J/MNRAS/484/2000 Study of Lithium-rich giants with GALAH (Deepak+, 2019)
Study of Lithium-rich giants with the GALAH spectroscopic survey.
Deepak, Reddy B.E.
<Mon. Not. R. Astron. Soc., 484, 2000-2008 (2019)>
=2019MNRAS.484.2000D 2019MNRAS.484.2000D (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Abundances ; Effective temperatures ; Stars, giant ;
Optical
Keywords: nuclear reactions, nucleosynthesis, abundances - surveys -
stars: abundances - stars: evolution -
stars: kinematics and dynamics -
Hertzsprung-Russell and colour-magnitude diagrams
Abstract:
In this article, we speculate on the possible mechanisms for Li
enhancement origin in RGB stars based on a large data set of around
340299 stars collected from the GALAH survey combined with the Gaia
astrometry. Data has 51982 low mass (M=<2M☉) RGB stars with
reliable atmospheric parameters. The data set shows a well-populated
RGB with well-defined luminosity bump and red clump with significant
number of stars at each of these two key phases. We found 335 new
Li-rich RGB stars with Li abundance, A(Li)≥1.80±0.14dex, of which
20 are super Li-rich with A(Li)≥3.20dex. Most of them appear to be in
the red clump region which, when combined with stellar evolutionary
time-scales on RGB, indicates that the Li enhancement origin may lie
at RGB tip during He-flash rather than by external source of merging
of sub-stellar objects or during luminosity bump evolution. Kinematic
properties of sample stars suggest that Li-rich giants are relatively
more prevalent among giants of thin disc compared to thick disc and
halo.
Description:
The GALAH spectrograph is a large-scale spectroscopic survey of
spectral resolution of R(=Δλ/λ)∼28,000 with
spectrograph attached to 4-m Anglo-Australian Telescope (AAT). In the
GALAH Data Release 2 (GALAH DR2), the GALAH team has provided
quantitatively derived abundances of about 23 elements including the
light element Li, which is the focus of this article, for a sample of
342682 stars (see Buder et al. 2018MNRAS.478.4513B 2018MNRAS.478.4513B, Cat.
J/MNRAS/478/4513). The sample is searched for corresponding
astrometric and photometric data from the Gaia Data Release 2
(hereafter Gaia DR2) of 1.7 billion stars. Source matching is done
using the Gaia DR2 source identifier provided in the GALAH DR2 data
set (see Buder et al. 2018MNRAS.478.4513B 2018MNRAS.478.4513B, Cat. J/MNRAS/478/4513; Gaia
Collaboration et al. 2018A&A...616A...1G 2018A&A...616A...1G, Cat. I/345). This resulted
in a sample of 340299 common stars among the two data sets.
For this study, we adopt a single limit of A(Li)=1.8dex, instead of
using two upper limits, as most of the Li-rich giants in the sample
are in the higher metallicity group (i.e [Fe/H]>-0.6 dex). This is
also the same upper limit set by standard models for low-mass
(1M☉) Li-normal giants. In addition, given the relatively larger
uncertainties (~±0.14) involved in the derivation of Li abundances
from the spectra, adoption of a slightly higher limit to avoid
contamination with Li-normal giants is justified. With this
definition, we found 335 giants with A(Li)≥1.8dex. This is about 0.64
per cent of total RGB giants considered in this study and confirms the
previous survey results (Brown et al. 1989ApJS...71..293B 1989ApJS...71..293B; Kumar et
al. 2011ApJ...730L..12K 2011ApJ...730L..12K; Kirby et al. 2012ApJ...752L..16K 2012ApJ...752L..16K) that
Li-rich giants are a rare group.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
suptable.dat 93 335 Stellar parameters of Li-rich giants with Li
abundance of A(Li)≥1.8dex in our sample
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See also:
J/MNRAS/478/4513 : GALAH Survey DR2 (Buder+, 2018)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: suptable.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- ID Object ID
5- 12 A8 --- --- [Gaia DR2]
14- 32 I19 --- GaiaDR2 Gaia DR2 source id
34- 40 F7.2 K Teff Effective temperature (1)
42- 46 F5.2 K e_Teff Error on Teff (1)
48- 51 F4.2 [cm/s2] logg Surface gravity (1)
53- 56 F4.2 [cm/s2] e_logg Error on logg (1)
58- 62 F5.2 [-] [Fe/H] Iron to hydrogen abundance ratio
64- 67 F4.2 [-] e_[Fe/H] Error on [Fe/H]
69- 73 F5.2 mag Vmag Apparent visual magnitude
75- 78 F4.2 [Lsun] logL Star luminosity (2)
80- 83 F4.2 [Lsun] e_logL Error on logL (2)
85- 88 F4.2 --- A(Li) Lithium abundance
90- 93 F4.2 --- e_A(Li) Error on A(Li)
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Note (1): Values of effective temperature and logarithmic surface gravity are
adopted from the GALAH catalogue (Buder et al. 2018MNRAS.478.4513B 2018MNRAS.478.4513B,
Cat. J/MNRAS/478/4513)
Note (2): The values of luminosities are based on parallaxes and apparent
magnitudes taken from the Gaia catalogue
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 17-Aug-2022