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We have obtained new Hubble Space Telescope (HST) observations of M84, a nearby massive elliptical galaxy whose nucleus contains a 1.5 X 10^9 Msun dark compact object, which presumably is a supermassive black hole. Our Space Telescope Imaging Spectrograph (STIS) spectrum provides the first clear detection of emission lines in the blue (e.g., [O II] 3727, Hbeta, and [O III] 4959, 5007), which arise from a compact region 0.28" across centered on the nucleus. Our Near Infrared Camera and Multi-Object Spectrometer (NICMOS) images exhibit the best view through the prominent dust lanes evident at optical wavelengths and provide a more accurate correction for the internal extinction. The relative fluxes of the emission lines we have detected in the blue together with those detected in the wavelength range 6295 - 6867 AA by Bower et al. (1998, ApJ, 492, L111) indicate that the gas at the nucleus is photoionized by a nonstellar process, instead of hot stars. Stellar absorption features from cool stars at the nucleus are very weak. We update the spectral energy distribution of the nuclear point source and find that although it is roughly flat in most bands, the optical to UV continuum is very red, similar to the spectral energy distribution of BL Lac. Thus, the nuclear point source seen in high-resolution optical images (Bower et al. 1997, ApJ, 483, L33) is not a star cluster but is instead a nonstellar source. Assuming isotropic emission from this source, we estimate that the ratio of bolometric luminosity to Eddington luminosity is 5 X 10^(-7). However, this could be underestimated if this source is a misaligned BL Lac object, which is a possibility suggested by the spectral energy distribution and the evidence of optical variability we describe., Comment: 24 pages, 7 figures, accepted for publication in The Astrophysical Journal

We report on Hubble Space Telescope observations of the optical transient discovered in the error box of GRB970508. The object was imaged on 1997 June 2 with the Space Telescope Imaging Spectrograph and Near-Infrared Camera and Multi-Object Spectrometer. The observations reveal a point-like source with R = 23.1 +- 0.2 and H = 20.6 +- 0.3, in agreement with the power-law temporal decay seen in previous ground-based monitoring. Unlike the case of GRB970228, no nebulosity is detected surrounding the OT of GRB970508, although Mg I absorption and [O II] emission seen in Keck spectra at a redshift of z = 0.835 suggest the presence of a dense, star-forming medium. The HST observations set very conservative upper limits of R ~24.5 and H ~22.2 on the brightness of any underlying extended source. If this subtends a substantial fraction of an arcsecond, then the R band limit is ~25.5. Subsequent photometry suggests a flattening of the light curve at later epochs. Assuming the OT decline follows a pure power-law and ascribing the flattening to the presence of an underlying component of constant flux, we find that this must have R = 25.4, consistent with the upper limits determined by HST. At z = 0.8, this would correspond to an absolute magnitude in the U band of ~-18, similar to that of the Large Magellanic Cloud. We propose a scenario in which the host galaxy of the GRB is of Magellanic type, possibly being a ``satellite'' of one of the bright galaxies located at few arcseconds from the optical transient., Comment: 5 pages, 1 figure, to appear in the Proceedings of the Fourth Gamma Ray Bursts Symposium, eds. C. A. Meegan, R. Preece, and T. Koshut

We search the Hubble Space Telescope (HST) archive for previously unanalyzed observations of stellar H I Lyman-alpha emission lines, our primary purpose being to look for new detections of Lyman-alpha absorption from the outer heliosphere, and to also search for analogous absorption from the astrospheres surrounding the observed stars. The astrospheric absorption is of particular interest because it can be used to study solar-like stellar winds that are otherwise undetectable. We find and analyze 33 HST Lyman-alpha spectra in the archive. All the spectra were taken with the E140M grating of the Space Telescope Imaging Spectrograph (STIS) instrument on board HST. The HST/STIS spectra yield 4 new detections of heliospheric absorption (70 Oph, Xi Boo, 61 Vir, and HD 165185) and 7 new detections of astrospheric absorption (EV Lac, 70 Oph, Xi Boo, 61 Vir, Delta Eri, HD 128987, and DK UMa), doubling the previous number of heliospheric and astrospheric detections. When combined with previous results, 10 of 17 lines of sight within 10 pc yield detections of astrospheric absorption. This high detection fraction implies that most of the ISM within 10 pc must be at least partially neutral, since the presence of H I within the ISM surrounding the observed star is necessary for an astrospheric detection. In contrast, the detection percentage is only 9.7% (3 out of 31) for stars beyond 10 pc. Our Lyman-alpha analyses provide measurements of ISM H I and D I column densities for all 33 lines of sight, and we discuss some implications of these results. Finally, we measure chromospheric Lyman-alpha fluxes from the observed stars. We use these fluxes to determine how Lyman-alpha flux correlates with coronal X-ray and chromospheric Mg II emission, and we also study how Lyman-alpha emission depends on stellar rotation., 56 pages, 15 figures; AASTEX v5.0 plus EPSF extensions in mkfig.sty; accepted by ApJS

We present a census of z(abs) < 2, intrinsic (those showing partial coverage) and associated [z(abs) ~ z(em)] quasar absorption-line systems detected in the Hubble Space Telescope archive of Space Telescope Imaging Spectrograph echelle spectra. This work complements the Misawa et al. (2007) survey of 2 < z(em) < 4 quasars that selects systems using similar techniques. We confirm the existence of so-called "strong N V" intrinsic systems (where the equivalent width of H I Ly alpha is small compared to N V 1238) presented in that work, but find no convincing cases of "strong C IV" intrinsic systems at low redshift/luminosity. Moreover, we also report on the existence of "strong O VI" systems. From a comparison of partial coverage results as a function of ion, we conclude that systems selected by the N V ion have the highest probability of being intrinsic. By contrast, the C IV and O VI ions are poor selectors. Of the 30 O VI systems tested, only two of the systems in the spectrum on 3C 351 show convincing evidence for partial coverage. However, there is a 3-sigma excess in the number of absorbers near the quasar redshift (|Delta v, 40 pages, including 4 tables, and 49 figures; accepted for publication in MNRAS

We present Far Ultraviolet Spectroscopic Explorer (FUSE) and Space Telescope Imaging Spectrograph observations of the weak interstellar N I doublet at 1160 Angstroms toward 17 high-density sight lines [N(Htot)>=10^21 cm^-2]. When combined with published data, our results reveal variations in the fractional N I abundance showing a systematic deficiency at large N(Htot). At the FUSE resolution (~20 km s^-1), the effects of unresolved saturation cannot be conclusively ruled out, although O I at 1356 Angstroms shows little evidence of saturation. We investigated the possibility that the N I variability is due to the formation of N_2 in our mostly dense regions. The 0-0 band of the c'_4 ^1Sigma^+_u - X ^1Sigma^+_g transition of N_2 at 958 Angstroms should be easily detected in our FUSE data; for 10 of the denser sight lines, N_2 is not observed at a sensitivity level of a few times 10^14 cm^-2. The observed N I variations are suggestive of an incomplete understanding of nitrogen chemistry. Based on observations made with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer, which is operated for NASA by the Johns Hopkins University under NASA contract NAS 5-32985, and the NASA/ESA Hubble Space Telescope, obtained from the Multimission Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under the NASA contract NAS 5-26555., 12 pages, 3 figures, accepted for publication in ApJ Letters