Subdwarf O Stars from SDSS and SPY

TL;DR

This paper conducts a detailed spectral analysis of subdwarf O stars from SDSS, revealing their temperature, gravity, and helium content, and discusses their evolutionary links and possible formation scenarios.

Contribution

It provides the first comprehensive spectral analysis of sdO stars from SDSS, identifying their physical parameters and proposing evolutionary pathways.

Findings

Helium-enriched sdO stars cluster at Teff=40,000-50,000K and log(g)=5.5-6.0.

sdB stars are likely predecessors of helium-deficient sdO stars.

Two main scenarios explain helium-enriched sdO stars: white dwarf mergers and late hot flashers.

Abstract

We present the results of quantitative spectral analysis of sdOs from the SDSS database. Fitting the Balmer, HeI and HeII lines to non-LTE model spectra, we derived their effective temperatures, surface gravities and helium abundances. We find the helium-enriched sdO stars to rally in a small intervall of Teff = 40,000K to 50,000K and log(g) = 5.5 to 6.0. We conclude, that the sdB stars are linked with the helium-deficient sdO stars, i.e. the sdBs are predecessors for the helium-deficient sdOs. To explain the helium-enriched sdO stars in their entirety, we regard two scenarios as most promising: The merging of two helium-core white dwarfs and the late hot flashers.