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Session 71 - Globular Clusters.
Display session, Wednesday, January 15
IC 1257 is a faint, compact star cluster that was discovered more than a century ago by Spitaler (1890, AN, 125, 282). It lies at Galactic coordinates l = 17 deg, b = +15 deg behind a rather heavy (but uniform) sheet of foreground reddening. Since its discovery, IC 1257 has always been listed as an open cluster, although no photometric study of it has ever been published. In September 1996, we obtained new CCD photometry of this cluster with the Palomar 5-m prime focus camera which shows that it is unquestionably a moderately low-luminosity, low-metallicity globular cluster located well beyond the Galactic center. The color-magnitude diagram shows an M13-like morphology, with an extremely blue horizontal branch and a moderately steep red-giant branch. Using the CMD to estimate its reddening, metallicity, and distance, we find an apparent distance modulus (m-M)v = 19.2, a foreground reddening E(B-V) = 0.75, and a metallicity [Fe/H] = -1.7. The cluster is about 24 kpc from the Sun and 16 kpc beyond the Galactic center. Unlike the great majority of non-NGC globular clusters that have been found over the past few decades, IC 1257 is therefore unusual in being neither in the Galactic bulge nor the outermost halo, but rather in the mid-halo region.
We are indebted to Czernic Crute, Barbara Wilson, and Brian Skiff for bringing this object to our attention.
Program listing for Wednesday