Characteristics of Disk and Halo Populations Derived from Photographic Photometry

Citation

Weistrop, Donna Etta (1971) Characteristics of Disk and Halo Populations Derived from Photographic Photometry. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/YAZV-KE91. https://resolver.caltech.edu/CaltechETD:etd-05122008-131358

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The nature of faint stars at high galactic latitudes was investigated through U,B,V photometry of several thousand stars between V = 12 and 18 near the North Galactic Pole. Magnitudes were determined from iris photometer measurements of plates taken with the 48-inch Schmidt telescope. Calibration was provided by a photoelectric sequence in the field. Several models for the luminosity function and density distribution of Population II field stars were assumed. Assuming also that all stars bluer than (B-V)[...] = .5 and fainter than V = 17 are members of Population II, an upper limit of 7 x 10[...] solar masses per pc[...] was calculated for the local Population II density, a result significantly lower than local densities computed from the number of nearby stars suspected of halo membership. Some of the discrepancy may be due to the method used. Having estimated the contributions to the star counts due to Population II stars and disk giants and subgiants, the remaining stars were assumed to constitute a pure disk dwarf population. Density distributions for stars in successive (B-V)[...] intervals were calculated and combined to form a composite disk density distribution. The agreement with Oort's K giant distribution is satisfactory. There was some indication that the faintest dwarfs are concentrated in a narrow layer in the plane, but further investigation is required. Determination of the luminosity function for the reddest disk dwarfs indicated these stars are five to ten times as numerous as was previously thought, thus accounting for a significant fraction of the missing mass in the solar neighborhood. Luminosity functions extrapolated to account for all the missing mass are indicated.

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