J/MNRAS/484/4591 The GALAH Survey lithium-strong KM dwarfs (Zerjal+, 2019)
The GALAH Survey: lithium-strong KM dwarfs.
Zerjal M., Ireland M.J., Nordlander T., Lin J., Buder S., Casagrande L.,
Cotar K., De Silva G., Horner J., Martell S., Traven G., Zwitter T.,
(the GALAH Collaboration)
<Mon. Not. R. Astron. Soc., 484, 4591-4600 (2019)>
=2019MNRAS.484.4591Z 2019MNRAS.484.4591Z (SIMBAD/NED BibCode)
ADC_Keywords: Abundances ; Stars, late-type ; Stars, pre-main sequence ;
Space velocities ; Equivalent widths
Keywords: stars: abundances - stars: late-type - stars: pre-main-sequence
Abstract:
Identifying and characterizing young stars in the Solar neighbourhood
is essential to find and describe planets in the early stages of their
evolution. This work seeks to identify nearby young stars showing a
lithium 6708Å absorption line in the GALAH survey. A robust,
data-driven approach is used to search for corresponding templates in
the pool of 434215 measured dwarf spectra in the survey. It enables a
model-free search for best-matching spectral templates for all stars,
including M dwarfs with strong molecular absorption bands. 3147 stars
have been found to have measurable lithium: 1408G and 892 K0-K5 dwarfs
(EW(Li)>0.1Å), 335 K5-K9 (>0.07Å) and 512 M0-M4 dwarfs
(>0.05Å). Stars with such lithium features are used to investigate
the possibility of searching for young stars above the main sequence
based merely on their parallaxes and broad-band photometry. The
selection of young stars above the main sequence is highly effective
for M dwarfs, moderately effective for K dwarfs and ineffective for G
dwarfs. Using a combination of the lithium information and the
complete 6D kinematics from Gaia and GALAH, 305 new candidate moving
group members have been found, 123 of which belong to the
Scorpius-Centaurus association, 36 to the Pleiades and 25 to the
Hyades clusters.
Description:
GALAH (De Silva et al. 2015MNRAS.449.2604D 2015MNRAS.449.2604D) is an ongoing large-scale
spectroscopic survey that makes use of the multi-object (392)
spectrograph HERMES (Barden et al. 2010SPIE.7735E..09B 2010SPIE.7735E..09B) at the
3.9-metre Anglo-Australian Telescope, located at the Siding Spring
Observatory, Australia. The high-resolution spectrograph (∼28000) is
composed of four optical channels covering 4713-4903Å,
5648-5873Å, 6478-6737Å, and 7585-7887Å.
The main goal of the GALAH survey is to address the chemical
abundances of the stars in the Milky Way galaxy. Lithium abundances
have been determined for the majority of the stars in the GALAH
database. However, due to difficulties in modelling M dwarfs with
strong TiO bands and a subsequent lack of a reliable training set,
lithium data is unavailable below 4000K. For this work, we are hence
using an independent estimate of the equivalent widths of the lithium
line for low-mass stars. The same method is used for both K and M
dwarfs to provide consistent measurements across the entire parameter
space.
For this study, we restrict ourselves to the red arm of the
spectrograph to determine the presence of the lithium absorption line
in 438888 dwarfs. In total, 434215 spectra of 400302 unique objects
are used in this work. The sample consists of three different subsets:
350901 GALAH, 62551 K2 and 28955 TESS spectra from the HERMES
programs.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 48 434215 List of GALAH stars with measured lithium
equivalent width
table3.dat 186 395 List of candidate members of known moving groups
based on the Banyan Σ (Gagne et al.
2018ApJ...856...23G 2018ApJ...856...23G, Cat. J/ApJ/856/23)
algorithms
--------------------------------------------------------------------------------
See also:
J/ApJ/856/23 : BANYAN. XI. The BANYAN Σ algorithm (Gagne+, 2018)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 28 A28 --- Name Gaia DR2 or 2MASS identifier
30- 36 F7.3 0.1nm EW(Li) ? Equivalent width of the lithium 6708Å
line
38- 42 F5.3 0.1nm e_EW(Li) ? Lower error on EW(Li)
44- 48 F5.3 0.1nm E_EW(Li) ? Upper error on EW(Li)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- --- [Gaia DR2]
10- 28 I19 --- GaiaDR2 Gaia DR2 source identifier
30- 35 F6.3 0.1nm EW(Li) ? Equivalent width of the lithium 6708Å
line
37- 41 F5.3 0.1nm e_EW(Li) ? Lower error on EW(Li)
43- 47 F5.3 0.1nm E_EW(Li) ? Upper error on EW(Li)
49- 69 A21 --- bonafide Moving group of bonafide stars (confirmed
members) from Gagne et al.
2018ApJ...856...23G 2018ApJ...856...23G, Cat. J/ApJ/856/23)
71- 76 A6 --- hypot Best hypothesis from the Banyan Σ
results (1)
78- 83 F6.4 --- p Probability from the Banyan Σ
results (1)
85- 89 A5 --- f_EW(Li) Flag indicating whether lithium is at least
as strong as expected for stellar age
91- 98 F8.2 pc X Galactic X position
100-107 F8.2 pc Y Galactic Y position
109-116 F8.2 pc Z Galactic Z position
118-124 F7.2 pc e_X Error on X
126-132 F7.2 pc e_Y Error on Y
134-140 F7.2 pc e_Z Error on Z
142-148 F7.2 km/s U U-velocity component
150-156 F7.2 km/s V V-velocity component
158-164 F7.2 km/s W W-velocity component
166-172 F7.2 km/s e_U Error on U
174-179 F6.2 km/s e_V Error on V
181-186 F6.2 km/s e_W Error on W
--------------------------------------------------------------------------------
Note (1): BANYAN Σ is a Bayesian algorithm to identify members of young
stellar associations within 150pc of the Sun (see Gagne et al.
2018ApJ...856...23G 2018ApJ...856...23G, Cat. J/ApJ/856/23)
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 05-Sep-2022