2 NEW EXTREMELY IRON-RICH HOT DA WHITE-DWARFS AND THE NATURE OF THE EUV OPACITY

We have obtained IUE echelle spectra of two bright extreme ultraviolet (EUV) sources discovered by the ROSAT wide field camera all-sky surve y. These stars, RE 2214-492 and RE 0623-377, are previously uncataloge d hot DA white dwarfs with respective apparent visual magnitudes of 11 .71 and 12.09 and exhibit short-wavelength EUV cutoffs steeper than mo st other DAs. The IUE echelle spectra are rich in absorption lines due to a large number of Fe V and Fe VI features, in addition to the high ly ionized C, N, O ions frequently seen in other hot DA white dwarfs. No He is observed in either star. Comparison of RE 2214-492 and RE 062 3-377 with two well-studied hot DA white dwarfs, G191 B2B and Feige 24 , indicates that these new stars are both significantly hotter and mor e metal-rich than G191 B2B and Feige 24. From optical and UV line prof iles we find T(eff) = 63,500 K and 60,300 K for RE 2214-492 and RE 062 3-377, respectively. From modeling of Fe V features in the echelle spe ctra we find corresponding Fe abundances of log [N(Fe)/n(H)] = -4.25 /- 0.25. The association of steep EUV cutoffs in these stars, and in G 191 B2B and Feige 24, with the observed presence of Fe suggests that i ron-group elements along with other heavy elements are responsible for much of the EUV opacity observed by ROSAT in the hottest DA stars.