A Study of the Galactic Structure in a Clear Region in Cygnus.
Abstract
This paper, like previous ones of the series, is primarily concerned with the study of the fluctuation of the stellar luminosity function. The field under investigation has an area of 11 square degrees with a center at R.A. = 2OhOOm, Dec. = -+38?O (1950). It is relatively free from space absorption, with the exception of about 1 square degree at its southern boundary. The photographic and photored magnitudes and the spectral types of 1230 stars were obtained. Stars of spectral type FO and later, with a few exceptions, were classified either as giants or as dwarfs down to the limiting photographic magnitude of 12.2. For nearly all stars brighter than 11.0 mag., four luminosity classes were used. The linear absorption coefficient in the clear region (areas A, B, and C) was derived from 683 stars and found to be 0.53 mag. per kiloparsec. The division of the stars into giants and dwarfs in each spectral group indicates that there is a rapid decrease in the ratio of dwarfs to giants between the FO-F5 group and the G8-K3 group. In the former we have about 83 per cent dwarfs and in the latter about 7 per cent. Space densities, corrected for absorption, were computed for each spectral grnup in areas A, B, and C (Table 10 and Fig. 5). The densitieswere used to compute luminosity functions at distances of 100, 200, 400, and 600 parsecs. These show very little variation with distance. Likewise, no significant differences exist when our results are compared with the standard van Rhijn luminosity function, with the exception of the range of absolute magnitude between - 1.5 and +1.0. Here the maximum excess in our case in log 4(M) is 0.3. The color excesses of the stars in the obscured region (area D) indicate that an interstellar cloud sets in at about 900 parsecs With a maximum absorption of about 0.9 mag. over and above the general absorption of the other three areas. A comparison between the general star counts to the seventeenth photo- graphic magnitude in area D and in the other areas yields nearly the same value for the total absorption. An analysis of the space density of the stars in area D indicates that the density for the early-type stars is between two and three times greater than the corresponding density in the other areas
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 1949
- DOI:
- 10.1086/145175
- Bibcode:
- 1949ApJ...110...40N