Discussion D: Observational problems with Li, Be and B

AbstractIn Discussion D the following problems were addressed: Has 6Li really been detected in the atmospheres of metal-poor halo stars? Is there a downward trend or increased scatter of Li abundances in stars on the ‘Li-plateau’ at metallicities [Fe/H] ≲ −2.5? Are there significant differences of Li abundances in main-sequence, turn-off, and sub-giant stars in globular clusters? Is the Li abundance in solar-type stars related to the presence of planets? How does the Be abundance in dwarf stars increase with the heavy-element abundance, and is there a cosmic scatter in Be at a given [Fe/H]? The discussion of these problems is summarized and some suggestions for future observational and theoretical studies are mentioned.

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Light element abundance inhomogeneities in globular clusters: probing star formation and evolution in the early Milky Way

Canadian Journal of Physics ◽

10.1139/p94-101 ◽

1994 ◽

Vol 72 (11-12) ◽

pp. 772-781 ◽

Cited By ~ 24

Author(s):

Michael M. Briley ◽

Roger A. Bell ◽

James E. Hesser ◽

Graeme H. Smith

Keyword(s):

Star Formation ◽

Globular Clusters ◽

Main Sequence ◽

Light Element ◽

Star Formation History ◽

Element Abundance ◽

Chemical Compositions ◽

Original Material ◽

Abundance Patterns ◽

Red Giant

Abundance patterns of the elements C, N, and O are sensitive probes of stellar nucleosynthesis processes and, in addition, O abundances are an important input for stellar age determinations. Understanding the nature of the observed distribution of these elements is key to constraining protogalactic star formation history. Patterns deduced from low-resolution spectroscopy of the CN, CH, NH, and CO molecules for low-mass stars in their core-hydrogen or first shell-hydrogen burning phases in the oldest ensembles known, the Galactic globular star clusters, are reviewed. New results for faint stars in NGC 104 (47 Tuc, C0021-723) reveal that the bimodal, anticorrelated pattern of CN and CH strengths found among luminous evolved stars is also present in stars nearing the end of their main-sequence lifetimes. In the absence of known mechanisms to mix newly synthesized elements from the interior to the observable surface layers of such unevolved stars, those particular inhomogeneities imply that the original material from which the stars formed some 15 billion years ago was chemically inhomogeneous in the C and N elements. However, in other clusters, observations of abundance ratios and C isotope ratios suggest that alterations to surface chemical compositions are produced as stars evolve from the main sequence through the red giant branch. Thus, the current observed distributions of C, N, and O among the brightest stars (those also observed most often) may not reflect the true distribution from which the protocluster cloud formed. The picture that is emerging of the C, N, and O abundance patterns within globular clusters may be one which requires a complicated combination of stellar evolutionary and primordial effects for its explanation.

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The Pan-Pacific Planet Search – VIII. Complete results and the occurrence rate of planets around low-luminosity giants

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3378 ◽

2019 ◽

Vol 491 (4) ◽

pp. 5248-5257 ◽

Cited By ~ 3

Author(s):

Robert A Wittenmyer ◽

R P Butler ◽

Jonathan Horner ◽

Jake Clark ◽

C G Tinney ◽

...

Keyword(s):

Radial Velocity ◽

Main Sequence ◽

Giant Planets ◽

Occurrence Rate ◽

Velocity Measurements ◽

Intermediate Mass ◽

Giant Stars ◽

Intermediate Mass Stars ◽

Final Data ◽

Solar Type

ABSTRACT Our knowledge of the populations and occurrence rates of planets orbiting evolved intermediate-mass stars lags behind that for solar-type stars by at least a decade. Some radial velocity surveys have targeted these low-luminosity giant stars, providing some insights into the properties of their planetary systems. Here, we present the final data release of the Pan-Pacific Planet Search (PPPS), a 5 yr radial velocity survey using the 3.9 m Anglo-Australian Telescope. We present 1293 precise radial velocity measurements for 129 stars, and highlight 6 potential substellar-mass companions, which require additional observations to confirm. Correcting for the substantial incompleteness in the sample, we estimate the occurrence rate of giant planets orbiting low-luminosity giant stars to be approximately 7.8$^{+9.1}_{-3.3}$ per cent. This result is consistent with the frequency of such planets found to orbit main-sequence A-type stars, from which the PPPS stars have evolved.

