Observational signatures of lithium depletion in the metal-poor globular cluster NGC6397

AbstractThe “stellar” solution to the cosmological lithium problem proposes that surface depletion of lithium in low-mass, metal-poor stars can reconcile the lower abundances found for Galactic halo stars with the primordial prediction. Globular clusters are ideal environments for studies of the surface evolution of lithium, with large number statistics possible to obtain for main sequence stars as well as giants. We discuss the Li abundances measured for >450 stars in the globular cluster NGC 6397, focusing on the evidence for lithium depletion and especially highlighting how the inferred abundances and interpretations are affected by early cluster self-enrichment and systematic uncertainties in the effective temperature determination.

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Age-related observations of low mass pre-main and young main sequence stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309031731 ◽

2008 ◽

Vol 4 (S258) ◽

pp. 81-94 ◽

Cited By ~ 1

Author(s):

Lynne A. Hillenbrand

Keyword(s):

Main Sequence ◽

Rotation Period ◽

Age Dating ◽

Main Sequence Stars ◽

Solar Mass ◽

Age Related ◽

Stellar Ages ◽

Dating Methods ◽

Low Mass ◽

Lithium Depletion

AbstractThis overview summarizes the age dating methods available for young sub-solar mass stars. Pre-main sequence age diagnostics include the Hertzsprung-Russell (HR) diagram, spectroscopic surface gravity indicators, and lithium depletion; asteroseismology is also showing recent promise. Near and beyond the zero-age main sequence, rotation period or vsiniand activity (coronal and chromospheric) diagnostics along with lithium depletion serve as age proxies. Other authors in this volume present more detail in each of the aforementioned areas. Herein, I focus on pre-main sequence HR diagrams and address the questions: Do empirical young cluster isochrones match theoretical isochrones? Do isochrones predict stellar ages consistent with those derived via other independent techniques? Do the observed apparent luminosity spreads at constant effective temperature correspond to true age spreads? While definitive answers to these questions are not provided, some methods of progression are outlined.

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The Globular Cluster Population of X-ray Binaries

Symposium - International Astronomical Union ◽

10.1017/s0074180900160711 ◽

1987 ◽

Vol 125 ◽

pp. 187-197 ◽

Cited By ~ 5

Author(s):

Frank Verbunt ◽

Piet Hut

Keyword(s):

Globular Cluster ◽

Globular Clusters ◽

Mass Function ◽

Initial Mass Function ◽

Encounter Rate ◽

Formation Mechanisms ◽

Main Sequence Stars ◽

X Ray ◽

Low Mass ◽

X Ray Binaries

We discuss formation mechanisms for low-mass X-ray binaries in globular clusters. We apply the most efficient mechanism, tidal capture in close two-body encounters between neutron and main-sequence stars, to the clusters of our galaxy. The observed number of X-ray sources in these can be explained if the birth velocities of neutron stars are higher than estimated from velocity measurements of radiopulsars, or if the initial mass function steepens at high masses. We perform a statistical test on the distribution of X-ray sources with respect to the number of close encounters in globular clusters, and find satisfactory agreement between the tidal capture theory and observation, apart from the presence of low-mass X-ray binaries in four clusters with a very low encounter rate: Ter 1, Ter 2, Gr 1 and NGC 6712.EXOSAT observations indicate that some dim globular cluster sources may be less luminous than hitherto assumed, and support the view that the brighter dim sources may be soft X-ray transients in quiescence.

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The Gaia-ESO Survey: lithium depletion in the Gamma Velorum cluster and inflated radii in low-mass pre-main-sequence stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stw2458 ◽

2016 ◽

Vol 464 (2) ◽

pp. 1456-1465 ◽

Cited By ~ 29

Author(s):

R. D. Jeffries ◽

R. J. Jackson ◽

E. Franciosini ◽

S. Randich ◽

D. Barrado ◽

...

Keyword(s):

Main Sequence ◽

Main Sequence Stars ◽

Low Mass ◽

Lithium Depletion

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A Search for Tidal Stellar Debris from the Magellanic Clouds: Survey Results from the First Two Years

Symposium - International Astronomical Union ◽

10.1017/s007418090011873x ◽

1999 ◽

Vol 190 ◽

pp. 508-510 ◽

Cited By ~ 8

Author(s):

S. R. Majewski ◽

J. C. Ostheimer ◽

W. E. Kunkel ◽

K. V. Johnston ◽

R. J. Patterson ◽

...

