Most lithium-rich low-mass evolved stars revealed as red clump stars by asteroseismology and spectroscopy

Yan, Hui‐Juan; Zhou, Yawen; Zhang, Xianfei; Li, Yaguang; Gao, Qi; Shi, Jianrong; Zhao, Gang; Aoki, Wako; Matsuno, Tadafumi; Li, Yan; Xu, X.; Li, Haining; Wu, Yaqian; Jin, Mengqi; Mosser, B.; Bi, Shaolan; Fu, Jian-Ning; Pan, Kaike; Suda, Takuma; Liu, Yujuan; Zhao, Jingkun; Liang, Xian-Ting

doi:10.1038/s41550-020-01217-8

Cited by 44 publications

(51 citation statements)

References 76 publications

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“…We do not replicate the upper limit on RGB star lithium abundances reported in LAMOST data by Yan et al (2021) in our full data set, but we do see a similar pattern in the asteroseismically confirmed RGB stars, none of which are lithium-rich (Fig. 4, lower middle panel).…”

Section: Summary Of Observational Phenomenologycontrasting

confidence: 84%

“…luminous red giants, as in Gonzalez et al 2009 andLebzelter et al 2012, or stars on the RC, as in Lambert 2011 andSingh et al 2019b). Large-sample studies such as Deepak & Reddy (2019), Casey et al (2019), andYan et al (2021) found that 68 per cent, 80 per cent, and 86 per cent, respectively, of lithium-rich giants belong to the RC.…”

Section: Summary Of Observational Phenomenologymentioning

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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Section: Summary Of Observational Phenomenologycontrasting

confidence: 84%

Section: Summary Of Observational Phenomenologymentioning

confidence: 99%

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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“…Singh et al 2021). The studies of Deepak & Lambert (2021) and Yan et al (2021) cross-referenced asteroseismic classifications with high lithium abundances via LAMOST data, but none of our merger candidates appear in their publicly available samples, suggesting they are likely not strongly lithium enhanced. While the catalogue of Casey et al (2019) contains 23 lithium-rich giants that have also been asteroseismically observed by Kepler, only 2 of them have been identified to be on the RGB, and none of them coincide with any of our 24 merger remnant candidates.…”

Section: Additional Merger Signalsmentioning

confidence: 82%

Asteroseismic fingerprints of stellar mergers

Rui

Fuller

2021

Monthly Notices of the Royal Astronomical Society

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Stellar mergers are important processes in stellar evolution, dynamics, and transient science. However, it is difficult to identify merger remnant stars because they cannot easily be distinguished from single stars based on their surface properties. We demonstrate that merger remnants can potentially be identified through asteroseismology of red giant stars using measurements of the gravity mode period spacing together with the asteroseismic mass. For mergers that occur after the formation of a degenerate core, remnant stars have over-massive envelopes relative to their cores, which is manifested asteroseismically by a g mode period spacing smaller than expected for the star’s mass. Remnants of mergers which occur when the primary is still on the main sequence or whose total mass is less than ≈2 M⊙ are much harder to distinguish from single stars. Using the red giant asteroseismic catalogs of Vrard et al. (2016) and Yu et al. (2018), we identify 24 promising candidates for merger remnant stars. In some cases, merger remnants could also be detectable using only their temperature, luminosity, and asteroseismic mass, a technique that could be applied to a larger population of red giants without a reliable period spacing measurement.

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“…We extracted a sample of 6955 low mass (M ≤ 2 M ) giants that are classified as RC stars based on Kepler asteroseismic data (Yu et al 2018). We then searched the literature for ∆Π 1 values (Mosser et al 2012a(Mosser et al , 2014Vrard et al 2016) and Li abundances (Takeda & Tajitsu 2017;Bharat Kumar et al 2018;Singh et al 2019;Yan et al 2020). We found 37 stars with A(Li) and ∆Π 1 , and we measured ∆Π 1 in 10 more (Sec.…”

Section: Sample Selectionmentioning

confidence: 99%

Tracking the evolution of lithium in giants using asteroseismology: Super-Li-rich stars are almost exclusively young red-clump stars

Singh,

Reddy,

Campbell

et al. 2021

Preprint

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We report novel observational evidence on the evolutionary status of lithium-rich giant stars by combining asteroseismic and lithium abundance data. Comparing observations and models of the asteroseismic gravity-mode period spacing ∆Π 1 , we find that super-Li-rich giants (SLR, A(Li) > 3.2 dex) are almost exclusively young red-clump (RC) stars. Depending on the exact phase of evolution, which requires more data to refine, SLR stars are either (i) less than ∼ 2 Myr or (ii) less than ∼ 40 Myr past the main core helium flash (CHeF). Our observations set a strong upper limit for the time of the inferred Li-enrichment phase of < 40 Myr post-CHeF, lending support to the idea that lithium is produced around the time of the CHeF. In contrast, the more evolved RC stars (> 40 Myr post-CHeF) generally have low lithium abundances (A(Li) < 1.0 dex). Between the young, super-Li-rich phase, and the mostly old, Li-poor RC phase, there is an average reduction of lithium by about 3 orders of magnitude. This Li-destruction may occur rapidly. We find the situation to be less clear with stars having Li abundances between the two extremes of super-Li-rich and Li-poor. This group, the 'Li-rich' stars (3.2 > A(Li) > 1.0 dex), shows a wide range of evolutionary states.

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Most lithium-rich low-mass evolved stars revealed as red clump stars by asteroseismology and spectroscopy

Cited by 44 publications

References 76 publications

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

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

Asteroseismic fingerprints of stellar mergers

Tracking the evolution of lithium in giants using asteroseismology: Super-Li-rich stars are almost exclusively young red-clump stars

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