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Astron. Astrophys. 319, 244-249 (1997)


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Infrared observations of peculiar carbon stars *

A. Ulla 1, 2, P. Thejll 3, T. Kipper 4 and U.G. Jorgensen 5

1 Instituto de Astrofísica de Canarias, E-38200 La Laguna, Spain
2 Laboratorio de Astrofísica Espacial y Física Fundamental, Apdo. 50727, E-28080 Madrid, Spain
3 NORDITA, Blegdamsvej 17, DK-2100 Copenhagen, Denmark
4 Tartu Astrophysical Observatory, Toravere, EE2444, Estonia
5 Niels Bohr Institute, University Observatory, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark

Received 18 March 1996 / Accepted 2 July 1996

Abstract

We present a uniform and high quality set of infrared photometric (JHK) observations of the 6 peculiar carbon giant stars V Ari, UV Cam, BD+34 911, TU Gem, BD+57 2161 and BD+34 4134. All of these belong to the small group of known cool CH giants populating the Galactic halo. Comparison of the [FORMULA] and [FORMULA] colours to "normal" C stars show our stars to be "bluer" (i.e., having lower values of [FORMULA] and [FORMULA]) than the bulk of the Galactic C stars. Comparison with synthetic JHK colours reveal 5 of our 6 stars as having considerably lower metallicities and/or higher temperatures than the bulk. Using standard assumptions we derive estimates of their effective temperatures, gravities, luminosities and distances. Their derived luminosities place them close to (or below) the theoretical first He shell flash luminosity, although other observations indicate their carbon excess to be intrinsic.

Key words: stars: evolution – stars: carbon – infrared: stars – stars: fundamental parameters

* Based on observations made with the Carlos Sánchez Telescope operated on the island of Tenerife by the Instituto de Astrofísica de Canarias in the Spanish Observatorio del Teide.

Send offprint requests to: A. Ulla, email address: aulla@iac.es

© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998

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