The SALT survey of helium-rich hot subdwarfs: final sample and classification

TL;DR

This paper presents a comprehensive spectroscopic survey of helium-rich hot subdwarfs using SALT, expanding the sample size significantly and classifying various subclasses to aid future evolutionary and kinematic studies.

Contribution

It extends the sample of helium-rich hot subdwarfs to 697 stars, providing detailed spectral classifications and identifying new exotic objects within this class.

Findings

Largest homogeneous sample of helium-rich hot subdwarfs to date.

Discovery of magnetic hot subdwarfs and extremely hot pre-white dwarfs.

Identification of new extreme helium stars and double-subdwarf candidates.

Abstract

A medium-resolution spectroscopic survey of helium-rich hot subdwarfs has been carried out using the Southern African Large Telescope (SALT). Objectives include the discovery of exotic hot subdwarfs, resolving distinct subclasses, identifying evolutionary sequences, and establishing the past and future histories of many of these unusual stars. This paper extends the sample described by Jeffery et al. (2021) (arXiv:2011.09523) from 100 to 697 stars. It describes the selection criteria and presents spectral classifications based on the MK-like Drilling system. The sample includes 283 extremely helium-rich hot subdwarfs, 17 extreme helium stars, 110 intermediate helium-rich hot subdwarfs, as well as 21 helium-rich stars of other types. It now represents the largest homogeneous sample of both "normal" He-sdOs and "luminous" or "hot" He-sdOs. Interesting stars discovered include magnetic hot subdwarfs, extremely hot pre-white dwarfs and hot subdwarfs, including hot subdwarfs showing NV emission, one short-period binary, new extreme helium stars and several double-subdwarf candidates. The data form the basis for kinematic and model atmosphere analyses to follow.