AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 73. AGN: Radio Galaxies, QSO's and Blazars
Display, Wednesday, June 2, 1999, 10:00am-6:30pm, Southeast Exhibit Hall

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[73.10] A Disappearing Mg II Broad Absorption Line in the Low-Ionization BALQSO LBQS 0103-2753

V.T. Junkkarinen, R.D. Cohen, F. Hamann (CASS/UCSD)

We present new spectra of the low-ionization broad absorption line (BAL) QSO LBQS 0103-2753 that show a dramatic change in the absorption spectrum. LBQS 0103-2753 was observed by Morris et al. (1991, AJ, 102, 1627) as part of the LBQS survey on 26 August 1987. Morris et al. found a QSO with ze = 0.848, strong Fe II emission, and a broad Mg II \lambda2798 absorption trough at roughly za = 0.769. The broad Mg II \lambda2798 absorption, which is about 50% deep on the Morris et al. spectrum, makes LBQS 0103-2753 a relatively rare low-ionization BALQSO (Voit et al. 1993, ApJ, 413, 95). While carrying out an HST/STIS-plus-optical campaign to measure the spectra of several low and intermediate redshift BALQSOs, we observed LBQS 0103-2753 on 22 August 1998 at CTIO. The new spectra, obtained at 3Å\ FWHM resolution and good S/N with the CTIO 4m telescope, show no Mg II \lambda2798 absorption feature. The central depth is \le10% . Weaker Mg II absorption features are difficult to measure because Fe II emission produces an undulating pseudo--continuum blueward of Mg II emission. Large variations in BAL troughs have been measured in other BALQSOs (e.g. Barlow et al. 1992, ApJ, 397, 81), but this is the first example of such changes in a low--ionization BALQSO and the first example where a strong observed BAL feature has disappeared. Because the Mg II BAL is the only BAL observed so far in the spectrum of LBQS 0103-2753, it is unknown at this time whether the object is now a typical high--ionization BALQSO or whether it has no BALs.

We will discuss the implications of these results, and include spectra covering the strong high--ionization UV lines if we obtain our scheduled HST/STIS observation of LBQS 0103-2753 before the AAS meeting.

This research has been supported in part by STScI/NASA grant GO 7359.

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