J/A+A/661/A103 High-precision chemical abundances of Sequoia (Matsuno+, 2022)
High-precision chemical abundances of Galactic building blocks.
The distinct chemical abundance sequence of Sequoia.
Matsuno T., Koppelman H.H., Helmi A., Aoki W., Ishigaki M.N., Suda T.,
Yuan Z., Hattori K.
<Astron. Astrophys. 661, A103 (2022)>
=2022A&A...661A.103M 2022A&A...661A.103M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, halo ; Abundances ; Spectroscopy ; Equivalent widths ;
Optical
Keywords: stars: abundances - Galaxy: abundances - Galaxy: halo
Abstract:
Sequoia is a retrograde kinematic substructures in the nearby Galactic
halo, whose properties are a matter of debate. For example, previous
studies do not necessarily agree on the chemical abundances of Sequoia
stars, which are important for understanding its nature. We
characterize the chemical properties of a sample of stars from Sequoia
by determining high-precision abundances. Methods: We measure
abundances of Na, Mg, Si, Ti, Cr, Mn, Ni, Zn, Y, and Ba from a
differential abundance analysis on high signal-to-noise ratio,
high-resolution spectra from new observations and from archival data.
We compare precisely-measured chemical abundances of 12 Sequoia
candidates with those of typical halo stars from literature, which
include also stars from Gaia-Enceladus. This allows us to characterize
Sequoia and compare it to another Galactic building block. The
comparison is made after putting all the abundances onto the same
scale using standard stars. There are significant difference in
[Na/Fe], [Mg/Fe], [Ca/Fe], [Ti/Fe], [Zn/Fe], and [Y/Fe] between
Sequoia and Gaia-Enceladus stars at -1.8<[Fe/H]←1.4 in the sense
that these abundance ratios are lower in Sequoia. These differences
are similar to those seen between Gaia-Enceladus and in-situ stars at
higher metallicity, suggesting that Sequoia is affected by type∼Ia
supernovae at lower metallicity than Gaia-Enceladus. We also confirm
that the low [Mg/Fe] of Sequoia is seen in literature and in surveys,
namely APOGEE DR16 and GALAH DR3, if the stars are kinematically
selected in the same way. Sequoia stars have a distinct chemical
abundance pattern and can be chemically separated from in-situ stars
or Gaia-Enceladus stars if abundances are measured with sufficient
precision, namely sigma([X/Fe])<0.07dex.
Description:
We tabulate measured equivalent widths and their uncertainties
together with information on the lines, such as wavelength, excitation
potential, and log(gf)-values. We also include line-by-line
abundances, for which we also provide uncertainties due to stellar
parameters and equivalent widths. The weights used to compute the best
estimate of the abundance of each species is also included. These data
can be used to reproduce all the figures and the abundance table.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 65 15 List of studied stars
line.dat 104 3173 Line list
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Object Object name used in this study
13- 14 I2 h RAh Right ascension (J2000)
16- 17 I2 min RAm Right ascension (J2000)
19- 23 F5.2 s RAs Right ascension (J2000)
25 A1 --- DE- Declination sign (J2000)
26- 27 I2 deg DEd Declination (J2000)
29- 30 I2 arcmin DEm Declination (J2000)
32- 35 F4.1 arcsec DEs Declination (J2000)
37- 65 A29 --- OName Gaia EDR3 name (Gaia EDR3 NNNNNNNNNNNNNNNNNNN)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: line.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Object Object name used in this study
12- 15 A4 --- species Name of the species
17- 24 F8.3 0.1nm lambda Wavelength
26- 30 F5.3 eV chi Excitation potential
32- 37 F6.3 --- loggf loggf value
39- 43 F5.1 0.1pm EW Equivalent width (mÅ)
45- 48 F4.1 0.1pm e_EW Uncertainty in equivalent width (mÅ)
50- 55 F6.3 --- A Abundance from this line
57- 62 F6.3 --- eAteff Uncertainty in abundance due to
effective temperature
64- 69 F6.3 --- eAlogg Uncertainty in abundance due to
surface gravity
71- 76 F6.3 --- eAvt Uncertainty in abundance due to
microturbulent velocity
78- 83 F6.3 --- eA[Fe/H] Uncertainty in abundance due to metallicity
85- 89 A5 --- eAEW Uncertainty in abundance due to
equivalent widths of this star and
the reference star
91- 95 F5.3 --- sX Uncertainty floor
97-104 F8.3 --- Weight Weight used to obtain the best estimate for
the abundance of the species
--------------------------------------------------------------------------------
Acknowledgements:
Tadafumi Matsuno, matsuno(at)astro.rug.nl
(End) Patricia Vannier [CDS] 19-Apr-2022