Geoffrey S. Burks

A study of ultraviolet absorption lines through the complete Galactic halo by the analysis of HST faint object spectrograph spectra of active Galactic nuclei, 1

The ultraviolet (1150 - 2850 A) spectra of a number of active galactic nuclei (AGNs) observed with the Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) have been used to study the properties of the Galactic halo. The objects that served as probes are 3C 273, PKS 0454-220, Pg 1211+143, CSO 251, Ton 951, and PG 1351+640. The equivalent widths of certain interstellar ions have been measured, with special attention paid to the C IV/C II and Si IV/Si II ratios. These ratios have been intercompared, and the highest values are found in the direction of 3C 273, where C IV/C II = 1.2 and Si IV/Si II greater than 1. These high ratios may be due to a nearby supernova remnant, rather than to ionized gas higher up in the Galactic halo. Our data give some support to the notion that QSO metal-line systems may arise from intervening galaxies which contain high supernova rates, galactic fountains, and turbulent mixing layers.

Predicted scattering characteristics of the Hubble Space Telescope/COSTAR/Faint Object Spectrograph

We describe recent orbital test data acquired with the COSTAR/Faint Object Spectrograph (FOS) on the Hubble Space Telescope (HST). These data exhibit possible internal thruput deficit and scattering features in the FOS. We then describe some data from laboratory measurements of COSTAR optical components carried out at Ball Aerospace Corporation and NASA/Goddard Space Flight Center, which we initially thought might bear on some of the orbital test data. We use next, a theoretical model to simulate some of the HST/COSTAR/FOS imaging and spectral performance. We apply the model to the current data to assist in evaluating COSTAR iamging performance, to attempt to isolate the origin of the thruput deficit and scattering features. The results of these studies will permit a better understanding of the limits of HST performance and permit development of optimal strategies for performing spatially resolved spectroscopy in the FOS scientific observing program.