, Burton F.; Mcnamara, Brian R.

    1989-01-01

    Seven or eight new, late-type members of the poor open cluster IC 2391 are identified, and membership is confirmed for two other stars. The new members fall approximately along a 3 x 10 to the 7th yr isochrone, which is the age estimated for the cluster on the basis of it super main-seqence turnoff. Echelle spectra were obtained for the most probable cluster members. Most show H-alpha in emission and a strong Li 6707 A absorption line, and a few are rapid rotators. The Li abundances for cluster stars cooler than the sun are considerably less than the primordial Li abundance, providing the first direct evidence for substantial premain-sequence Li burning. The rotational velocities show a range from about 15 to 150 km/s, with a distribution of rotational velocities not significantly different from that observed for low-mass stars in the Pleiades.

  7. DNA Damage: A Main Determinant of Vascular Aging

    PubMed Central

    Bautista-Niño, Paula K.; Portilla-Fernandez, Eliana; Vaughan, Douglas E.; Danser, A. H. Jan; Roks, Anton J. M.

    2016-01-01

    Vascular aging plays a central role in health problems and mortality in older people. Apart from the impact of several classical cardiovascular risk factors on the vasculature, chronological aging remains the single most important determinant of cardiovascular problems. The causative mechanisms by which chronological aging mediates its impact, independently from classical risk factors, remain to be elucidated. In recent years evidence has accumulated that unrepaired DNA damage may play an important role. Observations in animal models and in humans indicate that under conditions during which DNA damage accumulates in an accelerated rate, functional decline of the vasculature takes place in a similar but more rapid or more exaggerated way than occurs in the absence of such conditions. Also epidemiological studies suggest a relationship between DNA maintenance and age-related cardiovascular disease. Accordingly, mouse models of defective DNA repair are means to study the mechanisms involved in biological aging of the vasculature. We here review the evidence of the role of DNA damage in vascular aging, and present mechanisms by which genomic instability interferes with regulation of the vascular tone. In addition, we present potential remedies against vascular aging induced by genomic instability. Central to this review is the role of diverse types of DNA damage (telomeric, non-telomeric and mitochondrial), of cellular changes (apoptosis, senescence, autophagy), mediators of senescence and cell growth (plasminogen activator inhibitor-1 (PAI-1), cyclin-dependent kinase inhibitors, senescence-associated secretory phenotype (SASP)/senescence-messaging secretome (SMS), insulin and insulin-like growth factor 1 (IGF-1) signaling), the adenosine monophosphate-activated protein kinase (AMPK)-mammalian target of rapamycin (mTOR)-nuclear factor kappa B (NFκB) axis, reactive oxygen species (ROS) vs. endothelial nitric oxide synthase (eNOS)-cyclic guanosine monophosphate (c

  8. A probable pre-main sequence chemically peculiar star in the open cluster Stock 16

    NASA Astrophysics Data System (ADS)

    Netopil, M.; Fossati, L.; Paunzen, E.; Zwintz, K.; Pintado, O. I.; Bagnulo, S.

    2014-08-01

    We used the Ultraviolet and Visual Echelle Spectrograph of the ESO-Very Large Telescope to obtain a high resolution and high signal-to-noise ratio spectrum of Stock 16-12, an early-type star which previous Δa photometric observations suggest being a chemically peculiar (CP) star. We used spectral synthesis to perform a detailed abundance analysis obtaining an effective temperature of 8400 ± 400 K, a surface gravity of 4.1 ± 0.4, a microturbulence velocity of 3.4^{+0.7}_{-0.3} km s-1, and a projected rotational velocity of 68 ± 4 km s-1. We provide photometric and spectroscopic evidence showing the star is most likely a member of the young Stock 16 open cluster (age 3-8 Myr). The probable cluster membership, the star's position in the Hertzsprung-Russell diagram, and the found infrared excess strongly suggest the star is still in the pre-main-sequence (PMS) phase. We used PMS evolutionary tracks to determine the stellar mass, which ranges between 1.95 and 2.3 M⊙, depending upon the adopted spectroscopic or photometric data results. Similarly, we obtained a stellar age ranging between 4 and 6 Myr, in agreement with that of the cluster. Because the star's chemical abundance pattern resembles well that known of main sequence CP metallic line (Am) stars, the object sets important constraints to the diffusion theory. Additional spectroscopic and spectropolarimetric data allowed us to conclude that the object is probably a single non-magnetic star.

  9. V4046 Sgr: Touchstone to Investigate Spectral Type Discrepancies for Pre-main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Kastner, Joel H.; Rapson, Valerie; Sargent, Benjamin; Smith, C. T.; Rayner, John

    2015-01-01

    Determinations of the fundamental properties (e.g., masses and ages) of late-type, pre-main sequence (pre-MS) stars are complicated by the potential for significant discrepancies between the spectral types of such stars as ascertained via optical vs. near-infrared observations. To address this problem, we have obtained near-IR spectroscopy of the nearby, close binary T Tauri system V4046 Sgr AB with the NASA Infrared Telescope Facility (IRTF) SPEX spectrometer. The V4046 Sgr close binary (and circumbinary disk) system provides an important test case for spectral type determination thanks to the stringent observational constraints on its component stellar masses (i.e., ˜0.9 M_⊙ each) as well as on its age (12--21 Myr) and distance (73 pc). Analysis of the IRTF data indicates that the composite near-IR spectral type for V4046 Sgr AB lies in the range M0--M1, i.e., significantly later than the K5+K7 composite type previously determined from optical spectroscopy. However, the K5+K7 composite type is in better agreement with theoretical pre-MS evolutionary tracks, given the well-determined properties of V4046 Sgr AB. These results serve as a cautionary tale for studies that rely on near-infrared spectroscopy as a primary means to infer the ages and masses of pre-MS stars.

  10. Soft X-ray observations of pre-main sequence stars in the chamaeleon dark cloud

    NASA Technical Reports Server (NTRS)

    Feigelson, Eric D.; Kriss, Gerard A.

    1987-01-01

    Einstein IPC observations of the nearby Chamaeleon I star forming cloud show 22 well-resolved soft X-ray sources in a 1x2 deg region. Twelve are associated with H-alpha emission line pre-main sequence (PMS) stars, and four with optically selected PMS stars. Several X-ray sources have two or more PMS stars in their error circles. Optical spectra were obtained at CTIO of possible stellar counterparts of the remaining X-ray sources. They reveal 5 probable new cloud members, K7-MO stars with weak or absent emission lines. These naked X-ray selected PMS stars are similar to those found in the Taurus-Auriga cloud. The spatial distributions and H-R diagrams of the X-ray and optically selected PMS stars in the cloud are very similar. Luminosity functions indicate the Chamaeleon stars are on average approximately 5 times more X-ray luminous than Pleiad dwarfs. A significant correlation between L sub x and optical magnitude suggests this trend may continue within the PMS phase of stellar evolution. The relation of increasing X-ray luminosity with decreasing stellar ages is thus extended to stellar ages as young as 1 million years.

  11. STELLAR DIAMETERS AND TEMPERATURES. I. MAIN-SEQUENCE A, F, AND G STARS

    SciTech Connect

    Boyajian, Tabetha S.; McAlister, Harold A.; Gies, Douglas R.; O'Brien, David; Parks, J. Robert; Richardson, Noel D.; Touhami, Yamina; White, Russel; Van Belle, Gerard; Ten Brummelaar, Theo A.; Farrington, Chris; Goldfinger, P. J.; Schaefer, Gail; Sturmann, Laszlo; Sturmann, Judit; Turner, Nils H.; Von Braun, Kaspar; Ridgway, Stephen

    2012-02-10

    We have executed a survey of nearby, main-sequence A-, F-, and G-type stars with the CHARA Array, successfully measuring the angular diameters of forty-four stars with an average precision of {approx}1.5%. We present new measures of the bolometric flux, which in turn leads to an empirical determination of the effective temperature for the stars observed. In addition, these CHARA-determined temperatures, radii, and luminosities are fit to Yonsei-Yale model isochrones to constrain the masses and ages of the stars. These results are compared to indirect estimates of these quantities obtained by collecting photometry of the stars and applying them to model atmospheres and evolutionary isochrones. We find that for most cases, the models overestimate the effective temperature by {approx}1.5%-4% when compared to our directly measured values. The overestimated temperatures and underestimated radii in these works appear to cause an additional offset in the star's surface gravity measurements, which consequently yield higher masses and younger ages, in particular for stars with masses greater than {approx}1.3 M{sub Sun }. Additionally, we compare our measurements to a large sample of eclipsing binary stars, and excellent agreement is seen within both data sets. Finally, we present temperature relations with respect to (B - V) and (V - K) colors as well as spectral type, showing that calibration of effective temperatures with errors {approx}1% is now possible from interferometric angular diameters of stars.

  12. ROTATION PERIODS OF 34,030 KEPLER MAIN-SEQUENCE STARS: THE FULL AUTOCORRELATION SAMPLE

    SciTech Connect

    McQuillan, A.; Mazeh, T.; Aigrain, S.

    2014-04-01

    We analyzed three years of data from the Kepler space mission to derive rotation periods of main-sequence stars below 6500 K. Our automated autocorrelation-based method detected rotation periods between 0.2 and 70 days for 34,030 (25.6%) of the 133,030 main-sequence Kepler targets (excluding known eclipsing binaries and Kepler Objects of Interest), making this the largest sample of stellar rotation periods to date. In this paper we consider the detailed features of the now well-populated period-temperature distribution and demonstrate that the period bimodality, first seen by McQuillan et al. in the M-dwarf sample, persists to higher masses, becoming less visible above 0.6 M {sub ☉}. We show that these results are globally consistent with the existing ground-based rotation-period data and find that the upper envelope of the period distribution is broadly consistent with a gyrochronological age of 4.5 Gyr, based on the isochrones of Barnes, Mamajek, and Hillenbrand and Meibom et al. We also performed a detailed comparison of our results to those of Reinhold et al. and Nielsen et al., who measured rotation periods of field stars observed by Kepler. We examined the amplitude of periodic variability for the stars with detection rotation periods, and found a typical range between ∼950 ppm (5th percentile) and ∼22,700 ppm (95th percentile), with a median of ∼5600 ppm. We found typically higher amplitudes for shorter periods and lower effective temperatures, with an excess of low-amplitude stars above ∼5400 K.

  13. BEYOND THE MAIN SEQUENCE: TESTING THE ACCURACY OF STELLAR MASSES PREDICTED BY THE PARSEC EVOLUTIONARY TRACKS

    SciTech Connect

    Ghezzi, Luan; Johnson, John Asher

    2015-10-20

    Characterizing the physical properties of exoplanets and understanding their formation and orbital evolution requires precise and accurate knowledge of their host stars. Accurately measuring stellar masses is particularly important because they likely influence planet occurrence and the architectures of planetary systems. Single main-sequence stars typically have masses estimated from evolutionary tracks, which generally provide accurate results due to their extensive empirical calibration. However, the validity of this method for subgiants and giants has been called into question by recent studies, with suggestions that the masses of these evolved stars could have been overestimated. We investigate these concerns using a sample of 59 benchmark evolved stars with model-independent masses (from binary systems or asteroseismology) obtained from the literature. We find very good agreement between these benchmark masses and the ones estimated using evolutionary tracks. The average fractional difference in the mass interval ∼0.7–4.5 M{sub ⊙} is consistent with zero (−1.30 ± 2.42%), with no significant trends in the residuals relative to the input parameters. A good agreement between model-dependent and -independent radii (−4.81 ± 1.32%) and surface gravities (0.71 ± 0.51%) is also found. The consistency between independently determined ages for members of binary systems adds further support for the accuracy of the method employed to derive the stellar masses. Taken together, our results indicate that determination of masses of evolved stars using grids of evolutionary tracks is not significantly affected by systematic errors, and is thus valid for estimating the masses of isolated stars beyond the main sequence.

  14. A young cluster with an extended main-sequence turnoff: confirmation of a prediction of the stellar rotation scenario

    NASA Astrophysics Data System (ADS)

    Bastian, N.; Niederhofer, F.; Kozhurina-Platais, V.; Salaris, M.; Larsen, S.; Cabrera-Ziri, I.; Cordero, M.; Ekström, S.; Geisler, D.; Georgy, C.; Hilker, M.; Kacharov, N.; Li, C.; Mackey, D.; Mucciarelli, A.; Platais, I.

    2016-07-01

    We present Hubble Space Telescope photometry of NGC 1850, a ˜100 Myr, ˜105 M⊙ cluster in the Large Magellanic Cloud. The colour-magnitude diagram clearly shows the presence of an extended main-sequence turnoff (eMSTO). The use of non-rotating stellar isochrones leads to an age spread of ˜40 Myr. This is in good agreement with the age range expected when the effects of rotation in the main-sequence turnoff (MSTO) stars are wrongly interpreted in terms of age spread. We also do not find evidence for multiple, isolated episodes of star formation bursts within the cluster, in contradiction to scenarios that invoke actual age spreads to explain the eMSTO phenomenon. NGC 1850 therefore continues the trend of eMSTO clusters, where the inferred age spread is proportional to the age of the cluster. While our results confirm a key prediction of the scenario where stellar rotation causes the eMSTO feature, direct measurements of the rotational rate of MSTO stars is required to definitively confirm or refute whether stellar rotation is the origin of the eMSTO phenomenon or if it is due to an as yet undiscovered effect.

  15. Standard pre-main sequence models of low-mass stars

    SciTech Connect

    Prada Moroni, P. G.; Degl'Innocenti, S.; Tognelli, E.

    2014-05-09

    The main characteristics of standard pre-main sequence (PMS) models are described. A discussion of the uncer-tainties affecting the current generation of PMS evolutionary tracks and isochrones is also provided. In particular, the impact of the uncertainties in the adopted equation of state, radiative opacity, nuclear cross sections, and initial chemical abundances are analysed.

  16. The main sequences of NGC 2808: constraints on the early disc accretion scenario

    NASA Astrophysics Data System (ADS)

    Cassisi, Santi; Salaris, Maurizio

    2014-03-01

    A new scenario - early disc accretion - has been proposed very recently to explain the origin of the multiple population phenomenon in Galactic globular clusters. It envisages the possibility that a fraction of low- and very low-mass cluster stars may accrete the ejecta of interacting massive binary (and possibly also fast rotating massive) stars during the fully convective, pre-main sequence stage, to reproduce the CN and ONa anticorrelations observed among stars in individual clusters. This scenario is assumed to be able to explain the presence (and properties) of the multiple populations in the majority of globular clusters in the Milky Way. Here we have considered the well studied cluster NGC 2808, which displays a triple main sequence with well defined and separate He abundances. Knowledge of these abundances allowed us to put strong constraints on the He mass fraction and amount of matter to be accreted by low-mass pre-main sequence stars. We find that the minimum He mass fraction in the accreted gas has to be ~0.44 to produce the observed sequences and that at fixed initial mass of the accreting star, different efficiencies for the accretion are required to produce stars placed onto the multiple main sequences. This may be explained by differences in the orbital properties of the progenitors and/or different spatial distribution of intracluster gas with varying He abundances. Both O-Na and C-N anticorrelations appear naturally along the main sequences, once considering the predicted relationship between He and CNONa abundances in the ejecta of the polluters. As a consequence of the accretion, we predict no discontinuity between the abundance ranges covered by intermediate and blue main sequence stars, but we find a sizeable (several 0.1 dex) discontinuity of the N and Na abundances between objects on the intermediate and red main sequences. There is in principle enough polluting gas with the right He abundances to explain the observed main sequences by early

  17. Pre main sequence stars as UV sources for the World Space Observatory-UV mission

    NASA Astrophysics Data System (ADS)

    Gomez de Castro, Ana I.; Lamzin, Sergei A.

    2011-09-01

    Pre-main sequence stars are bright UV (UV) sources compared with their main sequence analogues. The source of this excess is the high energy processes associated with the physics of accretion/outflow during early stellar evolution. In this review, the main sources of UV excess are described as well as the most significant "unknowns" in the field. Special emphasis is made on the results from the last observations carried out with the Hubble Space Telescope and on the relevance of future dedicated monitoring programs with the World Space Observatory-UV.

  18. Molecular and atomic gas along and across the main sequence of star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Saintonge, Amelie; Catinella, Barbara; Cortese, Luca; Genzel, Reinhard; Giovanelli, Riccardo; Haynes, Martha P.; Janowiecki, Steven; Kramer, Carsten; Lutz, Katharina A.; Schiminovich, David; Tacconi, Linda J.; Wuyts, Stijn; Accurso, Gioacchino

    2016-10-01

    We use spectra from the ALFALFA, GASS and COLD GASS surveys to quantify variations in the mean atomic and molecular gas mass fractions throughout the SFR-M* plane and along the main sequence (MS) of star-forming galaxies. Although galaxies well below the MS tend to be undetected in the Arecibo and IRAM observations, reliable mean atomic and molecular gas fractions can be obtained through a spectral stacking technique. We find that the position of galaxies in the SFR-M* plane can be explained mostly by their global cold gas reservoirs as observed in the H I line, with in addition systematic variations in the molecular-to-atomic ratio and star formation efficiency. When looking at galaxies within ±0.4 dex of the MS, we find that as stellar mass increases, both atomic and molecular gas mass fractions decrease, stellar bulges become more prominent, and the mean stellar ages increase. Both star formation efficiency and molecular-to-atomic ratios vary little for massive MS galaxies, indicating that the flattening of the MS is due to the global decrease of the cold gas reservoirs of galaxies rather than to bottlenecks in the process of converting cold atomic gas to stars.

  19. Fundamental Parameters of Main-Sequence Stars in an Instant with Machine Learning

    NASA Astrophysics Data System (ADS)

    Bellinger, Earl P.; Angelou, George C.; Hekker, Saskia; Basu, Sarbani; Ball, Warrick H.; Guggenberger, Elisabeth

    2016-10-01

    Owing to the remarkable photometric precision of space observatories like Kepler, stellar and planetary systems beyond our own are now being characterized en masse for the first time. These characterizations are pivotal for endeavors such as searching for Earth-like planets and solar twins, understanding the mechanisms that govern stellar evolution, and tracing the dynamics of our Galaxy. The volume of data that is becoming available, however, brings with it the need to process this information accurately and rapidly. While existing methods can constrain fundamental stellar parameters such as ages, masses, and radii from these observations, they require substantial computational effort to do so. We develop a method based on machine learning for rapidly estimating fundamental parameters of main-sequence solar-like stars from classical and asteroseismic observations. We first demonstrate this method on a hare-and-hound exercise and then apply it to the Sun, 16 Cyg A and B, and 34 planet-hosting candidates that have been observed by the Kepler spacecraft. We find that our estimates and their associated uncertainties are comparable to the results of other methods, but with the additional benefit of being able to explore many more stellar parameters while using much less computation time. We furthermore use this method to present evidence for an empirical diffusion–mass relation. Our method is open source and freely available for the community to use.6

  20. Main sequence of the metal-poor globular cluster M30 (NGC 7099)

    SciTech Connect

    Alcaino, G.; Liller, W.

    1980-10-01

    We present photographic photometry for 673 stars in the metal-poor globular cluster M30 (NGC 7099). The Racine wedge was used with the CTIO 1-m Yale telescope (..delta..m=3/sup m/.60), the CTIO 4-m telescope (..delta..m=6/sup m/.83), and the ESO 3.6-m telescope (..delta..m=4/sup m/.12) to extend the photoelectric limit from Vapprox. =16.3 to Vapprox. =20.4. For the main-sequence turn-off, we have determined its position to lie at V=18.4 +- 0.1 (m.e.) and B-V=0.49 +- 0.03 (m.e.). From these values, we calculate the intrinsic values M/sub v/ =3.87 and (B-V)/sub 0/=0.47. For the cluster as a whole, we derive a distance modulus (m-M)/sub V/=14.53 +- 0.15 and reddening E(B-V)=0.02 +- 0.02. Using the models of Iben and Rood (Astrophys. J. 159, 605 (1970)) and the isochrones of Demarque and McClure ((1977), in Evolution of Galaxies and Stellar Populations, edited by B. Tinsley and R. B. Larson (Yale University Observatory, New Haven), p. 199), we deduce the cluster's age to be 14.5( +- 4.0) x 10/sup 9/ yr. The large uncertainty in this value emphasizes the dire need for more work on cluster evolution.

  1. WHITE-DWARF-MAIN-SEQUENCE BINARIES IDENTIFIED FROM THE LAMOST PILOT SURVEY

    SciTech Connect

    Ren Juanjuan; Luo Ali; Li Yinbi; Wei Peng; Zhao Jingkun; Zhao Yongheng; Song Yihan; Zhao Gang E-mail: lal@nao.cas.cn

    2013-10-01

    We present a set of white-dwarf-main-sequence (WDMS) binaries identified spectroscopically from the Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST, also called the Guo Shou Jing Telescope) pilot survey. We develop a color selection criteria based on what is so far the largest and most complete Sloan Digital Sky Survey (SDSS) DR7 WDMS binary catalog and identify 28 WDMS binaries within the LAMOST pilot survey. The primaries in our binary sample are mostly DA white dwarfs except for one DB white dwarf. We derive the stellar atmospheric parameters, masses, and radii for the two components of 10 of our binaries. We also provide cooling ages for the white dwarf primaries as well as the spectral types for the companion stars of these 10 WDMS binaries. These binaries tend to contain hot white dwarfs and early-type companions. Through cross-identification, we note that nine binaries in our sample have been published in the SDSS DR7 WDMS binary catalog. Nineteen spectroscopic WDMS binaries identified by the LAMOST pilot survey are new. Using the 3{sigma} radial velocity variation as a criterion, we find two post-common-envelope binary candidates from our WDMS binary sample.

  2. Pre-Main-Sequence Star Candidates in the Bar of the Large Magellanic Cloud

    PubMed

    Beaulieu; Lamers; Grison; Julien; Lanciaux; Ferlet; Vidal-Madjar; Bertin; Maurice; Prevot; Gry; Guibert; Moreau; Tajhmady; Aubourg; Bareyre; de Kat J; Gros; Laurent; Lachieze-Rey; Lesquoy; Magneville; Milsztajn; Moscoso; Queinnec; Renault; Rich; Spiro; Vigroux; Zylberajch; Ansari; Cavalier; Moniez

    1996-05-17

    Candidate pre-main-sequence stars were observed in the bar of the Large Magellanic Cloud during the search for dark matter in the galactic halo. Seven blue stars of apparent visual magnitude 15 to 17 had irregular photometric variations and hydrogen emission lines in their optical spectra, which suggested that these stars are pre-main-sequence stars of about 10 solar masses. These stars are slightly more massive and definitely more luminous than are Herbig AeBe pre-main-sequence stars in our own galaxy. Continued observations of these very young stars from another galaxy, which are probably at the pre-hydrogen-burning stage, should provide important clues about early stages of star formation.

  3. The extended main-sequence turn-off cluster NGC 1856: rotational evolution in a coeval stellar ensemble

    NASA Astrophysics Data System (ADS)

    D'Antona, F.; Di Criscienzo, M.; Decressin, T.; Milone, A. P.; Vesperini, E.; Ventura, P.

    2015-11-01

    Multiple or extended turn-offs in young clusters in the Magellanic Clouds have recently received large attention. A number of studies have shown that they may be interpreted as the result of a significant age spread (several 108 yr in clusters aged 1-2 Gyr), while others attribute them to a spread in stellar rotation. We focus on the cluster NGC 1856, showing a splitting in the upper part of the main sequence, well visible in the colour mF336W - mF555W, and a very wide turn-off region. Using population synthesis available from the Geneva stellar models, we show that the cluster data can be interpreted as superposition of two main populations having the same age (˜350 Myr), composed for 2/3 of very rapidly rotating stars, defining the upper turn-off region and the redder main sequence, and for 1/3 of slowly/non-rotating stars. Since rapid rotation is a common property of the B-A type stars, the main question raised by this model concerns the origin of the slowly/non-rotating component. Binary synchronization is a possible process behind the slowly/non-rotating population; in this case, many slowly/non-rotating stars should still be part of binary systems with orbital periods in the range from 4 to 500 d. For these orbital periods, Roche lobe overflow occurs during the evolution of the primary off the main sequence, so most primaries may not be able to ignite core helium burning, consistently why the lack of a red clump progeny of the slowly rotating population.

  4. Empirical tests of pre-main-sequence stellar evolution models with eclipsing binaries

    NASA Astrophysics Data System (ADS)

    Stassun, Keivan G.; Feiden, Gregory A.; Torres, Guillermo

    2014-06-01

    We examine the performance of standard pre-main-sequence (PMS) stellar evolution models against the accurately measured properties of a benchmark sample of 26 PMS stars in 13 eclipsing binary (EB) systems having masses 0.04-4.0 M⊙ and nominal ages ≈1-20 Myr. We provide a definitive compilation of all fundamental properties for the EBs, with a careful and consistent reassessment of observational uncertainties. We also provide a definitive compilation of the various PMS model sets, including physical ingredients and limits of applicability. No set of model isochrones is able to successfully reproduce all of the measured properties of all of the EBs. In the H-R diagram, the masses inferred for the individual stars by the models are accurate to better than 10% at ≳1 M⊙, but below 1 M⊙ they are discrepant by 50-100%. Adjusting the observed radii and temperatures using empirical relations for the effects of magnetic activity helps to resolve the discrepancies in a few cases, but fails as a general solution. We find evidence that the failure of the models to match the data is linked to the triples in the EB sample; at least half of the EBs possess tertiary companions. Excluding the triples, the models reproduce the stellar masses to better than ∼10% in the H-R diagram, down to 0.5 M⊙, below which the current sample is fully contaminated by tertiaries. We consider several mechanisms by which a tertiary might cause changes in the EB properties and thus corrupt the agreement with stellar model predictions. We show that the energies of the tertiary orbits are comparable to that needed to potentially explain the scatter in the EB properties through injection of heat, perhaps involving tidal interaction. It seems from the evidence at hand that this mechanism, however it operates in detail, has more influence on the surface properties of the stars than on their internal structure, as the lithium abundances are broadly in good agreement with model predictions. The

  5. Quantifying the contamination by old main-sequence stars in young moving groups: the case of the Local Association

    NASA Astrophysics Data System (ADS)

    López-Santiago, J.; Micela, G.; Montes, D.

    2009-05-01

    Context: The associations and moving groups of young stars are excellent laboratories for investigating stellar formation in the solar neighborhood. Previous results have confirmed that a non-negligible fraction of old main-sequence stars is present in the lists of possible members of young stellar kinematic groups. A detailed study of the properties of these samples is needed to separate the young stars from old main-sequence stars with similar space motion, and identify the origin of these structures. Aims: Our intention is to characterize members of the young moving groups, determine their age distribution, and quantify the contamination by old main-sequence stars, in particular, for the Local Association. Methods: We used stars possible members of the young (~10-650 Myr) moving groups from the literature. To determine the age of the stars, we used several suitable age indicators for young main sequence stars, i.e., X-ray fluxes from the Rosat All-sky Survey database, photometric data from the Tycho-2, Hipparcos, and 2MASS database. We also used spectroscopic data, in particular the equivalent width of the lithium line Li i λ6707.8 Å and Hα, to constrain the range of ages of the stars. Results: By combining photometric and spectroscopic data, we were able to separate the young stars (10-650 Myr) from the old (>1 Gyr) field ones. We found, in particular, that the Local Association is contaminated by old field stars at the level of ~30%. This value must be considered as the contamination for our particular sample, and not of the entire Local Association. For other young moving groups, it is more difficult to estimate the fraction of old stars among possible members. However, the level of X-ray emission can, at least, help to separate two age populations: stars with <200 Myr and stars older than this. Conclusions: Among the candidate members of the classical moving groups, there is a non-negligible fraction of old field stars that should be taken into account

  6. MAIN-SEQUENCE STARS MASQUERADING AS YOUNG STELLAR OBJECTS IN THE CENTRAL MOLECULAR ZONE

    SciTech Connect

    Koepferl, Christine M.; Robitaille, Thomas P.; Morales, Esteban F. E.; Johnston, Katharine G.

    2015-01-20

    In contrast to most other galaxies, star formation rates in the Milky Way can be estimated directly from young stellar objects (YSOs). In the central molecular zone the star formation rate calculated from the number of YSOs with 24 μm emission is up to an order of magnitude higher than the value estimated from methods based on diffuse emission (such as free-free emission). Whether this effect is real or whether it indicates problems with either or both star formation rate measures is not currently known. In this paper, we investigate whether estimates based on YSOs could be heavily contaminated by more evolved objects such as main-sequence stars. We present radiative transfer models of YSOs and of main-sequence stars in a constant ambient medium which show that the main-sequence objects can indeed mimic YSOs at 24 μm. However, we show that in some cases the main-sequence models can be marginally resolved at 24 μm, whereas the YSO models are always unresolved. Based on the fraction of resolved MIPS 24 μm sources in the sample of YSOs previously used to compute the star formation rate, we estimate the fraction of misclassified ''YSOs'' to be at least 63%, which suggests that the star formation rate previously determined from YSOs is likely to be at least a factor of three too high.

  7. Analysis of flares in the chromosphere and corona of main- and pre-main-sequence M-type stars

    NASA Astrophysics Data System (ADS)

    Crespo-Chacón, I.

    2015-11-01

    This Ph.D. Thesis revolves around flares on main- and pre-main-sequence M-type stars. We use observations in different wavelength ranges with the aim of analysing the effects of flares at different layers of stellar atmospheres. In particular, optical and X-ray observations are used so that we can study how flares affect, respectively, the chromosphere and the corona of stars. In the optical range we carry out a high temporal resolution spectroscopic monitoring of UV Ceti-type stars aimed at detecting non-white-light flares (the most typical kind of solar flares) in stars other than the Sun. With these data we confirm that non-white-light flares are a frequent phenomenon in UV Ceti-type stars, as observed in the Sun. We study and interpret the behaviour of different chromospheric lines during the flares detected on AD Leo. By using a simplified slab model of flares (Jevremović et al. 1998), we are able to determine the physical parameters of the chromospheric flaring plasma (electron density and electron temperature), the temperature of the underlying source, and the surface area covered by the flaring plasma. We also search for possible relationships between the physical parameters of the flaring plasma and other properties such as the flare duration, area, maximum flux and released energy. This work considerably extends the existing sample of stellar flares analysed with good quality spectroscopy in the optical range. In X-rays we take advantage of the great sensitivity, wide energy range, high energy resolution, and continuous time coverage of the EPIC detectors - on-board the XMMNewton satellite - in order to perform time-resolved spectral analysis of coronal flares. In particular, in the UV Ceti-type star CC Eri we study two flares that are weaker than those typically reported in the literature (allowing us to speculate about the role of flares as heating agents of stellar atmospheres); while in the pre-main-sequence M-type star TWA 11B (with no signatures of

  8. Main-Sequence Effective Temperatures from a Revised Mass-Luminosity Relation Based on Accurate Properties

    NASA Astrophysics Data System (ADS)

    Eker, Z.; Soydugan, F.; Soydugan, E.; Bilir, S.; Yaz Gökçe, E.; Steer, I.; Tüysüz, M.; Şenyüz, T.; Demircan, O.

    2015-04-01

    The mass-luminosity (M-L), mass-radius (M-R), and mass-effective temperature (M-{{T}eff}) diagrams for a subset of galactic nearby main-sequence stars with masses and radii accurate to ≤slant 3% and luminosities accurate to ≤slant 30% (268 stars) has led to a putative discovery. Four distinct mass domains have been identified, which we have tentatively associated with low, intermediate, high, and very high mass main-sequence stars, but which nevertheless are clearly separated by three distinct break points at 1.05, 2.4, and 7 {{M}⊙ } within the studied mass range of 0.38-32 {{M}⊙ }. Further, a revised mass-luminosity relation (MLR) is found based on linear fits for each of the mass domains identified. The revised, mass-domain based MLRs, which are classical (L\\propto {{M}α }), are shown to be preferable to a single linear, quadratic, or cubic equation representing an alternative MLR. Stellar radius evolution within the main sequence for stars with M\\gt 1 {{M}⊙ } is clearly evident on the M-R diagram, but it is not clear on the M-{{T}eff} diagram based on published temperatures. Effective temperatures can be calculated directly using the well known Stephan-Boltzmann law by employing the accurately known values of M and R with the newly defined MLRs. With the calculated temperatures, stellar temperature evolution within the main sequence for stars with M\\gt 1 {{M}⊙ } is clearly visible on the M-{{T}eff} diagram. Our study asserts that it is now possible to compute the effective temperature of a main-sequence star with an accuracy of ˜6%, as long as its observed radius error is adequately small (\\lt 1%) and its observed mass error is reasonably small (\\lt 6%).

  9. Multiple main sequence of globular clusters as a result of inhomogeneous big bang nucleosynthesis

    SciTech Connect

    Moriya, Takashi; Shigeyama, Toshikazu

    2010-02-15

    A new mechanism for enhancing the helium abundance in the blue main sequence stars of {omega} Centauri and NGC 2808 is investigated. We suggest that helium enhancement was caused by the inhomogeneous big bang nucleosynthesis. Regions with extremely high baryon-to-photon ratios are assumed to be caused by the baryogenesis. Its mass scale is also assumed to be 10{sup 6}M{sub {center_dot}.} An example of the mechanisms to realize these two things was already proposed as the Affleck-Dine baryogenesis. As the baryon-to-photon ratio becomes larger, the primordial helium abundance is enhanced. We calculated the big bang nucleosynthesis and found that there exists a parameter region yielding enough helium to account for the split of the main sequence in the aforementioned globular clusters while keeping the abundance of other elements compatible with observations. Our mechanism predicts that heavy elements with the mass number of around 100 is enhanced in the blue main sequence stars. We estimate the time scales of diffusion of the enhanced helium and mass accretion in several stages after the nucleosynthesis to investigate whether these processes diminish the enhancement of helium. We found that the diffusion does not influence the helium content. A cloud with a sufficiently large baryon-to-photon ratio to account for the multiple main sequence collapsed immediately after the recombination. Subsequently, the cloud accreted the ambient matter with the normal helium content. If the star formation occurred both in the collapsed core and the accreted envelope, then the resultant star cluster has a double main sequence.

  10. Comparison of the main sequence of reflexive saccades and the quick phases of optokinetic nystagmus

    PubMed Central

    Garbutt, S.; Harwood, M.; Harris, C.

    2001-01-01

    BACKGROUND/AIMS—Abnormalities in the saccadic main sequence are an important finding and may indicate pathology of the ocular motor periphery or central neurological disorders. In young or uncooperative patients it can be difficult eliciting a sufficient number of saccades to measure the main sequence. It is often assumed that the quick phases of optokinetic nystagmus (OKN) are identical to saccades. If this were the case, it would be feasible to use OKN, an involuntary response that is easily evoked, as a simple way of eliciting many saccades. The aim of this study was to determine whether reflexive saccades and the quick phases of OKN are indeed identical, and whether OKN quick phases could have a clinical role in identifying patients with slow saccades.
METHODS—OKN and reflexive saccades were recorded from 10 healthy adults using an infrared limbus eye tracker and bitemporal DC electro-oculography simultaneously. OKN was stimulated by rotating a full field patterned curtain around the subject at 10-50°/s. Reflexive saccades were elicited to red LED targets at 5-20° eccentricity.
RESULTS—OKN quick phases tended to have a longer duration compared to saccades, but these differences were not significant. OKN quick phases had a slightly lower peak velocity compared to saccades, which was statistically significant (p<0.05).
CONCLUSION—The main sequence for duration is the same for reflexive saccades and OKN quick phases. The main sequence for peak velocity is slightly faster for reflexive saccades than OKN quick phases, but the difference is unlikely to be of clinical significance. As an illustration of the potential of this technique, the authors demonstrate that OKN quick phases show similar slowness to saccades in a child with brainstem pathology caused by Gaucher disease type III. It is concluded that recording OKN may be a simple clinical means for approximating the main sequence.

 PMID:11734524

  11. Is main-sequence galaxy star formation controlled by halo mass accretion?

    NASA Astrophysics Data System (ADS)

    Rodríguez-Puebla, Aldo; Primack, Joel R.; Behroozi, Peter; Faber, S. M.

    2016-01-01

    The galaxy stellar-to-halo mass relation (SHMR) is nearly time-independent for z < 4. We therefore construct a time-independent SHMR model for central galaxies, wherein the in situ star formation rate (SFR) is determined by the halo mass accretion rate (MAR), which we call stellar halo accretion rate coevolution (SHARC). We show that the ˜0.3 dex dispersion of the halo MAR matches the observed dispersion of the SFR on the star formation main sequence (MS). In the context of `bathtub'-type models of galaxy formation, SHARC leads to mass-dependent constraints on the relation between SFR and MAR. Despite its simplicity and the simplified treatment of mass growth from mergers, the SHARC model is likely to be a good approximation for central galaxies with M* = 109-1010.5 M⊙ that are on the MS, representing most of the star formation in the Universe. SHARC predictions agree with observed SFRs for galaxies on the MS at low redshifts, agree fairly well at z ˜ 4, but exceed observations at z ≳ 4. Assuming that the interstellar gas mass is constant for each galaxy (the `equilibrium condition' in bathtub models), the SHARC model allows calculation of net mass loading factors for inflowing and outflowing gas. With assumptions about preventive feedback based on simulations, SHARC allows calculation of galaxy metallicity evolution. If galaxy SFRs indeed track halo MARs, especially at low redshifts, that may help explain the success of models linking galaxy properties to haloes (including age-matching) and the similarities between two-halo galaxy conformity and halo mass accretion conformity.

  12. THE QUADRUPLE PRE-MAIN-SEQUENCE SYSTEM LkCa 3: IMPLICATIONS FOR STELLAR EVOLUTION MODELS

    SciTech Connect

    Torres, Guillermo; Latham, David W.; Ruiz-Rodriguez, Dary; Prato, L.; Wasserman, Lawrence H.; Badenas, Mariona; Schaefer, G. H.; Mathieu, Robert D.

    2013-08-10

    We report the discovery that the pre-main-sequence (PMS) object LkCa 3 in the Taurus-Auriga star-forming region is a hierarchical quadruple system of M stars. It was previously known to be a close ({approx}0.''5) visual pair, with one component being a moderately eccentric 12.94 day single-lined spectroscopic binary. A re-analysis of archival optical spectra complemented by new near-infrared (NIR) spectroscopy shows both visual components to be double lined; the second one has a period of 4.06 days and a circular orbit. In addition to the orbital elements, we determine optical and NIR flux ratios, effective temperatures, and projected rotational velocities for all four stars. Using existing photometric monitoring observations of the system that had previously revealed the rotational period of the primary in the longer-period binary, we also detect the rotational signal of the primary in the 4.06 day binary, which is synchronized with the orbital motion. With only the assumption of coevality, a comparison of all of these constraints with current stellar evolution models from the Dartmouth series points to an age of 1.4 Myr and a distance of 133 pc, consistent with previous estimates for the region and suggesting that the system is on the near side of the Taurus complex. Similar comparisons of the properties of LkCa 3 and the well-known quadruple PMS system GG Tau with the widely used models from the Lyon series for a mixing length parameter of {alpha}{sub ML} = 1.0 strongly favor the Dartmouth models.

  13. Pre-main-sequence population in NGC 1893 region: X-ray properties

    NASA Astrophysics Data System (ADS)

    Pandey, A. K.; Samal, M. R.; Yadav, Ram Kesh; Richichi, Andrea; Lata, Sneh; Pandey, J. C.; Ojha, D. K.; Chen, W. P.

    2014-05-01

    Continuing the attempt to understand the properties of the stellar content in the young cluster NGC 1893 we have carried out a comprehensive multi-wavelength study of the region. The present study focuses on the X-ray properties of T-Tauri Stars (TTSs) in the NGC 1893 region. We found a correlation between the X-ray luminosity, LX, and the stellar mass (in the range 0.2-2.0 M) of TTSs in the NGC 1893 region, similar to those reported in some other young clusters, however the value of the power-law slope obtained in the present study (∼0.9) for NGC 1893 is smaller than those (∼1.4-3.6) reported in the case of TMC, ONC, IC 348 and Chameleon star forming regions. However, the slope in the case of Class III sources (Weak line TTSs) is found to be comparable to that reported in the case of NGC 6611 (∼1.1). It is found that the presence of circumstellar disks has no influence on the X-ray emission. The X-ray luminosity for both CTTSs and WTTSs is found to decrease systematically with age (in the range ∼0.4-5 Myr). The decrease of the X-ray luminosity of TTSs (slope ∼-0.6) in the case of NGC 1893 seems to be faster than observed in the case of other star-forming regions (slope -0.2 to -0.5). There is indication that the sources having relatively large NIR excess have relatively lower LX values. TTSs in NGC 1893 do not follow the well established X-ray activity - rotation relation as in the case of main-sequence stars.

  14. Mass loss from pre-main-sequence accretion disks. I - The accelerating wind of FU Orionis

    NASA Technical Reports Server (NTRS)

    Calvet, Nuria; Hartmann, Lee; Kenyon, Scott J.

    1993-01-01

    We present evidence that the wind of the pre-main-sequence object FU Orionis arises from the surface of the luminous accretion disk. A disk wind model calculated assuming radiative equilibrium explains the differential behavior of the observed asymmetric absorption-line profiles. The model predicts that strong lines should be asymmetric and blueshifted, while weak lines should be symmetric and double-peaked due to disk rotation, in agreement with observations. We propose that many blueshifted 'shell' absorption features are not produced in a true shell of material, but rather form in a differentially expanding wind that is rapidly rotating. The inference of rapid rotation supports the proposal that pre-main-sequence disk winds are rotationally driven.

  15. Main-sequence progenitor configurations of the NN Ser candidate circumbinary planetary system are dynamically unstable

    NASA Astrophysics Data System (ADS)

    Mustill, Alexander; Marshall, Jonathan; Villaver, Eva; Veras, Dimitri; Davis, Philip; Horner, Jonathan; Witenmyer, Robert

    2013-07-01

    Recent observations of the NN Serpentis post-common envelope binary system have revealed eclipse timing variations that have been attributed to the presence of two Jovian-mass exo-planets. Under the assumption that these planets are real and survived from the binary's Main-Sequence state, we reconstruct initial binaries that give rise to the present NN Ser configuration and test the dynamical stability of the original system. Under standard assumptions regarding binary evolution, we find that survival of the planets through the entire Main-Sequence life-time is very unlikely. Hence, we conclude that the planets are not survivors from before the Common Envelope phase, implying that either they formed recently out of material ejected from the primary, or that the observed signals are of non-planetary origin.

  16. Main-sequence progenitor configurations of the NN Ser candidate circumbinary planetary system are dynamically unstable

    NASA Astrophysics Data System (ADS)

    Mustill, Alexander J.; Marshall, Jonathan P.; Villaver, Eva; Veras, Dimitri; Davis, Philip J.; Horner, Jonathan; Wittenmyer, Robert A.

    2013-12-01

    Recent observations of the NN Serpentis post-common envelope binary system have revealed eclipse timing variations that have been attributed to the presence of two Jovian-mass exo-planets. Under the assumption that these planets are real and survived from the binary's main-sequence state, we reconstruct initial binaries that give rise to the present NN Ser configuration and test the dynamical stability of the original system. Under standard assumptions about binary evolution, we find that survival of the planets through the entire main-sequence lifetime is very unlikely. Hence, we conclude that the planets are not survivors from before the common envelope phase, implying that either they formed recently out of material ejected from the primary or that the observed signals are of non-planetary origin.

  17. Masses of Pre-Main Sequence Binary Stars-Part 2

    NASA Astrophysics Data System (ADS)

    Simon, Michal

    1991-07-01

    There are still no pre-main sequence stars with reliably known masses. This represents a serious gap in our understanding of low-mass star formation. The goal of this long-term program is to measure the masses of pre-main sequence binaries selected from our survey (ref. 3) of the Taurus star forming region by IR lunar occultation and imaging. We propose to use the Fine Guide Sensors in the Transfer Function Mode to determine the apparent orbits of the binaries. Since the distance to the region is known, the apparent orbits will yield the total masses of the binaries. THIS PROPOSAL CONTAINS ONE FOLLOW-UP VISIT TO HV-TAU-C ONLY. THE REST OF THE EXPOSURES ARE IN 3842.

  18. A Turn-over in the Galaxy Main Sequence of Star Formation at M* ~ 1010 Msun

    NASA Astrophysics Data System (ADS)

    Lee, Nicholas; Cosmos Team

    2015-01-01

    The relationship between galaxy star formation rates (SFR) and stellar masses (M*) is re-examined using a mass-selected sample of ~62,000 star-forming galaxies at z < 1.3 in the COSMOS 2 deg2 field. We measure infrared luminosities and SFRs using photometry from Herschel-PACS and SPIRE, Spitzer 24 μm, and the NRK method based on galaxies' locations in the restframe color-color diagram (NUV-r) vs. (r-K). Using these new SFRs, we find that the relationship between median SFR and M* follows a power-law at low stellar masses, but flattens to nearly constant SFR at high stellar masses. We describe a new parameterization that provides the best fit to the main sequence and charaterizes the low mass power-law slope, turnover mass, and overall scaling of the relationship. The turnover in the main sequence occurs at a characteristic mass of about M0 ~ 1010 Msun at all redshifts. The low mass power-law slope ranges from 0.9-1.3 and the overall scaling of the main sequence rises as a function of (1+z)4.2±0.10. A broken power-law fit below and above the turnover mass gives relationships of SFR ∝ M*0.88±0.06 below the turnover mass and SFR ∝ M*0.27±0.04 above the turnover mass. On average, galaxies more massive than M* > 1010 Msun have a much lower specfic star formation rate (SSFR = SFR/M*) than would be expected by simply extrapolating the traditional linear fit to the main sequence found for less massive galaxies.

  19. A survey for rapid variability among early main sequence A-stars

    NASA Astrophysics Data System (ADS)

    Schutt, Randy L.

    This thesis is a survey of non-peculiar early (A0 to A5) main sequence A-stars for rapid (4 to 30 minutes), low amplitude (less than 10 millimagnitudes) variability. Peculiar stars (roAp stars) are presently the only objects known to exhibit this behavior on or near the main sequence. There are also reasons for suspecting variability in normal stars; survey objects are in close proximity, in an Hertzsprung-Russell (HR) diagram, to the cepheid instability strip where many pulsational variables are found (i.e. the delta Scuti and roAp stars), and there is evidence of pulsational variability (at slightly longer periods) in the non-peculiar delta Scuti stars. The survey is also an independent test of the main sequence mass-loss theory proposed by Wilson et al. 1986. Finally, surveys of this type may produce objects of asteroseismological interest. The purpose of the survey is to detect variability, not to resolve all frequencies that may be involved. All observations were gathered with the University of Wisconsin Two-Star Photometer. This instrument coupled with computerized high-speed data collection used the small (16 to 24 in.) telescopes at Pine Bluff Observatory and Table Mountain Observatory. Several period-searching methods were used to analyze time series of differential photometric data. The survey produced a few stars suspected of variability, however, there is no evidence for large scale rapid variability among the non-peculiar main sequence A-stars. The survey also produced several low-amplitude delta Scuti stars, which are in or blueward of the recognized instability strip. These stars verify predictions that delta Scuti stars exist at lower amplitudes, and may also indicate they are present at earlier spectral types.

  20. Evolution and detectability of comet clouds during post-main-sequence stellar evolution

    NASA Technical Reports Server (NTRS)

    Stern, S. Alan; Brandt, John C.; Shull, J. Michael

    1990-01-01

    The destruction of volatile-rich comet disks and Oort-type clouds around luminous post-main-sequence stars is modeled. The models are in agreement with several aspects of existing observations of water and complex molecules in the envelopes of giant and supergiant stars. If confirmed, these results would establish the common existence of Oort-type clouds around other stars and would constitute indirect evidence for sites of past planetary formation.

  1. The coronal temperatures of low-mass main-sequence stars

    NASA Astrophysics Data System (ADS)

    Johnstone, C. P.; Güdel, M.

    2015-06-01

    Aims: We study the X-ray emission of low-mass main-sequence stars to derive a reliable general scaling law between coronal temperature and the level of X-ray activity. Methods: We collect ROSAT measurements of hardness ratios and X-ray luminosities for a large sample of stars to derive which stellar X-ray emission parameter is most closely correlated with coronal temperature. We calculate average coronal temperatures for a sample of 24 low-mass main-sequence stars with measured emission measure distributions (EMDs) collected from the literature. These EMDs are based on high-resolution X-ray spectra measured by XMM-Newton and Chandra. Results: We confirm that there is one universal scaling relation between coronal average temperature and surface X-ray flux, FX, that applies to all low-mass main-sequence stars. We find that coronal temperature is related to FX by T̅cor = 0.11 FX0.26, where T̅cor is in MK and FX is in erg s-1 cm-2.

  2. Deep CCD photometry in globular clusters. I. The Main sequence of M4

    SciTech Connect

    Richer, H.B.; Fahlman, G.G.

    1984-02-01

    From deep UBV CCD images obtained with CTIO 4 m telescope, we have constructed color-magnitude and color-color diagrams in a 4' x 3' field of the globular cluster M4. Inspection of the color-magnitude diagram indicates that the main sequence down to almost 3 mag below the turnoff has an intrinsic width no wider than +- 0.02 magnitudes in (B--V) implying that the variation in helium abundance (..delta..Y) in these stars must be less than +- 0.07 (..delta..Z = 0) or that the fractional variation in metallicity (..delta..Z/Z) is no larger than +- 0.22 (..delta..Y = 0). To a similar limit on the main sequence, the binary frequency in the field studied must be very small and does not exceed 3% of all main-sequence stars (and may be zero). The luminosity function of M4 is rather flat and definitely turns over by V = 20 (M/sub v/ = 7.5).

  3. Exo-Planetary Phoenix: Rebirth of Planetary Systems Beyond the Main Sequence

    NASA Astrophysics Data System (ADS)

    Marengo, M.

    2014-04-01

    Mounting evidence suggests that planetary systems may be a common feature of stars that have evolved beyond the main sequence. Warm debris disks around white dwarfs and "pulsar" planets orbiting a neutron star are a strong indication that planetary systems may, at least in same cases, survive the dramatic phenomena leading to stellar death. A close look at these late evolutionary stages, however, suggests that these systems may be more than mere survivors of doomed pre-existing exo-planetary systems. The circumstellar environment of post-main sequence stars bears surprising similarities to the conditions leading to pre-main sequence planetary formation: a metal-rich environment often characterized by the presence of circumstellar or circumbinary disks. Are these conditions conducive to the birth of a second-generation planetary system, like a phoenix rising from the ashes of ancient worlds? In this talk we will discuss how the physical conditions in the winds of dusty giant stars may be favorable for renewed planetary formation, with particular emphasis on the effects of enhanced metallicity, binarity and the timescales available for the formation of a new generation of planets.

  4. W134: A new pre-main-sequence double-lined spectroscopic binary

    NASA Technical Reports Server (NTRS)

    Padgett, Deborah L.; Stapelfeldt, Karl R.

    1994-01-01

    We report the discovery that the pre-main-sequence star Walker 134 in the young cluster NGC 2264 is a double-lined spectroscopic binary. Both components are G stars with strong Li I 6708 A absorption lines. Twenty radial velocity measurements have been used to determined the orbital elements of this system. The orbit has a period of 6.3532 +/- 0.0012 days and is circular within the limits of our velocity resolution; e less than 0.01. The total system mass is stellar mass sin(exp 3) i = 3.16 solar mass with a mass ratio of 1.04. Estimates for the orbit inclination angle and stellar radii place the system near the threshold for eclipse observability; howerver, no decrease in brightness was seen during two attempts at photometric monitoring. The circular orbit of W 134 fills an important gap in the period distribution of pre-main-sequence binaries and thereby constrains the effectiveness of tidal orbital circularization during the pre-main sequence.

  5. Lithium in lower-main-sequence stars of the Alpha Persei cluster

    NASA Technical Reports Server (NTRS)

    Balachandran, Suchitra; Lambert, David L.; Stauffer, John R.

    1988-01-01

    Lithium abundances are presented for main-sequence stars of spectral types F, G, and K in the young open cluster Alpha Per. For 46 cluster members, a correlation between Li abundance and projected rotational velocity v sin i is found: all of the Li-poor stars are slow rotators. Two explanations are proposed to account for the correlation: (1) that the Li depletion is introduced following a rapid spin-down phase experienced by young low-mass stars, and that this episode of Li depletion may be the dominant one determining the spread of Li abundances among young low-mass main-sequence stars, and (2) that star formation has occurred over a finite period such that the older stars have undergone a spin-down and depletion of Li by a means that may or may not depend on rotation. The Li abundance in the warm and rapidly rotating stars appears to be undepleted, as is predicted by recent models of pre-main-sequence stars. The depletion observed in the cool stars exceeds the level predicted by these models.

  6. A buried marine depositional sequence (Presumpscot FM. ) N. of the marine limit, Waterboro, Maine

    SciTech Connect

    Morency, R.E. )

    1993-03-01

    Subsurface investigations conducted in Waterboro, ME (York Co.) in connection with studies of two hazardous waste sites and a municipal water supply exploration project, have demonstrated that a laterally extensive sequence of marine deposits underlies surficial sediments mapped as non-esker ice contact glacio-fluvial deposits. The marine deposits consist of a fining-downwards sequence of grey, micaceous sands (fine to medium, grading down to a silty-fine sand), which grade downward into a thick ([plus minus] 30 feet) grey silt/clay unit, which itself shows a fining-downward trend. The stratigraphy is likely correlative to the Presumpscot Formation, as described by Bloom (1963). The bottom of the regressive marine sequence is marked at several locations by a thin layer of sand-sized biotite mica. Lodgement till was encountered only at scattered localities (in boreholes) at each site. The bedrock surface is of considerable relief, with changes of 200--300 feet over short distances detected. The sequence appears to be the record of a rapidly transgressing sea which inundated a valley where outwash had been deposited by meltwater ahead of retreating ice. As the sea retreated, up to 70 feet of sediment was deposited in a continuous, coarsening-upwards sequence. Subsequent to the marine regression, the sediments were reworked in a subaerial (braided stream) environment. The Surficial Geologic Map of Maine shows that the inland limit of late-glacial marine submergence is located approximately 8 miles southwest of Waterboro, in Alfred, Maine. The marine limit in Alfred takes the form of a NNE trending, blunt-ended embayment. The results of this study suggest that the marine embayment once extended northward from Alfred, and is now a buried feature, possibly representing a preglacial valley, which hosted an estuary in late Wisconsonian time.

  7. Main-Sequence CMEs as Magnetic Explosions: Compatibility with Observed Kinematics

    NASA Technical Reports Server (NTRS)

    Moore, Ron; Falconer, David; Sterling, Alphonse

    2004-01-01

    We examine the kinematics of 26 CMEs of the morphological main sequence of CMEs, those having the classic three-part bubble structure of (1) a bright front eveloping (2) a dark cavity within which rides (3) a bright blob/filamentary feature. Each CME is observed in Yohkoh/SXT images to originate from near the limb (> or equal to 0.7 R(sub Sun) from disk center). The basic data (from the SOHO LASCO CME Catalog) for the kinematics of each CME are the sequence of LASCO images of the CME, the time of each image, the measured radial distance of the front edge of the CME in each image, and the measured angular extent of the CME. About half of our CMEs (12) occur with a flare, and the rest (14) occur without a flare. While the average linear-fit speed of the flare CMEs (1000 km/s) is twice that of the non-flare CMEs (510 km/s), the flare CMEs and the non-flare CMEs are similar in that some have nearly flat velocity-height (radial extent) profiles (little acceleration), some have noticeably falling velocity profiles (noticeable deceleration), and the rest have velocity profiles that rise considerably through the outer corona (blatant acceleration). This suggests that in addition to sharing similar morphology, main-sequence CMEs all have basically the same driving mechanism. The observed radial progression of each of our 26 CMEs is fit by a simple model magnetic plasmoid that is in pressure balance with the radial magnetic field in the outer corona and that propels itself outward by magnetic expansion, doing no net work on its surroundings. On average over the 26 CMEs, this model fits the observations as well as the assumption of constant acceleration. This is compatible with main-sequence CMEs being magnetically driven, basically magnetic explosions, with the velocity profile in the outer corona being largely dictated by the initial Alfien speed in the CME (when the front is at approx. 3 (sub Sun), analogous to the mass of a main-sequence star dictating the luminosity.

  8. Whole-Genome Sequencing of a Healthy Aging Cohort.

    PubMed

    Erikson, Galina A; Bodian, Dale L; Rueda, Manuel; Molparia, Bhuvan; Scott, Erick R; Scott-Van Zeeland, Ashley A; Topol, Sarah E; Wineinger, Nathan E; Niederhuber, John E; Topol, Eric J; Torkamani, Ali

    2016-05-01

    Studies of long-lived individuals have revealed few genetic mechanisms for protection against age-associated disease. Therefore, we pursued genome sequencing of a related phenotype-healthy aging-to understand the genetics of disease-free aging without medical intervention. In contrast with studies of exceptional longevity, usually focused on centenarians, healthy aging is not associated with known longevity variants, but is associated with reduced genetic susceptibility to Alzheimer and coronary artery disease. Additionally, healthy aging is not associated with a decreased rate of rare pathogenic variants, potentially indicating the presence of disease-resistance factors. In keeping with this possibility, we identify suggestive common and rare variant genetic associations implying that protection against cognitive decline is a genetic component of healthy aging. These findings, based on a relatively small cohort, require independent replication. Overall, our results suggest healthy aging is an overlapping but distinct phenotype from exceptional longevity that may be enriched with disease-protective genetic factors. VIDEO ABSTRACT. PMID:27114037

  9. The Main Sequence of Explosive Solar Active Regions: Comparison of Emerging and Mature Active Regions

    NASA Technical Reports Server (NTRS)

    Falconer, David; Moore, Ron

    2011-01-01

    For mature active regions, an active region s magnetic flux content determines the maximum free energy the active region can have. Most Large flares and CMEs occur in active regions that are near their free-energy limit. Active-region flare power radiated in the GOES 1-8 band increases steeply as the free-energy limit is approached. We infer that the free-energy limit is set by the rate of release of an active region s free magnetic energy by flares, CMEs and coronal heating balancing the maximum rate the Sun can put free energy into the active region s magnetic field. This balance of maximum power results in explosive active regions residing in a "mainsequence" in active-region (flux content, free energy content) phase space, which sequence is analogous to the main sequence of hydrogen-burning stars in (mass, luminosity) phase space.

  10. Learning of bimanual motor sequences in normal aging

    PubMed Central

    Bhakuni, Rashmi; Mutha, Pratik K.

    2015-01-01

    While it is well accepted that motor performance declines with age, the ability to learn simple procedural motor tasks appears to remain intact to some extent in normal aging. Here we examined the impact of aging on the acquisition of a simple sequence of bimanual actions. We further asked whether such learning results from an overall decrease in response time or is also associated with improved coordination between the hands. Healthy young and old individuals performed a bimanual version of the classic serial reaction time task. We found no learning deficit in older adults and noted that older subjects were able to learn as much as young participants. We also observed that learning in both groups was associated with an overall decrease in response time, but switch cost, the increase in response time when a switch in hands was required during sequence execution, did not decrease with learning. Surprisingly however, overall switch cost was lower in the older group compared to the younger subjects. These findings are discussed in the context of interactions between procedural and declarative memory, reduced interhemispheric inhibition and more symmetric cortical activation during motor performance in normal aging. PMID:26005417

  11. Angular momentum transport efficiency in post-main sequence low-mass stars

    NASA Astrophysics Data System (ADS)

    Spada, F.; Gellert, M.; Arlt, R.; Deheuvels, S.

    2016-05-01

    Context. Using asteroseismic techniques, it has recently become possible to probe the internal rotation profile of low-mass (≈1.1-1.5 M⊙) subgiant and red giant stars. Under the assumption of local angular momentum conservation, the core contraction and envelope expansion occurring at the end of the main sequence would result in a much larger internal differential rotation than observed. This suggests that angular momentum redistribution must be taking place in the interior of these stars. Aims: We investigate the physical nature of the angular momentum redistribution mechanisms operating in stellar interiors by constraining the efficiency of post-main sequence rotational coupling. Methods: We model the rotational evolution of a 1.25M⊙ star using the Yale Rotational stellar Evolution Code. Our models take into account the magnetic wind braking occurring at the surface of the star and the angular momentum transport in the interior, with an efficiency dependent on the degree of internal differential rotation. Results: We find that models including a dependence of the angular momentum transport efficiency on the radial rotational shear reproduce very well the observations. The best fit of the data is obtained with an angular momentum transport coefficient scaling with the ratio of the rotation rate of the radiative interior over that of the convective envelope of the star as a power law of exponent ≈3. This scaling is consistent with the predictions of recent numerical simulations of the Azimuthal Magneto-Rotational Instability. Conclusions: We show that an angular momentum transport process whose efficiency varies during the stellar evolution through a dependence on the level of internal differential rotation is required to explain the observed post-main sequence rotational evolution of low-mass stars.

  12. Kinematic Distances of Pre-main Sequence Stars in the Lupus Star-Forming Region

    NASA Astrophysics Data System (ADS)

    Galli, P. A. B.; Teixeira, R.; Ducourant, C.; Bertout, C.

    2014-06-01

    The problem of the determination of distances has always played a central role in astronomy. However, little recent progress has been made in the distance determination of faint young stellar objects such as pre-main sequence (PMS) stars. Many of the PMS stars were neither observed by the Hipparcos satellite due to their magnitude nor have any trigonometric parallax measured from the ground due to their distance. Here we investigate the kinematic properties of the Lupus moving group with the primary objective of deriving individual parallaxes for each group member of this star-forming region.

  13. X-rays from Pre-Main Sequence Stars: Recent Results and Future Challenges

    NASA Astrophysics Data System (ADS)

    Skinner, S.

    2016-08-01

    I will summarize recent results of X-ray observations of pre-main sequence (PMS) stars, focusing on XMM-Newton RGS and Chandra HETG observations of RY Tau. These observations provide the best grating spectra obtained so far of a jet-driving T Tauri star. I will also identify key questions regarding the origin and nature of X-ray emission from PMS stars that have emerged from 16 years of XMM-Newton and Chandra observations and which present challenges for the next decade.

  14. Theoretical study of γ Doradus pulsations in pre-main sequence stars

    NASA Astrophysics Data System (ADS)

    Bouabid, M.-P.; Montalbán, J.; Miglio, A.; Dupret, M.-A.; Grigahcène, A.; Noels, A.

    2010-12-01

    The question of the existence of the pre-main sequence (PMS) γ Doradus (γ Dor) pulsators has been raised by observations of young clusters such as NGC 884 hosting γ Dor members. We have explored the properties of γ Dor-type pulsations with a grid of PMS models covering the mass range {1.2 < M_*/M_⊙ < 2.5} and we derive the theoretical instability strip (IS) for the PMS γ Dor pulsators. We explore the possibility of distinguishing between PMS and MS γ Dor by the behaviour of the period spacing of their high order gravity modes (g-modes).

  15. Analysis of C II resonance lines in some main sequence early-type stars

    NASA Technical Reports Server (NTRS)

    Cugier, H.; Hardorp, J.

    1988-01-01

    IUE data are used to investigate C II resonance lines at 1335 A in eight main-sequence stars of spectral types from A0 to B3, and both LTE and non-LTE line profiles have been computed. In stars with low rotational velocities (such as Vega, Pi Cet, and Tau Her), logarithmic carbon abundances log N(C/H) of -3.55 to -3.45 are obtained for the non-LTE case. The LTE analysis reveals lower carbon abundances by about 0.1 dex. Significant differences among the fast rotating stars are pointed out.

  16. Upper limits on extreme ultraviolet radiation from nearby main sequence and subgiant stars

    NASA Technical Reports Server (NTRS)

    Ayres, T. R.; Linsky, J. L.; Margon, B.; Bowyer, S.

    1978-01-01

    Flux upper limits for 44-800 A radiation were measured in a sample of nearby main sequence stars and one subgiant star with the aid of the Apollo-Soyuz grazing incidence telescope. Comparisons of emission measure upper limits with three different methods for predicting coronal properties cannot yet determine which, if any, are valid. Data for Alpha Centauri A and B are consistent with recent HEAO-1 soft X-ray measurements which suggest that the surface flux of coronal emission from the Alpha Cen system is comparable to that of the 'normal' sun.

  17. Multiple stellar populations in Magellanic Cloud clusters - IV. The double main sequence of the young cluster NGC 1755

    NASA Astrophysics Data System (ADS)

    Milone, A. P.; Marino, A. F.; D'Antona, F.; Bedin, L. R.; Da Costa, G. S.; Jerjen, H.; Mackey, A. D.

