Search Publications
Physics and chemistry of ions in the pile-up region of comet P/Halley.
Altwegg, K.; Balsiger, H.; Geiss, J. +1 more
Measurements by the mass spectrometers onboard Giotto during the flyby at comet P/Halley showed a steep increase in the ion density outside the diamagnetic cavity at a distance of about 8000km from the nucleus (Balsiger et al. 1986a; Krankowsky et al. 1986). The maximum ion density was observed at a distance of 12000km from the nucleus rather than…
Multifrequency Spectra of EXOSAT Blazars
Ghosh, K. K.; Soundararajaperumal, S.
Blazars have been divided into two groups: radio-selected blazars (RBLs) and X-ray-selected blazars (XBLs). Results of the X-ray spectral analysis of 28 such blazars which were observed with EXOSAT are presented in this paper, and in four these are new results which were not published earlier. X-ray results suggest that XBLs are steep-spectrum sou…
Reverberation Mapping by Regularized Linear Inversion
Krolik, Julian H.; Done, Christine
Reverberation mapping of active galactic nucleus emission-line regions requires the numerical deconvolution of two time series. We suggest the application of a new method, regularized linear inversion, to the solution of this problem. This method possesses many good features; it imposes no restrictions on the sign of the response function; it can …
He 3-1475 and Its Jets
Grebel, E. K.; Zijlstra, A. A.; Tinney, C. G. +5 more
We present spectra and high-resolution images taken with the Hubble Space Telescope (HST), the NTT, the VLA, and the MPIA/ESO 2.2 m telescope of the emission-line star He 3-1475, which we suggest is a postasymptotic giant branch star. The star is presumed to be at the origin of a 15" long structure containing symmetrically opposing bright knots. T…
Lensing by Distant Clusters: HST Observations of Weak Shear in the Field of 3C 324
Dickinson, Mark; Smail, Ian
We present the detection of weak gravitational lensing in the field of the radio galaxy 3C 324 (z = 1.206) using deep HST imaging. From an analysis of the shapes of faint R = 24.5--27.5 galaxies in the field we measure a weak, coherent distortion centered close to the radio source. This shear field most likely arises from gravitational lensing of …
Probing the Galactic Disk and Halo. III. The Galactic and Intergalactic Sight Line to H1821+643
Sembach, Kenneth R.; Savage, Blair D.; Lu, Limin
We present intermediate-resolution (FWHM ∼10-20 km s-1) GHRS observations of interstellar and intergalactic absorption lines in the spectrum of the bright quasar H1821+643. The interstellar species detected include S II, Si II, Mg II, C IV, and N V. The intergalactic lines include Lyα (six lines), Lyβ (2 lines), Lyγ, and C III. The Gala…
Discovery of an Optical Synchrotron Jet in 3C 78
Baum, Stefi A.; Sparks, William B.; Miley, George K. +5 more
We report the discovery of an optical synchrotron jet emanating from the nucleus of NGC 1218, the galaxy hosting the radio source 3C 78. The jet is similar to that of M87, although smaller in projected length. The observations were obtained as part of our Hubble Space Telescope "snapshot" program to acquire broadband images with high spatial resol…
Hydra A: star formation and dust production in a cooling flow.
Norgaard-Nielsen, H. U.; Jorgensen, H. E.; Hansen, L.
Optical images and spectroscopy are presented for the radio galaxy Hydra A which contains a substantial flow of cooling X-ray gas. A young stellar population is observed as an excess light around the center showing blue colour and Balmer lines in absorption. The same area also exhibits strong optical emission lines. Our IUE spectra show Lyα and an…
UIT and Optical Imagery of Large Magellanic Cloud Associations LH 52 and LH 53: Ages and Initial Mass Function Slopes
O'Connell, Robert W.; Hill, Robert S.; Bohlin, Ralph C. +4 more
A 40' field including the stellar associations LH 52 and LH 53 and the supernova remnant N49 in the Large Magellanic Cloud was observed by the Ultraviolet Imaging Telescope (UIT) during the Astro-1 Space Shuttle mission in 1990 December. The image in the 162 nm bandpass is discussed together with ground-based BV data on subfields containing LH 52 …
Cataclysmic and Close Binaries in Star Clusters. III. Recovery of the Quiescent Nova 1860 a.d. (T Scorpii) in the Core of the Globular Cluster M80
Drissen, Laurent; Shara, Michael M.
Only two candidate classical nova eruptions have ever been seen in globular clusters. Only one, that of Nova 1860 (T Sco in M80), seems beyond any doubt a cluster member. We have obtained Hubble Space Telescope (HST) imagery of the central regions of M80 and find a very blue candidate within 1" of the astrometric position reported in 1860. Only on…