Lyman Spectra of Hot DA White Dwarfs

During the extremely successful Astro-2 mission flown in March 1995, high-quality spectra were obtained for 9 DA white dwarfs hotter than about 20,000 K with the Hopkins Ultraviolet Telescope. The spectra covered the range of 820–1840 A and were thus ideal for our purpose of investigating Stark broadening in the Lyman series. The objects observed included GD 50, one of the most massive known DA; RE 0512–004, the least massive known DA in this temperature range; RE 1738+665, the hottest known field DA; the HST standards G191-B2B, GD 153, GD 71, and HZ 43; and GD 394 and Wolf 1346. Our major conclusion is that the wings of the Lyman lines are in reality significantly weaker than predicted using the standard (Vidal-Cooper-Smith) Stark broadening theory. We also discovered satellite features in the Lyman s profile of Wolf 1346; these have now been successfully modeled using the same techniques that were previously applied to Ly α satellites.