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The Helium-Rich Subdwarf Cpd−20°1123: A Post-Common-Envelope Binary Evolving On To The Extended Horizontal Branch, Naslim N., S. Geier, C. S. Jeffery, N. T. Behara, V. M. Woolf, L. Classen

Physics Faculty Publications

Subluminous B stars come in a variety of flavours including single stars, close and wide binaries, and pulsating and non-pulsating variables. A majority have helium-poor surfaces (helium by number n_He < 1 per cent), whilst a minority have extremely helium rich surfaces (n_He > 90 per cent). A small number have an intermediate surface helium abundance (≈10–30 per cent), accompanied by peculiar abundances of other elements. The questions posed are (i) whether these abundance peculiarities are associated with radiatively driven and time-dependent stratification of elements within the photosphere as the star evolves from a helium-enriched progenitor to become a normal helium-poor sdB star and (ii) whether these phenomena occur only in …

The M Dwarf Problem In The Galaxy, Vincent M. Woolf, Andrew A. West

Physics Faculty Publications

We present evidence that there is an M dwarf problem similar to the previously identified G dwarf and K dwarf problems: the number of low-metallicity M dwarfs is not sufficient to match simple closed-box models of local Galactic chemical evolution. We estimated the metallicity of 4141 M dwarf stars with spectra from the Sloan Digital Sky Survey (SDSS) using a molecular band strength versus metallicity calibration developed using high resolution spectra of nearby M dwarfs. Using a sample of M dwarfs with measured magnitudes, parallaxes and metallicities, we derived a relation that describes the absolute magnitude variation as a function …

An Abundance Analysis Of A Chemically Peculiar B Star – Jl 87*,**, A. Ahmad, N. T. Behara, C. S. Jeffery, T. Sahin, V. M. Woolf

Physics Faculty Publications

Aims. The aim of this study is to understand the nature and origin of a chemically peculiar star JL 87 by measuring its physical parameters and chemical abundances.

Methods. Physical parameters – effective temperature, surface gravity and helium abundance were measured from a moderate resolution optical spectrum using fully line-blanketed LTE model atmospheres. The effective temperature and extinction were verified by comparing FUSE, IUE spectrophotometry and optical/IR broadband photometry with theoretical flux distributions from LTE model atmospheres. The photospheric chemical abundances were measured from a high-resolution optical spectrum using LTE model atmospheres and spectral synthesis.

Results. On the basis of …