NE-VIII LAMBDA-774 AND TIME VARIABLE ASSOCIATED ABSORPTION IN THE QSOUM-675

We discuss measurements of Ne VIII lambda 774 absorption and the time variability of other lines in the z(alpha) approximate to z(e) absorpt ion system of the z(e) = 2.15 QSO UM 675 (0150-203). The C IV lambda 1 549 and N V lambda 1240 doublets at z(a) = 2.1340 (shifted similar to 1500 km s(-1) from z(e)) strengthened by a factor of similar to 3 betw een observations by Sargent, Boksenberg, and Steidel (1981 November) a nd our earliest measurements (1990 November and December). We have no information on changes in other z(a) approximate to z(e) absorption li nes. Continued monitoring since 1990 November shows no clear changes i n any of the absorptions between similar to 1100 and 1640 Angstrom res t.The short timescale of the variability (less than or similar to 2.9 yr rest) strongly suggests that the clouds are dense, compact, close t o the QSO, and photoionized by the QSO continuum. If the line variabil ity is caused by changes in the ionization, the timescale requires den sities greater than similar to 4000 cm(-3). Photoionization calculatio ns place the absorbing clouds within similar to 200 pc of the continuu m source. The full range of line ionizations (from Ne VIII lambda 774 to CIII lambda 977) in optically thin gas (no Lyman limit) implies tha t the absorbing regions span a factor of more than similar to 10 in di stance or similar to 100 in density. Across these regions, the total h ydrogen (H I + H II) column ranges from a few times 10(18) cm(-2) in t he low-ionization gas to similar to 10(20) cm(-2) where the Ne VIII do ublet forms. The metallicity is roughly solar or higher, with nitrogen possibly more enhanced by factors of a few. The clouds might contribu te significant line emission if they nearly envelop the QSO. The prese nce of highly ionized Ne VIII lambda 774 absorption near the QSO suppo rts recent studies that link z(a) approximate to z(e) systems with X-r ay ''warm absorbers.'' We show that the Ne wr absorbing gas would itse lf produce measurable warm absorption-characterized by bound-free O VI I or O VIII edges near 0.8 keV-if the column densities were N-H greate r than or similar to 10(21) cm(-2) (for solar abundances).