Discovery of ubiquitous lithium production in low-mass stars

Kumar, Yerra Bharat; Reddy, Bacham E.; Campbell, Simon; Maben, Sunayana; Zhao, Gang; Ting, Yuan-Sen

doi:10.1038/s41550-020-1139-7

Cited by 64 publications

(123 citation statements)

References 36 publications

(87 reference statements)

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“…With the new more reliable data from GALAH+ DR3, more scenarios of Li production during binary interaction or the He-flash in giant stars (see e.g. Casey et al 2019;Kumar et al 2020) can be tested more reliably, indicating that lithium-rich giant stars require multiple formation channels (Martell et al 2020).…”

Section: Galactic and Stellar Chemical Evolutionmentioning

confidence: 99%

The GALAH Survey: second data release

Buder

Asplund

Duong

et al. 2018

Monthly Notices of the Royal Astronomical Society

354

447

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The Galactic Archaeology with HERMES (GALAH) survey is a large-scale stellar spectroscopic survey of the Milky Way and designed to deliver chemical information complementary to a large number of stars covered by the Gaia mission. We present the GALAH second public data release (GALAH DR2) containing 342,682 stars. For these stars, the GALAH collaboration provides stellar parameters and abundances for up to 23 elements to the community. Here we present the target selection, observation, data reduction and detailed explanation of how the spectra were analysed to estimate stellar parameters and element abundances. For the stellar analysis, we have used a multi-step approach. We use the physics-driven spectrum synthesis of Spectroscopy Made Easy (SME) to derive stellar labels (T eff , log g, [Fe/H], [X/Fe], v mic , v sin i, A K S ) for a representative training set of stars. This information is then propagated to the whole survey with the data-driven method of The Cannon. Special care has been exercised in the spectral synthesis to only consider spectral lines that have reliable atomic input data and are little affected by blending lines. Departures from local thermodynamic equilibrium (LTE) are considered for several key elements, including Li, O, Na, Mg, Al, Si, and Fe, using 1D stellar atmosphere models. Validation tests including repeat observations, Gaia benchmark stars, open and globular clusters, and K2 asteroseismic targets lend confidence to our methods and results. Combining the GALAH DR2 catalogue with the kinematic information from Gaia will enable a wide range of Galactic Archaeology studies, with unprecedented detail, dimensionality, and scope.

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Section: Galactic and Stellar Chemical Evolutionmentioning

confidence: 99%

The GALAH Survey: second data release

Buder

Asplund

Duong

et al. 2018

Monthly Notices of the Royal Astronomical Society

354

447

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show abstract

Section: Galactic and Stellar Chemical Evolutionmentioning

confidence: 99%

The GALAH+ survey: Third data release

Buder

Sharma

Kos

et al. 2021

Monthly Notices of the Royal Astronomical Society

370

295

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The ensemble of chemical element abundance measurements for stars, along with precision distances and orbit properties, provides high-dimensional data to study the evolution of the Milky Way. With this third data release of the Galactic Archaeology with HERMES (GALAH) survey, we publish 678 423 spectra for 588 571 mostly nearby stars (81.2% of stars are within < 2 kpc), observed with the HERMES spectrograph at the Anglo-Australian Telescope. This release (hereafter GALAH+ DR3) includes all observations from GALAH Phase 1 (bright, main, and faint survey, 70%), K2-HERMES (17%), TESS-HERMES (5%), and a subset of ancillary observations (8%) including the bulge and > 75 stellar clusters. We derive stellar parameters Teff, log g, [Fe/H], vmic, vbroad, and vradusing our modified version of the spectrum synthesis code Spectroscopy Made Easy (sme) and 1D marcs model atmospheres. We break spectroscopic degeneracies in our spectrum analysis with astrometry from Gaia DR2 and photometry from 2MASS. We report abundance ratios [X/Fe] for 30 different elements (11 of which are based on non-LTE computations) covering five nucleosynthetic pathways. We describe validations for accuracy and precision, flagging of peculiar stars/measurements and recommendations for using our results. Our catalogue comprises 65% dwarfs, 34% giants, and 1% other/unclassified stars. Based on unflagged chemical composition and age, we find 62% young low-α, 9% young high-α, 27% old high-α, and 2% stars with [Fe/H] ≤ −1. Based on kinematics, 4% are halo stars. Several Value-Added-Catalogues, including stellar ages and dynamics, updated after GaiaeDR3, accompany this release and allow chrono-chemodynamic analyses, as we showcase.

