Chemical Abundance Analysis Of Symbiotic Giants. Metallicity And CNO Abundance Patterns In 14 Northern S-type Systems

By Keith Cowing
Status Report
July 19, 2023
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Chemical Abundance Analysis Of Symbiotic Giants. Metallicity And CNO Abundance Patterns In 14 Northern S-type Systems
Oxygen relative to iron for our northern (blue circles) and southern (red circles) samples compared to the abundances coming from the entire selected sample of the APOGEE DR16 release (gray points) and the extracted sample of giant stars (orange points) corresponding to the atmospheric parameters (3100 ≤ 𝑇eff ≤ 4100 K, and 0 ≤ log 𝑔 ≤ 1.5) similar to our sample of SySt. The APOGEE abundances have been scaled to the solar composition by Asplund et al. (2009) and Scott et al. (2015) for oxygen and iron, respectively. Typical 3𝜎 error bar is shown in the top-right corner. — astro-ph.SR

In previous works, we computed abundances for the red giant in nearly four dozen S-type symbiotic systems (SySt). The abundances provide information about metallicity, evolutionary status, and possible memberships in Galactic stellar populations. Here, we extend our studies with a northern hemisphere sample of SySt.

This northern sample is dominated by Galactic disk/halo objects, whereas our previous southern sample is heavily biased toward the bulge population. Spectrum synthesis of high-resolution (R∼50000), near-IR spectra using standard LTE analysis and atmospheric models have been used to measure abundances of CNO and elements around the iron peak (Fe, Ti, Ni, Sc) in the atmospheres of the red giant component. The SySt sample shows generally slightly sub-solar metallicity, as expected for an older disk population, with a median at [Fe/H]\,∼−0.2 dex.

Enhanced 14N, depleted 12C, and decreased 12C/13C indicate that all these giants have experienced the first dredge-up. Comparison with theoretical predictions indicates that additional mixing processes had to occur to explain the observed C and N abundances. Relative O and Fe abundances agree with those represented by Galactic disc and bulge giant populations in the {\sl APOGEE} data, with a few cases that can be attributed to membership in the extended thick-disc/halo. As an interesting byproduct of this study, we observed a blue-shifted additional component on the wings of absorption lines in the spectra of AG Peg which could be connected with accretion onto the hot component.

Cezary Gałan, Joanna Mikołajewska, Kenneth H. Hinkle, Richard R. Joyce

Comments: 10 pages + 3 appendixes. Accepted for publication at MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2307.09596 [astro-ph.SR] (or arXiv:2307.09596v1 [astro-ph.SR] for this version)
Submission history
From: Cezary Galan
[v1] Thu, 13 Jul 2023 14:58:09 UTC (7,004 KB)
Astrobiology, Astrochemistry

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