Optical Identification of Joint EUVE and ROSAT PSPC Detections in the Southern Hemisphere: New Southern White Dwarfs

N. Craig, J. Dupuis

Bull. American Astron. Soc., 188, #73.02.


We report the optical identifications of four new DA white dwarfs coinciding with the position of faint sources jointly detected during the EUVE all-sky survey in the 58-174 Å (0.071-0.0214 keV) band and the ROSAT PSPC in the 0.1-0.28 keV X-ray band. We present low resolution spectra of the possible optical counterparts found within the error circle of these four EUVE/ROSAT NOID fields, obtained with 1.5-m telescope at CTIO in December 1995 and February 1996. In the four fields, we find DA stars for which we report Balmer line profile analyses. Our preliminary analyses indicate these stars have relatively high effective temperatures (in the 25,000 -- 50,000 K range), consistent with being EUV sources. One of the white dwarfs is potentially interesting since it appears to have a relatively low effective temperature of 20,000 K and a surface gravity possibly exceeding log g of 9. The joint detection in the EUVE Lexan band and by ROSAT XRT indicates these stars have a low abundance of metals, and that their EUV emission is mostly attenuated by the local ISM. Note that out of the 42 EUVE/ROSAT NOID fields observed so far, only 4 were found to have a DA as the most probable optical counterpart. We will further discuss this low turnout of white dwarf detections among the NOID fields in terms of the log N - log S distribution of white dwarfs observed in the EUVE all-sky survey. This work is supported by NASA contract NAS5-29298.

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