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An Einstein Observatory SAO-based catalog of B-type stars
About 4000 X-ray images obtained with the Einstein Observatory are usedto measure the 0.16-4.0 keV emission from 1545 B-type SAO stars fallingin the about 10 percent of the sky surveyed with the IPC. Seventy-fourdetected X-ray sources with B-type stars are identified, and it isestimated that no more than 15 can be misidentified. Upper limits to theX-ray emission of the remaining stars are presented. In addition tosummarizing the X-ray measurements and giving other relevant opticaldata, the present extensive catalog discusses the reduction process andanalyzes selection effects associated with both SAO catalog completenessand IPC target selection procedures. It is concluded that X-rayemission, at the level of Lx not less than 10 exp 30 ergs/s, is quitecommon in B stars of early spectral types (B0-B3), regardless ofluminosity class, but that emission, at the same level, becomes lesscommon, or nonexistent, in later B-type stars.
| HD 52961 - an extremely metal-deficient, CNO- and S-rich, pulsating star embedded in a dust cloud
Results of an LTE atmosphere analysis of the seventh-magnitude star HD52961 are presented. The iron abundance of HD 52961 is found to be aslow as -4.8; the abundances of carbon, nitrogen, oxygen, and alsosulphur are enhanced with respect to iron by several orders ofmagnitude. HD 52961 displays an infrared excess which is due tocircumstellar dust; the dust shell does not cause significantcircumstellar absorption. It is suggested that HD 52961 is a slightlycooler analog of the peculiar supergiant HR 4049. The first detection ofa metal line in the optical spectrum of the latter star is reported; theiron abundance derived from it is also -4.8. One possible explanation ofthe IR excess and the abundances in these stars is that they arepresently evolving away from the AGB. This possibility is discussedconsidering the short timescale of this phase and the lack of observedprogenitors with such extreme metallicities. It is suggested that thesulphur anomaly may have its origin in the violent core flashes thatvery-low-metallicity stars possibly undergo.
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