The SALT survey of helium-rich hot subdwarfs: methods, classification, and coarse analysis

Abstract

A medium- and high-resolution spectroscopic survey of helium-rich hot subdwarfs is being carried out using the Southern African Large Telescope (SALT). Objectives include the discovery of exotic hot subdwarfs and of sequences connecting chemically-peculiar subdwarfs of different types. The first phase consists of medium-resolution spectroscopy of over 100 stars selected from low-resolution surveys. This paper describes the selection criteria, and the observing, classification and analysis methods. It presents 107 spectral classifications on the MK-like Drilling system and 106 coarse analyses ($T_{\mathrm{eff}},\log g,\log y$) based on a hybrid grid of zero-metal non-LTE and line-blanketed LTE model atmospheres. For 75 stars, atmospheric parameters have been derived for the first time. The sample may be divided into 6 distinct groups including the classical `helium-rich' sdO stars with spectral types (Sp) sdO6.5 - sdB1 (74) comprising carbon-rich (35) and carbon-weak (39) stars, very hot He-sdO's with Sp $\lesssim$ sdO6 (13), extreme helium stars with luminosity class $\lesssim 5$ (5), intermediate helium-rich subdwarfs with helium class 25 -- 35 (8), and intermediate helium-rich subdwarfs with helium class $10-25$ (6). The last covers a narrow spectral range (sdB0 -- sdB1) including two known and four candidate heavy-metal subdwarfs. Within other groups are several stars of individual interest, including an extremely metal-poor helium star, candidate double-helium subdwarf binaries, and a candidate low-gravity He-sdO star.

MNRAS Accepted 18/11/20, 20 pages + 26 pages supplementary material

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Cited by in corpus (9)

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• Infrared Excesses around Bright White Dwarfs from Gaia and unWISE. II
• Discovery of hot subdwarfs with extremely high carbon and oxygen abundances
• Hot white dwarfs and pre-white dwarfs discovered with SALT
• Spectroscopic analysis of BPS CS 22940-0009: connecting evolved helium stars
• Abundance analysis of a nitrogen-rich extreme-helium hot subdwarf from the SALT survey
• Gaia-supported re-discovery of a remarkable weak line quasar from a variability and proper motion survey
• Discovery and analysis of three magnetic hot subdwarf stars: evidence for merger-induced magnetic fields
• EC 22536-5304: a lead-rich and metal-poor long-period binary