A Close-Separation Double Quasar Lensed by a Gas-rich Galaxy

In the course of a Cycle 8 snapshot survey, we have discovered that thez=1.565 quasar HE 0512-3329 is a double with image separation 0.644", almostcertainly due to gravitational lensing. The two components differ in brightnessby only 0.4 magnitudes and a high signal-to-noise ground-based compositeoptical spectrum shows no trace of any stellar features at zero redshift,essentially ruling out the possibility that one of the two components is anordinary Galactic star. The optical spectrum shows strong absorption featuresof MgII, MgI, FeII, FeI, and CaI, all at an identical intervening redshift ofz=0.9313, probably due to the lensing object. The strength of the MgII and thepresence of the other low ionization absorption features is strong evidence fora damped Lyman alpha system, likely the disk of a spiral galaxy. Point spreadfunction fitting to remove the two quasar components from the STIS image leadsto a tentative detection of a third object which may be the nucleus of thelensing galaxy. The brighter component is significantly redder than thefainter, due to either differential extinction or microlensing.Comment: AASTEX preprint format, 11 pages, 3 figures; accepted by the Astronomical Journal; replaced with revised, accepted versio