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The Main Sequence Evolution of Inhomogeneous Stars

Publications of the Astronomical Society of Australia ◽

10.1017/s1323358000021251 ◽

1982 ◽

Vol 4 (4) ◽

pp. 396-400 ◽

Cited By ~ 1

Author(s):

J. Lattanzio

Keyword(s):

Gravitational Collapse ◽

Heavy Element ◽

Main Sequence ◽

Element Abundance ◽

Sequence Evolution ◽

Interstellar Gas ◽

Convective Mixing ◽

The Core ◽

Gas Cloud

Duley (1974) has shown that, at the temperatures usually associated with interstellar gas clouds, we would expect CNO grains to be present. During gravitational collapse these grains migrate to the centre of the gas cloud, leading to an enhancement of the heavy-element abundance in the core (Prentice 1976, 1978). It was Krautschneider (1977) who verified such a scenario, by considering the dynamical collapse of gas and grain clouds. If such an initial radial abundance inhomogeneity existed, Prentice (1976a) showed that this configuration may well survive the later convective mixing phase and thus approach the zero-age main-sequence (ZAMS) with a small (-v 3% by mass) metal enhanced core.

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The Eclipsing Triple System U Ophiuchi Revisited

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307003894 ◽

2006 ◽

Vol 2 (S240) ◽

pp. 109-110

Author(s):

Luiz Paulo R. Vaz ◽

Johannes Andersen ◽

Antônio Claret

Keyword(s):

Radial Velocity ◽

Triple System ◽

Heavy Element ◽

Main Sequence ◽

Element Abundance ◽

Apsidal Motion ◽

Eclipsing Binary ◽

The Third ◽

Sequence Band ◽

Nearby Stars

AbstractWe have redetermined the absolute dimensions of the mid B-type eclipsing binary U Oph from new light and radial-velocity curves, accounting for both the apsidal motion and the light-time orbit around the third star. The stars in U Oph have masses of 5.27 and 4.74 M⊙(±1.5%) and are located in the middle of the main-sequence band for an an age of ∼50 Myr. U Oph and three other systems (V760 Sco, MU, Cas and DI Her) all have components within 10% of 5M⊙ and ages below 100 Myr; we find significant heavy-element abundance differences between these young nearby stars.

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Study of the effects of magnetic braking on the lithium abundances of the Sun and solar-type stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1569 ◽

2020 ◽

Vol 496 (2) ◽

pp. 1343-1354

Author(s):

R Caballero Navarro ◽

A García Hernández ◽

A Ayala ◽

J C Suárez

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Globular Clusters ◽

Main Sequence ◽

The Sun ◽

Depletion Rate ◽

Solar Type ◽

Magnetic Braking ◽

Physical Phenomena ◽

The Impact

ABSTRACT The study of lithium (Li) surface abundance in the Sun and young stellar globular clusters which are seemingly anomalous in present-day scenarios, as well as the influence of rotation and magnetic braking (MB) on its depletion during pre-main sequence (PMS) and main sequence (MS). In this work, the effects of rotational mixing and of the rotational hydrostatic effects on Li abundances are studied by simulating several grids of PMS and MS rotating and non-rotating models. Those effects are combined with the additional impact of the MB (with magnetic field intensities ranging between 3.0 and 5.0 G). The data obtained from simulations are confronted by comparing different stellar parameters. The results show that the surface Li abundance for the Sun-like models at the end of the PMS and throughout the MS decreases when rotational effects are included, that is the Li depletion rate for rotating models is higher than for non-rotating ones. This effect is attenuated when the MB produced by a magnetic field is present. This physical phenomena impacts also the star effective temperature (Teff) and its location in the HR diagram. The impact of MB in Li depletion is sensitive to the magnetic field intensity: the higher it is, the lower the Li destruction. A direct link between the magnetic fields and the convective zone (CZ) size is observed: stronger magnetic fields produce shallower CZ’s. This result suggests that MB effect must be taken into consideration during PMS if we aim to reproduce Li abundances in young clusters.

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Testing planet formation theories with giant stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308016621 ◽

2007 ◽

Vol 3 (S249) ◽

pp. 209-222

Author(s):

Luca Pasquini ◽

M.P. Döllinger ◽

A. Hatzes ◽

J. Setiawan ◽

L. Girardi ◽

...

Keyword(s):

Main Sequence ◽

Planet Formation ◽

Mass Range ◽

Stellar Mass ◽

Giant Planets ◽

Main Sequence Stars ◽

Giant Stars ◽

Solar Type ◽

The Subject ◽

Host Stars

AbstractPlanet searches around evolved giant stars are bringing new insights to planet formation theories by virtue of the broader stellar mass range of the host stars compared to the solar-type stars that have been the subject of most current planet searches programs. These searches among giant stars are producing extremely interesting results. Contrary to main sequence stars planet-hosting giants do not show a tendency of being more metal rich. Even if limited, the statistics also suggest a higher frequency of giant planets (at least 10%) that are more massive compared to solar-type main sequence stars.The interpretation of these results is not straightforward. We propose that the lack of a metallicity-planet connection among giant stars is due to pollution of the star while on the main sequence, followed by dillution during the giant phase. We also suggest that the higher mass and frequency of the planets are due to the higher stellar mass. Even if these results do not favor a specific formation scenario, they suggest that planetary formation might be more complex than what has been proposed so far, perhaps with two mechanisms at work and one or the other dominating according to the stellar mass. We finally stress as the detailed study of the host stars and of the parent sample is essential to derive firm conclusions.

