Space reddening and density gradients for the anti-center.

Abstract

view Abstract Citations (3) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Space reddening and density gradients for the anti-center. Bok, Bart J. ; Boutelle, B. D. ; Olmsted, M. Abstract A study has been made of the color indices and the space distribution of the stars with known Henry Draper Extension spectra for galactic longitudes 1600 to 1750, latitudes 40 to t70. Regions obviously affected by strong local obscuration have been avoided. The space reddening appears to be variable. At 1 = 1700, b = 00 the absorption for photographic light amounts to 0.5 mag. per kiloparsec, whereas at 1 = I 6~ 0, b = 0 0 the average absorption amounts to 1.2 mag. per kiloparsec. At b = +70 the absorption is only 0.5 mag. per kiloparsec to a limiting distance of 2500 parsecs. Heavy local obscuration is found south of the galactic circle, extension of the dark nebulae in Orion and Taurus. For the B8-Ao stars negative density gradients are found, with the star densities at 1000 parsecs being only 0.4 those near the sun. The AI-A7 and Fo-F8 stars have steep negative density gradients within 500 parsecs, whereas the G-M stars have roughly constant space densities to 500 parsecs from the sun. The absence of distant objects of high intrinsic luminosity is noteworthy. Early B and 0 stars are scarce and c stars few in number. Many of these stars congregate in the region immediately surrounding X(JC 2244-2237, but none appear to be more than 2500 parsecs away. Trumpler lists three galactic clusters beyond 3500 parsecs, but one of these is in a highly obscured region, whereas the other two derived large distances reflect only the smallness of the angular diameters of the objects; Cuffey has already shown that distances based on angular diameters of small clusters are apt to prove too large. There are five known Cepheids with distances that may be in excess of 3500 parsecs, but all of these fall in or close to obscured fields. For the present we do not possess any evidence, for the section of the Milky Way between galactic longitudes 1600 and 1750, that there exist galactic objects at distances greater than 3500 parsecs from the sun. It is significant to note that the section 1 = 1600 to 1750 is perhaps the least obscured part of the anti-center region. The importance of future studies of distant galactic clusters and faint Cepheid variables in the anti-center section is stressed. Harvard College Observatory, Cambridge, Mass. Publication: The Astronomical Journal Pub Date: January 1948 DOI: 10.1086/106119 Bibcode: 1948AJ.....53Q.197B full text sources ADS |