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K. Z. Stanek (Harvard-Smithsonian CfA), P. M. Garnavich (University of Notre Dame)
The ideal distance indicator would be a standard candle abundant enough to provide many examples within reach of parallax measurements and sufficiently bright to be seen out to Local Group galaxies. As developed by Paczynski & Stanek (1998), the red clump method precisely fits this description. These stars are the metal rich equivalent of the better known horizontal branch stars, with weak metallicity and age brightness dependence. Indeed the absolute magnitude-color diagram of Hipparcos clearly shows how compact the red clump is: Stanek and Garnavich (1998) determined that the variance in the I-band magnitude is only 0.15 mag.
To date the red clump method has been used to measure accurate distances to the Galactic center (Paczynski & Stanek 1998), M31 (Stanek & Garnavich 1998), LMC (Udalski et al. 1998; Stanek et al. 1998; Udalski 1999) and some clusters in our Galaxy (e.g. 47Tuc: Kaluzny et al. 1998). As with all the distance indicators, the main worry lies in the possible systematics of the method, in this case its dependence on the stellar metallicity and age. Both of these dependences were investigated by Udalski (1998a) and Udalski (1998b). More recently, the metallicity dependence of the red clump brightness was investigated by Stanek et al. (1999), Udalski (1999) and Popowski (1999). So far all these studies indicate that indeed the population effects on the red clump brightness are small. We discuss further planned studies of the red clump properties.
Perhaps the most important result from the red clump method was the determination of the ``short'' distance to the Large Magellanic Cloud (Udalski et al. 1998; Stanek, Zaritsky & Harris 1998; Udalski 1999). If accurate, this distance to the LMC shorter by 15% than the ``standard'' value, has very important implications for the Cepheid distance scale and the determination of the Hubble constant.
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The author(s) of this abstract have provided an email address for comments about the abstract: kstanek@cfa.harvard.edu