    2016-06-01

    Nearly all the star clusters with ages of ˜1-2 Gyr in both Magellanic Clouds exhibit an extended main-sequence turn-off (eMSTO) whose origin is under debate. The main scenarios suggest that the eMSTO could be either due to multiple generations of stars with different ages or to coeval stellar populations with different rotation rates. In this paper we use Hubble Space Telescope images to investigate the ˜80-Myr old cluster NGC 1755 in the LMC. We find that the MS is split with the blue and the red MS hosting about the 25 per cent and the 75 per cent of the total number of MS stars, respectively. Moreover, the MSTO of NGC 1755 is broadened in close analogy with what is observed in the ˜300-Myr-old NGC 1856 and in most intermediate-age Magellanic-Cloud clusters. We demonstrate that both the split MS and the eMSTO are not due to photometric errors, field-stars contamination, differential reddening, or non-interacting binaries. These findings make NGC 1755 the youngest cluster with an eMSTO. We compare the observed CMD with isochrones and conclude that observations are not consistent with stellar populations with difference in age, helium, or metallicity only. On the contrary, the split MS is well reproduced by two stellar populations with different rotation, although the fit between the observed eMSTO and models with different rotation is not fully satisfactory. We speculate whether all stars in NGC 1755 were born rapidly rotating, and a fraction has slowed down on a rapid time-scale, or the dichotomy in rotation rate was present already at star formation. We discuss the implication of these findings on the interpretation of eMSTO in young and intermediate-age clusters.

  18. An Analysis of the Population of Extended Main Sequence Turn-off Clusters in the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Piatti, Andrés E.; Bastian, Nate

    2016-08-01

    We combine a number of recent studies of the extended main sequence turn-off (eMSTO) phenomenon in intermediate age stellar (1 - 2 Gyr) clusters in the Large Magellanic Cloud (LMC) in order to investigate its origin. By employing the largest sample of eMSTO LMC clusters so far used, we show that cluster core radii, masses, and dynamical state are not related to the genesis of eMSTOs. Indeed, clusters in our sample have core radii, masses and age-relaxation time ratios in the range ≈ 2-6 pc, 3.35- 5.50 (log(Mcls/M⊙) and 0.2-8.0, respectively. These results imply that the eMSTO phenomenon is not caused by actual age spreads within the clusters. Furthermore, we confirm from a larger cluster sample recent results including young eMSTO LMC clusters, that the FWHM at the MSTOs correlates most strongly with cluster age, suggesting that a stellar evolutionary effect is the underlying cause.

  19. THE EXTENDED MAIN-SEQUENCE TURNOFF CLUSTERS OF THE LARGE MAGELLANIC CLOUD-MISSING LINKS IN GLOBULAR CLUSTER EVOLUTION

    SciTech Connect

    Keller, Stefan C.; Mackey, A. Dougal; Da Costa, Gary S.

    2011-04-10

    Recent observations of intermediate-age (1-3 Gyr) massive star clusters in the Large Magellanic Cloud have revealed that the majority possess bifurcated or extended main-sequence turnoff (EMSTO) morphologies. This effect can be understood to arise from subsequent star formation among the stellar population with age differences between constituent stars amounting to 50-300 Myr. Age spreads of this order are similarly invoked to explain the light-element abundance variations witnessed in ancient globular clusters (GCs). In this paper, we explore the proposition that the clusters exhibiting the EMSTO phenomenon are a general phase in the evolution of massive clusters, one that naturally leads to the particular chemical properties of the ancient GC population. We show that the isolation of EMSTO clusters to intermediate ages is the consequence of observational selection effects. In our proposed scenario, the EMSTO phenomenon is identical to that which establishes the light-element abundance variations that are ubiquitous in the ancient GC population. Our scenario makes a strong prediction: EMSTO clusters will exhibit abundance variations in the light-elements characteristic of the ancient GC population.

  20. The Angular Momentum Evolution of 0.1-10 Msolar Stars from the Birth Line to the Main Sequence

    NASA Astrophysics Data System (ADS)

    Wolff, S. C.; Strom, S. E.; Hillenbrand, L. A.

    2004-02-01

    Projected rotational velocities (vsini) have been measured for a sample of 145 stars with masses between 0.4 and greater than 10 Msolar (median mass 2.1 Msolar) located in the Orion star-forming complex. These measurements have been supplemented with data from the literature for Orion stars with masses as low as 0.1 Msolar. The primary finding from analysis of these data is that the upper envelope of the observed values of angular momentum per unit mass (J/M) varies as M0.25 for stars on convective tracks having masses in the range ~0.1 to ~3 Msolar. This power law extends smoothly into the domain of more massive stars (3-10 Msolar), which in Orion are already on the zero-age main sequence. This result stands in sharp contrast to the properties of main-sequence stars, which show a break in the power law and a sharp decline in J/M with decreasing mass for stars with M<2 Msolar. A second result of our study is that this break is seen already among the pre-main-sequence stars in our Orion sample that are on radiative tracks, even though these stars are only a few million years old. A comparison of rotation rates seen for stars on either side of the convective-radiative boundary shows that stars do not rotate as solid bodies during the transition from convective to radiative tracks. As a preliminary demonstration of how observations can be used to constrain the processes that control early stellar angular momentum, we show that the broad trends in the data can be accounted for by simple models that posit that stars (1) lose angular momentum before they are deposited on the birth line, plausibly through star-disk interactions; (2) undergo additional braking as they evolve down their convective tracks; and (3) are subject to core-envelope decoupling during the convective-radiative transition.

  1. Pre-main sequence candidates in the very young open cluster NGC 6611

    NASA Astrophysics Data System (ADS)

    de Winter, D.; Koulis, C.; The, P. S.; van den Ancker, M. E.; Perez, M. R.; Bibo, E. A.

    1997-02-01

    For the search of Herbig Ae/Be objects in the extremely young open cluster NGC 6611 we have selected a sample of 52 pre-main sequence candidates, discovered by Walker (1961), Sagar & Joshi (1979), Chini & Wargau (1990) and The et al. (1990). We continue the approach of the last paper by studying each star individually with new and unpublished Walraven WULBV, Johnson/Cousins UBV(RI)_C and Johnson JHKLM photometric data as well as low resolution spectroscopy. Each object is shown to have its own extinction law, which is investigated using their spectral energy distribution (SED). There does not seem to be a clear relationship between the location of a star and the extinction law. This means that the extinction is generated locally and its correction must be taken individually. For each object accurate astrophysical parameters are then derived. Plotting the objects in an HR-diagram, together with the values for the E(B-V), the probability of membership value P and the extinction characteristics, helps to discriminate between cluster members and non-cluster members. Most foreground stars are of late spectral type and are labeled as Group III objects. Group I, to which most members of this cluster belong, contains objects of early spectral type. Part of them seem to be in their post-ZAMS phase and the other part in their pre-ZAMS stage. By comparing the evolutionary tracks of Palla & Stahler (1993) for pre-MS objects and of Maeder & Meyenet (1988) for post-MS stars we have concluded that the cluster contains objects of a few 0.1 Myr as well as objects of about 6 Myr. As most of the Group I objects do not show well-known Herbig Ae/Be characteristics, the time scale of clearing the disk material must be typically less than about 0.1 Myr for the more massive objects. Objects that show an IR-excess are found among the less luminous ones. They could still be in their pre-ZAMS phase, having an age of about 1 Myr. Such an age is appropriate for the Group II objects, which are

  2. Main-Sequence Binary Stars in the Core of NGC 6397

    NASA Astrophysics Data System (ADS)

    Bolton, A. S.; Cool, A. M.; Anderson, J.

    1999-12-01

    Using HST WFPC2 data, we isolate main-sequence binary candidates in the central region of the globular cluster NGC 6397 based on their locations in an I vs. V - I color--magnitude diagram. We have largely eliminated field stars from the sample beforehand based on proper motions determined from two sets of position data separated by approximately three years. Binary candidates are fit to models based on the empirically derived main-sequence ridge line for the cluster, and component masses are determined using theoretical mass--luminosity relations appropriate to the cluster. Preliminary results suggest an upper limit of 3% on the binary fraction for stars in the apparent magnitude range 17.0 <= V555 <= 20.7 ( 0.8 to 0.5 Msun) and binary mass ratios greater than approximately 0.45. We also present preliminary results for the distribution of binaries as a function of primary mass and mass ratio, as well as a comparison of these results to previously published findings for field stars.

  3. Theory of winds in late-type evolved and pre-main-sequence stars

    NASA Technical Reports Server (NTRS)

    Macgregor, K. B.

    1983-01-01

    Recent observational results confirm that many of the physical processes which are known to occur in the Sun also occur among late-type stars in general. One such process is the continuous loss of mass from a star in the form of a wind. There now exists an abundance of either direct or circumstantial evidence which suggests that most (if not all) stars in the cool portion of the HR diagram possess winds. An attempt is made to assess the current state of theoretical understanding of mass loss from two distinctly different classes of late-type stars: the post-main-sequence giant/supergiant stars and the pre-main-sequence T Tauri stars. Toward this end, the observationally inferred properties of the wind associated with each of the two stellar classes under consideration are summarized and compared against the predictions of existing theoretical models. Although considerable progress has been made in attempting to identify the mechanisms responsible for mass loss from cool stars, many fundamental problems remain to be solved.

  4. Estimating the Radius of the Convective Core of Main-sequence Stars from Observed Oscillation Frequencies

    NASA Astrophysics Data System (ADS)

    Yang, Wuming

    2016-10-01

    The determination of the size of the convective core of main-sequence stars is usually dependent on the construction of models of stars. Here we introduce a method to estimate the radius of the convective core of main-sequence stars with masses between about 1.1 and 1.5 M ⊙ from observed frequencies of low-degree p-modes. A formula is proposed to achieve the estimation. The values of the radius of the convective core of four known stars are successfully estimated by the formula. The radius of the convective core of KIC 9812850 estimated by the formula is 0.140 ± 0.028 R ⊙. In order to confirm this prediction, a grid of evolutionary models was computed. The value of the convective-core radius of the best-fit model of KIC 9812850 is 0.149 R ⊙, which is in good agreement with that estimated by the formula from observed frequencies. The formula aids in understanding the interior structure of stars directly from observed frequencies. The understanding is not dependent on the construction of models.

  5. Theoretical seismic properties of pre-main sequence γ Doradus pulsators

    NASA Astrophysics Data System (ADS)

    Bouabid, M.-P.; Montalbán, J.; Miglio, A.; Dupret, M.-A.; Grigahcène, A.; Noels, A.

    2011-07-01

    Context. The late A and F-type γ Doradus (γ Dor) stars pulsate with high-order gravity modes (g-modes). The existence of different evolutionary phases crossing the γ Dor instability strip raises the question whether pre-main sequence (PMS) γ Dor stars exist. Aims: We intend to study the differences between the asteroseismic behaviour of PMS and main sequence (MS) γ Dor pulsators as predicted by the current theory of stellar evolution and stability. Methods: We explore the adiabatic and non-adiabatic properties of high-order g-modes in a grid of PMS and MS models covering the mass range 1.2 M⊙ < M∗ < 2.5 M⊙. Results: We have derived the theoretical instability strip (IS) for the PMS γ Dor pulsators. This IS covers the same effective temperature range as the MS γ Dor one. Nevertheless, the frequency domain of unstable modes in PMS models with a fully radiative core is greater than in MS models, even if they present the same number of unstable modes. Moreover, the differences between MS and PMS internal structures are reflected in the average values of the period spacing, as well as in the dependence of the period spacing on the radial order of the modes, opening the window to determination of the evolutionary phase of γ Dor stars from their pulsation spectra.

  6. ACCRETION RATES ON PRE-MAIN-SEQUENCE STARS IN THE YOUNG OPEN CLUSTER NGC 6530

    SciTech Connect

    Gallardo, Jose; Del Valle, Luciano; Ruiz, Maria Teresa E-mail: ldelvall@das.uchile.cl

    2012-01-15

    It is well accepted that during the star formation process, material from a protoplanetary disk is accreted onto the central object during the first {approx}1-5 Myr. Different authors have published measurements of accretion rates for young low- and intermediate-mass stars in several nearby star-forming regions (SFRs). Due to its somewhat larger distance, the SFR M8 (the Lagoon Nebula) has not been studied to the same extent, despite its abundant population of young stellar objects. We have obtained optical band low-resolution spectra of a sample of pre-main-sequence stars in the open cluster NGC 6530 located in the aforementioned nebulae using the Gemini Multi Object Spectrograph at Gemini-South in multi-object mode. Spectra cover the H{sub {alpha}} emission line used to measure the accretion rate, following the method presented by Natta et al. The observed spectral characteristics are fully consistent with pre-main-sequence stars, showing lithium absorption lines, which are very common in young stellar objects, as well as prominent and broad H{sub {alpha}} emission lines, indicating a T Tauri evolutionary stage. This work presents the first determinations of mass accretion rates of young stellar objects in the open cluster NGC 6530, confirming that they are classical T Tauri stars going through the accretion phase. These observations contribute to a better understanding of the stellar content and evolutionary phase of the very active Lagoon Nebula SFR.

  7. Main-sequence of star-formation, between universality and tension

    NASA Astrophysics Data System (ADS)

    Elbaz, David

    2015-08-01

    We will present a new method to push the deepest Herschel surveys even deeper in sensitivity and redshift range. A comparison to UV techniques such as the Lyman break technique will be given showing that a population of M*>5x10^10 Msun galaxies is systematically missed by this standard approach at high z. We will discuss how SFR estimates of starbursting galaxies can be wrongly estimated when using the UV corrected for extinction. A discussion of the relative growth of disks and bulges will be presented.We will show that at least 2/3 of the star-formation history of galaxies took place in a main-sequence mode, i.e. with a characteristic specific SFR +/- 0.3 dex, suggesting that star-formation at the scale of galaxies over the Hubble time is a relatively universal process. This result matches surprisingly well the cold flow paradigm which states that at least 2/3 of the mass growth of galaxies came from smooth accretion of intergalactic matter suggesting that the main-sequence is a direct result of smooth gas accretion. However we will also show that both paradigms lead to a major tension in their relative growth rates as a function of cosmic time showing that either a major regulatory process of star-formation is still missing or that we misunderstand the behavior of baryons at large scales.

  8. PRE-MAIN-SEQUENCE TURN-ON AS A CHRONOMETER FOR YOUNG CLUSTERS: NGC 346 AS A BENCHMARK

    SciTech Connect

    Cignoni, M.; Tosi, M.; Sabbi, E.; Nota, A.; Degl'Innocenti, S.; Moroni, P. G. Prada; Gallagher, J. S.

    2010-03-20

    We present a novel approach to deriving the age of very young star clusters, by using the Turn-On (TOn). The TOn is the point in the color-magnitude diagram (CMD) where the pre-main sequence (PMS) joins the main sequence (MS). In the MS luminosity function (LF) of the cluster, the TOn is identified as a peak followed by a dip. We propose that by combining the CMD analysis with the monitoring of the spatial distribution of MS stars it is possible to reliably identify the TOn in extragalactic star-forming regions. Compared to alternative methods, this technique is complementary to the turnoff dating and avoids the systematic biases affecting the PMS phase. We describe the method and its uncertainties and apply it to the star-forming region NGC 346, which has been extensively imaged with the Hubble Space Telescope (HST). This study extends the LF approach in crowded extragalactic regions and opens the way for future studies with HST/WFC3, the James Webb Space Telescope and from the ground with adaptive optics.

  9. An M Dwarf Companion to an F-type Star in a Young Main-sequence Binary

    NASA Astrophysics Data System (ADS)

    Eigmüller, Ph.; Eislöffel, J.; Csizmadia, Sz.; Lehmann, H.; Erikson, A.; Fridlund, M.; Hartmann, M.; Hatzes, A.; Pasternacki, Th.; Rauer, H.; Tkachenko, A.; Voss, H.

    2016-03-01

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

  10. Confronting uncertainties in stellar physics. II. Exploring differences in main-sequence stellar evolution tracks

    NASA Astrophysics Data System (ADS)

    Stancliffe, R. J.; Fossati, L.; Passy, J.-C.; Schneider, F. R. N.

    2016-02-01

    We assess the systematic uncertainties in stellar evolutionary calculations for low- to intermediate-mass, main-sequence stars. We compare published stellar tracks from several different evolution codes with our own tracks computed using the stellar codes stars and mesa. In particular, we focus on tracks of 1 and 3 M⊙ at solar metallicity. We find that the spread in the available 1 M⊙ tracks (computed before the recent solar composition revision) can be covered by tracks between 0.97-1.01 M⊙ computed with the stars code. We assess some possible causes of the origin of this uncertainty, including how the choice of input physics and the solar constraints used to perform the solar calibration affect the tracks. We find that for a 1 M⊙ track, uncertainties of around 10% in the initial hydrogen abundance and initial metallicity produce around a 2% error in mass. For the 3 M⊙ tracks, there is very little difference between the tracks from the various different stellar codes. The main difference comes in the extent of the main sequence, which we believe results from the different choices of the implementation of convective overshooting in the core. Uncertainties in the initial abundances lead to a 1-2% error in the mass determination. These uncertainties cover only part of the total error budget, which should also include uncertainties in the input physics (e.g., reaction rates, opacities, convective models) and any missing physics (e.g., radiative levitation, rotation, magnetic fields). Uncertainties in stellar surface properties such as luminosity and effective temperature will further reduce the accuracy of any potential mass determinations.

  11. The Evolution of Main-Sequence and Starburst Galaxies Across Cosmic Time

    NASA Astrophysics Data System (ADS)

    Aravena, Manuel

    2015-08-01

    In the last decade, significant progress has been achieved in the understanding of the evolution of star formation in galaxies as a function of redshift. Its is now clear that the majority of galaxies at z<3 form a nearly linear correlation between their stellar mass and star formation rates and appear to create most of their stars in timescales of ~1 Gyr. At the highest luminosities, a significant fraction of galaxies deviate from this ‘main-sequence’, showing short duty cycles and thus producing most of their stars in a single burst of star formation (‘starburst’) within a few 100 Myr, being likely driven by major merger activity. Despite the large luminosities of starbursts, main-sequence galaxies appear to dominate the star formation density of the Universe at its peak.While progress has been impressive, a number of questions are still unanswered. In this talk, I will review our current observational understanding of this ‘main-sequence’ vs ‘starburst’ galaxy paradigm, and will address how future observations (e.g. with ALMA) will help us to have better insights into the fundamental properties of these galaxies.

  12. Soft X-ray observations of pre-main-sequence stars in the Chamaeleon dark cloud

    NASA Technical Reports Server (NTRS)

    Feigelson, Eric D.; Kriss, Gerard A.

    1989-01-01

    X-ray observations of the Chamaeleon I cloud, a star-forming region, are reported. A total of 22 distinct X-ray sources, most associated with previously identified premain sequence stars, are found. The spatial distributions and HR diagrams of the stars are very similar, suggesting that they are coeval. Luminosity functions suggest that the stars have an average X-ray luminosity (Lx) several times that of the Pleiades dwarfs. The value of Lx is significantly correlated with optical magnitude, though no relation between X-ray emission and any photometric or emission line characteristic is present. It is suggested that a Skumanich-type power-law relation may be present over the entire range of stellar ages between 10 to the 6th and 10 to the 10th yr.

  13. Mass functions for globular cluster main sequences based on CCD photometry and stellar models

    NASA Astrophysics Data System (ADS)

    McClure, Robert D.; Vandenberg, Don A.; Smith, Graeme H.; Fahlman, Gregory G.; Richer, Harvey B.; Hesser, James E.; Harris, William E.; Stetson, Peter B.; Bell, R. A.

    1986-08-01

    Main-sequence luminosity functions constructed from CCD observations of globular clusters reveal a strong trend in slope with metal abundance. Theoretical luminosity functions constructed from VandenBerg and Bell's (1985) isochrones have been fitted to the observations and reveal a trend between x, the power-law index of the mass function, and metal abundance. The most metal-poor clusters require an index of about x = 2.5, whereas the most metal-rich clusters exhibit an index of x of roughly -0.5. The luminosity functions for two sparse clusters, E3 and Pal 5, are distinct from those of the more massive clusters, in that they show a turndown which is possibly a result of mass loss or tidal disruption.

  14. Post Main Sequence Orbital Circularization of Binary Stars in the Large and Small Magellanic Clouds.

    SciTech Connect

    Faccioli, L; Alcock, C; Cook, K

    2007-11-20

    We present results from a study of the orbits of eclipsing binary stars (EBs) in the Magellanic Clouds. The samples comprise 4510 EBs found in the Large Magellanic Cloud (LMC) by the MACHO project, 2474 LMC EBs found by the OGLE-II project (of which 1182 are also in the MACHO sample), 1380 in the Small Magellanic Cloud (SMC) found by the MACHO project, and 1317 SMC EBs found by the OGLE-II project (of which 677 are also in the MACHO sample); we also consider the EROS sample of 79 EBs in the bar of the LMC. Statistics of the phase differences between primary and secondary minima allow us to infer the statistics of orbital eccentricities within these samples. We confirm the well-known absence of eccentric orbit in close binary stars. We also find evidence for rapid circularization in longer period systems when one member evolves beyond the main sequence, as also found by previous studies.

  15. The Discovery of Solar-like Activity Cycles Beyond the End of the Main Sequence?

    NASA Astrophysics Data System (ADS)

    Route, Matthew

    2016-10-01

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

  16. Calibrating the Mass-Luminosity Relation at the End of the Main Sequence

    NASA Astrophysics Data System (ADS)

    Henry, Todd

    2000-07-01

    This is a continuation of GO 6047/6566/7493/8282. We use HST-FGS3/1R to calibrate the mass-luminosity relation {MLR} for stars less massive than 0.2 Msun, with special emphasis on objects near the stellar/brown dwarf border. Our goals are to determine Mv values to 0.10 magnitude, masses to 5%, and more than double the number of objects with masses determined to be less than 0.20 Msun. This program uses the combination of HST-FGS3/1R at optical wavelengths and ground-based infrared speckle work to examine nearby, subarcsecond binary systems. Several of the objects included have M < 0.1 Msun, placing them at the very end of the stellar main sequence, and making them brown dwarf candidates.

  17. Calibrating the Mass-Luminosity Relation at the End of the Main Sequence

    NASA Astrophysics Data System (ADS)

    Henry, Todd

    1999-07-01

    This is a continuation request for GO 6047/6566/7493. We will use HST-FGS1R to calibrate the mass-luminosity relation {MLR} for stars less massive than 0.2 Msun, with special emphasis on objects near the stellar/brown dwarf border. Our goals are to determine M_V values to 0.10 magnitude, masses to 5%, and more than double the number of objects with masses determined to be less than 0.20 Msun. This program uses the combination of HST-FGS3/FGS1R at optical wavelengths and ground-based infrared speckle work to examine nearby, subarcsecond binary systems. Several of the objects included have M < 0.1 Msun, placing them at the very end of the stellar main sequence, and making them brown dwarf candidates.

  18. Thermal infrared imaging of GGD27-IRS. The active pre-main sequence star revealed

    NASA Astrophysics Data System (ADS)

    Aspin, C.; Puxley, P. J.; Blanco, P. R.; Pina, R. K.; Pickup, D. A.; Paterson, M. J.; Sylvester, J.; Laird, D. C.; Bridger, A.; Daly, P. N.; Griffin, J. L.

    1994-12-01

    We present near-IR (NIR) 2.2-4.7 micrometer imaging of the core region of the pre-main sequence bipolar CO outflow source GGD27-IRS. Indirect evidence from earlier imaging polarimetry and long-slit spectroscopy suggested that the true young active star in the region, GGD27-ILL, is heavily embedded and completely obscured even at 2 micrometers. Our new 4.7 micrometer images directly detect this source for the first time locating it at 2.0 sec west, 1.3 sec south of the bright NIR source IRS2. This position is 0.2 sec from the position derived from our earlier NIR polarization maps. New mid-IR images of the core region show three point-like sources which are identified as GGD27-ILL, IRS7 and IRS8. We discuss the morphological composition of the core region in light of our discovery.

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

    NASA Technical Reports Server (NTRS)

    Smith, Jeffrey J.

    2005-01-01

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

  20. ASCA X-ray observations of pre-main-sequence stars

    NASA Technical Reports Server (NTRS)

    Skinner, S. L.; Walter, F. M.; Yamauchi, S.

    1996-01-01

    The results of recent Advanced Satellite for Cosmology and Astrophysics (ASCA) X-ray observations of two pre-main sequence stars are presented: the weak emission line T Tauri star HD 142361, and the Herbig Ae star HD 104237. The solid state imaging spectrometer spectra for HD 142361 shows a clear emission line from H-like Mg 7, and spectral fits reveal a multiple temperature plasma with a hot component of at least 16 MK. The spectra of HD 104237 show a complex temperature structure with the hottest plasma at temperatures of greater than 30 MK. It is concluded that mechanisms that predict only soft X-ray emission can be dismissed for Herbig Ae stars.

  1. Possibility that the far ultraviolet excess in M31 is due to main sequence stars

    NASA Technical Reports Server (NTRS)

    Tinsley, B. M.

    1972-01-01

    The far ultraviolet excess in the central region of M31, observed by OAO-2, could be due to young main sequence stars. More than enough such stars are present in the model for the M31 inner disk population derived by Tinsley and Spinrad (1971) to match line- and color-indices at longer wavelengths. If the far ultraviolet radiation of typical galaxies arises from young stars, the theoretical ultraviolet background is enhanced greatly by evolutionary effects. For evolution at the rate of Tinsley and Spinrad's model for M31, or of Arnett's (1971) linear model for our galaxy, the enhancement is a factor 2.5 to 14, depending on the Hubble constant and the spectrum at wavelengths below 1700 A.

  2. Far-infrared observations of main sequence stars surrounded by dust shells

    NASA Technical Reports Server (NTRS)

    Harvey, Paul M.; Smith, Beverly J.; Difrancesco, J.

    1995-01-01

    We have used a 20-channel bolometer array on NASA's Kuiper Airborne Observatory to obtain photometry and size information for several main sequence stars surrounded by dust shells. The observations were made at 50 and/or 100 micrometers on flights based in Christchurch, New Zealand, in 1992, 1993. The stars include the 'Vega-like' star, Beta Pic, as well as two stars, HD 135344 and HD 139614, suggested by subsequent studies to belong possibly to the same class. The results of our observations are best interpreted as upper limits to the far-infrared sizes of the dust clouds around these stars. In addition to the basic size and flux measurements, we have fit simple, optically thin models to the Beta Pic data to explore the range of shell parameters consistent with our limits and with previous observations.

  3. Global Multilocus Sequence Typing Analysis of Mycoplasma bovis Isolates Reveals Two Main Population Clusters

    PubMed Central

    Churchward, C. P.; Schnee, C.; Sachse, K.; Lysnyansky, I.; Catania, S.; Iob, L.; Ayling, R. D.; Nicholas, R. A. J.

    2014-01-01

    Mycoplasma bovis is a major bovine pathogen associated with bovine respiratory disease complex and is responsible for substantial economic losses worldwide. M. bovis is also associated with other clinical presentations in cattle, including mastitis, otitis, arthritis, and reproductive disorders. To gain a better understanding of the genetic diversity of this pathogen, a multilocus sequence typing (MLST) scheme was developed and applied to the characterization of 137 M. bovis isolates from diverse geographical origins, obtained from healthy or clinically infected cattle. After in silico analysis, a final set of 7 housekeeping genes was selected (dnaA, metS, recA, tufA, atpA, rpoD, and tkt). MLST analysis demonstrated the presence of 35 different sequence types (STs) distributed in two main clonal complexes (CCs), defined at the double-locus variant level, namely, CC1, which included most of the British and German isolates, and CC2, which was a more heterogeneous and geographically distant group of isolates, including European, Asian, and Australian samples. Index of association analysis confirmed the clonal nature of the investigated M. bovis population, based on MLST data. This scheme has demonstrated high discriminatory power, with the analysis showing the presence of genetically distant and divergent clusters of isolates predominantly associated with geographical origins. PMID:25540400

  4. EXOZODIACAL DUST LEVELS FOR NEARBY MAIN-SEQUENCE STARS: A SURVEY WITH THE KECK INTERFEROMETER NULLER

    SciTech Connect

    Millan-Gabet, R.; Serabyn, E.; Mennesson, B.; Traub, W. A.; Stapelfeldt, K.; Bryden, G.; Colavita, M. M.; Booth, A. J.; Barry, R. K.; Danchi, W. C.; Kuchner, M.; Stark, C. C.; Ragland, S.; Hrynevych, M.; Woillez, J.

    2011-06-10

    The Keck Interferometer Nuller (KIN) was used to survey 25 nearby main-sequence stars in the mid-infrared, in order to assess the prevalence of warm circumstellar (exozodiacal) dust around nearby solar-type stars. The KIN measures circumstellar emission by spatially blocking the star but transmitting the circumstellar flux in a region typically 0.1-4 AU from the star. We find one significant detection ({eta} Crv), two marginal detections ({gamma} Oph and {alpha} Aql), and 22 clear non-detections. Using a model of our own solar system's zodiacal cloud, scaled to the luminosity of each target star, we estimate the equivalent number of target zodis needed to match our observations. Our three zodi detections are {eta} Crv (1250 {+-} 260), {gamma} Oph (200 {+-} 80), and {alpha} Aql (600 {+-} 200), where the uncertainties are 1{sigma}. The 22 non-detected targets have an ensemble weighted average consistent with zero, with an average individual uncertainty of 160 zodis (1{sigma}). These measurements represent the best limits to date on exozodi levels for a sample of nearby main-sequence stars. A statistical analysis of the population of 23 stars not previously known to contain circumstellar dust (excluding {eta} Crv and {gamma} Oph) suggests that, if the measurement errors are uncorrelated (for which we provide evidence) and if these 23 stars are representative of a single class with respect to the level of exozodi brightness, the mean exozodi level for the class is <150 zodis (3{sigma} upper limit, corresponding to 99% confidence under the additional assumption that the measurement errors are Gaussian). We also demonstrate that this conclusion is largely independent of the shape and mean level of the (unknown) true underlying exozodi distribution.

  5. Winds in hot main-sequence stars near the static limit

    NASA Technical Reports Server (NTRS)

    Morrison, Nancy D.

    1995-01-01

    This project began with the acquisition of short-wavelength, high-dispersion IUE spectra of selected late O- and early B-type stars that are near the main sequence in open clusters and associations. The profiles of the resonance lines of N(V), Si(IV), and C(IV) were studied, and we found that the C(IV) lines are the most sensitive indicators of mass loss (stellar winds) in stars of this type. The mass loss manifests itself as an extension of the short-wavelength absorption wing of the doublet, while there is no P Cygni-type emission on the long-wavelength side of the line profile. We investigated whether the short-wavelength extension could be caused by blended lines of other ionic species formed in the photosphere. Although blending is present and introduces uncertainty into the estimation of the precise location on the main sequence of the onset of the mass-loss signature, it is a crucial issue only in a few marginal cases. Mass loss certainly overwhelms blending in its influence on the spectrum between spectral types B0 and B1 (effective temperatures in the range 25,000-27,000 K). We defined a parameter called P(sub w), to describe the degree of asymmetry of the C(IV) resonance-line profile, and we studied the dependence of this parameter on the fundamental stellar parameters. For this purpose, we derived new estimates of the stellar T(eff) and log g from a non-LTE, line-blanketed model-atmosphere analysis of these stars (Grigsby, Morrison, and Anderson 1992). In order to estimate the stellar luminosities, we performed an exhaustive search of the literature for the most reliable available estimates of the distances of the clusters and associations to which the program stars belong. The dependence of P(sub w) on stellar temperature and luminosity is also studied.

  6. A candidate infrared companion in the pre-main sequence multiple system V773 Tau

    NASA Astrophysics Data System (ADS)

    Duchene, G.; Ghez, A. M.; McCabe, C.

    2001-12-01

    We present new near-infrared (1.6 and 2.2 micron) adaptive optics images with the 10m-Keck II telescope of the low-mass pre-main sequence multiple system V773 Tau. In addition to the already known unresolved double-lined spectroscopic binary and its 83 milliarcsec companion, our images reveal a fourth star located only 0.21'' (projected distance: 30 AU) away from the brightest component. This object appears to be much redder than the other stars in the system. We also obtained a medium-resolution (R=3500) long-slit spectrum of this object which covers the 2.0-2.4 micron wavelength range. The spectrum of this dim fourth component in the system shows no photospheric feature but has a small Brγ emission line (equivalent width of about 0.5Å). If this object is not an extincted background giant, which the hydrogen emission line seems to exclude, it is very reminiscent of a small class of objects known as "infrared companions" to T Tauri stars. The tight visual binary has been followed over the last years through speckle interferometry technique, and these data indicate a strange behaviour with a large "jump" in position angle. This may reveal some strong photometric variability in the candidate IRC, which would reinforce its status. We also emphasize that such a quadruple system, with four stars located within 30 AU or so, is extremely rare among main sequence solar-type objects while many T Tauri binaries in Taurus turned out to have additionalcompanions when observed with higher resolution and/or sensitivity. This may indicate that this region is all but typical of star formation in the Galaxy.

  7. The magnetic field of the pre-main sequence Herbig Ae star HD 190073

    NASA Astrophysics Data System (ADS)

    Catala, C.; Alecian, E.; Donati, J.-F.; Wade, G. A.; Landstreet, J. D.; Böhm, T.; Bouret, J.-C.; Bagnulo, S.; Folsom, C.; Silvester, J.

    2007-01-01

    Context: The general context of this paper is the study of magnetic fields in the pre-main sequence intermediate mass Herbig Ae/Be stars. Magnetic fields are likely to play an important role in pre-main sequence evolution at these masses, in particular in controlling the gains and losses of stellar angular momentum. Aims: The particular aim of this paper is to announce the detection of a structured magnetic field in the Herbig Ae star HD 190073, and to discuss various scenarii for the geometry of the star, its environment and its magnetic field. Methods: We have used the ESPaDOnS spectropolarimeter at CFHT in 2005 and 2006 to obtain high-resolution, high signal-to-noise circular polarization spectra which demonstrate unambiguously the presence of a magnetic field in the photosphere of this star. Results: Nine circular polarization spectra were obtained, each one showing a clear Zeeman signature. This signature is suggestive of a magnetic field structured on large scales. The signature, which corresponds to a longitudinal magnetic field of 74± 10 G, does not vary detectably on a one-year timeframe, indicating either an azimuthally symmetric field, a zero inclination angle between the rotation axis and the line of sight, or a very long rotation period. The optical spectrum of HD 190073 exhibits a large number of emission lines. We discuss the formation of these emission lines in the framework of a model involving a turbulent heated region at the base of the stellar wind, possibly powered by magnetic accretion. Conclusions: .This magnetic detection contributes an important new observational discovery which will aid our understanding of stellar magnetism at intermediate masses. 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.

  8. VizieR Online Data Catalog: White dwarf main-sequence binaries (Rebassa-Mansergas+, 2013)

    NASA Astrophysics Data System (ADS)

    Rebassa-Mansergas, A.; Agurto-Gangas, C.; Schreiber, M. R.; Gansicke, B. T.; Koester, D.

    2014-07-01

    The spectroscopic catalogue of white dwarf main-sequence (WDMS) binaries from the Sloan Digital Sky Survey (SDSS) is the largest and most homogeneous sample of compact binary stars currently known. However, because of selection effects, the current sample is strongly biased against systems containing cool white dwarfs and/or early-type companions, which are predicted to dominate the intrinsic population. In this study, we present colour selection criteria that combines optical (ugriz DR8 SDSS) plus infrared (yjhk DR9 UKIRT Infrared Sky Survey, JHK Two Micron All Sky Survey and/or W1W2 Wide-Field Infrared Survey Explorer) magnitudes to select 3419 photometric candidates of harbouring cool white dwarfs and/or dominant (M dwarf) companions. We demonstrate that 84 percent of our selected candidates are very likely genuine WDMS binaries, and that the white dwarf effective temperatures and secondary star spectral types of 71 percent of our selected sources are expected to be below <~10000-15000K, and concentrated at ~M2-3, respectively. We also present an updated version of the spectroscopic SDSS WDMS binary catalogue, which incorporates 47 new systems from SDSS DR8. The bulk of the DR8 spectroscopy is made up of main-sequence stars and red giants that were targeted as part of the Sloan Extension for Galactic Understanding and Exploration (SEGUE) Survey, therefore the number of new spectroscopic WDMS binaries in DR 8 is very small compared to previous SDSS data releases. Despite their low number, DR8 WDMS binaries are found to be dominated by systems containing cool white dwarfs and therefore represent an important addition to the spectroscopic sample. The updated SDSS DR8 spectroscopic catalogue of WDMS binaries consists of 2316 systems. We compare our updated catalogue with recently published lists of WDMS binaries and conclude that it currently represents the largest, most homogeneous and cleanest sample of spectroscopic WDMS binaries from SDSS. (5 data files).

  9. The Solar Neighborhood. XXXVII: The Mass–Luminosity Relation for Main-sequence M Dwarfs

    NASA Astrophysics Data System (ADS)

    Benedict, G. F.; Henry, T. J.; Franz, O. G.; McArthur, B. E.; Wasserman, L. H.; Jao, Wei-Chun; Cargile, P. A.; Dieterich, S. B.; Bradley, A. J.; Nelan, E. P.; Whipple, A. L.

    2016-11-01

    We present a mass–luminosity relation (MLR) for red dwarfs spanning a range of masses from 0.62 {{ M }}ȯ to the end of the stellar main sequence at 0.08 {{ M }}ȯ . The relation is based on 47 stars for which dynamical masses have been determined, primarily using astrometric data from Fine Guidance Sensors (FGS) 3 and 1r, white-light interferometers on the Hubble Space Telescope (HST), and radial velocity data from McDonald Observatory. For our HST/FGS sample of 15 binaries, component mass errors range from 0.4% to 4.0% with a median error of 1.8%. With these and masses from other sources, we construct a V-band MLR for the lower main sequence with 47 stars and a K-band MLR with 45 stars with fit residuals half of those of the V band. We use GJ 831 AB as an example, obtaining an absolute trigonometric parallax, π abs = 125.3 ± 0.3 mas, with orbital elements yielding {{ M }}{{A}}=0.270+/- 0.004 {{ M }}ȯ and {{ M }}{{B}}=0.145+/- 0.002 {{ M }}ȯ . The mass precision rivals that derived for eclipsing binaries. A remaining major task is the interpretation of the intrinsic cosmic scatter in the observed MLR for low-mass stars in terms of physical effects. In the meantime, useful mass values can be estimated from the MLR for the ubiquitous red dwarfs that account for 75% of all stars, with applications ranging from the characterization of exoplanet host stars to the contribution of red dwarfs to the mass of the universe. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

  10. The slowly pulsating B-star 18 Pegasi: A testbed for upper main sequence stellar evolution

    NASA Astrophysics Data System (ADS)

    Irrgang, A.; Desphande, A.; Moehler, S.; Mugrauer, M.; Janousch, D.

    2016-06-01

    The predicted width of the upper main sequence in stellar evolution models depends on the empirical calibration of the convective overshooting parameter. Despite decades of discussions, its precise value is still unknown and further observational constraints are required to gauge it. Based on a photometric and preliminary asteroseismic analysis, we show that the mid B-type giant 18 Peg is one of the most evolved members of the rare class of slowly pulsating B-stars and, thus, bears tremendous potential to derive a tight lower limit for the width of the upper main sequence. In addition, 18 Peg turns out to be part of a single-lined spectroscopic binary system with an eccentric orbit that is greater than 6 years. Further spectroscopic and photometric monitoring and a sophisticated asteroseismic investigation are required to exploit the full potential of this star as a benchmark object for stellar evolution theory. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 265.C-5038(A), 069.C-0263(A), and 073.D-0024(A). 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), proposals H2005-2.2-016 and H2015-3.5-008. Based on observations made with the 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, proposal W15BN015. Based on observations obtained with telescopes of the University Observatory Jena, which is operated by the Astrophysical Institute of the Friedrich-Schiller-University.

  11. PRE-MAIN-SEQUENCE STELLAR POPULATIONS ACROSS SHAPLEY CONSTELLATION III. I. PHOTOMETRIC ANALYSIS AND IDENTIFICATION ,

    SciTech Connect

    Gouliermis, Dimitrios A.; Gennaro, Mario; Henning, Thomas; Da Rio, Nicola; Brandner, Wolfgang; Dolphin, Andrew E.; Robberto, Massimo; Panagia, Nino; Gruendl, Robert A.; Chu, You-Hua; Rosa, Michael; Romaniello, Martino; De Marchi, Guido; Zinnecker, Hans

    2011-09-10

    We present our investigation of pre-main-sequence (PMS) stellar populations in the Large Magellanic Cloud (LMC) from imaging with Hubble Space Telescope Wide-Field Planetary Camera 2. Our targets of interest are four star-forming regions located at the periphery of the super-giant shell LMC 4 (Shapley Constellation III). The PMS stellar content of the regions is revealed through the differential Hess diagrams and the observed color-magnitude diagrams (CMDs). Further statistical analysis of stellar distributions along cross sections of the faint part of the CMDs allowed the quantitative assessment of the PMS stars census, and the isolation of faint PMS stars as the true low-mass stellar members of the regions. These distributions are found to be well represented by a double-Gaussian function, the first component of which represents the main-sequence field stars and the second the native PMS stars of each region. Based on this result, a cluster membership probability was assigned to each PMS star according to its CMD position. The higher extinction in the region LH 88 did not allow the unambiguous identification of its native stellar population. The CMD distributions of the PMS stars with the highest membership probability in the regions LH 60, LH 63, and LH 72 exhibit an extraordinary similarity among the regions, suggesting that these stars share common characteristics, as well as common recent star formation history. Considering that the regions are located at different areas of the edge of LMC 4, this finding suggests that star formation along the super-giant shell may have occurred almost simultaneously.

  12. Dynamical Estimate of Post-main-sequence Stellar Masses in 47 Tucanae

    NASA Astrophysics Data System (ADS)

    Parada, Javiera; Richer, Harvey; Heyl, Jeremy; Kalirai, Jason; Goldsbury, Ryan

    2016-07-01

    We use the effects of mass segregation on the radial distribution of different stellar populations in the core of 47 Tucanae to find estimates for the masses of stars at different post-main-sequence evolutionary stages. We take samples of main-sequence (MS) stars from the core of 47 Tucanae, at different magnitudes (i.e., different masses), and use the effects of this dynamical process to develop a relation between the radial distance (RD) at which the cumulative distribution reaches the 20th and 50th percentile and stellar mass. From these relations we estimate the masses of different post-MS populations. We find that mass remains constant for stars going through the evolutionary stages from the upper MS up to the horizontal branch (HB). By comparing RDs of the HB stars with stars of lower masses, we can exclude a mass loss greater than 0.09 {M}⊙ during the red giant branch (RGB) stage at nearly the 3σ level. The slightly higher mass estimates for the asymptotic giant branch (AGB) are consistent with the AGB having evolved from somewhat more massive stars. The AGB also exhibits evidence of contamination by more massive stars, possibly blue straggler stars (BSSs), going through the RGB phase. We do not include the BSSs in this paper due to the complexity of these objects; instead, the complete analysis of this population is left for a companion paper. The process to estimate the masses described in this paper is exclusive to the core of 47 Tuc.

  13. Accretion Rates on Pre-main-sequence Stars in the Young Open Cluster NGC 6530

    NASA Astrophysics Data System (ADS)

    Gallardo, José; del Valle, Luciano; Ruiz, María Teresa

    2012-01-01

    It is well accepted that during the star formation process, material from a protoplanetary disk is accreted onto the central object during the first ~1-5 Myr. Different authors have published measurements of accretion rates for young low- and intermediate-mass stars in several nearby star-forming regions (SFRs). Due to its somewhat larger distance, the SFR M8 (the Lagoon Nebula) has not been studied to the same extent, despite its abundant population of young stellar objects. We have obtained optical band low-resolution spectra of a sample of pre-main-sequence stars in the open cluster NGC 6530 located in the aforementioned nebulae using the Gemini Multi Object Spectrograph at Gemini-South in multi-object mode. Spectra cover the Hα emission line used to measure the accretion rate, following the method presented by Natta et al. The observed spectral characteristics are fully consistent with pre-main-sequence stars, showing lithium absorption lines, which are very common in young stellar objects, as well as prominent and broad Hα emission lines, indicating a T Tauri evolutionary stage. This work presents the first determinations of mass accretion rates of young stellar objects in the open cluster NGC 6530, confirming that they are classical T Tauri stars going through the accretion phase. These observations contribute to a better understanding of the stellar content and evolutionary phase of the very active Lagoon Nebula SFR. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciencia e Tecnologia (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva

  14. Identification of novel Arabidopsis thaliana upstream open reading frames that control expression of the main coding sequences in a peptide sequence-dependent manner

    PubMed Central

    Ebina, Isao; Takemoto-Tsutsumi, Mariko; Watanabe, Shun; Koyama, Hiroaki; Endo, Yayoi; Kimata, Kaori; Igarashi, Takuya; Murakami, Karin; Kudo, Rin; Ohsumi, Arisa; Noh, Abdul Latif; Takahashi, Hiro; Naito, Satoshi; Onouchi, Hitoshi

    2015-01-01

    Upstream open reading frames (uORFs) are often found in the 5′-leader regions of eukaryotic mRNAs and can negatively modulate the translational efficiency of the downstream main ORF. Although the effects of most uORFs are thought to be independent of their encoded peptide sequences, certain uORFs control translation of the main ORF in a peptide sequence-dependent manner. For genome-wide identification of such peptide sequence-dependent regulatory uORFs, exhaustive searches for uORFs with conserved amino acid sequences have been conducted using bioinformatic analyses. However, whether the conserved uORFs identified by these bioinformatic approaches encode regulatory peptides has not been experimentally determined. Here we analyzed 16 recently identified Arabidopsis thaliana conserved uORFs for the effects of their amino acid sequences on the expression of the main ORF using a transient expression assay. We identified five novel uORFs that repress main ORF expression in a peptide sequence-dependent manner. Mutational analysis revealed that, in four of them, the C-terminal region of the uORF-encoded peptide is critical for the repression of main ORF expression. Intriguingly, we also identified one exceptional sequence-dependent regulatory uORF, in which the stop codon position is not conserved and the C-terminal region is not important for the repression of main ORF expression. PMID:25618853

  15. AN OBJECTIVE DEFINITION FOR THE MAIN SEQUENCE OF STAR-FORMING GALAXIES

    SciTech Connect

    Renzini, Alvio; Peng, Ying-jie E-mail: y.peng@mrao.cam.ac.uk

    2015-03-10

    The main sequence (MS) of star-forming (SF) galaxies plays a fundamental role in driving galaxy evolution and our efforts to understand it. However, different studies find significant differences in the normalization, slope, and shape of the MS. These discrepancies arise mainly from the different selection criteria adopted to isolate SF galaxies, which may include or exclude galaxies with a specific star formation rate (SFR) substantially below the MS value. To obviate this limitation of all current criteria, we propose an objective definition of the MS that does not rely at all on a pre-selection of SF galaxies. Constructing the 3D SFR–mass–number plot, the MS is then defined as the ridge line of the SF peak, as illustrated with various figures. The advantages of such a definition are manifold. If generally adopted, it will facilitate the inter-comparison of results from different groups using the same SFR and stellar mass diagnostics, or it will highlight the relative systematics of different diagnostics. All of this could help to understand MS galaxies as systems in a quasi-steady state equilibrium and would also provide a more objective criterion for identifying quenching galaxies.

  16. Galaxy Zoo: spiral galaxy morphologies and their relation to the star-forming main sequence

    NASA Astrophysics Data System (ADS)

    Willett, Kyle; Schawinski, Kevin; Masters, Karen; Melvin, Tom; Skibba, Ramin A.; Nichol, Robert; Cheung, Edmond; Lintott, Chris; Simmons, Brooke D.; Kaviraj, Sugata; Keel, William C.; Fortson, Lucy; Galaxy Zoo volunteers

    2015-01-01

    We examine the relationship between stellar mass and star formation rate in disk galaxies at z<0.085, measuring different populations of spirals as classified by their kiloparsec-scale structure. The morphologies of disk galaxies are obtained from the Galaxy Zoo 2 project, which includes the number of spiral arms, the arm pitch angle, and the presence of strong galactic bars. We show that both the slope and dispersion of the star-forming main sequence (SFMS) is constant no matter what the morphology of the spiral disk. We also show that mergers (both major and minor), which represent the strongest conditions for increases in star formation at a constant mass, only boost the SFR above the main relation by 0.3 dex; this is a significant reduction over the increase seen in merging systems at higher redshifts (z > 1). Of the galaxies that do lie significantly above the SFMS in the local Universe, more than 50% are mergers, with a large contribution from the compact green pea galaxies. We interpret our results as evidence that the number and pitch angle of spiral arms, which are imperfect reflections of the galaxy's current gravitational potential, are either fully independent of the various quenching mechanisms for star formation or are completely overwhelmed by the combination of outflows and feedback.

  17. Who saves the best for last? Age differences in preferences for affective sequences.

    PubMed

    Löckenhoff, Corinna E; Reed, Andrew E; Maresca, Skye N

    2012-12-01

    We examined age differences in preferences for the temporal sequence of emotional events. In 2 studies, participants were asked to select the order in which they would like to view a series of emotionally salient images. Study 1 (N = 87; aged 21-88 years) elicited sequence preferences both directly (via a sequence construction task) and indirectly (via a temporal discounting task). Study 2 (N = 90; aged 21-89 years) used a modified version of the sequence construction task in which the sequence was selected prospectively instead of concurrently. Across both studies, younger participants preferred increasingly positive sequences, but this preference was negatively associated with age. Future time perspective was associated with both age and sequence preferences. In contrast, age differences in sequence preferences were not explained by personality traits, affective responses, or age-related decrements in cognitive functioning.

  18. Variations of the ISM Compactness Across the Main Sequence of Star Forming Galaxies: Observations and Simulations

    NASA Astrophysics Data System (ADS)

    Martínez-Galarza, J. R.; Smith, H. A.; Lanz, L.; Hayward, Christopher C.; Zezas, A.; Rosenthal, L.; Weiner, A.; Hung, C.; Ashby, M. L. N.; Groves, B.

    2016-01-01

    The majority of star-forming galaxies follow a simple empirical correlation in the star formation rate (SFR) versus stellar mass (M*) plane, of the form {{SFR}}\\propto {M}*α , usually referred to as the star formation main sequence (MS). The physics that sets the properties of the MS is currently a subject of debate, and no consensus has been reached regarding the fundamental difference between members of the sequence and its outliers. Here we combine a set of hydro-dynamical simulations of interacting galactic disks with state-of-the-art radiative transfer codes to analyze how the evolution of mergers is reflected upon the properties of the MS. We present Chiburst, a Markov Chain Monte Carlo spectral energy distribution (SED) code that fits the multi-wavelength, broad-band photometry of galaxies and derives stellar masses, SFRs, and geometrical properties of the dust distribution. We apply this tool to the SEDs of simulated mergers and compare the derived results with the reference output from the simulations. Our results indicate that changes in the SEDs of mergers as they approach coalescence and depart from the MS are related to an evolution of dust geometry in scales larger than a few hundred parsecs. This is reflected in a correlation between the specific star formation rate, and the compactness parameter { C }, that parametrizes this geometry and hence the evolution of dust temperature ({T}{{dust}}) with time. As mergers approach coalescence, they depart from the MS and increase their compactness, which implies that moderate outliers of the MS are consistent with late-type mergers. By further applying our method to real observations of luminous infrared galaxies (LIRGs), we show that the merger scenario is unable to explain these extreme outliers of the MS. Only by significantly increasing the gas fraction in the simulations are we able to reproduce the SEDs of LIRGs.

  19. INTRINSIC COLORS, TEMPERATURES, AND BOLOMETRIC CORRECTIONS OF PRE-MAIN-SEQUENCE STARS

    SciTech Connect

    Pecaut, Mark J.; Mamajek, Eric E.

    2013-09-01

    We present an analysis of the intrinsic colors and temperatures of 5-30 Myr old pre-main-sequence (pre-MS) stars using the F0- through M9-type members of nearby, negligibly reddened groups: the η Cha cluster, the TW Hydra Association, the β Pic Moving Group, and the Tucana-Horologium Association. To check the consistency of spectral types from the literature, we estimate new spectral types for 52 nearby pre-MS stars with spectral types F3 through M4 using optical spectra taken with the SMARTS 1.5 m telescope. Combining these new types with published spectral types and photometry from the literature (Johnson-Cousins BVI{sub C} , 2MASS JHK{sub S} and WISE W1, W2, W3, and W4), we derive a new empirical spectral type-color sequence for 5-30 Myr old pre-MS stars. Colors for pre-MS stars match dwarf colors for some spectral types and colors, but for other spectral types and colors, deviations can exceed 0.3 mag. We estimate effective temperatures (T {sub eff}) and bolometric corrections (BCs) for our pre-MS star sample through comparing their photometry to synthetic photometry generated using the BT-Settl grid of model atmosphere spectra. We derive a new T {sub eff} and BC scale for pre-MS stars, which should be a more appropriate match for T Tauri stars than often-adopted dwarf star scales. While our new T {sub eff} scale for pre-MS stars is within ≅100 K of dwarfs at a given spectral type for stars sequence for O9V-M9V MS stars based on an extensive literature survey, (2) a revised Q-method relation for dereddening UBV photometry of OB-type stars, and (3) introduce two candidate spectral standard stars as representatives of spectral types K8V and K9V.

  20. Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-main-sequence Stars

    NASA Astrophysics Data System (ADS)

    Pecaut, Mark J.; Mamajek, Eric E.

    2013-09-01

    We present an analysis of the intrinsic colors and temperatures of 5-30 Myr old pre-main-sequence (pre-MS) stars using the F0- through M9-type members of nearby, negligibly reddened groups: the η Cha cluster, the TW Hydra Association, the β Pic Moving Group, and the Tucana-Horologium Association. To check the consistency of spectral types from the literature, we estimate new spectral types for 52 nearby pre-MS stars with spectral types F3 through M4 using optical spectra taken with the SMARTS 1.5 m telescope. Combining these new types with published spectral types and photometry from the literature (Johnson-Cousins BVIC , 2MASS JHKS and WISE W1, W2, W3, and W4), we derive a new empirical spectral type-color sequence for 5-30 Myr old pre-MS stars. Colors for pre-MS stars match dwarf colors for some spectral types and colors, but for other spectral types and colors, deviations can exceed 0.3 mag. We estimate effective temperatures (T eff) and bolometric corrections (BCs) for our pre-MS star sample through comparing their photometry to synthetic photometry generated using the BT-Settl grid of model atmosphere spectra. We derive a new T eff and BC scale for pre-MS stars, which should be a more appropriate match for T Tauri stars than often-adopted dwarf star scales. While our new T eff scale for pre-MS stars is within sime100 K of dwarfs at a given spectral type for stars sequence for O9V-M9V MS stars based on an extensive literature survey, (2) a revised Q-method relation for dereddening UBV photometry of OB-type stars, and (3) introduce two candidate spectral standard stars as representatives of spectral types K8V and K9V.

  1. MASS LOSS IN PRE-MAIN-SEQUENCE STARS VIA CORONAL MASS EJECTIONS AND IMPLICATIONS FOR ANGULAR MOMENTUM LOSS

    SciTech Connect

    Aarnio, Alicia N.; Matt, Sean P.

    2012-11-20

    We develop an empirical model to estimate mass-loss rates via coronal mass ejections (CMEs) for solar-type pre-main-sequence (PMS) stars. Our method estimates the CME mass-loss rate from the observed energies of PMS X-ray flares, using our empirically determined relationship between solar X-ray flare energy and CME mass: log (M {sub CME}[g]) = 0.63 Multiplication-Sign log (E {sub flare}[erg]) - 2.57. Using masses determined for the largest flaring magnetic structures observed on PMS stars, we suggest that this solar-calibrated relationship may hold over 10 orders of magnitude in flare energy and 7 orders of magnitude in CME mass. The total CME mass-loss rate we calculate for typical solar-type PMS stars is in the range 10{sup -12}-10{sup -9} M {sub Sun} yr{sup -1}. We then use these CME mass-loss rate estimates to infer the attendant angular momentum loss leading up to the main sequence. Assuming that the CME outflow rate for a typical {approx}1 M {sub Sun} T Tauri star is <10{sup -10} M {sub Sun} yr{sup -1}, the resulting spin-down torque is too small during the first {approx}1 Myr to counteract the stellar spin-up due to contraction and accretion. However, if the CME mass-loss rate is {approx}> 10{sup -10} M {sub Sun} yr{sup -1}, as permitted by our calculations, then the CME spin-down torque may influence the stellar spin evolution after an age of a few Myr.

  2. Near-Infrared Photometric Monitoring of the Pre-Main-Sequence Object KH 15D

    NASA Astrophysics Data System (ADS)

    Kusakabe, Nobuhiko; Tamura, Motohide; Nakajima, Yasushi; Kandori, Ryo; Ishihara, Akika; Nagata, Tetsuya; Nagayama, Takahiro; Nishiyama, Shogo; Baba, Daisuke; Sato, Shuji; Sugitani, Koji; Turner, Edwin L.; Abe, Lyu; Kimura, Hiroshi; Yamamoto, Tetsuo

    2005-10-01

    Extensive photometric monitoring of KH 15D, an enigmatic variable in the young star cluster NGC 2264, has been conducted. Simultaneous and accurate near-infrared photometry (JHKs bands) between 2003 December and 2005 March is presented, covering most of the variable phase. The infrared variability is characterized by a large-amplitude and long-lasting eclipse, as observed in the optical. The period of variability is 48.3+/-0.2 days, the maximum photometric amplitude of variability is ~4.2 mag, and the eclipse duration is ~0.5 in phase units. These are consistent with the most recent period, amplitude, and duration in the optical. The blueing of the J-H color (~0.16 mag) during eclipse, which has been suggested before, is unambiguously confirmed; a similar blueing at H-Ks is less clear but is probably present at a similar level. The overall shape of the JHKs light curves is very similar to the optical one, including a fair time symmetry and less stable flux during eclipse, with a slight hump near zero phase. Most of these variability features of KH 15D observed at near-infrared wavelengths can be explained with the recent model that employs an eclipse by an inclined, precessing disk and an outer scattering region around a pre-main-sequence binary.

  3. THE MULTIPLE PRE-MAIN-SEQUENCE SYSTEM HBC 515 IN L1622

    SciTech Connect

    Reipurth, Bo; Aspin, Colin; Herbig, George

    2010-04-15

    The bright pre-main-sequence star HBC 515 (HD 288313) located in the L1622 cometary cloud in Orion has been studied extensively with optical/infrared imaging and ultraviolet/optical/infrared spectroscopy. The spectra indicate that HBC 515 is a weakline T Tauri star (TTS) of spectral type K2V. Adaptive optics imaging in the K band reveals that HBC 515 is a binary with two equally bright components separated by 0.''5. A very faint third component is found 5'' to the northwest. Spitzer IRAC and MIPS observations show that at mid-infrared wavelengths this third source dominates the system, suggesting that it is a protostar still embedded in the nascent cloud of HBC 515. The close association of a weakline TTS with a newborn protostar in a multiple system is noteworthy. Two nearby TTSs are likely associated with the HBC 515 multiple system, and the dynamical evolution of the complex that would lead to such a configuration is considered.

  4. Equilibrium model prediction for the scatter in the star-forming main sequence

    NASA Astrophysics Data System (ADS)

    Mitra, Sourav; Davé, Romeel; Simha, Vimal; Finlator, Kristian

    2016-10-01

    The analytic "equilibrium model" for galaxy evolution using a mass balance equation is able to reproduce mean observed galaxy scaling relations between stellar mass, halo mass, star formation rate (SFR) and metallicity across the majority of cosmic time with a small number of parameters related to feedback. Here we aim to test this data-constrained model to quantify deviations from the mean relation between stellar mass and SFR, i.e. the star-forming galaxy main sequence (MS). We implement fluctuation in halo accretion rates parameterised from merger-based simulations, and quantify the intrinsic scatter introduced into the MS under the assumption that fluctuations in star formation follow baryonic inflow fluctuations. We predict the 1-σ MS scatter to be ˜0.2 - 0.25 dex over the stellar mass range 108M⊙ to 1011M⊙ and a redshift range 0.5⪉ z⪉ 3 for SFRs averaged over 100 Myr. The scatter increases modestly at z⪆ 3, as well as by averaging over shorter timescales. The contribution from merger-induced star formation is generally small, around 5% today and 10 - 15% during the peak epoch of cosmic star formation. These results are generally consistent with available observations, suggesting that deviations from the MS primarily reflect stochasticity in the inflow rate owing to halo mergers.

  5. The effect of disc inclination on the main sequence of star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Morselli, L.; Renzini, A.; Popesso, P.; Erfanianfar, G.

    2016-11-01

    We use the Sloan Digital Sky Survey (York et al.) data base to explore the effect of the disc inclination angle on the derived star formation rate (SFR), hence on the slope and width of the main-sequence (MS) relation for star-forming galaxies. We find that SFRs for nearly edge-on discs are underestimated by factors ranging from ˜0.2 dex for low-mass galaxies up to ˜0.4 dex for high-mass galaxies. This results in a substantially flatter MS relation for high-inclination discs compared to that for less inclined ones, though the global effect over the whole sample of star-forming galaxies is relatively minor, given the small fraction of high-inclination discs. However, we also find that galaxies with high-inclination discs represent a non-negligible fraction of galaxies populating the so-called green valley, with derived SFRs intermediate between the MS and those of quenched, passively evolving galaxies.

  6. Magnetospherically driven optical and radio aurorae at the end of the stellar main sequence.

    PubMed

    Hallinan, G; Littlefair, S P; Cotter, G; Bourke, S; Harding, L K; Pineda, J S; Butler, R P; Golden, A; Basri, G; Doyle, J G; Kao, M M; Berdyugina, S V; Kuznetsov, A; Rupen, M P; Antonova, A

    2015-07-30

    Aurorae are detected from all the magnetized planets in our Solar System, including Earth. They are powered by magnetospheric current systems that lead to the precipitation of energetic electrons into the high-latitude regions of the upper atmosphere. In the case of the gas-giant planets, these aurorae include highly polarized radio emission at kilohertz and megahertz frequencies produced by the precipitating electrons, as well as continuum and line emission in the infrared, optical, ultraviolet and X-ray parts of the spectrum, associated with the collisional excitation and heating of the hydrogen-dominated atmosphere. Here we report simultaneous radio and optical spectroscopic observations of an object at the end of the stellar main sequence, located right at the boundary between stars and brown dwarfs, from which we have detected radio and optical auroral emissions both powered by magnetospheric currents. Whereas the magnetic activity of stars like our Sun is powered by processes that occur in their lower atmospheres, these aurorae are powered by processes originating much further out in the magnetosphere of the dwarf star that couple energy into the lower atmosphere. The dissipated power is at least four orders of magnitude larger than what is produced in the Jovian magnetosphere, revealing aurorae to be a potentially ubiquitous signature of large-scale magnetospheres that can scale to luminosities far greater than those observed in our Solar System. These magnetospheric current systems may also play a part in powering some of the weather phenomena reported on brown dwarfs. PMID:26223623

  7. A Relationship between Mean Rotation Period in Lower Main-Sequence Stars and Its Observed Range

    NASA Astrophysics Data System (ADS)

    Donahue, Robert A.; Saar, Steven H.; Baliunas, Sallie L.

    1996-07-01

    Chromospheric Ca II H and K fluxes have been measured in a sample of ~100 stars on or near the main sequence at Mount Wilson Observatory. Observations were made several times a week and span more than ten years. Within an observing season, many stars show periodic variations due to rotation. Thirty-six of the stars have highly-significant periods in at least five seasons. We compute the range in the observed period, Delta P, and suggest that it is a measure of, and a lower limit to, the surface differential rotation (SDR). Several physical and selection effects can affect the measured Delta P value. An analysis of the cumulative variance distribution at various time scales, however, demonstrates that Ca II variations due to active region growth and decay are of longer period and smaller amplitude than those due to rotation. We argue that other effects (e.g., multiple active regions, latitude bands) are either small, or primarily act to reduce the measured Delta P relative to its true value. Including results for the Sun, we find that Delta P depends on the mean seasonal rotation period , such that Delta P is proportional to to the power of 1.3 +/- 0.1, independent of mass. We briefly discuss this in the context of dynamo models, and other observations of surface differential rotation and active region structure.

  8. The Evolved Main-sequence Channel: HST and LBT Observations of CSS120422:111127+571239

    NASA Astrophysics Data System (ADS)

    Kennedy, M.; Garnavich, P.; Callanan, P.; Szkody, P.; Littlefield, C.; Pogge, R.

    2015-12-01

    The “evolved main-sequence (EMS)” channel is thought to contribute significantly to the population of AM CVn-type systems in the Galaxy, and also to the number of cataclysmic variables (CVs) detected below the period minimum for hydrogen rich systems. CSS 120422:J111127+571239 was discovered by the Catalina Sky Survey in 2012 April. Its period was found to be 56 minutes, well below the minimum, and the optical spectrum is clearly depleted in hydrogen relative to helium, but still has two orders of magnitude more hydrogen than AM CVn stars. Doppler tomography of the Hα line hinted at a spiral structure existing in the disk. Here we present spectroscopy of CSS 120422:J111127+571239 using the Cosmic Origins Spectrograph FUV instrument on the Hubble Space Telescope and using the MODS spectrograph on the Large Binocular Telescope. The UV spectrum shows Si iv, N v, and He ii, but no detectable C iv. The anomalous nitrogen/carbon ratio is seen in a small number of other CVs and confirms a unique binary evolution. We also present and compare the optical spectrum of V418 Ser and advocate that it is also an EMS system.

