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Post Info TOPIC: CPD-20 1123


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Posts: 131433
Date:
Albus 1
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Title: The helium-rich subdwarf CPD-20 1123: a post-common envelope binary evolving onto the extended horizontal branch 
Authors: Naslim. N, S. Geier, C. S. Jeffery, N. T. Behara, V. M. Woolf, L. Classen 

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 nHe90%). A small number have an intermediate surface helium abundance (~ 10 - 30%), 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 an helium-enriched progenitor to become a normal helium-poor sdB star, and ii) whether these phenomena occur only in single sdB stars or are also associated with sdB stars in binaries. 
We present a fine analysis of the bright intermediate-helium sdB star CPD-20 1123 (Albus 1) which shows it to be cool, for a hot subdwarf, with Teff~23\,000 K and with a surface helium abundance ~17% by number. Other elements do not show extraordinary anomalies; in common with majority sdB stars, carbon and oxygen are substantially depleted, whilst nitrogen is enriched. Magnesium through sulphur appear to be depleted by ~0.5 dex, but chlorine and argon are substantially enhanced. We also present a series of radial-velocity measurements which show the star to be a close binary with an orbital period of 2.3 d, suggesting it to be a post-common-envelope system. 
The discovery of an intermediate helium-rich sdB star in a close binary in addition to known and apparently single exemplars supports the view that these are very young sdB stars in which radiatively-driven stratification of the photosphere is incomplete. 

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Posts: 131433
Date:
CPD-20 1123
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Title: CPD-20 1123 (Albus 1) is a bright He-B Subdwarf
Authors: Stephane Vennes, Adela Kawka, J. Allyn Smith

Date: August 2007

Based on photometric and astrometric data it has been proposed that Albus 1 (also known as CPD-20 1123) might be a hot white dwarf similar to G191-B2B or, alternatively, a hot subdwarf. We obtained a series of optical spectra showing that CPD-20 1123 is a bright He-B subdwarf. We analysed the HI Balmer and HeI line spectra and measured T_eff = 19800 ±400 K, log g = 4.55 ±0.10, and log N(He)/N(H) = 0.15 ±0.15. This peculiar object belongs to a family of evolved helium-rich stars that may be the products of double-degenerate mergers, or, alternatively, the products of post horizontal- or giant-branch evolution. 

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