J/A+A/655/A117 Carbon and oxygen in microlensed bulge dwarfs (Bensby+, 2021)
Chemical evolution of the Galactic bulge as traced by microlensed dwarf and
subgiant stars. VIII. Carbon and oxygen .
Bensby T., Gould A., Asplund M., Feltzing S., Melendez J., Johnson J.A.,
Lucatello S., Udalski A., Yee J.C.
<Astron. Astrophys. 655, A117 (2021)>
=2021A&A...655A.117B 2021A&A...655A.117B (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, G-type ; Abundances ; Radio lines
Keywords: gravitational lensing: micro - Galaxy: bukge - Galaxy: formation -
Galaxy: evolution - stars: abundances
Abstract:
Next to H and He, carbon is, together with oxygen, the most abundant
element in the Universe and widely used when modelling the formation
and evolution of galaxies and their stellar populations. For the Milky
Way bulge, there are currently essentially no measurements of carbon
in un-evolved stars, hampering our abilities to properly compare
Galactic chemical evolution models to observational data for this
still enigmatic stellar population.
We aim to determine carbon abundances for our sample of 91 microlensed
dwarf and subgiant stars in the Galactic bulge. Together with new
determinations for oxygen this forms the first statistically
significant sample of bulge stars that have C and O abundances
measured, and for which the C abundances have not been altered by the
nuclear burning processes internal to the stars.
Our analysis is based on high-resolution spectra for a sample of 91
dwarf and subgiant stars that were obtained during microlensing events
when the brightnesses of the stars were highly magnified. Carbon
abundances were determined through spectral line synthesis of six
CI lines around 9100Å, and oxygen abundances using the three
OI lines at about 7770Å. One-dimensional (1D) MARCS model stellar
atmospheres calculated under the assumption of local thermodynamic
equilibrium (LTE) were used, and non-LTE corrections were applied when
calculating the synthetic spectra for both C and O.
Carbon abundances was possible to determine for 70 of the 91 stars in
the sample and oxygen abundances for 88 of the 91 stars in the sample.
The [C/Fe] ratio evolves essentially in lockstep with [Fe/H], centred
around solar values at all [Fe/H]. The [O/Fe]-[Fe/H] trend has an
appearance very similar to that observed for other alpha-elements in
the bulge, with the exception of a continued decrease in [O/Fe] at
super-solar [Fe/H], where other alpha-elements tend to level out. When
dividing the bulge sample into two sub-groups, one younger than 8Gyr
and one older than 8Gyr, the stars in the two groups follow exactly
the elemental abundance trends defined by the solar neighbourhood thin
and thick disks, respectively. Comparisons with recent models of
Galactic chemical evolution in the [C/O]-[O/H] plane show that the
models that best match the data are the ones that have been calculated
with the Galactic thin and thick disks in mind.
We conclude that carbon, oxygen, and the combination of the two
support the idea that the majority of the stars in the Galactic bulge
have a secular origin; that is, they are formed from disk material. We
cannot exclude that a fraction of stars in the bulge could be
classified as a classical bulge population, but it would have to be
small. More dedicated and advanced models of the inner region of the
Milky Way are needed to make more detailed comparisons to the
observations.
Description:
We perform a detailed analysis of C and O in 91 microlensed dwarf
stars in the Galactic bulge. Abundances were determined through
spectral line synthesis of three oxygen lines at 777nm and six carbon
lines at 910nm. The stellar sample traces the evolution of the
Galactic bulge, and is the same as previously analysed by Bensby et
al. (2017, Cat. J/A+A/605/A89) where stellar parameters and ages were
taken from.
For each star we give the NLTE corrected C and O abundances, and their
uncertainties based on the same analysis but increasing and decreasing
the stellar parameters (effective temperature, surface gravity,
metallicity, microturbulence) with their uncertainties. The abundances
have been normalised to the Sun, based on our analysis of the Sun, on
a line-by-line basis. We also give the absolute abundances for
individual lines. For each carbon line we give a flag (0, 1, or 2)
depending on whether the spectral line is close to a telluric
absorption line or not:
0 = not affected;
1 = closer than 0.03nm to a weak telluric line (depth smaller than 15%
of the continuum level);
2 = closer than 0.03 nm to a strong telluric line (depth greater than
15 % of the continuum level).