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

    NASA Astrophysics Data System (ADS)

    Schaffenroth, Veronika; Geier, Stephan; Heber, Uli

    2014-09-01

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

  10. A theoretical study of acoustic glitches in low-mass main-sequence stars

    SciTech Connect

    Verma, Kuldeep; Antia, H. M.; Basu, Sarbani; Mazumdar, Anwesh E-mail: antia@tifr.res.in E-mail: anwesh@tifr.res.in

    2014-10-20

    There are regions in stars, such as ionization zones and the interface between radiative and convective regions, that cause a localized sharp variation in the sound speed. These are known as 'acoustic glitches'. Acoustic glitches leave their signatures on the oscillation frequencies of stars, and hence these signatures can be used as diagnostics of these regions. In particular, the signatures of these glitches can be used as diagnostics for the position of the second helium ionization zone and that of the base of the envelope convection zone. With the help of stellar models, we study the properties of these acoustic glitches in main-sequence stars. We find that the acoustic glitch due to the helium ionization zone does not correspond to the dip in the adiabatic index Γ{sub 1} caused by the ionization of He II, but to the peak in Γ{sub 1} between the He I and He II ionization zones. We find that it is easiest to study the acoustic glitch that is due to the helium ionization zone in stars with masses in the range 0.9-1.2 M {sub ☉}.

  11. Magnetospherically driven optical and radio aurorae at the end of the stellar main sequence.

    PubMed

    Hallinan, G; Littlefair, S P; Cotter, G; Bourke, S; Harding, L K; Pineda, J S; Butler, R P; Golden, A; Basri, G; Doyle, J G; Kao, M M; Berdyugina, S V; Kuznetsov, A; Rupen, M P; Antonova, A

    2015-07-30

    Aurorae are detected from all the magnetized planets in our Solar System, including Earth. They are powered by magnetospheric current systems that lead to the precipitation of energetic electrons into the high-latitude regions of the upper atmosphere. In the case of the gas-giant planets, these aurorae include highly polarized radio emission at kilohertz and megahertz frequencies produced by the precipitating electrons, as well as continuum and line emission in the infrared, optical, ultraviolet and X-ray parts of the spectrum, associated with the collisional excitation and heating of the hydrogen-dominated atmosphere. Here we report simultaneous radio and optical spectroscopic observations of an object at the end of the stellar main sequence, located right at the boundary between stars and brown dwarfs, from which we have detected radio and optical auroral emissions both powered by magnetospheric currents. Whereas the magnetic activity of stars like our Sun is powered by processes that occur in their lower atmospheres, these aurorae are powered by processes originating much further out in the magnetosphere of the dwarf star that couple energy into the lower atmosphere. The dissipated power is at least four orders of magnitude larger than what is produced in the Jovian magnetosphere, revealing aurorae to be a potentially ubiquitous signature of large-scale magnetospheres that can scale to luminosities far greater than those observed in our Solar System. These magnetospheric current systems may also play a part in powering some of the weather phenomena reported on brown dwarfs.

  12. A comprehensive set of simulations of high-velocity collisions between main-sequence stars

    NASA Astrophysics Data System (ADS)

    Freitag, Marc; Benz, Willy

    2005-04-01

    We report on a very large set of simulations of collisions between two main-sequence (MS) stars. These computations were carried out with the smoothed particle hydrodynamics method. Realistic stellar structure models for evolved MS stars were used. In order to sample an extended domain of initial parameters space (masses of the stars, relative velocity and impact parameter), more than 14000 simulations were carried out. We considered stellar masses ranging between 0.1 and 75 Msolar and relative velocities up to a few thousand km s-1. To limit the computational burden, a resolution of 1000-32000 particles per star was used. The primary goal of this study was to build a complete data base from which the result of any collision can be interpolated. This allows us to incorporate the effects of stellar collisions with an unprecedented level of realism into dynamical simulations of galactic nuclei and other dense stellar clusters. We make the data describing the initial condition and outcome (mass and energy loss, angle of deflection) of all our simulations available on the Internet. We find that the outcome of collisions depends sensitively on the stellar structure and that, in most cases, using polytropic models is inappropriate. Published fitting formulae for the collision outcomes, established from a limited set of collisions, prove of limited use because they do not allow robust extrapolation to other stellar structures or relative velocities.

  13. Iron-group Abundances in the Metal-poor Main-Sequence Turnoff Star HD~84937

    NASA Astrophysics Data System (ADS)

    Sneden, Christopher; Cowan, John J.; Kobayashi, Chiaki; Pignatari, Marco; Lawler, James E.; Den Hartog, Elizabeth A.; Wood, Michael P.

    2016-01-01

    We have derived new, very accurate abundances of the Fe-group elements Sc through Zn (Z = 21-30) in the bright main-sequence turnoff star HD 84937 based on high-resolution spectra covering the visible and ultraviolet spectral regions. New or recent laboratory transition data for 14 species of seven elements have been used. Abundances from more than 600 lines of non-Fe species have been combined with about 550 Fe lines in HD 84937 to yield abundance ratios of high precision. The abundances have been determined from both neutral and ionized transitions, which generally are in agreement with each other. We find no substantial departures from the standard LTE Saha ionization balance in this [Fe/H] = -2.32 star. Noteworthy among the abundances are [Co/Fe] = +0.14 and [Cu/Fe] = -0.83, in agreement with past studies of abundance trends in this and other low-metallicity stars, and < [{{Sc,Ti,V/Fe}}]> = +0.31, which has not been noted previously. A detailed examination of scandium, titanium, and vanadium abundances in large-sample spectroscopic surveys reveals that they are positively correlated in stars with [Fe/H] < -2 HD 84937 lies at the high end of this correlation. These trends constrain the synthesis mechanisms of Fe-group elements. We also examine the Galactic chemical evolution abundance trends of the Fe-group elements, including a new nucleosynthesis model with jet-like explosion effects.

  14. A DETAILED FAR-ULTRAVIOLET SPECTRAL ATLAS OF MAIN-SEQUENCE B STARS

    SciTech Connect

    Smith, Myron A.

    2010-02-01

    We have constructed a detailed spectral atlas covering the wavelength region 930-1225 A for 10 sharp-lined B0-B9 stars near the main sequence. Most of the spectra we assembled are from the archives of the Far Ultraviolet Spectroscopic Explorer satellite, but for nine stars, wavelength coverage above 1188 A was taken from high-resolution International Ultraviolet Explorer or echelle Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra. To represent the tenth star at type B0.2 V, we used the Copernicus atlas of {tau} Sco. We made extensive line identifications in the region 949-1225 A of all atomic features having published oscillator strengths at types B0, B2, and B8. These are provided as a supplementary data product-hence the term detailed atlas. Our list of found features totals 2288, 1612, and 2469 lines, respectively. We were able to identify 92%, 98%, and 98% of these features with known atomic transitions with varying degrees of certainty in these spectra. The remaining lines do not have published oscillator strengths. Photospheric lines account for 94%, 87%, and 91%, respectively, of all our identifications, with the remainder being due to interstellar (usually molecular H{sub 2}) lines. We also discuss the numbers of lines with respect to the distributions of various ions for these three most studied spectral subtypes. A table is also given of 162 least blended lines that can be used as possible diagnostics of physical conditions in B star atmospheres.

  15. Phylogenetic reconstruction of Bantu kinship challenges Main Sequence Theory of human social evolution

    PubMed Central

    Opie, Christopher; Shultz, Susanne; Atkinson, Quentin D.; Currie, Thomas

    2014-01-01

    Kinship provides the fundamental structure of human society: descent determines the inheritance pattern between generations, whereas residence rules govern the location a couple moves to after they marry. In turn, descent and residence patterns determine other key relationships such as alliance, trade, and marriage partners. Hunter-gatherer kinship patterns are viewed as flexible, whereas agricultural societies are thought to have developed much more stable kinship patterns as they expanded during the Holocene. Among the Bantu farmers of sub-Saharan Africa, the ancestral kinship patterns present at the beginning of the expansion are hotly contested, with some arguing for matrilineal and matrilocal patterns, whereas others maintain that any kind of lineality or sex-biased dispersal only emerged much later. Here, we use Bayesian phylogenetic methods to uncover the history of Bantu kinship patterns and trace the interplay between descent and residence systems. The results suggest a number of switches in both descent and residence patterns as Bantu farming spread, but that the first Bantu populations were patrilocal with patrilineal descent. Across the phylogeny, a change in descent triggered a switch away from patrifocal kinship, whereas a change in residence triggered a switch back from matrifocal kinship. These results challenge “Main Sequence Theory,” which maintains that changes in residence rules precede change in other social structures. We also indicate the trajectory of kinship change, shedding new light on how this fundamental structure of society developed as farming spread across the globe during the Neolithic. PMID:25422461

  16. Evidence of accretion triggered oscillations in the pre-main-sequence interacting binary AK Sco

    NASA Astrophysics Data System (ADS)

    Gómez, de Castro, Ana I.; López-Santiago, Javier; Talavera, Antonio

    2013-02-01

    Pre-main sequence (PMS) binaries are surrounded by circumbinary discs from which matter falls on to both components. The material dragged from the circumbinary disc flows on to each star through independent streams channelled by the variable gravitational field. The action of the bar-like potential is most prominent in high eccentricity systems made of two equal mass stars. AK Sco is a unique PMS system composed of two F5 stars in an orbit with e = 0.47. Henceforth, it is an ideal laboratory to study matter infall in binaries and its role in orbit circularization. In this Letter, we report the detection of a 1.3 mHz ultra low-frequency oscillation in the ultraviolet light curve at periastron passage. This oscillation lasts 7 ks being most likely fed by the gravitational energy released when the stream's tails spiralling on to each star get in contact at periastron passage enhancing the accretion flow; this unveils a new mechanism for angular momentum loss during PMS evolution and a new type of interacting binary.

  17. THE EVOLVED MAIN-SEQUENCE CHANNEL: HST AND LBT OBSERVATIONS OF CSS 120422:111127+571239

    SciTech Connect

    Kennedy, M.; Callanan, P.; Garnavich, P.; Littlefield, C.; Szkody, P.; Pogge, R.

    2015-12-20

    The “evolved main-sequence (EMS)” channel is thought to contribute significantly to the population of AM CVn-type systems in the Galaxy, and also to the number of cataclysmic variables (CVs) detected below the period minimum for hydrogen rich systems. CSS 120422:J111127+571239 was discovered by the Catalina Sky Survey in 2012 April. Its period was found to be 56 minutes, well below the minimum, and the optical spectrum is clearly depleted in hydrogen relative to helium, but still has two orders of magnitude more hydrogen than AM CVn stars. Doppler tomography of the Hα line hinted at a spiral structure existing in the disk. Here we present spectroscopy of CSS 120422:J111127+571239 using the Cosmic Origins Spectrograph FUV instrument on the Hubble Space Telescope and using the MODS spectrograph on the Large Binocular Telescope. The UV spectrum shows Si iv, N v, and He ii, but no detectable C iv. The anomalous nitrogen/carbon ratio is seen in a small number of other CVs and confirms a unique binary evolution. We also present and compare the optical spectrum of V418 Ser and advocate that it is also an EMS system.

  18. STELLAR DIAMETERS AND TEMPERATURES. II. MAIN-SEQUENCE K- AND M-STARS

    SciTech Connect

    Boyajian, Tabetha S.; McAlister, Harold A.; Jones, Jeremy; White, Russel; Henry, Todd; Gies, Douglas; Jao, Wei-Chun; Parks, J. Robert; Von Braun, Kaspar; Kane, Stephen R.; Ciardi, David; Van Belle, Gerard; Ten Brummelaar, Theo A.; Schaefer, Gail; Sturmann, Laszlo; Sturmann, Judit; Muirhead, Philip S.; Lopez-Morales, Mercedes; Ridgway, Stephen; Rojas-Ayala, Barbara; and others

    2012-10-01

    We present interferometric angular diameter measurements of 21 low-mass, K- and M-dwarfs made with the CHARA Array. This sample is enhanced by adding a collection of radius measurements published in the literature to form a total data set of 33 K-M-dwarfs with diameters measured to better than 5%. We use these data in combination with the Hipparcos parallax and new measurements of the star's bolometric flux to compute absolute luminosities, linear radii, and effective temperatures for the stars. We develop empirical relations for {approx}K0 to M4 main-sequence stars that link the stellar temperature, radius, and luminosity to the observed (B - V), (V - R), (V - I), (V - J), (V - H), and (V - K) broadband color index and stellar metallicity [Fe/H]. These relations are valid for metallicities ranging from [Fe/H] = -0.5 to +0.1 dex and are accurate to {approx}2%, {approx}5%, and {approx}4% for temperature, radius, and luminosity, respectively. Our results show that it is necessary to use metallicity-dependent transformations in order to properly convert colors into stellar temperatures, radii, and luminosities. Alternatively, we find no sensitivity to metallicity on relations we construct to the global properties of a star omitting color information, e.g., temperature-radius and temperature-luminosity. Thus, we are able to empirically quantify to what order the star's observed color index is impacted by the stellar iron abundance. In addition to the empirical relations, we also provide a representative look-up table via stellar spectral classifications using this collection of data. Robust examinations of single star temperatures and radii compared to evolutionary model predictions on the luminosity-temperature and luminosity-radius planes reveal that models overestimate the temperatures of stars with surface temperatures <5000 K by {approx}3%, and underestimate the radii of stars with radii <0.7 R{sub Sun} by {approx}5%. These conclusions additionally suggest that

  19. Gaia-ESO Survey: Analysis of pre-main sequence stellar spectra

    NASA Astrophysics Data System (ADS)

    Lanzafame, A. C.; Frasca, A.; Damiani, F.; Franciosini, E.; Cottaar, M.; Sousa, S. G.; Tabernero, H. M.; Klutsch, A.; Spina, L.; Biazzo, K.; Prisinzano, L.; Sacco, G. G.; Randich, S.; Brugaletta, E.; Delgado Mena, E.; Adibekyan, V.; Montes, D.; Bonito, R.; Gameiro, J. F.; Alcalá, J. M.; González Hernández, J. I.; Jeffries, R.; Messina, S.; Meyer, M.; Gilmore, G.; Asplund, M.; Binney, J.; Bonifacio, P.; Drew, J. E.; Feltzing, S.; Ferguson, A. M. N.; Micela, G.; Negueruela, I.; Prusti, T.; Rix, H.-W.; Vallenari, A.; Alfaro, E. J.; Allende Prieto, C.; Babusiaux, C.; Bensby, T.; Blomme, R.; Bragaglia, A.; Flaccomio, E.; Francois, P.; Hambly, N.; Irwin, M.; Koposov, S. E.; Korn, A. J.; Smiljanic, R.; Van Eck, S.; Walton, N.; Bayo, A.; Bergemann, M.; Carraro, G.; Costado, M. T.; Edvardsson, B.; Heiter, U.; Hill, V.; Hourihane, A.; Jackson, R. J.; Jofré, P.; Lardo, C.; Lewis, J.; Lind, K.; Magrini, L.; Marconi, G.; Martayan, C.; Masseron, T.; Monaco, L.; Morbidelli, L.; Sbordone, L.; Worley, C. C.; Zaggia, S.

    2015-04-01

    Context. The Gaia-ESO Public Spectroscopic Survey is obtaining high-quality spectroscopy of some 100 000 Milky Way stars using the FLAMES spectrograph at the VLT, down to V = 19 mag, systematically covering all the main components of the Milky Way and providing the first homogeneous overview of the distributions of kinematics and chemical element abundances in the Galaxy. Observations of young open clusters, in particular, are giving new insights into their initial structure, kinematics, and their subsequent evolution. Aims: This paper describes the analysis of UVES and GIRAFFE spectra acquired in the fields of young clusters whose population includes pre-main sequence (PMS) stars. The analysis is applied to all stars in such fields, regardless of any prior information on membership, and provides fundamental stellar atmospheric parameters, elemental abundances, and PMS-specific parameters such as veiling, accretion, and chromospheric activity. Methods: When feasible, different methods were used to derive raw parameters (e.g. line equivalent widths) fundamental atmospheric parameters and derived parameters (e.g. abundances). To derive some of these parameters, we used methods that have been extensively used in the past and new ones developed in the context of the Gaia-ESO survey enterprise. The internal precision of these quantities was estimated by inter-comparing the results obtained by these different methods, while the accuracy was estimated by comparison with independent external data, such as effective temperature and surface gravity derived from angular diameter measurements, on a sample of benchmarks stars. A validation procedure based on these comparisons was applied to discard spurious or doubtful results and produce recommended parameters. Specific strategies were implemented to resolve problems of fast rotation, accretion signatures, chromospheric activity, and veiling. Results: The analysis carried out on spectra acquired in young cluster fields during

  20. Exploring pre-main-sequence variables of the ONC: the new variables

    NASA Astrophysics Data System (ADS)

    Parihar, Padmakar; Messina, Sergio; Distefano, Elisa; Shantikumar, N. S.; Medhi, Biman J.

    2009-12-01

    Since 2004, we have been engaged in a long-term observing programme to monitor young stellar objects (YSOs) in the Orion Nebula Cluster (ONC). We have collected about 2000 frames in V, R and I broad-band filters on more than 200 nights distributed over five consecutive observing seasons. The high-quality and time-extended photometric data give us an opportunity to address various phenomena associated with young stars. The prime motivations of this project are (i) to explore various manifestations of stellar magnetic activity in very young low-mass stars, (ii) to search for new pre-main-sequence eclipsing binaries and (iii) to look for any EXor and FUor-like transient activities associated with YSOs. Since this is the first paper on this programme, we give a detailed description of the science drivers, the observation and the data reduction strategies as well. In addition to these, we also present a large number of new periodic variables detected from our first 5 yr of time-series photometric data. Our study reveals that about 72 per cent of classical T Tauri stars (CTTS) in our field of view are periodic, whereas only 32 per cent of weak-lined T Tauri stars (WTTS) are periodic. This indicates that inhomogeneity patterns on the surface of CTTS of the ONC stars are much more stable than on WTTS. From our multiyear monitoring campaign, we found that the photometric surveys based on single season are incapable of identifying all periodic variables. And any study on evolution of angular momentum based on single-season surveys must be carried out with caution.

  1. YSOVAR: SIX PRE-MAIN-SEQUENCE ECLIPSING BINARIES IN THE ORION NEBULA CLUSTER

    SciTech Connect

    Morales-Calderon, M.; Stauffer, J. R.; Rebull, L. M.; Stassun, K. G.; Vrba, F. J.; Prato, L.; Hillenbrand, L. A.; Carpenter, J. M.; Terebey, S.; Angione, J.; Covey, K. R.; Terndrup, D. M.; Gutermuth, R.; Song, I.; Plavchan, P.; Marchis, F.; Garcia, E. V.; Margheim, S.; Luhman, K. L.; Irwin, J. M.

    2012-07-10

    Eclipsing binaries (EBs) provide critical laboratories for empirically testing predictions of theoretical models of stellar structure and evolution. Pre-main-sequence (PMS) EBs are particularly valuable, both due to their rarity and the highly dynamic nature of PMS evolution, such that a dense grid of PMS EBs is required to properly calibrate theoretical PMS models. Analyzing multi-epoch, multi-color light curves for {approx}2400 candidate Orion Nebula Cluster (ONC) members from our Warm Spitzer Exploration Science Program YSOVAR, we have identified 12 stars whose light curves show eclipse features. Four of these 12 EBs are previously known. Supplementing our light curves with follow-up optical and near-infrared spectroscopy, we establish two of the candidates as likely field EBs lying behind the ONC. We confirm the remaining six candidate systems, however, as newly identified ONC PMS EBs. These systems increase the number of known PMS EBs by over 50% and include the highest mass ({theta}{sup 1} Ori E, for which we provide a complete set of well-determined parameters including component masses of 2.807 and 2.797 M{sub Sun }) and longest-period (ISOY J053505.71-052354.1, P {approx} 20 days) PMS EBs currently known. In two cases ({theta}{sup 1} Ori E and ISOY J053526.88-044730.7), enough photometric and spectroscopic data exist to attempt an orbit solution and derive the system parameters. For the remaining systems, we combine our data with literature information to provide a preliminary characterization sufficient to guide follow-up investigations of these rare, benchmark systems.

  2. X-ray Emission from Pre-Main-Sequence Stars - Testing the Solar Analogy

    NASA Technical Reports Server (NTRS)

    Skinner, Stephen L.

    2000-01-01

    This LTSA award funded my research on the origin of stellar X-ray emission and the validity of the solar-stellar analogy. This research broadly addresses the relevance of our current understanding of solar X-ray physics to the interpretation of X-ray emission from stars in general. During the past five years the emphasis has been on space-based X-ray observations of very young stars in star-forming regions (T Tauri stars and protostars), cool solar-like G stars, and evolved high-mass Wolf-Rayet (WR) stars. These observations were carried out primarily with the ASCA and ROSAT space-based observatories (and most recently with Chandra), supplemented by ground-based observations. This research has focused on the identification of physical processes that are responsible for the high levels of X-ray emission seen in pre-main-sequence (PMS) stars, active cool stars, and WR stars. A related issue is how the X-ray emission of such stars changes over time, both on short timescales of days to years and on evolutionary timescales of millions of years. In the case of the Sun it is known that magnetic fields play a key role in the production of X-rays by confining the coronal plasma in loop-like structures where it is heated to temperatures of several million K. The extent to which the magnetically-confined corona interpretation can be applied to other X-ray emitting stars is the key issue that drives the research summarized here.

  3. Pre-main-sequence stars older than 8 Myr in the Eagle nebula

    NASA Astrophysics Data System (ADS)

    De Marchi, Guido; Panagia, Nino; Guarcello, M. G.; Bonito, Rosaria

    2013-11-01

    Attention is given to a population of 110 stars in the NGC 6611 cluster of the Eagle nebula that have prominent near-infrared excess and optical colours typical of pre-main-sequence (PMS) stars older than 8 Myr. At least half of those for which spectroscopy exists have a Hα emission line profile revealing active accretion. In principle, the V - I colours of all these stars would be consistent with those of young PMS objects (<1 Myr) whose radiation is heavily obscured by a circumstellar disc seen at high inclination and in small part scattered towards the observer by the back side of the disc. However, using theoretical models it is shown here that objects of this type can only account for a few per cent of this population. In fact, the spatial distribution of these objects, their X-ray luminosities, their optical brightness, their positions in the colour-magnitude diagram and the weak Li absorption lines of the stars studied spectroscopically suggest that most of them are at least eight times older than the ˜1 Myr-old PMS stars already known in this cluster and could be as old as ˜30 Myr. This is the largest homogeneous sample to date of Galactic PMS stars considerably older than 8 Myr that are still actively accreting from a circumstellar disc and it allows us to set a lower limit of 7 per cent to the disc frequency at ˜16 Myr in NGC 6611. These values imply a characteristic exponential lifetime of ˜6 Myr for disc dissipation.

  4. Oscillation mode linewidths and heights of 23 main-sequence stars observed by Kepler

    NASA Astrophysics Data System (ADS)

    Appourchaux, T.; Antia, H. M.; Benomar, O.; Campante, T. L.; Davies, G. R.; Handberg, R.; Howe, R.; Régulo, C.; Belkacem, K.; Houdek, G.; García, R. A.; Chaplin, W. J.

    2014-06-01

    Context. Solar-like oscillations have been observed by Kepler and CoRoT in many solar-type stars, thereby providing a way to probe the stars using asteroseismology. Aims: We provide the mode linewidths and mode heights of the oscillations of various stars as a function of frequency and of effective temperature. Methods: We used a time series of nearly two years of data for each star. The 23 stars observed belong to the simple or F-like category. The power spectra of the 23 main-sequence stars were analysed using both maximum likelihood estimators and Bayesian estimators, providing individual mode characteristics such as frequencies, linewidths, and mode heights. We study the source of systematic errors in the mode linewidths and mode heights, and we present a way to correct these errors with respect to a common reference fit. Results: Using the correction, we can explain all sources of systematic errors, which could be reduced to less than ±15% for mode linewidths and heights, and less than ±5% for amplitude, when compared to the reference fit. The effect of a different estimated stellar background and a different estimated splitting will provide frequency-dependent systematic errors that might affect the comparison with theoretical mode linewidth and mode height, therefore affecting the understanding of the physical nature of these parameters. All other sources of relative systematic errors are less dependent upon frequency. We also provide the dependence of the so-called linewidth dip in the middle of the observed frequency range as a function of effective temperature. We show that the depth of the dip decreases with increasing effective temperature. The dependence of the dip on effective temperature may imply that the mixing length parameter α or the convective flux may increase with effective temperature. Tables 4-27 and Appendices are available in electronic form at http://www.aanda.org

  5. Oscillation mode frequencies of 61 main-sequence and subgiant stars observed by Kepler

    NASA Astrophysics Data System (ADS)

    Appourchaux, T.; Chaplin, W. J.; García, R. A.; Gruberbauer, M.; Verner, G. A.; Antia, H. M.; Benomar, O.; Campante, T. L.; Davies, G. R.; Deheuvels, S.; Handberg, R.; Hekker, S.; Howe, R.; Régulo, C.; Salabert, D.; Bedding, T. R.; White, T. R.; Ballot, J.; Mathur, S.; Silva Aguirre, V.; Elsworth, Y. P.; Basu, S.; Gilliland, R. L.; Christensen-Dalsgaard, J.; Kjeldsen, H.; Uddin, K.; Stumpe, M. C.; Barclay, T.

    2012-07-01

    Context. Solar-like oscillations have been observed by Kepler and CoRoT in several solar-type stars, thereby providing a way to probe the stars using asteroseismology Aims: We provide the mode frequencies of the oscillations of various stars required to perform a comparison with those obtained from stellar modelling. Methods: We used a time series of nine months of data for each star. The 61 stars observed were categorised in three groups: simple, F-like, and mixed-mode. The simple group includes stars for which the identification of the mode degree is obvious. The F-like group includes stars for which the identification of the degree is ambiguous. The mixed-mode group includes evolved stars for which the modes do not follow the asymptotic relation of low-degree frequencies. Following this categorisation, the power spectra of the 61 main-sequence and subgiant stars were analysed using both maximum likelihood estimators and Bayesian estimators, providing individual mode characteristics such as frequencies, linewidths, and mode heights. We developed and describe a methodology for extracting a single set of mode frequencies from multiple sets derived by different methods and individual scientists. We report on how one can assess the quality of the fitted parameters using the likelihood ratio test and the posterior probabilities. Results: We provide the mode frequencies of 61 stars (with their 1-σ error bars), as well as their associated échelle diagrams. Appendices are available in electronic form at http://www.aanda.org

  6. A Search for Planets and Brown Dwarfs around Post Main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Otani, Tomomi; Oswalt, Terry D.

    2016-06-01

    The most promising current theory for the origin of subdwarf B (sdB) stars is that they were formed during binary star evolution. This project was conducted to test this hypothesis by searching for companions around six sdB pulsators using the Observed-minus-Calculated (O-C) method. A star’s position in space will wobble due to the gravitational forces of any companion. If it is emitting a periodic signal, the orbital motion of the star around the system’s center of mass causes periodic changes in the light pulse arrival times. O-C diagrams for six sdB pulsators were constructed from several years’ observations, providing useful limits on suspected companions’ minimum masses and semimajor axes. The results were constrained by “period vs. amplitude” and “mass vs. semimajor axis” models to quantify companion masses and semimajor axes that are consistent with the observational data, if any. Two of our targets, V391 Peg and HS0702+6043, are noted in previous publications to have substellar companions. These were used to validate the method used in this research. The results of this study yielded the same masses and semimajor axes for these two stars as the published values, within the uncertainties. Another of the targets, EC20117-4014, is noted in the literature as a binary system containing an sdB and F5V star, however the orbital period and separation were unknown. The new data obtained in this study contain the signal of a companion candidate with a period of 158.01 days. Several possible mass and semimajor axis combinations for the companion are consistent with the observations. One of the other targets in this study displayed preliminary evidence for a companion that will require further observation. Though still a small sample, these results suggest that planets often survive the post-main-sequence evolution of their parent stars.

  7. Do C/O > 1 main-sequence stars build carbon planets?

    NASA Astrophysics Data System (ADS)

    Bergfors, Carolina; Farihi, Jay

    2015-12-01

    The existence of rocky yet carbon-dominated planets is predicated on a C-dominated (rather than O-dominated) nebular birthplace. Planet-forming stars with unusually high C/O > 0.8 could provide such a favourable environment. Therefore the highest C/O ratios in potential host stars is of interest, as it has a direct impact on the frequency of C-dominated planetary systems.Interestingly, C/O > 1 main-sequence stars are relatively common, and have distinctive optical spectra dominated by strong molecular carbon features. These dwarf carbon (dC) stars are even more numerous than carbon giants, but their origins may be fundamentally tied to binarity -- where the C/O ratio is increased by C-rich material accreted from an AGB star (now a white dwarf). We are undertaking a survey of dC stars to measure their binary fraction, and to ascertain if any C/O > 1 stars are single and thus favourable to C-rich planet formation.We present first results from our ongoing search for radial velocity companions to dC stars. Multi-epoch observations of 22 systems show clear RV variability for > 70% of targets, suggesting that most, if not all, dC stars are in binary systems. The presence of a formerly more massive companion suggests their C/O > 1 is an enhancement via mass transfer, and not primordial. If correct, C/O > 1 stars may host oxygen-dominated (possibly circumbinary) planets, significantly reducing the Galactic real estate available for carbon planets.

  8. Time Variability of the Dust Sublimation Zones in Pre-Main Sequence Disk Systems

    NASA Technical Reports Server (NTRS)

    Sitko, Michael L.; Carpenter, W. J.; Grady, C. A.; Russel, R. W.; Lynch, D. K.; Rudy, R. J.; Mazuk, S. M.; Venturini, C. C.; Kimes, R. L.; Beerman, L. C.; Ablordeppey, K. E.; Puetter, R. C.; Wisnewski, P.; Brafford, S. M.; Polomski, E. R.; Hammel, H. B.; Perry, R. B.; Wilde, J. L.

    2007-01-01

    The dust sublimation zone (DSZ) is the region of pre-main sequence (PMS) disks where dust grains most easily anneal, sublime, and condense out of the gas. Because of this, it is a location where crystalline material may be enhanced and redistributed throughout the rest of the disk. A decade-long program to monitor the thermal emission of the grains located in this region demonstrates that large changes in emitted flux occur in many systems. Changes in the thermal emission between 3 and 13.5 microns were observed in HD 31648 (MWC 480), HD 163296 (MWC 275), and DG Tau. This emission is consistent with it being produced at the DSZ, where the transition from a disk of gas to one of gas+dust occurs. In the case of DG Tau, the outbursts were accompanied by increased emission on the 10 micron silicate band on one occasion, while on another occasion it went into absorption. This requires lofting of the material above the disk into the line of sight. Such changes will affect the determination of the inner disk structure obtained through interferometry measurements, and this has been confirmed in the case of HD 163296. Cyclic variations in the heating of the DSZ will lead to the annealing of large grains, the sublimation of smaller grains, possibly followed by re-condensation as the zone enters a cooling phase. Lofting of dust above the disk plane, and outward acceleration by stellar winds and radiation pressure, can re-distribute the processed material to cooler regions of the disk, where cometesimals form. This processing is consistent with the detection of the preferential concentration of large crystalline grains in the inner few AU of PMS disks using interferometric spectroscopy with the VLTI.

  9. Mid-IR observations of circumstellar disks. I. Pre-main sequence objects

    NASA Astrophysics Data System (ADS)

    Schütz, O.; Meeus, G.; Sterzik, M. F.

    2005-02-01

    We present new N-band photometry and spectroscopy for a sample of eight pre-main sequence stars including T Tauri, Herbig Ae/Be stars and FU Ori objects using the ESO TIMMI2 camera at the La Silla observatory (Chile). For some objects this is their first N-band spectroscopic observation ever. The FU Ori stars V 346 Nor, V 883 Ori and Z CMa show a broad absorption band which we attribute to silicates, while for BBW 76 we find silicate emission. A comparison with ISO-SWS spectra of V 346 Nor and Z CMa taken in 1996/1997 reveals no differences in spectral shape. All T Tauri and Herbig Ae/Be stars possess N-band emission features. We model the emission spectra with a mixture of silicates consisting of different grain sizes and composition. The Herbig Ae star HD 34282 shows strong features of PAHs but none of silicate, while the emission spectrum of the Herbig Ae star HD 72106 resembles those of solar-system comets and known Herbig sources of evolved dust. We demonstrate that HD 72106 is host to highly processed silicates and find evidence for enstatite, which is not common in young objects. Evolved dust is also seen in the T Tauri stars HD 98800 and MP Mus. We further detected MP Mus at 1200 μm with the bolometer array SIMBA at the SEST in La Silla. The findings of our analysis are given in the context of previous dust studies of young stellar objects. Based on observations collected at the European Southern Observatory, La Silla, Chile (69.C-0073, 70.C-0468, 71.C-0001, 73.C-0372).

  10. HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: DEPENDENCE ON PLANETARY MASS

    SciTech Connect

    Kopparapu, Ravi Kumar; Ramirez, Ramses M.; Kasting, James F.; SchottelKotte, James; Domagal-Goldman, Shawn; Eymet, Vincent

    2014-06-01

    The ongoing discoveries of extra-solar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this Letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K-7200 K, for planetary masses between 0.1 M {sub ⊕} and 5 M {sub ⊕}. Assuming H{sub 2}O-(inner HZ) and CO{sub 2}-(outer HZ) dominated atmospheres, and scaling the background N{sub 2} atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets will have less dense atmospheres, the inner edge of the HZ (runaway greenhouse limit) moves outward (∼10% lower than Earth flux) for low mass planets due to larger greenhouse effect arising from the increased H{sub 2}O column depth. For larger planets, the H{sub 2}O column depth is smaller, and higher temperatures are needed before water vapor completely dominates the outgoing longwave radiation. Hence the inner edge moves inward (∼7% higher than Earth's flux). The outer HZ changes little due to the competing effects of the greenhouse effect and an increase in albedo. New, three-dimensional climate model results from other groups are also summarized, and we argue that further, independent studies are needed to verify their predictions. Combined with our previous work, the results presented here provide refined estimates of HZs around main-sequence stars and provide a step toward a more comprehensive analysis of HZs.

  11. Characterizing Pre-Main Sequence Populations in Stellar Associations of the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Gouliermis, Dimitrios

    2007-07-01

    The Large Magellanic Cloud {LMC} offers an extremely rich sample of resolved low-mass stars {below 1 Solar Mass} in the act of formation that has not been explored sufficiently yet. These pre-main sequence {PMS} stars provide a unique snapshot of the star formation process, as it is being recorded for the last 20 Myr, and they give important information on the low-mass Initial Mass Function {IMF} of their host stellar systems. Studies of young, rich LMC clusters like 30 Doradus are crowding limited, even at the angular resolution facilitated by HST in the optical. To learn more about low-mass PMS stars in the LMC, one has to study less crowded regions like young stellar assocations. We propose to employ WFPC2 to obtain deep photometry {V 25.5 mag} of four selected LMC stellar associations in order to perform an original optical analysis of their red PMS and blue bright MS stellar populations. With these observations we aim at a comprehensive study, which will add substantial information on the most recent star formation and the IMF in the LMC. The data reduction and analysis will be performed with a 2D photometry software package especially developped by us for WFPC2 imaging of extended stellar associations with variable background. Our targets have been selected optimizing a combination of criteria, namely spatial resolution, crowding, low extinction, nebular contamination, and background confusion in comparison to other regions in the Local Group. Parallel NICMOS imaging will provide additional information on near-infrared properties of the stellar population in the regions surrounding these systems.

  12. VLT/X-shooter spectroscopy of massive pre-main-sequence stars in M17

    NASA Astrophysics Data System (ADS)

    Ramirez-Tannus, Maria Claudia; Kaper, Lex

    2015-08-01

    The formation process of massive stars is still poorly understood. Formation timescales are short, the corresponding accretion rates very high, and the forming stars are hidden from view due to vast amounts of interstellar extinction. On top of that, massive stars are rare, are located at relatively large distances, and play a major role in shaping the interstellar medium due to their strong UV radiation fields and stellar winds. Although massive stars show most spectral features in the UV and optical range, so far only for a handful of massive Young Stellar Objects (mYSOs) optical and near-infrared spectra have been obtained. For some of these their pre-main-sequence (PMS) nature has now been firmly established (e.g. Ochsendorf et al. 2011, Ellerbroek et al. 2013). The objective of our project is to determine the physical properties of mYSOs, to search for signatures remnant of their formation process and to better understand the feedback on their environment.To this aim the optical to near-infrared (300-2500 nm) spectra of six candidate mYSOs (Hanson et al. 1997), deeply embedded in the massive star forming region M17, have been obtained with X-Shooter on the ESO Very Large Telescope. These mYSO candidates have been identified based on their infrared excess and spectral features (double-peaked emission lines, CO band-head emission) indicating the presence of a disk. In most cases, we detect a photospheric spectrum allowing us to measure the physical properties of the mYSO and to confirm its PMS nature. We also uncover many emission features, including forbidden lines, providing information on the (active) formation process of these young (massive) stars.

  13. Habitable Zones Around Main-Sequence Stars: Dependence on Planetary Mass

    NASA Technical Reports Server (NTRS)

    Kopparapu, Ravi Kumar; Ramirez, Ramses M.; Kotte, James Schottel; Kasting, James F.; Domagal-Goldman, Shawn; Eymet, Vincent

    2014-01-01

    The ongoing discoveries of extra-solar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this Letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K-7200 K, for planetary masses between 0.1M and 5M. Assuming H2O-(inner HZ) and CO2-(outer HZ) dominated atmospheres, and scaling the background N2 atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets will have less dense atmospheres, the inner edge of the HZ (runaway greenhouse limit) moves outward (approx.10% lower than Earth flux) for low mass planets due to larger greenhouse effect arising from the increased H2O column depth. For larger planets, the H2O column depth is smaller, and higher temperatures are needed before water vapor completely dominates the outgoing long-wave radiation. Hence the inner edge moves inward (approx.7% higher than Earth's flux). The outer HZ changes little due to the competing effects of the greenhouse effect and an increase in albedo. New, three-dimensional climate model results from other groups are also summarized, and we argue that further, independent studies are needed to verify their predictions. Combined with our previous work, the results presented here provide refined estimates of HZs around main-sequence stars and provide a step toward a more comprehensive analysis of HZs.

  14. From CoRoT 102899501 to the Sun. A time evolution model of chromospheric activity on the main sequence

    NASA Astrophysics Data System (ADS)

    Gondoin, P.; Gandolfi, D.; Fridlund, M.; Frasca, A.; Guenther, E. W.; Hatzes, A.; Deeg, H. J.; Parviainen, H.; Eigmüller, P.; Deleuil, M.

    2012-12-01

    Aims: The present study reports measurements of the rotation period of a young solar analogue, estimates of its surface coverage by photospheric starspots and of its chromospheric activity level, and derivations of its evolutionary status. Detailed observations of many young solar-type stars, such as the one reported in the present paper, provide insight into rotation and magnetic properties that may have prevailed on the Sun in its early evolution. Methods: Using a model based on the rotational modulation of the visibility of active regions, we analysed the high-accuracy CoRoT lightcurve of the active star CoRoT 102899501. Spectroscopic follow-up observations were used to derive its fundamental parameters. We compared the chromospheric activity level of Corot 102899501 with the R'HK index distribution vs age established on a large sample of solar-type dwarfs in open clusters. We also compared the chromospheric activity level of this young star with a model of chromospheric activity evolution established by combining relationships between the R'HK index and the Rossby number with a recent model of stellar rotation evolution on the main sequence. Results: We measure the spot coverage of the stellar surface as a function of time and find evidence for a tentative increase from 5 - 14% at the beginning of the observing run to 13-29% 35 days later. A high level of magnetic activity on Corot 102899501 is corroborated by a strong emission in the Balmer and Ca ii H and K lines (R'HK ~ -4). The starspots used as tracers of the star rotation constrain the rotation period to 1.625 ± 0.002 days and do not show evidence for differential rotation. The effective temperature (Teff = 5180 ± 80 K), surface gravity (log g = 4.35 ± 0.1), and metallicity ([M/H] = 0.05 ± 0.07 dex) indicate that the object is located near the evolutionary track of a 1.09 ± 0.12 M⊙ pre-main sequence star at an age of 23 ± 10 Myr. This value is consistent with the "gyro-age" of about 8-25 Myr

  15. OLD MAIN-SEQUENCE TURNOFF PHOTOMETRY IN THE SMALL MAGELLANIC CLOUD. II. STAR FORMATION HISTORY AND ITS SPATIAL GRADIENTS

    SciTech Connect

    Noel, Noelia E. D.; Gallart, Carme; Hidalgo, Sebastian L.; Aparicio, Antonio; Costa, Edgardo; Mendez, Rene A. E-mail: carme@iac.e E-mail: antapaj@iac.e E-mail: rmendez@das.uchile.c

    2009-11-10

    We present a quantitative analysis of the star formation history (SFH) of 12 fields in the Small Magellanic Cloud (SMC) based on unprecedented deep [(B - R), R] color-magnitude diagrams (CMDs). Our fields reach down to the oldest main-sequence turnoff with a high photometric accuracy, which is vital for obtaining accurate SFHs, particularly at intermediate and old ages. We use the IAC-pop code to obtain the SFH, using synthetic CMDs generated with IAC-star. We obtain the SFH as a function psi(t, z) of age and metallicity. We also consider several auxiliary functions: the initial mass function (IMF), phi(m), and a function accounting for the frequency and relative mass distribution of binary stars, beta(f, q). We find that there are several main periods of enhancement of star formation: a young one peaked at approx0.2-0.5 Gyr old, only present in the eastern and in the central-most fields; two at intermediate ages present in all fields: a conspicuous one peaked at approx4-5 Gyr, and a less significant one peaked at approx1.5-2.5; and an old one, peaked at approx10 Gyr in all fields but the western ones. In the western fields, this old enhancement splits into two, one peaked at approx8 Gyr old and another at approx12 Gyr old. This 'two-enhancement' zone is unaffected by our choice of stellar evolutionary library but more data covering other fields of the SMC are necessary in order to ascertain its significancy. Correlation between star formation rate enhancements and SMC-Milky Way encounters is not clear. Some correlation could exist with encounters taken from the orbit determination of Kallivayalil et al. But our results would also fit in a first pericenter passage scenario like the one claimed by Besla et al. For SMC-Large Magellanic Cloud encounters, we find a correlation only for the most recent encounter approx0.2 Gyr ago. This coincides with the youngest psi(t) enhancement peaked at these ages in our eastern fields. The population younger than 1 Gyr represents

  16. Lithium evolution from Pre-Main Sequence to the Spite plateau: an environmental solution to the cosmological lithium problem

    NASA Astrophysics Data System (ADS)

    Fu, Xiaoting; Bressan, Alessandro; Molaro, Paolo; Marigo, Paola

    2016-08-01

    Lithium abundance derived in metal-poor main sequence stars is about three times lower than the primordial value of the standard Big Bang nucleosynthesis prediction. This disagreement is referred to as the lithium problem. We reconsider the stellar Li evolution from the pre-main sequence to the end of main sequence phase by introducing the effects of overshooting and residual mass accretion. We show that 7Li could be significantly depleted by convective overshooting in the pre-main sequence phase and then partially restored in the stellar atmosphere by residual accretion which follows the Li depletion phase and could be regulated by EUV photo-evaporation. By considering the conventional nuclear burning and diffusion along the main sequence we can reproduce the Spite plateau for stars with initial mass m 0=0.62-0.80 M ⊙, and the Li declining branch for lower mass dwarfs, e.g, m 0=0.57-0.60 M ⊙, for a wide range of metallicities (Z=0.00001 to Z=0.0005), starting from an initial Li abundance A(Li) = 2.72.

  17. A Wide Angle Survey of Young Stellar Associations for Hot Jupiters and Pre-Main Sequence Binaries

    NASA Astrophysics Data System (ADS)

    Oelkers, Ryan J.; Macri, Lucas M.; Marshall, Jennifer L.; Depoy, Darren L.; Garcia Lambas, Diego

    2016-01-01

    The past two decades have seen a significant advancement in the detection, classification and understanding of exoplanets and binary star systems. The vast majority of these systems consist of objects on the main sequence or the giant branch, leading to a dearth of knowledge of properties at early times (<50 Myr). Only a dozen binaries and 1 possible transiting Hot Jupiter are known among pre-main sequence objects, yet these are the systems that can provide the best constraints on stellar formation and planetary migration models. The deficiency in the number of well characterized systems is driven by the inherent and aperiodic variability found in pre-main sequence objects which can mask and mimic eclipse signals. Nevertheless a dramatic increase in the total number of systems at early times is required to alleviate the conflict between theory and observation. I have recently completed a photometric survey of 3 nearby (<150 pc) and young (<50 Myr) moving groups with a small aperture telescope. I have discovered over 300 likely pre-main sequence binaries and have ruled out 7 possible transiting Hot Jupiters using techniques developed by reducing crowded, defocused images from an analogous system. I will present the photometric detection and follow-up for these systems, the spectroscopic measurements of pre-main sequence binary candidates and my lower bound on the Hot Jupiter migration timescale.

  18. Measuring the mass of a pre-main sequence binary star through the orbit of TWA5A

    SciTech Connect

    Konopacky, Q; Ghez, A; Duchene, G; McCabe, C; Macintosh, B

    2007-01-18

    We present the results of a five year monitoring campaign of the close binary TWA 5Aab in the TW Hydrae association, using speckle and adaptive optics on the W.M. Keck 10 m telescopes. These measurements were taken as part of our ongoing monitoring of pre-main sequence (PMS) binaries in an effort to increase the number of dynamically determined PMS masses and thereby calibrate the theoretical PMS evolutionary tracks. Our observations have allowed us to obtain the first determination of this system's astrometric orbit. We find an orbital period of 5.94 {+-} 0.09 years and a semi-major axis of 0.''066 {+-} 0.''005. Combining these results with a kinematic distance, we calculate a total mass of 0.71 {+-} 0.14 M{sub {circle_dot}} (D/44 pc){sup 3}. for this system. This mass measurement, as well as the estimated age of this system, are consistent to within 2{sigma} of all theoretical models considered. In this analysis, we properly account for correlated uncertainties, and show that while these correlations are generally ignored, they increase the formal uncertainties by up to a factor of five and therefore are important to incorporate. With only a few more years of observation, this type of measurement will allow the theoretical models to be distinguished.

  19. Discovery of 15 Myr Old pre-Main Sequence Stars with Active Accretion and Sizeable Discs in NGC 6611

    NASA Astrophysics Data System (ADS)

    De Marchi, Guido; Panagia, N.; Guarcello, M. G.; Bonito, R.

    2012-01-01

    Attention is given to a population of 110 stars with prominent near-infrared (NIR) excess in the NGC 6611 cluster of the Eagle Nebula that have optical colours typical of pre-main sequence (PMS) stars older than 10 Myr. In principle, their V-I colours would be consistent with those of young PMS objects (< 1 Myr), whose radiation is heavily obscured by a circumstellar disc seen at high inclination and in small part scattered towards the observer by the back side of the disc. However, using theoretical models it is shown here that objects of this type can only account for a few percent of this population. In fact, the spatial distribution of these objects, their X-ray luminosities, their optical brightness and their positions in the colour-magnitude diagram unambiguously indicate that most of these stars are intrinsically older than 10 Myr. Ages range from 8 to 30 Myr with a median value of 15 Myr. This is the largest homogeneous sample to date of Galactic PMS stars considerably older than 10 Myr that are still actively accreting from a circumstellar disc and it allows us to set a lower limit of 5% to the disc frequency at 15 Myr in NGC 6611. These values imply a characteristic exponential lifetime of 5 Myr for disc dissipation.

  20. Coronagraphic imaging of pre-main-sequence stars: Remnant evvelopes of star formation seen in reflection

    NASA Technical Reports Server (NTRS)

    Nakajima, Tadashi; Golimowski, David A.

    1995-01-01

    We have obtained R- and I-band coronagraphic images of the vicinities of 11 pre-main sequence (PMS) stars to search for faint, small-scale reflection nebulae. The inner radius of the search and the field of view are 1.9 arcsec and 1x1 arcmin, respectively. Reflection nebulae were imaged around RY Tau, T Tau,DG Tau, SU Aur, AB Aur, FU Ori, and Z CMa. No nebulae were detected around HBC 347, GG Tau, V773 Tau, and V830 Tau. Categorically speaking, most of the classical T Tauri program stars and all the FU Orionis-type program stars are associated with the reflection nebulae, while none of the weak-line T Tauri program stars are associated with nebulae. The detected nebulae range in size from 250 to 37 000 AU. From the brightness ratios of the stars and nebulae, we obtain a lower limit to the visual extinction of PMS star light through the nebulae of (A(sub V))(sub neb) = 0.1. The lower limits of masses and volume densities of the nebulae associated with the classical T Tauri stars are 10(exp-6) Solar mass and N(sub H) = 10(exp 5)/cu cm, respectively. Lower limits for the nebulae around FU Orionis stars are 10(exp -5) Solar mass and n(sub H) = 10 (exp 5)/cu cm, respectively. Some reflection nebulae may trace the illuminated surfaces of the optically thick dust nebulae, so these mass estimates are not stringent. All the PMS stars with associated nebulae are strong far-infrared emitters. Both the far-infrared emission and the reflection nebulae appear to originate from the remnant envelopes of star formation. The 100 micrometers emitting regions of SU Aur and FU Ori are likely to be cospatial with the reflection nebulae. A spatial discontinuity between FU Ori and its reflection nebula may explain the dip in the far-infrared spectral energy distribution at 60 micrometers. The warped, disk-like nebulae around T Tau and Z CMa are aligned with and embrace the inner star/circumstellar disk systems. The arc-shaped nebula around DG Tau may be in contact with the coaligned inner

  1. Ionization Structure and Mass-Loss for Rapidly-Rotating Near Main-Sequence B Stars

    NASA Astrophysics Data System (ADS)

    Bjorkman, J. E.; Abbott, B. P.

    1999-05-01

    Ultraviolet resonance line profiles of rapidly-rotating near main-sequence B stars indicate that the two-dimensional ionization structure of the circumstellar envelope can be crucial to our understanding of the mass-loss rate. We investigate these two-dimensional effects through the use of a radiation transfer model to construct piece-wise spherical ionization fractions for the wind-compressed disk model of a rotating stellar wind. Using these ionization fractions, we generate theoretical line profiles using a two-dimensional Monte Carlo simulation of the radiation transport for the UV resonance lines of Si iii, Si iv, C iii, C iv, and N v. For the B2.5 IV star chosen for this study, we find the mass-loss rate to be on the order of a few times 10(-9) Msuntextrm { yr}(-1) and the X-ray emission measure log EM_X ~ 52.5 cm(-3) . This result is consistent with observed X-ray luminosities as well as UV resonance line profiles. Our mass-loss rate is higher by a factor of 5--10 over those predicted theoretically (via spherically symmetric radiation-driven wind theory) and observationally (due to uncertainties in the ionization fractions). In addition, we also examine the effects of a latitudinal density gradient on the line profiles. We find that the line profiles are sensitive to two-dimensional effects, showing disproportionate amounts of emission versus absorption as the viewing location changes from pole to equator. Specifically, N v, which is abundant in the polar regions and depleted in the equator, shows enhanced emission for an observer looking edge-on to the equatorial wind-compressed disk. We show that spherically symmetric models cannot account for the anomalously strong emission or absorption resulting from a latitudinal ionization gradient in the wind. This work has been supported under NASA grants NAG5-3447 (BPA) and NAG5-3248 (JEB) to the University of Toledo.

  2. The Star-Forming Main Sequence as a Natural Consequence of the Central Limit Theorem

    NASA Astrophysics Data System (ADS)

    Kelson, Daniel David

    2015-08-01

    Star-formation rates (SFR) of disk galaxies correlate with stellar mass, with a small dispersion in SSFR at fixed mass, sigma~0.3 dex. With such scatter this star-formation main sequence (SFMS) has been interpreted as deterministic and fundamental. Here I demonstrate that such a correlation arises naturally from the central limit theorem. The derivation begins by approximating in situ stellar mass growth as a stochastic process, much like a random walk, where the expectation of SFR at any time is equal to the SFR at the previous time. The SFRs of real galaxies, however, do not experience wholly random stochastic changes over time, but change in a highly correlated fashion due to the long reach of gravity and the correlation of structure in the universe. We therefore generalize the results for star-formation as a stochastic process that has random correlations over random and potentially infinite timescales. For unbiased samples of (disk) galaxies we derive expectation values for SSFR and its scatter, such that =2/T, and Sig[SFR/M]=. Note that this relative scatter is independent of mass and time. This derived correlation between SFR and stellar mass, and its evolution, matches published data to z=10 with sufficient accuracy to constrain cosmological parameters from the data. This statistical approach to the diversity of star-formation histories reproduces several important observables, including: the scatter in SSFR at fixed mass; the forms of SFHs of nearby dwarf galaxies and the Milky Way. At least one additional process beyond a single one responsible for in situ stellar mass growth will be required to match the evolution of the stellar mass function, and we discuss ways to generalize the framework. The implied dispersion in SFHs, and the SFMS's insensitivity to timescales of stochasticity, thus substantially limits the ability to connect massive galaxies to their progenitors over long cosmic baselines. Such analytical work shows promise for

  3. Convection in the atmospheres and envelopes of Pre-Main Sequence stars

    NASA Astrophysics Data System (ADS)

    Montalbán, J.; D'Antona, F.; Kupka, F.; Heiter, U.

    2004-03-01

    The Teff location of Pre-Main Sequence (PMS) evolutionary tracks depends on the treatment of over-adiabaticity (D'Antona & Mazzitelli \\cite{Antona1994}, \\cite{Antona1998}). Since the convection penetrates into the stellar atmosphere, also the treatment of convection in the modeling of stellar atmospheres will affect the location of the Hayashi tracks. In this paper we present new non-grey PMS tracks for Teff,>4000 K. We compute several grids of evolutionary tracks varying: i) the treatment of convection: either the Mixing Length Theory (MLT) or Canuto et al. (\\cite{Canuto1996e}, CGM) formulation of a Full Spectrum of Turbulence; ii) the atmospheric boundary conditions: we use the new Vienna grids of ATLAS9 atmospheres (Heiter et al. \\cite{Heiter2002a}), which were computed using either MLT (with α=Λ/Hp=0.5) or CGM treatments. For comparison, we also compute grids of models with the NextGen (Allard & Hauschildt \\cite{Allard1997}, AH97) atmosphere models, and a 1 {M⊙} grey MLT evolutionary track using the α calibration based on 2D-hydrodynamical models (Ludwig et al. \\cite{Ludwig1999}). These different grids of models allow us to analyze the effects of convection modeling on the non-grey PMS evolutionary tracks. We disentangle the effect of the wavelength dependent opacity on a self-consistent treatment of convection in the atmosphere from the role of the convection model itself in the atmosphere and in the interior. While for some parts of the HR diagram (e.g., A stars) a low efficiency of atmospheric convection is clearly indicated by the data, for others the evidence is conflicting, showing the weaknesses of all the presently adopted local convection models. Nevertheless, the assumption of a low photospheric efficiency permits us to reproduce a larger amount of data and we have hence restricted our study to this case and draw the following conclusions for it: i) in spite of the solar calibration, if MLT convection is adopted a large uncertainty results

  4. Long-term evolution of three-planet systems to the post-main sequence and beyond

    NASA Astrophysics Data System (ADS)

    Mustill, Alexander J.; Veras, Dimitri; Villaver, Eva

    2014-01-01

    We study the stability of systems of three giant planets orbiting 3-8 M⊙ stars at orbital distances of >10 au as the host star ages through the main sequence (MS) and well into the white dwarf (WD) stage. Systems are stable on the MS if the planets are separated by more than ˜9 Hill radii. Most systems surviving the MS will remain stable until the WD phase, although planets scattered on to small pericentres in unstable systems can be swallowed by the expanding stellar envelope when the star ascends the giant branches. Mass-loss at the end of the asymptotic giant branch triggers delayed instability in many systems, leading to instabilities typically occurring at WD cooling ages of a few 100 Myr. This instability occurs both in systems that survived the star's previous evolution unscathed, and in systems that previously underwent scattering instabilities. The outcome of such instability around WDs is overwhelmingly the ejection of one of the planets from the system, with several times more ejections occurring during the WD phase than during the MS. Furthermore, few planets are scattered close to the WD, just outside the Roche limit, where they can be tidally circularized. Hence, we predict that planets in WD systems rarely dynamically evolve to become `hot Jupiters'. Nor does it appear that the observed frequency of metal pollution in WD atmospheres can be entirely explained by planetesimals being destabilized following instability in systems of multiple giant planets, although further work incorporating low-mass planets and planetesimals is needed.

  5. PHOTOMETRIC DETERMINATION OF THE MASS ACCRETION RATES OF PRE-MAIN-SEQUENCE STARS. IV. RECENT STAR FORMATION IN NGC 602

    SciTech Connect

    De Marchi, Guido; Beccari, Giacomo; Panagia, Nino E-mail: gbeccari@eso.org

    2013-09-20

    We have studied the young stellar populations in NGC 602, in the Small Magellanic Cloud, using a novel method that we have developed to combine Hubble Space Telescope photometry in the V, I, and Hα bands. We have identified about 300 pre-main-sequence (PMS) stars, all of which are still undergoing active mass accretion, and have determined their physical parameters (effective temperature, luminosity, age, mass, and mass accretion rate). Our analysis shows that star formation has been present in this field over the last 60 Myr. In addition, we can recognize at least two clear, distinct, and prominent episodes in the recent past: one about 2 Myr ago, but still ongoing in regions of higher nebulosity, and one (or more) older than 30 Myr, encompassing both stars dispersed in the field and two smaller clusters located about 100'' north of the center of NGC 602. The relative locations of younger and older PMS stars do not imply a causal effect or triggering of one generation on the other. The strength of the two episodes appears to be comparable, but the episodes occurring more than 30 Myr ago might have been even stronger than the current one. We have investigated the evolution of the mass accretion rate, M-dot{sub acc}, as a function of the stellar parameters finding that log M-dot{sub acc}≅-0.6 log t + log m + c, where t is the age of the star, m is its mass, and c is a decreasing function of the metallicity.

  6. A Wide Angle Search for Hot Jupiters and Pre-Main Sequence Binaries in Young Stellar Associations

    NASA Astrophysics Data System (ADS)

    Oelkers, Ryan J.; Macri, Lucas M.; Marshall, Jennifer L.; Depoy, Darren L.; Colazo, Carlos; Guzzo, Pablo; Lambas, Diego G.; Quiñones, Ceci; Stringer, Katelyn; Tapia, Luis; Wisdom, Colin

    2016-01-01

    The past two decades have seen a significant advancement in the detection, classification and understanding of exoplanets and binary star systems. The vast majority of these systems consist of stars on the main sequence or on the giant branch, leading to a dearth of knowledge of properties at early times (<50 Myr). Only one transiting planet candidate and a dozen eclipsing binaries are known among pre-main sequence objects, yet these are the systems that can provide the best constraints on stellar and planetary formation models. We have recently completed a photometric survey of 3 young (<50 Myr), nearby (D<150 pc) moving groups with a small-aperture instrument, nicknamed ``AggieCam''. We detected 7 candidate Hot Jupiters and over 200 likely pre-main sequence binaries, which are now being followed up photometrically and spectroscopically.

  7. Monte Carlo Simulations of the Post-Common-Envelope White-Dwarf Main-Sequence Binary Population

    SciTech Connect

    Camacho, Judit; Torres, Santiago; Garcia-Berro, Enrique; Schreiber, Matthias R.

    2010-12-22

    We present a detailed Monte Carlo simulator of the population of binary systems within the solar neighborhood. We have used the most up-to-date stellar evolutionary models, a complete treatment of the Roche lobe overflow episode, as well as a full implementation of the orbital evolution of the binary system. Preliminary results are presented for the population of white-dwarf main-sequence binaries, resulting from a common envelope episode. We also study the role played by the binding energy parameter, {lambda}, and by the common envelope efficiency, {alpha}{sub CE}. Finally, results are compared with the population of identified white-dwarf main-sequence binaries.

  8. Hunting for millimeter flares from magnetic reconnection in pre-main sequence spectroscopic binaries

    NASA Astrophysics Data System (ADS)

    Kóspál, Á.; Salter, D. M.; Hogerheijde, M. R.; Moór, A.; Blake, G. A.

    2011-03-01

    Context. Recent observations of the low-mass pre-main sequence (PMS), eccentric spectroscopic binaries DQ Tau and V773 Tau A reveal that their millimeter spectrum is occasionally dominated by flares from non-thermal emission processes. The transient activity is believed to be synchrotron in nature, resulting from powerful magnetic reconnection events when the separate magnetic structures of the binary components are briefly capable of interacting and forced to reorganize, typically near periastron. Aims: We conducted the first systematic study of the millimeter variability toward a sample of 12 PMS spectroscopic binaries with the aim to characterize the proliferation of flares amongst sources likely to experience similar interbinary reconnection events. The source sample consists entirely of short-period, close-separation binaries that possess either a high orbital eccentricity (e > 0.1) or a circular orbit (e ≈ 0). Methods: Using the MAMBO2 array on the IRAM 30 m telescope, we carried out continuous monitoring at 1.25 mm (240 GHz) over a 4-night period during which all of the high-eccentricity binaries approached periastron. We also obtained simultaneous optical VRI measurements, since a strong link is often observed between stellar reconnection events (traced via X-rays) and optical brightenings. Results: UZ Tau E is the only source to be detected at millimeter wavelengths, and it exhibited significant variation (F1.25mm = 87-179 mJy); it is also the only source to undergo strong simultaneous optical variability (ΔR ≈ 0.9 mag). The binary possesses the largest orbital eccentricity in the current sample, a predicted factor in star-star magnetic interaction events. With orbital parameters and variable accretion activity similar to DQ Tau, the millimeter behavior of UZ Tau E draws many parallels to the DQ Tau model for colliding magnetospheres. However, on the basis of our observations alone, we cannot determine whether the variability is repetitive, or if it

  9. A Wide-field Survey for Transiting Hot Jupiters and Eclipsing Pre-main-sequence Binaries in Young Stellar Associations

    NASA Astrophysics Data System (ADS)

    Oelkers, Ryan J.; Macri, Lucas M.; Marshall, Jennifer L.; DePoy, Darren L.; Lambas, Diego G.; Colazo, Carlos; Stringer, Katelyn

    2016-09-01

    The past two decades have seen a significant advancement in the detection, classification, and understanding of exoplanets and binaries. This is due, in large part, to the increase in use of small-aperture telescopes (<20 cm) to survey large areas of the sky to milli-mag precision with rapid cadence. The vast majority of the planetary and binary systems studied to date consists of main-sequence or evolved objects, leading to a dearth of knowledge of properties at early times (<50 Myr). Only a dozen binaries and one candidate transiting Hot Jupiter are known among pre-main-sequence objects, yet these are the systems that can provide the best constraints on stellar formation and planetary migration models. The deficiency in the number of well characterized systems is driven by the inherent and aperiodic variability found in pre-main-sequence objects, which can mask and mimic eclipse signals. Hence, a dramatic increase in the number of young systems with high-quality observations is highly desirable to guide further theoretical developments. We have recently completed a photometric survey of three nearby (<150 pc) and young (<50 Myr) moving groups with a small-aperture telescope. While our survey reached the requisite photometric precision, the temporal coverage was insufficient to detect Hot Jupiters. Nevertheless, we discovered 346 pre-main-sequence binary candidates, including 74 high-priority objects for further study. This paper includes data taken at The McDonald Observatory of The University of Texas at Austin.

  10. Chandra Spectroscopy of the Hot Star Beta Cru and the Discovery of a Pre-Main Sequence Companion

    NASA Astrophysics Data System (ADS)

    Kuhn, Michael A.; Cohen, D. H.; Jensen, E. L.; Gagne, M.

    2006-12-01

    Using a 75 ks Chandra grating observation, we have studied x-ray emission from the B0.5 III star beta Cru one of the four bright stars in the Southern Cross and a newly discovered companion. The companion is separated from beta Cru by 4" and it has about 3 times fewer x-ray counts. The flux contrast must be much greater in the optical, though, or the companion would have been discovered earlier. The system is a member of the Sco-Cen association, and is estimated to be 8 to 11 million years old; old enough for the B star primary to have evolved off the main sequence, but young enough that a coeval, late-type companion would still be descending to the main sequence. We marginally resolved individual line profiles of the primary in the grating spectra. The lines show slight broadening, suggesting an origin in a slow stellar wind rather than a corona. The secondary has a harder spectral energy distribution (temperatures > 20 million K) than the primary (< 4 million K), making it a probable pre-main-sequence star. The secondary is also more variable than the primary, consistent with the x-ray flaring seen in pre-main-sequence stars. We acknowledge grants GO2-3030A and AR5-6003X to Swarthmore College from the Chandra X-ray Center at the Smithsonian Astrophysical Observatory, and also support from Swarthmore College via a Eugene M. Lang Summer Research Fellowship.

