NE-VIII LAMBDA-774 AND TIME VARIABLE ASSOCIATED ABSORPTION IN THE QSO UM-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) absorption system of the z(e) = 2.15 QSO UM 675 (0150-203). The C IV lambda 1549 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 between observations by Sargent, Boksenberg, and Steidel (1981 November) and our earliest measurements (1990 November and December). We have no information on changes in other z(a) approximate to z(e) absorption lines. Continued monitoring since 1990 November shows no clear changes in any of the absorptions between similar to 1100 and 1640 Angstrom rest. The short timescale of the variability (less than or similar to 2.9 yr rest) strongly suggests that the clouds are dense, compact, close to the QSO, and photoionized by the QSO continuum. If the line variability is caused by changes in the ionization, the timescale requires densities greater than similar to 4000 cm(-3). Photoionization calculations place the absorbing clouds within similar to 200 pc of the continuum source. The full range of line ionizations (from Ne VIII lambda 774 to CIII lambda 977) in optically thin gas (no Lyman limit) implies that the absorbing regions span a factor of more than similar to 10 in distance or similar to 100 in density. Across these regions, the total hydrogen (H I + H II) column ranges from a few times 10(18) cm(-2) in the low-ionization gas to similar to 10(20) cm(-2) where the Ne VIII doublet forms. The metallicity is roughly solar or higher, with nitrogen possibly more enhanced by factors of a few. The clouds might contribute significant line emission if they nearly envelop the QSO. The presence of highly ionized Ne VIII lambda 774 absorption near the QSO supports recent studies that link z(a) approximate to z(e) systems with X-ray ''warm absorbers.'' We show that the Ne wr absorbing gas would itself produce measurable warm absorption-characterized by bound-free O VII or O VIII edges near 0.8 keV-if the column densities were N-H greater than or similar to 10(21) cm(-2) (for solar abundances).