Carbon stars and C/M ratio in the WLM dwarf irregular galaxy

Free access article

Issue		A&A Volume 466, Number 2, May I 2007


Page(s)		501 - 507
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20054536

A&A 466, 501-507 (2007)
DOI: 10.1051/0004-6361:20054536

Carbon stars and C/M ratio in the WLM dwarf irregular galaxy

A. T. Valcheva¹, V. D. Ivanov², E. P. Ovcharov¹, and P. L. Nedialkov¹

¹ Department of Astronomy, University of Sofia, 5 James Bourchier, Sofia 1164, Bulgaria
e-mail: [valcheva;evgeni;japet]@phys.uni-sofia.bg
² European Southern Observatory, Ave. Alonso de Cordova 3107, Casilla 19, Santiago 19001, Chile
e-mail: vivanov@eso.org

(Received 17 November 2005 / Accepted 18 January 2007)

Abstract
We identify the rich carbon star population of the Magellanic-type dwarf irregular galaxy WLM (Wolf-Lundmark-Melotte) and study its photometric properties from deep near-IR observations. The galaxy also exhibits a clear presence of oxygen-rich population. We derive a carbon to M-star ratio of C/M = 0.56 $\pm$ 0.12, relatively high in comparison with many galaxies. The spatial distribution of the AGB stars in WLM hints at the presence of two stellar complexes with a size of a few hundred parsecs. Using the $\ion{H}{i}$ map of WLM and the derived gas-to-dust ratio for this galaxy N( $\ion{H}{i}$ )/E(B-V) = 60 $\pm$ 10 [ 10²¹ at. cm^-2 mag^-1] we re-determined the distance modulus of WLM from the IR photometry of four known Cepheids, obtaining (m-M)₀ = 24.84 $\pm$ 0.14 mag. In addition, we determine the scale length of 0.75 $\pm$ 0.14 kpc of WLM disk in the J-band.

Key words: galaxies: individual: WLM -- stars: AGB and post-AGB -- stars: carbon -- galaxies: irregular -- Local Group

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