  11. Therapeutic effect of interventional therapy for unprotected left main coronary artery lesions in aged patients

    PubMed Central

    Wei, Zhong-Hai; Song, Jie; Wang, Lian; Zhang, Jing-Mei; Huang, Wei; Xu, Biao

    2015-01-01

    Objective To assesse the therapeutic effect of interventional therapy in aged patients with unprotected left main coronary artery (UPLM) lesions. Methods A total of 61 patients who were over 60 years and accepted interventional therapy of UPLM from January 2012 to November 2013 in our hospital were followed up for average 14.6 months by telephone call or outpatient visits. We analyzed the clinical features data of the interventional therapy and assessed the factors that likely influenced the clinical prognosis. Results The average age of the 61 patients was 73.9 years. The average left ventricular ejection fraction (LVEF) was 47.7%. The median of the estimated glomerular filtration rate (eGFR) was 52 mL/min per 1.73 mm2. The average SYNTAX score was 27.4 and the median of stent length was 36 mm. The cumulative incidence of cardiac death at 30 days and major adverse cardiac events (MACE) after one year was 6.6% and 32.5% estimated by Kaplan-Meier plots respectively. No severe hemorrhagic complications were observed during follow-up period. On multivariate regression analysis with a COX proportional hazards model, LVEF was an independent predictor of cardiac death at 30 days [Hazard ratio (HR): 0.7, P = 0.01]. As for MACE after one year, LVEF and eGFR were both independent predictors (HR: 0.91, P = 0.06 for LVEF, HR: 0.03, P = 0.097 for eGFR). Conclusions The interventional therapy for UPLM was effective and safe in aged patients. LVEF was the only predictor of cardiac death at 30 days, while LVEF and eGFR were both independent predictors of MACE after one year. PMID:26788040

  12. Age effects in discrimination of intervals within rhythmic tone sequences.

    PubMed

    Fitzgibbons, Peter J; Gordon-Salant, Sandra

    2015-01-01

    This study measured listener sensitivity to increments of a target inter-onset interval (IOI) embedded within tone sequences that featured different rhythmic patterns. The sequences consisted of six 50-ms 1000-Hz tone bursts separated by silent intervals that were adjusted to create different timing patterns. Control sequences were isochronous, with all tonal IOIs fixed at either 200 or 400 ms, while other patterns featured combinations of the two IOIs arranged to create different sequential tonal groupings. Duration difference limens in milliseconds for increments of a single sequence IOI were measured adaptively by adjusting the duration of an inter-tone silent interval. Specific target IOIs within sequences differed across discrimination conditions. Listeners included younger normal-hearing adults and groups of older adults with and without hearing loss. Discrimination performance measured for each of the older groups of listeners was observed to be equivalent, with each group exhibiting significantly poorer discrimination performance than the younger listeners in each sequence condition. Additionally, the specific influence of variable rhythmic grouping on temporal sensitivity was found to be greatest among older listeners. PMID:25618068

  13. A HIGHLY CONSISTENT FRAMEWORK FOR THE EVOLUTION OF THE STAR-FORMING ''MAIN SEQUENCE'' FROM z ∼ 0-6

    SciTech Connect

    Speagle, J. S.; Steinhardt, C. L.; Silverman, J. D.; Capak, P. L.

    2014-10-01

    Using a compilation of 25 studies from the literature, we investigate the evolution of the star-forming galaxy (SFG) main sequence (MS) in stellar mass and star formation rate (SFR) out to z ∼ 6. After converting all observations to a common set of calibrations, we find a remarkable consensus among MS observations (∼0.1 dex 1σ interpublication scatter). By fitting for time evolution of the MS in bins of constant mass, we deconvolve the observed scatter about the MS within each observed redshift bin. After accounting for observed scatter between different SFR indicators, we find the width of the MS distribution is ∼0.2 dex and remains constant over cosmic time. Our best fits indicate the slope of the MS is likely time-dependent, with our best-fit log SFR(M {sub *}, t) = (0.84 ± 0.02 – 0.026 ± 0.003 × t)log M {sub *} – (6.51 ± 0.24 – 0.11 ± 0.03 × t), where t is the age of the universe in Gyr. We use our fits to create empirical evolutionary tracks in order to constrain MS galaxy star formation histories (SFHs), finding that (1) the most accurate representations of MS SFHs are given by delayed-τ models, (2) the decline in fractional stellar mass growth for a ''typical'' MS galaxy today is approximately linear for most of its lifetime, and (3) scatter about the MS can be generated by galaxies evolving along identical evolutionary tracks assuming an initial 1σ spread in formation times of ∼1.4 Gyr.

  14. Dependence of coronal X-ray emission on spot-induced brightness variations in cool main sequence stars

    NASA Astrophysics Data System (ADS)

    Messina, S.; Pizzolato, N.; Guinan, E. F.; Rodonò, M.

    2003-11-01

    The maximum amplitude (Amax) of spot-induced brightness variations from long-term V-band photometry and the ratio LX/Lbol between X-ray and bolometric luminosities are suitable indicators of the level of magnetic activity in the photosphere and in the corona of late-type stars, respectively. By using these activity indicators we investigate the dependence of coronal X-ray emission on the level of photospheric starspot activity in a homogeneous sample of low mass main sequence field and cluster stars of different ages (IC 2602, IC 4665, IC 2391, alpha Persei, Pleiades and Hyades). First, the activity-rotation connection at the photospheric level is re-analysed, as well as its dependence on spectral type and age. The upper envelope of Amax increases monotonically with decreasing rotational period (P) and Rossby number (R0) showing a break around 1.1 d that separates two rotation regimes where the starspot activity shows different behaviours. The Amax-P and Amax-R0 relations are fitted with linear, exponential and power laws to look for the function which best represents the trend of the data. The highest values of Amax are found among K-type stars and at the ages of alpha Persei and Pleiades. We also analyse the activity-rotation connection at the coronal level as well as its dependence on spectral type. The level of X-ray emission increases with increasing rotation rate up to a saturation level. The rotational period at which saturation occurs is colour-dependent and increases with advancing spectral type. Also the LX/Lbol-P and LX/Lbol-R0 relations are fitted with linear, exponential and power laws to look for the best fitting function. Among the fastest rotating stars (P<=0.3 d) there is evidence of super-saturation. Also the highest values of LXLbol are found among K-type stars. Finally, the photospheric-coronal activity connection is investigated by using for the first time the largest ever sample of light curve amplitudes as indicators of the magnetic filling

  15. Kepler observations of A-F pre-main-sequence stars in Upper Scorpius: discovery of six new δ Scuti and one γ Doradus stars

    NASA Astrophysics Data System (ADS)

    Ripepi, V.; Balona, L.; Catanzaro, G.; Marconi, M.; Palla, F.; Giarrusso, M.

    2015-12-01

    We present light curves and periodograms for 27 stars in the young Upper Scorpius association (age = 11 ± 1 Myr) obtained with the Kepler spacecraft. This association is only the second stellar grouping to host several pulsating pre-main-sequence (PMS) stars which have been observed from space. From an analysis of the periodograms, we identify six δ Scuti variables and one γ Doradus star. These are most likely PMS stars or else very close to the zero-age main sequence. Four of the δ Scuti variables were observed in short-cadence mode, which allows us to resolve the entire frequency spectrum. For these four stars, we are able to infer some qualitative information concerning their ages. For the remaining two δ Scuti stars, only long-cadence data are available, which means that some of the frequencies are likely to be aliases. One of the stars appears to be a rotational variable in a hierarchical triple system. This is a particularly important object, as it allows the possibility of an accurate mass determination when radial velocity observations become available. We also report on new high-resolution echelle spectra obtained for some of the stars of our sample.

  16. Genome sequence of the necrotrophic fungus Penicillium digitatum, the main postharvest pathogen of citrus

    PubMed Central

    2012-01-01

    Background Penicillium digitatum is a fungal necrotroph causing a common citrus postharvest disease known as green mold. In order to gain insight into the genetic bases of its virulence mechanisms and its high degree of host-specificity, the genomes of two P. digitatum strains that differ in their antifungal resistance traits have been sequenced and compared with those of 28 other Pezizomycotina. Results The two sequenced genomes are highly similar, but important differences between them include the presence of a unique gene cluster in the resistant strain, and mutations previously shown to confer fungicide resistance. The two strains, which were isolated in Spain, and another isolated in China have identical mitochondrial genome sequences suggesting a recent worldwide expansion of the species. Comparison with the closely-related but non-phytopathogenic P. chrysogenum reveals a much smaller gene content in P. digitatum, consistent with a more specialized lifestyle. We show that large regions of the P. chrysogenum genome, including entire supercontigs, are absent from P. digitatum, and that this is the result of large gene family expansions rather than acquisition through horizontal gene transfer. Our analysis of the P. digitatum genome is indicative of heterothallic sexual reproduction and reveals the molecular basis for the inability of this species to assimilate nitrate or produce the metabolites patulin and penicillin. Finally, we identify the predicted secretome, which provides a first approximation to the protein repertoire used during invasive growth. Conclusions The complete genome of P. digitatum, the first of a phytopathogenic Penicillium species, is a valuable tool for understanding the virulence mechanisms and host-specificity of this economically important pest. PMID:23171342

  17. Memory for Sequences of Events Impaired in Typical Aging

    ERIC Educational Resources Information Center

    Allen, Timothy A.; Morris, Andrea M.; Stark, Shauna M.; Fortin, Norbert J.; Stark, Craig E. L.

    2015-01-01

    Typical aging is associated with diminished episodic memory performance. To improve our understanding of the fundamental mechanisms underlying this age-related memory deficit, we previously developed an integrated, cross-species approach to link converging evidence from human and animal research. This novel approach focuses on the ability to…

  18. The naked T Tauri stars - The low-mass pre-main sequence unveiled

    NASA Technical Reports Server (NTRS)

    Walter, Frederick M.

    1987-01-01

    The search for low-mass premain-sequence (PMS) stars associated with X-ray sources in regions of star formation is discussed. The survey to date has revealed at least 30 low-mass PMS stars in the Tau-Aur region, and a comparable number in Oph. These stars are the naked T Tau stars, unveiled versions of the well-known classical T Tau stars. The properties of these newly discovered PMS stars and their relation to the classical T Tau stars are discussed, and it is concluded that the naked T Tau stars are the true low-mass PMS stars, and that the observable characteristics defining the classical T Tau stars are due to the interaction of an underlying, fairly normal star with a dominant circumstellar environment. The impact the naked T Tau stars are likely to have on models of the PMS evolution of low-mass stars is considered.

  19. The main challenges that remain in applying high-throughput sequencing to clinical diagnostics.

    PubMed

    Loeffelholz, Michael; Fofanov, Yuriy

    2015-01-01

    Over the last 10 years, the quality, price and availability of high-throughput sequencing instruments have improved to the point that this technology may be close to becoming a routine tool in the diagnostic microbiology laboratory. Two groups of challenges, however, have to be resolved in order to move this powerful research technology into routine use in the clinical microbiology laboratory. The computational/bioinformatics challenges include data storage cost and privacy concerns, requiring analysis to be performed without access to cloud storage or expensive computational infrastructure. The logistical challenges include interpretation of complex results and acceptance and understanding of the advantages and limitations of this technology by the medical community. This article focuses on the approaches to address these challenges, such as file formats, algorithms, data collection, reporting and good laboratory practices. PMID:26394651

  20. High-resolution Imaging of PHIBSS z ˜ 2 Main-sequence Galaxies in CO J = 1 → 0

    NASA Astrophysics Data System (ADS)

    Bolatto, A. D.; Warren, S. R.; Leroy, A. K.; Tacconi, L. J.; Bouché, N.; Förster Schreiber, N. M.; Genzel, R.; Cooper, M. C.; Fisher, D. B.; Combes, F.; García-Burillo, S.; Burkert, A.; Bournaud, F.; Weiss, A.; Saintonge, A.; Wuyts, S.; Sternberg, A.

    2015-08-01

    We present Karl Jansky Very Large Array observations of the CO J=1-0 transition in a sample of four z˜ 2 main-sequence galaxies. These galaxies are in the blue sequence of star-forming galaxies at their redshift, and are part of the IRAM Plateau de Bure HIgh-z Blue Sequence Survey which imaged them in CO J=3-2. Two galaxies are imaged here at high signal-to-noise, allowing determinations of their disk sizes, line profiles, molecular surface densities, and excitation. Using these and published measurements, we show that the CO and optical disks have similar sizes in main-sequence galaxies, and in the galaxy where we can compare CO J=1-0 and J=3-2 sizes we find these are also very similar. Assuming a Galactic CO-to-H2 conversion, we measure surface densities of {{{Σ }}}{mol}˜ 1200 {M}⊙ pc-2 in projection and estimate {{{Σ }}}{mol}˜ 500-900 {M}⊙ pc-2 deprojected. Finally, our data yields velocity-integrated Rayleigh-Jeans brightness temperature line ratios r31 that are approximately at unity. In addition to the similar disk sizes, the very similar line profiles in J=1-0 and J=3-2 indicate that both transitions sample the same kinematics, implying that their emission is coextensive. We conclude that in these two main-sequence galaxies there is no evidence for significant excitation gradients or a large molecular reservoir that is diffuse or cold and not involved in active star formation. We suggest that r31 in very actively star-forming galaxies is likely an indicator of how well-mixed the star formation activity and the molecular reservoir are.

  1. A tale of two anomalies: Depletion, dispersion, and the connection between the stellar lithium spread and inflated radii on the pre-main sequence

    SciTech Connect

    Somers, Garrett; Pinsonneault, Marc H. E-mail: pinsono@astronomy.ohio-state.edu

    2014-07-20

    We investigate lithium depletion in standard stellar models (SSMs) and main sequence (MS) open clusters, and explore the origin of the Li dispersion in young, cool stars of equal mass, age, and composition. We first demonstrate that SSMs accurately predict the Li abundances of solar analogs at the zero-age main sequence (ZAMS) within theoretical uncertainties. We then measure the rate of MS Li depletion by removing the [Fe/H]-dependent ZAMS Li pattern from three well-studied clusters, and comparing the detrended data. MS depletion is found to be mass-dependent, in the sense of more depletion at low mass. A dispersion in Li abundance at fixed T{sub eff} is nearly universal, and sets in by ∼200 Myr. We discuss mass and age dispersion trends, and the pattern is mixed. We argue that metallicity impacts the ZAMS Li pattern, in agreement with theoretical expectations but contrary to the findings of some previous studies, and suggest Li as a test of cluster metallicity. Finally, we argue that a radius dispersion in stars of fixed mass and age, during the epoch of pre-MS Li destruction, is responsible for the spread in Li abundances and the correlation between rotation and Li in young cool stars, most well known in the Pleiades. We calculate stellar models, inflated to match observed radius anomalies in magnetically active systems, and the resulting range of Li abundances reproduces the observed patterns of young clusters. We discuss ramifications for pre-MS evolutionary tracks and age measurements of young clusters, and suggest an observational test.

  2. A Tale of Two Anomalies: Depletion, Dispersion, and the Connection between the Stellar Lithium Spread and Inflated Radii on the Pre-main Sequence

    NASA Astrophysics Data System (ADS)

    Somers, Garrett; Pinsonneault, Marc H.

    2014-07-01

    We investigate lithium depletion in standard stellar models (SSMs) and main sequence (MS) open clusters, and explore the origin of the Li dispersion in young, cool stars of equal mass, age, and composition. We first demonstrate that SSMs accurately predict the Li abundances of solar analogs at the zero-age main sequence (ZAMS) within theoretical uncertainties. We then measure the rate of MS Li depletion by removing the [Fe/H]-dependent ZAMS Li pattern from three well-studied clusters, and comparing the detrended data. MS depletion is found to be mass-dependent, in the sense of more depletion at low mass. A dispersion in Li abundance at fixed T eff is nearly universal, and sets in by ~200 Myr. We discuss mass and age dispersion trends, and the pattern is mixed. We argue that metallicity impacts the ZAMS Li pattern, in agreement with theoretical expectations but contrary to the findings of some previous studies, and suggest Li as a test of cluster metallicity. Finally, we argue that a radius dispersion in stars of fixed mass and age, during the epoch of pre-MS Li destruction, is responsible for the spread in Li abundances and the correlation between rotation and Li in young cool stars, most well known in the Pleiades. We calculate stellar models, inflated to match observed radius anomalies in magnetically active systems, and the resulting range of Li abundances reproduces the observed patterns of young clusters. We discuss ramifications for pre-MS evolutionary tracks and age measurements of young clusters, and suggest an observational test.

  3. CCD photometry in the globular cluster NGC 288. I - Blue stragglers and main-sequence binary stars

    NASA Technical Reports Server (NTRS)

    Bolte, Michael

    1992-01-01

    Photometry based on a mosaic of CCD images in B and V is presented for the globular cluster NGC 288. The spatial coverage ranges from the cluster core to about 6 core radii, and stars have been measured over the absolute visual magnitude range -1.2 to 8.4. The cluster is shown to contain a significant number of blue straggler stars in the central regions, and there is an excess of objects brighter and redder than the single-star main-sequence in the color-magnitude plane. These objects are interpreted as a population of main-sequence binary stars. With this interpretation, the explicity measured fraction of binary stars is 10 percent, which sets a lower limit for the total binary population.

  4. The Connection Between Rotation, Circumstellar Disks, and Accretion Among Low-Mass Pre-Main-Sequence Stars

    NASA Astrophysics Data System (ADS)

    Stassun, Keivan Guadalupe

    2000-07-01

    Circumstellar disks have come to be seen as dominant players in the rotational evolution of low-mass stars during the pre-main-sequence (PMS) phase. In fact, most rotational evolution models today rely chiefly on magnetic disk-locking to successfully connect the rotational properties of T Tauri stars (TTS) to those of zero-age main sequence (ZAMS) stars. The principal aim of this dissertation is to summarize recent observations (Stassun et al. 1999; Stassun et al. 2000) that challenge this picture of disk-regulated PMS rotational evolution. We present photometrically derived rotation periods for 254 stars in an area 40 × 80 arcmin centered on the Orion Nebula. We show that these stars are likely members of the young (~106 yr) Orion OBIc/d association. The rotation period distribution we determine, sensitive to periods 0.1 < Prot < 8 days, shows a sharp cutoff for periods Prot < 0.5 days, corresponding to breakup velocity for these stars; a population of stars rotating near breakup is already present at 1 Myr. Above 0.5 days the distribution is consistent with a uniform distribution; we do not find evidence for a ``gap" of periods at 4--5 days. We find signatures of active accretion among stars at all periods; active accretion does not occur preferentially among slow rotators in our sample. We find no correlation between rotation period and the presence of near-infrared signatures of circumstellar disks. We do not find compelling agreement between our observations and the requirements of the disk-locking hypothesis. We use near-IR photometry to argue that inner cavities in TTS disks are typically much smaller than allowed by theory for the regulation of stellar angular momentum. We further use mid-IR (primarily 10 microns) photometry to confirm that TTS lacking near-IR excesses do not harbor disks with large inner truncation radii. With a few exceptions, stars in our sample lacking near-IR excesses do not possess disks, truncated or otherwise. Evidently, many young

  5. Carbon and greenhouse gas balances in an age sequence of temperate pine plantations

    NASA Astrophysics Data System (ADS)

    Peichl, M.; Arain, A. M.; Moore, T. R.; Brodeur, J. J.; Khomik, M.; Ullah, S.; Restrepo-Coupé, N.; McLaren, J.; Pejam, M. R.

    2014-10-01

    This study investigated differences in the magnitude and partitioning of the carbon (C) and greenhouse gas (GHG) balances in an age sequence of four white pine (Pinus strobus L.) afforestation stands (7, 20, 35 and 70 years old as of 2009) in southern Ontario, Canada. The 4-year (2004-2008) mean annual carbon dioxide (CO2) exchanges, based on biometric and eddy covariance data, were combined with the 2-year means of static chamber measurements of methane (CH4) and nitrous oxide (N2O) fluxes (2006-2007) and dissolved organic carbon (DOC) export below 1 m soil depth (2004-2005). The total ecosystem C pool increased with age from 46 to 197 t C ha-1 across the four stands. Rates of organic matter cycling (i.e. litterfall and decomposition) were similar among the three older stands. In contrast, considerable differences related to stand age and site quality were observed in the magnitude and partitioning of individual CO2 fluxes, showing a peak in production and respiration rates in the middle-age (20-year-old) stand growing on fertile post-agricultural soil. The DOC export accounted for 10% of net ecosystem production (NEP) at the 7-year-old stand but <2% at the three older stands. The GHG balance from the combined exchanges of CO2, CH4 and N2O was 2.6, 21.6, 13.5 and 4.8 t CO2 equivalent ha-1 year-1 for the 7-, 20-, 35- and 70-year-old stands, respectively. The maximum annual contribution from the combined exchanges of CH4 and N2O to the GHG balance was 13 and 8% in the 7- and 70-year-old stands, respectively, but <1% in the two highly productive middle-age (20- and 35-year-old) stands. Averaged over the entire age sequence, the CO2 exchange was the main driver of the GHG balance in these forests. The cumulative CO2 sequestration over the 70 years was estimated at 129 t C and 297 t C ha-1 year-1 for stands growing on low- and high-productivity sites, respectively. This study highlights the importance of accounting for age and site quality effects on forest C and GHG

  6. Carbon and greenhouse gas balances in an age-sequence of temperate pine plantations

    NASA Astrophysics Data System (ADS)

    Peichl, M.; Arain, A. M.; Moore, T. R.; Brodeur, J. J.; Khomik, M.; Ullah, S.; Restrepo-Coupé, N.; McLaren, J.; Pejam, M. R.

    2014-06-01

    This study investigated differences in the magnitude and partitioning of the carbon (C) and greenhouse gas (GHG) balances in an age-sequence of four white pine (Pinus strobus L.) afforestation stands (7, 20, 35 and 70 years old as of 2009) in southern Ontario, Canada. The 4 year (2004-2008) mean annual carbon dioxide (CO2) exchanges, based on biometric and eddy covariance data, were combined with the 2-year means of static chamber measurements of methane (CH4) and nitrous oxide (N2O) fluxes (2006-2007) and dissolved organic carbon (DOC) export below 1 m soil depth (2004-2005). The total ecosystem C pool increased with age from 9 to 160 t C ha-1 across the four stands. Rates of organic matter cycling (i.e. litter-fall and decomposition) were similar among the three older stands. In contrast, considerable differences related to stand age and site quality were observed in the magnitude and partitioning of individual CO2 fluxes showing a peak in production and respiration rates in the middle-age (20 year-old) stand growing on fertile post-agricultural soil. The DOC export accounted for 10% of net ecosystem production (NEP) at the 7 year old stand but < 2% at the three older stands. The GHG balance from the combined exchanges of CO2, CH4 and N2O fluxes was 2.6, 21.6, 13.5 and 4.8 t CO2 eq ha-1 yr-1 for the 7, 20, 35, and 70 year-old stands, respectively. The maximum annual contribution from the combined exchanges of CH4, N2O and DOC to the GHG balance was 8% and 15% in the 7 and 70 year-old stands, respectively, but < 1% in the two highly productive middle-age (20 and 35 year-old) stands. Averaged over the entire age-sequence, the CO2 exchange was the main driver of the GHG balance in these forests. The cumulative CO2 sequestration over the 70 years was estimated at 129 \\unit{t} C and 297 t C ha-1 yr-1 for stands growing on low and high productive sites, respectively. This study highlights the importance of accounting for age and site quality effects on forest C and

  7. Magnetic inhibition of convection and the fundamental properties of low-mass stars. II. Fully convective main-sequence stars

    SciTech Connect

    Feiden, Gregory A.; Chaboyer, Brian E-mail: brian.chaboyer@dartmouth.edu

    2014-07-01

    We examine the hypothesis that magnetic fields are inflating the radii of fully convective main-sequence stars in detached eclipsing binaries (DEBs). The magnetic Dartmouth stellar evolution code is used to analyze two systems in particular: Kepler-16 and CM Draconis. Magneto-convection is treated assuming stabilization of convection and also by assuming reductions in convective efficiency due to a turbulent dynamo. We find that magnetic stellar models are unable to reproduce the properties of inflated fully convective main-sequence stars, unless strong interior magnetic fields in excess of 10 MG are present. Validation of the magnetic field hypothesis given the current generation of magnetic stellar evolution models therefore depends critically on whether the generation and maintenance of strong interior magnetic fields is physically possible. An examination of this requirement is provided. Additionally, an analysis of previous studies invoking the influence of star spots is presented to assess the suggestion that star spots are inflating stars and biasing light curve analyses toward larger radii. From our analysis, we find that there is not yet sufficient evidence to definitively support the hypothesis that magnetic fields are responsible for the observed inflation among fully convective main-sequence stars in DEBs.

  8. Hypervelocity Stars. III. The Space Density and Ejection History of Main-Sequence Stars from the Galactic Center

    NASA Astrophysics Data System (ADS)

    Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J.; Kurtz, Michael J.; Bromley, Benjamin C.

    2007-12-01

    We report the discovery of three new unbound hypervelocity stars (HVSs), stars traveling with such extreme velocities that dynamical ejection from a massive black hole (MBH) is their only suggested origin. We also detect a population of possibly bound HVSs. The significant asymmetry we observe in the velocity distribution-we find 26 stars with vrf>275 km s-1 and one star with vrf<-275 km s-1-shows that HVSs must be short-lived, probably 3-4 Msolar main-sequence stars. Any population of hypervelocity post-main-sequence stars should contain stars falling back onto the Galaxy, contrary to the observations. The spatial distribution of HVSs also supports the main-sequence interpretation: longer lived 3 Msolar HVSs fill our survey volume; shorter lived 4 Msolar HVSs are missing at faint magnitudes. We infer that there are 96+/-10 HVSs of mass 3-4 Msolar within R<100 kpc, possibly enough HVSs to constrain ejection mechanisms and potential models. Depending on the mass function of HVSs, we predict that SEGUE may find up to 5-15 new HVSs. The travel times of our HVSs favor a continuous ejection process, although a ~120 Myr old burst of HVSs is also allowed.

  9. Gas and dust in the pre-main-sequence multiple system GG Tauri

    NASA Technical Reports Server (NTRS)

    Koerner, D. W.; Sargent, A. I.; Beckwith, S. V. W.

    1993-01-01

    We present 1.4 and 2.7 mm aperture synthesis maps of the gas and dust continuum emission around GG Tauri, a very young component of a premain-sequence multiple star system; both GG Tau and its apparent companion, GG Tau/c, at 1500 AU separation, are themselves binaries. At 1.4 mm, dust continuum emission of about 750 AU in extent is associated with GG Tau, and a secondary peak is near GG Tau/c. Spectral line images reveal gaseous structure around GG Tau, elongated along the GG Tau-GG Tau/c axis. There is some suggestion that the gas associated with GG Tau/c alone is extended in a different direction. Marked changes in the morphology and velocity structure of the molecular emission near GG Tau/c also indicate that this system is differently oriented. Clumps between the two systems may be vestiges of a connecting bar. GG Tau and GG Tau/c appear to have originated in a common cloud; their different systemic orientations suggest that they formed from an initially prolate cloud rather than from an extensive and highly flattened disk.

  10. New Neighbors from 2MASS: Activity and Kinematics at the Bottom of the Main Sequence

    NASA Astrophysics Data System (ADS)

    Gizis, John E.; Monet, David G.; Reid, I. Neill; Kirkpatrick, J. Davy; Liebert, James; Williams, Rik J.

    2000-08-01

    We have combined 2MASS and POSS II data in a search for nearby ultracool (later than M6.5) dwarfs with Ks<12. Spectroscopic follow-up observations identify 53 M7-M9.5 dwarfs and seven L dwarfs. The observed space density is 0.0045+/-0.0008 M8-M9.5 dwarfs per cubic parsec, without accounting for biases, consistent with a mass function that is smooth across the stellar/substellar limit. We show the observed frequency of Hα emission peaks at ~100% for M7 dwarfs and then decreases for cooler dwarfs. In absolute terms, however, as measured by the ratio of Hα to bolometric luminosity, none of the ultracool M dwarfs can be considered very active compared to earlier M dwarfs, and we show that the decrease that begins at spectral type M6 continues to the latest L dwarfs. We find that flaring is common among the coolest M dwarfs and estimate the frequency of flares at 7% or higher. We show that the kinematics of relatively active (EW>6 Å) ultracool M dwarfs are consistent with an ordinary old disk stellar population, while the kinematics of inactive ultracool M dwarfs are more typical of a 0.5 Gyr old population. The early L dwarfs in the sample have kinematics consistent with old ages, suggesting that the hydrogen-burning limit is near spectral types L2-L4. We use the available data on M and L dwarfs to show that chromospheric activity drops with decreasing mass and temperature and that at a given (M8 or later) spectral type, the younger field (brown) dwarfs are less active than many of the older, more massive field stellar dwarfs. Thus, contrary to the well-known stellar age-activity relationship, low activity in field ultracool dwarfs can be an indication of comparative youth and substellar mass.

  11. Earthquake source parameters for the 2010 January Haiti main shock and aftershock sequence

    NASA Astrophysics Data System (ADS)

    Nettles, Meredith; Hjörleifsdóttir, Vala

    2010-10-01

    Previous analyses of geological and geodetic data suggest that the obliquely compressive relative motion across the Caribbean-North America plate boundary in Hispaniola is accommodated through strain partitioning between near-vertical transcurrent faults on land and low-angle thrust faults offshore. In the Dominican Republic, earthquake focal-mechanism geometries generally support this interpretation. Little information has been available about patterns of seismic strain release in Haiti, however, due to the small numbers of moderate-to-large earthquakes occurring in western Hispaniola during the modern instrumental era. Here, we analyse the damaging MW = 7.0 earthquake that occurred near Port au Prince on 2010 January 12 and aftershocks occurring in the four months following this event, to obtain centroid-moment-tensor (CMT) solutions for 50 earthquakes with magnitudes as small as MW = 4.0. While the 2010 January main shock exhibited primarily strike-slip motion on a steeply dipping nodal plane (strike=250°, dip=71° and rake=22°), we find that nearly all of the aftershocks show reverse-faulting motion, typically on high-angle (30°-45°) nodal planes. Two small aftershocks (MW 4.5 and 4.6), located very close to the main shock epicentre, show strike-slip faulting with geometries similar to the main shock. One aftershock located off the south coast of Haiti shows low-angle thrust faulting. We also examine earthquakes occurring in this region from 1977-2009 successful analysis of four such events provides evidence for both strike-slip and reverse faulting. The pattern of seismic strain release in southern Haiti thus indicates that partitioning of plate motion between transcurrent and reverse structures extends far west within Hispaniola. While we see limited evidence for low-angle underthrusting offshore, most reverse motion appears to occur on high-angle fault structures adjacent to the Enriquillo fault. Our results highlight the need to incorporate seismogenic

  12. DETECTION OF GROUNDWATER AGES WITH 85 KR IN ARSENIC-BEARING, FRACTURED CRYSTALLINE BEDROCK OF THE GOOSE RIVER BASIN, MAINE

    EPA Science Inventory

    Young groundwater from various depths in crystalline bedrock of the Goose River basin, mid-coastal Maine, is documented from 85Kr isotope age analyses (1963 ? 1987) but not from 3H isotope age analyses. Elevated geogenic arsenic in drinking water from groundwater wells and sprin...

  13. A Simple Nonlinear Model for the Rotation of Main-sequence Cool Stars. I. Introduction, Implications for Gyrochronology, and Color-Period Diagrams

    NASA Astrophysics Data System (ADS)

    Barnes, Sydney A.

    2010-10-01

    We here introduce a simple nonlinear model to describe the rotational evolution of cool stars on the main sequence. It is formulated only in terms of the Rossby number (Ro = P/τ), its inverse, and two dimensionless constants which we specify using solar and open-cluster data. The model has two limiting cases of stellar rotation, previously called C and I, that correspond to two observed sequences of fast and slowly rotating stars in young open clusters. The model describes the evolution of stars from C-type, with particular mass and age dependencies, to I-type, with different mass and age dependencies, through the rotational gap, g, separating them. The proposed model explains various aspects of stellar rotation, and provides an exact expression for the age of a rotating cool star in terms of P and τ, thereby generalizing gyrochronology. Using it, we calculate the time interval required for stars to reach the rotational gap—a monotonically increasing, mildly nonlinear function of τ. Beginning with the range of initial periods indicated by observations, we show that the (mass-dependent) dispersion in rotation period initially increases, and then decreases rapidly with the passage of time. The initial dispersion in period contributes up to 128 Myr to the gyro-age errors of solar-mass field stars. Finally, we transform to color-period space, calculate appropriate isochrones, and show that this model explains some detailed features in the observed color-period diagrams of open clusters, including the positions and shapes of the sequences, and the observed density of stars across these diagrams.

  14. V 3903 Sagittarii: a massive main-sequence (O7V+O9V) detached eclipsing binary

    NASA Astrophysics Data System (ADS)

    Vaz, L. P. R.; Cunha, N. C. S.; Vieira, E. F.; Myrrha, M. L. M.

    1997-11-01

    We present for the first time an analysis based on uvby light curves, Hβ indices and on new spectroscopic data of the massive detached double-lined O-type eclipsing binary V 3903Sgr. The uvby light curves are analysed with the WINK (initial solutions) and the Wilson-Devinney (WD, final solution) programs. Both codes were used in their extended versions, with stellar atmospheres and taking into account the geometric distortions and photometric effects caused by proximity of the components. The spectroscopic CCD observations were analysed with the harmonic ``Wilsing-Russell'' and the ``Lehman-Filhes'' methods. We conclude that V 3903Sgr is one of the rare O-type detached systems where both components are still on the initial phases of the main sequence, with an age of either 1.6x10(6) yrs or 2.5x10(6) yrs (depending on the evolutionary model adopted) at a distance of ~1500pc, the same as for the Lagoon Nebula (Messier8) complex, of which the system is probably a member. We determine the absolute dimensions: M_A=27.27+/-0.55, R_A=8.088+/-% 0.086, M_B=19.01+/-0.44 and R_B=6.125+/-0.060 (solar units). There is no evidence of mass transfer and the system is detached. The orbit is circular, and both components show synchronous rotation, despite their early evolutionary stage. The absolute dimensions determined should be representative for normal single stars. Amongst the massive systems (M>17Msun) with precise absolute dimensions (errors <2%), V 3903Sgr is that with the most massive primary, with the largest mass difference between the components, and it is the youngest one. Based on data collected with the 60$\\,$cm and 1.6$\\,$m telescopes at the Pico dos Dias Observatory, Na\\-tional Laboratory of Astrophysics, LNA-CNPq, Bra\\-só\\-polis, MG, Brazil and with the Danish 50$\\,$cm telescope (SAT) at the European Southern Observatory (ESO), La Silla, Chile

  15. Cryptococcus gattii in the Age of Whole-Genome Sequencing.

    PubMed

    Meyer, Wieland

    2015-11-17

    Cryptococcus gattii, the sister species of Cryptococcus neoformans, is an emerging pathogen which gained importance in connection with the ongoing cryptococcosis outbreak on Vancouver Island. Many molecular studies have divided this species into for major lineages: VGI, VGII, VGIII, and VGIV. This commentary summarizes the whole-genome sequencing (WGS) studies that have been carried out with this species, re-emphasizing the phylogenetic relationships, showing chromosomal rearrangements between those four groups, and identifying VGII as ancestral population within C. gattii. In addition, WGS specific to VGII, containing the Vancouver Island outbreak genotypes and those from the Pacific Northwest region of the United States, has placed the origin of this lineage within South America and identified specific genes responsible for either brain or lung infection. It also showed, that many genotypes are spread across a number of different continents, as has been previously shown by multilocus sequence typing (MLST). In addition, it showed that recombination occurs more frequently between mitochondrial than nuclear genomes.

  16. Cryptococcus gattii in the Age of Whole-Genome Sequencing.

    PubMed

    Meyer, Wieland

    2015-01-01

    Cryptococcus gattii, the sister species of Cryptococcus neoformans, is an emerging pathogen which gained importance in connection with the ongoing cryptococcosis outbreak on Vancouver Island. Many molecular studies have divided this species into for major lineages: VGI, VGII, VGIII, and VGIV. This commentary summarizes the whole-genome sequencing (WGS) studies that have been carried out with this species, re-emphasizing the phylogenetic relationships, showing chromosomal rearrangements between those four groups, and identifying VGII as ancestral population within C. gattii. In addition, WGS specific to VGII, containing the Vancouver Island outbreak genotypes and those from the Pacific Northwest region of the United States, has placed the origin of this lineage within South America and identified specific genes responsible for either brain or lung infection. It also showed, that many genotypes are spread across a number of different continents, as has been previously shown by multilocus sequence typing (MLST). In addition, it showed that recombination occurs more frequently between mitochondrial than nuclear genomes. PMID:26578680

  17. Duration of inverted metamorphic sequence formation across the Himalayan Main Central Thrust (MCT), Sikkim

    NASA Astrophysics Data System (ADS)

    Cioldi, Stefania; Moulas, Evangelos; Tajcmanová, Lucie; Burg, Jean-Pierre

    2016-04-01

    Collision between the Indian and Eurasian plates since the Eocene (50 Ma) caused the closure of the Neo-Tethys and the underthrusting of India beneath the Tibetan Plateau, generating the 2500 km extended Himalayan belt. The Main Central Thrust (MCT) marks the boundary of the underlying Midland Lower Himalaya metasediments zone (LH) in the south from the overlying high grade metamorphic Higher Himalaya (HH) in the north. Several models considering petrochronology, geothermobarometry and structural geology have been discussed to explain the inverted metamorphic gradient in the LH metasediments without reaching a common agreement. This study investigates the tectonic setting and the timescale of inverted isograds related to crustal-scale thrusting at the MCT in the Sikkim region, northeast India. The aim is to contribute to the understanding of the link between mechanical and thermal evolution of major thrust zones and to clarify the nature and the origin of orogenic heat applying garnet geospeedometry. Garnets provide a sensitive record of metamorphic conditions and are potential chronometer. Their compositional zoning is used as a gauge for rate estimates of element diffusion within the mineral and allows estimating the absolute time of the thermal evolution. Inverse-fitting numerical model considering FRactIonation and Diffusion in GarnEt (FRIDGE) calculates garnet composition profiles by introducing P-T-t paths and bulk-rock composition of a specific sample. P-T conditions were estimated by convectional geothermobarometry supported by phase equilibria modelling and measured garnet chemical compositions. Simulation were compared with measured garnet profiles. Simple step function and FRIDGE preliminary results of Fe-Mg - Ca - Mn garnet fractionation-diffusion modelling indicate very short timescale (between 3 and 6 Ma) for peak metamorphic conditions in the northeast Himalayan collisional system. This duration does not allow thermal re-equilibration. It is an

  18. Age-Related Declines in Early Sensory Memory: Identification of Rapid Auditory and Visual Stimulus Sequences

    PubMed Central

    Fogerty, Daniel; Humes, Larry E.; Busey, Thomas A.

    2016-01-01

    Age-related temporal-processing declines of rapidly presented sequences may involve contributions of sensory memory. This study investigated recall for rapidly presented auditory (vowel) and visual (letter) sequences presented at six different stimulus onset asynchronies (SOA) that spanned threshold SOAs for sequence identification. Younger, middle-aged, and older adults participated in all tasks. Results were investigated at both equivalent performance levels (i.e., SOA threshold) and at identical physical stimulus values (i.e., SOAs). For four-item sequences, results demonstrated best performance for the first and last items in the auditory sequences, but only the first item for visual sequences. For two-item sequences, adults identified the second vowel or letter significantly better than the first. Overall, when temporal-order performance was equated for each individual by testing at SOA thresholds, recall accuracy for each position across the age groups was highly similar. These results suggest that modality-specific processing declines of older adults primarily determine temporal-order performance for rapid sequences. However, there is some evidence for a second amodal processing decline in older adults related to early sensory memory for final items in a sequence. This selective deficit was observed particularly for longer sequence lengths and was not accounted for by temporal masking. PMID:27199737

  19. Age-Related Declines in Early Sensory Memory: Identification of Rapid Auditory and Visual Stimulus Sequences.

    PubMed

    Fogerty, Daniel; Humes, Larry E; Busey, Thomas A

    2016-01-01

    Age-related temporal-processing declines of rapidly presented sequences may involve contributions of sensory memory. This study investigated recall for rapidly presented auditory (vowel) and visual (letter) sequences presented at six different stimulus onset asynchronies (SOA) that spanned threshold SOAs for sequence identification. Younger, middle-aged, and older adults participated in all tasks. Results were investigated at both equivalent performance levels (i.e., SOA threshold) and at identical physical stimulus values (i.e., SOAs). For four-item sequences, results demonstrated best performance for the first and last items in the auditory sequences, but only the first item for visual sequences. For two-item sequences, adults identified the second vowel or letter significantly better than the first. Overall, when temporal-order performance was equated for each individual by testing at SOA thresholds, recall accuracy for each position across the age groups was highly similar. These results suggest that modality-specific processing declines of older adults primarily determine temporal-order performance for rapid sequences. However, there is some evidence for a second amodal processing decline in older adults related to early sensory memory for final items in a sequence. This selective deficit was observed particularly for longer sequence lengths and was not accounted for by temporal masking.

  20. Age-Related Declines in Early Sensory Memory: Identification of Rapid Auditory and Visual Stimulus Sequences.

    PubMed

    Fogerty, Daniel; Humes, Larry E; Busey, Thomas A

    2016-01-01

    Age-related temporal-processing declines of rapidly presented sequences may involve contributions of sensory memory. This study investigated recall for rapidly presented auditory (vowel) and visual (letter) sequences presented at six different stimulus onset asynchronies (SOA) that spanned threshold SOAs for sequence identification. Younger, middle-aged, and older adults participated in all tasks. Results were investigated at both equivalent performance levels (i.e., SOA threshold) and at identical physical stimulus values (i.e., SOAs). For four-item sequences, results demonstrated best performance for the first and last items in the auditory sequences, but only the first item for visual sequences. For two-item sequences, adults identified the second vowel or letter significantly better than the first. Overall, when temporal-order performance was equated for each individual by testing at SOA thresholds, recall accuracy for each position across the age groups was highly similar. These results suggest that modality-specific processing declines of older adults primarily determine temporal-order performance for rapid sequences. However, there is some evidence for a second amodal processing decline in older adults related to early sensory memory for final items in a sequence. This selective deficit was observed particularly for longer sequence lengths and was not accounted for by temporal masking. PMID:27199737

  1. Pre-main sequence stars with disks in the Eagle Nebula observed in scattered light

    NASA Astrophysics Data System (ADS)

    Guarcello, M. G.; Damiani, F.; Micela, G.; Peres, G.; Prisinzano, L.; Sciortino, S.

    2010-10-01

    Context. NGC 6611 and its parental cloud, the Eagle Nebula (M 16), are well-studied star-forming regions, thanks to their large content of both OB stars and stars with disks and the observed ongoing star formation. In our previous studies of the Eagle Nebula, we identified 834 disk-bearing stars associated with the cloud, after detecting their excesses in NIR bands from J band to 8.0 μ m. Aims: In this paper, we study in detail the nature of a subsample of disk-bearing stars that show peculiar characteristics. They appear older than the other members in the V vs. V-I diagram, and/or they have one or more IRAC colors at pure photospheric values, despite showing NIR excesses, when optical and infrared colors are compared. Methods: We confirm the membership of these stars to M 16 by a spectroscopic analysis. The physical properties of these stars with disks are studied by comparing their spectral energy distributions (SEDs) with the SEDs predicted by models of T Tauri stars with disks and envelopes. Results: We show that the age of these stars estimated from the V vs. V-I diagram is unreliable since their V-I colors are altered by the light scattered by the disk into the line of sight. Only in a few cases their SEDs are compatible with models with excesses in V band caused by optical veiling. Candidate members with disks and photospheric IRAC colors are selected by the used NIR disk diagnostic, which is sensitive to moderate excesses, such as those produced by disks with low masses. In 1/3 of these cases, scattering of stellar flux by the disks can also be invoked. Conclusions: The photospheric light scattered by the disk grains into the line of sight can affect the derivation of physical parameters of Class II stars from photometric optical and NIR data. Besides, the disks diagnostic we defined are useful for selecting stars with disks, even those with moderate excesses or whose optical colors are altered by veiling or photospheric scattered light. Table with the

  2. Is groundwater age the main control for slow turnover of nitrate in a fractured groundwater system?

    NASA Astrophysics Data System (ADS)

    Osenbrück, Karsten; Schwientek, Marc; Rügner, Hermann; Grathwohl, Peter

    2015-04-01

    Slow transformation processes are known to control the chemical, isotopic, and redox evolution of large-scale aquifers (Edmunds et al., 1982; Katz et al., 1995). However, at the field scale some of the crucial biogeochemical processes governing pollutant turnover and their interrelations with hydrology are poorly understood. Particularly, only little is known about denitrification in fractured rock aquifers. Therefore, the main objective of the presented study is to assess where and how slow turnover of nitrate ans other pollutants in the deeper subsurface take place. The studied fractured and partly karstified aquifer consisting of Triassic black limestones and dolomites is located in the catchment of the Ammer river (ca. 350 km²) close to Tübingen in southern Germany. Near the recharge area, the aquifer is covered by loess allowing intensive agriculture. Further downgradient, the cover consist of a series of mudstones and sandstones of variable permeability. The aquifer is used for drinking water purposes by regional water suppliers. Land-use is dominated by agriculture with arable land covering nearly 50% of the catchment. Over the last years a variety of groundwater samples have been collected from the groundwater system including 6 water supply wells, 4 karstic springs, and 9 monitoring wells in the recharge area. This allowed to identify spatial and temporal patterns of water quality including concentrations of major ions, dissolved organic carbon (DOC), organic pollutants (e.g., pesticides), and environmental isotopes. Groundwater age distributions at most of these locations were derived from tritium, 3He, CFCs and SF6. Groundwaters in the recharge area show high concentrations of nutrients (e.g. 20-51 mg/L of nitrate and 0.2 to 0.05 µg/L of phosphate). Of special concern are disparate nitrate concentrations ranging from below 0.4 to 20 mg/L in water supply wells although screen depths of the production wells are similar. Concentrations of dissolved

  3. The "multiple hormone deficiency" theory of aging: is human senescence caused mainly by multiple hormone deficiencies?

    PubMed

    Hertoghe, T

    2005-12-01

    In the human body, the productions, levels and cell receptors of most hormones progressively decline with age, gradually putting the body into various states of endocrine deficiency. The circadian cycles of these hormones also change, sometimes profoundly, with time. In aging individuals, the well-balanced endocrine system can fall into a chaotic condition with losses, phase-advancements, phase delays, unpredictable irregularities of nycthemeral hormone cycles, in particular in very old or sick individuals. The desynchronization makes hormone activities peak at the wrong times and become inefficient, and in certain cases health threatening. The occurrence of multiple hormone deficits and spilling through desynchronization may constitute the major causes of human senescence, and they are treatable causes. Several arguments can be put forward to support the view that senescence is mainly a multiple hormone deficiency syndrome: First, many if not most of the signs, symptoms and diseases (including cardiovascular diseases, cancer, obesity, diabetes, osteoporosis, dementia) of senescence are similar to physical consequences of hormone deficiencies and may be caused by hormone deficiencies. Second, most of the presumed causes of senescence such as excessive free radical formation, glycation, cross-linking of proteins, imbalanced apoptosis system, accumulation of waste products, failure of repair systems, deficient immune system, may be caused or favored by hormone deficiencies. Even genetic causes such as limits to cell proliferation (such as the Hayflick limit of cell division), poor gene polymorphisms, premature telomere shortening and activation of possible genetic "dead programs" may have links with hormone deficiencies, being either the consequence, the cause, or the major favoring factor of hormone deficiencies. Third, well-dosed and -balanced hormone supplements may slow down or stop the progression of signs, symptoms, or diseases of senescence and may often

  4. Nuclear power plant Generic Aging Lessons Learned (GALL). Main report and appendix A

    SciTech Connect

    Kaza, K.E.; Diercks, D.R.; Holland, J.W.; Choi, S.U.

    1996-12-01

    The purpose of this generic aging lessons learned (GALL) review is to provide a systematic review of plant aging information in order to assess materials and component aging issues related to continued operation and license renewal of operating reactors. Literature on mechanical, structural, and thermal-hydraulic components and systems reviewed consisted of 97 Nuclear Plant Aging Research (NPAR) reports, 23 NRC Generic Letters, 154 Information Notices, 29 Licensee Event Reports (LERs), 4 Bulletins, and 9 Nuclear Management and Resources Council Industry Reports (NUMARC IRs) and literature on electrical components and systems reviewed consisted of 66 NPAR reports, 8 NRC Generic Letters, 111 Information Notices, 53 LERs, 1 Bulletin, and 1 NUMARC IR. More than 550 documents were reviewed. The results of these reviews were systematized using a standardized GALL tabular format and standardized definitions of aging-related degradation mechanisms and effects. The tables are included in volume s 1 and 2 of this report. A computerized data base has also been developed for all review tables and can be used to expedite the search for desired information on structures, components, and relevant aging effects. A survey of the GALL tables reveals that all ongoing significant component aging issues are currently being addressed by the regulatory process. However, the aging of what are termed passive components has been highlighted for continued scrutiny. This document is Volume 1, consisting of the executive summary, summary and observations, and an appendix listing the GALL literature review tables.

  5. A detailed study of the main sequence of the globular cluster NGC 6397: can we derive constraints on the existence of multiple populations?

    NASA Astrophysics Data System (ADS)

    di Criscienzo, M.; D'Antona, F.; Ventura, P.

    2010-02-01

    best distance modulus for each age. For a population all made by stars with standard helium Y=0.24, standard CNO abundances, and an age of 12 Gyr, choosing a double power law mass function ∝M-0.7 for M > 0.18 M⊙ and ∝M-0.9 for M<0.18 M⊙, the resulting theoretical luminosity function agrees well with the observed one (KS ~ 0.75 for a distance modulus (m-M)F814W = 12.31 ± 0.05 mag). Using non-standard CNO abundance for all the stars or for a fraction of 70%, the KS test provides comparable agreement (~KS > 0.55) with the observed luminosity function. Conclusions: The study of the width of the main sequence at a different interval of magnitude is consistent with the hypothesis that both generations are present in the cluster. If the CNO increase suggested by spectroscopic observation is taken into account the small helium spread of the main sequence in NGC 6397 implies a substantial helium uniformity (Δ Y ~ 0.02) between first and second generation stars. The possible spread in helium doubles if an higher larger increase of CNO is considered. The luminosity function is in any case well consistent with the observed data.

  6. Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases

    NASA Astrophysics Data System (ADS)

    Pizzolato, N.; Maggio, A.; Sciortino, S.

    2000-09-01

    We have investigated the variation of coronal X-ray emission during early post-main-sequence phases for a sample of 120 late-type stars within 100 pc, and with estimated masses in the range 1-3 Msun, based on Hipparcos parallaxes and recent evolutionary models. These stars were observed with the ROSAT/PSPC, and the data processed with the Palermo-CfA pipeline, including detection and evaluation of X-ray fluxes (or upper limits) by means of a wavelet transform algorithm. We have studied the evolutionary history of X-ray luminosity and surface flux for stars in selected mass ranges, including stars with inactive A-type progenitors on the main sequence and lower mass solar-type stars. Our stellar sample suggests a trend of increasing X-ray emission level with age for stars with masses M > 1.5 Msun, and a decline for lower-mass stars. A similar behavior holds for the average coronal temperature, which follows a power-law correlation with the X-ray luminosity, independently of their mass and evolutionary state. We have also studied the relationship between X-ray luminosity and surface rotation rate for stars in the same mass ranges, and how this relationships departs from the Lx ~ vrot2 law followed by main-sequence stars. Our results are interpreted in terms of a magnetic dynamo whose efficiency depends on the stellar evolutionary state through the mass-dependent changes of the stellar internal structure, including the properties of envelope convection and the internal rotation profile.

  7. The effect of cognitive aging on implicit sequence learning and dual tasking.

    PubMed

    Vandenbossche, Jochen; Coomans, Daphné; Homblé, Koen; Deroost, Natacha

    2014-01-01

    We investigated the influence of attentional demands on sequence-specific learning by means of the serial reaction time task (Nissen and Bullemer, 1987) in young (age 18-25) and aged (age 55-75) adults. Participants had to respond as fast as possible to a stimulus presented in one of four horizontal locations by pressing a key corresponding to the spatial position of the stimulus. During the training phase sequential blocks were accompanied by (1) no secondary task (single), (2) a secondary tone counting task (dual tone), or (3) a secondary shape counting task (dual shape). Both secondary tasks were administered to investigate whether low and high interference tasks interact with implicit learning and age. The testing phase, under baseline single condition, was implemented to assess differences in sequence-specific learning between young and aged adults. Results indicate that (1) aged subjects show less sequence learning compared to young adults, (2) young participants show similar implicit learning effects under both single and dual task conditions when we account for explicit awareness, and (3) aged adults demonstrate reduced learning when the primary task is accompanied with a secondary task, even when explicit awareness is included as a covariate in the analysis. These findings point to implicit learning deficits under dual task conditions that can be related to cognitive aging, demonstrating the need for sufficient cognitive resources while performing a sequence learning task.

  8. What is the unusual material orbiting the dustiest main sequence A-type stars HD 131488 and HD 121191?

    NASA Astrophysics Data System (ADS)

    Melis, Carl

    2015-10-01

    Only a small percentage of main sequence stars exhibit excess mid-infrared emission indicative of substantial quantities of warm (T >~ 300 K), inner planetary system material that likely originated in recent transient collisional processes. Detailed study of these events can provide us with insight into how rocky terrestrial-like planets form and evolve through collisional pathways. We have identified two young A-type stars with mid-infrared luminosity brighter than and spectrally distinct from that at any other known main-sequence A-type star. T-ReCS N-band and IRTF SpeX spectroscopy combined with IRAS, Herschel, WISE, and T-ReCS photometric measurements indicate that these stars host two distinct infrared emitting regions, one with characteristic temperatures of >300 K (equivalent to temperatures inside 1 AU in the solar system) and a second of ~100 K (equivalent to the temperature near Saturn). The T-ReCS N-band spectra present an enigma: a putative emission feature with peak wavelength near 6-7 microns is not reproducible with common silicate species. SOFIA-FORCAST narrow-band imaging is the only means available to settling the identity of these strange emission features and hence clarify the nature of the inner planetary system material around these two stars.

  9. JUPITER WILL BECOME A HOT JUPITER: CONSEQUENCES OF POST-MAIN-SEQUENCE STELLAR EVOLUTION ON GAS GIANT PLANETS

    SciTech Connect

    Spiegel, David S.; Madhusudhan, Nikku E-mail: Nikku.Madhusudhan@yale.edu

    2012-09-10

    When the Sun ascends the red giant branch (RGB), its luminosity will increase and all the planets will receive much greater irradiation than they do now. Jupiter, in particular, might end up more highly irradiated than the hot Neptune GJ 436b and, hence, could appropriately be termed a 'hot Jupiter'. When their stars go through the RGB or asymptotic giant branch stages, many of the currently known Jupiter-mass planets in several-AU orbits will receive levels of irradiation comparable to the hot Jupiters, which will transiently increase their atmospheric temperatures to {approx}1000 K or more. Furthermore, massive planets around post-main-sequence stars could accrete a non-negligible amount of material from the enhanced stellar winds, thereby significantly altering their atmospheric chemistry as well as causing a significant accretion luminosity during the epochs of most intense stellar mass loss. Future generations of infrared observatories might be able to probe the thermal and chemical structure of such hot Jupiters' atmospheres. Finally, we argue that, unlike their main-sequence analogs (whose zonal winds are thought to be organized in only a few broad, planetary-scale jets), red-giant hot Jupiters should have multiple, narrow jets of zonal winds and efficient day-night redistribution.

  10. HLIMIT 2.0: Towards a Deeper Understanding of the Low Mass End of the Main Sequence

    NASA Astrophysics Data System (ADS)

    Dieterich, Sergio B.; Boss, Alan P.; Weinberger, Alycia J.; Henry, Todd J.; Winters, Jennifer G.; Jao, Wei-Chun; Recons

    2015-01-01

    We describe the observing strategies and scientific goals of a project aimed at providing a deeper understanding of the low mass end of the stellar main sequence. The work outlined here will expand upon the results presented in Dieterich et al. 2014, where radius trends in the local M and L dwarf population were used to gain insight about the stellar/substellar boundary, with evidence for the end of the stellar main sequence at spectral type L2. We now discuss our plans to make the sample volume-complete so that population properties can be studied in a non-biased manner. We also plan to analyze the effects of variations in metallicity using spectroscopy, and link observational properties to known dynamical masses. This work is made possible by the NSF Astronomy and Astrophysics Postdoctoral Fellowship Program through grant AST-1400680. Additional support comes from NSF grants AST-0908402, AST-1109445, AST-1412026, and from the Carnegie Institution for Science. Observations are made possible in part by the SMARTS Consortium.

  11. TESTING SCALING RELATIONS FOR SOLAR-LIKE OSCILLATIONS FROM THE MAIN SEQUENCE TO RED GIANTS USING KEPLER DATA

    SciTech Connect

    Huber, D.; Bedding, T. R.; Stello, D.; Hekker, S.; Mathur, S.; Mosser, B.; Verner, G. A.; Elsworth, Y. P.; Hale, S. J.; Chaplin, W. J.; Bonanno, A.; Buzasi, D. L.; Campante, T. L.; Kallinger, T.; Silva Aguirre, V.; De Ridder, J.; Garcia, R. A.; Frandsen, S.; Houdek, G.; and others

    2011-12-20

    We have analyzed solar-like oscillations in {approx}1700 stars observed by the Kepler Mission, spanning from the main sequence to the red clump. Using evolutionary models, we test asteroseismic scaling relations for the frequency of maximum power ({nu}{sub max}), the large frequency separation ({Delta}{nu}), and oscillation amplitudes. We show that the difference of the {Delta}{nu}-{nu}{sub max} relation for unevolved and evolved stars can be explained by different distributions in effective temperature and stellar mass, in agreement with what is expected from scaling relations. For oscillation amplitudes, we show that neither (L/M){sup s} scaling nor the revised scaling relation by Kjeldsen and Bedding is accurate for red-giant stars, and demonstrate that a revised scaling relation with a separate luminosity-mass dependence can be used to calculate amplitudes from the main sequence to red giants to a precision of {approx}25%. The residuals show an offset particularly for unevolved stars, suggesting that an additional physical dependency is necessary to fully reproduce the observed amplitudes. We investigate correlations between amplitudes and stellar activity, and find evidence that the effect of amplitude suppression is most pronounced for subgiant stars. Finally, we test the location of the cool edge of the instability strip in the Hertzsprung-Russell diagram using solar-like oscillations and find the detections in the hottest stars compatible with a domain of hybrid stochastically excited and opacity driven pulsation.

  12. Mathematical Assessment of Physical and Chemical Processes from the middle B to the early F Type Main Sequence Stars

    NASA Astrophysics Data System (ADS)

    Yuce, Kutluay; Adelman, Saul J.

    2016-07-01

    The middle B to the early F main sequence stars are thought to have some of the most quiet atmospheres. In this part of the HR diagram we find stars with atmospheres in radiative equilibrium. They lack the convective circulations of the middle F and cooler stars and the massive stellar winds of hotter stars. Diffusion theory requires the Chemically Peculiar stars to have relatively quiet atmospheres and if there are no magnetic fields they should lack abundance spots. If we look at stars evolving off the Main Sequence in this part of the HR diagram, we see that the evolutionary paths of stars of different mass do not cross. So if we compare stars with the same effective temperature and surface gravity, we are studying stars of the same luminosity and mass. By comparing their elemental abundances, we might be able to identify physical processes which cause their abundances to be different. In this work we begin with stars whose effective temperatures and surface gravities are similar, and which has been analyzed by us using spectra obtained from the Dominion Astrophysical Observatory.

  13. The effect of old age on the learning of supraspan sequences.

    PubMed

    Turcotte, Josée; Gagnon, Sylvain; Poirier, Marie

    2005-06-01

    Two experiments examined age-related differences in sequence learning using computerized versions of the D. O. Hebb (1961) paradigm. In this learning task, the participant executes immediate serial recall of 24 supraspan sequences. Without the participants' knowledge, 1 sequence is presented several times. Repetition leads to improved recall of this repeated sequence relative to random sequences. Results showed a dissociation in age-related learning deficits depending on the nature of the to-be-remembered material. The effect of repetition is similar for younger and older adults with familiar and unfamiliar verbal material (words and pseudowords) but is significantly reduced in older adults when learning is assessed with a visuospatial version of Hebb's supraspan learning task (P. M. Corsi, 1972).

  14. The effect of old age on the learning of supraspan sequences.

    PubMed

    Turcotte, Josée; Gagnon, Sylvain; Poirier, Marie

    2005-06-01

    Two experiments examined age-related differences in sequence learning using computerized versions of the D. O. Hebb (1961) paradigm. In this learning task, the participant executes immediate serial recall of 24 supraspan sequences. Without the participants' knowledge, 1 sequence is presented several times. Repetition leads to improved recall of this repeated sequence relative to random sequences. Results showed a dissociation in age-related learning deficits depending on the nature of the to-be-remembered material. The effect of repetition is similar for younger and older adults with familiar and unfamiliar verbal material (words and pseudowords) but is significantly reduced in older adults when learning is assessed with a visuospatial version of Hebb's supraspan learning task (P. M. Corsi, 1972). PMID:16029089

  15. Age Dating Ultraluminous Infrared Galaxies along the Merger Sequence

    NASA Astrophysics Data System (ADS)

    Murphy, T. W., Jr.; Soifer, B. T.; Matthews, K.; Armus, L.

    2001-09-01

    Imaging spectroscopy using the new Palomar Integral Field Spectrograph is presented for the Paα line in four ultraluminous infrared galaxies. The resulting integral field data cubes reveal line emission possessing a wide range of complex spatial morphologies, often quite different from the appearance of the continuum. The velocity fields are equally diverse in nature, often failing to resemble typical modes of galactic motion. We see a variety of interesting phenomena in the individual mergers including star formation rates of 2-5 Msolar yr-1 in young tidal tails; a postencounter disk that obeys the Tully-Fisher relation; a large-scale emission-line nebula possibly associated with a massive outflow; an apparently single merging system possessing two distinct kinematical axes belying the presence of a second galaxy, mostly obscured by its merging companion; and possible formation of tidal dwarf galaxies. In most cases, we are able to establish the geometry of the merger and thus estimate the time in the merger process at which we are viewing the system. The resulting range in estimated ages, some of which are very young encounters (~5×107 yr), is not predicted by merger models, which produce high rates of star formation either 1-2×108 yr after the first encounter or very late (~109 yr) in the merger process. Even in the very young mergers, despite a sample selection based on extended line emission, the ultraluminous activity appears to be centrally concentrated on the nucleus of one of the progenitor galaxies-namely, the galaxy with a prograde orbital geometry. The inferred extinction to these concentrations is high, usually at least 1 mag at the wavelength of Paα. The presence of a significant population of very young ultraluminous mergers, together with the majority of ultraluminous infrared galaxies existing in the final stages of merger activity, indicates that the ultraluminous galaxy phase is at least bimodal in time. An evolutionary scenario is proposed

  16. Calibrating convective-core overshooting with eclipsing binary systems. The case of low-mass main-sequence stars

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    Context. Double-lined eclipsing binaries have often been adopted in literature to calibrate the extension of the convective-core overshooting beyond the border defined by the Schwarzschild criterion. Aims: In a robust statistical way, we quantify the magnitude of the uncertainty that affects the calibration of the overshooting efficiency parameter β that is owing to the uncertainty on the observational data. We also quantify the biases on the β determination that is caused by the lack of constraints on the initial helium content and on the efficiencies of the superadiabatic convection and microscopic diffusion. Methods: We adopted a modified grid-based SCEPtER pipeline to recover the β parameter from synthetic stellar data. Our grid spans the mass range [1.1; 1.6] M⊙ and evolutionary stages from the zero-age main sequence (MS) to the central hydrogen depletion. The β estimates were obtained by generalising the maximum likelihood technique described in our previous works. As observational constraint, we adopted the effective temperatures, [Fe/H], masses, and radii of the two stars. Results: By means of Monte Carlo simulations, adopting a reference scenario of mild overshooting β = 0.2 for the synthetic data, and taking typical observational errors into account, we found both large statistical uncertainties and biases on the estimated values of β. For the first 80% of the MS evolution, β is biased by about -0.04, with the 1σ error practically unconstrained in the whole explored range [0.0; 0.4]. In the last 5% of the evolution the bias vanishes and the 1σ error is about 0.05. The 1σ errors are similar when adopting different reference values of β. Interestingly, for synthetic data computed without convective-core overshooting, the estimated β is biased by about 0.12 in the first 80% of the MS evolution, and by 0.05 afterwards. Assuming an uncertainty of ±1 in the helium-to-metal enrichment ratio ΔY/ ΔZ, we found a large systematic uncertainty in the

  17. ENHANCED RECOVERY METHODS FOR 85KR AGE-DATING GROUNDWATER: ROYAL WATERSHED, MAINE

    EPA Science Inventory

    Potential widespread use of 85Kr, having a constant input function in the northern hemisphere, for groundwater age-dating would advance watershed investigations. The current input function of tritium is not sufficient to estimate young modern recharge waters. While tri...

