Ron W. Lyons

LBQS 0103–2753: A 0.″3 Binary Quasar*

Imaging and spectroscopy with HST show that LBQS 0103-2753 (V = 17.8, z = 0.848) is a binary quasar with a separation of 0.3 arcsec or 2.3 kpc. This is by far the smallest separation binary quasar reported to date. The two components have very different spectra, including the presence of strong broad absorption lines (BALs) in component A only. The emission-line redshifts, based on the broad high ionization C IV lines, are z_A = 0.834 and z_B = 0.858; their difference is 3900 km/s in velocity units. The broad C IV lines, however, are probably not a good indicator of systemic redshift; and LBQS 0103-2753 A and B could have a much smaller systemic redshift difference, like the other known binary quasars. If the systemic redshift difference is small, then LBQS 0103-2753 would most likely be a galaxy merger that has led to a binary supermassive black hole. There is now one known 0.3 arcsec binary among roughly 500 QSOs that have been observed in a way that would reveal such a close binary. This suggests that QSO activity is substantially more likely for black hole binaries at spacings ~2 kpc than at ~15 to 60 kpc. Between 1987 and 1998, the observed Mg II BAL disappeared.

The Dust-to-Gas Ratio in the Damped Lyα Clouds toward the Gravitationally Lensed QSO 0957+561

We present HST/FOS spectra of the two bright images (A and B) of the gravitationally lensed QSO 0957+561 in the wavelength range 2200-3300 A. We find that the absorption system (zabs = 1.3911) near zem is a weak, damped Lyα system with strong Lyα absorption lines seen in both images. However, the H I column densities are different, with the line of sight to image A intersecting a larger column density. The continuum shapes of the two spectra differ in the sense that the flux level of image A increases more slowly toward shorter wavelengths than that of image B. We explain this as the result of differential reddening by dust grains in the damped Lyα absorber. A direct outcome of this explanation is a determination of the dust-to-gas ratio, k, in the damped Lyα system. We derive k = 0.55 ± 0.18 for a simple 1/λ extinction law and k = 0.31 ± 0.10 for the Galactic extinction curve. For gravitationally lensed systems with damped Lyα absorbers, our method is a powerful tool for determining the values and dispersion of k, and the shapes of extinction curves, especially in the FUV and EUV regions. We compare our results with previous work.

Discovery of a 2 Kpc binary quasar

LBQS 0103–2753 is a binary quasar with a separation of only 0.3 arcsec. The projected spacing of 2.3 kpc at the distance of the source (z=0.848) is much smaller than that of any other known binary QSO. The binary nature is demonstrated by the very different spectra of the two components and the low probability of a chance pairing. LBQS 0103–2753 presumably is a galaxy merger with a small physical separation between the two supermassive black holes. Such objects may provide important constraints on the evolution of binary black holes and the fueling of AGN.

Performance of the FOS Detectors in a Variable External Magnetic Field

We present the results of an investigation of the in-orbit performance of the Digicon detectors in the Faint Object Spectrograph (FOS), conducted as part of the commissioning phase of the Hubble Space Telescope. This paper includes orbital results on detector background noise, sensor image stability, and photometric stability along with several typical FOS observations. This information should be of general interest to designers of future spacecraft detectors and to astronomers observing with the FOS instrument.

Cerenkov background radiation in imaging detectors

The authors discuss results of an analysis of background dark data obtained with the Digicon detector in the faint object spectrograph on board the Hubble Space Telescope. Time sequenced data are presented which show the background recorded by the detector as it orbits the Earth at an altitude of 600 km. The authors propose that Cerenkov radiation produced by cosmic ray particle interactions with the MgF2 faceplate comprises the major source of this detector noise. Cerenkov light will be emitted whenever a high-energy particle traverses the detector faceplate and can result in large portions of the detector array being illuminated simultaneously. The effects of Cerenkov radiation have been modeled in image tubes by means of a Monte Carlo simulation. This model produces images which qualitatively resemble observed dark data. Moreover, the model closely reproduces the observed average background level and calculates background count statistics which are difficult to determine directly given the rapid sampling rate that would be required. The model can provide optimal settings for the detector burst noise rejection algorithm so that the signal-to-noise ratio of astronomical data can be maximized.