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18. Other ground-based work

18.1. Galactic Cluster and LMC Calibration

While currently the most commonly adopted route for calibrating the zero point of the Cepheid PL relation is through the Large Magellanic Cloud, a more traditional approach is to use individual Cepheids in Galactic clusters. Following this route, main sequence fitting and B-star reddenings can provide (in principle) individual moduli, absolute magnitudes and intrinsic colors for the member Cepheid(s). In practice this approach has turned out to be limited in a number of ways: very few clusters have known Cepheids as bona fide members, those examples generally only cover periods up to about ten days, and many of the clusters are either very sparse or behind considerable amounts of (perhaps variable) extinction, or both.

While sample size and the period distribution of that sample is not likely to be changed considerably, the treatment of the reddening and measurement of the true distance moduli can be re-examined with new technology. In a long-term collaboration Persson et al. (1996) have embarked on a project at Las Campanas and Palomar of infrared imaging of the main sequences of all Galactic clusters containing classical Cepheids. These clusters include NGC 7790, NGC 129, NGC 6649, NGC 6664 and Lynga 6. A parallel study of many of these clusters is also underway by Fry & Carney (1997, private communication).

Finally, in addition to the recalibration of Galactic clusters, multiple epochs of JHK photometry are being obtained for a sample of over 90 Cepheids in the LMC. This sample will serve as a fiducial calibrating sample for anticipated NICMOS observations of Cepheids. Also, at Las Campanas we have been obtaining JHK observations of the known Cepheids in IC 1613 and NGC 300.

18.2. Recent Ground-Based Searches for Cepheids

Easily accessed only from the southern hemisphere, the South Polar (Sculptor) Group contains the last of the relatively nearby spiral galaxies to be searched for Cepheids from the ground. Three of its members (NGC 247, NGC 300 and NGC 7793) are of the proper type and inclination to become Tully-Fisher calibrators, given independent distance measurements. Using the CTIO 4m and the Las Campanas 2.5m we have been following up the Cepheids discovered in NGC 300 (Graham 1984, Madore et al. 1987) and monitoring NGC 247, NGC 7793 (and NGC 253) for new variables. Based on BVRI CCD data of 10 Cepheids Freedman et al. (1992) determined a distance to NGC 300 of 2.1 ± 0.1 Mpc.

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