  18. APPARENT 85KRYPTON AGES OF GROUNDWATER WITHIN THE ROYAL WATERSHED, MAINE, USA

    EPA Science Inventory

    85Kr activities were determined in 264 domestic and municipal wells from 2002-2004 in the Royal watershed (361 km2), Maine. Gas extraction for 85Kr from wells was effected directly via a well-head methodology permitting efficient widespread analys...

  19. Post-common envelope binaries from SDSS - VII. A catalogue of white dwarf-main sequence binaries

    NASA Astrophysics Data System (ADS)

    Rebassa-Mansergas, A.; Gänsicke, B. T.; Schreiber, M. R.; Koester, D.; Rodríguez-Gil, P.

    2010-02-01

    We present a catalogue of 1602 white-dwarf-main-sequence (WDMS) binaries from the spectroscopic Sloan Digital Sky Survey Data Release 6 (SDSS DR6). Among these, we identify 440 as new WDMS binaries. We select WDMS binary candidates by template fitting all 1.27 million DR6 spectra, using combined constraints in both χ2 and signal-to-noise ratio. In addition, we use Galaxy Evolution Explorer (GALEX) and UKIRT Infrared Sky Survey (UKIDSS) magnitudes to search for objects in which one of the two components dominates the SDSS spectrum. We use a decomposition/fitting technique to measure the effective temperatures, surface gravities, masses and distances to the white dwarfs, as well as the spectral types and distances to the companions in our catalogue. Distributions and density maps obtained from these stellar parameters are then used to study both the general properties and the selection effects of WDMS binaries in the SDSS. A comparison between the distances measured to the white dwarfs and the main-sequence companions shows dsec > dwd for approximately one-fifth of the systems, a tendency already found in our previous work. The hypothesis that magnetic activity raises the temperature of the inter-spot regions in active stars that are heavily covered by cool spots, leading to a bluer optical colour compared to inactive stars, remains the best explanation for this behaviour. We also make use of SDSS-GALEX-UKIDSS magnitudes to investigate the distribution of WDMS binaries, as well as their white-dwarf effective temperatures and companion star spectral types, in ultraviolet to infrared colour space. We show that WDMS binaries can be very efficiently separated from single main-sequence stars and white dwarfs when using a combined ultraviolet, optical and infrared colour selection. Finally, we also provide radial velocities for 1068 systems measured from the NaI λλ8183.27, 8194.81 absorption doublet and/or the Hα emission line. Among the systems with multiple SDSS

  20. Carboniferous U-Pb age of the Sebago batholith, southwestern Maine: metamorphic and tectonic implications.

    USGS Publications Warehouse

    Aleinikoff, J.H.; Moench, R.H.; Lyons, J.B.

    1985-01-01

    Two phases (pink and white granite) of the Sebago batholith have been dated by the U/Pb zircon method. The age of both phases is 325 m.y. Zircon in the pink phase has been reset in intrusion of the Pleasant Mountain stock approx 114 m.y. ago. Zircon in the white phase lost lead only recently. Metamorphic isograds in the vicinity of the batholith approximately parallel its shape, and may be at least partly Hercynian in age. Cooling and uplift of the Sebago batholith appear to have followed a complicated path involving little or no uplift in the Middle Carboniferous to Middle Permian, rapid cooling from 275 to 225 m.y. ago, and a slow cooling since Middle Triassic. Different rates of cooling may be related to changes in the tectonic regime.-L.C.H.

  1. Energy excess is the main cause of accelerated aging of mammals

    PubMed Central

    Biliński, Tomasz; Paszkiewicz, Tadeusz; Zadrag-Tecza, Renata

    2015-01-01

    The analysis of cases of unusually high longevity of naked mole rats and an alternative explanation of the phenomenon of calorie restriction effects in monkeys allowed for postulating that any factor preventing an excess of energy consumed, leads to increased lifespan, both in evolutionary and an individual lifetime scale. It is postulated that in mammals the most destructive processes resulting in shortening of life are not restricted to the phenomena explained by the hyperfunction theory of Mikhail Blagosklonny. Hyperfunction, understood as unnecessary or even adverse syntheses of cell components, can be to some extent prevented by lowered intake of nutrients when body growth ceases. We postulate also the contribution of glyco/lipotoxicity to aging, resulting from the excess of energy. Besides two other factors seem to participate in aging. One of them is lack of telomerase activity in some somatic cells. The second factor concerns epigenetic phenomena. Excessive activity of epigenetic maintenance system probably turns off some crucial organismal functions. Another epigenetic factor playing important role could be the micro RNA system deciding on expression of numerous age-related diseases. However, low extrinsic mortality from predation is a conditio sine qua non of the expression of all longevity phenotypes in animals. Among all long-lived animals, naked mole rats are unique in the elimination of neoplasia, which is accompanied by delayed functional symptoms of senescence. The question whether simultaneous disappearance of neoplasia and delayed senescence is accidental or not remains open. PMID:26079722

  2. Detection of a dozen X-ray-emitting main-sequence B6-A3 stars in Orion

    NASA Technical Reports Server (NTRS)

    Caillault, Jean-Pierre; Zoonematkermani, Saeid

    1989-01-01

    The detection of 12 X-ray-emitting main-sequence B6-A3 stars in the Orion Nebula is reported. The luminosity of these stars in the 0.2-3.5 keV band is considerably in excess of field stars of the same spectral type. Consideration is given to the possibilities that these stars may not actually be the source of the X-rays, but that the emission may be attributable to T Tauri or 'naked' T Tauri star companions, or that these hot stars are indeed the sources of emission and that current theories of X-ray emission from early-type stars must be amended.

  3. X-ray emission from the pre-main sequence star ZCMa during a FUOri-type outburst

    NASA Astrophysics Data System (ADS)

    Stelzer, Beate

    2007-09-01

    We propose for the first X-ray spectrum of an FUOri object during outburst. The FUOR phenomenon is associated with a sudden increase of the accretion rate in some pre-main sequence (PMS) stars, possibly due to changes in the magnetic field. In the first X-ray survey of FUORs Skinner et al. (2007) have detected two of four targets. None of them was in outburst at the time. The typical two-temperature spectrum of a PMS star requires in the case of FUOri different absorptions for the soft and hard components (Skinner et al. 2006). Our target ZCMa is a young F-type FUOR. In Feb 2008 ZCMa started its so far largest outburst, with a further enhancement ~2 weeks ago. In May 2008 we have detected its magnetic field. Now we aim at an X-ray detection of ZCMa in its `super-outburst'.

  4. X-ray sources in regions of star formation. II - The pre-main-sequence G star HDE 283572

    NASA Technical Reports Server (NTRS)

    Walter, F. M.; Brown, A.; Linsky, J. L.; Rydgren, A. E.; Vrba, F.

    1987-01-01

    This paper reports the detection of HDE 283572, a ninth-magnitude G star 8 arcmin south of RY Tau, as a bright X-ray source. The observations reveal this object to be a fairly massive (about 2 solar masses) pre-main-sequence star associated with the Taurus-Auriga star formation complex. It exhibits few of the characteristics of the classical T Tauri stars and is a good example of a 'naked' T Tauri star. The star is a mid-G subgiant, of about three solar radii and rotates with a period of 1.5 d. The coronal and chromospheric surface fluxes are similar to those of the most active late type stars (excluding T Tauri stars). The X-ray and UV lines most likely arise in different atmospheric structures. Radiative losses are some 1000 times the quiet solar value and compare favorably with those of T Tauri stars.

  5. Stellar Activity at the End of the Main Sequence: GHRS Observations of the M8 Ve Star VB 10

    NASA Technical Reports Server (NTRS)

    Linsky, Jeffrey L.; Wood, Brian E.; Brown, Alexander; Giampapa, Mark S.; Ambruster, Carol

    1995-01-01

    We present Goddard High Resolution Spectrograph observations of the M8 Ve star VB 10 (equal to G1 752B), located very near the end of the stellar main sequence, and its dM3.5 binary companion G1 752A. These coeval stars provide a test bed for studying whether the outer atmospheres of stars respond to changes in internal structure as stars become fully convective near mass 0.3 solar mass (about spectral type M5), where the nature of the stellar magnetic dynamo presumably changes, and near the transition from red to brown dwarfs near mass 0.08 solar mass (about spectral type M9), when hydrogen burning ceases at the end of the main sequence. We obtain upper limits for the quiescent emission of VB 10 but observe a transition region spectrum during a large flare, which indicates that some type of magnetic dynamo must be present. Two indirect lines of evidence-scaling from the observed X-ray emission and scaling from a time-resolved flare on AD Leo suggest that the fraction of the stellar bolometric luminosity that heats the transition region of VB 10 outside of obvious flares is comparable to, or larger than, that for G1 752A. This suggests an increase in the magnetic heating rates, as measured by L(sub line)/L(sub bol) ratios, across the radiative/convective core boundary and as stars approach the red/brown dwarf boundary. These results provide new constraints for dynamo models and models of coronal and transition-region heating in late-type stars.

  6. Delayed Gratification Habitable Zones: When Deep Outer Solar System Regions Become Balmy During Post-Main Sequence Stellar Evolution

    NASA Astrophysics Data System (ADS)

    Stern, S. Alan

    2003-06-01

    Like all low- and moderate-mass stars, the Sun will burn as a red giant during its later evolution, generating of solar luminosities for some tens of millions of years. During this post-main sequence phase, the habitable (i.e., liquid water) thermal zone of our Solar System will lie in the region where Triton, Pluto-Charon, and Kuiper Belt objects orbit. Compared with the 1 AU habitable zone where Earth resides, this "delayed gratification habitable zone" (DGHZ) will enjoy a far less biologically hazardous environment - with lower harmful radiation levels from the Sun, and a far less destructive collisional environment. Objects like Triton, Pluto-Charon, and Kuiper Belt objects, which are known to be rich in both water and organics, will then become possible sites for biochemical and perhaps even biological evolution. The Kuiper Belt, with >105 objects >=50 km in radius and more than three times the combined surface area of the four terrestrial planets, provides numerous sites for possible evolution once the Sun's DGHZ reaches it. The Sun's DGHZ might be thought to only be of academic interest owing to its great separation from us in time. However, ~109 Milky Way stars burn as luminous red giants today. Thus, if icy-organic objects are common in the 20-50 AU zones of these stars, as they are in our Solar System (and as inferred in numerous main sequence stellar disk systems), then DGHZs may form a niche type of habitable zone that is likely to be numerically common in the Galaxy.

  7. PS1-10jh: The disruption of a main-sequence star of near-solar composition

    SciTech Connect

    Guillochon, James; Manukian, Haik; Ramirez-Ruiz, Enrico

    2014-03-01

    When a star comes within a critical distance to a supermassive black hole (SMBH), immense tidal forces disrupt the star, resulting in a stream of debris that falls back onto the SMBH and powers a luminous flare. In this paper, we perform hydrodynamical simulations of the disruption of a main-sequence star by an SMBH to characterize the evolution of the debris stream after a tidal disruption. We demonstrate that this debris stream is confined by self-gravity in the two directions perpendicular to the original direction of the star's travel and as a consequence has a negligible surface area and makes almost no contribution to either the continuum or line emission. We therefore propose that any observed emission lines are not the result of photoionization in this unbound debris, but are produced in the region above and below the forming elliptical accretion disk, analogous to the broad-line region (BLR) in steadily accreting active galactic nuclei. As each line within a BLR is observationally linked to a particular location in the accretion disk, we suggest that the absence of a line indicates that the accretion disk does not yet extend to the distance required to produce that line. This model can be used to understand the spectral properties of the tidal disruption event PS1-10jh, for which He II lines are observed, but the Balmer series and He I are not. Using a maximum likelihood analysis, we show that the disruption of a main-sequence star of near-solar composition can reproduce this event.

  8. Delayed gratification habitable zones: when deep outer solar system regions become balmy during post-main sequence stellar evolution.

    PubMed

    Stern, S Alan

    2003-01-01

    Like all low- and moderate-mass stars, the Sun will burn as a red giant during its later evolution, generating of solar luminosities for some tens of millions of years. During this post-main sequence phase, the habitable (i.e., liquid water) thermal zone of our Solar System will lie in the region where Triton, Pluto-Charon, and Kuiper Belt objects orbit. Compared with the 1 AU habitable zone where Earth resides, this "delayed gratification habitable zone" (DGHZ) will enjoy a far less biologically hazardous environment - with lower harmful radiation levels from the Sun, and a far less destructive collisional environment. Objects like Triton, Pluto-Charon, and Kuiper Belt objects, which are known to be rich in both water and organics, will then become possible sites for biochemical and perhaps even biological evolution. The Kuiper Belt, with >10(5) objects > or =50 km in radius and more than three times the combined surface area of the four terrestrial planets, provides numerous sites for possible evolution once the Sun's DGHZ reaches it. The Sun's DGHZ might be thought to only be of academic interest owing to its great separation from us in time. However, approximately 10(9) Milky Way stars burn as luminous red giants today. Thus, if icy-organic objects are common in the 20-50 AU zones of these stars, as they are in our Solar System (and as inferred in numerous main sequence stellar disk systems), then DGHZs may form a niche type of habitable zone that is likely to be numerically common in the Galaxy.

  9. Evidence for Chemical Processing of Precometary Icy Grains In Circumstellar Environments of Pre-Main-Sequence Stars

    NASA Technical Reports Server (NTRS)

    Teglier, Stephen C.; Weintraub, David A.; Rettig, Terrence W.; Pendleton, Yvonne J.; Whittet, Douglas C.; Kulesa, Craig A.

    1995-01-01

    We report the detection of a broad absorption feature near 2166 cm-1 in the spectrum of the Taurus cloud source Elias 18. This pre-main-sequence source is the second in Taurus, the third in our survey, and the fifth known in the sky to show the broad 2166 cm-1 absorption feature. Of equal importance, this feature is not seen toward several other embedded sources in our survey, nor is it seen toward the source Elias 16, located behind the Taurus cloud. Laboratory experiments with interstellar ice analogs show that such a feature is associated with a complex C=-N containing compound [called X(C=-N)] that results from high-energy processing (ultraviolet irradiation or ion bombardment) of simple ice components into more complex, organic components, We find a nonlinear anticorrelation between the abundance of X(C=-N) and frozen CO in non- polar lattices. We find no correlation between the abundance of X(C=-N) and frozen CO in polar lattices. Because the abundances of frozen CO and H20 are strongly correlated with each other and with visual extinction toward sources embedded in and located behind the Taurus molecular cloud, these ice components usually are associated with intracloud material. Our results indicate that X(C=-N) molecules result from chemical processing of dust grains dominated by nonpolar icy mantles in the local environments of pre-main- sequence stars. Such processing of icy grains in the early solar system may be an important source of organic compounds observed in minor solar system bodies. The delivery of these organic compounds to the surface of the primitive Earth through comet impacts may have provided the raw materials for prebiotic chemistry.

  10. Delayed gratification habitable zones: when deep outer solar system regions become balmy during post-main sequence stellar evolution.

    PubMed

    Stern, S Alan

    2003-01-01

    Like all low- and moderate-mass stars, the Sun will burn as a red giant during its later evolution, generating of solar luminosities for some tens of millions of years. During this post-main sequence phase, the habitable (i.e., liquid water) thermal zone of our Solar System will lie in the region where Triton, Pluto-Charon, and Kuiper Belt objects orbit. Compared with the 1 AU habitable zone where Earth resides, this "delayed gratification habitable zone" (DGHZ) will enjoy a far less biologically hazardous environment - with lower harmful radiation levels from the Sun, and a far less destructive collisional environment. Objects like Triton, Pluto-Charon, and Kuiper Belt objects, which are known to be rich in both water and organics, will then become possible sites for biochemical and perhaps even biological evolution. The Kuiper Belt, with >10(5) objects > or =50 km in radius and more than three times the combined surface area of the four terrestrial planets, provides numerous sites for possible evolution once the Sun's DGHZ reaches it. The Sun's DGHZ might be thought to only be of academic interest owing to its great separation from us in time. However, approximately 10(9) Milky Way stars burn as luminous red giants today. Thus, if icy-organic objects are common in the 20-50 AU zones of these stars, as they are in our Solar System (and as inferred in numerous main sequence stellar disk systems), then DGHZs may form a niche type of habitable zone that is likely to be numerically common in the Galaxy. PMID:14577880

  11. Characterization and age of the Mesoproterozoic Debaca sequence in the Tucumcari Basin, New Mexico

    NASA Astrophysics Data System (ADS)

    Amarante, Jose F. A.; Kelley, Shari A.; Heizler, Matthew T.; Barnes, Melanie A.; Miller, Kate C.; Anthony, Elizabeth Y.

    Petrographic, geochronologic, and well log data from two deep oil wells (Mescalero 1 and State Mr. Jones 1) in the Tucumcari Basin, New Mexico are used to characterize a thick vertical section of the Mesoproterozoic Debaca sequence and portions of the underlying crystalline basement. This information is coupled with industry seismic data to constrain the geometry of the northernmost extent of the Mesoproterozoic Debaca basin. The Debaca sequence, a weakly metamorphosed sedimentary-volcanic package, is composed of volcaniclastic sandstone, tuffaceous sandstone, rhyolite, quartz-rich dolostone, dolomitic quartzite, sandstone, and arkose. The sequence rests disconformably on deeply weathered quartz syenite of the underlying Mesoproterozoic Panhandle Igneous Complex. Numerous sills and dikes of gabbro cut the Debaca sequence, imparting contact metamorphism to the adjacent rock units. U-Pb SHRIMP and 40Ar/39Ar ages for samples from the Mescalero 1 well indicate that Debaca sequence was formed ca. 1105-1332 Ma. Zircon from a quartz diorite (gradationally below the syenite) that is part of the crystalline basement beneath the Debaca sequence yields a SHRIMP U-Pb age of 1332±18 Ma. Eight detrital grains of zircon from the arkose, the basal unit of the Debaca sequence, yield SHRIMP U-Pb zircon ages ranging from 1308±52 to 1708±14 Ma. 40Ar/39Ar ages on hornblende and biotite indicate a mean emplacement age of 1105±3 Ma for the gabbro. Three pulses of magmatism, one bimodal episode at 1.33 Ga, one felsic episode at ˜1.26 Ga, and one mafic episode at 1.09 Ga, have been identified in Mescalero 1.

  12. Identification of main-sequence stars with mid-infrared excesses: Frequency of beta Pictoris analogs and transition disk systems

    NASA Astrophysics Data System (ADS)

    Uzpen, Brian Robert

    There is solid evidence of life on only one planet in the Universe: Earth. Since current technologies are not capable of directly observing planets, we must rely on secondary indicators, such as circumstellar disks to detect them. Circumstellar disks are commonplace around pre-main-sequence stars; it is believed these disks are a natural byproduct of star formation where planets can form. The general theoretical evolutionary sequence from the optically thick pre-main-sequence stars (T-Tauri and Herbig AeBe) to optically thin "debris disks", is as follows: After particles grow through condensation, they reach a critical value and form planetary cores; these cores accrete the gas around them and form planets. As the available circumstellar material decreases, the inner disk will develop a hole. Circumstellar material dissipates in the outer disk, while particles collide creating a population of grains that re-radiate stellar energy in the far-IR, a characteristic of debris disks. These debris disks represent a final stage of planet formation. Given that most stars originally have circumstellar disks, it is likely that planetary systems are common. Material similar in temperature to Earth emits primarily at ~10 mm (mid-IR wavelengths). By identifying stars with circumstellar material that emits in the mid-IR, it may be possible to locate Earth-like planetary systems; mid-IR excesses may also be an indicator of disks undergoing clearing processes with inner disk holes of a few AU. The purpose of this work is to identify and characterize a large sample of stellar sources with circumstellar disks that re-radiate energy at mid-IR wavelengths and place them in the greater context of disk evolution and planet formation. To achieve this goal, a large number of stellar sources with mid-IR excesses are identified through wide-area Galactic surveys. Far-IR photometry is utilized to confirm the mid-IR excess in a majority of the newly identified sources. Follow-up optical

  13. The 1997 Umbria-Marche, Italy, Earthquake Sequence: A first look at the main shocks and aftershocks

    NASA Astrophysics Data System (ADS)

    Amato, A.; Azzara, R.; Chiarabba, C.; Cimini, G. B.; Cocco, M.; Di Bona, M.; Margheriti, L.; Mazza, S.; Mele, F.; Selvaggi, G.; Basili, A.; Boschi, E.; Courboulex, F.; Deschamps, A.; Gaffet, S.; Bittarelli, G.; Chiaraluce, L.; Piccinini, D.; Ripepe, M.

    A long sequence of earthquakes, six with magnitudes between 5 and 6, struck Central Italy starting on September 26, 1997, causing severe damages and loss of human lives. The seismogenic structure consists of a NW-SE elongated fault zone extending for about 40 km. The focal mechanisms of the largest shocks reveal normal faulting with NE-SW extension perpendicular to the trend of the Apennines, consistently with the Quaternary tectonic setting of the internal sector of the belt and with previous earthquakes in adjacent regions. Preliminary data on the main shocks and aftershocks show that extension in this region of the Apennines is accomplished by normal faults dipping at low angle (∼40°) to the southwest, and confined in the upper ∼8 km of the crust. These normal faults might have reactivated thrust planes of the Pliocene compressional tectonics. The aftershock distribution and the damage patterns also suggest that the three main shocks ruptured distinct 5 to 15 km-long fault segments, adjacent and slightly offset from one another.

  14. Cyclostratigraphy for Chinese red clay sequences: Implications to changing previous age models and paleoclimate interpretations

    NASA Astrophysics Data System (ADS)

    Anwar, T.; Kravchinsky, V. A.; Zhang, R.

    2015-12-01

    The Chinese Loess Plateau contains red clay sequence which has continuous alternation of sedimentary cycles with recurrent paleoclimatic fluctuations. Absence of abundant fossils and inability of radiometric dating method made magnetostratigraphy a leading method to build age model for the red clay. Here magnetostratigraphic age model in red clay sequence is tested using cyclostratigraphy as orbital parameters of Earth are known. Milankovitch periodicities recorded in magnetic susceptibility and grain size in the Shilou red clay section are investigated and previously found age of 11 Ma for this section is re-evaluated. Magnetostratigraphy dating based on only visual correlation could potentially lead to erroneous age model. In this study the correlation is executed through the iteration procedure until it is supported by cyclostratigraphy; i.e. Milankovitch cycles are resolved in the best possible manner. Our new approach provides an age of 5.2 Ma for the Shilou profile. Wavelet analysis reveals that a 400 kyr eccentricity cycle is well preserved and the existence of a 100 kyr eccentricity in the red clay sequence on the eastern Chinese Loess Plateau suggests that eccentricity plays a vital role in Pliocene climate evolution. Paleomonsoon evolution is reconstructed and divided into three intervals (5.2-4.5 Ma, 4.5-3.6 Ma and 3.6-2.58 Ma). The earliest stage indicates that summer and winter monsoon cycles may rapidly alter, whereas the middle stage reflects an intensification of winter monsoon and aridification in Asia, and the youngest stage is characterized by relatively intensified summer monsoon. This study demonstrates that cyclostratigraphy can greatly assist magnetostratigraphy in dating the red clay sequences, and implies that many published age models for the red clay sequences should likely be re-assessed where possible. An evaluation of the monsoon system and climate change in eastern Asia might prominently benefit from this approach.

  15. [sup 40]Ar/[sup 39]Ar mineral ages from southwestern Penobscot Bay, Maine: Evidence for Silurian metamorphism

    SciTech Connect

    West, D.P. Jr.; Guidotti, C.V.; Lux, D.R. . Dept. of Geological Sciences)

    1992-01-01

    The nature and timing of metamorphic events in the Coastal Lithotectonic Block of Maine remain poorly understood. Immediately west and southwest of Penobscot Bay the rocks are polymetamorphic showing evidence for at least two episodes of amphibolite facies metamorphism and later, perhaps regionally extensive, retrograde events. Hornblende mineral separates from two amphibolites din the Port Clyde area have identical Ar-40/Ar-39 plateau ages of 414.0 [+-] 3.3 and 414.0 [+-] 3.9 Ma. These ages are interpreted to reflect the time of cooling following the last significant thermal event in this area. Biotite from an amphibolite in the Port Clyde area gives a total gas age of 346.5 [+-] 3.2 Ma. Hornblende from an amphibolite 7 km to the west near Friendship gives a nearly concordant release spectrum with a plateau age of 369.0 [+-] 3.7 Ma. Coexisting biotite from this amphibolite gives a total gas age of 289.2 [+-] 2.7 Ma. Muscovite from the Waldoboro pluton has a nearly concordant release spectrum with a plateau age of 306.3 [+-] 2.2 Ma. Biotite from this sample gives a total gas age of 288.9 [+-] 2.2 Ma. The 414.0 Ma hornblende cooling ages from the Port Clyde area reflect cooling following a significant high grade Silurian thermal event. This Silurian metamorphism is the same age as tectonothermal events in the Nashoba Terrane in eastern Massachusetts, the Kingston Complex in southern New Brunswick, the Aspy Terrane in Cape Breton island, Nova Scotia, and the Hermitage Flexure in southern Newfoundland.d Thus a distinctive Silurian tectonothermal province located along the western edge of the Avalon Zone appears to extend discontinuously from Massachusetts to Newfoundland.

  16. The properties and environment of primitive solar nebulae as deduced from observations of solar-type pre-main sequence stars

    NASA Technical Reports Server (NTRS)

    Strom, Stephen E.; Edwards, Suzan; Strom, Karen M.

    1991-01-01

    The following topics were discussed: (1) current observation evidence for the presence of circumstellar disks associated with solar type pre-main sequence (PMS) stars; (2) the properties of such disks; and (3) the disk environment.

  17. Searching for faint companions with VLTI/PIONIER. II. 92 main sequence stars from the Exozodi survey

    NASA Astrophysics Data System (ADS)

    Marion, L.; Absil, O.; Ertel, S.; Le Bouquin, J.-B.; Augereau, J.-C.; Blind, N.; Defrère, D.; Lebreton, J.; Milli, J.

    2014-10-01

    Context. The Exozodi survey aims to determine the occurrence rate of bright exozodiacal discs around nearby main sequence stars using infrared interferometry. Although the Exozodi survey targets have been carefully selected to avoid the presence of binary stars, the results of this survey can still be biased by the presence of unidentified stellar companions. Aims: Using the PIONIER data set collected within the Exozodi survey in 2012, we aim to search for the signature of point-like companions around the Exozodi target stars. Methods: We make use of both the closure phases and squared visibilities collected by PIONIER to search for companions within the ~100 mas interferometric field of view. The presence of a companion is assessed by computing the goodness of fit to the data for a series of binary models with various separations and contrasts. Results: Five stellar companions are resolved for the first time around five A-type stars: HD 4150, HD 16555, HD 29388, HD 202730, and HD 224392 (although the companion to HD 16555 was independently resolved by speckle interferometry while we were carrying out the survey). In the most likely case of main sequence companions, their spectral types range from A5V to K4V. Three of these stars were already suspected to be binaries from Hipparcos astrometric measurements, although no information was available on the companions themselves so far. In addition to debiasing the statistics of the Exozodi survey, these results can also be used to revise the fraction of visual binaries among A-type stars, suggesting that an extra ~13% A-type stars are visual binaries in addition to the ones detected in previous direct imaging surveys. Conclusions: We estimate that about half the population of nearby A-type stars could be resolved as visual binaries using a combination of state-of-the-art interferometry and single-aperture imaging, and we suggest that a significant fraction of these binaries remains undetected to date. Based on

  18. Dusty OB Stars in the Small Magellanic Cloud. I. Optical Spectroscopy Reveals Predominantly Main-sequence OB Stars

    NASA Astrophysics Data System (ADS)

    Sheets, Holly A.; Bolatto, Alberto D.; van Loon, Jacco Th.; Sandstrom, Karin; Simon, Joshua D.; Oliveira, Joana M.; Barbá, Rodolfo H.

    2013-07-01

    We present the results of optical spectroscopic follow-up of 125 candidate main sequence OB stars in the Small Magellanic Cloud (SMC) that were originally identified in the S3MC infrared imaging survey as showing an excess of emission at 24 μm indicative of warm dust, such as that associated with a transitional or debris disks. We use these long-slit spectra to investigate the origin of the 24 μm emission and the nature of these stars. A possible explanation for the observed 24 μm excess, that these are emission line stars with dusty excretion disks, is disproven for the majority of our sources. We find that 88 of these objects are normal stars without line emission, with spectral types mostly ranging from late-O to early-B; luminosity classes from the literature for a sub-set of our sample indicate that most are main-sequence stars. We further identify 17 emission-line stars, 7 possible emission-line stars, and 5 other objects with forbidden-line emission in our sample. We discover a new O6 Iaf star; it exhibits strong He II 4686 Å emission but relatively weak N III 4640 Å emission which we attribute to the lower nitrogen abundance in the SMC. Two other objects are identified with planetary nebulae, one with a young stellar object, and two with X-ray binaries. To shed additional light on the nature of the observed 24 μm excess we use optical and infrared photometry to estimate the dust properties of the objects with normal O and B star spectra and compare these properties to those of a sample of hot spots in the Galactic interstellar medium (ISM). We find that the dust properties of the dusty OB star sample resemble the properties of the Galactic sample of hot spots. Some may be runaway systems with bow-shocks resulting from a large velocity difference between star and ISM. We further investigate the nature of these dusty OB stars in a companion paper presenting mid-infrared spectroscopy and additional imaging.

  19. Decreasing Sports Activity with Increasing Age? Findings from a 20-Year Longitudinal and Cohort Sequence Analysis

    ERIC Educational Resources Information Center

    Breuer, Christoph; Wicker, Pamela

    2009-01-01

    According to cross-sectional studies in sport science literature, decreasing sports activity with increasing age is generally assumed. In this paper, the validity of this assumption is checked by applying more effective methods of analysis, such as longitudinal and cohort sequence analyses. With the help of 20 years' worth of data records from the…

  20. Asteroseismology of the Hyades with K2: first detection of main-sequence solar-like oscillations in an open cluster

    NASA Astrophysics Data System (ADS)

    Lund, Mikkel N.; Basu, Sarbani; Silva Aguirre, Víctor; Chaplin, William J.; Serenelli, Aldo M.; García, Rafael A.; Latham, David W.; Casagrande, Luca; Bieryla, Allyson; Davies, Guy R.; Viani, Lucas S.; Buchhave, Lars A.; Miglio, Andrea; Soderblom, David R.; Valenti, Jeff A.; Stefanik, Robert P.; Handberg, Rasmus

    2016-08-01

    The Hyades open cluster was targeted during Campaign 4 (C4) of the NASA K2 mission, and short-cadence data were collected on a number of cool main-sequence stars. Here, we report results on two F-type stars that show detectable oscillations of a quality that allows asteroseismic analyses to be performed. These are the first ever detections of solar-like oscillations in main-sequence stars in an open cluster.

  1. Conscientiousness and (un)healthy eating: the role of impulsive eating and age in the consumption of daily main meals.

    PubMed

    Olsen, Svein Ottar; Tuu, Ho Huy; Honkanen, Pirjo; Verplanken, Bas

    2015-08-01

    The present study aims to explore the relationship between conscientiousness and the consumption of healthy versus unhealthy main meals. Impulsive eating was tested as a mediator in this relationship, as well as direct effects of age on those constructs. A nationwide representative sample of 1,006 Norwegian adults (18-70 years) within a prospective design was used to test a theoretical model. The structural equation model (SEM), in combination with bootstrapping procedures in AMOS, was the principal analytical method. Conscientiousness was negatively associated with unhealthy and impulsive eating. Impulsive eating was a partial mediator between conscientiousness and unhealthy eating and a full mediator between conscientiousness and healthy eating. Age was positively correlated with conscientiousness and this relationship had an inverted U-shape form. Finally, age was negatively associated with unhealthy and impulsive eating, and positively associated with healthy eating. This study confirmed the relevance of conscientiousness for healthy, unhealthy, and impulsive eating.

  2. PHOTOMETRIC DETERMINATION OF THE MASS ACCRETION RATES OF PRE-MAIN-SEQUENCE STARS. II. NGC 346 IN THE SMALL MAGELLANIC CLOUD

    SciTech Connect

    De Marchi, Guido; Sirianni, Marco; Panagia, Nino; Sabbi, Elena; Romaniello, Martino; Prada Moroni, Pier Giorgio; Degl'Innocenti, Scilla E-mail: panagia@stsci.edu

    2011-10-10

    We have studied the properties of the stellar populations in the field of the NGC 346 cluster in the Small Magellanic Cloud, using a novel self-consistent method that allows us to reliably identify pre-main-sequence (PMS) objects actively undergoing mass accretion, regardless of their age. The method does not require spectroscopy and combines broadband V and I photometry with narrowband H{alpha} imaging to identify all stars with excess H{alpha} emission and derive the accretion luminosity L{sub acc} and mass accretion rate M-dot{sub acc} for all of them. The application of this method to existing Hubble Space Telescope (HST)/Advanced Camera for Surveys photometry of the NGC 346 field has allowed us to identify and study 680 bona fide PMS stars with masses from {approx}0.4 M{sub sun} to {approx}4 M{sub sun} and ages in the range from {approx}1 Myr to {approx}30 Myr. Previous investigations of this region, based on the same data, had identified young ({approx}3 Myr old) candidate PMS stars on the basis of their broadband colors. In this study, we show that there are at least two, almost equally numerous, young populations with distinct ages of, respectively, {approx}1 and {approx}20 Myr. We provide accurate physical parameters for all of them. We take advantage of the unprecedented size of our PMS sample and of its spread in mass and age to study the evolution of the mass accretion rate as a function of stellar parameters. We find that, regardless of stellar mass, the mass accretion rate decreases with roughly the square root of the age, or about three times slower than predicted by current models of viscous disk evolution, and that more massive stars systematically have a higher mass accretion rate in proportion to their mass. A multivariate linear regression fit reveals that log M-dot{sub acc}{approx_equal}-0.6 log t + log m + c, where t is the age of the star, m is its mass, and c is a quantity that is higher at lower metallicity. This result is consistent with

  3. The SDSS spectroscopic catalogue of white dwarf-main-sequence binaries: new identifications from DR 9-12

    NASA Astrophysics Data System (ADS)

    Rebassa-Mansergas, A.; Ren, J. J.; Parsons, S. G.; Gänsicke, B. T.; Schreiber, M. R.; García-Berro, E.; Liu, X.-W.; Koester, D.

    2016-06-01

    We present an updated version of the spectroscopic catalogue of white dwarf-main-sequence (WDMS) binaries from the Sloan Digital Sky Survey (SDSS). We identify 938 WDMS binaries within the data releases (DR) 9-12 of SDSS plus 40 objects from DR 1-8 that we missed in our previous works, 646 of which are new. The total number of spectroscopic SDSS WDMS binaries increases to 3294. This is by far the largest and most homogeneous sample of compact binaries currently available. We use a decomposition/fitting routine to derive the stellar parameters of all systems identified here (white dwarf effective temperatures, surface gravities and masses, and secondary star spectral types). The analysis of the corresponding stellar parameter distributions shows that the SDSS WDMS binary population is seriously affected by selection effects. We also measure the Na I λλ 8183.27, 8194.81 absorption doublet and H α emission radial velocities (RV) from all SDSS WDMS binary spectra identified in this work. 98 objects are found to display RV variations, 62 of which are new. The RV data are sufficient enough to estimate the orbital periods of three close binaries.

  4. On the origin of the correlations between the accretion luminosity and emission line luminosities in pre-main-sequence stars

    NASA Astrophysics Data System (ADS)

    Mendigutía, I.; Oudmaijer, R. D.; Rigliaco, E.; Fairlamb, J. R.; Calvet, N.; Muzerolle, J.; Cunningham, N.; Lumsden, S. L.

    2015-09-01

    Correlations between the accretion luminosity and emission line luminosities (Lacc and Lline) of pre-main-sequence (PMS) stars have been published for many different spectral lines, which are used to estimate accretion rates. Despite the origin of those correlations is unknown, this could be attributed to direct or indirect physical relations between the emission line formation and the accretion mechanism. This work shows that all (near-UV/optical/near-IR) Lacc-Lline correlations are the result of the fact that the accretion luminosity and the stellar luminosity (L*) are correlated, and are not necessarily related with the physical origin of the line. Synthetic and observational data are used to illustrate how the Lacc-Lline correlations depend on the Lacc-L* relationship. We conclude that because PMS stars show the Lacc-L* correlation immediately implies that Lacc also correlates with the luminosity of all emission lines, for which the Lacc-Lline correlations alone do not prove any physical connection with accretion but can only be used with practical purposes to roughly estimate accretion rates. When looking for correlations with possible physical meaning, we suggest that Lacc/L* and Lline/L* should be used instead of Lacc and Lline. Finally, the finding that Lacc has a steeper dependence on L* for T Tauri stars than for intermediate-mass Herbig Ae/Be stars is also discussed. That is explained from the magnetospheric accretion scenario and the different photospheric properties in the near-UV.

  5. Using A New Model for Main Sequence Turnoff Absolute Magnitudes to Measure Stellar Streams in the Milky Way Halo

    NASA Astrophysics Data System (ADS)

    Weiss, Jake; Newberg, Heidi Jo; Arsenault, Matthew; Bechtel, Torrin; Desell, Travis; Newby, Matthew; Thompson, Jeffery M.

    2016-01-01

    Statistical photometric parallax is a method for using the distribution of absolute magnitudes of stellar tracers to statistically recover the underlying density distribution of these tracers. In previous work, statistical photometric parallax was used to trace the Sagittarius Dwarf tidal stream, the so-called bifurcated piece of the Sagittaritus stream, and the Virgo Overdensity through the Milky Way. We use an improved knowledge of this distribution in a new algorithm that accounts for the changes in the stellar population of color-selected stars near the photometric limit of the Sloan Digital Sky Survey (SDSS). Although we select bluer main sequence turnoff stars (MSTO) as tracers, large color errors near the survey limit cause many stars to be scattered out of our selection box and many fainter, redder stars to be scattered into our selection box. We show that we are able to recover parameters for analogues of these streams in simulated data using a maximum likelihood optimization on MilkyWay@home. We also present the preliminary results of fitting the density distribution of major Milky Way tidal streams in SDSS data. This research is supported by generous gifts from the Marvin Clan, Babette Josephs, Manit Limlamai, and the MilkyWay@home volunteers.

  6. First discovery of a magnetic field in a main-sequence δ Scuti star: the Kepler star HD 188774

    NASA Astrophysics Data System (ADS)

    Neiner, C.; Lampens, P.

    2015-11-01

    The Kepler space mission provided a wealth of δ Sct-γ Dor hybrid candidates. While some may be genuine hybrids, others might be misclassified due to the presence of a binary companion or to rotational modulation caused by magnetism and related surface inhomogeneities. In particular, the Kepler δ Sct-γ Dor hybrid candidate HD 188774 shows a few low frequencies in its light and radial velocity curves, whose origin is unclear. In this work, we check for the presence of a magnetic field in HD 188774. We obtained two spectropolarimetric measurements with an Echelle SpectroPolarimetric Device for the Observation of Stars (ESPaDOnS) at Canada-France-Hawaii Telescope. The data were analysed with the least-squares deconvolution (LSD) method. We detected a clear magnetic signature in the Stokes V LSD profiles. The origin of the low frequencies detected in HD 188774 is therefore most probably the rotational modulation of surface spots possibly related to the presence of a magnetic field. Consequently, HD 188774 is not a genuine hybrid δ Sct-γ Dor star, but the first known magnetic main-sequence δ Sct star. This makes it a prime target for future asteroseismic and spot modelling. This result casts new light on the interpretation of the Kepler results for other δ Sct-γ Dor hybrid candidates.

  7. EXTENDED MAGNETOSPHERES IN PRE-MAIN-SEQUENCE EVOLUTION: FROM T TAURI STARS TO THE BROWN DWARF LIMIT

    SciTech Connect

    Gomez de Castro, Ana I.; Marcos-Arenal, Pablo

    2012-04-20

    Low-mass pre-main-sequence stars, i.e., T Tauri stars (TTSs), strongly radiate at high energies, from X-rays to the ultraviolet (UV). This excess radiation with respect to main-sequence cool stars (MSCSs) is associated with the accretion process, i.e., it is produced in the extended magnetospheres, in the accretion shocks on the stellar surface, and in the outflows. Although evidence of accretion shocks and outflow contribution to the high-energy excess have been recently addressed, there is not an updated revision of the magnetospheric contribution. This article addresses this issue. The UV observations of the TTSs in the well-known Taurus region have been analyzed together with the XMM-Newton observations compiled in the XEST survey. For the first time the high sensitivity of the Hubble Space Telescope UV instrumentation has allowed measurement of the UV line fluxes of TTSs to M8 type. UV- and X-ray-normalized fluxes have been determined to study the extent and properties of the TTS magnetospheres as a class. They have been compared with the atmospheres of the MSCSs. The main results from this analysis are (1) the normalized fluxes of all the tracers are correlated; this correlation is independent of the broad mass range and the hardness of the X-ray radiation field; (2) the TTS correlations are different than the MSCS correlations; (3) there is a very significant excess emission in O I in the TTSs compared with MSCSs that seems to be caused by recombination radiation from the disk atmosphere after photoionization by extreme UV radiation; the Fe II/Mg II recombination continuum has also been detected in several TTSs and most prominently in AA Tau; and (4) the normalized flux of the UV tracers anticorrelates with the strength of the X-ray flux, i.e., the stronger the X-ray surface flux is, the weaker the observed UV flux. This last behavior is counterintuitive within the framework of stellar dynamo theory and suggests that UV emission can be produced in the

  8. Extended Magnetospheres in Pre-main-sequence Evolution: From T Tauri Stars to the Brown Dwarf Limit

    NASA Astrophysics Data System (ADS)

    Gómez de Castro, Ana I.; Marcos-Arenal, Pablo

    2012-04-01

    Low-mass pre-main-sequence stars, i.e., T Tauri stars (TTSs), strongly radiate at high energies, from X-rays to the ultraviolet (UV). This excess radiation with respect to main-sequence cool stars (MSCSs) is associated with the accretion process, i.e., it is produced in the extended magnetospheres, in the accretion shocks on the stellar surface, and in the outflows. Although evidence of accretion shocks and outflow contribution to the high-energy excess have been recently addressed, there is not an updated revision of the magnetospheric contribution. This article addresses this issue. The UV observations of the TTSs in the well-known Taurus region have been analyzed together with the XMM-Newton observations compiled in the XEST survey. For the first time the high sensitivity of the Hubble Space Telescope UV instrumentation has allowed measurement of the UV line fluxes of TTSs to M8 type. UV- and X-ray-normalized fluxes have been determined to study the extent and properties of the TTS magnetospheres as a class. They have been compared with the atmospheres of the MSCSs. The main results from this analysis are (1) the normalized fluxes of all the tracers are correlated; this correlation is independent of the broad mass range and the hardness of the X-ray radiation field; (2) the TTS correlations are different than the MSCS correlations; (3) there is a very significant excess emission in O I in the TTSs compared with MSCSs that seems to be caused by recombination radiation from the disk atmosphere after photoionization by extreme UV radiation; the Fe II/Mg II recombination continuum has also been detected in several TTSs and most prominently in AA Tau; and (4) the normalized flux of the UV tracers anticorrelates with the strength of the X-ray flux, i.e., the stronger the X-ray surface flux is, the weaker the observed UV flux. This last behavior is counterintuitive within the framework of stellar dynamo theory and suggests that UV emission can be produced in the

  9. THE CLUSTERED NATURE OF STAR FORMATION. PRE-MAIN-SEQUENCE CLUSTERS IN THE STAR-FORMING REGION NGC 602/N90 IN THE SMALL MAGELLANIC CLOUD

    SciTech Connect

    Gouliermis, Dimitrios A.; Gennaro, Mario; Schmeja, Stefan; Dolphin, Andrew E.; Tognelli, Emanuele; Prada Moroni, Pier Giorgio

    2012-03-20

    Located at the tip of the wing of the Small Magellanic Cloud (SMC), the star-forming region NGC 602/N90 is characterized by the H II nebular ring N90 and the young cluster of pre-main-sequence (PMS) and early-type main-sequence stars NGC 602, located in the central area of the ring. We present a thorough cluster analysis of the stellar sample identified with Hubble Space Telescope/Advanced Camera for Surveys in the region. We show that apart from the central cluster low-mass PMS stars are congregated in 13 additional small, compact sub-clusters at the periphery of NGC 602, identified in terms of their higher stellar density with respect to the average background density derived from star counts. We find that the spatial distribution of the PMS stars is bimodal, with an unusually large fraction ({approx}60%) of the total population being clustered, while the remaining is diffusely distributed in the intercluster area, covering the whole central part of the region. From the corresponding color-magnitude diagrams we disentangle an age difference of {approx}2.5 Myr between NGC 602 and the compact sub-clusters, which appear younger, on the basis of comparison of the brighter PMS stars with evolutionary models, which we accurately calculated for the metal abundance of the SMC. The diffuse PMS population appears to host stars as old as those in NGC 602. Almost all detected PMS sub-clusters appear to be centrally concentrated. When the complete PMS stellar sample, including both clustered and diffused stars, is considered in our cluster analysis, it appears as a single centrally concentrated stellar agglomeration, covering the whole central area of the region. Considering also the hot massive stars of the system, we find evidence that this agglomeration is hierarchically structured. Based on our findings, we propose a scenario according to which the region NGC 602/N90 experiences an active clustered star formation for the last {approx}5 Myr. The central cluster NGC 602 was

  10. The Pietra Grande thrust (Brenta Dolomites, Italy): looking for co-seismic indicators along a main fault in carbonate sequences

    NASA Astrophysics Data System (ADS)

    Viganò, Alfio; Tumiati, Simone; Martin, Silvana; Rigo, Manuel

    2013-04-01

    At present, pseudotachylytes (i.e. solidified frictional melts) are the only unambiguous geological record of seismic faulting. Even if pseudotachylytes are frequently observed along faults within crystalline rocks they are discovered along carbonate faults in very few cases only, suggesting that other chemico-physical processes than melting could occur (e.g. thermal decomposition). In order to investigate possible co-seismic indicators we study the Pietra Grande thrust, a carbonate fault in the Brenta Dolomites (Trentino, NE Italy), to analyse field structure, microtextures and composition of rocks from the principal slip plane, the fault core and the damage zone. The Pietra Grande thrust is developed within limestones and dolomitic limestones of Late Triassic-Early Jurassic age (Calcari di Zu and Monte Zugna Formations). The thrust, interpreted as a north-vergent décollement deeply connected with the major Cima Tosa thrust, is a sub-horizontal fault plane gently dipping to the North that mainly separates the massive Monte Zugna Fm. limestones (upper side) from the stratified Calcari di Zu Fm. limestones with intercalated marls (lower side). On the western face of the Pietra Grande klippe the thrust is continuously well-exposed for about 1 km. The main fault plane shows reddish infillings, which form veins with thicknesses between few millimetres to several decimetres. These red veins lie parallel to the thrust plane or in same cases inject lateral fractures and minor high-angle faults departing from the main fault plane. Veins have carbonate composition and show textures characterized by fine-grained reddish matrix with embedded carbonate clasts of different size (from few millimetres to centimetres). In some portions carbonate boulders (dimension of some decimetres) are embedded in the red matrix, while clast content generally significantly decreases at the vein borders (chilled margins). Red veins are typically associated with cohesive cataclasites and

  11. The confinement of star-forming galaxies into a main sequence through episodes of gas compaction, depletion and replenishment

    NASA Astrophysics Data System (ADS)

    Tacchella, Sandro; Dekel, Avishai; Carollo, C. Marcella; Ceverino, Daniel; DeGraf, Colin; Lapiner, Sharon; Mandelker, Nir; Primack Joel, R.

    2016-04-01

    Using cosmological simulations, we address the properties of high-redshift star-forming galaxies (SFGs) across their main sequence (MS) in the plane of star formation rate (SFR) versus stellar mass. We relate them to the evolution of galaxies through phases of gas compaction, depletion, possible replenishment, and eventual quenching. We find that the high-SFR galaxies in the upper envelope of the MS are compact, with high gas fractions and short depletion times (`blue nuggets'), while the lower SFR galaxies in the lower envelope have lower central gas densities, lower gas fractions, and longer depletion times, consistent with observed gradients across the MS. Stellar-structure gradients are negligible. The SFGs oscillate about the MS ridge on time-scales ˜0.4tHubble (˜1 Gyr at z ˜ 3). The propagation upwards is due to gas compaction, triggered, e.g. by mergers, counter-rotating streams, and/or violent disc instabilities. The downturn at the upper envelope is due to central gas depletion by peak star formation and outflows while inflow from the shrunken gas disc is suppressed. An upturn at the lower envelope can occur once the extended disc has been replenished by fresh gas and a new compaction can be triggered, namely as long as the replenishment time is shorter than the depletion time. The mechanisms of gas compaction, depletion, and replenishment confine the SFGs to the narrow (±0.3 dex) MS. Full quenching occurs in massive haloes (Mvir > 1011.5 M⊙) and/or at low redshifts (z < 3), where the replenishment time is long compared to the depletion time, explaining the observed bending down of the MS at the massive end.

  12. An IUE Atlas of Pre-Main-Sequence Stars. II. Far-Ultraviolet Accretion Diagnostics in T Tauri Stars

    NASA Astrophysics Data System (ADS)

    Johns-Krull, Christopher M.; Valenti, Jeff A.; Linsky, Jeffrey L.

    2000-08-01

    We use our ultraviolet (UV) atlas of pre-main-sequence stars constructed from all useful, short-wavelength, low-resolution spectra in the International Ultraviolet Explorer (IUE) satellite Final Archive to analyze the short-wavelength UV properties of 49 T Tauri stars (TTSs). We compare the line and continuum fluxes in these TTSs with each other and with previously published parameters of these systems, including rotation rate, infrared excess, and mass accretion rate. The short-wavelength continuum in the classical TTSs (CTTSs) appears to originate in a ~10,000 K optically thick plasma, while in the naked TTSs (NTTSs-stars without dusty disks) the continuum appears to originate in the stellar atmosphere. We show that all of the TTSs in our sample lie in the regime of ``saturated'' magnetic activity due to their small Rossby numbers. However, while some of the TTSs show emission line surface fluxes consistent with this saturation level, many CTTSs show significantly stronger emission than predicted by saturation. In these stars, the emission line luminosity in the high ionization lines present in the spectrum between 1200 and 2000 Å correlates well with the mass accretion rate. Therefore, we conclude that the bulk of the short-wavelength emission seen in CTTSs results from accretion related processes and not from dynamo-driven magnetic activity. Using CTTSs with known mass accretion rates, we calibrate the relationship between M and LC IV to derive the mass accretion rate for some CTTSs which for various reasons have never had their mass accretion rates measured. Finally, several of the CTTSs show strong emission from molecular hydrogen. While emission from H2 cannot form in gas at a temperature of ~105 K, the strength of the molecular hydrogen emission is nevertheless well correlated with all the other emissions displayed in the IUE short-wavelength bandpass. This suggests that the H2 emission is in fact fluorescent emission pumped by the emission (likely Ly

  13. KEPLER-4b: A HOT NEPTUNE-LIKE PLANET OF A G0 STAR NEAR MAIN-SEQUENCE TURNOFF

    SciTech Connect

    Borucki, William J.; Koch, David G.; Caldwell, Douglas A.; Jenkins, Jon M.; Lissauer, Jack J.; Rowe, Jason F.; Basri, Gibor; Marcy, Geoffrey W.; Batalha, Natalie M.; Cochran, William D.; Dunham, Edward W.; Gautier, Thomas N.; Gilliland, Ronald L.; Howell, Steve B.; Monet, David

    2010-04-20

    Early time-series photometry from NASA's Kepler spacecraft has revealed a planet transiting the star we term Kepler-4, at R.A. = 19{sup h}02{sup m}27.{sup s}68, {delta} = +50{sup 0}08'08.''7. The planet has an orbital period of 3.213 days and shows transits with a relative depth of 0.87 x 10{sup -3} and a duration of about 3.95 hr. Radial velocity (RV) measurements from the Keck High Resolution Echelle Spectrometer show a reflex Doppler signal of 9.3{sup +1.1} {sub -1.9} m s{sup -1}, consistent with a low-eccentricity orbit with the phase expected from the transits. Various tests show no evidence for any companion star near enough to affect the light curve or the RVs for this system. From a transit-based estimate of the host star's mean density, combined with analysis of high-resolution spectra, we infer that the host star is near turnoff from the main sequence, with estimated mass and radius of 1.223{sup +0.053} {sub -0.091} M {sub sun} and 1.487{sup +0.071} {sub -0.084} R {sub sun}. We estimate the planet mass and radius to be {l_brace}M {sub P}, R {sub P}{r_brace} = {l_brace}24.5 {+-} 3.8 M {sub +}, 3.99 {+-} 0.21 R {sub +}{r_brace}. The planet's density is near 1.9 g cm{sup -3}; it is thus slightly denser and more massive than Neptune, but about the same size.

  14. The pre-main-sequence star V1184 Tauri (CB 34V) at the end of prolonged eclipse

    NASA Astrophysics Data System (ADS)

    Semkov, E. H.; Peneva, S. P.; Ibryamov, S. I.

    2015-10-01

    Aims: V1184 Tau (CB 34V) lies in the field of the Bok globule CB 34 and was discovered as a large amplitude variable in 1993. According to the first hypothesis of the variability of the star, it is a FU Orionis candidate erupted between 1951 and 1993. During subsequent observations, the star manifests large amplitude variability interpreted as obscuration from circumstellar clouds of dust. We included V1184 Tau (CB 34V) in our target list of highly variable pre-main-sequence stars to determine the reasons for the variations in the brightness of this object. Methods: Data from BVRI photometric observations of the young stellar object V1184 Tau, obtained in the period 2008-2015, are presented in the paper. These data are a continuation of our optical photometric monitoring of the star began in 2000 and continuing to date. The photometric observations of V1184 Tau were performed in two observatories with two medium-sized and two small telescopes. Results: Our results indicate that during periods of maximum light the star shows characteristics typical of T Tauri stars. During the observed deep minimum in brightness, however, V1184 Tau is rather similar to UX Orionis objects. The deep drop in brightness began in 2003 ended in 2015 as the star has returned to maximum light. The light curve during the drop is obviously asymmetric as the decrease in brightness lasts two times longer than the rise. The observed colour reverse on the colour-magnitude diagrams is also confirmation of obscuration from circumstellar clouds of dust as a reason for the large amplitude variability in the brightness. Appendix A is available in electronic form at http://www.aanda.org

  15. Polarimetric Variations of Binary Stars. IV. Pre-Main-Sequence Spectroscopic Binaries Located in Taurus, Auriga, and Orion

    NASA Astrophysics Data System (ADS)

    Manset, N.; Bastien, P.

    2002-08-01

    We present polarimetric observations of 14 pre-main-sequence (PMS) binaries located in the Taurus, Auriga, and Orion star-forming regions. The majority of the average observed polarizations are below 0.5%, and none are above 0.9%. After removal of estimates of the interstellar polarization, about half the binaries have an intrinsic polarization above 0.5%, even though most of them do not present other evidences for the presence of circumstellar dust. Various tests reveal that 77% of the PMS binaries have or possibly have a variable polarization. LkCa 3, Par 1540, and Par 2494 present detectable periodic and phase-locked variations. The periodic polarimetric variations are noisier and of a lesser amplitude (~0.1%) than for other types of binaries, such as hot stars. This could be due to stochastic events that produce deviations in the average polarization, a nonfavorable geometry (circumbinary envelope), or the nature of the scatterers (dust grains are less efficient polarizers than electrons). Par 1540 is a weak-line T Tauri star but nonetheless has enough dust in its environment to produce detectable levels of polarization and variations. A fourth interesting case is W134, which displays rapid changes in polarization that could be due to eclipses. We compare the observations with some of our numerical simulations and also show that an analysis of the periodic polarimetric variations with the Brown, McLean, & Emslie (BME) formalism to find the orbital inclination is for the moment premature: nonperiodic events introduce stochastic noise that partially masks the periodic low-amplitude variations and prevents the BME formalism from finding a reasonable estimate of the orbital inclination.

  16. Single-neuron transcriptome and methylome sequencing for epigenomic analysis of aging.

    PubMed

    Moroz, Leonid L; Kohn, Andrea B

    2013-01-01

    Enormous heterogeneity in transcription and signaling is the feature that slows down progress in our understanding of the mechanisms of normal aging and age-related diseases. This is critical for neurobiology of aging where the enormous diversity of neuronal populations presents a significant challenge in experimental design. Here, we introduce Aplysia as a model for genomic analysis of aging at the single-cell level and provide protocols for integrated transcriptome and methylome profiling of individually identified neurons during the aging process. These single-cell RNA-seq and DNA methylation assays (methyl-capture/methyl enrichment) are compatible with all major next generation sequencing platforms (we used Roche/454 and SOLiD/Life Technologies as illustrative examples) and can be used to integrate an epigenetic signature with transcriptional output. The described sequencing library construction protocol provides both quantitative and directional information from transcriptional profiling of individual cells. Our results also confirm that different copies of DNA in polyploid Aplysia neurons behave similarly with respect to their DNA methylation.

  17. A multi-wavelength study of pre-main sequence stars in the Taurus-Auriga star-forming region

    NASA Astrophysics Data System (ADS)

    Guenther, E. W.; Stelzer, B.; Neuhäuser, R.; Hillwig, T. C.; Durisen, R. H.; Menten, K. M.; Greimel, R.; Barwig, H.; Englhauser, J.; Robb, R. M.

    2000-05-01

    Although many lowmass pre-main sequence stars are strong X-ray sources, the origin of the X-ray emission is not well known. Since these objects are variable at all frequencies, simultaneous observations in X-rays and in other wavelengths are able to constrain the properties of the X-ray emitting regions. In this paper, we report quasi-simultaneous observations in X-rays, the optical, and the radio regime for classical and weak-line T Tauri stars from the Taurus-Auriga star-forming region. We find that all detected T Tauri stars show significant night-to-night variations of the X-ray emission. For three of the stars, FM Tau and CW Tau, both classical T Tauri stars, and V773 Tau, a weak-line T Tauri star, the variations are especially large. From observations taken simultaneously, we also find that there is some correspondence between the strength of Hα and the X-ray brightness in V773 Tau. The lack of a strong correlation leads us to conclude that the X-ray emission of V773 Tau is not a superposition of flares. However, we suggest that a weak correlation occurs because chromospherically active regions and regions of strong X-ray emission are generally related. V773 Tau was detected at 8.46 GHz as a weakly circularly polarised but highly variable source. We also find that the X-ray emission and the equivalent width of Hα remained unchanged, while large variations of the flux density in the radio regime were observed. This clearly indicates that the emitting regions are different. Using optical spectroscopy we detected a flare in Hα and event which showed a flare-like light-curve of the continuum brightness in FM Tau. However, ROSAT did not observe the field at the times of these flares. Nevertheless, an interesting X-ray event was observed in V773 Tau, during which the flux increased for about 8 hours and then decreased back to the same level in 5 hours. We interpret this as a long-duration event similar to those seen on the sun and other active stars. In the

  18. CONSTRAINING THE EXOZODIACAL LUMINOSITY FUNCTION OF MAIN-SEQUENCE STARS: COMPLETE RESULTS FROM THE KECK NULLER MID-INFRARED SURVEYS

    SciTech Connect

    Mennesson, B.; Serabyn, E.; Colavita, M. M.; Bryden, G.; Doré, O.; Traub, W.; Millan-Gabet, R.; Absil, O.; Wyatt, M.; Danchi, W.; Kuchner, M.; Stapelfeldt, K.; Defrère, D.; Hinz, P.; Ragland, S.; Scott, N.; Woillez, J.

    2014-12-20

    Forty-seven nearby main-sequence stars were surveyed with the Keck Interferometer mid-infrared Nulling instrument (KIN) between 2008 and 2011, searching for faint resolved emission from exozodiacal dust. Observations of a subset of the sample have already been reported, focusing essentially on stars with no previously known dust. Here we extend this previous analysis to the whole KIN sample, including 22 more stars with known near- and/or far-infrared excesses. In addition to an analysis similar to that of the first paper of this series, which was restricted to the 8-9 μm spectral region, we present measurements obtained in all 10 spectral channels covering the 8-13 μm instrumental bandwidth. Based on the 8-9 μm data alone, which provide the highest signal-to-noise measurements, only one star shows a large excess imputable to dust emission (η Crv), while four more show a significant (>3σ) excess: β Leo, β UMa, ζ Lep, and γ Oph. Overall, excesses detected by KIN are more frequent around A-type stars than later spectral types. A statistical analysis of the measurements further indicates that stars with known far-infrared (λ ≥ 70 μm) excesses have higher exozodiacal emission levels than stars with no previous indication of a cold outer disk. This statistical trend is observed regardless of spectral type and points to a dynamical connection between the inner (zodi-like) and outer (Kuiper-Belt-like) dust populations. The measured levels for such stars are clustering close to the KIN detection limit of a few hundred zodis and are indeed consistent with those expected from a population of dust that migrated in from the outer belt by Poynting-Robertson drag. Conversely, no significant mid-infrared excess is found around sources with previously reported near-infrared resolved excesses, which typically have levels of the order of 1% over the photospheric flux. If dust emission is really at play in these near-infrared detections, the absence of a strong mid

  19. Monte Carlo simulations of post-common-envelope white dwarf + main sequence binaries: The effects of including recombination energy

    NASA Astrophysics Data System (ADS)

    Zorotovic, M.; Schreiber, M. R.; García-Berro, E.; Camacho, J.; Torres, S.; Rebassa-Mansergas, A.; Gänsicke, B. T.

    2014-08-01

    Context. Detached white dwarf + main sequence (WD+MS) post-common-envelope binaries (PCEBs) are perhaps the most suitable objects for testing predictions of close-compact binary-star evolution theories, in particular, common-envelope (CE) evolution. Consequently, the population of WD+MS PCEBs has been simulated by several authors in the past and the predictions have been compared with the observations. However, most of those theoretical predictions did not take into account the possible contributions to the envelope ejection from additional sources of energy (mostly recombination energy) stored in the envelope. Aims: Here we update existing binary population models of WD+MS PCEBs by assuming that in addition to a fraction αCE of the orbital energy, a fraction αrec of the recombination energy available within the envelope contributes to ejecting the envelope. Methods: We performed Monte Carlo simulations of 107 MS+MS binaries for 9 different combinations of αCE and αrec using standard assumptions for the initial primary mass function, binary separations, and initial-mass-ratio distribution and evolved these systems using the publicly available binary star evolution (BSE) code. Results: Including a fraction of the recombination energy leads to a clear prediction of a large number of long orbital period (≳10 days) systems mostly containing high-mass WDs. The fraction of systems with He-core WD primaries (MWD ≲ 0.5 M⊙) increases with the CE efficiency and the existence of very low-mass He WDs (≲0.3 M⊙) is only predicted for high values of the CE efficiency, i.e. αCE ≳ 0.5. All models predict on average longer orbital periods for PCEBs containing C/O-core WDs (MWD ≳ 0.5 M⊙) than for PCEBs containing He WDs. This effect increases with increasing values of both efficiencies, i.e., αCE and αrec. Longer periods after the CE phase are also predicted for systems containing more massive secondary stars. The initial-mass-ratio distribution affects the

  20. Constraining the Exozodiacal Luminosity Function of Main-sequence Stars: Complete Results from the Keck Nuller Mid-infrared Surveys

    NASA Astrophysics Data System (ADS)

    Mennesson, B.; Millan-Gabet, R.; Serabyn, E.; Colavita, M. M.; Absil, O.; Bryden, G.; Wyatt, M.; Danchi, W.; Defrère, D.; Doré, O.; Hinz, P.; Kuchner, M.; Ragland, S.; Scott, N.; Stapelfeldt, K.; Traub, W.; Woillez, J.

