Journal Article

The CH fraction of carbon stars at high Galactic latitudes

Aruna Goswami, Drisya Karinkuzhi and N. S. Shantikumar

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 402, issue 2, pages 1111-1125
Published in print February 2010 | ISSN: 0035-8711
Published online February 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.15939.x
The CH fraction of carbon stars at high Galactic latitudes

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CH stars form a distinct class of objects with characteristic properties like iron deficiency, enrichment of carbon and overabundance of heavy elements. These properties can provide strong observational constraints for the theoretical computation of nucleosynthesis at low metallicity. An important issue is the relative surface density of CH stars, which can provide valuable input to our understanding of the role of low- to intermediate-mass stars in early Galactic chemical evolution. Spectroscopic characterization provides an effective way of identifying CH stars. The present analysis aims at a quantitative assessment of the fraction of CH stars in a sample using a set of spectral classification criteria. The sample consists of 92 objects selected from a collection of candidate faint high-latitude carbon stars from the Hamburg/ESO survey. Medium-resolution (λ/δλ∼ 1300) spectra for these objects were obtained using the Optomechanics Research (OMR) spectrograph at the Vainu Bappu Observatory (VBO), Kavalur and the Himalaya Faint Object Spectrograph (HFOSC) at the Himalayan Chandra Telescope (HCT), Indian Astronomical Observatory, Hanle, during 2007–2009, spanning a wavelength range 3800–6800 Å. Spectral analysis shows 36 of the 92 objects to be potential CH stars; combined with our earlier studies this implies ∼37 per cent (of 243 objects) as the CH fraction. We present spectral descriptions of the newly identified CH star candidates. Estimated effective temperatures, 12C/13C isotopic ratios and their locations on the two-colour JH versus HK plot are used to support their identification.

Keywords: stars: AGB and post-AGB; stars: carbon; stars: fundamental parameters; stars: Population II; stars: variables: other

Journal Article.  10117 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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