Search Publications
The Crab Nebula's Moving Wisps in Radio
Frail, D. A.; Hester, J. J.; Bietenholz, M. F.
We present three high-resolution radio images of the Crab Nebula, taken in 1998.6, 1998.8, and 2000.1 with the VLA. These are the best radio images of the Crab to date. We show that, near the pulsar, there are significant changes between our three observing epochs. These changes have an elliptical geometry very similar to that of the optical wisps…
Spatially Resolved O II Recombination Line Observations of the Ring Nebula, NGC 6720
Garnett, Donald R.; Dinerstein, Harriet L.
We present new long-slit CCD spectra of O II permitted lines and [O III] forbidden lines in the Ring Nebula NGC 6720. These observations provide spatially resolved information on both O II and [O III] over the 70" diameter of the main shell. We find significant differences in the spatial distribution of the O II lines and [O III] λ4959. The [O III…
The Intrinsic Absorber in QSO 2359-1241: Keck and HUBBLE SPACE TELESCOPE Observations
White, Richard L.; Gregg, Michael D.; Becker, Robert H. +4 more
We present detailed analyses of the absorption spectrum seen in QSO 2359-1241 (NVSS J235953-124148). Keck HIRES data reveal absorption from 20 transitions arising from He I, Mg I, Mg II, Ca II, and Fe II. Hubble Space Telescope data show broad absorption lines (BALs) from Al III λ1857, C IV λ1549, Si IV λ1397, and N V λ1240. Absorption from excite…
GRB 000418: A Hidden Jet Revealed
Berger, E.; Bloom, J. S.; Cline, T. +15 more
We report on optical, near-infrared, and centimeter radio observations of GRB 000418 that allow us to follow the evolution of the afterglow from 2 to 200 days after the γ-ray burst (GRB). In modeling these broadband data, we find that an isotropic explosion in a constant-density medium is unable to simultaneously fit both the radio and optical dat…
Multiwavelength Monitoring of the Narrow-Line Seyfert 1 Galaxy Arakelian 564. II. Ultraviolet Continuum and Emission-Line Variability
Brandt, W. N.; Clavel, J.; Kriss, G. A. +15 more
We present results of an intensive 2 month campaign of approximately daily spectrophotometric monitoring of the narrow-line Seyfert 1 galaxy (NLS1) Ark 564 with the Hubble Space Telescope. The fractional variability amplitude of the continuum variations between 1365 and 3000 Å is ~6%, about a factor of 3 less than that found in typical Seyfert 1 g…
Space Telescope Imaging Spectrograph Observations of Interstellar Oxygen and Krypton in Translucent Clouds
Meyer, David M.; Cartledge, Stefan I. B.; Lauroesch, J. T. +1 more
We have obtained high-resolution Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) observations of O I λ1356 and Kr I λ1236 absorption in 11 sight lines characterized by high extinction, large H I column densities, and/or long path lengths. Previous Goddard High Resolution Spectrograph (GHRS) measurements of these weak featu…
Theoretical Modeling of Infrared Emission from Neutral and Charged Polycyclic Aromatic Hydrocarbons. II.
Tielens, A. G. G. M.; Bakes, E. L. O.; Bauschlicher, Charles W., Jr. +2 more
The nature of the carriers of the interstellar infrared (IR) emission features between 3.3 and 12.7 µm is complex. We must consider emission from a family of polycyclic aromatic hydrocarbons (PAHs) in a multiplicity of cationic charge states (+1, +2, +3, and so on), along with neutral and anionic PAHs. The adopted intrinsic IR cross sections…
Optical Detection of a Variable Millisecond Pulsar Companion in 47 Tucanae
Heinke, Craig O.; Gilliland, Ronald L.; Edmonds, Peter D. +2 more
Using results from radio and X-ray observations of millisecond pulsars in 47 Tucanae, and extensive Hubble Space Telescope U, V, and I imaging of the globular cluster core, we have derived a common astrometric solution good to less than 0.1". A close positional coincidence is found for 47 Tuc U, a 4.3 ms pulsar in a 0.429 day orbit, detected in ra…
Helium White Dwarfs and BY Draconis Binaries in the Globular Cluster NGC 6397
Cool, A. M.; Grindlay, J. E.; Edmonds, P. D. +1 more
We examine 15 orbits of Hubble Space Telescope observations of the nearby post-core-collapsed globular cluster NGC 6397 using narrowband photometry in Hα with broadband photometry in V, R, and I. We recover the candidate helium white dwarfs (He WDs) recently discovered by Cool et al., of which one was examined spectroscopically by Edmonds et al., …
Hard X-Radiation from a Fast Coronal Ejection
Hudson, H. S.; Nitta, N. V.; Shimojo, M. +1 more
We have observed a high-speed coronal ejection in hard X-rays, detectable to an altitude of some 2×105 km in the Yohkoh 23-53 keV energy bands. Simultaneous imaging at 17 and 34 GHz from the Nobeyama radioheliograph shows complex moving features simultaneous with the ejection, including a compact source that we identify with the rapid X…