We present new Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) NUV-MAMA and STIS CCD observations of the BL Lac object AO 0235+164 and the intervening damped Lyα (DLA) line at za = 0.524. The line profile gives N(H ) = × 1021 cm-2 and, combined with the H I 21 cm absorption data, leads to a spin temperature of Ts = 220 ± 60 K. Those spectra also show a strong, broad feature at the expected position of the 2175 Å graphitic dust feature at za = 0.524. Assuming a Galactic-type dust extinction curve at za = 0.524 gives a dust-to-gas ratio of 0.19 times the Galactic value, but the fit, assuming that the underlying, unreddened spectrum is a single power law, is poor in the far-UV. A dust-to-gas ratio of 0.19 times the Galactic value is similar to the LMC, but the AO 0235+164 spectrum does not fit either the LMC extinction curve or the SMC extinction curve (which has practically no 2175 Å feature). A possible interpretation includes dust similar to that in the Galaxy, but with fewer of the small particles that produce the far-UV extinction. The metallicity of the za = 0.524 absorber, estimated from the observed N(H ) and excess X-ray absorption (beyond Galactic) derived from contemporaneous and archival ASCA and ROSAT X-ray data, is Z = 0.72 ± 0.28 Z☉, implying in turn a dust-to-metals ratio of 0.27 times the Galactic value. If the dust mass density is the same in the za = 0.524 DLA system as in our Galaxy, only 14% (±6%) of the metals (by mass) are in dust, compared to 51%, 36%, and 46% for the Galaxy, LMC, and SMC, respectively. Such a dusty za = 0.524 AO 0235+164 absorption system is a good example of the kind of DLA system that will be missed because of selection effects, which in turn can bias the measurement of the comoving density of interstellar gas (in units of the closure density), Ωg, as a function of z.

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 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 zA = 0.834 and zB = 0.858; their difference is 3900 km s −1 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 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. Subject headings: galaxies: active — quasars: general — black hole physics — quasars: individual (LBQS 0103-2753) Based on observations made with the NASA/ESA Hubble Space Telescope. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS5-26555. Center for Astrophysics and Space Sciences, University of California, San Diego, La Jolla, CA 92093-0424; vesa@ucsd.edu, mburbidge@ucsd.edu, rdcohen@ucsd.edu. Visiting Astronomer, Cerro Tololo Inter–American Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. Department of Astronomy, University of Texas, Austin TX 78712; shields@bluebump.as.utexas.edu. Department of Astronomy, University of Florida, Gainsville FL 32611-2055; hamann@astro.ufl.edu.

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.

We analyze HST/GHRS spectra of AB Doradus, the prototypical ultra-rapidly rotating K dwarf. We observed chromospheric (Mg II) and transition region (C II, Si IV, C IV, and N V) lines periodically throughout the stellar rotation period, and provide a low dispersion stellar atlas of 78 emission lines. The quiescent line profiles of the chromospheric and transition region lines show narrow cores superposed on very broad wings. The broad wings of the Mg II k h lines and of the transition region lines can be explained by emission from gas co-rotating with the star and extending out to near the Keplerian co-rotation radius (2.8 stellar radii). While this is not a unique solution, it is consistent with previous studies of H-alpha emission that are naturally explained by large co-rotating prominences. We find no evidence for rotational modulation of the emission line fluxes. The density diagnostics suggest that the transition region is formed at constant pressure, with an electron density 2-3 E12 /cm^3 at a temperature of 30,000 K. The electron pressure is about 100 times larger than that for the quiet Sun. The emission measure distribution shows a minimum between log(T) = 5 and 5.5. The Mg II line exhibits three interstellar absorption components along the 15 pc line of sight. We identify the lowest velocity component with the G cloud, but the other components are not identified with any interstellar clouds previously detected from other lines of sight.

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.

Goddard High Resolution Spectrograph observations of the nucleus of the bright, nearby Seyfert galaxy NGC 4151 are presented and briefly described.

Observations of the ultra–sharp-lined, chemically peculiar star χ Lupi taken by the Goddard High Resolution Spectrograph in echelle mode are presented. Thirty-six intervals of the spectral region between 1249 and 2688 Å are covered with resolving powers in the range 75,000–93,000. Line identifications are provided, and the observed spectra are compared with synthetic spectra calculated using the SYNTHE program and associated line lists with changes to the line lists. The significance of these spectra for the χ Lupi Pathfinder Project and the closely related atomic physics effort is discussed in a companion paper.

