J/A+A/665/A46 High-precision abundance of the Helmi streams (Matsuno+, 2022)
High-precision chemical abundances of Galactic building blocks.
II. Revisiting the chemical distinctness of the Helmi streams.
Matsuno T., Dodd E., Koppelman H.H., Helmi A., Ishigaki M.N., Aoki W.,
Zhao J.-K., Yuan Z., Hattori K.
<Astron. Astrophys. 665, A46 (2022)>
=2022A&A...665A..46M 2022A&A...665A..46M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, halo; ; Abundances ; Spectroscopy ; Equivalent widths ;
Optical
Keywords: Galaxy: abundances - Galaxy: halo - stars: abundances -
Galaxy: stellar content
Abstract:
The Helmi streams are a kinematic substructure whose progenitor is
likely a dwarf galaxy. Although 20 years have passed since their
discovery, it is still unclear whether their members are chemically
distinguishable from other halo stars in the Milky Way. We aim to
precisely characterize the chemical properties of the Helmi streams.
We analyzed high-resolution, high signal-to-noise ratio spectra for 11
Helmi stream stars through a line-by-line abundance analysis. We
compared the derived abundances to homogenized literature abundances
of the other halo stars, including those belonging to other kinematic
substructures, such as Gaia-Enceladus and Sequoia. Compared to typical
halo stars, the Helmi stream members clearly show low values of [X/Fe]
in elements produced by massive stars, such as Na and alpha-elements.
This tendency is seen down to metallicities of at least [Fe/H]~-2.2,
suggesting type Ia supernovae already started to contribute to the
chemical evolution at this metallicity. We find that the [alpha/Fe]
ratio does not evolve significantly with metallicity, making the Helmi
stream stars less distinguishable from Gaia-Enceladus stars at
[Fe/H]>-1.5. The almost constant but low value of [alpha/Fe] might be
indicative of quiescent star formation with low efficiency at the
beginning and bursty star formation at later times. We also find
extremely low values of [Y/Fe] at low metallicity, providing further
support for the claim that light neutron-capture elements are
deficient in Helmi streams. While Zn is deficient at low metallicity,
it shows a large spread at high metallicity. The origin of the
extremely low Y abundances and Zn variations remains unclear. The
Helmi stream stars are distinguishable from the majority of the halo
stars if homogeneously derived abundances are compared.
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:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 46 11 Summary of the data
table5.dat 104 1952 Linelist and line-by-line abundance
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Object Object name used in this study
12- 30 I19 --- GaiaDR2 Gaia DR2 identification number
32- 34 I3 --- S/N4500 Signal-to-noise ratio at 4500Å
36- 38 I3 --- S/N5533 Signal-to-noise ratio at 5533Å
40- 42 I3 --- S/N6370 Signal-to-noise ratio at 6370Å
44- 46 I3 --- N Number of measurements in linelist.dat file
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See also:
J/A+A/661/A103 : High-precision chemical abundances of Sequoia (Matsuno+, 2022)
Byte-by-byte Description of file: table5.dat
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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 log gf value
39- 43 F5.1 0.1pm EW Equivalent width (in mÅ)
45- 48 F4.1 0.1pm e_EW Uncertainty in equivalent width (in 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 F5.3 --- 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
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Acknowledgements:
Tadafumi Matsuno, matsuno(at)astro.rug.nl
References:
Matsuno et al., Paper I 2022A&A...661A.103M 2022A&A...661A.103M, Cat. J/A+A/661/A103
(End) Patricia Vannier [CDS] 06-Jul-2022