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Scientific paper
Jan 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999iaus..192..144a&link_type=abstract
The stellar content of Local Group galaxies, Proceedings of the 192nd symposium of the International Astronomical Union held in
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12
Scientific paper
Earlier near-infrared low-dispersion spectroscopic surveys for late type stars in the Fornax dwarf spheroidal galaxy by Blanco & McCarthy(1) and by Westerlund(2) resulted in the identification of 47 carbon (C) star candidates. Subsequently, our(3) CFHT blue-green objective grating photographic survey of this system led to the detection of about 30 additional C star candidates. More recently, we have completed our systematic survey for C stars in Fornax, using the CFHT Multi-Object Spectrograph (MOS) in the slitless spectroscopy mode, and discovered several new very faint C star candidates in five 10 arcmin square CCD frames covering the central regions of this system.(4) Additional medium resolution spectroscopic observations carried out at La Silla led us to confirm the carbon star nature of 64 candidates. With 111 C stars known, Fornax contains by far the largest number of these objects among the Local Group dwarf spheroidals. Theoretical predictions of the dependence of mean C star luminosity on metallicity led to the expectation that, for two systems with similar star-formation histories (i.e., similar initial stellar mass functions and star formation rates), the mean luminosity of C stars would be lower in the system with lower metallicity. From their surveys, Frogel et al.(1) drew the conclusion that the observed C star luminosity functions of the LMC, SMC and Fornax do not provide evidence supporting these theoretical predictions. Since then, Westerlund et al.(5,6,7) have discovered low-luminosity C stars in the SMC with Mbol between -1.4 to -2.7 mag ((m-M)0 = 18.8 mag). Near infrared JHK photometry of nearly all the C stars found in Fornax, carried out very recently with IRAC 2 at the ESO 2.2-m telescope, allowed us to obtain virtually the entire C star luminosity function for this system, confirming the presence of low-luminosity C stars as faint as Mbol ≍ -1.2 ((m-M)0=21.0 mag). This gives proof of the existence of very-low-luminosity C stars in a metal-poor galaxy other than the SMC, and hence contributes to strongly corroborate the theoretical predictions. References: (1) Frogel J.A., Blanco V.M., McCarthy M.F., Cohen J.G., 1982, ApJ 252, 133 (2) Westerlund B.E, Edvardsson B., Lundgren K., 1987, A&A 178, 41 (3) Azzopardi M., 1997, IAU Symp.177, (in press) (4) Muratorio G., Azzopardi, M., 1997, in ``Wide-Field Spectroscopy'' Proceedings of the 2nd Conference of the Working Group of IAU Commission 9 on ``Wide-Field Imaging'', p. 209 (5,6,7) Westerlund B.E., Azzopardi M., Breysacher J., Rebeirot E., 1991, A&AS 91, 425 ; 1992, A&A 260, L4 ; 1995, A&A 303, 107.
Azzopardi Marc
Breysacher Jacques
Muratorio Gérard
Westerlund Bengt E.
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