The evolved pulsating CEMP star HD112869

TL;DR

This study investigates the pulsating, carbon-enhanced metal-poor star HD112869 through multi-method observations, revealing its evolutionary status, atmospheric composition, and pulsation characteristics, suggesting it is a low-mass AGB star.

Contribution

It provides a comprehensive analysis combining radial velocity, photometry, and spectroscopy to clarify the star's evolutionary stage and atmospheric properties, including unique isotope ratios.

Findings

Confirmed semiregular pulsations with ~115-day period

Found extremely high carbon isotope ratios (^{12}C/^{13}C > 1500)

Determined the star's atmosphere is less metal-poor than previously thought

Abstract

Radial velocity measurements, $BVR_C$ photometry, and high-resolution spectroscopy in the wavelength region from blue to near infrared are employed in order to clarify the evolutionary status of the carbon-enhanced metal-poor star HD112869 with unique ratio of carbon isotopes in the atmosphere. An LTE abundance analysis was carried out using the method of spectral synthesis and new self consistent 1D atmospheric models. The radial velocity monitoring confirmed semiregular variations with a peak-to-peak amplitude of about 10 km $s^{-1}$ and a dominating period of about 115 days. The light, color and radial velocity variations are typical of the evolved pulsating stars. The atmosphere of HD112869 appears to be less metal-poor than reported before, [Fe/H] = -2.3 $\pm$0.2 dex. Carbon to oxygen and carbon isotope ratios are found to be extremely high, C/O $\simeq$ 12.6 and $^{12}C/^{13}C \gtrsim$ 1500, respectively. The s-process elements yttrium and barium are not enhanced, but neodymium appears to be overabundant. The magnesium abundance seems to be lower than the average found for CEMP stars, [Mg/Fe] < +0.4 dex. HD112869 could be a single low mass halo star in the stage of asymptotic giant branch evolution