Keyword(s):

Globular Clusters ◽

Main Sequence ◽

Galactic Halo ◽

Large Magellanic Cloud ◽

Main Sequence Stars ◽

Tidal Disruption ◽

Negative Results ◽

Ram Pressure ◽

Survey Results ◽

Magellanic Stream

An important discriminant between leading models for the origin of the Magellanic Stream is the presence of a stellar counterpart to the HI gas stream: ram pressure stripping of gas by a putative hot Galactic halo would act only on Magellanic gas while gravitational tidal stripping would act on both gas and stars. Several previous attempts to find tidal stellar debris have failed to find carbon stars, A stars, or other main sequence stars in the Magellanic Stream (Mathewson et al. 1979; Recillas-Cruz 1982; Brück & Hawkins 1983; Guhathakurta & Lin 1999). However, there has long been a suggestion (Kunkel 1979; Lynden-Bell 1982) of a possible Magellanic association of satellite galaxies and globular clusters that have similar orbits and may derive from the break up of a greater Magellanic galaxy (Lynden-Bell & Lynden-Bell 1995; Majewski et al. 1997). Recent models (Moore & Davis 1994; Johnston 1998) of the tidal disruption of Large Magellanic Cloud (LMC)-like systems indicate a wide dispersal of debris, much wider than the rather confined HI stream, so that the contrast of tidal debris against the Galactic fore/background would be low. If true, this could explain some of the previous negative results for tidal debris searches.

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Peculiar Stars of Low Luminosity

Symposium - International Astronomical Union ◽

10.1017/s0074180900228015 ◽

1995 ◽

Vol 166 ◽

pp. 157-162

Author(s):

J. Liebert ◽

C.C. Dahn

Keyword(s):

Globular Clusters ◽

Main Sequence ◽

Main Sequence Stars ◽

M Dwarfs ◽

Stellar Objects ◽

Trigonometric Parallax ◽

Peculiar Stars ◽

Nearby Stars ◽

Low Mass ◽

Cool White Dwarfs

Precise trigonometric parallax measurements orders of magnitude more accurate than a milliarcsecond will contribute greatly to our understanding of peculiar, low luminosity stellar objects of several types. First, the volume of space out to which luminosities may be determined to the accuracy of the best, very-nearby stars will be increased greatly. For the relatively rare field Population II stars, this will lead to the first accurate empirical calibrations of the main sequence at the low mass end, for comparison with globular clusters of various metallicities. Parallaxes at 1 kpc or farther will be adequate to help in the discovery or confirmation of the rare carbon dwarfs - main sequence stars with carbon-rich atmospheres. For cool white dwarfs, luminosities accurate to a few per cent or better will identify unresolved binaries, and objects of unusually high and low mass. For our most numerous solar neighbors, the M dwarfs and especially those near the stellar mass limit, accurate luminosities can help in the determinations of the chemical composition and age distributions.

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Rediscovering the origins of the stellar halo with chemical tagging

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317007487 ◽

2017 ◽

Vol 13 (S334) ◽

pp. 38-42 ◽

Cited By ~ 1

Author(s):

Sarah L Martell

Keyword(s):

Globular Cluster ◽

Globular Clusters ◽

Galactic Halo ◽

Light Element ◽

Element Abundance ◽

Tidal Interactions ◽

Halo Stars ◽

The Galaxy ◽

Stellar Halo ◽

Light Element Abundance

AbstractThe Galactic halo has a complex assembly history, which can be seen in its wealth of kinematic and chemical substructure. Globular clusters lose stars through tidal interactions with the Galaxy and cluster evaporation processes, meaning that they are inevitably a source of halo stars. These “migrants” from globular clusters can be recognized in the halo field by the characteristic light element abundance anticorrelations that are commonly observed only in globular cluster stars, and the number of halo stars that can be chemically tagged to globular clusters can be used to place limits on the formation pathways of those clusters.

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Evolution of Globular Clusters Including a Degenerate Component

Symposium - International Astronomical Union ◽

10.1017/s0074180900043515 ◽

1988 ◽

Vol 126 ◽

pp. 665-666

Author(s):

Hyung Mok Lee

Keyword(s):

Globular Clusters ◽

Main Sequence ◽

High Mass ◽

Main Sequence Stars ◽

Compact Binaries ◽

The Core ◽

Degenerate Component ◽

Low Mass ◽

Mass Segregation ◽

Very High

Low mass X-ray sources observed in many globular clusters are usually interpreted as compact binaries with degenerate components (e.g., Hertz and Grindlay 1983). Degenerate stars can exist in globular clusters if the IMF contains a sufficiently large number of high mass stars. Since the main-sequence lifetime is a very steep function of stellar mass, most of degenerate stars can be regarded as primordial. If the typical mass of degenerate stars is higher than that of main-sequence stars, mass segregation makes the core crowded with degenerate stars. Tidally captured binaries between degenerates and main-sequence stars can abundantly form as the core density becomes very high.

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Are sdAs helium core stars?

Open Astronomy ◽

10.1515/astro-2017-0433 ◽

2017 ◽

Vol 26 (1) ◽

Cited By ~ 4

Author(s):

Ingrid Pelisoli ◽

S. O. Kepler ◽

Detlev Koester

Keyword(s):

Main Sequence ◽

Galactic Disk ◽

Physical Nature ◽

Sloan Digital Sky Survey ◽

Distance Modulus ◽

Main Sequence Stars ◽

Sky Survey ◽

Balmer Lines ◽

Low Mass ◽

Binary Evolution

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

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