| Summary: | 碩士 === 國立臺灣師範大學 === 地球科學系 === 101 === For accurately estimating the distance and age of an open cluster with Johnson UBV photometry, the membership of the cluster should be determine first. The probability of membership for each star in the two open clusters: NGC 7142 and M45 are determined in terms of the normal bivariate frequency function with proper motion data. The database of proper motion and UBV photometry calculated from the images for NGC 7142 observed in this work, and proper motion database of M45 taken from the Tycho-2 catalog.
The observations of NGC 7142 carried out with the Lulin-One meter Telescope of National Central University on August 7, 2003 and July 8, 2012, respectively. A catalog contained 1697 stars with UBV photometry, proper motion and membership probability data is set up. From the main-sequence fitting on the Two-Color Diagram with the UBV reddening slope 0.72, the estimate value of the metallicity Z is 0.008, represents [Fe/H] = -0.37, and the E(B – V) = 0.36. The distance modulus is (m-M)0 = 11.02, represents distance is about 1600pc. From the isochrones fitting, the age of NGC 7142 is 7.9 Gyr.
The M45 been chosen for comparison with almost no extinction and distance well known. With the E(B-V) = 0.04, (m-M)0 = 5.66 and [Fe/H] = 0.022, the isochrones fitting of age is 126 Myr. From the main-sequence comparison with the distance of M45 (136 pc), the distance of NGC 7142 is 1920 pc.
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