Chemical abundance analysis of symbiotic giants. Metallicity and CNO abundance patterns in 14 northern S-type systems

Abstract

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$\sim$50000), near-$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]\,$\sim -0.2$ dex. Enhanced ${}^{14}$N, depleted ${}^{12}$C, and decreased ${}^{12}$C/${}^{13}$C 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.

10 pages + 3 appendixes

References in corpus (10)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• APOGEE Data and Spectral Analysis from SDSS Data Release 16: Seven Years of Observations Including First Results from APOGEE-South
• Thermohaline mixing: A physical mechanism governing the photospheric composition of low-mass giants
• The elemental composition of the Sun II. The iron group elements Sc to Ni
• Line lists for the A2PI-X2Sigma+ (red) and {B2Sigma+-X2Sigma} (violet) Systems of CN, 13C14N, and 12C15N, and Application to Astronomical Spectra
• Infrared Spectroscopy of Symbiotic Stars. VII. Binary Orbit and Long Secondary Period Variability of CH Cygni
• Chemical abundance analysis of 13 southern symbiotic giants from high-resolution spectra at ~1.56 μm
• AG Pegasi - now a classical symbiotic star in outburst?
• Chemical abundance analysis of symbiotic giants. I. RW Hya and SY Mus
• Line formation regions of the UV spectrum of CI Cygni

Cited by in corpus (4)

• Symbiotic stars in the era of modern ground- and space-based surveys
• Resolving the mass transfer in the symbiotic recurrent nova T Coronae Borealis
• The formation of the magnetic symbiotic star FN Sgr
• A search for new symbiotic stars in the Milky Way: Using machine learning techniques applied to photometric databases