An Anomalous Bluing Effect in the B-V Colors of Distant A Stars.

Abstract

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An Anomalous Bluing Effect in the B-V Colors of Distant A Stars. Philip, A. G. Davis Abstract UBV photometry in a region at b11- 290, III~760 in Pegasus (Philip, Astron J. 70, 146, 1965) shows, that for A stars with distance moduli greater than 10.5, the color excesses decrease as fainter stars are reached. At a distance modulus of 12.0, the color excesses are 0.2 mag. less than those at a distance modulus of 10.5. The stars were each classified on an average of nine different Schmidt spectral plates, taken on Kodak IIa0 emulsion with the Schmidt telescope of the Warner and Swasey Observatory. The probable error of the mean classification was *0.3 classes on the Case 40 classification system. The UBV photometry was done at Kitt Peak National Observatory on the 36-in. telescope. The probable errors in V and B-V were *0.01 and *0.02, respectively. Eleven regions are now being investigated along the Carina-Cygnus spiral arm at 111=760, spaced from the north to the south galactic poles. Spectral plates have been taken in each region with the Case Schmidt telescope. All A0-A3 stars that have been found are now in the process of being observed in the UB V system at Kitt Peak National Observatory. The bluing effect in the color excess noted in the Pegasus region for the fainter A stars has now been found in four additional regions, at b11 - 900, 600, 450, and 300. Possible explanations for the effect, discussed in the report are: a systematic error in the classification of faint stars; uneven absorption, an effect that would tend to make the more distant stars appear bluer than normal; and population differences as distances greater than 600 pc from the galactic plane are reached. This work is supported by the National Science Foundation. Publication: The Astronomical Journal Pub Date: 1965 DOI: 10.1086/109669 Bibcode: 1965AJ.....70T.687P full text sources ADS |