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2 2000

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Variable Stars in the Field of the Globular Cluster E3

Mochejska B. J., Kaluzny J., Thompson I.

Acta Astronomica

2000

Vol. 50, No. 1

105--111

We present the results of a search for variable stars in the faint sparse globular cluster E3. We have found two variable stars: an SX Phe variable (V1) and a W UMa eclipsing binary (V2). We have applied period-luminosity and period-color-luminosity relations to the variables to obtain their distance moduli. V1 seems to be a blue straggler belonging to E3, based on its distance modulus and location in the CMD. V2 is probably located behind the cluster, in the Milky Way halo. We also present V/B-V and V/V-I color magnitude diagrams of E3.

UBVI Color-Magnitude Diagrams in Baade's Window: Metallicity Range, Implications for the Red Clump Method, Color "Anomaly" and the Distances to the Galactic Center and the Large Magellanic Cloud

Stanek K. Z., Kaluzny J., Wysocka A., Thompson I.

Acta Astronomica

2000

Vol. 50, No. 2

191--210

We analyze the UBVI color-magnitude diagrams towards the Galactic bulge in a relatively low-reddening region of Baade's Window. The dereddened red giant branch is very wide [≈1.0 mag in (U-B)0 and ≈0.4 mag in (B-V) 0 and (V-I) 0], indicating a significant dispersion of stellar metallicities, which by comparison with the theoretical isochrones and data for Galactic clusters we estimate to lie between approximately -0.7<[Fe/H]<+0.3, i.e., spanning about 1 dex in metallicity, in good agreement with earlier spectroscopic studies. We also discuss the metallicity dependence of the red clump I-band brightness and we show that it is between 0.1-0.2 mag/dex. This agrees well with the previous empirical determinations and the models of stellar evolution. The dereddened (V-I)0 color of the red clump in the observed bulge field is ⟨(V-I)0⟩=1.066, σ(V-I)0=0.14, i.e., 0.056 mag redder than the local stars with good parallaxes measured by Hipparcos. It seems that the large "color anomaly" of ≈0.2 mag noticed by Paczyński and Stanek and discussed in many recent papers was mostly due to earlier problems with photometric calibration. When we use our data to re-derive the red clump distance to the Galactic center, we obtain the Galactocentric distance modulus μ0,GC=14.69±0.1 mag (R0=8.67± 0.4 kpc), with error dominated by the systematics of photometric calibration. We then discuss the systematics of the red clump method and how they affect the red clump distance to the Large Magellanic Cloud. We argue that the value of distance modulus μ0,LMC=18.24±0.08 (44.5±1.7 kpc), recently refined by Udalski, is currently the most secure and robust of all LMC distance estimates. This has the effect of increasing any LMC-tied Hubble constant by about 12%, including the recent determinations by the HST Key Project and Sandage et al. The UBVI photometry is available through the anonymous ftp service.