70 stars have the carbon abundance measured and 89 stars have the
oxygen abundance measured.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 180 91 C and O abundances and uncertainties.
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See also:
J/A+A/605/A89 : Abundances of microlensed bulge stars (Bensby+, 2017)
J/A+A/634/A130 : Lithium abundances in microlensed dwarf stars (Bensby+, 2020)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
3- 21 A19 --- Name Name of microlensing source star
25- 30 I6 --- Num Internal numbering of star
34- 38 F5.2 [-] [C/H] ? [C/H] abundance normalised to Sun
42- 46 F5.2 [-] [O/H] ? [O/H] abundance normalised to Sun
50- 53 F4.2 [-] e_[C/H] ? Error on [C/H]
57- 60 F4.2 [-] e_[O/H] ? Error on [O/H]
64- 67 F4.2 [-] e_[C/O] ? Error on [C/O]
71- 74 F4.2 [-] e_[C/Fe] ? Error on [C/Fe]
78- 81 F4.2 [-] e_[O/Fe] ? Error on [O/Fe]
85- 88 F4.2 --- AO7772 ? Absolute abundance for O 7772 line
92- 95 F4.2 --- AO7774 ? Absolute abundance for O 7774 line
99-102 F4.2 --- AO7775 ? Absolute abundance for O 7775 line
106-109 F4.2 --- AC9061 ? Absolute abundance for C 9061 line
113-116 F4.2 --- AC9063 ? Absolute abundance for C 9063 line
120-123 F4.2 --- AC9078 ? Absolute abundance for C 9078 line
127-130 F4.2 --- AC9089 ? Absolute abundance for C 9089 line
134-137 F4.2 --- AC9094 ? Absolute abundance for C 9094 line
141-144 F4.2 --- AC9111 ? Absolute abundance for C 9111 line
150 I1 --- Flag1 [0/2]? Flag on C 9061 line (1)
156 I1 --- Flag2 [0/2]? Flag on C 9063 line (1)
162 I1 --- Flag3 [0/2]? Flag on C 9078 line (1)
168 I1 --- Flag4 [0/2]? Flag on C 9089 line (1)
174 I1 --- Flag5 [0/2]? Flag on C 9094 line (1)
180 I1 --- Flag6 [0/2]? Flag on C 9111 line (1)
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Note (1): Flag as follows:
0 = not affected
1 = closer than 0.03nm to a weak telluric line (depth smaller than 15%
of the continuum level)
2 = closer than 0.03 nm to a strong telluric line (depth greater than
15 % of the continuum level)
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Acknowledgements:
Thomas Bensby, tbensby(at)astro.lu.se
References:
Bensby et al., Paper I 2009A&A...499..737B 2009A&A...499..737B, Cat. J/A+A/499/737
Bensby et al., Paper II 2010A&A...512A..41B 2010A&A...512A..41B, Cat. J/A+A/512/A41
Bensby et al., Paper III 2010A&A...521L..57B 2010A&A...521L..57B
Bensby et al., Paper IV 2011A&A...533A.134B 2011A&A...533A.134B, Cat. J/A+A/533/A134
Bensby et al., Paper V 2013A&A...549A.147B 2013A&A...549A.147B, Cat. J/A+A/549/A147
Bensby et al., Paper VI 2017A&A...605A..89B 2017A&A...605A..89B, Cat. J/A+A/605/A89
Bensby et al., Paper VII 2020A&A...634A.130B 2020A&A...634A.130B, Cat. J/A+A/634/A130
(End) Thomas Bensby [Lund Obs., Sweden], Patricia Vannier [CDS] 10-Sep-2021