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Astron. Astrophys. 357, 37-50 (2000)


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HST spectroscopy of the double QSO HS 1216+5032 AB *

S. Lopez, H.-J. Hagen and D. Reimers

Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany

Received 6 August 1999 / Accepted 27 March 2000

Abstract

We report on Hubble Space Telescope Faint Object Spectrograph observations of the double QSO HS 1216+5032 AB ([FORMULA]; [FORMULA], and angular separation [FORMULA]). The spectral coverage is 910 Å to 1340 Å in the QSO rest-frame. An unusual broad-absorption-line (BAL) system is observed only in the B component: maximum outflow velocity of [FORMULA] km s-1; probably a mixture of broad and narrow components. Observed ions are: HI , CII , CIII , NIII , NV , OVI , and possibly SIV and SVI . We also discuss two outstanding intervening systems: (1) a complex CIV system at [FORMULA] of similar strength in A and B, with a velocity span of 1500 km s-1 along the lines of sight (LOSs; LOS separation: [FORMULA] kpc); and (2) a possible strong MgII system at [FORMULA] observed in B only, presumably arising in a damped Ly[FORMULA] system.

We assume HS 1216+5032 is a binary QSO but discuss the possibility of a gravitational lens system. The size of Ly[FORMULA] forest clouds is constrained using [FORMULA] kpc at redshifts between [FORMULA] and 1.45. Four Ly[FORMULA] systems not associated with metal lines and producing lines with [FORMULA] Å are observed in both spectra, while five appear in only one spectrum. This sample, although scarce due to the redshift path blocked out by the BALs in B, allows us to place upper limits on the transverse cloud sizes. Modelling the absorbers as non-evolving spheres, a maximum-likelihood analysis yields a most probable cloud diameter [FORMULA] kpc and [FORMULA] bounds of [FORMULA] kpc. If the clouds are modelled as filamentary structures, the same analysis yields lower transverse dimensions by a factor of two. Independently of the maximum-likelihood approach, the equivalent width differences provide evidence for coherent structures. The suggestion that the size of Ly[FORMULA] forest clouds increases with decreasing redshift is not confirmed. Finally, we discuss two [FORMULA] Ly[FORMULA] systems observed in both QSO spectra.

Key words: galaxies: quasars: absorption lines – galaxies: quasars: general – cosmology: observations – galaxies: quasars: individual: HS 1216+5032

* Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the STScI, which is operated by AURA, Inc., under NASA contract NAS5-26 555.

Present address: Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile

Send offprint requests to: S. Lopez (slopez@das.uchile.cl)

© European Southern Observatory (ESO) 2000

Online publication: May 3, 2000

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