A NLTE model atmosphere analysis of the pulsating sdO star SDSS J1600+0748

TL;DR

This study develops and applies NLTE model atmospheres with metals to analyze the pulsating sdO star SDSS J1600+0748, providing precise stellar parameters and highlighting the need for further model improvements.

Contribution

The paper introduces a grid of NLTE model atmospheres including metals for hot sdO stars and applies it to a pulsating star, refining stellar parameter determination.

Findings

Best fit with NLTE models including C, N, O in solar abundances

Derived stellar parameters: Teff ~69,060 K, log g ~6.00, log N(He)/N(H) ~-0.61

Identified the need for improved He II line fitting, possibly by including Fe

Abstract

We started a program to construct several grids of suitable model atmospheres and synthetic spectra for hot subdwarf O stars computed, for comparative purposes, in LTE, NLTE, with and without metals. For the moment, we use our grids to perform fits on our spectrum of SDSS J160043.6+074802.9 (J1600+0748 for short), this unique pulsating sdO star. Our best fit is currently obtained with NLTE model atmospheres including carbon, nitrogen and oxygen in solar abundances, which leads to the following parameters for SDSS J1600+0748 : Teff = 69 060 +/- 2080 K, log g = 6.00 +/- 0.09 and log N(He)/N(H) = -0.61 +/- 0.06. Improvements are needed, however, particularly for fitting the available He II lines. It is hoped that the inclusion of Fe will help remedy the situation.