    2014-12-01

    Forty-seven nearby main-sequence stars were surveyed with the Keck Interferometer mid-infrared Nulling instrument (KIN) between 2008 and 2011, searching for faint resolved emission from exozodiacal dust. Observations of a subset of the sample have already been reported, focusing essentially on stars with no previously known dust. Here we extend this previous analysis to the whole KIN sample, including 22 more stars with known near- and/or far-infrared excesses. In addition to an analysis similar to that of the first paper of this series, which was restricted to the 8-9 μm spectral region, we present measurements obtained in all 10 spectral channels covering the 8-13 μm instrumental bandwidth. Based on the 8-9 μm data alone, which provide the highest signal-to-noise measurements, only one star shows a large excess imputable to dust emission (η Crv), while four more show a significant (>3σ) excess: β Leo, β UMa, ζ Lep, and γ Oph. Overall, excesses detected by KIN are more frequent around A-type stars than later spectral types. A statistical analysis of the measurements further indicates that stars with known far-infrared (λ >= 70 μm) excesses have higher exozodiacal emission levels than stars with no previous indication of a cold outer disk. This statistical trend is observed regardless of spectral type and points to a dynamical connection between the inner (zodi-like) and outer (Kuiper-Belt-like) dust populations. The measured levels for such stars are clustering close to the KIN detection limit of a few hundred zodis and are indeed consistent with those expected from a population of dust that migrated in from the outer belt by Poynting-Robertson drag. Conversely, no significant mid-infrared excess is found around sources with previously reported near-infrared resolved excesses, which typically have levels of the order of 1% over the photospheric flux. If dust emission is really at play in these near-infrared detections, the absence of a strong mid

  1. Polarimetric Variations of Binary Stars. V. Pre-Main-Sequence Spectroscopic Binaries Located in Ophiuchus and Scorpius

    NASA Astrophysics Data System (ADS)

    Manset, N.; Bastien, P.

    2003-06-01

    We present polarimetric observations of seven pre-main-sequence (PMS) spectroscopic binaries located in the ρ Ophiuchus and Upper Scorpius star-forming regions (SFRs). The average observed polarizations at 7660 Å are between 0.5% and 3.5%. After estimates of the interstellar polarization are removed, all binaries have an intrinsic polarization above 0.4%, even though most of them do not present other evidences for circumstellar dust. Two binaries, NTTS 162814-2427 and NTTS 162819-2423S, present high levels of intrinsic polarization between 1.5% and 2.1%, in agreement with the fact that other observations (photometry, spectroscopy) indicate the presence of circumstellar dust. Tests reveal that all seven PMS binaries have a statistically variable or possibly variable polarization. Combining these results with our previous sample of binaries located in the Taurus, Auriga, and Orion SFRs, 68% of the binaries have an intrinsic polarization above 0.5%, and 90% of the binaries are polarimetrically variable or possibly variable. NTTS 160814-1857, 162814-2427, and 162819-2423S are clearly polarimetrically variable. The first two also exhibit phase-locked variations over ~10 and ~40 orbits, respectively. Statistically, NTTS 160905-1859 is possibly variable, but it shows periodic variations not detected by the statistical tests; those variations are not phased locked and only present for short intervals of time. The amplitudes of the variations reach a few tenths of a percent, greater than for the previously studied PMS binaries located in the Taurus, Orion, and Auriga SFRs. The high-eccentricity system NTTS 162814-2427 shows single-periodic variations, in agreement with our previous numerical simulations. We compare the observations with some of our numerical simulations and also show that an analysis of the periodic polarimetric variations with the Brown, McLean, & Emslie (BME) formalism to find the orbital inclination is for the moment premature: nonperiodic events

  2. ISOCAM observations of the rho Ophiuchi cloud: Luminosity and mass functions of the pre-main sequence embedded cluster

    NASA Astrophysics Data System (ADS)

    Bontemps, S.; André, P.; Kaas, A. A.; Nordh, L.; Olofsson, G.; Huldtgren, M.; Abergel, A.; Blommaert, J.; Boulanger, F.; Burgdorf, M.; Cesarsky, C. J.; Cesarsky, D.; Copet, E.; Davies, J.; Falgarone, E.; Lagache, G.; Montmerle, T.; Pérault, M.; Persi, P.; Prusti, T.; Puget, J. L.; Sibille, F.

    2001-06-01

    We present the results of the first extensive mid-infrared (IR) imaging survey of the rho Ophiuchi embedded cluster, performed with the ISOCAM camera on board the ISO satellite. The main rho Ophiuchi molecular cloud L1688, as well as the two secondary clouds L1689N and L1689S, have been completely surveyed for point sources at 6.7 mu m and 14.3 mu m. A total of 425 sources are detected in ~ 0.7 deg2, including 16 Class I, 123 Class II, and 77 Class III young stellar objects (YSOs). Essentially all of the mid-IR sources coincide with near-IR sources, but a large proportion of them are recognized for the first time as YSOs. Our dual-wavelength survey allows us to identify essentially all the YSOs with IR excess in the embedded cluster down to Fnu ~ 10-15 mJy. It more than doubles the known population of Class II YSOs and represents the most complete census to date of newly formed stars in the rho Ophiuchi central region. There are, however, reasons to believe that several tens of Class III YSOs remain to be identified below Lstar ~ 0.2 Lsolar. The mid-IR luminosities of most ( ~ 65%) Class II objects are consistent with emission from purely passive circumstellar disks. The stellar luminosity function of the complete sample of Class II YSOs is derived with good accuracy down to Lstar ~ 0.03 Lsolar. It is basically flat (in logarithmic units) below Lstar ~ 2 Lsolar, exhibits a possible local maximum at Lstar ~ 1.5 Lsolar, and sharply falls off at higher luminosities. A modeling of the luminosity function, using available pre-main sequence tracks and plausible star formation histories, allows us to derive the mass distribution of the Class II YSOs which arguably reflects the initial mass function (IMF) of the embedded cluster. After correction for the presence of unresolved binary systems, we estimate that the IMF in rho Ophiuchi is well described by a two-component power law with a low-mass index of -0.35+/-0.25, a high-mass index of -1.7 (to be compared with the

  3. SEARCHING FOR YOUNG JUPITER ANALOGS AROUND AP COL: L-BAND HIGH-CONTRAST IMAGING OF THE CLOSEST PRE-MAIN-SEQUENCE STAR

    SciTech Connect

    Quanz, Sascha P.; Avenhaus, Henning; Meyer, Michael R.; Crepp, Justin R.; Hillenbrand, Lynne A.; Janson, Markus

    2012-08-01

    The nearby M-dwarf AP Col was recently identified by Riedel et al. as a pre-main-sequence star (age 12-50 Myr) situated only 8.4 pc from the Sun. The combination of its youth, distance, and intrinsically low luminosity make it an ideal target to search for extrasolar planets using direct imaging. We report deep adaptive optics observations of AP Col taken with VLT/NACO and Keck/NIRC2 in the L band. Using aggressive speckle suppression and background subtraction techniques, we are able to rule out companions with mass m {>=} 0.5-1 M{sub Jup} for projected separations a > 4.5 AU, and m {>=} 2 M{sub Jup} for projected separations as small as 3 AU, assuming an age of 40 Myr using the COND theoretical evolutionary models. Using a different set of models, the mass limits increase by a factor of {approx}>2. The observations presented here are the deepest mass-sensitivity limits yet achieved within 20 AU on a star with direct imaging. While Doppler radial velocity surveys have shown that Jovian bodies with close-in orbits are rare around M-dwarfs, gravitational microlensing studies predict that 17{sup +6}{sub -9}% of these stars host massive planets with orbital separations of 1-10 AU. Sensitive high-contrast imaging observations, like those presented here, will help to validate results from complementary detection techniques by determining the frequency of gas giant planets on wide orbits around M-dwarfs.

  4. The evolution of stellar metallicity gradients of the Milky Way disk from LSS-GAC main sequence turn-off stars: a two-phase disk formation history?

    NASA Astrophysics Data System (ADS)

    Xiang, Mao-Sheng; Liu, Xiao-Wei; Yuan, Hai-Bo; Huang, Yang; Wang, Chun; Ren, Juan-Juan; Chen, Bing-Qiu; Sun, Ning-Chen; Zhang, Hua-Wei; Huo, Zhi-Ying; Rebassa-Mansergas, Alberto

    2015-08-01

    Accurate measurements of stellar metallicity gradients in the radial and vertical directions of the disk and their temporal variations provide important constraints on the formation and evolution of the Milky Way disk. We use 297 042 main sequence turn-off stars selected from the LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC) to determine the radial and vertical gradients of stellar metallicity, Δ[Fe/H]/ΔR and Δ[Fe/H]/Δ|Z| of the Milky Way disk in the direction of the anticenter. We determine ages of those turn-off stars by isochrone fitting and measure the temporal variations of metallicity gradients. We have carried out a detailed analysis of the selection effects resulting from the selection, observation and data reduction of LSS-GAC targets and the potential biases of a magnitude limited sample on the determinations of metallicity gradients. Our results show that the gradients, both in the radial and vertical directions, exhibit significant spatial and temporal variations. The radial gradients yielded by stars with the oldest ages (≳ 11 Gyr) are essentially zero at all heights from the disk midplane, while those given by younger stars are always negative. The vertical gradients deduced from stars with the oldest ages (≳ 11 Gyr) are negative and only show very weak variations with Galactocentric distance in the disk plane, R, while those yielded by younger stars show strong variations with R. After being essentially flat at the earliest epochs of disk formation, the radial gradients steepen as age decreases, reaching a maximum (steepest) at age 7-8 Gyr, and then they flatten again. Similar temporal trends are also found for the vertical gradients. We infer that the assembly of the Milky Way disk may have experienced at least two distinct phases. The earlier phase is probably related to a slow, pressure-supported collapse of gas, when the gas settles down to the disk mainly in the vertical direction. In the later phase, there are

  5. Slip rate, magnitudes and ages of surface-rupturing events along the Main Frontal Thrust in Bhutan (Himalaya)

    NASA Astrophysics Data System (ADS)

    Ritz, J.; Berthet, T.; Ferry, M. A.; Pelgay, P.; Cattin, R.; Drukpa, D.; Braucher, R.; Chophel, J.; Thinley, K.; Hetényi, G.

    2013-12-01

    The Himalayas absorb about 20 mm.yr-1 of the convergence between India and Eurasia plate. Morphotectonics studies East of Bhutan yielded a Holocene shortening rate of 23 × 6.2 mm/yr consistent with the 21 × 1.5 mm/yr estimated in Nepal. Most of this crustal shortening is accommodated along the Main Frontal Thrust by major earthquakes (M≥8) that occurred in the past 1000 years. Between 89°E and 92°E, the MFT runs along the southern border of the Kingdom of Bhutan where no reliable historical record of major earthquakes exists (one strong historical earthquake would have occurred in 1713 after a Tibetan eyewitness reports). However, recent paleoseismic investigations in Nepal and on both side of Bhutan border suggest that a great earthquake may have ruptured a 700 to 800 km long section of the MFT during a single event around AD 1100. In December 2012, we carried out a first morphotectonic and paleosismologic study within two sites (Sarpang, Gelephu) along the MFT in central Bhutan. We identified several sequences of abandoned fluvial terraces that have been uplifted along the fault. From a kinematic GPS survey, we estimated that the oldest terrace sequence (T2) has a cumulative offset of 53.6 × 2.3 m. A younger sequence (T1) shows offsets of 4.5 × 0.5 m on the lower terrace (T1a) and 7.9 × 0.5 m on the upper one (T1b). The uplift on T1b may cumulate the vertical components of the two last seismic events that would have produced each a vertical offset of several meters. These preliminary observations suggest that the latest seismic event as well as the penultimate event correspond to two major seismic events with magnitudes greater than M8. After 14C dating (charcoals in sands on top of T1 terraces sequence), these two last seismic events occurred after 1000 AD. The youngest event may correspond to the historical event reported in 1713 AD, while the penultimate event could correspond the great medieval earthquake observed in trenches East and West of Bhutan

  6. A Near-Infrared Imaging Survey of the Lupus 3 Dark Cloud: A Modest Cluster of Low-Mass, Pre-Main-Sequence Stars

    NASA Astrophysics Data System (ADS)

    Nakajima, Yasushi; Tamura, Motohide; Oasa, Yumiko; Nakajima, Tadashi

    2000-02-01

    We present the first report on results of a near-infrared imaging survey of the Lupus 3 dark cloud. This cloud is known to be associated with a modest cluster of T Tauri stars from a previous optical Hα emission-line star survey. The survey covers 7'x11', which corresponds to a projected area of ~0.35x0.55 pc at a distance of 150 pc. Mapping was carried out at J, H, and Ks, to 10 σ limiting magnitudes of J=17.0, H=16.5, and Ks=15.5. A total of 229 sources brighter than Ks<15.8 were detected at all bands with a 90% completeness limit. Source classification is performed based on the near-infrared colors. Ten sources are candidates of Lada's Class II pre-main-sequence (PMS) stars, as they have a color excess that cannot be explained by reddening resulting from interstellar dust. We also identified 11 Class I-like candidates that were not detected at J and have a large color excess (H-Ks>=2), which is unlikely to arise from extinction in the Lupus dark cloud. There are four subclusters in this survey area of which three are embedded and mainly consist of the Class I-like candidates. The average density of PMS stars is around 500 pc-3, suggesting the presence of a modest cluster of embedded PMS stars. We estimate masses of the Class II candidates with aid of an evolutionary model of PMS stars. Ten of them have masses less than 0.08 Msolar if we assume their age to be 106 yr. Hence, we consider them to be young brown dwarf (YBD) candidates. The relative population of YBDs in the Lupus 3 dark cloud is larger than in the Taurus.

  7. Distinctive patterns of age-dependent hypomethylation in interspersed repetitive sequences.

    PubMed

    Jintaridth, Pornrutsami; Mutirangura, Apiwat

    2010-04-01

    Interspersed repetitive sequences (IRSs) are a major contributor to genome size and may contribute to cellular functions. IRSs are subdivided according to size and functionally related structures into short interspersed elements, long interspersed elements (LINEs), DNA transposons, and LTR-retrotransposons. Many IRSs may produce RNA and regulate genes by a variety of mechanisms. The majority of DNA methylation occurs in IRSs and is believed to suppress IRS activities. Global hypomethylation, or the loss of genome-wide methylation, is a common epigenetic event not only in senescent cells but also in cancer cells. Loss of LINE-1 methylation has been characterized in many cancers. Here, we evaluated the methylation levels of peripheral blood mononuclear cells of LINE-1, Alu, and human endogenous retrovirus K (HERV-K) in 177 samples obtained from volunteers between 20 and 88 yr of age. Age was negatively associated with methylation levels of Alu (r = -0.452, P < 10(-3)) and HERV-K (r = -0.326, P < 10(-3)) but not LINE-1 (r = 0.145, P = 0.055). Loss of methylation of Alu occurred during ages 34-68 yr, and loss of methylation of HERV-K occurred during ages 40-63 yr and again during ages 64-83 yr. Interestingly, methylation of Alu and LINE-1 are directly associated, particularly at ages 49 yr and older (r = 0.49, P < 10(-3)). Therefore, only some types of IRSs lose methylation at certain ages. Moreover, Alu and HERV-K become hypomethylated differently. Finally, there may be several mechanisms of global methylation. However, not all of these mechanisms are age-dependent. This finding may lead to a better understanding of not only the biological causes and consequences of genome-wide hypomethylation but also the role of IRSs in the aging process.

  8. Aging as accelerated accumulation of somatic variants: whole-genome sequencing of centenarian and middle-aged monozygotic twin pairs.

    PubMed

    Ye, Kai; Beekman, Marian; Lameijer, Eric-Wubbo; Zhang, Yanju; Moed, Matthijs H; van den Akker, Erik B; Deelen, Joris; Houwing-Duistermaat, Jeanine J; Kremer, Dennis; Anvar, Seyed Yahya; Laros, Jeroen F J; Jones, David; Raine, Keiran; Blackburne, Ben; Potluri, Shobha; Long, Quan; Guryev, Victor; van der Breggen, Ruud; Westendorp, Rudi G J; 't Hoen, Peter A C; den Dunnen, Johan; van Ommen, Gert Jan B; Willemsen, Gonneke; Pitts, Steven J; Cox, David R; Ning, Zemin; Boomsma, Dorret I; Slagboom, P Eline

    2013-12-01

    It has been postulated that aging is the consequence of an accelerated accumulation of somatic DNA mutations and that subsequent errors in the primary structure of proteins ultimately reach levels sufficient to affect organismal functions. The technical limitations of detecting somatic changes and the lack of insight about the minimum level of erroneous proteins to cause an error catastrophe hampered any firm conclusions on these theories. In this study, we sequenced the whole genome of DNA in whole blood of two pairs of monozygotic (MZ) twins, 40 and 100 years old, by two independent next-generation sequencing (NGS) platforms (Illumina and Complete Genomics). Potentially discordant single-base substitutions supported by both platforms were validated extensively by Sanger, Roche 454, and Ion Torrent sequencing. We demonstrate that the genomes of the two twin pairs are germ-line identical between co-twins, and that the genomes of the 100-year-old MZ twins are discerned by eight confirmed somatic single-base substitutions, five of which are within introns. Putative somatic variation between the 40-year-old twins was not confirmed in the validation phase. We conclude from this systematic effort that by using two independent NGS platforms, somatic single nucleotide substitutions can be detected, and that a century of life did not result in a large number of detectable somatic mutations in blood. The low number of somatic variants observed by using two NGS platforms might provide a framework for detecting disease-related somatic variants in phenotypically discordant MZ twins. PMID:24182360

  9. DNA sequence variability of IGHG3 alleles associated to the main G3m haplotypes in human populations.

    PubMed

    Dard, P; Lefranc, M P; Osipova, L; Sanchez-Mazas, A

    2001-10-01

    The present study investigates the molecular basis of the G3m polymorphism expressed by the heavy constant domains of human immunoglobulins gamma 3 chains. By using a new protocol allowing the specific cloning of IGHG3 genes, a total of 51 full-length IGHG3 genomic sequences (about 2 kb) isolated from African, Siberian, West Asian and European population samples were sequenced. IGHG3 sequences were assigned precise G3m haplotypes on the basis of specific associations between G3m allotypes and IGHG3 RFLPs. Specific DNA substitutions involved in the expression of G3m(5), G3m(6), G3m(15), G3m(16), G3m(21), G3m(24) and G3m(28) allotypes were then deduced, elucidating almost completely the determination of the G3m polymorphism at the DNA level. The molecular evolution of G3m haplotypes was investigated by a maximum likelihood phylogeny of IGHG3 sequences. Sequence clusters are shown to be G3m haplotype-specific, corroborating the Gm molecular model deduced from serology, and showing that populations differentiation is much more recent than G3m haplotypes differentiation. The widely distributed G3m(5,10,11,13,14) haplotype is likely to be ancestral to the other G3m haplotypes presently found at high frequencies in different continental areas.

  10. How Dusty Is Alpha Centauri? Excess or Non-excess over the Infrared Photospheres of Main-sequence Stars

    NASA Technical Reports Server (NTRS)

    Wiegert, J.; Liseau, R.; Thebault, P.; Olofsson, G.; Mora, A.; Bryden, G.; Marshall, J. P.; Eiroa, C.; Montesinos, B.; Ardila, D.; Augereau, J. C.; Aran, A. Bayo; Danchi, W. C.; del Burgo, C.; Ertel, S.; Fridlund, M. C. W.; Hajigholi, M.; Krivov, A. V.; Pilbratt, G. L.; Roberge, A.; White, G. J.; Wolf, S.

    2014-01-01

    Context. Debris discs around main-sequence stars indicate the presence of larger rocky bodies. The components of the nearby, solar-type binary Centauri have metallicities that are higher than solar, which is thought to promote giant planet formation. Aims. We aim to determine the level of emission from debris around the stars in the Cen system. This requires knowledge of their photospheres.Having already detected the temperature minimum, Tmin, of CenA at far-infrared wavelengths, we here attempt to do the same for the moreactive companion Cen B. Using the Cen stars as templates, we study the possible eects that Tmin may have on the detectability of unresolveddust discs around other stars. Methods.We used Herschel-PACS, Herschel-SPIRE, and APEX-LABOCA photometry to determine the stellar spectral energy distributions in thefar infrared and submillimetre. In addition, we used APEX-SHeFI observations for spectral line mapping to study the complex background around Cen seen in the photometric images. Models of stellar atmospheres and of particulate discs, based on particle simulations and in conjunctionwith radiative transfer calculations, were used to estimate the amount of debris around these stars. Results. For solar-type stars more distant than Cen, a fractional dust luminosity fd LdustLstar 2 107 could account for SEDs that do not exhibit the Tmin eect. This is comparable to estimates of fd for the Edgeworth-Kuiper belt of the solar system. In contrast to the far infrared,slight excesses at the 2:5 level are observed at 24 m for both CenA and B, which, if interpreted as due to zodiacal-type dust emission, wouldcorrespond to fd (13) 105, i.e. some 102 times that of the local zodiacal cloud. Assuming simple power-law size distributions of the dustgrains, dynamical disc modelling leads to rough mass estimates of the putative Zodi belts around the Cen stars, viz.4106 M$ of 4 to 1000 msize grains, distributed according to n(a) a3:5. Similarly, for filled-in Tmin

  11. The environmental impacts on the star formation main sequence: An Hα study of the newly discovered rich cluster at z = 1.52

    SciTech Connect

    Koyama, Yusei; Kodama, Tadayuki; Tadaki, Ken-ichi; Hayashi, Masao; Tanaka, Ichi; Shimakawa, Rhythm

    2014-07-01

    We report the discovery of a strong over-density of galaxies in the field of a radio galaxy at z = 1.52 (4C 65.22) based on our broadband and narrow-band (Hα) photometry with the Subaru Telescope. We find that Hα emitters are located in the outskirts of the density peak (cluster core) dominated by passive red-sequence galaxies. This resembles the situation in lower-redshift clusters, suggesting that the newly discovered structure is a well-evolved rich galaxy cluster at z = 1.5. Our data suggest that the color-density and stellar mass-density relations are already in place at z ∼ 1.5, mostly driven by the passive red massive galaxies residing within r{sub c} ≲ 200 kpc from the cluster core. These environmental trends almost disappear when we consider only star-forming (SF) galaxies. We do not find SFR-density or SSFR-density relations amongst SF galaxies, and the location of the SF main sequence does not significantly change with environment. Nevertheless, we find a tentative hint that star-bursting galaxies (up-scattered objects from the main sequence) are preferentially located in a small group at ∼1 Mpc away from the main body of the cluster. We also argue that the scatter of the SF main sequence could be dependent on the distance to the nearest neighboring galaxy.

  12. Zodiacal Exoplanets in Time (ZEIT). III. A Short-period Planet Orbiting a Pre-main-sequence Star in the Upper Scorpius OB Association

    NASA Astrophysics Data System (ADS)

    Mann, Andrew W.; Newton, Elisabeth R.; Rizzuto, Aaron C.; Irwin, Jonathan; Feiden, Gregory A.; Gaidos, Eric; Mace, Gregory N.; Kraus, Adam L.; James, David J.; Ansdell, Megan; Charbonneau, David; Covey, Kevin R.; Ireland, Michael J.; Jaffe, Daniel T.; Johnson, Marshall C.; Kidder, Benjamin; Vanderburg, Andrew

    2016-09-01

    We confirm and characterize a close-in ({P}{{orb}} = 5.425 days), super-Neptune sized ({5.04}-0.37+0.34 {R}\\oplus ) planet transiting K2-33 (2MASS J16101473-1919095), a late-type (M3) pre-main-sequence (11 Myr old) star in the Upper Scorpius subgroup of the Scorpius–Centaurus OB association. The host star has the kinematics of a member of the Upper Scorpius OB association, and its spectrum contains lithium absorption, an unambiguous sign of youth (\\lt 20 Myr) in late-type dwarfs. We combine photometry from K2 and the ground-based MEarth project to refine the planet’s properties and constrain the host star’s density. We determine K2-33’s bolometric flux and effective temperature from moderate-resolution spectra. By utilizing isochrones that include the effects of magnetic fields, we derive a precise radius (6%–7%) and mass (16%) for the host star, and a stellar age consistent with the established value for Upper Scorpius. Follow-up high-resolution imaging and Doppler spectroscopy confirm that the transiting object is not a stellar companion or a background eclipsing binary blended with the target. The shape of the transit, the constancy of the transit depth and periodicity over 1.5 yr, and the independence with wavelength rule out stellar variability or a dust cloud or debris disk partially occulting the star as the source of the signal; we conclude that it must instead be planetary in origin. The existence of K2-33b suggests that close-in planets can form in situ or migrate within ˜10 Myr, e.g., via interactions with a disk, and that long-timescale dynamical migration such as by Lidov–Kozai or planet–planet scattering is not responsible for all short-period planets.

  13. STAR FORMATION HISTORY OF A YOUNG SUPER-STAR CLUSTER IN NGC 4038/39: DIRECT DETECTION OF LOW-MASS PRE-MAIN SEQUENCE STARS

    SciTech Connect

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

    2010-02-20

    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 {approx}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.

  14. Zodiacal Exoplanets in Time (ZEIT). III. A Short-period Planet Orbiting a Pre-main-sequence Star in the Upper Scorpius OB Association

    NASA Astrophysics Data System (ADS)

    Mann, Andrew W.; Newton, Elisabeth R.; Rizzuto, Aaron C.; Irwin, Jonathan; Feiden, Gregory A.; Gaidos, Eric; Mace, Gregory N.; Kraus, Adam L.; James, David J.; Ansdell, Megan; Charbonneau, David; Covey, Kevin R.; Ireland, Michael J.; Jaffe, Daniel T.; Johnson, Marshall C.; Kidder, Benjamin; Vanderburg, Andrew

    2016-09-01

    We confirm and characterize a close-in ({P}{{orb}} = 5.425 days), super-Neptune sized ({5.04}-0.37+0.34 {R}\\oplus ) planet transiting K2-33 (2MASS J16101473-1919095), a late-type (M3) pre-main-sequence (11 Myr old) star in the Upper Scorpius subgroup of the Scorpius-Centaurus OB association. The host star has the kinematics of a member of the Upper Scorpius OB association, and its spectrum contains lithium absorption, an unambiguous sign of youth (\\lt 20 Myr) in late-type dwarfs. We combine photometry from K2 and the ground-based MEarth project to refine the planet’s properties and constrain the host star’s density. We determine K2-33’s bolometric flux and effective temperature from moderate-resolution spectra. By utilizing isochrones that include the effects of magnetic fields, we derive a precise radius (6%-7%) and mass (16%) for the host star, and a stellar age consistent with the established value for Upper Scorpius. Follow-up high-resolution imaging and Doppler spectroscopy confirm that the transiting object is not a stellar companion or a background eclipsing binary blended with the target. The shape of the transit, the constancy of the transit depth and periodicity over 1.5 yr, and the independence with wavelength rule out stellar variability or a dust cloud or debris disk partially occulting the star as the source of the signal; we conclude that it must instead be planetary in origin. The existence of K2-33b suggests that close-in planets can form in situ or migrate within ˜10 Myr, e.g., via interactions with a disk, and that long-timescale dynamical migration such as by Lidov-Kozai or planet-planet scattering is not responsible for all short-period planets.

  15. A High-resolution Multiband Survey of Westerlund 2 with the Hubble Space Telescope. II. Mass Accretion in the Pre-main-sequence Population

    NASA Astrophysics Data System (ADS)

    Zeidler, Peter; Grebel, Eva K.; Nota, Antonella; Sabbi, Elena; Pasquali, Anna; Tosi, Monica; Bonanos, Alceste Z.; Christian, Carol

    2016-10-01

    We present a detailed analysis of the pre-main-sequence (PMS) population of the young star cluster Westerlund 2 (Wd2), the central ionizing cluster of the H ii region RCW 49, using data from a high-resolution multiband survey with the Hubble Space Telescope. The data were acquired with the Advanced Camera for Surveys in the F555W, F814W, and F658N filters and with the Wide Field Camera 3 in the F125W, F160W, and F128N filters. We find a mean age of the region of 1.04 ± 0.72 Myr. The combination of dereddened F555W and F814W photometry in combination with F658N photometry allows us to study and identify stars with Hα excess emission. With a careful selection of 240 bona-fide PMS Hα excess emitters we were able to determine their Hα luminosity, which has a mean value L({{H}}α )=1.67× {10}-31 {{erg}} {{{s}}}-1. Using the PARSEC 1.2S isochrones to obtain the stellar parameters of the PMS stars, we determined a mean mass accretion rate {\\dot{M}}{{acc}}=4.43× {10}-8 {M}⊙ {{{yr}}}-1 per star. A careful analysis of the spatial dependence of the mass accretion rate suggests that this rate is ˜25% lower in the center of the two density peaks of Wd2 in close proximity to the luminous OB stars, compared to the Wd2 average. This rate is higher with increasing distance from the OB stars, indicating that the PMS accretion disks are being rapidly destroyed by the far-ultraviolet radiation emitted by the OB population.

  16. The Distances to Open Clusters from Main-sequence Fitting. V. Extension of Color Calibration and Test Using Cool and Metal-rich Stars in NGC 6791

    NASA Astrophysics Data System (ADS)

    An, Deokkeun; Terndrup, Donald M.; Pinsonneault, Marc H.; Lee, Jae-Woo

    2015-09-01

    We extend our effort to calibrate stellar isochrones in the Johnson-Cousins ({{BVI}}C) and the 2MASS ({{JHK}}s) filter systems based on observations of well-studied open clusters. Using cool main-sequence (MS) stars in Praesepe, we define empirical corrections to the Lejeune et al. color-effective temperature ({T}{eff}) relations down to {T}{eff}˜ 3600 {{K}}, complementing our previous work based on the Hyades and the Pleiades. We apply empirically corrected isochrones to existing optical and near-infrared photometry of cool ({T}{eff}≲ 5500 {{K}}) and metal-rich ([{Fe}/{{H}}]= +0.37) MS stars in NGC 6791. The current methodology relies on an assumption that color-{T}{eff} corrections are independent of metallicity, but we find that estimates of color excess and distance from color-magnitude diagrams with different color indices converge on each other at the precisely known metallicity of the cluster. Along with a satisfactory agreement with eclipsing binary data in the cluster, we view the improved internal consistency as a validation of our calibrated isochrones at super-solar metallicities. For very cool stars ({T}{eff}≲ 4800 {{K}}), however, we find that B - V colors of our models are systematically redder than the cluster photometry by ˜0.02 mag. We use color-{T}{eff} transformations from the infrared flux method and alternative photometry to examine a potential color-scale error in the input cluster photometry. After excluding B - V photometry of these cool MS stars, we derive E(B\\-\\V)=0.105+/- 0.014, [M/H]\\=\\+0.42+/- 0.07, {(m\\-\\M)}0=13.04+/- 0.08, and the age of 9.5 ± 0.3 Gyr for NGC 6791.

  17. The SCUBA-2 Cosmology Legacy Survey: galaxies in the deep 850 μm survey, and the star-forming `main sequence'

    NASA Astrophysics Data System (ADS)

    Koprowski, M. P.; Dunlop, J. S.; Michałowski, M. J.; Roseboom, I.; Geach, J. E.; Cirasuolo, M.; Aretxaga, I.; Bowler, R. A. A.; Banerji, M.; Bourne, N.; Coppin, K. E. K.; Chapman, S.; Hughes, D. H.; Jenness, T.; McLure, R. J.; Symeonidis, M.; Werf, P. van der

    2016-06-01

    We investigate the properties of the galaxies selected from the deepest 850-μm survey undertaken to date with (Submillimetre Common-User Bolometer Array 2) SCUBA-2 on the James Clerk Maxwell Telescope as part of the SCUBA-2 Cosmology Legacy Survey. A total of 106 sources (>5σ) were uncovered at 850 μm from an area of ≃150 arcmin2 in the centre of the COSMOS/UltraVISTA/Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field, imaged to a typical depth of σ850 ≃ 0.25 mJy. We utilize the available multifrequency data to identify galaxy counterparts for 80 of these sources (75 per cent), and to establish the complete redshift distribution for this sample, yielding bar{z} = 2.38± 0.09. We have also been able to determine the stellar masses of the majority of the galaxy identifications, enabling us to explore their location on the star formation rate:stellar mass (SFR:M*) plane. Crucially, our new deep 850-μm-selected sample reaches flux densities equivalent to SFR ≃ 100 M⊙ yr-1, enabling us to confirm that sub-mm galaxies form the high-mass end of the `main sequence' (MS) of star-forming galaxies at z > 1.5 (with a mean specific SFR of sSFR = 2.25 ± 0.19 Gyr-1 at z ≃ 2.5). Our results are consistent with no significant flattening of the MS towards high masses at these redshifts. However, our results add to the growing evidence that average sSFR rises only slowly at high redshift, resulting in log10sSFR being an apparently simple linear function of the age of the Universe.

  18. Sequencing, speech production, and selective effects of aging on phonological and morphological speech errors.

    PubMed

    MacKay, Donald G; James, Lori E

    2004-03-01

    To test age-linked predictions of node structure theory (NST) and other theories, young and older adults performed a task that elicited large numbers of phonological and morphological speech errors. Stimuli were visually presented words containing either /p/ or /b/, and participants changed the /p/ to /b/ or vice versa and produced the resulting word as quickly as possible. For example, the correct response was "bunk" for the stimulus PUNK, and "ripped" for RIBBED. Consistent with NST predictions, the elicited speech errors exhibited selective effects of aging. Some error types decreased with aging. For example, young adults produced more nonsequential substitution errors (as a percentage of total errors) than older adults (e.g., intended bills misproduced as "gills"). However, other error types remained constant or increased with aging. For example, older adults produced more omission errors than young adults, especially omissions involving inflectional endings (e.g. intended ripped misproduced as "np"). In addition, older adults exhibited special difficulties with 2 types of phonological and morphological sequencing processes.

  19. Lithofacies, Age, and Sequence Stratigraphy of the Carboniferous Lisburne Group in the Skimo Creek Area, Central Brooks Range

    USGS Publications Warehouse

    Dumoulin, Julie A.; Whalen, Michael T.; Harris, Anita G.

    2008-01-01

    The Lisburne Group, a mainly Carboniferous carbonate succession that is widely distributed across northern Alaska, contains notable amounts of oil and gas at Prudhoe Bay. Detailed studies of the Lisburne in the Skimo Creek area, central Brooks Range, delineate its lithofacies, age, conodont biofacies, depositional environments, and sequence stratigraphy and provide new data on its hydrocarbon source-rock and reservoir potential, as well as its thermal history, in this area. We have studied the Lisburne Group in two thrust sheets of the Endicott Mountains allochthon, herein called the Skimo and Tiglukpuk thrust sheets. The southern, Skimo Creek section, which is >900 m thick, is composed largely of even-bedded to nodular lime mudstone and wackestone intercalated with intervals of thin- to thick-bedded bioclastic packstone and grainstone. Some parts of the section are partially to completely dolomitized and (or) replaced by chert. A distinctive, 30-m-thick zone of black, organic-rich shale, lime mudstone, and phosphorite is exposed 170 m below the top of the Lisburne. The uppermost 40 m of section is also distinctive and made up of dark shale, lime mudstone, spiculite, and glauconitic grainstone. The northern, Tiglukpuk Creek section, which is similar to the Skimo Creek section but only ~760 m thick, includes more packstone and grainstone and less organic-rich shale. Analyses of conodonts and foraminifers indicate that both sections range in age from late Early Mississippian (Osagean) through Early Pennsylvanian (early Morrowan) and document a hiatus of at least 15 m.y. at the contact between the Lisburne and the overlying Siksikpuk Formation. No evidence of subaerial exposure was observed along this contact, which may represent a submarine erosional surface. Lithofacies and biofacies imply that the Lisburne Group in the study area was deposited mainly in midramp to outer-ramp settings. Deepest water strata are mud rich and formed below storm or fair-weather wave

  20. Three-dimensional simulations of near-surface convection in main-sequence stars. III. The structure of small-scale magnetic flux concentrations

    NASA Astrophysics Data System (ADS)

    Beeck, B.; Schüssler, M.; Cameron, R. H.; Reiners, A.

    2015-09-01

    Context. The convective envelopes of cool main-sequence stars harbour magnetic fields with a complex global and local structure. These fields affect the near-surface convection and the outer stellar atmospheres in many ways and are responsible for the observable magnetic activity of stars. Aims: Our aim is to understand the local structure in unipolar regions with moderate average magnetic flux density. These correspond to plage regions covering a substantial fraction of the surface of the Sun (and likely also the surface of other Sun-like stars) during periods of high magnetic activity. Methods: We analyse the results of 18 local-box magnetohydrodynamics simulations covering the upper layers of the convection zones and the photospheres of cool main-sequence stars of spectral types F to early M. The average vertical field in these simulations ranges from 20 to 500 G. Results: We find a substantial variation of the properties of the surface magnetoconvection between main-sequence stars of different spectral types. As a consequence of a reduced efficiency of the convective collapse of flux tubes, M dwarfs lack bright magnetic structures in unipolar regions of moderate field strength. The spatial correlation between velocity and the magnetic field as well as the lifetime of magnetic structures and their sizes relative to the granules vary significantly along the model sequence of stellar types. Movies associated to Fig. A.1 are available in electronic form at http://www.aanda.org

  1. Music as a Mnemonic to Learn Gesture Sequences in Normal Aging and Alzheimer’s Disease

    PubMed Central

    Moussard, Aline; Bigand, Emmanuel; Belleville, Sylvie; Peretz, Isabelle

    2014-01-01

    Strong links between music and motor functions suggest that music could represent an interesting aid for motor learning. The present study aims for the first time to test the potential of music to assist in the learning of sequences of gestures in normal and pathological aging. Participants with mild Alzheimer’s disease (AD) and healthy older adults (controls) learned sequences of meaningless gestures that were either accompanied by music or a metronome. We also manipulated the learning procedure such that participants had to imitate the gestures to-be-memorized in synchrony with the experimenter or after the experimenter during encoding. Results show different patterns of performance for the two groups. Overall, musical accompaniment had no impact on the controls’ performance but improved those of AD participants. Conversely, synchronization of gestures during learning helped controls but seemed to interfere with retention in AD. We discuss these findings regarding their relevance for a better understanding of auditory–motor memory, and we propose recommendations to maximize the mnemonic effect of music for motor sequence learning for dementia care. PMID:24860476

  2. Music as a mnemonic to learn gesture sequences in normal aging and Alzheimer's disease.

    PubMed

    Moussard, Aline; Bigand, Emmanuel; Belleville, Sylvie; Peretz, Isabelle

    2014-01-01

    Strong links between music and motor functions suggest that music could represent an interesting aid for motor learning. The present study aims for the first time to test the potential of music to assist in the learning of sequences of gestures in normal and pathological aging. Participants with mild Alzheimer's disease (AD) and healthy older adults (controls) learned sequences of meaningless gestures that were either accompanied by music or a metronome. We also manipulated the learning procedure such that participants had to imitate the gestures to-be-memorized in synchrony with the experimenter or after the experimenter during encoding. Results show different patterns of performance for the two groups. Overall, musical accompaniment had no impact on the controls' performance but improved those of AD participants. Conversely, synchronization of gestures during learning helped controls but seemed to interfere with retention in AD. We discuss these findings regarding their relevance for a better understanding of auditory-motor memory, and we propose recommendations to maximize the mnemonic effect of music for motor sequence learning for dementia care.

  3. Music as a mnemonic to learn gesture sequences in normal aging and Alzheimer's disease.

    PubMed

    Moussard, Aline; Bigand, Emmanuel; Belleville, Sylvie; Peretz, Isabelle

    2014-01-01

    Strong links between music and motor functions suggest that music could represent an interesting aid for motor learning. The present study aims for the first time to test the potential of music to assist in the learning of sequences of gestures in normal and pathological aging. Participants with mild Alzheimer's disease (AD) and healthy older adults (controls) learned sequences of meaningless gestures that were either accompanied by music or a metronome. We also manipulated the learning procedure such that participants had to imitate the gestures to-be-memorized in synchrony with the experimenter or after the experimenter during encoding. Results show different patterns of performance for the two groups. Overall, musical accompaniment had no impact on the controls' performance but improved those of AD participants. Conversely, synchronization of gestures during learning helped controls but seemed to interfere with retention in AD. We discuss these findings regarding their relevance for a better understanding of auditory-motor memory, and we propose recommendations to maximize the mnemonic effect of music for motor sequence learning for dementia care. PMID:24860476

  4. PHOTOMETRIC DETERMINATION OF THE MASS ACCRETION RATES OF PRE-MAIN-SEQUENCE STARS. I. METHOD AND APPLICATION TO THE SN 1987A FIELD

    SciTech Connect

    De Marchi, Guido; Panagia, Nino; Romaniello, Martino E-mail: panagia@stsci.ed

    2010-05-20

    We have developed and successfully tested a new self-consistent method to reliably identify pre-main-sequence (PMS) objects actively undergoing mass accretion in a resolved stellar population, regardless of their age. The method does not require spectroscopy and combines broadband V and I photometry with narrowband H{alpha} imaging to (1) identify all stars with excess H{alpha} emission, (2) convert the excess H{alpha} magnitude into H{alpha} luminosity L(H{alpha}), (3) estimate the H{alpha} emission equivalent width, (4) derive the accretion luminosity L{sub acc} from L(H{alpha}), and finally (5) obtain the mass accretion rate M-dot{sub acc} from L{sub acc} and the stellar parameters (mass and radius). By selecting stars with an accuracy of 15% or better in the H{alpha} photometry, the statistical uncertainty on the derived M-dot{sub acc} is typically {approx_lt}17% and is dictated by the precision of the H{alpha} photometry. Systematic uncertainties, of up to a factor of 3 on the value of M-dot{sub acc}, are caused by our incomplete understanding of the physics of the accretion process and affect all determinations of the mass accretion rate, including those based on a spectroscopic H{alpha} line analysis. As an application of our method, we study the accretion process in a field of 9.16 arcmin{sup 2} around SN 1987A, using existing Hubble Space Telescope photometry. We identify as bona fide PMS stars a total of 133 objects with a H{alpha} excess above the 4{sigma} level and a median age of 13.5 Myr. Their median mass accretion rate of 2.6 x 10{sup -8} M{sub sun} yr{sup -1} is in excellent agreement with previous determinations based on the U-band excess of the stars in the same field, as well as with the value measured for G-type PMS stars in the Milky Way. The accretion luminosity of these PMS objects shows a strong dependence on their distance from a group of hot massive stars in the field and suggests that the ultraviolet radiation of the latter is rapidly

  5. Effects of Age and Estrogen on Skeletal Gene Expression in Humans as Assessed by RNA Sequencing

    PubMed Central

    Fujita, Koji; Nicks, Kristy M.; Cunningham, Julie M.; Atkinson, Elizabeth J.; Therneau, Terry M.; McCready, Louise K.; Peterson, James M.; Drake, Matthew T.; Monroe, David G.; Khosla, Sundeep

    2015-01-01

    Precise delineation of the specific genes and pathways altered with aging and estrogen (E) therapy may lead to new skeletal biomarkers and the development of novel bone therapeutics. Previous human bone studies, however, have been limited by only examining pre-specified genes and pathways. High-throughput RNA sequencing (RNAseq), on the other hand, offers an unbiased approach to examine the entire transcriptome. Here we present an RNAseq analysis of human bone samples, obtained from iliac crest needle biopsies, to yield the first in vivo interrogation of all genes and pathways that may be altered in bone with aging and E therapy in humans. 58 healthy women were studied, including 19 young women (mean age ± SD, 30.3 ± 5.4 years), 19 old women (73.1 ± 6.6 years), and 20 old women treated with 3 weeks of E therapy (70.5 ± 5.2 years). Using generally accepted criteria (false discovery rate [q] < 0.10), aging altered a total of 678 genes and 12 pathways, including a subset known to regulate bone metabolism (e.g., Notch). Interestingly, the LEF1 transcription factor, which is a classical downstream target of the Wnt/β-catenin signaling pathway, was significantly downregulated in the bones from the old versus young women; consistent with this, LEF1 binding sites were significantly enriched in the promoter regions of the differentially expressed genes in the old versus young women, suggesting that aging was associated with alterations in Wnt signaling in bone. Further, of the 21 unique genes altered in bone by E therapy, the expression of INHBB (encoding for the inhibin, beta B polypeptide), which decreased with aging (by 0.6-fold), was restored to young adult levels in response to E therapy. In conclusion, our data demonstrate that aging alters a substantial portion of the skeletal transcriptome, whereas E therapy appears to have significant, albeit less wide-ranging effects. These data provide a valuable resource for the potential identification of novel biomarkers

  6. Estimation of submarine mass failure probability from a sequence of deposits with age dates

    USGS Publications Warehouse

    Geist, Eric L.; Chaytor, Jason D.; Parsons, Thomas E.; ten Brink, Uri S.

    2013-01-01

    The empirical probability of submarine mass failure is quantified from a sequence of dated mass-transport deposits. Several different techniques are described to estimate the parameters for a suite of candidate probability models. The techniques, previously developed for analyzing paleoseismic data, include maximum likelihood and Type II (Bayesian) maximum likelihood methods derived from renewal process theory and Monte Carlo methods. The estimated mean return time from these methods, unlike estimates from a simple arithmetic mean of the center age dates and standard likelihood methods, includes the effects of age-dating uncertainty and of open time intervals before the first and after the last event. The likelihood techniques are evaluated using Akaike’s Information Criterion (AIC) and Akaike’s Bayesian Information Criterion (ABIC) to select the optimal model. The techniques are applied to mass transport deposits recorded in two Integrated Ocean Drilling Program (IODP) drill sites located in the Ursa Basin, northern Gulf of Mexico. Dates of the deposits were constrained by regional bio- and magnetostratigraphy from a previous study. Results of the analysis indicate that submarine mass failures in this location occur primarily according to a Poisson process in which failures are independent and return times follow an exponential distribution. However, some of the model results suggest that submarine mass failures may occur quasiperiodically at one of the sites (U1324). The suite of techniques described in this study provides quantitative probability estimates of submarine mass failure occurrence, for any number of deposits and age uncertainty distributions.

  7. A search for pre-main-sequence stars in high-latitude molecular clouds. 3: A survey of the Einstein database

    NASA Technical Reports Server (NTRS)

    Caillault, Jean-Pierre; Magnani, Loris; Fryer, Chris

    1995-01-01

    In order to discern whether the high-latitude molecular clouds are regions of ongoing star formation, we have used X-ray emission as a tracer of youthful stars. The entire Einstein database yields 18 images which overlap 10 of the clouds mapped partially or completely in the CO (1-0) transition, providing a total of approximately 6 deg squared of overlap. Five previously unidentified X-ray sources were detected: one has an optical counterpart which is a pre-main-sequence (PMS) star, and two have normal main-sequence stellar counterparts, while the other two are probably extragalactic sources. The PMS star is located in a high Galactic latitude Lynds dark cloud, so this result is not too suprising. The translucent clouds, though, have yet to reveal any evidence of star formation.

  8. A Planet in an 840 Day Orbit around a Kepler Main-sequence A Star Found from Phase Modulation of Its Pulsations

    NASA Astrophysics Data System (ADS)

    Murphy, Simon J.; Bedding, Timothy R.; Shibahashi, Hiromoto

    2016-08-01

    We have detected a 12 M {}{Jup} planet orbiting in or near the habitable zone of a main-sequence A star via the pulsational phase shifts induced by orbital motion. The planet has an orbital period of 840 ± 20 days and an eccentricity of 0.15. All known planets orbiting main-sequence A stars have been found via the transit method or by direct imaging. The absence of astrometric or radial velocity detections of planets around these hosts makes ours the first discovery using the orbital motion. It is also the first A star known to host a planet within 1σ of the habitable zone. We find evidence for planets in a large fraction of the parameter space where we are able to detect them. This supports the idea that A stars harbor high-mass planets in wide orbits.

  9. A search for pre-main sequence stars in the high-latitude molecular clouds. II - A survey of the Einstein database

    NASA Technical Reports Server (NTRS)

    Caillault, Jean-Pierre; Magnani, Loris

    1990-01-01

    The preliminary results are reported of a survey of every EINSTEIN image which overlaps any high-latitude molecular cloud in a search for X-ray emitting pre-main sequence stars. This survey, together with complementary KPNO and IRAS data, will allow the determination of how prevalent low mass star formation is in these clouds in general and, particularly, in the translucent molecular clouds.

  10. Erratum: From the Top to the Bottom of the Main Sequence: A Complete Mass Function of the Young Open Cluster M35

    NASA Astrophysics Data System (ADS)

    Barrado y Navascués, David; Stauffer, John R.; Bouvier, Jerôme; Martín, Eduardo L.

    2001-07-01

    In the paper ``From the Top to the Bottom of the Main Sequence: A Complete Mass Function of the Young Open Cluster M35'' by David Barrado y Navascués, John R. Stauffer, Jerôme Bouvier, and Eduardo L. Martín (ApJ, 546, 1006 [2001]), Table 3 contains several typographical errors. These errors affect neither the discussion and conclusions nor the figures. The corrected Table 3 is presented below.

  11. Testing the companion hypothesis for the origin of the X-ray emission from intermediate-mass main-sequence stars

    NASA Astrophysics Data System (ADS)

    Stelzer, B.; Huélamo, N.; Micela, G.; Hubrig, S.

    2006-06-01

    Context: .The X-ray emission from B-type main-sequence stars is a longstanding mystery in stellar coronal research. Since there is no theory at hand that explains intrinsic X-ray emission from intermediate-mass main-sequence stars, the observations have often been interpreted in terms of (unknown) late-type magnetically active companion stars. Aims: .Resolving the hypothesized companions requires high spatial resolution observations in the infrared and in X-rays. We use Chandra imaging observations to spatially resolve a sample of main-sequence B-type stars with recently discovered companions at arcsecond separation. Methods: .Our strategy is to search for X-ray emission at the position of both the B-type primary and the faint companion. Results: .We find that all spatially resolved companions are X-ray emitters, but seven out of eleven intermediate-mass stars are also X-ray sources. If this emission is interpreted in terms of additional sub-arcsecond or spectroscopic companions, this implies a high multiplicity of B-type stars. Firm results on B star multiplicity pending, the alternative, that B stars produce intrinsic X-rays, cannot be discarded. An appropriate scenario would be a magnetically confined wind, as suggested for the X-ray emission of the magnetic Ap star IQ Aur. However, the only Ap star in the Chandra sample is not detected in X-rays, and therefore does not support this picture.

  12. Does the upper main sequence extend across the whole H-R diagram. [radiative opacities of stellar evolution models

    NASA Technical Reports Server (NTRS)

    Stothers, R.; Chin, C.-W.

    1977-01-01

    The effect of using Carson's (1976) radiative opacities in evolutionary sequences of stellar models has been studied over the mass range from 7 to 60 solar masses. The opacities are very large in the outer part of the envelope and induce such enormous radii for masses greater than about 30 solar masses for a heavy-element fraction of 0.02 or about 20 solar masses for a heavy-element fraction of 0.04 that the evolutionary tracks during the phase of core hydrogen burning extend across the whole H-R diagram. The choice of the Schwarschild or Ledoux criterion for convection makes very little difference for the behavior of the tracks. Evolution through the effective-temperature range (in logarithms) of 3.6 to 4.0 occurs in all cases on a rapid (secular) time scale. Core helium burning takes place exclusively in the red-supergiant configuration for stellar masses exceeding 8 solar masses (heavy-element fraction of 0.02) or 6 solar masses (heavy-element fraction of 0.04). These stellar models seem to be in significantly better agreement with the observed distribution of bright stars on the H-R diagram than are the older models based on the Cox-Stewart opacities. It can be inferred that a large envelope opacity (e.g., Carson's) exists and that substantial mass loss takes place in very massive late-type supergiants.

  13. What is the main driver of ageing in long-lived winter honeybees: antioxidant enzymes, innate immunity, or vitellogenin?

    PubMed

    Aurori, Cristian M; Buttstedt, Anja; Dezmirean, Daniel S; Mărghitaş, Liviu A; Moritz, Robin F A; Erler, Silvio

    2014-06-01

    To date five different theories compete in explaining the biological mechanisms of senescence or ageing in invertebrates. Physiological, genetical, and environmental mechanisms form the image of ageing in individuals and groups. Social insects, especially the honeybee Apis mellifera, present exceptional model systems to study developmentally related ageing. The extremely high phenotypic plasticity for life expectancy resulting from the female caste system provides a most useful system to study open questions with respect to ageing. Here, we used long-lived winter worker honeybees and measured transcriptional changes of 14 antioxidative enzyme, immunity, and ageing-related (insulin/insulin-like growth factor signaling pathway) genes at two time points during hibernation. Additionally, worker bees were challenged with a bacterial infection to test ageing- and infection-associated immunity changes. Gene expression levels for each group of target genes revealed that ageing had a much higher impact than the bacterial challenge, notably for immunity-related genes. Antimicrobial peptide and antioxidative enzyme genes were significantly upregulated in aged worker honeybees independent of bacterial infections. The known ageing markers vitellogenin and IlP-1 were opposed regulated with decreasing vitellogenin levels during ageing. The increased antioxidative enzyme and antimicrobial peptide gene expression may contribute to a retardation of senescence in long-lived hibernating worker honeybees.

  14. A Canis Major Overdensity Imaging Survey. I. Stellar Content and Star-Count Maps: A Distinctly Elongated Body of Main-Sequence Stars

    NASA Astrophysics Data System (ADS)

    Butler, D. J.; Martínez-Delgado, D.; Rix, H.-W.; Peñarrubia, J.; de Jong, J. T. A.

    2007-05-01

    We present the first results from a large-area (~80deg×20deg), sparsely sampled, two-filter (B and R) imaging survey toward the Canis Major stellar overdensity, which is claimed to be a disrupting Milky Way satellite galaxy. Using stellar color-magnitude diagrams reaching to B~22 mag, we provide a first delineation of its surface density distribution using main-sequence stars. It is located below the Galactic midplane, and can be discerned to at least b=-15deg. Its projected shape is highly elongated, nearly parallel to the Galactic plane, with an axis ratio of at least 5:1, substantially more so than what Martin and coworkers originally found. We also provide a first map of a prominent overdensity of blue, presumably younger main-sequence stars, which extends in latitude to b~-10deg. We estimate an upper limit on the line-of-sight depth σlos of the old population based on the main-sequence width, obtaining σlos<1.8+/-0.3 kpc at an adopted Dsolar=7.5+/-1 kpc. For the young stellar population, we find σlos<1.5 kpc. The overall picture presented is one of a young stellar population that is less extended, both in terms of its line-of-sight depth and angular size, than the older population. While the data provide no firm arguments against an out-of-plane spiral arm interpretation, the data provide clear implications for others: (1) We infer from the strong elongation of the overdensity in longitude, and simulations in the literature, that the CMa overdensity is unlikely to be a gravitationally bound system at the present epoch, but may well be just a recently disrupted satellite remnant. The possible ``flattening'' of the young main-sequence population may, however, be a complexity for the satellite origin. (2) Based on modeling, the line-of-sight depth of the main-sequence overdensity in old stars is clearly inconsistent with published locally axisymmetric descriptions of the warped Galactic disk, such as those considered by Momany and coworkers. Without detailed

  15. X-Ray Properties of Low-mass Pre-main Sequence Stars in the Orion Trapezium Cluster

    NASA Astrophysics Data System (ADS)

    Schulz, Norbert S.; Huenemoerder, David P.; Günther, Moritz; Testa, Paola; Canizares, Claude R.

    2015-09-01

    The Chandra HETG Orion Legacy Project (HOLP) is the first comprehensive set of observations of a very young massive stellar cluster that provides high-resolution X-ray spectra of very young stars over a wide mass range (0.7-2.3 {M}⊙ ). In this paper, we focus on the six brightest X-ray sources with T Tauri stellar counterparts that are well-characterized at optical and infrared wavelengths. All stars show column densities which are substantially smaller than expected from optical extinction, indicating that the sources are located on the near side of the cluster with respect to the observer as well as that these stars are embedded in more dusty environments. Stellar X-ray luminosities are well above 1031 erg s-1, in some cases exceeding 1032 erg s-1 for a substantial amount of time. The stars during these observations show no flares but are persistently bright. The spectra can be well fit with two temperature plasma components of 10 MK and 40 MK, of which the latter dominates the flux by a ratio 6:1 on average. The total emission measures range between 3-8 × 1054 cm-3 and are comparable to active coronal sources. The fits to the Ne ix He-Like K-shell lines indicate forbidden to inter-combination line ratios consistent with the low-density limit. Observed abundances compare well with active coronal sources underlying the coronal nature of these sources. The surface flux in this sample of 0.6-2.3 {M}⊙ classical T Tauri stars shows that coronal activity increases significantly between ages 0.1 and 10 Myr. The results demonstrate the power of X-ray line diagnostics to study coronal properties of T Tauri stars in young stellar clusters.

  16. Discovering novel microRNAs and age-related nonlinear changes in rat brains using deep sequencing.

    PubMed

    Yin, Lanxuan; Sun, Yubai; Wu, Jinfeng; Yan, Siyu; Deng, Zhenglu; Wang, Jun; Liao, Shenke; Yin, Dazhong; Li, Guolin

    2015-02-01

    Elucidating the molecular mechanisms of brain aging remains a significant challenge for biogerontologists. The discovery of gene regulation by microRNAs (miRNAs) has added a new dimension for examining this process; however, the full complement of miRNAs involved in brain aging is still not known. In this study, miRNA profiles of young, adult, and old rats were obtained to evaluate molecular changes during aging. High-throughput deep sequencing revealed 547 known and 171 candidate novel miRNAs that were differentially expressed among groups. Unexpectedly, miRNA expression did not decline progressively with advancing age; moreover, genes targeted by age-associated miRNAs were predicted to be involved in biological processes linked to aging and neurodegenerative diseases. These findings provide novel insight into the molecular mechanisms underlying brain aging and a resource for future studies on age-related brain disorders.

  17. Whole exome sequencing of extreme age-related macular degeneration phenotypes

    PubMed Central

    Sardell, Rebecca J.; Bailey, Jessica N Cooke; Courtenay, Monique D.; Whitehead, Patrice; Laux, Reneé A.; Adams, Larry D.; Fortun, Jorge A.; Brantley, Milam A.; Kovach, Jaclyn L.; Schwartz, Stephen G.; Agarwal, Anita; Scott, William K.; Haines, Jonathan L.

    2016-01-01

    Purpose Demographic, environmental, and genetic risk factors for age-related macular degeneration (AMD) have been identified; however, a substantial portion of the variance in AMD disease risk and heritability remains unexplained. To identify AMD risk variants and generate hypotheses for future studies, we performed whole exome sequencing for 75 individuals whose phenotype was not well predicted by their genotype at known risk loci. We hypothesized that these phenotypically extreme individuals were more likely to carry rare risk or protective variants with large effect sizes. Methods A genetic risk score was calculated in a case–control set of 864 individuals (467 AMD cases, 397 controls) based on 19 common (≥1% minor allele frequency, MAF) single nucleotide variants previously associated with the risk of advanced AMD in a large meta-analysis of advanced cases and controls. We then selected for sequencing 39 cases with bilateral choroidal neovascularization with the lowest genetic risk scores to detect risk variants and 36 unaffected controls with the highest genetic risk score to detect protective variants. After minimizing the influence of 19 common genetic risk loci on case-control status, we targeted single variants of large effect and the aggregate effect of weaker variants within genes and pathways. Single variant tests were conducted on all variants, while gene-based and pathway analyses were conducted on three subsets of data: 1) rare (≤1% MAF in the European population) stop, splice, or damaging missense variants, 2) all rare variants, and 3) all variants. All analyses controlled for the effects of age and sex. Results No variant, gene, or pathway outside regions known to be associated with risk for advanced AMD reached genome-wide significance. However, we identified several variants with substantial differences in allele frequency between cases and controls with strong additive effects on affection status after controlling for age and sex

  18. Whole exome sequencing of extreme age-related macular degeneration phenotypes

    PubMed Central

    Sardell, Rebecca J.; Bailey, Jessica N Cooke; Courtenay, Monique D.; Whitehead, Patrice; Laux, Reneé A.; Adams, Larry D.; Fortun, Jorge A.; Brantley, Milam A.; Kovach, Jaclyn L.; Schwartz, Stephen G.; Agarwal, Anita; Scott, William K.; Haines, Jonathan L.

    2016-01-01

    Purpose Demographic, environmental, and genetic risk factors for age-related macular degeneration (AMD) have been identified; however, a substantial portion of the variance in AMD disease risk and heritability remains unexplained. To identify AMD risk variants and generate hypotheses for future studies, we performed whole exome sequencing for 75 individuals whose phenotype was not well predicted by their genotype at known risk loci. We hypothesized that these phenotypically extreme individuals were more likely to carry rare risk or protective variants with large effect sizes. Methods A genetic risk score was calculated in a case–control set of 864 individuals (467 AMD cases, 397 controls) based on 19 common (≥1% minor allele frequency, MAF) single nucleotide variants previously associated with the risk of advanced AMD in a large meta-analysis of advanced cases and controls. We then selected for sequencing 39 cases with bilateral choroidal neovascularization with the lowest genetic risk scores to detect risk variants and 36 unaffected controls with the highest genetic risk score to detect protective variants. After minimizing the influence of 19 common genetic risk loci on case-control status, we targeted single variants of large effect and the aggregate effect of weaker variants within genes and pathways. Single variant tests were conducted on all variants, while gene-based and pathway analyses were conducted on three subsets of data: 1) rare (≤1% MAF in the European population) stop, splice, or damaging missense variants, 2) all rare variants, and 3) all variants. All analyses controlled for the effects of age and sex. Results No variant, gene, or pathway outside regions known to be associated with risk for advanced AMD reached genome-wide significance. However, we identified several variants with substantial differences in allele frequency between cases and controls with strong additive effects on affection status after controlling for age and sex

  19. Observation and modelling of main-sequence star chromospheres - XIV. Rotation of dM1 stars

    NASA Astrophysics Data System (ADS)

    Houdebine, E. R.

    2010-09-01

    We have measured v sin i for a selected sample of dM1-type stars. We give 114 measurements of v sin i for 88 different stars, and six upper detection limits. These are the first measurements of v sin i for most of the stars studied here. This represents the largest sample of v sin i measurements for M dwarfs at a given spectral type. For these measurements, we used four different spectrographs: HARPS (ESO), SOPHIE (OHP), ÉLODIE (OHP) and UVES (ESO). Two of these spectrographs (HARPS and SOPHIE) are particularly stable in wavelength since they were designed for exoplanet searches. We measured v sin i down to an accuracy of 0.3kms-1 for the highest resolution spectrographs and a detection limit of about 1kms-1. We show that this unprecedented accuracy for M dwarfs in our data set is possible because all the targets have the same spectral type. This is an advantage and it facilitates the determination of the narrowest line profiles for v sin i ~ 0. Although it is possible to derive the zero-point profiles using several spectral types at a time. These values were combined with other measurements taken from the literature. The total sample represents detected rotation for 100 stars (10 dM1e and 90 dM1 stars). We confirm our finding of Paper VII that the distribution of the projected rotation period is bimodal for dM1 stars with a much larger sample, i.e. there are two groups of stars: the fast rotators with P/sin i ~ 4.5d and the slow rotators with P/sin i ~ 14.4d. There is a gap between these two groups. We find that the distribution of stars as a function of P/sin i has two very abrupt cuts, below 10d and above 18d. There are very few stars observed out of this range 10-18d. We also observe that the distribution increases slightly from 18 to 10d. We find that the M1 subdwarfs (very low metallicity dwarfs) rotate with an average period of P/sin i ~ 7.2d, which is about twice faster as the main group of normal M1 dwarfs. We also find a correlation for P/sin i to

  20. Preliminary fission track ages for samples from western Maine: Implications for the low temperature thermal history of the region

    SciTech Connect

    Lux, D.R. . Dept. of Geological Sciences); Johnson, K. )

    1992-01-01

    In order to elucidate the low temperature cooling history of the region, 12 preliminary samples from a N-S traverse from the central Sebago batholith to the Chain of Ponds pluton were selected for fission track dating. The range of Ar-40/Ar-39 ages from the selected samples is 140 Ma (371--231 Ma) for biotites, 63 Ma (304--241 Ma) for muscovites and 61 Ma (375--304 Ma) for hornblendes. Twelve samples were dated by the external detector method and yield ages between 114 and 79 Ma. The southern most samples from the Sebago batholith and Songo pluton, within the highest metamorphic zones, are the youngest and range from 101 to 79 Ma. Those from the Mooselookmeguntic and Chain of Ponds plutons, within lower metamorphic zones, vary between 114 and 92 Ma. This general discordance trend is similar but of much smaller magnitude than the regional pattern of Ar-40/Ar-39 cooling ages. The much smaller range of apatite ages than biotite ages suggests that large differences in the thermal regime across of the region during Late Paleozoic time had largely been erased by the Early Cretaceous. The new fission track ages are interpreted to represent regional cooling through the apatite closure temperature, assumed to be ca 100 C. Young apatite ages may be the result of a regional thermal disturbance related to the intrusion of magmas of the White Mountains Plutonic Suite, as the youngest plutons are similar in age to the apatites. Alternatively, they could be the result of regional exhumation of the Acadian orogen. The authors conclude that the latter interpretation is more consistent with their data and attribute the ages to time of regional exhumation and uplift through the apatite closure temperature.

