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Session 46 - Variable Stars - Late Type.
Display session, Thursday, January 08
Exhibit Hall,

[46.02] A New Effective Temperature Scale for M Giants

R. A. Bell, M. L. Houdashelt (U. Maryland)

M giants play a significant role in determining the shape of the spectral energy distribution of elliptical galaxies, producing the TiO bands seen at optical wavelengths and contributing the majority of the flux in the infrared. However, these stars have proven to be notoriously difficult to model. Previous measurements of angular diameters by Ridgway et al. (1980), Dyck et al. (1996) and di Benedetto amp; Rabbia (1987) have produced very similar relations between spectral type and effective temperature for K and M giants. We present here an alternative temperature scale for these stars which is based upon recent angular diameter measurements of Mozurkewich. This new relation is in reasonable agreement with the older ones for K giants but differs from them in being sytematically cooler at a given spectral type for the M giants. In this poster, we contrast models based upon this new effective temperature scale and that of Dyck et al. (1996). We examine the effects on the synthetic spectra which we use in our galaxy population synthesis program, concentrating upon the TiO and CO molecular absorption features. We estimate the spectral types of our synthetic spectra using three methods - the strengths of the TiO bands, the equivalent width of the CO bandhead near 2.3 \mum and the eight-color photometric system of Wing - and check the agreement of the three.

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Program listing for Thursday