Magnitudes and Colors in the Globular Cluster Messier 12 and Selected Area 108.

Abstract

view Abstract Citations (3) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Magnitudes and Colors in the Globular Cluster Messier 12 and Selected Area 108. Nassau, J. J. ; Hynek, J. A. Abstract The present report deals with the determination of red magnitudes of stars in Selected Area 108 and with blue and red magnitudes in Messier 12, which is three degrees from the Selected Area. The red magnitudes of the bright stars of the former were determined by direct comparison with the North Polar Sequence; those of the faint stars, by means of a 72-inch wire objective grating attached to the 69-inch Perkins reflector. The red magnitudes of stars in Harvard Standard Region C9 were used to check the determinations for the brighter stars, and the relation between color indices and red indices was utilized to check the grating magnitudes. A sequence of stars with limiting red magnitude 15.21 and with an average probable error of ± O~O5 is given. From this sequence the red magnitudes of all stars brighter than 15~'18 in SA 108 have been determined. The adopted photographic modulus of M 12 is 13'~'9O, a value determined from the published modulus by correcting for interstellar absorption by means of the observed color excess of the cluster. This modu- lus gives 6.0 kpc for the distance of the cluster. The corresponding red modulus was found to be 14m70. Both red-and blue-magnitude sequences are given for the cluster. The red indices of all stars brighter than 13.46 red magnitude within 2~3 of the center of the cluster have been determined, and likewise the red indices of all stars brighter than 15.18 red magnitude within zones of 2 ~3 and 1O~4 are given. The frequency distribution of the red indices does not change with the distance from the center of the cluster. The essential features of the color-magnitude diagram of the stars in the cluster are: (a) the total absence of early-type supergiants; (b) the presence of very few stars in the region ordinarily occupied by cluster-type variables; (c) an abundance of red supergiants, together with a total absence of red giants; and (d) the presence of essentially two groups of stars, one group of early spectral class with constant absolute magnitude, and the other of late spectral class with absolute luminosity increasing with the red index (the two groups meet in the diagram at Mr ,= 0.0 and C~ = 0.75) Publication: The Astrophysical Journal Pub Date: July 1942 DOI: 10.1086/144431 Bibcode: 1942ApJ....96...37N full text sources ADS | data products SIMBAD (2)