A survey of ultraviolet objects

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Abstract
2989 objects more ultraviolet than an unreddened B8 V star were observed with the S2/68 ultraviolet sky survey telescope. 633 of these stars have luminosity classes I to IV; 776 are main sequence and the remaining 1580 have yet to be classified on the MK system. The MK unclassified objects appear to be relatively unreddened and have apparent magnitudes in the range 7.0 < mv < 10.0. A statistical analysis of these ultraviolet objects indicates that many of them are subdwarf stars lying at least 2 mag below the main sequence in the spectral range O to B3. The populations of these subdwarfs turn out to be similar to the main-sequence population with values: O stars, 1.3 × 10−8 pc−3; B0−B1, 4 × 10−8 pc−3; B2−B3, 3 − 10−7 pc−3. Thus there appears to be a larger number of hot subdwarf stars lying a few magnitudes below the main sequence than previously thought. The scale heights for the subdwarfs are calculated to be: 0−B1, 280 pc; B2−B3, 124 pc. The scale height for the hottest group is comparable to that of the central stars of planetary nebulae. The scale height for the interstellar dust was also examined and found to have a value of 113 pc. A catalogue list containing the S2/68 ultraviolet data is given for the 464 objects whose observed (m1565−m2740) colour is more ultraviolet than −1.50, corresponding to an unreddened B4 V star.

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