  1. Linear Relation for Wind-blown Bubble Sizes of Main-sequence OB Stars in a Molecular Environment and Implication for Supernova Progenitors

    NASA Astrophysics Data System (ADS)

    Chen, Yang; Zhou, Ping; Chu, You-Hua

    2013-05-01

    We find a linear relationship between the size of a massive star's main-sequence bubble in a molecular environment and the star's initial mass: R b ≈ 1.22 M/M ⊙ - 9.16 pc, assuming a constant interclump pressure. Since stars in the mass range of 8 to 25-30 M ⊙ will end their evolution in the red supergiant phase without launching a Wolf-Rayet wind, the main-sequence wind-blown bubbles are mainly responsible for the extent of molecular gas cavities, while the effect of the photoionization is comparatively small. This linear relation can thus be used to infer the masses of the massive star progenitors of supernova remnants (SNRs) that are discovered to evolve in molecular cavities, while few other means are available for inferring the properties of SNR progenitors. We have used this method to estimate the initial masses of the progenitors of eight SNRs: Kes 69, Kes 75, Kes 78, 3C 396, 3C 397, HC 40, Vela, and RX J1713-3946.

  2. LINEAR RELATION FOR WIND-BLOWN BUBBLE SIZES OF MAIN-SEQUENCE OB STARS IN A MOLECULAR ENVIRONMENT AND IMPLICATION FOR SUPERNOVA PROGENITORS

    SciTech Connect

    Chen Yang; Zhou Ping; Chu Youhua

    2013-05-20

    We find a linear relationship between the size of a massive star's main-sequence bubble in a molecular environment and the star's initial mass: R{sub b} Almost-Equal-To 1.22 M/M{sub Sun} - 9.16 pc, assuming a constant interclump pressure. Since stars in the mass range of 8 to 25-30 M{sub Sun} will end their evolution in the red supergiant phase without launching a Wolf-Rayet wind, the main-sequence wind-blown bubbles are mainly responsible for the extent of molecular gas cavities, while the effect of the photoionization is comparatively small. This linear relation can thus be used to infer the masses of the massive star progenitors of supernova remnants (SNRs) that are discovered to evolve in molecular cavities, while few other means are available for inferring the properties of SNR progenitors. We have used this method to estimate the initial masses of the progenitors of eight SNRs: Kes 69, Kes 75, Kes 78, 3C 396, 3C 397, HC 40, Vela, and RX J1713-3946.

  3. New [sup 40]Ar/[sup 39]Ar mica ages from eastern New Hampshire and southern Maine: Implications for the exhumation history of the region

    SciTech Connect

    Lux, D.R.; West, D.P. Jr. . Dept. of Geological Science)

    1993-03-01

    It has long been recognized that micas from the high-grade metamorphic terrane of Maine and New Hampshire have anomalously young K-Ar ages. Furthermore, ages show systematic spatial patterns. Samples from western New Hampshire are youngest and become progressively older towards the east. In the Kearsarge-Central Maine Synclinorium (KCMS) of western Maine, ages are oldest along the northern terminus of high grade metamorphism and become progressively younger towards the southwest. In order to understand this peculiar relationship, micas from 20 sites in eastern New Hampshire and southern Maine were dated by the [sup 40]Ar/[sup 39]Ar method. The following relationships are observed: (1) Micas from the KCMS of southern New Hampshire have Permo-Carboniferous ages and coexisting micas are highly discordant, (2) micas from within or very near the Massabesic Gneiss Complex have young ages ([approximately]240--250 Ma) and show little to no discordance, (3) with one exception, micas from south of the Sebago batholith in Maine are also young ([approximately]240--250 Ma) and show little to no discordance. North of the Sebago batholith the transition to older micas is gradual. Mica ages from the Massabesic Gneiss Complex are younger than in surrounding regions and the transition to older ages roughly coincides with the Campbell Hill and Flint Hill faults. Outside the zone of young micas, cooling curves are concave upward for the same temperature interval. The young micas are concordant indicating rapid cooling but they are [approximately]40 Ma younger than the time of Late Paleozoic metamorphism. Therefore the young ages cannot be explained by rapid post-metamorphic cooling. The authors believe the accelerated cooling is the result of regional tectonic exhumation related to the earliest stages of rifting associated with opening of the Atlantic.

  4. Low-resolution spectroscopy of main sequence stars belonging to 12 Galactic globular clusters. I. CH and CN band strength variations

    NASA Astrophysics Data System (ADS)

    Pancino, E.; Rejkuba, M.; Zoccali, M.; Carrera, R.

    2010-12-01

    Context. Globular clusters show star-to-star abundance variations for light elements that are not yet well understood. The preferred explanation involves a self-enrichment scenario, within which two subsequent generations of stars co-exist in globular clusters. Observations of chemical abundances in the main sequence and sub-giant branch stars allow us to investigate the signature of this chemically processed material without the complicating effects caused by stellar evolution and internal mixing. Aims: Our main goal is to investigate the carbon-nitrogen anti-correlation with low-resolution spectroscopy of 20-50 stars fainter than the first dredge-up in seven Galactic globular clusters (NGC 288, NGC 1851, NGC 5927, NGC 6352, NGC 6388, and Pal 12) with different properties. We complemented our observations with 47 Tuc archival data, with four additional clusters from the literature (M 15, M 22, M 55, NGC 362), and with additional literature data on NGC 288. Methods: In this first paper, we measured the strengh of the CN and CH band indices, which correlate with the N and C abundances, and we investigated the anti-correlation and bimodality of these indices. We compared rCN, the ratio of stars belonging to the CN-strong and weak groups, with 15 different cluster parameters. Results: We clearly see bimodal anti-correlation of the CH and CN band stregths in the metal-rich clusters (Pal 12, 47 Tuc, NGC 6352, NGC 5927). Only M 15 among the metal-poor clusters shows a clearly bimodal anti-correlation. We found weak correlations (sligthly above 1σ) of rCN with the cluster orbital parameters, present-day total mass, cluster concentration, and age. Conclusions: Our findings support the self-enrichment scenario, and suggest that the occurrence of more than two major generations of stars in a GGC should be rare. Small additional generations (<10-20% of the total) would be difficult to detect with our samples. The first generation, which corresponds to the CN-weak stars

  5. Frontostriatal and mediotemporal lobe contributions to implicit higher-order spatial sequence learning declines in aging and Parkinson's disease.

    PubMed

    Schendan, Haline E; Tinaz, Sule; Maher, Stephen M; Stern, Chantal E

    2013-04-01

    Sequence learning depends on the striatal system, but recent findings also implicate the mediotemporal lobe (MTL) system. Schendan, Searl, Melrose, and Stern (2003) found higher-order associative, learning-related activation in the striatum, dorsolateral prefrontal cortex, and the MTL during the early acquisition phase of both implicit and explicit variants of a serial response time task. This functional MRI (fMRI) study capitalized on this task to determine how changes in MTL function observed in aging and compromised frontostriatal function characteristic of patients with Parkinson's disease (PD) impacts sequence learning and memory under implicit instructions. Brain activity was compared between "sequence" and "random" conditions in 12 nondemented patients with PD and education- and gender-matched healthy control participants of whom 12 were age matched (MC) and 14 were younger (YC). Behaviorally, sequence-specific learning of higher-order associations was reduced with aging and changed further with PD and resulted primarily in implicit knowledge in the older participants. fMRI revealed reduced intensity and extent of sequence learning-related activation in older relative to younger people in frontostriatal circuits and the MTL. This was because signal was greater for the sequence than random condition in younger people, whereas older people, especially those with PD, showed the opposite pattern. Both older groups also showed increased activation to the task itself relative to baseline fixation. In addition, right MTL showed hypoactivation and left MTL hyperactivation in PD relative to the MC group. The results suggest changes in frontostriatal and MTL activity occur during aging that affect task-related activity and the initial acquisition phase of implicit higher-order sequence learning. In addition, the results suggest that Parkinson's disease adversely affects processes in the MTL including sequence learning and memory.

  6. Artificial Aging Effects on Cryogenic Fracture Toughness of the Main Structural Alloy for the Super Lightweight Tank

    NASA Technical Reports Server (NTRS)

    Chen, P. S.; Stanton, W. P.

    2002-01-01

    In 1996, Marshall Space Flight Center developed a multistep heating rate-controlled (MSRC) aging technique that significantly enhanced cryogenic fracture toughness (CFT) and reduced the statistical spread of fracture toughness values in alloy 2195 by controlling the location and size of strengthening precipitate T1. However, it could not be readily applied to flight-related hardware production, primarily because large-scale production furnaces are unable to maintain a heating rate of 0.6 C (1 F)/hr. In August 1996, a new program was initiated to determine whether the MSRC aging treatment could be further modified to facilitate its implementation to flight hardware production. It was successfully redesigned into a simplified two-step aging treatment consisting of 132 C (270 F)/20 hr + 138 C (280 F)/40 hr. Results indicated that two-step aging can achieve the same yield strength levels as those produced by conventional aging while providing greatly improved ductility. Two-step aging proved to be very effective at enhancing CFT, enabling previously rejected materials to meet simulated service requirements. Cryogenic properties are improved by controlling T1 nucleation and growth so that they are promoted in the matrix and suppressed in the subgrain boundaries.

  7. A Turnover in the Galaxy Main Sequence of Star Formation at M * ~ 1010 M ⊙ for Redshifts z < 1.3

    NASA Astrophysics Data System (ADS)

    Lee, Nicholas; Sanders, D. B.; Casey, Caitlin M.; Toft, Sune; Scoville, N. Z.; Hung, Chao-Ling; Le Floc'h, Emeric; Ilbert, Olivier; Zahid, H. Jabran; Aussel, Hervé; Capak, Peter; Kartaltepe, Jeyhan S.; Kewley, Lisa J.; Li, Yanxia; Schawinski, Kevin; Sheth, Kartik; Xiao, Quanbao

    2015-03-01

    The relationship between galaxy star formation rates (SFRs) and stellar masses (M *) is reexamined using a mass-selected sample of ~62,000 star-forming galaxies at z <= 1.3 in the COSMOS 2 deg2 field. Using new far-infrared photometry from Herschel-PACS and SPIRE and Spitzer-MIPS 24 μm, along with derived infrared luminosities from the NRK method based on galaxies' locations in the restframe color-color diagram (NUV - r) versus (r - K), we are able to more accurately determine total SFRs for our complete sample. At all redshifts, the relationship between median SFR and M * follows a power law at low stellar masses, and flattens to nearly constant SFR at high stellar masses. We describe a new parameterization that provides the best fit to the main sequence and characterizes the low mass power-law slope, turnover mass, and overall scaling. The turnover in the main sequence occurs at a characteristic mass of about M 0 ~ 1010 M ⊙ at all redshifts. The low mass power-law slope ranges from 0.9-1.3 and the overall scaling rises in SFR as a function of (1 + z)4.12 ± 0.10. A broken power-law fit below and above the turnover mass gives relationships of SFR \\propto M*0.88 +/- 0.06 below the turnover mass and SFR \\propto M*0.27 +/- 0.04 above the turnover mass. Galaxies more massive than M * >~ 1010 M ⊙ have a much lower average specific star formation rate (sSFR) than would be expected by simply extrapolating the traditional linear fit to the main sequence found for less massive galaxies.

  8. STELLAR DIAMETERS AND TEMPERATURES. III. MAIN-SEQUENCE A, F, G, AND K STARS: ADDITIONAL HIGH-PRECISION MEASUREMENTS AND EMPIRICAL RELATIONS

    SciTech Connect

    Boyajian, Tabetha S.; Jones, Jeremy; White, Russel; McAlister, Harold A.; Gies, Douglas; Von Braun, Kaspar; Van Belle, Gerard; Farrington, Chris; Schaefer, Gail; Ten Brummelaar, Theo A.; Sturmann, Laszlo; Sturmann, Judit; Turner, Nils H.; Goldfinger, P. J.; Vargas, Norm; Ridgway, Stephen

    2013-07-01

    Based on CHARA Array measurements, we present the angular diameters of 23 nearby, main-sequence stars, ranging from spectral types A7 to K0, 5 of which are exoplanet host stars. We derive linear radii, effective temperatures, and absolute luminosities of the stars using Hipparcos parallaxes and measured bolometric fluxes. The new data are combined with previously published values to create an Angular Diameter Anthology of measured angular diameters to main-sequence stars (luminosity classes V and IV). This compilation consists of 125 stars with diameter uncertainties of less than 5%, ranging in spectral types from A to M. The large quantity of empirical data is used to derive color-temperature relations to an assortment of color indices in the Johnson (BVR{sub J} I{sub J} JHK), Cousins (R{sub C} I{sub C}), Kron (R{sub K} I{sub K}), Sloan (griz), and WISE (W{sub 3} W{sub 4}) photometric systems. These relations have an average standard deviation of {approx}3% and are valid for stars with spectral types A0-M4. To derive even more accurate relations for Sun-like stars, we also determined these temperature relations omitting early-type stars (T{sub eff} > 6750 K) that may have biased luminosity estimates because of rapid rotation; for this subset the dispersion is only {approx}2.5%. We find effective temperatures in agreement within a couple of percent for the interferometrically characterized sample of main-sequence stars compared to those derived via the infrared flux method and spectroscopic analysis.

  9. Plio-Plistocene in-sequence thrust propagation along the Main Central Thrust zone (Kumaon-Garhwal Himalaya, India): New thermochronological data

    NASA Astrophysics Data System (ADS)

    Singh, Paramjeet; Patel, R. C.; Lal, Nand

    2012-10-01

    The Kumaon and Garhwal Himalayas, NW-India have similar geologic, tectonic, topographic and precipitation pattern. However, low-temperature thermochronological age pattern varies significantly along the strike as well as across the strike of major faults. Here, we interpret the new set of thermochronological age data across the strike of major faults namely Vaikrita Thrust (VT), Munsiari Thrust (MT), Berinag Thrust (BT) and the Baijnath nappe along Pindari valley in the Kumaon-Garhwal Himalaya. In the present work, 18 new apatite fission track (AFT) ages of samples collected along a north-south transect have been reported. Ages in the hanging wall of VT which range from 2.1 ± 0.2 to 4.2 ± 0.7 Ma, have been found to be becoming younger linearly with distance from north to the VT. This trend crosses the VT with significant jump in ages. In the south of the VT, ages are lying between 0.3 ± 0.1 and 3.9 ± 0.8 Ma, and show linear variation with distance from the VT to BT. No significant jump in ages across the MT is observed and the linear trend of younging southward is continuing till the BT. The break and displacement in age pattern with youngest ages close to thrusts possibly indicate progressive late thrust movement. It reflects sequential uplift and cooling towards the south from the VT to BT which is consistent with an in-sequence style of thrust propagation. We compare our new data to the published thermochronological data from its adjacent traverses along the Goriganga and Dhauliganga valleys (~ 25 km away from the present traverse towards east and west respectively) in the Kumaon-Garhwal Himalaya in order to understand potential along-strike variations in the kinematics. Our observations indicate a dynamic coupling between tectonic and surface processes in the Garhwal-Kumaon Himalaya and support that the geometry of crustal scale faults and their associated kinematics control exhumation pathways of rocks.

  10. A New Aging Treatment for Improving Cryogenic Toughness of the Main Structural Alloy of the Super Lightweight Tank

    NASA Technical Reports Server (NTRS)

    Chen, P. S.; Stanton, W. P.

    1996-01-01

    Marshall Space Flight Center (MSFC) has developed a new technique that can enhance cryogenic fracture toughness and reduce the statistical spread of toughness values in alloy 2195. This aging treatment can control the location and size of strengthening precipitate T1, making improvements possible in cryogenic fracture toughness (CFT) and fracture toughness ratio (FTR). At the start of this program, design of experiments (DOE) ingot No. 10 was used as a baseline for aging process development and optimization. The new aging treatment was found to be very effective, improving CFT by approximately 15 to 20 percent for DOE ingot No. 10. To further evaluate the repeatability and effectiveness of this new treatment, the investigators selected and tested three more lots of alloy 2195, using 1.75-in-thick gauge plates with FTR values ranging from 0.85 to 1.07. The new aging treatment effectively enhanced CFT and FTR values for all three lots. In one instance, the material was considered rejectable because it did not meet the minimum FTR value (1.0) of the super lightweight tank (SLWT). The new aging treatment improved its FTR from 0.85 to 1.01, making this material acceptable for use in the SLWT.

  11. Therapeutics with SPION-labeled stem cells for the main diseases related to brain aging: a systematic review

    PubMed Central

    Alvarim, Larissa T; Nucci, Leopoldo P; Mamani, Javier B; Marti, Luciana C; Aguiar, Marina F; Silva, Helio R; Silva, Gisele S; Nucci-da-Silva, Mariana P; DelBel, Elaine A; Gamarra, Lionel F

    2014-01-01

    The increase in clinical trials assessing the efficacy of cell therapy for structural and functional regeneration of the nervous system in diseases related to the aging brain is well known. However, the results are inconclusive as to the best cell type to be used or the best methodology for the homing of these stem cells. This systematic review analyzed published data on SPION (superparamagnetic iron oxide nanoparticle)-labeled stem cells as a therapy for brain diseases, such as ischemic stroke, Parkinson’s disease, amyotrophic lateral sclerosis, and dementia. This review highlights the therapeutic role of stem cells in reversing the aging process and the pathophysiology of brain aging, as well as emphasizing nanotechnology as an important tool to monitor stem cell migration in affected regions of the brain. PMID:25143726

  12. Dating slate belts using 40Ar/39Ar geochronology and zircon ages from crosscutting plutons: A case study from east-central Maine, USA

    NASA Astrophysics Data System (ADS)

    Ghanem, Hind; Kunk, Michael; Ludman, Allan; Bish, David; Wintsch, Robert

    2016-04-01

    Determining the tectonic significance of slate belts is a persistent problem in many orogenic belts because of the lack of time constraints on the age of deposition and the age(s) of cleavages. We have solved this problem in east-central Maine where the ages of the regional Acadian cleavage (S1) and local ductile fault zone cleavage (S2) were both constrained using 40Ar/39Ar geochronology and the ages of crosscutting plutons. Applying 40Ar/39Ar geochronology to rocks with multiple generations of muscovite was possible because each cleavage-forming muscovite records a crystallization age rather than a cooling age due to the low grade of regional metamorphism. Evidence for metamorphic crystallization in rocks dominated by regional Acadian cleavage (S1) comes from the truncations of detrital and authigenic muscovite and chlorite grains by new muscovite and chlorite grains that define the S1 foliation. In rocks that display two foliations, the evidence comes from the truncations of chlorite and muscovite grains defining all earlier fabrics by new muscovite grains in the younger folia (S2). Step-heating experiments using the 40Ar/39Ar technique on twelve samples all yielded sigmoidal age spectra. The low-temperature steps produced a hump in the age spectra, indicating 39Ar recoil into adjacent interlayered chlorite grains, the latter interlayering confirmed by back-scattered electron imaging. Continuing steps climbed steadily from those with minimum apparent ages as young as ~381 Ma to steps with maximum ages as old as 466 Ma. The samples with the lowest minimum apparent age steps are those in which the S2 cleavage-forming mica population dominates. In contrast, the oldest apparent age steps are from samples that have the highest modal abundance of detrital micas. The Middle Ordovician age of the maximum age steps is interpreted to be the minimum cooling age of the detrital micas. The minimum 40Ar/39Ar age steps of muscovite in the samples that display only S1 cleavage

  13. Radiocarbon ages of lacustrine deposits in volcanic sequences of the Lomas Coloradas area, Socorro Island, Mexico

    SciTech Connect

    Farmer, J.D. ); Farmer, M.C. . Dept. of Geography and Anthropology); Berger, R. . Depts. of Geography and Anthropology and Institute of Geophysics and Planetary Sciences)

    1993-01-01

    Extensive eruptions of alkalic basalt from low-elevation fissures and vents on the southern flank of the dormant volcano, Cerro Evermann, accompanied the most recent phase of volcanic activity on Socorro Island, and created the Lomas Coloradas, a broad, gently sloping terrain comprising the southern part of the island. The authors obtained [sup 14]C ages of 4690 [plus minus] 270 Bp (5000-5700 cal Bp) and 5040 [plus minus] 460 Bp (53090-6300 cal Bp) from lacustrine deposits that occur within volcanic sequences of the lower Lonas Coloradas. Apparently, the sediments accumulated within a topographic depression between two scoria cones shortly after they formed. The lacustrine environment was destroyed when the cones were breached by headward erosion of adjacent stream drainages. This was followed by the eruption of a thin basaltic flow from fissures near the base of the northernmost cone. The flow moved downslope for a short distance and into the drainages that presently bound the study area on the east and west. The flow postdates development of the present drainage system and may be very recent. These [sup 14]C data, along with historical accounts of volcanic activity over the last century, including submarine eruptions that occurred a few km west of Socorro in early 1993, underscore the high risk for explosive volcanism in the region and the need for a detailed volcanic hazards plan and seismic monitoring.

  14. Radiocarbon ages of lacustrine deposits in volcanic sequences of the Lomas Coloradas area, Socorro Island, Mexico

    NASA Technical Reports Server (NTRS)

    Farmer, J. D.; Farmer, M. C.; Berger, R.

    1993-01-01

    Extensive eruptions of alkalic basalt from low-elevation fissures and vents on the southern flank of the dormant volcano, Cerro Evermann, accompanied the most recent phase of volcanic activity on Socorro Island, and created the Lomas Coloradas, a broad, gently sloping terrain comprising the southern part of the island. We obtained 14C ages of 4690 +/- 270 BP (5000-5700 cal BP) and 5040 +/- 460 BP (5300-6300 cal BP) from lacustrine deposits that occur within volcanic sequences of the lower Lomas Coloradas. Apparently, the sediments accumulated within a topographic depression between two scoria cones shortly after they formed. The lacrustine environment was destroyed when the cones were breached by headward erosion of adjacent stream drainages. This was followed by the eruption of a thin basaltic flow from fissures near the base of the northernmost cone. The flow moved downslope for a short distance and into the drainages that presently bound the study area on the east and west. The flow postdates development of the present drainage system and may be very recent. Our 14C data, along with historical accounts of volcanic activity over the last century, including submarine eruptions that occurred a few km west of Socorro in early 1993, underscore the high risk for explosive volcanism in this region and the need for a detailed volcanic hazards plan and seismic monitoring.

  15. Radiocarbon ages of lacustrine deposits in volcanic sequences of the Lomas Coloradas area, Socorro Island, Mexico.

    PubMed

    Farmer, J D; Farmer, M C; Berger, R

    1993-01-01

    Extensive eruptions of alkalic basalt from low-elevation fissures and vents on the southern flank of the dormant volcano, Cerro Evermann, accompanied the most recent phase of volcanic activity on Socorro Island, and created the Lomas Coloradas, a broad, gently sloping terrain comprising the southern part of the island. We obtained 14C ages of 4690 +/- 270 BP (5000-5700 cal BP) and 5040 +/- 460 BP (5300-6300 cal BP) from lacustrine deposits that occur within volcanic sequences of the lower Lomas Coloradas. Apparently, the sediments accumulated within a topographic depression between two scoria cones shortly after they formed. The lacrustine environment was destroyed when the cones were breached by headward erosion of adjacent stream drainages. This was followed by the eruption of a thin basaltic flow from fissures near the base of the northernmost cone. The flow moved downslope for a short distance and into the drainages that presently bound the study area on the east and west. The flow postdates development of the present drainage system and may be very recent. Our 14C data, along with historical accounts of volcanic activity over the last century, including submarine eruptions that occurred a few km west of Socorro in early 1993, underscore the high risk for explosive volcanism in this region and the need for a detailed volcanic hazards plan and seismic monitoring. PMID:11539414

  16. Minimum age of the Neoproterozoic Seven Hundred Acre Island Formation and the tectonic setting of the Islesboro Formation, Islesboro block, Maine

    USGS Publications Warehouse

    Stewart, D.B.; Tucker, R.D.; Ayuso, R.A.; Lux, D.R.

    2001-01-01

    Two platformal stratigraphic sequences occur on Islesboro, Penobscot Bay, Maine. The older Seven Hundred Acre Island Formation is at least 200 m thick, its base is not exposed, and it makes up fault-bounded blocks of siliceous colour-banded dolomitic marble, muscovite-rich quartzite, coarse-grained splendent muscovite-garnet-staurolite-andalusite schist, and calcareous metapelite, with minor garnet amphibolite and amphibolite. It was initially metamorphosed to lower amphibolite facies and was later to lower greenschist facies. The lower amphibolite facies metamorphism is Neoproterozoic (670 to 650 Ma) as inferred from the 40Ar/39Ar high temperature release spectra of hornblende separates. A U-Pb zircon age of 646.7 ?? 2.7 Ma obtained for a pegmatite that intruded deformed rocks is taken to be the minimum age of the Formation. The platformal Islesboro Formation probably unconformably overlies the Seven Hundred Acre Island Formation. It is primarily turbiditic pelite with many beds of quartzite, impure dolomitic marble, some conglomerate, and a few feldsparrich volcaniclastic beds and is thought to be either Neoproterozoic or Cambrian. It was metamorphosed only to lower greenschist facies, possibly in the same event that retrograded the Seven Hundred Acre Island Formation. Geochemical interpretations of minor and trace element analyses of six amphibolite and four schist samples from the Seven Hundred Acre Island Formation show that the protoliths of the amphibolite samples were intermediate between tholeiitic and within-plate type basaltic flows or dikes that intruded attenuated continental crust, or were eroded from these basalts. Four amphibolite and three schist samples analyzed for Pb isotopes were found to be enriched in radiogenic Pb. The Pb isotopic compositions are similar to those in peri-Gondwanan basement rocks from Atlantic Canada. The peri-Gondwanan Islesboro block was placed against the peri-Gondwanan Middle and Late Cambrian Ellsworth terrane on the

  17. Stress rotations due to the M6.5 foreshock and M7.3 main shock in the 2016 Kumamoto, SW Japan, earthquake sequence

    NASA Astrophysics Data System (ADS)

    Yoshida, Keisuke; Hasegawa, Akira; Saito, Tatsuhiko; Asano, Youichi; Tanaka, Sachiko; Sawazaki, Kaoru; Urata, Yumi; Fukuyama, Eiichi

    2016-10-01

    A shallow M7.3 event with a M6.5 foreshock occurred along the Futagawa-Hinagu fault zone in Kyushu, SW Japan. We investigated the spatiotemporal variation of the stress orientations in and around the source area of this 2016 Kumamoto earthquake sequence by inverting 1218 focal mechanisms. The results show that the σ3 axis in the vicinity of the fault plane significantly rotated counterclockwise after the M6.5 foreshock and rotated clockwise after the M7.3 main shock in the Hinagu fault segment. This observation indicates that a significant portion of the shear stress was released both by the M6.5 foreshock and M7.3 main shock. It is estimated that the stress release by the M6.5 foreshock occurred in the shallower part of the Hinagu fault segment, which brought the stress concentration in its deeper part. This might have caused the M7.3 main shock rupture mainly along the deeper part of the Hinagu fault segment after 28 h.

  18. Trajectory of the main GABAergic interneuron populations from early development to old age in the rat primary auditory cortex.

    PubMed

    Ouellet, Lydia; de Villers-Sidani, Etienne

    2014-01-01

    In both humans and rodents, decline in cognitive function is a hallmark of the aging process; the basis for this decrease has yet to be fully characterized. However, using aged rodent models, deficits in auditory processing have been associated with significant decreases in inhibitory signaling attributed to a loss of GABAergic interneurons. Not only are these interneurons crucial for pattern detection and other large-scale population dynamics, but they have also been linked to mechanisms mediating plasticity and learning, making them a prime candidate for study and modeling of modifications to cortical communication pathways in neurodegenerative diseases. Using the rat primary auditory cortex (A1) as a model, we probed the known markers of GABAergic interneurons with immunohistological methods, using antibodies against gamma aminobutyric acid (GABA), parvalbumin (PV), somatostatin (SOM), calretinin (CR), vasoactive intestinal peptide (VIP), choline acetyltransferase (ChAT), neuropeptide Y (NPY), and cholecystokinin (CCK) to document the changes observed in interneuron populations across the rat's lifespan. This analysis provided strong evidence that several but not all GABAergic neurons were affected by the aging process, showing most dramatic changes in expression of parvalbumin (PV) and somatostatin (SOM) expression. With this evidence, we show how understanding these trajectories of cell counts may be factored into a simple model to quantify changes in inhibitory signaling across the course of life, which may be applied as a framework for creating more advanced simulations of interneuronal implication in normal cerebral processing, normal aging, or pathological processes.

  19. Genotyping-by-sequencing approach indicates geographic distance as the main factor affecting genetic structure and gene flow in Brazilian populations of Grapholita molesta (Lepidoptera, Tortricidae).

    PubMed

    Silva-Brandão, Karina Lucas; Silva, Oscar Arnaldo Batista Neto E; Brandão, Marcelo Mendes; Omoto, Celso; Sperling, Felix A H

    2015-06-01

    The oriental fruit moth Grapholita molesta is one of the major pests of stone and pome fruit species in Brazil. Here, we applied 1226 SNPs obtained by genotyping-by-sequencing to test whether host species associations or other factors such as geographic distance structured populations of this pest. Populations from the main areas of occurrence of G. molesta were sampled principally from peach and apple orchards. Three main clusters were recovered by neighbor-joining analysis, all defined by geographic proximity between sampling localities. Overall genetic structure inferred by a nonhierarchical amova resulted in a significant ΦST value = 0.19109. Here, we demonstrate for the first time that SNPs gathered by genotyping-by-sequencing can be used to infer genetic structure of a pest insect in Brazil; moreover, our results indicate that those markers are very informative even over a restricted geographic scale. We also demonstrate that host plant association has little effect on genetic structure among Brazilian populations of G. molesta; on the other hand, reduced gene flow promoted by geographic isolation has a stronger impact on population differentiation. PMID:26029261

  20. Genotyping-by-sequencing approach indicates geographic distance as the main factor affecting genetic structure and gene flow in Brazilian populations of Grapholita molesta (Lepidoptera, Tortricidae)

    PubMed Central

    Silva-Brandão, Karina Lucas; Silva, Oscar Arnaldo Batista Neto e; Brandão, Marcelo Mendes; Omoto, Celso; Sperling, Felix A H

    2015-01-01

    The oriental fruit moth Grapholita molesta is one of the major pests of stone and pome fruit species in Brazil. Here, we applied 1226 SNPs obtained by genotyping-by-sequencing to test whether host species associations or other factors such as geographic distance structured populations of this pest. Populations from the main areas of occurrence of G. molesta were sampled principally from peach and apple orchards. Three main clusters were recovered by neighbor-joining analysis, all defined by geographic proximity between sampling localities. Overall genetic structure inferred by a nonhierarchical amova resulted in a significant ΦST value = 0.19109. Here, we demonstrate for the first time that SNPs gathered by genotyping-by-sequencing can be used to infer genetic structure of a pest insect in Brazil; moreover, our results indicate that those markers are very informative even over a restricted geographic scale. We also demonstrate that host plant association has little effect on genetic structure among Brazilian populations of G. molesta; on the other hand, reduced gene flow promoted by geographic isolation has a stronger impact on population differentiation. PMID:26029261

  1. Detection of the Main-Sequence Turnoff of a Newly Discovered Milky Way Halo Structure in the Triangulum-Andromeda Region

    NASA Astrophysics Data System (ADS)

    Majewski, Steven R.; Ostheimer, James C.; Rocha-Pinto, Helio J.; Patterson, Richard J.; Guhathakurta, Puragra; Reitzel, David

    2004-11-01

    An upper main sequence (MS) and main-sequence turnoff (MSTO) feature appears in the color-magnitude diagram (CMD) of a large-area photometric survey of the southern half of M31 stretching to M33. Imaging in the Washington M, T2, DDO51 system allows us to remove the background M31/M33 giants from our CMD and more clearly see the dwarf star feature, which has an MSTO near M~20.5. The corresponding stellar population shows little density variation over the 12deg×6deg area of the sky sampled and is of very low surface brightness, Σ>32 mag arcsec-2. We show that this feature is not the same as a previously identified MS+MSTO in the foreground of the Andromeda galaxy that has been associated with the tidal stream ringing the Milky Way disk at less than half the distance. Thus, the new stellar system is a separate, more distant entity, perhaps a segment of tidal debris from a disrupted satellite galaxy. It is most likely related to the structure with similar distance, location, and density uniformity seen as an excess of K and M giants in the Two Micron All Sky Survey reported in the companion paper by Rocha-Pinto and coworkers.

  2. Genotyping-by-sequencing approach indicates geographic distance as the main factor affecting genetic structure and gene flow in Brazilian populations of Grapholita molesta (Lepidoptera, Tortricidae).

    PubMed

    Silva-Brandão, Karina Lucas; Silva, Oscar Arnaldo Batista Neto E; Brandão, Marcelo Mendes; Omoto, Celso; Sperling, Felix A H

    2015-06-01

    The oriental fruit moth Grapholita molesta is one of the major pests of stone and pome fruit species in Brazil. Here, we applied 1226 SNPs obtained by genotyping-by-sequencing to test whether host species associations or other factors such as geographic distance structured populations of this pest. Populations from the main areas of occurrence of G. molesta were sampled principally from peach and apple orchards. Three main clusters were recovered by neighbor-joining analysis, all defined by geographic proximity between sampling localities. Overall genetic structure inferred by a nonhierarchical amova resulted in a significant ΦST value = 0.19109. Here, we demonstrate for the first time that SNPs gathered by genotyping-by-sequencing can be used to infer genetic structure of a pest insect in Brazil; moreover, our results indicate that those markers are very informative even over a restricted geographic scale. We also demonstrate that host plant association has little effect on genetic structure among Brazilian populations of G. molesta; on the other hand, reduced gene flow promoted by geographic isolation has a stronger impact on population differentiation.

  3. Imaging the high-frequency energy radiation process of a main shock and its early aftershock sequence: The case of the 2008 Iwate-Miyagi Nairiku earthquake, Japan

    NASA Astrophysics Data System (ADS)

    Sawazaki, Kaoru; Enescu, Bogdan

    2014-06-01

    To understand the energy release process that operates at the end of the main shock rupture and start of the aftershock activity, we propose an inversion method that uses continuous high-frequency seismogram envelopes of the main shock and early aftershocks (i.e., events that occur at short times after the main shock). In our approach, the aftershock sequence is regarded as a continuous energy release process, rather than a discrete time series of events. To correct for the contribution of coda wave energy excited by multiple scattering, we use the theoretical envelope synthesized on the basis of the radiative transfer theory as a Green's function. The site amplification factors are corrected considering the conservation of energy flux and using the coda normalization method. The inverted temporal energy release rate for the 2008 MW 6.9 Iwate-Miyagi Nairiku earthquake, Japan, decays following t-1.1, at the lapse time t of 40-900 s after the main shock origin time. This exponent of the decay rate is similar to the p value of the modified Omori law. The amount of estimated energy release is consistent with that calculated from the magnitude listed in the aftershock catalog. Although the uncertainty is large, the location of large energy release at the lapse times of 40-900 s approximately overlaps to that of the aftershocks, which surrounds the large energy release area during the main shock faulting. The maxima of the energy release rate normalized by the average decay rate distributes following a power law, similar to the Gutenberg-Richter law.

  4. Neural correlates of the age-related changes in motor sequence learning and motor adaptation in older adults.

    PubMed

    King, Bradley R; Fogel, Stuart M; Albouy, Geneviève; Doyon, Julien

    2013-01-01

    As the world's population ages, a deeper understanding of the relationship between aging and motor learning will become increasingly relevant in basic research and applied settings. In this context, this review aims to address the effects of age on motor sequence learning (MSL) and motor adaptation (MA) with respect to behavioral, neurological, and neuroimaging findings. Previous behavioral research investigating the influence of aging on motor learning has consistently reported the following results. First, the initial acquisition of motor sequences is not altered, except under conditions of increased task complexity. Second, older adults demonstrate deficits in motor sequence memory consolidation. And, third, although older adults demonstrate deficits during the exposure phase of MA paradigms, the aftereffects following removal of the sensorimotor perturbation are similar to young adults, suggesting that the adaptive ability of older adults is relatively intact. This paper will review the potential neural underpinnings of these behavioral results, with a particular emphasis on the influence of age-related dysfunctions in the cortico-striatal system on motor learning.

  5. Radiometric dating of the Earlier Stone Age sequence in excavation I at Wonderwerk Cave, South Africa: preliminary results.

    PubMed

    Chazan, Michael; Ron, Hagai; Matmon, Ari; Porat, Naomi; Goldberg, Paul; Yates, Royden; Avery, Margaret; Sumner, Alexandra; Horwitz, Liora Kolska

    2008-07-01

    We present here the results of 44 paleomagnetic measurements, and single cosmogenic burial and optically stimulated luminescence ages for the Earlier Stone Age deposits from Wonderwerk Cave, Northern Cape, South Africa. The resulting paleomagnetic sequence: N>R>N>R>N constrains the Earlier Stone Age strata in this part of the site to between approximately 0.78-1.96 Ma. A single cosmogenic date of approximately 2.0 Ma from the base of the section offers some corroboration for the paleomagnetic sequence. Preliminary results indicate that the small lithic assemblage from the basal stratum may contain an Oldowan facies. This is overlain by several strata containing Acheulean industries. The preliminary radiometric dates reported here place the onset of the Acheulean at this site to approximately 1.6 Ma, which is roughly contemporaneous with that of East Africa.

  6. Whole transcriptome sequencing of the aging rat brain reveals dynamic RNA changes in the dark matter of the genome.

    PubMed

    Wood, Shona H; Craig, Thomas; Li, Yang; Merry, Brian; de Magalhães, João Pedro

    2013-06-01

    Brain aging frequently underlies cognitive decline and is a major risk factor for neurodegenerative conditions. The exact molecular mechanisms underlying brain aging, however, remain unknown. Whole transcriptome sequencing provides unparalleled depth and sensitivity in gene expression profiling. It also allows non-coding RNA and splice variant detection/comparison across phenotypes. Using RNA-seq to sequence the cerebral cortex transcriptome in 6-, 12- and 28-month-old rats, age-related changes were studied. Protein-coding genes related to MHC II presentation and serotonin biosynthesis were differentially expressed (DE) in aging. Relative to protein-coding genes, more non-coding genes were DE over the three age-groups. RNA-seq quantifies not only levels of whole genes but also of their individual transcripts. Over the three age-groups, 136 transcripts were DE, 37 of which were so-called dark matter transcripts that do not map to known exons. Fourteen of these transcripts were identified as novel putative long non-coding RNAs. Evidence of isoform switching and changes in usage were found. Promoter and coding sequence usage were also altered, hinting of possible changes to mitochondrial transport within neurons. Therefore, in addition to changes in the expression of protein-coding genes, changes in transcript expression, isoform usage, and non-coding RNAs occur with age. This study demonstrates dynamic changes in RNA with age at various genomic levels, which may reflect changes in regulation of transcriptional networks and provides non-coding RNA gene candidates for further studies.

  7. Age of the fossil Dali Man in north-central China deduced from chronostratigraphy of the loess?paleosol sequence

    NASA Astrophysics Data System (ADS)

    Xiao, Jule; Jin, Changzhu; Zhu, Yizhi

    2002-11-01

    Dali Man, an archaic type of early Homo sapiens, is of great significance to the origin of Homo sapiens. Achievements have been made during the past decades in the understanding of the fossil human skull as well as the accompanying mammalian fossils and stone artifacts. However, the absolute age of the fossil Dali Man still remains unclear. Based on the magnetic susceptibility of loess sediments and the relationship of terracing process with climatic condition, we correlated the loess sequence and the subjacent terrace alluvium at the Dali Man site with the well-studied loess-paleosol sequence at Luochuan in the central part of the Chinese Loess Plateau. The correlation indicates that the loess-paleosol sequence at the Dali Man site extends down to the paleosol S2, and the underlying fluvial deposits correspond to the loess L3. Because the Dali Man skull appears in the basal gravel layer of the terrace, and because the deposition of the terrace gravels would occur during the transition from S3 paleosol formation to L3 loess accumulation, the age of the fossil Dali Man is inferred to be ca 270 ka, which is equivalent to the age of the boundary between the loess L3 and paleosol S3 on the magnetic susceptibility time series of the Luochuan loess-paleosol sequence.

  8. Whole-Genome Sequence Analysis Reveals the Enterovirus D68 Isolates during the United States 2014 Outbreak Mainly Belong to a Novel Clade

    PubMed Central

    Huang, Weihua; Wang, Guiqing; Zhuge, Jian; Nolan, Sheila M.; Dimitrova, Nevenka; Fallon, John T.

    2015-01-01

    In the late summer and the fall of 2014, the United States experienced an unprecedented outbreak of enterovirus D68 (EV-D68) infections. During the outbreak, we collected nasopharyngeal swab specimens from patients in the Lower Hudson Valley of New York. Here, we conduct a retrospective study on the genomic diversity of EV-D68 strains. We first employ a metagenomic shotgun sequencing protocol on a total of 93 clinical samples, including 21 negative controls, the results of which allow assembly of 20 EV-D68 genomes, six complete and 14 near-complete. We then investigate their genetic relationships, along with additional 20 EV-D68 strains having whole-genome sequences publicly available. Our comparative genomic analysis uncovers that the majority (26/29) of EV-D68 strains circulating in the 2014 outbreak differ significantly from prior ones, have a main feature of three variables, C1817T, C3277A, and A4020G, and belong to a new clade. C3277A causes amino acid substitution T860N in the protease 2Apro cleavage site between VP1 and 2A, whereas A4020G causes S1108G in a 3Cpro cleavage site between 2B and 2C. The two functional mutations may alter the proteases’ cleavage efficiency, leading to increased rate of viral replication and transmission. These provide insights into the evolution of epidemic EV-D68 strains. PMID:26469882

  9. PHIBSS: MOLECULAR GAS CONTENT AND SCALING RELATIONS IN z {approx} 1-3 MASSIVE, MAIN-SEQUENCE STAR-FORMING GALAXIES

    SciTech Connect

    Tacconi, L. J.; Genzel, R.; Wuyts, S.; Foerster Schreiber, N. M.; Gracia-Carpio, J.; Lutz, D.; Saintonge, A.; Neri, R.; Cox, P.; Combes, F.; Bolatto, A.; Cooper, M. C.; Bournaud, F.; Comerford, J.; Davis, M.; Newman, S.; Garcia-Burillo, S.; Naab, T.; Omont, A. E-mail: genzel@mpe.mpg.de; and others

    2013-05-01

    We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO 3-2 survey of the molecular gas properties in massive, main-sequence star-forming galaxies (SFGs) near the cosmic star formation peak. PHIBSS provides 52 CO detections in two redshift slices at z {approx} 1.2 and 2.2, with log(M{sub *}(M{sub Sun })) {>=} 10.4 and log(SFR(M{sub Sun }/yr)) {>=} 1.5. Including a correction for the incomplete coverage of the M{sub *} -SFR plane, and adopting a ''Galactic'' value for the CO-H{sub 2} conversion factor, we infer average gas fractions of {approx}0.33 at z {approx} 1.2 and {approx}0.47 at z {approx} 2.2. Gas fractions drop with stellar mass, in agreement with cosmological simulations including strong star formation feedback. Most of the z {approx} 1-3 SFGs are rotationally supported turbulent disks. The sizes of CO and UV/optical emission are comparable. The molecular-gas-star-formation relation for the z = 1-3 SFGs is near-linear, with a {approx}0.7 Gyr gas depletion timescale; changes in depletion time are only a secondary effect. Since this timescale is much less than the Hubble time in all SFGs between z {approx} 0 and 2, fresh gas must be supplied with a fairly high duty cycle over several billion years. At given z and M{sub *}, gas fractions correlate strongly with the specific star formation rate (sSFR). The variation of sSFR between z {approx} 0 and 3 is mainly controlled by the fraction of baryonic mass that resides in cold gas.

  10. Associated terrestrial and marine fossils in the late-glacial Presumpscot Formation, southern Maine, USA, and the marine reservoir effect on radiocarbon ages

    USGS Publications Warehouse

    Thompson, W.B.; Griggs, C.B.; Miller, N.G.; Nelson, R.E.; Weddle, T.K.; Kilian, T.M.

    2011-01-01

    Excavations in the late-glacial Presumpscot Formation at Portland, Maine, uncovered tree remains and other terrestrial organics associated with marine invertebrate shells in a landslide deposit. Buds of Populus balsamifera (balsam poplar) occurred with twigs of Picea glauca (white spruce) in the Presumpscot clay. Tree rings in Picea logs indicate that the trees all died during winter dormancy in the same year. Ring widths show patterns of variation indicating responses to environmental changes. Fossil mosses and insects represent a variety of species and wet to dry microsites. The late-glacial environment at the site was similar to that of today's Maine coast. Radiocarbon ages of 14 tree samples are 11,907??31 to 11,650??5014C yr BP. Wiggle matching of dated tree-ring segments to radiocarbon calibration data sets dates the landslide occurrence at ca. 13,520+95/??20calyr BP. Ages of shells juxtaposed with the logs are 12,850??6514C yr BP (Mytilus edulis) and 12,800??5514C yr BP (Balanus sp.), indicating a marine reservoir age of about 1000yr. Using this value to correct previously published radiocarbon ages reduces the discrepancy between the Maine deglaciation chronology and the varve-based chronology elsewhere in New England. ?? 2011 University of Washington.

  11. Associated terrestrial and marine fossils in the late-glacial Presumpscot Formation, southern Maine, USA, and the marine reservoir effect on radiocarbon ages

    NASA Astrophysics Data System (ADS)

    Thompson, Woodrow B.; Griggs, Carol B.; Miller, Norton G.; Nelson, Robert E.; Weddle, Thomas K.; Kilian, Taylor M.

    2011-05-01

    Excavations in the late-glacial Presumpscot Formation at Portland, Maine, uncovered tree remains and other terrestrial organics associated with marine invertebrate shells in a landslide deposit. Buds of Populus balsamifera (balsam poplar) occurred with twigs of Picea glauca (white spruce) in the Presumpscot clay. Tree rings in Picea logs indicate that the trees all died during winter dormancy in the same year. Ring widths show patterns of variation indicating responses to environmental changes. Fossil mosses and insects represent a variety of species and wet to dry microsites. The late-glacial environment at the site was similar to that of today's Maine coast. Radiocarbon ages of 14 tree samples are 11,907 ± 31 to 11,650 ± 50 14C yr BP. Wiggle matching of dated tree-ring segments to radiocarbon calibration data sets dates the landslide occurrence at ca. 13,520 + 95/-20 cal yr BP. Ages of shells juxtaposed with the logs are 12,850 ± 65 14C yr BP ( Mytilus edulis) and 12,800 ± 55 14C yr BP ( Balanus sp.), indicating a marine reservoir age of about 1000 yr. Using this value to correct previously published radiocarbon ages reduces the discrepancy between the Maine deglaciation chronology and the varve-based chronology elsewhere in New England.

  12. Impacts of sources and aging on submicrometer aerosol properties in the marine boundary layer across the Gulf of Maine

    NASA Astrophysics Data System (ADS)

    Quinn, P. K.; Bates, T. S.; Coffman, D.; Onasch, T. B.; Worsnop, D.; Baynard, T.; de Gouw, J. A.; Goldan, P. D.; Kuster, W. C.; Williams, E.; Roberts, J. M.; Lerner, B.; Stohl, A.; Pettersson, A.; Lovejoy, E. R.

    2006-12-01

    Measurements were made on board the NOAA RV Ronald H. Brown during the second New England Air Quality Study (NEAQS 2004) to determine the source of the aerosol in the region and how sources and aging processes affect submicrometer aerosol chemical composition and optical properties. Using the Lagrangian particle dispersion model FLEXPART in combination with gas phase tracer compounds, local (urban), regional (NE U.S. urban corridor of Washington, D.C.; New York; and Boston), and distant (midwest industries and North American forest fires) sources were identified. Submicrometer aerosol measured near the source region (Boston Harbor) had a molar equivalence ratio near one with respect to NH4+, NO3-, and SO4=, had a large mass fraction of particulate organic matter (POM) relative to SO4=, and had relatively unoxidized POM. As distance from the source region increased, the submicrometer aerosol measured in the marine boundary layer became more acidic and had a lower POM mass fraction, and the POM became more oxidized. The relative humidity dependence of light extinction reflected the change in aerosol composition being lower for the near-source aerosol and higher for the more processed aerosol. A factor analysis performed on a combined data set of aerosol and gas phase parameters showed that the POM measured during the experiment was predominantly of secondary anthropogenic origin.

  13. Observation and modelling of main-sequence star chromospheres - XII. Two-component model chromospheres for five active dM1e stars

    NASA Astrophysics Data System (ADS)

    Houdebine, E. R.

    2009-08-01

    We aim to constrain the Hα, CaII H and CaII K profiles from quiescent and active regions on active dM1e stars. A preliminary analysis of all the data available for dM1e stars shows that the Hα/CaII equivalent width (EW) ratio varies by up to a factor of 7 for different stars in our sample. We find that spectroscopic binaries have a significantly smaller ratio than single dM1e stars. We also find that the pre-main-sequence stars Gl 616.2, GJ 1264 and Gl 803 have a ratio lower than main-sequence single dM1e stars. These differences imply that different chromospheric structures are present on different stars, notably the temperature minimum must decrease with an increasing Hα/CaII EW ratio. For these reasons, it is impossible to reproduce all observations with only one grid of model chromospheres. We show that the grid of model chromospheres of Paper VI is adequate to describe the physical conditions that prevail in the chromospheres of spectroscopic binaries and pre-main-sequence M1e stars, but not for the conditions in single dM1e stars. One or more additional grids of model chromospheres will be necessary to reproduce all observations. We use the method developed in Paper XI in this series, in order to build two-component model chromospheres for five M1e field stars: FF And A, FF And B, GJ 1264, AU Mic and Gl 815A. Our solutions provide an exact match of the Hα and the mean CaII H & K EWs within measurement uncertainties. We compare the theoretical profiles and the observed profiles of Hα and the CaII H & K resonance lines. On the one hand, our fits to the CaII lines are reasonably good. On the other hand, our models tend to produce Hα profiles with a central absorption that is too deep. This suggests that the column mass at the transition region for plages is underestimated, but this would imply that the contrast factor between quiescent and active regions in the CaII lines is larger than 5. We find that, except in the cases of FF And A and AU Mic, the total

  14. Sequence of Age-Associated Changes to the Mouse Neuromuscular Junction and the Protective Effects of Voluntary Exercise

    PubMed Central

    Cheng, Anson; Morsch, Marco; Murata, Yui; Ghazanfari, Nazanin; Reddel, Stephen W.; Phillips, William D.

    2013-01-01

    Loss of connections between motor neurons and skeletal muscle fibers contribute to motor impairment in old age, but the sequence of age-associated changes that precede loss of the neuromuscular synapse remains uncertain. Here we determine changes in the size of neuromuscular synapses within the tibialis anterior muscle across the life span of C57BL/6J mice. Immunofluorescence, confocal microscopy and morphometry were used to measure the area occupied by nerve terminal synaptophysin staining and postsynaptic acetylcholine receptors at motor endplates of 2, 14, 19, 22, 25 and 28month old mice. The key findings were: 1) At middle age (14-months) endplate acetylcholine receptors occupied 238±11 µm2 and nerve terminal synaptophysin 168±14 µm2 (mean ± SEM). 2) Between 14-months and 19-months (onset of old age) the area occupied by postsynaptic acetylcholine receptors declined 30%. At many endplates the large acetylcholine receptor plaque became fragmented into multiple smaller acetylcholine receptor clusters. 3) Between 19- and 25-months, the fraction of endplate acetylcholine receptors covered by synaptophysin fell 21%. By 28-months, half of the endplates imaged retained ≤50 µm2 area of synaptophysin staining. 4) Within aged muscles, the degree to which an endplate remained covered by synaptophysin did not depend upon the total area of acetylcholine receptors, nor upon the number of discrete receptor clusters. 5) Voluntary wheel-running exercise, beginning late in middle-age, prevented much of the age-associated loss of nerve terminal synaptophysin. In summary, a decline in the area of endplate acetylcholine receptor clusters at the onset of old age was followed by loss of nerve terminal synaptophysin from the endplate. Voluntary running exercise, begun late in middle age, substantially inhibited the loss of nerve terminal from aging motor endplates. PMID:23844140

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  16. Chandra Observation of the Trifid Nebula: X-ray emission from the exciting O star complex and Pre-main sequence stars

    NASA Astrophysics Data System (ADS)

    Rho, J.; Ramirez, S.; Corcoran, M.; Hamaguchi, K.; Lefloch, B.

    2003-12-01

    The Trifid Nebula, one of the youngest star-forming HII regions, was observed for 16 hours by the ACIS-I detector on board of the Chandra X-ray Observatory. We detected 304 X-ray sources, thirty percent of which are hard sources, with near-infrared counterparts for two-thirds of the X-ray sources. Chandra resolved the HD164492 multiple system into a number of discrete X-ray sources. X-ray emission is detected from components HD164492A (an O7.5III star which ionizes the nebula), B and C (a B6V star), and possibly D (a Be star). Component C is blended with an unidentified source (we called Component C2, hereafter). HD164492A has a soft spectrum (kT 0.5 keV) while the component C blend shows much harder emission (kT 6 keV). This blend and other hard sources are responsible for the hard emission and Fe K line seen by the ASCA, which was previously attributed entirely to HD 164492A. The soft spectrum of the O star is similar to emission seen from other single O stars and is probably produced by shocks within its massive stellar wind. Lack of hard emission suggests that neither a magnetically confined wind shock nor colliding wind emission is important in HD164492A. A dozen stars are found to have flares in the field and most of them are pre-main sequence stars (PMS). Six sources with flares have both optical and 2MASS counterparts. These counterparts are not embedded and thus it is likely that these sources are in later stage of PMS evolution, possibly Class II or III. Two flare sources did not have any near-IR, optical, or radio counterparts. We suggest these X-ray flare stars are in an early pre-main sequence stage (Class I or earlier). We also detected X-ray sources apparently associated with two massive star forming cores, TC1 and TC4. The spectra of these sources show high extinction and X-ray luminosities of 2 - 5x 1031 erg s-1. If these source are Class 0 objects, it is unclear if their X-ray emission is due to solar-type magnetic activities as in Class I objects

  17. Targeted sequencing in candidate genes for atrial fibrillation: The Cohorts for Heart and Aging Research in Genomic Epidemiology Targeted Sequencing Study

    PubMed Central

    Lin, Honghuang; Sinner, Moritz F.; Brody, Jennifer A.; Arking, Dan E.; Lunetta, Kathryn L.; Rienstra, Michiel; Lubitz, Steven A.; Magnani, Jared W.; Sotoodehnia, Nona; McKnight, Barbara; McManus, David D.; Boerwinkle, Eric; Psaty, Bruce M.; Rotter, Jerome I.; Bis, Joshua C.; Gibbs, Richard A.; Muzny, Donna; Kovar, Christie L.; Morrison, Alanna C.; Gupta, Mayetri; Folsom, Aaron R.; Kääb, Stefan; Heckbert, Susan R.; Alonso, Alvaro; Ellinor, Patrick T.; Benjamin, Emelia J.

    2014-01-01

    Background Genome-wide association studies (GWAS) have identified common genetic variants that predispose to atrial fibrillation (AF). It is unclear whether rare and low-frequency variants in genes implicated by such GWAS confer additional risk of AF. Objective To study the association of genetic variants with AF at GWAS top loci. Methods In the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) Targeted Sequencing Study, we selected and sequenced 77 target gene regions from GWAS loci of complex diseases or traits, including 4 genes hypothesized to be related to AF (PRRX1, CAV1, CAV2, and ZFHX3). Sequencing was performed in participants with (n = 948) and without (n = 3330) AF from the Atherosclerosis Risk in Communities Study, the Cardiovascular Health Study, the Framingham Heart Study, and the Massachusetts General Hospital. Results One common variant (rs11265611; P = 1.70 × 10−6) intronic to IL6R (interleukin-6 receptor gene) was significantly associated with AF after Bonferroni correction (odds ratio 0.70; 95% confidence interval 0.58–0.85). The variant was not genotyped or imputed by prior GWAS, but it is in linkage disequilibrium (r2 = .69) with the single-nucleotide polymorphism, with the strongest association with AF so far at this locus (rs4845625). In the rare variant joint analysis, damaging variants within the PRRX1 region showed significant association with AF after Bonferroni correction (P = .01). Conclusions We identified 1 common single-nucleotide polymorphism and 1 gene region that were significantly associated with AF. Future sequencing efforts with larger sample sizes and more comprehensive genome coverage are anticipated to identify additional AF-related variants. PMID:24239840

  18. GOODS-HERSCHEL: STAR FORMATION, DUST ATTENUATION, AND THE FIR–RADIO CORRELATION ON THE MAIN SEQUENCE OF STAR-FORMING GALAXIES UP TO z ≃ 4

    SciTech Connect

    Pannella, M.; Elbaz, D.; Daddi, E.; Hwang, H. S.; Schreiber, C.; Strazzullo, V.; Aussel, H.; Bethermin, M.; Cibinel, A.; Juneau, S.; Floc’h, E. Le; Leiton, R.; Buat, V.; Charmandaris, V.; Magdis, G.; Ivison, R. J.; Borgne, D. Le; Lin, L.; Morrison, G. E.; and others

    2015-07-10

    We use deep panchromatic data sets in the GOODS-N field, from GALEX to the deepest Herschel far-infrared (FIR) and VLA radio continuum imaging, to explore the evolution of star-formation activity and dust attenuation properties of star-forming galaxies to z ≃ 4, using mass-complete samples. Our main results can be summarized as follows: (i) the slope of the star-formation rate–M{sub *} correlation is consistent with being constant ≃0.8 up to z ≃ 1.5, while its normalization keeps increasing with redshift; (ii) for the first time we are able to explore the FIR–radio correlation for a mass-selected sample of star-forming galaxies: the correlation does not evolve up to z ≃ 4; (iii) we confirm that galaxy stellar mass is a robust proxy for UV dust attenuation in star-forming galaxies, with more massive galaxies being more dust attenuated. Strikingly, we find that this attenuation relation evolves very weakly with redshift, with the amount of dust attenuation increasing by less than 0.3 mag over the redshift range [0.5–4] for a fixed stellar mass; (iv) the correlation between dust attenuation and the UV spectral slope evolves with redshift, with the median UV slope becoming bluer with redshift. By z ≃ 3, typical UV slopes are inconsistent, given the measured dust attenuations, with the predictions of commonly used empirical laws. (v) Finally, building on existing results, we show that gas reddening is marginally larger (by a factor of around 1.3) than the stellar reddening at all redshifts probed. Our results support a scenario where the ISM conditions of typical star-forming galaxies evolve with redshift, such that at z ≥ 1.5 Main Sequence galaxies have ISM conditions moving closer to those of local starbursts.

  19. Stellar Rotation and Variability in IC 348 and Indication of a 4.75 Year Period for the Unique, Apparently Eclipsing Pre-Main Sequence Star HMW 15

    NASA Astrophysics Data System (ADS)

    Nordhagen, S. C. J.; Rhode, K. L.; Herbst, W.; Williams, E. C.

    2005-12-01

    During the past two years of a seven-year photometric variability study of the young stellar cluster IC 348, numerous periodically variable T Tauri stars were discovered, bringing the total number of identified periodic variables in IC 348 to 69, or about 45 % of all cluster stars observed by us. This includes data from Herbst, Maley & Williams (2000, AJ 120, 394), Cohen, Herbst & Williams (2004, AJ 127, 1602) and Littlefair et al. (2005 MNRAS 358, 341). In addition to these photometric data, spectra of 30 cluster members were obtained with the WIYN 3.5m telescope and used to calculate radial velocities and v sin i rotation measurements, offering a generally complementary view of stellar rotation in IC 348. A mean heliocentric radial velocity for the cluster has been determined, and two radial velocity outliers discovered, which are possible spectroscopic binaries. The distribution of rotation periods, their relationship to v sin i measurements and the implications of these results for the rotation and radii of pre-main sequence stars in IC 348 will be presented. In addition, we discuss the recent behavior of the peculiar variable HMW 15 (Cohen, Herbst & Williams 2003 ApJ 596, L243), which now appears to be undergoing a periodic eclipse on a time scale of 4.75 years. We discuss possible origins for this extraordinarily long periodicity. S. Nordhagen was an undergraduate summer student at Wesleyan University, sponsored by the Keck Northeast Astronomy Consortium. Their REU program is supported by NSF grant AST-0353997.

  20. THE MOLECULAR GAS CONTENT OF z = 3 LYMAN BREAK GALAXIES: EVIDENCE OF A NON-EVOLVING GAS FRACTION IN MAIN-SEQUENCE GALAXIES AT z > 2

    SciTech Connect

    Magdis, Georgios E.; Rigopoulou, D.; Daddi, E.; Sargent, M.; Elbaz, D.; Gobat, R.; Tan, Q.; Aussel, H.; Feruglio, C.; Charmandaris, V.; Dickinson, M.; Reddy, N.

    2012-10-10

    We present observations of the CO[J = 3 {yields} 2] emission toward two massive and infrared luminous Lyman break galaxies (LBGs) at z = 3.21 and z = 2.92, using the IRAM Plateau de Bure Interferometer, placing first constraints on the molecular gas masses (M{sub gas}) of non-lensed LBGs. Their overall properties are consistent with those of typical (main-sequence) galaxies at their redshifts, with specific star formation rates {approx}1.6 and {approx}2.2 Gyr{sup -1}, despite their large infrared luminosities (L{sub IR} Almost-Equal-To (2-3) Multiplication-Sign 10{sup 12} L{sub Sun }) derived from Herschel. With one plausible CO detection (spurious detection probability of 10{sup -3}) and one upper limit, we investigate the evolution of the molecular gas-to-stellar mass ratio (M{sub gas}/M{sub *}) with redshift. Our data suggest that the steep evolution of M{sub gas}/M{sub *} of normal galaxies up to z {approx} 2 is followed by a flattening at higher redshifts, providing supporting evidence for the existence of a plateau in the evolution of the specific star formation rate at z > 2.5.

  1. Helium-abundance and other composition effects on the properties of stellar surface convection in solar-like main-sequence stars

    SciTech Connect

    Tanner, Joel D.; Basu, Sarbani; Demarque, Pierre

    2013-12-01

    We investigate the effect of helium abundance and α-element enhancement on the properties of convection in envelopes of solar-like main-sequence stars using a grid of three-dimensional radiation hydrodynamic simulations. Helium abundance increases the mean molecular weight of the gas and alters opacity by displacing hydrogen. Since the scale of the effect of helium may depend on the metallicity, the grid consists of simulations with three helium abundances (Y = 0.1, 0.2, 0.3), each with two metallicities (Z = 0.001, 0.020). We find that changing the helium mass fraction generally affects structure and convective dynamics in a way opposite to that of metallicity. Furthermore, the effect is considerably smaller than that of metallicity. The signature of helium differs from that of metallicity in the manner in which the photospheric velocity distribution is affected. We also find that helium abundance and surface gravity behave largely in similar ways, but differ in the way they affect the mean molecular weight. A simple model for spectral line formation suggests that the bisectors and absolute Doppler shifts of spectral lines depend on the helium abundance. We look at the effect of α-element enhancement and find that it has a considerably smaller effect on the convective dynamics in the superadiabatic layer compared to that of helium abundance.

  2. Empirical L-M, R-M, and M-Teff relations for main-sequence stars: Components of close binary systems and low-mass stars

    NASA Astrophysics Data System (ADS)

    Gorda, S. Yu.; Svechnikov, M. A.

    1999-08-01

    A new catalog of photometric, geometric, and absolute elements of 112 detached main-sequence eclipsing variables with known photometric and spectroscopic orbital elements has been combined with speckle-interferometry data for low-mass stars to yield new mass-luminosity, mass-radius, and mass-spectrum relations: M_bol = 4.46 - 9.52 - (lg M > -0.4), M_bol = 6.18 - 5.91 lg M (lg M <= -0.4); lg R = 0.096 + 0.652 lg M (lg M > 0.14), lg R = 0.10 + 1.03 lg M (lg M <= 0.14); lg M = - 5.60 + 1.504 lg T_eff (lg T_eff > 3.6), and lg M = - 29.4 + 8.2 lg T_eff (lg T_eff <= 3.6). In most cases, the component masses and radii used are accurate to 2-3 and 2-4%, respectively; the errors for low-mass stars are larger by factors of 3-4. The coefficients in the relations were derived using linear least squares fitting with corrections for noise in the independent variable.

  3. ON A TRANSITION FROM SOLAR-LIKE CORONAE TO ROTATION-DOMINATED JOVIAN-LIKE MAGNETOSPHERES IN ULTRACOOL MAIN-SEQUENCE STARS

    SciTech Connect

    Schrijver, Carolus J.