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“…The short time-scales relevant to RC stars, and the time-scale differences between pRC and sRC stars, provide some useful insights into lithium enrichment and redepletion. The helium-burning lifetime of pRC stars is only ≈100 Myr (Girardi 1999), so if there is a universal lithium production process that occurs at the helium flash, as suggested by Kumar et al (2020), the lithium redepletion must be fast enough that 98.4 per cent of pRC stars descend to 0.5 < A Li < 1.5 in that time. At the beginning of their heliumburning phase, the sRC stars all have ages of ≈1 Gyr because only stars in a small range of mass and metallicity pass through the sRC, In all panels, we show the stars classified as RC or RGB by the isochrone-based BSTEP method (dots) and the asteroseismic classifications (black-edged star symbols).…”

Section: Lithium-rich Giants Across the Stellar Parameter Spacementioning

confidence: 99%

“…Recent work by Kumar et al (2020) indicates that lithium enrichment at the helium flash may be compulsory, given the lack of very lithium-depleted RC stars in their data set. This provides an intriguing and testable prediction for RC stars as a population, and may provide new insights into the internal rearrangement that happens as a result of the helium flash.…”

Section: T H E O R I G I N S O F L I T H I U M E N R I C H M E N T I N E Vo Lv E D S Ta R Smentioning

confidence: 99%

“…stars that are hydrogen-shell burning). The study of Kumar et al (2020), which is also based on GALAH data, posits a universal lithium production event at the helium flash based on the lack of RC stars that are as lithium-poor as the stars at the tip of the RGB, and Yan et al (2021) find indications of accompanying nitrogen enrichment in their large study of LAMOST data. To evaluate arguments about the source of lithium enrichment it is critical to know the evolutionary phase of the stars in question.…”

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confidence: 99%

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The GALAH survey: A census of lithium-rich giant stars

Martell

Simpson

Balasubramaniam

et al. 2021

Monthly Notices of the Royal Astronomical Society

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We investigate the properties of 1262 red giant stars with high photospheric abundances of lithium observed by the GALAH and K2-HERMES surveys, and discuss them in the context of proposed mechanisms for lithium enrichment and re-depletion in giant stars. We confirm that Li-rich giants are rare, making up only 1.2 per cent of our giant star sample. We use stellar parameters from the third public data release from the GALAH survey and a Bayesian isochrone analysis to divide the sample into first-ascent red giant branch and red clump stars, and confirm these classifications using asteroseismic data from K2. We find that red clump stars are 2.5 times as likely to be lithium-rich as red giant branch stars, in agreement with other recent work. The probability for a star to be lithium-rich is affected by a number of factors, though the causality in those correlations is not entirely clear. We show for the first time that primary and secondary red clump stars have distinctly different lithium enrichment patterns. The data set discussed here is large and heterogeneous in terms of evolutionary phase, metallicity, rotation rate and mass. We expect that if the various mechanisms that have been proposed for lithium enrichment in evolved stars are in fact active, they should all contribute to this sample of lithium-rich giants at some level.

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Discovery of ubiquitous lithium production in low-mass stars

Cited by 64 publications

References 36 publications

The GALAH Survey: second data release

The GALAH Survey: second data release

The GALAH+ survey: Third data release

The GALAH survey: A census of lithium-rich giant stars

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