Goddard High Resolution Spectrograph echelle-mode observations of the interstellar absorption lines of Mg II, Si IV, C IV, and N V toward mu Columbae (HD 38666) are presented. The observations have a spectral resolution of 3.5 km s(-1) and signal-to-noise ratios (S/Ns) of 20-200. The mu Col sight line (l = 237.degrees 3, b = -27.degrees 1, d = 0.40 kpc, z = -0.18 kpc) extends though the Local Bubble and the warm neutral, warm ionized, and hot ionized phases of the interstellar medium (ISM). The high-ionization column densities toward mu Col are log N(Si IV) = 12.16 +/- 0.05, log N(C IV) = 12.88 +/- 0.02, and log N(N V) = 11.8-12.3. Profile fits to Copernicus satellite measures of O VI absorption toward mu Col yield log N(O VI) = 13.82+/-0.01 and b = 38.7 km s(-1). This implies N(C IV)/N(O VI) = 0.11 +/- 0.01, which is typical of the values found for the hot ISM of the Galactic disk. The O vr profile is twice as broad as the C rv and N V profiles, even though these species have roughly similar average velocities. Some of the C IV, N V, and O VI absorption toward mu Col may occur at the interface of the Local Cloud and Local Bubble, although additional contributions to these ions probably also occur in more distant gas along the sight line. A substantial part of the Si Iv absorption likely arises in warm photoionized gas in an H II region surrounding mu Col. The profile width differences among the high-ionization lines of C IV, N V, and O VI could be produced if the line of sight passes through a highly evolved supernova remnant. The observations for mu Col and for other stars observed at high resolution with the GHRS reveal that multiple gas types (warm and hot) contribute to the absorption by the highly ionized atoms along both nearby and distant sight lines. Disentangling the relative contributions from the different gas types requires high-resolution and high-S/N observations. The Mg II observations, combined with a solar Mg reference abundance, imply that the Mg depletion toward mu Col is -0.31 dex. As observed for other sight lines through the warm neutral medium, the gas-phase observations of Mg, when combined with results for Fe and Si, suggest that Mg and Fe are more deficient from the gas phase than one would expect if these elements are only contained in silicate dust grains.

We review changes to the characteristics of the Goddard High Resolution Spectrograph (GHRS) which resulted from the installation of the Corrective Optics Space Telescope Axial Replacement (COSTAR) on the Hubble Space Telescope. The introduction of two new optical elements into the light path altered the spectral distribution of the light, decreasing the amount of light striking the instrument by about 30% at wavelengths greater than 1200 Å and effectively eliminated all radiation at wavelengths less than 1130 Å. However, at the longer wavelengths the improved focus offset this loss when the Large Science Aperture (LSA) was used and increased the overall throughput of the Small Science Aperture (SSA) by a factor of 2. The improved focus also enhanced the spectral resolution of LSA observations and improved the ability of the instrument to observe in crowded fields.

Observations of the narrow-lined O-type star 10 Lacertae taken with the Goddard High Resolution Spectrograph in 1992 November are presented. The spectra cover the wavelength range 1181-1777 Angstrom with a resolution of 15 km s(-1) and signal-to-noise ratio greater than 100:1. Absorption lines arising in the interstellar medium, the photosphere, and the stellar wind are identified and discussed.

We use new UV and optical spectra and an archival HST-WFPC2 image to study the z_a z_e absorber in the z_e = 0.20 QSO PKS 2135-147. The UV spectra, obtained with HST-FOS, show strong z_a z_e absorption lines of C IV, N V, O VI, Ly-alpha and Ly-beta. The z_a z_e line profiles are resolved, with deconvolved FWHM of 270 to 450 km/s. Lower limits on the total column densities are of order 10^15 cm-2 for all ions. If the absorber is photoionized by the QSO and the derived relative columns in C IV and H I are roughly correct, then the metallicity must be at least solar. The location of the z_a z_e absorber remains uncertain. Two L_* galaxies in a small cluster centered on PKS 2135-147 lie within 36h^-1 kpc projected distance and have redshifts consistent with causing or contributing to the z_a z_e lines. The extensive halo of the QSO's host galaxy could also contribute. Calculations show that the QSO is bright enough to photoionize gas up to O VI in the low-density halos of the host and nearby cluster galaxies. Nonetheless, there is indirect evidence for absorption much nearer the QSO, namely (1) the derived high (albeit uncertain) metallicity, (2) the relatively strong N V absorption lines, which might be caused by a higher nitrogen abundance in the metal-rich gas, and (3) strong, lobe-dominated steep-spectrum radio emission, which is known to correlate with a much higher incidence of (probably intrinsic) z_a z_e lines. We propose that the CIV/NV/OVI line ratios can be used as a general diagnostic of intrinsic versus intervening absorption, as long as the line saturation effects are understood.

We present HST/FOS1 spectra of the two bright images (A and B) of the gravitationally lensed QSO 0957 + 561 in the wavelength range 2200-3300 Angstrom. We find that the absorption system (z(abs) = 1.3911) near z(em) is a weak, damped Ly alpha system with strong Ly alpha 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 Ly alpha absorber. A direct outcome of this explanation is a determination of the dust-to-gas ratio, k, in the damped Ly alpha system. We derive k = 0.55 +/- 0.18 for a simple 1/lambda extinction law and k = 0.31 +/- 0.10 for the Galactic extinction curve. For gravitationally lensed systems with damped Ly alpha 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.

Observations of the quasar 3C 273 taken with the Goddard High Resolution Spectrograph in 1993 November and December are presented here. We have included both the fully-reduced spectra, and spectra combined with our earlier (1991) observations. There are a total of IO new medium resolution exposures covering four wavelength regions: 1164-1201 Angstrom, 1214-1251 Angstrom, 1537-1573 Angstrom, and 1633-1670 Angstrom. We confirm the suggestion of Morris et al. (1991, ApJ, 377, L21) that the galactic Si IV lambda 1393 line is blended with an extragalactic Ly alpha line by observing the Ly beta counterpart to this extragalactic line. We obtain an improved upper limit on the C IV/H I ratio in these weak low redshift Ly alpha absorption systems by coadding the corresponding C IV spectral regions. Improved line profiles for the galactic C IV and N V absorption are also presented and discussed. The improved measurements lead to a downward revision of the galactic C IV column density, log N(C IV) = 14.46+/-0.04. (C) 1997 American Astronomical Society.