    2009-07-10

    For main-sequence stars beyond spectral type M5, the characteristics of magnetic activity common to warmer solar-like stars change into the brown-dwarf domain: the surface magnetic field becomes more dipolar and the evolution of the field patterns slows, the photospheric plasma is increasingly neutral and decoupled from the magnetic field, chromospheric and coronal emissions weaken markedly, and the efficiency of rotational braking rapidly decreases. Yet, radio emission persists, and has been argued to be dominated by electron-cyclotron maser emission instead of the gyrosynchrotron emission from warmer stars. These properties may signal a transition in the stellar extended atmosphere. Stars warmer than about M5 have a solar-like corona and wind-sustained heliosphere in which the atmospheric activity is powered by convective motions that move the magnetic field. Stars cooler than early-L, in contrast, may have a Jovian-like rotation-dominated magnetosphere powered by the star's rotation in a scaled-up analog of the magnetospheres of Jupiter and Saturn. A dimensional scaling relationship for rotation-dominated magnetospheres by Fan et al. is consistent with this hypothesis.

  4. The Infrared Eye of the Wide-Field Camera 3 on the Hubble Space Telescope Reveals Multiple Main Sequences of Very Low Mass Stars in NGC 2808

    NASA Astrophysics Data System (ADS)

    Milone, A. P.; Marino, A. F.; Cassisi, S.; Piotto, G.; Bedin, L. R.; Anderson, J.; Allard, F.; Aparicio, A.; Bellini, A.; Buonanno, R.; Monelli, M.; Pietrinferni, A.

    2012-08-01

    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 ~65% and ~35% of stars, 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 stars reinforces the inference that they have a primordial origin. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

  5. Stellar Boron Abundances near the Main-sequence Turnoff of the Open Cluster NGC 3293 and Implications for the Efficiency of Rotationally Driven Mixing in Stellar Envelopes

    NASA Astrophysics Data System (ADS)

    Proffitt, Charles R.; Lennon, Daniel J.; Langer, Norbert; Brott, Ines

    2016-06-01

    Spectra from the Hubble Space Telescope Cosmic Origins Spectrograph and the Space Telescope Imaging Spectrograph covering the B iii resonance line have been obtained for 10 early-B stars near the turnoff of the young Galactic open cluster NGC 3293. This is the first sample of boron abundance determinations in a single, clearly defined population of early-B stars that also covers a substantial range of projected rotational velocities. In most of these stars we detect partial depletion of boron at a level consistent with that expected for rotational mixing in single stars, but inconsistent with expectations for depletion from close binary evolution. However, our results do suggest that the efficiency of rotational mixing is at or slightly below the low end of the range predicted by the available theoretical calculations. The two most luminous targets observed have a very large boron depletion and may be the products of either binary interactions or post-main-sequence evolution. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with proposal GO-12520.

  6. THE INFRARED EYE OF THE WIDE-FIELD CAMERA 3 ON THE HUBBLE SPACE TELESCOPE REVEALS MULTIPLE MAIN SEQUENCES OF VERY LOW MASS STARS IN NGC 2808

    SciTech Connect

    Milone, A. P.; Aparicio, A.; Monelli, M. E-mail: aparicio@iac.es; and others

    2012-08-01

    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 stars, 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 stars reinforces the inference that they have a primordial origin.

  7. Improving Auditory Sequencing Skills in the Kindergarten-Age Child through the Increased Instruction of Music.

    ERIC Educational Resources Information Center

    Brandt, Millicent Hume

    A music teacher specialist at an elementary school with a typical kindergarten music program implemented a 10-week practicum intervention designed to improve the auditory sequencing skills of kindergarten children through increased instruction in music. Test scores on screening measures indicated the need to improve the children's auditory memory…

  8. Single-cell RNA sequencing reveals molecular and functional platelet bias of aged haematopoietic stem cells

    PubMed Central

    Grover, Amit; Sanjuan-Pla, Alejandra; Thongjuea, Supat; Carrelha, Joana; Giustacchini, Alice; Gambardella, Adriana; Macaulay, Iain; Mancini, Elena; Luis, Tiago C.; Mead, Adam; Jacobsen, Sten Eirik W.; Nerlov, Claus

    2016-01-01

    Aged haematopoietic stem cells (HSCs) generate more myeloid cells and fewer lymphoid cells compared with young HSCs, contributing to decreased adaptive immunity in aged individuals. However, it is not known how intrinsic changes to HSCs and shifts in the balance between biased HSC subsets each contribute to the altered lineage output. Here, by analysing HSC transcriptomes and HSC function at the single-cell level, we identify increased molecular platelet priming and functional platelet bias as the predominant age-dependent change to HSCs, including a significant increase in a previously unrecognized class of HSCs that exclusively produce platelets. Depletion of HSC platelet programming through loss of the FOG-1 transcription factor is accompanied by increased lymphoid output. Therefore, increased platelet bias may contribute to the age-associated decrease in lymphopoiesis. PMID:27009448

  9. Single-cell RNA sequencing reveals molecular and functional platelet bias of aged haematopoietic stem cells.

    PubMed

    Grover, Amit; Sanjuan-Pla, Alejandra; Thongjuea, Supat; Carrelha, Joana; Giustacchini, Alice; Gambardella, Adriana; Macaulay, Iain; Mancini, Elena; Luis, Tiago C; Mead, Adam; Jacobsen, Sten Eirik W; Nerlov, Claus

    2016-01-01

    Aged haematopoietic stem cells (HSCs) generate more myeloid cells and fewer lymphoid cells compared with young HSCs, contributing to decreased adaptive immunity in aged individuals. However, it is not known how intrinsic changes to HSCs and shifts in the balance between biased HSC subsets each contribute to the altered lineage output. Here, by analysing HSC transcriptomes and HSC function at the single-cell level, we identify increased molecular platelet priming and functional platelet bias as the predominant age-dependent change to HSCs, including a significant increase in a previously unrecognized class of HSCs that exclusively produce platelets. Depletion of HSC platelet programming through loss of the FOG-1 transcription factor is accompanied by increased lymphoid output. Therefore, increased platelet bias may contribute to the age-associated decrease in lymphopoiesis. PMID:27009448

  10. National Trends in Main Causes of Hospitalization: A Multi-Cohort Register Study of the Finnish Working-Age Population, 1976–2010

    PubMed Central

    Kouvonen, Anne; Koskinen, Aki; Varje, Pekka; Kokkinen, Lauri; De Vogli, Roberto; Väänänen, Ari

    2014-01-01

    Background The health transition theory argues that societal changes produce proportional changes in causes of disability and death. The aim of this study was to identify long-term changes in main causes of hospitalization in working-age population within a nation that has experienced considerable societal change. Methodology National trends in all-cause hospitalization and hospitalizations for the five main diagnostic categories were investigated in the data obtained from the Finnish Hospital Discharge Register. The seven-cohort sample covered the period from 1976 to 2010 and consisted of 3,769,356 randomly selected Finnish residents, each cohort representing 25% sample of population aged 18 to 64 years. Principal Findings Over the period of 35 years, the risk of hospitalization for cardiovascular diseases and respiratory diseases decreased. Hospitalization for musculoskeletal diseases increased whereas mental and behavioral hospitalizations slightly decreased. The risk of cancer hospitalization decreased marginally in men, whereas in women an upward trend was observed. Conclusions/Significance A considerable health transition related to hospitalizations and a shift in the utilization of health care services of working-age men and women took place in Finland between 1976 and 2010. PMID:25379723

  11. Palaeomagnetism and 40Ar/39Ar age of a Pliocene lava flow sequence in the Lesser Caucasus: record of a clockwise rotation and analysis of palaeosecular variation

    NASA Astrophysics Data System (ADS)

    Caccavari, Ana; Calvo-Rathert, Manuel; Goguitchaichvili, Avto; Huaiyu, He; Vashakidze, Goga; Vegas, Néstor

    2014-06-01

    A palaeomagnetic and rock-magnetic investigation has been carried out on a Pliocene lava flow sequence in the Djavakheti Highland in the central Lesser Caucasus in the Republic of Georgia. In addition, a 40Ar/39Ar dating and electronic microscopic studies were performed on samples of this sequence, named the Saro section, which consists of 39 successive lava flows of doleritic basalts. A characteristic magnetization could be isolated in all studied 39 flows, yielding reverse-polarity directions in all cases, a mean direction D = 202.2°, I = -60.6° (N = 39, α95 = 2.0°, k = 138) being obtained. Thermomagnetic experiments (strong-field versus temperature curves) suggested low-Ti titanomagnetites and low Curie-temperature titanomagnetites with a rather high titanium content (x ≈ 0.5-0.7) as the main carriers of remanence. Their domain structure is characterized by a mixture of single- and multidomain grains. 40Ar/39Ar dating yielded an age of 1.73 ± 0.03 Ma, interpreted as the eruption age of the uppermost lava flow of the sequence. Analysis of palaeomagnetic results and radiometric data from the present and a previous study allows two different explanations about the time of emplacement of the section: (i) The lower 36 flows of the sequence might have been emitted between the normal-polarity Reunion and Olduvai chrons, and the upper three flows after the Olduvai chron, with a long hiatus in volcanic activity of more than 150 kyr or (ii) The whole sequence has been emitted between 1.778 and 1.73 ± 0.03 Ma, after the Olduvai chron. Comparison of the palaeomagnetic results obtained in this study with the expected direction shows that while inclination values agree well, declination shows an eastward deviation of 19.2° ± 5.8°. This discrepancy can be explained with a clockwise vertical-axis rotation of the sequence, which might have been produced by extensional structures with strike-slip component, which can be found in the study area. Virtual geomagnetic pole

  12. Age constraints, sedimentology, and tectonics from a well bedded sequence of Feuerstätter Sandstein south of Balderschwang, Allgäu Alps, Bavaria

    NASA Astrophysics Data System (ADS)

    Blaha, Ulrich; Scholz, Herbert; Rochow, Henning v.; Lebsanft, Frans

    2014-05-01

    The majority of the outcrops of the alpine Feuerstätter Sandstein in southwestern Bavaria and Vorarlberg (Austria) suggests rather massive, homogeneous, more or less glauconite-containing sandstone bodies than well bedded sequences. Normally, the up to 50 m thick Feuerstätter Sandstein formation is characterized by the absence of datable material, massive brittle tectonic deformation and recent mass movements. In contrast, an unusually well bedded sequence of Feuerstätter Sandstein is exposed in the Lappach valley south of the village of Balderschwang, lining the border between Bavaria and Vorarlberg. This specific sandstone succession contains several thin marly intercalations from which samples have been collected recently. Calcareous nannoplancton dating of these marl samples provides an upper Middle-Eocene depositional age which is the youngest age reported for the Feuerstätter Sandstein. The sequence of the quartz sandstone of the Lappach succession including the marly layers is tectonically undisturbed. The beds dip northwards, steeply inclined at the bottom (85°) and moderately in the uppermost part (40°) of the sequence. The sandstone beds of the main part of the complex reveal mostly layers which are 0.1 to 0.7 m thick. In contrast, the uppermost beds exposed within the sequence show an increasing thickness of 2.5 to 4.5 m. A variety of different sedimentary structures occur in individual beds of the lower part: graded bedding, varying grain sizes, different amounts of glauconite, local occurrence of feldspar clasts, fine lamination and N-S striking channel structures at the bottom of certain sandstone layers. Within the uppermost exposed particularly thick and poorly to unsorted deposits of the sequence coarser grain sizes occur, containing even small quartz pebbles. The continuous development from the well bedded and fine grained basal layers towards the massive and coarser grained sandstone deposits at the top suggests sedimentation from a distal

  13. A simplified soil extraction sequence to monitor the main and trace element speciation in soil after compost and mineral fertilizer additions upon the composition of wheat grains

    NASA Astrophysics Data System (ADS)

    Sager, Manfred; Erhart, Eva

    2016-04-01

    High quality biological waste treatment aims at producing compost in order to maintain a clean environment and to sustain soil organic carbon levels. Fertilization with compost as a source of organic carbon, nutrients, and accessory elements, as well as fertilization with mineral N- and PK fertilizer have been tested in a field experiment on a calcaric Fluvisol in the Danube wetlands, at 4 levels each. Yields of wheat were recorded, and grains and soils were sampled from each treatment, and analyzed for main and trace element composition. The corresponding soils were characterized by mobile phases, obtained by leaching with 0,16M acetic acid to cover exchangeables plus carbonates, and subsequently by 0,1M oxalate buffer pH 3 to dissolve the pedogenic oxides. Total amounts were obtained from digests with perchloric- nitric-hydrofluoric acid. For quasi-total amounts, aqua regia was replaced by pressure decomposition with KClO3 in dilute nitric acid. The proposed extraction sequence permits to analyze and interpret soil for main elements, trace elements, nutrients and anions simultaneously. Factor analyses of soil extracts obtained from dilute acetic acid revealed Ba-Be-Cd-Cu-Li-S (traces), Ca-Mg-Mn (main carbonates), Al-Fe-B, Y, and P-K (nutrients) as chemically feasible principal components. Subsequent soil extracts from oxalate contained Al-B-Co-K-Na-Pb-Si-V-S (maybe acid silicate weathering), Cr-Li-Ni-Sr-Ti (maybe basic silicate weathering), Be-Cu-Fe-P, Co-Mg-Mn-Zn (Mn-oxides) and Ba-Sc as principal components. Factor analyses of total element data distinguished the principal components Ce-La-Li-Sc-Y-P (rare earths), Al-Ca-Fe-K-Mg-Na-P (main elements), Cd-Co-Cr-Cu-Ni-Zn (trace elements), As-Pb (contaminants), Ba-Mn-Sr, and Ti, which looks chemically feasible also. Factor analyses of those soil fractions which presumably form the main fractions of exchangeables, carbonates, pedogenic oxides and silicates, showed no cross connections, except for P. Oxalate

  14. Radiocarbon Ages from Two Submerged Strandline Features in the Western Gulf of Maine and a Sea-Level Curve for the Northeastern Massachusetts Coastal Region

    USGS Publications Warehouse

    Oldale, R.N.; Colman, Steven M.; Jones, Glenn A.

    1993-01-01

    New radiocarbon dates provide ages for two submerged strandline features on the Massachusetts inner shelf. These ages provide limited control on a relative sea-level (RSL) curve for the late Wisconsinan and Holocene. The curve indicates a late Wisconsinan high stand of RSL of +33 m about 14,000 yr ago and a very short-lived relative low stand of about -43 m at about 12,000 yr ago followed by a rise to present sea level. Rapid changes of RSL around 12,000 yr ago may be related to changes in global glacial meltwater discharge and eustatic sea-level change shown by dated corals off Barbados. Variations in the magnitude and timing of RSL change from south to north along the coast of the western Gulf of Maine are due to greater crustal depression and later deglaciation to the north.

  15. Stability of repetitive-sequence PCR patterns with respect to culture age and subculture frequency.

    PubMed

    Kang, Hyunseok Peter; Dunne, W Michael

    2003-06-01

    To examine the stability of repetitive-sequence (rep) PCR profiles, six species of bacteria were subcultured to blood agar plates and DNA was extracted from the cultures after 24, 48, and 72 h of incubation at 35 degrees C. In addition, the same species were subcultured to fresh blood plates daily and DNA was extracted from the cultures after growth of 5, 10, and 15 subcultures, respectively. rep PCR analysis demonstrated that all rep PCR fingerprints from a single species were identical.

  16. The Mass Function of Main-Sequence Stars in NGC 6397 from Near-Infrared and Optical High-Resolution Hubble Space Telescope Observations

    NASA Astrophysics Data System (ADS)

    De Marchi, Guido; Paresce, Francesco; Pulone, Luigi

    2000-02-01

    We have investigated the properties of the stellar mass function in the globular cluster NGC 6397 through the use of a large set of Hubble Space Telescope (HST) observations. The latter include existing WFPC 2 images in the V and I bands, obtained at ~4.5‧ and 10' radial distances, as well as a series of deep images in the J and H bands obtained with the NIC 2 and NIC 3 cameras of the NICMOS instrument pointed, respectively, to regions located ~4.5‧ and ~3.2‧ from the center. These observations span the region from ~1 to ~3 times the cluster's half-light radius (rhl~=3') and have been subjected to the same, homogeneous data processing so as to guarantee that the ensuing results could be directly compared to one another. We have built color-magnitude diagrams that we use to measure the luminosity function of main-sequence stars extending from just below the turnoff all the way down to the hydrogen-burning limit. All luminosity functions derived in this way show the same, consistent behavior in that they all increase with decreasing luminosity up to a peak at MI~=8.5 or MH~=7 and then drop precipitously well before photometric incompleteness becomes significant. Within the observational uncertainties, at MI~=12 or MH~=10.5 (~0.09 Msolar) the luminosity functions are compatible with zero. The direct comparison of our NIC 2 field with previous WFPC 2 observations of the same area shows that down to MH~=11 there are no more faint, red stars than those already detected by the WFPC 2, thus excluding a significant population of faint, low-mass stars at the bottom of the main sequence. By applying the best available mass-luminosity relation appropriate to the metallicity of NGC 6397 and consistent with our color-magnitude diagrams to both the optical and the IR data, we obtain a mass function that shows a break in slope at ~0.3 Msolar. No single-exponent power-law distribution is compatible with these data, regardless of the value of the exponent. We find that a

  17. GOODS-Herschel: Star Formation, Dust Attenuation, and the FIR-radio Correlation on the Main Sequence of Star-forming Galaxies up to z ≃4

    NASA Astrophysics Data System (ADS)

    Pannella, M.; Elbaz, D.; Daddi, E.; Dickinson, M.; Hwang, H. S.; Schreiber, C.; Strazzullo, V.; Aussel, H.; Bethermin, M.; Buat, V.; Charmandaris, V.; Cibinel, A.; Juneau, S.; Ivison, R. J.; Le Borgne, D.; Le Floc'h, E.; Leiton, R.; Lin, L.; Magdis, G.; Morrison, G. E.; Mullaney, J.; Onodera, M.; Renzini, A.; Salim, S.; Sargent, M. T.; Scott, D.; Shu, X.; Wang, T.

    2015-07-01

    We use deep panchromatic data sets in the GOODS-N field, from GALEX to the deepest Herschel far-infrared (FIR) and VLA radio continuum imaging, to explore the evolution of star-formation activity and dust attenuation properties of star-forming galaxies to z ≃ 4, using mass-complete samples. Our main results can be summarized as follows: (i) the slope of the star-formation rate-M* correlation is consistent with being constant ≃0.8 up to z ≃ 1.5, while its normalization keeps increasing with redshift; (ii) for the first time we are able to explore the FIR-radio correlation for a mass-selected sample of star-forming galaxies: the correlation does not evolve up to z ≃ 4; (iii) we confirm that galaxy stellar mass is a robust proxy for UV dust attenuation in star-forming galaxies, with more massive galaxies being more dust attenuated. Strikingly, we find that this attenuation relation evolves very weakly with redshift, with the amount of dust attenuation increasing by less than 0.3 mag over the redshift range [0.5-4] for a fixed stellar mass; (iv) the correlation between dust attenuation and the UV spectral slope evolves with redshift, with the median UV slope becoming bluer with redshift. By z ≃ 3, typical UV slopes are inconsistent, given the measured dust attenuations, with the predictions of commonly used empirical laws. (v) Finally, building on existing results, we show that gas reddening is marginally larger (by a factor of around 1.3) than the stellar reddening at all redshifts probed. Our results support a scenario where the ISM conditions of typical star-forming galaxies evolve with redshift, such that at z ≥ 1.5 Main Sequence galaxies have ISM conditions moving closer to those of local starbursts. Based on observations collected at the Herschel, Spitzer, Keck, NRAO-VLA, Subaru, KPNO, and CFHT observatories. Herschel is an European Space Agency Cornerstone Mission with science instruments provided by European-led Principal Investigator consortia and

  18. EFFECT OF METALLICITY ON THE EVOLUTION OF THE HABITABLE ZONE FROM THE PRE-MAIN SEQUENCE TO THE ASYMPTOTIC GIANT BRANCH AND THE SEARCH FOR LIFE

    SciTech Connect

    Danchi, William C.; Lopez, Bruno E-mail: bruno.lopez@oca.eu

    2013-05-20

    During the course of stellar evolution, the location and width of the habitable zone changes as the luminosity and radius of the star evolves. The duration of habitability for a planet located at a given distance from a star is greatly affected by the characteristics of the host star. A quantification of these effects can be used observationally in the search for life around nearby stars. The longer the duration of habitability, the more likely it is that life has evolved. The preparation of observational techniques aimed at detecting life would benefit from the scientific requirements deduced from the evolution of the habitable zone. We present a study of the evolution of the habitable zone around stars of 1.0, 1.5, and 2.0 M{sub Sun} for metallicities ranging from Z = 0.0001 to Z = 0.070. We also consider the evolution of the habitable zone from the pre-main sequence until the asymptotic giant branch is reached. We find that metallicity strongly affects the duration of the habitable zone for a planet as well as the distance from the host star where the duration is maximized. For a 1.0 M{sub Sun} star with near solar metallicity, Z = 0.017, the duration of the habitable zone is >10 Gyr at distances 1.2-2.0 AU from the star, whereas the duration is >20 Gyr for high-metallicity stars (Z = 0.070) at distances of 0.7-1.8 AU, and {approx}4 Gyr at distances of 1.8-3.3 AU for low-metallicity stars (Z = 0.0001). Corresponding results have been obtained for stars of 1.5 and 2.0 solar masses.

  19. Three-Site Photometric Monitoring of the δ Sct-Type Pulsating Star V1162 Orionis: Period Change and its Implications for Pre-Main Sequence Evolution

    NASA Astrophysics Data System (ADS)

    Kim, Seung-Lee; Cha, Sang-Mok; Lim, Beomdu; Lee, Jae Woo; Lee, Chung-Uk; Lee, Yongseok; Kim, Dong-Jin; Lee, Dong-Joo; Koo, Jae-Rim; Hong, Kyeongsoo; Ryu, Yoon-Hyun; Park, Byeong-Gon

    2016-10-01

    We present photometric results of the δ Sct star V1162 Ori, which is extensively monitored for a total of 49 nights from mid-December 2014 to early-March 2015. The observations are made with three KMTNet (Korea Microlensing Telescope Network) 1.6 m telescopes installed in Chile, South Africa, and Australia. Multiple frequency analysis is applied to the data and resulted in clear detection of seven frequencies without an alias problem: five known frequencies and two new ones with small amplitudes of 1.2-1.7 mmag. The amplitudes of all but one frequency are significantly different from previous results, confirming the existence of long-term amplitude changes. We examine the variations in pulsation timings of V1162 Ori for about 30 years by using the times of maximum light obtained from our data and collected from the literatures. The O-C (Observed minus Calculated) timing diagram shows a combination of a downward parabolic variation with a period decreasing rate of (1/P)dP/dt = -4.22 × 10^{-6} year^{-1} and a cyclic change with a period of about 2780 days. The most probable explanation for this cyclic variation is the light-travel-time effect caused by an unknown binary companion, which has a minimum mass of 0.69 M_⊙. V1162 Ori is the first δ Sct-type pulsating star of which the observed fast period decrease can be interpreted as an evolutionary effect of a pre-main sequence star, considering its membership of the Orion OB 1c association.}

  20. A HIGHER EFFICIENCY OF CONVERTING GAS TO STARS PUSHES GALAXIES AT z ∼ 1.6 WELL ABOVE THE STAR-FORMING MAIN SEQUENCE

    SciTech Connect

    Silverman, J. D.; Rujopakarn, W.; Daddi, E.; Liu, D.; Sargent, M.; Renzini, A.; Feruglio, C.; Kashino, D.; Sanders, D.; Kartaltepe, J.; Nagao, T.; Arimoto, N.; Berta, S.; Lutz, D.; Béthermin, M.; Koekemoer, A.; and others

    2015-10-20

    Local starbursts have a higher efficiency of converting gas into stars, as compared to typical star-forming galaxies at a given stellar mass, possibly indicative of different modes of star formation. With the peak epoch of galaxy formation occurring at z > 1, it remains to be established whether such an efficient mode of star formation is occurring at high redshift. To address this issue, we measure the molecular gas content of seven high-redshift (z ∼ 1.6) starburst galaxies with the Atacama Large Millimeter/submillimeter Array and IRAM/Plateau de Bure Interferometer. Our targets are selected from the sample of Herschel far-infrared-detected galaxies having star formation rates (∼300–800 M{sub ⊙} yr{sup −1}) elevated (≳4×) above the star-forming main sequence (MS) and included in the FMOS-COSMOS near-infrared spectroscopic survey of star-forming galaxies at z ∼ 1.6 with Subaru. We detect CO emission in all cases at high levels of significance, indicative of high gas fractions (∼30%–50%). Even more compelling, we firmly establish with a clean and systematic selection that starbursts, identified as MS outliers, at high redshift generally have a lower ratio of CO to total infrared luminosity as compared to typical MS star-forming galaxies, although with a smaller offset than expected based on past studies of local starbursts. We put forward a hypothesis that there exists a continuous increase in star formation efficiency with elevation from the MS with galaxy mergers as a possible physical driver. Along with a heightened star formation efficiency, our high-redshift sample is similar in other respects to local starbursts, such as being metal rich and having a higher ionization state of the interstellar medium.

  1. Delayed Gratification Habitable Zones (DG-HZs): When Deep Outer Solar System Regions Become Balmy During Post-Main Sequence Stellar Evolution

    NASA Astrophysics Data System (ADS)

    Stern, S. A.

    2002-09-01

    Late in the Sun's evolution it, like all low and moderate mass stars, it will burn as a red giant, generating 1000s of solar luminosities for a few tens of millions of years. A dozen years ago this stage of stellar evolution was predicted to create observable sublimation signatures in systems where Kuiper Belts (KBs) are extant (Stern et al. 1990, Nature, 345, 305); recently, the SWAS spacecraft detected such systems (Melnick et al. 2001, 412, 160). During the red giant phase, the habitable zone of our solar system will lie in the region where Triton, Pluto-Charon, and KBOs orbit. Compared to the 1 AU habitable zone where Earth resided early in the solar system's history, this "delayed gratification habitable zone (DG-HZ)" will enjoy a far less biologically hazardous environment-- with far lower harmful UV radiation levels from the Sun, and a far quieter collisional environment. Objects like Triton, Pluto-Charon, and KBOs, which are known to be rich in both water and organics, will then become possible sites for biochemical and perhaps even biological evolution. The Sun's DG-HZ may only be of academic interest owing to its great separation from us in time. However, several 108 approximately solar-type Milky Way stars burn as luminous red giants today. Thus, if icy-organic objects are common in the 20-50 AU zones of these stars, as they are in our solar system (and as inferred in numerous main sequence stellar disk systems), then DG-HZs form a kind of niche habitable zone that is likely to be numerically common in the galaxy. I will show the calculated temporal evolution of DG-HZs around various stellar types using modern stellar evolution luminosity tracks, and then discuss various aspects of DG-HZs, including the effects of stellar pulsations and mass loss winds. This work was supported by NASA's Origins of Solar Systems Program.

  2. On the nature of Hα emitters at z ˜ 2 from the HiZELS survey: physical properties, Lyα escape fraction and main sequence

    NASA Astrophysics Data System (ADS)

    Oteo, I.; Sobral, D.; Ivison, R. J.; Smail, I.; Best, P. N.; Cepa, J.; Pérez-García, A. M.

    2015-09-01

    We present a detailed multiwavelength study (from rest-frame ultraviolet to far-infrared) of narrow-band selected, star-forming (SF) Hα emitters (HAEs) at z ˜ 2.23 taken from the High-Redshift(Z) Emission Line Survey (HiZELS). We find that HAEs have similar properties and colours derived from spectral energy distributions as sBzK galaxies, and probe a well-defined portion of the SF population at z ˜ 2. This is not true for Lyα emitters (LAEs), which are strongly biased towards blue, less massive galaxies (missing a significant percentage of the SF population). Combining our Hα observations with matched, existing Lyα data, we determine that the Lyα escape fraction (fesc) is low (only ˜4.5 per cent of HAEs show Lyα emission) and decreases with increasing dust attenuation, ultraviolet continuum slope, stellar mass and star formation rate (SFR). This suggests that Lyα preferentially escapes from blue galaxies with low dust attenuation. However, a small population of red and massive LAEs is also present, in agreement with previous works and indicating that dust and Lyα are not mutually exclusive. Using different and completely independent measures of the total SFR, we show that the Hα emission is an excellent tracer of star formation at z ˜ 2 with deviations typically lower than 0.3 dex for individual galaxies. We find that the slope and zero-point of the HAE main sequence at z ˜ 2 strongly depend on the dust-correction method used to recover the SFR, although they are consistent with previous works when similar assumptions are made.

  3. Mid-IR spectra of pre-main sequence Herbig stars: An explanation for the non-detections of water lines

    NASA Astrophysics Data System (ADS)

    Antonellini, S.; Kamp, I.; Lahuis, F.; Woitke, P.; Thi, W.-F.; Meijerink, R.; Aresu, G.; Spaans, M.; Güdel, M.; Liebhart, A.

    2016-01-01

    Context. The mid-IR detection rate of water lines in disks around Herbig stars disks is about 5%, while it is around 50% for disks around T Tauri stars. The reason for this is still unclear. Aims: In this study, we want to find an explanation for the different detection rates between low mass and high mass pre-main-sequence stars in the mid-IR regime. Methods: We ran disk models with stellar parameters adjusted to spectral types B9 through M2, using the radiation thermo-chemical disk modelling code ProDiMo. We explored also a small parameter space around a standard disk model, considering dust-to-gas mass ratio, disk gas mass, mixing coefficient for dust settling, flaring index, dust maximum size, and size power law distribution index. We produced convolved spectra at the resolution of Spitzer, IRS, JWST MIRI, and VLT VISIR spectrographs. We applied random noise derived from typical Spitzer spectra for a direct comparison with observations. Results: The strength of the mid-IR water lines correlates directly with the luminosity of the central star. The models show that it is possible to suppress the water emission; however, current observations are not sensitive enough to detect mid-IR lines in disks for most of the explored parameters. The presence of noise in the spectra, combined with the high continuum flux (noise level is proportional to the continuum flux), is the most likely explanation for the non-detections towards Herbig stars. Conclusions: Mid-IR spectra with resolution higher than 20 000 are needed to investigate water in protoplanetary disks. Intrinsic differences in disk structure, such as inner gaps, gas-to-dust ratio, dust size and distribution, and inner disk scale height, between Herbig and T Tauri star disks are able to explain a lower water detection rate in disks around Herbig stars.

  4. Searching for gas giant planets on Solar system scales - a NACO/APP L'-band survey of A- and F-type main-sequence stars

    NASA Astrophysics Data System (ADS)

    Meshkat, T.; Kenworthy, M. A.; Reggiani, M.; Quanz, S. P.; Mamajek, E. E.; Meyer, M. R.

    2015-11-01

    We report the results of a direct imaging survey of A- and F-type main-sequence stars searching for giant planets. A/F stars are often the targets of surveys, as they are thought to have more massive giant planets relative to solar-type stars. However, most imaging is only sensitive to orbital separations >30 au, where it has been demonstrated that giant planets are rare. In this survey, we take advantage of the high-contrast capabilities of the Apodizing Phase Plate coronagraph on NACO at the Very Large Telescope. Combined with optimized principal component analysis post-processing, we are sensitive to planetary-mass companions (2-12 MJup) at Solar system scales (≤30 au). We obtained data on 13 stars in the L' band and detected one new companion as part of this survey: an M6.0 ± 0.5 dwarf companion around HD 984. We re-detect low-mass companions around HD 12894 and HD 20385, both reported shortly after the completion of this survey. We use Monte Carlo simulations to determine new constraints on the low-mass (<80 MJup) companion frequency, as a function of mass and separation. Assuming solar-type planet mass and separation distributions, normalized to the planet frequency appropriate for A-stars, and the observed companion mass-ratio distribution for stellar companions extrapolated to planetary masses, we derive a truncation radius for the planetary mass companion surface density of <135 au at 95 per cent confidence.

  5. XMM-Newton Monitoring of the Close Pre-main-sequence Binary AK Sco. Evidence of Tide-driven Filling of the Inner Gap in the Circumbinary Disk

    NASA Astrophysics Data System (ADS)

    Gómez de Castro, Ana I.; López-Santiago, Javier; Talavera, Antonio; Sytov, A. Yu.; Bisikalo, D.

    2013-03-01

    AK Sco stands out among pre-main-sequence binaries because of its prominent ultraviolet excess, the high eccentricity of its orbit, and the strong tides driven by it. AK Sco consists of two F5-type stars that get as close as 11 R * at periastron passage. The presence of a dense (ne ~ 1011 cm-3) extended envelope has been unveiled recently. In this article, we report the results from an XMM-Newton-based monitoring of the system. We show that at periastron, X-ray and UV fluxes are enhanced by a factor of ~3 with respect to the apastron values. The X-ray radiation is produced in an optically thin plasma with T ~ 6.4 × 106 K and it is found that the N H column density rises from 0.35 × 1021 cm-2 at periastron to 1.11 × 1021 cm-2 at apastron, in good agreement with previous polarimetric observations. The UV emission detected in the Optical Monitor band seems to be caused by the reprocessing of the high-energy magnetospheric radiation on the circumstellar material. Further evidence of the strong magnetospheric disturbances is provided by the detection of line broadening of 278.7 km s-1 in the N V line with Hubble Space Telescope/Space Telescope Imaging Spectrograph. Numerical simulations of the mass flow from the circumbinary disk to the components have been carried out. They provide a consistent scenario with which to interpret AK Sco observations. We show that the eccentric orbit acts like a gravitational piston. At apastron, matter is dragged efficiently from the inner disk border, filling the inner gap and producing accretion streams that end as ring-like structures around each component of the system. At periastron, the ring-like structures come into contact, leading to angular momentum loss, and thus producing an accretion outburst.

  6. Construction of Graphic Symbol Sequences by Preschool-Aged Children: Learning, Training, and Maintenance

    ERIC Educational Resources Information Center

    Poupart, Annick; Trudeau, Natacha; Sutton, Ann

    2013-01-01

    The use of augmentative and alternative communication systems based on graphic symbols requires children to learn to combine symbols to convey utterances. The current study investigated how children without disabilities aged 4 to 6 years (n = 74) performed on a simple sentence (subject-verb and subject-verb-object) transposition task (i.e., spoken…

  7. Gene Expression Analysis in the Age of Mass Sequencing: An Introduction.

    PubMed

    Pilarsky, Christian; Nanduri, Lahiri Kanth; Roy, Janine

    2016-01-01

    During the last years the technology used for gene expression analysis has changed dramatically. The old mainstay, DNA microarray, has served its due course and will soon be replaced by next-generation sequencing (NGS), the Swiss army knife of modern high-throughput nucleic acid-based analysis. Therefore preparation technologies have to adapt to suit the emerging NGS technology platform. Moreover, interpretation of the results is still time consuming and employs the use of high-end computers usually not found in molecular biology laboratories. Alternatively, cloud computing might solve this problem. Nevertheless, these new challenges have to be embraced for gene expression analysis in general. PMID:26667455

  8. Genetic linkage analysis in the age of whole-genome sequencing.

    PubMed

    Ott, Jurg; Wang, Jing; Leal, Suzanne M

    2015-05-01

    For many years, linkage analysis was the primary tool used for the genetic mapping of Mendelian and complex traits with familial aggregation. Linkage analysis was largely supplanted by the wide adoption of genome-wide association studies (GWASs). However, with the recent increased use of whole-genome sequencing (WGS), linkage analysis is again emerging as an important and powerful analysis method for the identification of genes involved in disease aetiology, often in conjunction with WGS filtering approaches. Here, we review the principles of linkage analysis and provide practical guidelines for carrying out linkage studies using WGS data. PMID:25824869

  9. Main-Chain and Side-Chain Sequence-Regulated Vinyl Copolymers by Iterative Atom Transfer Radical Additions and 1:1 or 2:1 Alternating Radical Copolymerization.

    PubMed

    Soejima, Takamasa; Satoh, Kotaro; Kamigaito, Masami

    2016-01-27

    Main- and side-chain sequence-regulated vinyl copolymers were prepared by a combination of iterative atom transfer radical additions (ATRAs) of vinyl monomers for side-chain control and 1:1 or 2:1 alternating radical copolymerization of the obtained side-chain sequenced "oligomonomers" and vinyl comonomers for main-chain control. A complete set of sequence-regulated trimeric vinyl oligomers of styrene (S) and/or methyl acrylate (A) were first synthesized via iterative ATRAs of these monomers to a halide of monomeric S or A unit (X-S or X-A) under optimized conditions with appropriate ruthenium or copper catalysts, which were selected depending on the monomers and halides. The obtained halogen-capped oligomers were then converted into a series of maleimide (M)-ended oligomonomers with different monomer compositions and sequences (M-SSS, M-ASS, M-SAS, M-AAS, M-SSA, M-ASA, M-SAA, M-AAA) by a substitution reaction of the halide with furan-protected maleimide anion followed by deprotection of the furan units. These maleimide-ended oligomonomers were then radically copolymerized with styrene or limonene to enable the 1:1 or 2:1 monomer-sequence regulation in the main chain and finally result in the main- and side-chain sequence-regulated vinyl copolymers with high molecular weights in high yield. The properties of the sequence-regulated vinyl copolymers depended on not only the monomer compositions but also the monomer sequences. The solubility was highly affected by the outer monomer units in the side chains whereas the glass transition temperatures were primarily affected by the two successive monomer sequences. PMID:26761148

  10. A comparison of zircon U-Pb age results of the Red Clay sequence on the central Chinese Loess Plateau

    NASA Astrophysics Data System (ADS)

    Gong, Hujun; Nie, Junsheng; Wang, Zhao; Peng, Wenbin; Zhang, Rui; Zhang, Yunxiang

    2016-08-01

    Single grain zircon U-Pb geochronology has demonstrated great potentials in extracting tectonic and atmospheric circulation signal carried by aeolian, fluvial, and fluviolacustrine sediments. A routine in this sort of studies is analyzing 100–150 grains and then compares zircon U-Pb age spectra between the measured sample and the potential sources. Here we compared the zircon U-Pb age results of the late Miocene-Pliocene Red Clay sequence of two neighboring sites from the Chinese Loess Plateau where similar provenance signal is expected. Although the results from the 5.5 Ma sediment support this prediction, the results from the 3 Ma sediment at these two sites differ from each other significantly. These results emphasize the importance of increasing analysis number per sample and combining the zircon U-Pb geochronology with other provenance tools in order to get reliable provenance information.

  11. A comparison of zircon U-Pb age results of the Red Clay sequence on the central Chinese Loess Plateau

    PubMed Central

    Gong, Hujun; Nie, Junsheng; Wang, Zhao; Peng, Wenbin; Zhang, Rui; Zhang, Yunxiang

    2016-01-01

    Single grain zircon U-Pb geochronology has demonstrated great potentials in extracting tectonic and atmospheric circulation signal carried by aeolian, fluvial, and fluviolacustrine sediments. A routine in this sort of studies is analyzing 100–150 grains and then compares zircon U-Pb age spectra between the measured sample and the potential sources. Here we compared the zircon U-Pb age results of the late Miocene-Pliocene Red Clay sequence of two neighboring sites from the Chinese Loess Plateau where similar provenance signal is expected. Although the results from the 5.5 Ma sediment support this prediction, the results from the 3 Ma sediment at these two sites differ from each other significantly. These results emphasize the importance of increasing analysis number per sample and combining the zircon U-Pb geochronology with other provenance tools in order to get reliable provenance information. PMID:27538343

  12. A comparison of zircon U-Pb age results of the Red Clay sequence on the central Chinese Loess Plateau.

    PubMed

    Gong, Hujun; Nie, Junsheng; Wang, Zhao; Peng, Wenbin; Zhang, Rui; Zhang, Yunxiang

    2016-01-01

    Single grain zircon U-Pb geochronology has demonstrated great potentials in extracting tectonic and atmospheric circulation signal carried by aeolian, fluvial, and fluviolacustrine sediments. A routine in this sort of studies is analyzing 100-150 grains and then compares zircon U-Pb age spectra between the measured sample and the potential sources. Here we compared the zircon U-Pb age results of the late Miocene-Pliocene Red Clay sequence of two neighboring sites from the Chinese Loess Plateau where similar provenance signal is expected. Although the results from the 5.5 Ma sediment support this prediction, the results from the 3 Ma sediment at these two sites differ from each other significantly. These results emphasize the importance of increasing analysis number per sample and combining the zircon U-Pb geochronology with other provenance tools in order to get reliable provenance information.

  13. A comparison of zircon U-Pb age results of the Red Clay sequence on the central Chinese Loess Plateau.

    PubMed

    Gong, Hujun; Nie, Junsheng; Wang, Zhao; Peng, Wenbin; Zhang, Rui; Zhang, Yunxiang

    2016-01-01

    Single grain zircon U-Pb geochronology has demonstrated great potentials in extracting tectonic and atmospheric circulation signal carried by aeolian, fluvial, and fluviolacustrine sediments. A routine in this sort of studies is analyzing 100-150 grains and then compares zircon U-Pb age spectra between the measured sample and the potential sources. Here we compared the zircon U-Pb age results of the late Miocene-Pliocene Red Clay sequence of two neighboring sites from the Chinese Loess Plateau where similar provenance signal is expected. Although the results from the 5.5 Ma sediment support this prediction, the results from the 3 Ma sediment at these two sites differ from each other significantly. These results emphasize the importance of increasing analysis number per sample and combining the zircon U-Pb geochronology with other provenance tools in order to get reliable provenance information. PMID:27538343

  14. Termite hindguts and the ecology of microbial communities in the sequencing age.

    PubMed

    Tai, Vera; Keeling, Patrick J

    2013-01-01

    Advances in high-throughput nucleic acid sequencing have improved our understanding of microbial communities in a number of ways. Deeper sequence coverage provides the means to assess diversity at the resolution necessary to recover ecological and biogeographic patterns, and at the same time single-cell genomics provides detailed information about the interactions between members of a microbial community. Given the vastness and complexity of microbial ecosystems, such analyses remain challenging for most environments, so greater insight can also be drawn from analysing less dynamic ecosystems. Here, we outline the advantages of one such environment, the wood-digesting hindgut communities of termites and cockroaches, and how it is a model to examine and compare both protist and bacterial communities. Beyond the analysis of diversity, our understanding of protist community ecology will depend on using statistically sound sampling regimes at biologically relevant scales, transitioning from discovery-based to experimental ecology, incorporating single-cell microbiology and other data sources, and continued development of analytical tools. PMID:23710655

  15. Genomewide analysis of Drosophila circular RNAs reveals their structural and sequence properties and age-dependent neural accumulation

    PubMed Central

    Westholm, Jakub O.; Miura, Pedro; Olson, Sara; Shenker, Sol; Joseph, Brian; Sanfilippo, Piero; Celniker, Susan E.; Graveley, Brenton R.; Lai, Eric C.

    2014-01-01

    Circularization was recently recognized to broadly expand transcriptome complexity. Here, we exploit massive Drosophila total RNA-sequencing data, >5 billion paired-end reads from >100 libraries covering diverse developmental stages, tissues and cultured cells, to rigorously annotate >2500 fruitfly circular RNAs. These mostly derive from back-splicing of protein-coding genes and lack poly(A) tails, and circularization of hundreds of genes is conserved across multiple Drosophila species. We elucidate structural and sequence properties of Drosophila circular RNAs, which exhibit commonalities and distinctions from mammalian circles. Notably, Drosophila circular RNAs harbor >1000 well-conserved canonical miRNA seed matches, especially within coding regions, and coding conserved miRNA sites reside preferentially within circularized exons. Finally, we analyze the developmental and tissue specificity of circular RNAs, and note their preferred derivation from neural genes and enhanced accumulation in neural tissues. Interestingly, circular isoforms increase dramatically relative to linear isoforms during CNS aging, and constitute a novel aging biomarker. PMID:25544350

  16. XMM-NEWTON MONITORING OF THE CLOSE PRE-MAIN-SEQUENCE BINARY AK SCO. EVIDENCE OF TIDE-DRIVEN FILLING OF THE INNER GAP IN THE CIRCUMBINARY DISK

    SciTech Connect

    Gomez de Castro, Ana Ines; Lopez-Santiago, Javier; Talavera, Antonio; Sytov, A. Yu.; Bisikalo, D.

    2013-03-20

    AK Sco stands out among pre-main-sequence binaries because of its prominent ultraviolet excess, the high eccentricity of its orbit, and the strong tides driven by it. AK Sco consists of two F5-type stars that get as close as 11 R{sub *} at periastron passage. The presence of a dense (n{sub e} {approx} 10{sup 11} cm{sup -3}) extended envelope has been unveiled recently. In this article, we report the results from an XMM-Newton-based monitoring of the system. We show that at periastron, X-ray and UV fluxes are enhanced by a factor of {approx}3 with respect to the apastron values. The X-ray radiation is produced in an optically thin plasma with T {approx} 6.4 Multiplication-Sign 10{sup 6} K and it is found that the N{sub H} column density rises from 0.35 Multiplication-Sign 10{sup 21} cm{sup -2} at periastron to 1.11 Multiplication-Sign 10{sup 21} cm{sup -2} at apastron, in good agreement with previous polarimetric observations. The UV emission detected in the Optical Monitor band seems to be caused by the reprocessing of the high-energy magnetospheric radiation on the circumstellar material. Further evidence of the strong magnetospheric disturbances is provided by the detection of line broadening of 278.7 km s{sup -1} in the N V line with Hubble Space Telescope/Space Telescope Imaging Spectrograph. Numerical simulations of the mass flow from the circumbinary disk to the components have been carried out. They provide a consistent scenario with which to interpret AK Sco observations. We show that the eccentric orbit acts like a gravitational piston. At apastron, matter is dragged efficiently from the inner disk border, filling the inner gap and producing accretion streams that end as ring-like structures around each component of the system. At periastron, the ring-like structures come into contact, leading to angular momentum loss, and thus producing an accretion outburst.

  17. Accretion and Magnetic Reconnection in the Pre-Main Sequence Binary DQ Tau as Revealed through High-Cadence Optical Photometry

    NASA Astrophysics Data System (ADS)

    Tofflemire, Benjamin M.; Mathieu, Robert D.; Ardila, David R.; Akeson, Rachel L.; Ciardi, David R.; Herczeg, Gregory; Johns-Krull, Christopher M.; Vodniza, Alberto

    2016-01-01

    Protostellar disks are integral to the formation and evolution of low-mass stars and planets. A paradigm for the star-disk interaction has been extensively developed through theory and observation in the case of single stars. Most stars, however, form in binaries or higher order systems where the distribution of disk material and mass flows are more complex. Pre-main sequence (PMS) binary stars can have up to three accretion disks: two circumstellar disks and a circumbinary disk separated by a dynamically cleared gap. Theory suggests that mass may periodically flow in an accretion stream from a circumbinary disk across the gap onto circumstellar disks or stellar surfaces.The archetype for this theory is the eccentric, PMS binary DQ Tau. Moderate-cadence broadband photometry (~10 observations per orbital period) has shown pulsed brightening events near most periastron passages, just as numerical simulations would predict for a binary of similar orbital parameters. While this observed behavior supports the accretion stream theory, it is not exclusive to variable accretion rates. Magnetic reconnection events (flares) during the collision of stellar magnetospheres at periastron (when separated by 8 stellar radii) could produce the same periodic, broadband behavior when observed at a one-day cadence. Further evidence for magnetic activity comes from gyrosynchrotron, radio flares (typical of stellar flares) observed near multiple periastron passages. To reveal the physical mechanism seen in DQ Tau's moderate-cadence observations, we have obtained continuous, moderate-cadence, multi-band photometry over 10 orbital periods (LCOGT 1m network), supplemented with 32 nights of minute-cadence photometry centered on 4 separate periastron passages (WIYN 0.9m; APO ARCSAT). With detailed lightcurve morphologies we distinguish between the gradual rise and fall on multi-day time-scales predicted by the accretion stream theory and the hour time-scale, rapid-rise and exponential

  18. PRE-MAIN SEQUENCE VARIABLES IN THE VMR-D: IDENTIFICATION OF T TAURI-LIKE ACCRETING PROTOSTARS THROUGH SPITZER-IRAC VARIABILITY

    SciTech Connect

    Giannini, T.; Lorenzetti, D.; De Luca, M.; Nisini, B.; Elia, D.; Strafella, F.; Fazio, G.; Marengo, M.; Smith, H. A. E-mail: dloren@oa-roma.inaf.i E-mail: deluca@oa-roma.inaf.i E-mail: eliad@le.infn.i E-mail: massimo.de.luca@lra.ens.f E-mail: hsmith@cfa.harvard.ed

    2009-10-10

    We present a study of the infrared variability of young stellar objects by means of two Spitzer-IRAC images of the Vela Molecular Cloud D (VMR-D) obtained in observations separated in time by about six months. By using the same space-born IR instrumentation, this study eliminates all the unwanted effects due to differences in sensitivity, confusion, saturation, calibration, and filter bandpasses, issues that are usually unavoidable when comparing catalogs obtained from different instruments. The VMR-D map covers about 1.5 deg{sup 2} of a site where star formation is actively ongoing. We are interested in accreting pre-main sequence variables whose luminosity variations are due to intermittent events of disk accretion (i.e., active T Tauri stars and EXor-type objects). The variable objects have been selected from a catalog of more than 170,000 sources detected at an S/N >= 5. We then searched the sample of variables for ones whose photometric properties such as IR excess, color-magnitude relationships, and spectral energy distribution, are as close as possible to those of known EXor's. Indeed, the latter are monitored in a more systematic way than T Tauri stars and the mechanisms that regulate the observed phenomenology are exactly the same. Hence, the modalities of the EXor behavior are adopted as driving criterion for selecting variables in general. We ultimately selected 19 bona fide candidates that constitute a well defined sample of new variable targets for further investigation (monitoring, spectroscopy). Out of these, 10 sources present a Spitzer MIPS 24 mum counterpart, and have been classified as three Class I, five flat spectrum, and two Class II objects, while the spectral energy distribution of the other nine sources is compatible with evolutionary phases older than Class I. This is consistent with what is known about the small sample of known EXor's, whose properties have driven the present selection and suggests that the accretion flaring or EXor stage

  19. Chandra Observation of the Trifid Nebula: X-Ray Emission from the O Star Complex and Actively Forming Pre-Main-Sequence Stars

    NASA Astrophysics Data System (ADS)

    Rho, Jeonghee; Ramírez, Solange V.; Corcoran, Michael F.; Hamaguchi, Kenji; Lefloch, Bertrand

    2004-06-01

    The Trifid Nebula, a young star-forming H II region, was observed for 16 hr by the ACIS-I detector on board the Chandra X-Ray Observatory. We detected 304 X-ray sources, 30% of which are hard sources and 70% of which have near-infrared counterparts. Chandra resolved the HD 164492 multiple system into a number of discrete X-ray sources. X-ray emission is detected from components HD 164492A (an O7.5 III star that ionizes the nebula), B and C (a B6 V star), and possibly D (a Be star). Component C is blended with an unidentified source to the northwest. HD 164492A has a soft spectrum (kT~0.5 keV), while the component C blend shows much harder emission (kT~6 keV). This blend and other hard sources are responsible for the hard emission and Fe K line seen by ASCA, which was previously attributed entirely to HD 164492A. The soft spectrum of the O star is similar to emission seen from other single O stars and is probably produced by shocks within its massive stellar wind. Lack of hard emission suggests that neither a magnetically confined wind shock nor colliding wind emission is important in HD 164492A. A dozen stars are found to have flares in the field, and most of them are pre-main-sequence stars (PMS). Six sources with flares have both optical and Two Micron All Sky Survey counterparts. These counterparts are not embedded, and thus it is likely that these sources are in a later stage of PMS evolution, possibly Class II or III. Two flare sources did not have any near-IR, optical, or radio counterparts. We suggest that these X-ray flare stars are in an early PMS stage (Class I or earlier). We also detected X-ray sources apparently associated with two massive star-forming cores, TC 1 and TC 4. The spectra of these sources show high extinction and X-ray luminosities of (2-5)×1031 ergs s-1. If these sources are Class 0 objects, it is unclear whether their X-ray emission is due to solar-type magnetic activities, as in Class I objects, or to some other mechanism.

  20. The VLT-FLAMES Tarantula Survey. XVII. Physical and wind properties of massive stars at the top of the main sequence

    NASA Astrophysics Data System (ADS)

    Bestenlehner, J. M.; Gräfener, G.; Vink, J. S.; Najarro, F.; de Koter, A.; Sana, H.; Evans, C. J.; Crowther, P. A.; Hénault-Brunet, V.; Herrero, A.; Langer, N.; Schneider, F. R. N.; Simón-Díaz, S.; Taylor, W. D.; Walborn, N. R.

    2014-10-01

    The evolution and fate of very massive stars (VMS) is tightly connected to their mass-loss properties. Their initial and final masses differ significantly as a result of mass loss. VMS have strong stellar winds and extremely high ionising fluxes, which are thought to be critical sources of both mechanical and radiative feedback in giant H ii regions. However, how VMS mass-loss properties change during stellar evolution is poorly understood. In the framework of the VLT-Flames Tarantula Survey (VFTS), we explore the mass-loss transition region from optically thin O star winds to denser WNh Wolf-Rayet star winds, thereby testing theoretical predictions. To this purpose we select 62 O, Of, Of/WN, and WNh stars, an unprecedented sample of stars with the highest masses and luminosities known. We perform a spectral analysis of optical VFTS as well as near-infrared VLT/SINFONI data using the non-LTE radiative transfer code CMFGEN to obtain both stellar and wind parameters. For the first time, we observationally resolve the transition between optically thin O star winds and optically thick hydrogen-rich WNh Wolf-Rayet winds. Our results suggest the existence of a "kink" between both mass-loss regimes, in agreement with recent Monte Carlo simulations. For the optically thick regime, we confirm the steep dependence on the classical Eddington factor Γe from previous theoretical and observational studies. The transition occurs on the main sequence near a luminosity of 106.1L⊙, or a mass of 80 ... 90 M⊙. Above this limit, we find that - even when accounting for moderate wind clumping (with fv = 0.1) - wind mass-loss rates are enhanced with respect to standard prescriptions currently adopted in stellar evolution calculations. We also show that this results in substantial helium surface enrichment. Finally, based on our spectroscopic analyses, we are able to provide the most accurate ionising fluxes for VMS known to date, confirming the pivotal role of VMS in ionising and

  1. Spatial and seasonal patterns in abundance and age-composition of Calanus finmarchicus in the Gulf of Maine and on Georges Bank: 1977 1987

    NASA Astrophysics Data System (ADS)

    Meise, C. J.; O'Reilly, J. E.

    ubiquitously very abundant (> 10 4/10 m 2), and diverged from September to December. C. finmarchicus stage distribution in the GB-GOM area was highly negatively correlated with mean water column temperature during the stratified season. This seemed more related to the hydrography of the region, which isolates warmer well mixed Georges Bank from the Gulf of Maine and the stratified areas on the Bank, than to temperature, because Calanus abundances decline on the Bank before water temperatures exceed their preferences. A large part of the spatial and seasonal variation in C. finmarchicus abundance and age structure appears to be tightly coupled to major hydrographic regimes and to major circulation patterns in the region. There was a sharp ecotone between well-mixed Georges Bank and the Gulf of Maine as defined by C. finmarchicus abundance patterns and life history distributions. The ecotone is present year-round but is most apparent during the stratified season (May-October), when thermohaline density gradients and the near-surface current jet along the northern flank are generally strongest. The Gulf of Maine had the highest abundances of C. finmarchicus, and lowest spatial and seasonal variation in the region, while tidally mixed Georges Banks displayed the opposite pattern. This indication of stable population centers in the Gulf of Maine would make it a major source of Calanus in the region, particularly during March-April. Distributional patterns also suggest a strong Calanus influence from Scotian Shelf water in northern Gulf of Maine and on the southern flank of Georges Bank.

  2. High-precision Radio and Infrared Astrometry of LSPM J1314+1320AB. II. Testing Pre-main-sequence Models at the Lithium Depletion Boundary with Dynamical Masses

    NASA Astrophysics Data System (ADS)

    Dupuy, Trent J.; Forbrich, Jan; Rizzuto, Aaron; Mann, Andrew W.; Aller, Kimberly; Liu, Michael C.; Kraus, Adam L.; Berger, Edo

    2016-08-01

    We present novel tests of pre-main-sequence models based on individual dynamical masses for the M7 binary LSPM J1314+1320AB. Joint analysis of Keck adaptive optics astrometric monitoring along with Very Long Baseline Array radio data from a companion paper yield component masses of 92.8 ± 0.6 M Jup (0.0885 ± 0.0006 M ⊙) and 91.7 ± 1.0 M Jup (0.0875 ± 0.0010 M ⊙) and a parallactic distance of 17.249 ± 0.013 pc. We find component luminosities consistent with the system being coeval at 80.8 ± 2.5 Myr, according to BHAC15 evolutionary models. The presence of lithium is consistent with model predictions, marking the first test of the theoretical lithium depletion boundary using ultracool dwarfs of known mass. However, we find that the evolutionary model-derived average effective temperature (2950 ± 5 K) is 180 K hotter than that given by a spectral type-{T}{eff} relation based on BT-Settl models (2770 ± 100 K). We suggest that the dominant source of this discrepancy is model radii being too small by ≈13%. In a test mimicking the typical application of models by observers, we derive masses on the H-R diagram using luminosity and BT-Settl temperature. The estimated masses are lower by {46}-19+16 % (2.0σ) than we measure dynamically and would imply that this is a system of ≈50 M Jup brown dwarfs, highlighting the large systematic errors possible in H-R diagram properties. This is the first time masses have been measured for ultracool (≥M6) dwarfs displaying spectral signatures of low gravity. Based on features in the infrared, LSPM J1314+1320AB appears to have higher gravity than typical Pleiades and AB Dor members, opposite the expectation given its younger age. The components of LSPM J1314+1320AB are now the nearest, lowest mass pre-main-sequence stars with direct mass measurements. 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

  3. High-precision Radio and Infrared Astrometry of LSPM J1314+1320AB. II. Testing Pre-main-sequence Models at the Lithium Depletion Boundary with Dynamical Masses

    NASA Astrophysics Data System (ADS)

    Dupuy, Trent J.; Forbrich, Jan; Rizzuto, Aaron; Mann, Andrew W.; Aller, Kimberly; Liu, Michael C.; Kraus, Adam L.; Berger, Edo

    2016-08-01

    We present novel tests of pre-main-sequence models based on individual dynamical masses for the M7 binary LSPM J1314+1320AB. Joint analysis of Keck adaptive optics astrometric monitoring along with Very Long Baseline Array radio data from a companion paper yield component masses of 92.8 ± 0.6 M Jup (0.0885 ± 0.0006 M ⊙) and 91.7 ± 1.0 M Jup (0.0875 ± 0.0010 M ⊙) and a parallactic distance of 17.249 ± 0.013 pc. We find component luminosities consistent with the system being coeval at 80.8 ± 2.5 Myr, according to BHAC15 evolutionary models. The presence of lithium is consistent with model predictions, marking the first test of the theoretical lithium depletion boundary using ultracool dwarfs of known mass. However, we find that the evolutionary model-derived average effective temperature (2950 ± 5 K) is 180 K hotter than that given by a spectral type–{T}{eff} relation based on BT-Settl models (2770 ± 100 K). We suggest that the dominant source of this discrepancy is model radii being too small by ≈13%. In a test mimicking the typical application of models by observers, we derive masses on the H-R diagram using luminosity and BT-Settl temperature. The estimated masses are lower by {46}-19+16 % (2.0σ) than we measure dynamically and would imply that this is a system of ≈50 M Jup brown dwarfs, highlighting the large systematic errors possible in H-R diagram properties. This is the first time masses have been measured for ultracool (≥M6) dwarfs displaying spectral signatures of low gravity. Based on features in the infrared, LSPM J1314+1320AB appears to have higher gravity than typical Pleiades and AB Dor members, opposite the expectation given its younger age. The components of LSPM J1314+1320AB are now the nearest, lowest mass pre-main-sequence stars with direct mass measurements. 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

  4. Whole-genome sequencing suggests a chemokine gene cluster that modifies age at onset in familial Alzheimer's disease.

    PubMed

    Lalli, M A; Bettcher, B M; Arcila, M L; Garcia, G; Guzman, C; Madrigal, L; Ramirez, L; Acosta-Uribe, J; Baena, A; Wojta, K J; Coppola, G; Fitch, R; de Both, M D; Huentelman, M J; Reiman, E M; Brunkow, M E; Glusman, G; Roach, J C; Kao, A W; Lopera, F; Kosik, K S

    2015-11-01

    We have sequenced the complete genomes of 72 individuals affected with early-onset familial Alzheimer's disease caused by an autosomal dominant, highly penetrant mutation in the presenilin-1 (PSEN1) gene, and performed genome-wide association testing to identify variants that modify age at onset (AAO) of Alzheimer's disease. Our analysis identified a haplotype of single-nucleotide polymorphisms (SNPs) on chromosome 17 within a chemokine gene cluster associated with delayed onset of mild-cognitive impairment and dementia. Individuals carrying this haplotype had a mean AAO of mild-cognitive impairment at 51.0 ± 5.2 years compared with 41.1 ± 7.4 years for those without these SNPs. This haplotype thus appears to modify Alzheimer's AAO, conferring a large (~10 years) protective effect. The associated locus harbors several chemokines including eotaxin-1 encoded by CCL11, and the haplotype includes a missense polymorphism in this gene. Validating this association, we found plasma eotaxin-1 levels were correlated with disease AAO in an independent cohort from the University of California San Francisco Memory and Aging Center. In this second cohort, the associated haplotype disrupted the typical age-associated increase of eotaxin-1 levels, suggesting a complex regulatory role for this haplotype in the general population. Altogether, these results suggest eotaxin-1 as a novel modifier of Alzheimer's disease AAO and open potential avenues for therapy.

  5. Noble gas composition and 40Ar/39Ar age in eclogites from the main hole of the Chinese Continental Scientific Drilling project

    NASA Astrophysics Data System (ADS)

    Hopp, Jens; Schwarz, Winfried H.; Trieloff, Mario; Meyer, Hans-Peter; Hanel, Michael; Altherr, Rainer

    2016-10-01

    We present the first comprehensive noble gas study on eclogites. The four eclogite samples were recovered during the Chinese Continental Scientific Drilling and are from two distinct profile depth sections differing in their degree of interaction with meteoric water, based on their δ 18O-values (surface related and of mantle-type). Hence, noble gas analyses offer the potential to further discriminate between shallow (meteoric) and deep (mantle) fluid sources. Noble gas compositions reveal typical crustal fluid compositions, characterized by a variable mixture of atmospheric gases with significant contributions of nucleogenic neon, radiogenic 4He*, radiogenic 40Ar*, fissiogenic 131-136Xe, and presumably bariogenic 131Xe, but no significant addition of mantle gases. This signature can be also considered to represent one endmember component of eclogitic diamonds. Concentrations of non-radiogenic noble gases are rather low, with depletion of light relative to the heavier noble gases. Eclogites from lower depth which experienced a higher degree of interaction with meteoric water also showed higher contributions of atmospheric gas compared with eclogites recovered from greater depth. This is interpreted to result from interaction with high-salinity fluids during ultrahigh pressure (UH P). It demonstrates that the atmospheric noble gas abundance is a proxy for interaction with surface related fluids. 40Ar/39Ar (inverse) isochron ages of two phengite separates (241.2 ± 0.4 Ma and 275.0 ± 1.8 Ma, 1 σ-errors) predate the main phase of UH P metamorphism (ca. 220 Ma). Biotite yields an integrated age of about 1100 Ma. These age values are interpreted to reflect the likely addition of excess 40Ar without any chronological meaning.

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

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

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

  7. Age of volcanism and rifting in the Burji-Soyoma area, Amaro Horst, southern Main Ethiopian Rift: geo- and biochronologic data

    NASA Astrophysics Data System (ADS)

    WoldeGabriel, G.; Yemane, T.; Suwa, G.; White, T.; Asfaw, B.

    Late Eocene basalts capping late Mesozoic or early Tertiary basal sandstone are present in the Amaro Horst within southern sector of the Main Ethiopian Rift. This basaltic unit is time correlative to flows already reported from southwestern Ethiopia. The discovery of these lavas within the rift system proves that the oldest volcanic units of the Ethiopian volcanic province are not confined to the NW Plateau, west of the Main Ethiopian Rift as was generally believed. At the same time, the widely held notion of rift-ward migration of volcanism from the plateau is not supported by the occurrence of this Late Eocene basalt within the uplifted Amaro Horst. The Late Eocene basalt is blanketed by Early Oligocene basalt and silicic flows. Geochemical characteristics indicate that the volcanic succession consists of Late Eocene transitional tholeiitic basalt, Oligocene and Mid-Miocene hawaiites, and Mid-Miocene mildly alkaline basalt flows. The lower (Late Eo