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

Proceedings of the International Astronomical Union ◽

10.1017/s1743921310004229 ◽

2009 ◽

Vol 5 (S268) ◽

pp. 263-268 ◽

Cited By ~ 2

Author(s):

Karin Lind ◽

Francesca Primas ◽

Corinne Charbonnel ◽

Frank Grundahl ◽

Martin Asplund

Keyword(s):

Globular Cluster ◽

Globular Clusters ◽

Main Sequence ◽

Galactic Halo ◽

Main Sequence Stars ◽

Surface Evolution ◽

Halo Stars ◽

Systematic Uncertainties ◽

Low Mass ◽

Lithium Depletion

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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The mass fraction of halo stars contributed by the disruption of globular clusters in the E-MOSAICS simulations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa483 ◽

2020 ◽

Vol 493 (3) ◽

pp. 3422-3428 ◽

Cited By ~ 9

Author(s):

Marta Reina-Campos ◽

Meghan E Hughes ◽

J M Diederik Kruijssen ◽

Joel L Pfeffer ◽

Nate Bastian ◽

...

Keyword(s):

Mass Fraction ◽

Globular Clusters ◽

Milky Way ◽

Galactic Halo ◽

Light Element ◽

Element Abundance ◽

Host Galaxies ◽

Stellar Cluster ◽

Halo Stars ◽

Stellar Halo

ABSTRACT Globular clusters (GCs) have been posited, alongside dwarf galaxies, as significant contributors to the field stellar population of the Galactic halo. In order to quantify their contribution, we examine the fraction of halo stars formed in stellar clusters in the suite of 25 present-day Milky Way-mass cosmological zoom simulations from the E-MOSAICS project. We find that a median of 2.3 and 0.3 per cent of the mass in halo field stars formed in clusters and GCs, defined as clusters more massive than 5 × 103 and 105 M⊙, respectively, with the 25–75th percentiles spanning 1.9–3.0 and 0.2–0.5 per cent being caused by differences in the assembly histories of the host galaxies. Under the extreme assumption that no stellar cluster survives to the present day, the mass fractions increase to a median of 5.9 and 1.8 per cent. These small fractions indicate that the disruption of GCs plays a subdominant role in the build-up of the stellar halo. We also determine the contributed halo mass fraction that would present signatures of light-element abundance variations considered to be unique to GCs, and find that clusters and GCs would contribute a median of 1.1 and 0.2 per cent, respectively. We estimate the contributed fraction of GC stars to the Milky Way halo, based on recent surveys, and find upper limits of 2–5 per cent (significantly lower than previous estimates), suggesting that models other than those invoking strong mass loss are required to describe the formation of chemically enriched stellar populations in GCs.

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7Li in Metal-Poor Stars: The Spread of the Li Plateau

Symposium - International Astronomical Union ◽

10.1017/s0074180900166689 ◽

2000 ◽

Vol 198 ◽

pp. 249-258

Author(s):

Sean G. Ryan

Keyword(s):

Main Sequence ◽

Cosmic Ray ◽

Low Mass Stars ◽

Dwarf Stars ◽

Blue Stragglers ◽

Halo Stars ◽

Spallation Reactions ◽

Binary Mergers ◽

Low Mass ◽

Galactic Cosmic Ray

A highly homogeneous study of 23 halo field dwarf stars has achieved a Li abundance accuracy of 0.033 dex per star. The work shows that the intrinsic spread of the Li abundances of these stars at a given metallicity is < 0.02 dex, and consistent with zero. That is, the Spite Li plateau for halo field dwarfs is incredibly thin. The thinness rules out depletion by more than 0.1 dex by a rotational-induced extra-mixing mechanism. Despite the thinness of the plateau, an increase of Li with [Fe/H] is seen, interpreted as evidence of Galactic chemical evolution (GCE) of Li, primarily due to Galactic cosmic ray (GCR) spallation reactions in the era of halo formation. The rate of Li evolution is concordant with: (1) observations of spallative 6Li in halo dwarfs; (2) GCE models; and (3) data on Li in higher metallicity halo stars. New data have also revealed four new ultra-Li-deficient halo dwarfs, doubling the number known. Based on their propensity to cluster at the halo main sequence turnoff and also to exist redward of the turnoff, we hypothesise that they are the products of binary mergers that ultimately will become blue stragglers. We explain their low Li abundances by normal pre-main-sequence (and possibly main-sequence) destruction in the low mass stars prior to their merging. If this explanation is correct, then such stars need no longer be considered an embarrassment to the existence of negligible Li destruction in the majority of field halo dwarfs.

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