| Name: Sriram Krishna |
| Affiliation: Indian Institute of Astrophysics, Bangalore, India |
| Conference ID: ASI2026_249 |
| Title: Spectral analysis of hottest Extreme Helium stars HD 160641 and LS IV +06 2 |
| Abstract Type: Oral |
| Abstract Category: Stars, Interstellar Medium, and Astrochemistry in Milky Way |
| Author(s) and Co-Author(s) with Affiliation: Sriram Krishna(Indian Institute of Astrophysics, Bangalore - 560034, India), Gajendra Pandey(Indian Institute of Astrophysics, Bangalore - 560034, India) |
| Abstract: We present a comprehensive spectroscopic study of the two hottest known Extreme Helium (EHe) stars, HD 160641 and LS IV +06 2, using high-resolution optical spectra covering a wide wavelength range (3,100–10,000 Å). This work delivers the first detailed atmospheric and chemical abundance analysis for HD 160641. Given the extreme temperatures (Teff > 30,000 K) and helium-dominated composition of these objects, we computed custom LTE model atmospheres using TLUSTY, as no pre-existing grids are available for such compositions.
Our analysis yields refined stellar parameters - the effective temperature, the surface gravity and microturbulence - and surface chemical compositions. The detailed analysis reveals that HD 160641 has low surface gravity (log g = 3.0 in cgs) and high temperature (33,000 K) while LS IV +06 2 has a surface gravity of 4.2 and a similarly high temperature (32,000 K). The high-resolution study at this wide wavelength coverage enables detection of F II, and Ar III in LS IV +06 2. We have also refined the Iron abundance of LS IV +06 2 based on several newly identified Fe III lines.
Variation of radial velocity over several epochs are observed in both stars. These patterns are not consistent with binary motion, suggesting pulsations as the potential cause. However line asymmetry is observed only in HD 160641 and that further supports the pulsation hypothesis.
The lack of hydrogen and enhanced abundances of helium, carbon, nitrogen, and neon observed in both stars are consistent with predictions from a double white dwarf merger scenario. |
