Hot subdwarf stars in close-up view IV. Helium abundances and the ${}^3$He isotopic anomaly of subdwarf B star

Abstract

Atmospheric parameters and helium abundances of 44 bright subdwarf B stars have been determined. More than half of our sample consists of newly discovered stars from the Edinburgh Cape survey. We showed that effective temperatures and surface gravities can be derived from high resolution echelle spectra with sufficient accuracy. Systematic uncertainties have been determined by comparing the parameters derived from the high resolution data with the ones derived from medium resolution spectra. Helium abundances have been measured with high accuracy. Besides the known correlation of helium abundance with temperature, two distinct sequences in helium abundance have been confirmed. Significant isotopic shifts of helium lines due to an enrichment in ${}^3$He have been found in the spectra of 8 sdBs. Most of these stars cluster in a small temperature range between $27000\mathrm{K}$ and $31000\mathrm{K}$ very similar to the known ${}^3$He-rich main sequence B stars, which also cluster in such a small strip, but at different temperatures. Both the helium sequences and the isotopic anomaly are discussed.

12 pages, A&A accepted

References in corpus (7)

• A selection of hot subluminous stars in the GALEX survey II. Subdwarf atmospheric parameters
• White Dwarf Luminosity and Mass Functions from Sloan Digital Sky Survey Spectra
• Mass-loss and diffusion in subdwarf B stars and hot white dwarfs: do weak winds exist?
• Hot subdwarf stars in close-up view - II. Rotational properties of single and wide binary subdwarf B stars
• Abundance analyses of helium-rich subluminous B stars
• The subdwarf B star SB 290 - A fast rotator on the extreme horizontal branch
• CPD-20 1123 (Albus 1) is a bright He-B Subdwarf

Cited by in corpus (10)

• Hot subluminous stars
• New binaries among UV-selected, hot subdwarf stars and population properties
• The catalogue of radial velocity variable hot subluminous stars from the MUCHFUSS project
• A Catalogue of Potential Post Common Envelope Binaries
• Evolution models of helium white dwarf--main sequence star merger remnants
• Hot subdwarf stars identified in Gaia DR2 with spectra of LAMOST DR6 and DR7 I. Single-lined spectra
• Hydrogen in hot subdwarfs formed by double helium white dwarf mergers
• Heavy metals in a light white dwarf: Abundances of the metal-rich, extremely low-mass GALEX J1717+6757
• The population of hot subdwarf stars studied with Gaia I. The catalogue of known hot subdwarf stars
• Mode identification in three pulsating hot subdwarfs observed with TESS satellite