Search Publications
Gravitational Lensing of Quasars as Seen by the Hubble Space Telescope Snapshot Survey
Maoz, D.; Lahav, O.; Schneider, D. P. +4 more
As part of the ongoing HST Snapshot Survey, 152 additional high- luminosity z > 1 quasars were observed, bringing the total to 184 quasars. Each exposure was searched for evidence of gravitational lensing. Only one quasar among those observed, 1208+1011, is a candidate lens system with subarcsecond image separation. Six other quasars have point…
Chromospheric heating in late-type dwarfs : acoustic or magnetic ?
Doyle, J. G.; Mathioudakis, M.
Mg II h and k fluxes for 69 K and 88 M dwarfs have been analyzed. An empirical lower limit is found in the Mg II flux, extended down to the latest spectral types. Based on the data presented here it is the magnetic component that dominates the emission from the atmosphere of cool dwarfs, especially the M dwarfs. It, however, coexists with an acous…
New Calibrators for the Cepheid Period-Luminosity Relation
Evans, Nancy R.
IUE spectra of six Cepheids have been used to determine their absolute magnitudes from the spectral types of their binary companions. The stars observed are U Aql, V659 Cen, Y Lac, S Nor, V350 Sgr, and V636 Sco. The absolute magnitude for V659 Cen is more uncertain than for the others because its reddening is poorly determined and the spectral typ…
Deep Hubble Space Telescope Imaging of a Compact Radio Galaxy at Z = 2.390
Windhorst, Rogier; Keel, William C.; Mathis, Douglas F.
We present deep 4 hr HST/WFC images in V and I of the LBDS radio galaxy 53W002, a weak and compact narrow-line galaxy recently discovered at z = 2.390. After deconvolution, the resolution is 0.2" FWHM. Its I- band structure is quite compact with 30% +/- 10% of its flux in the central <~ 1 kpc, presumably from its AGN. This is surrounded by a cl…
The Broad Emission-Line Profiles and Profile Variability of the Seyfert 1 Galaxy Arakelian 120
Korista, Kirk T.
We present Hα and Hβ broad emission-line profiles of the Seyfert galaxy Arakelian 120 from the past ~10 yr, representing over 100 spectroscopic observations. The broad emission-line profiles of the Balmer lines are complex in structure and variable; the profile variations themselves are complex. We attempt to isolate separate emitting components w…
Variability of Emission Lines in the Planetary Nebulae IC 4997 and NGC 6572
Feibelman, Walter A.; Hyung, Siek; Aller, Lawrence H.
We compare the new IUE high dispersion data and recent ground-based spectra of the planetary nebulae IC 4997 and NGC 6572 with equivalent IUE observations taken in 1980 and optical data taken in 1974-1990. Significant changes are detected in many emission line fluxes in IC 4997, and primarily in He II and C IV for NGC 6572. We interpret these chan…
Highly Ionized Atoms toward HD 93521
Fitzpatrick, Edward L.; Spitzer, Lyman, Jr.
Results are reported from the HST High Resolution Spectrograph observations of absorption features of C IV and Si IV in the spectrum of the high-latitude O star HD 93521 (l = 183 deg; b = 62 deg). A comparison of Si IV and C IV profiles showed that the FWHM of both features is about 50 km/sec, in contrast to the 7 km/sec found for one of the sever…
Studies of symbiotic stars. VI. The eclipsing symbiotic nova AS 338.
Munari, U.
The nature and evolution of AS 338 is investigated. An extensive new set of photometric and spectrophotometric/UE, optical and IR data is presented, covering the period 1962-1991. It is found that AS 338 is a symbiotic nova that entered the outburst phase in late 1981. The outburst, far to be concluded, has been large in amplitude and of long dura…
Resolution and Noise Properties of the Goddard High Resolution Spectrograph
Ebbets, Dennis C.; Morris, Simon L.; Gilliland, Ronald L. +2 more
The Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST) provides an unprecedented capability for ultraviolet spectroscopy of a wide range of astronomical targets. The combination of high resolution (to R 100,000), good sensitivity (maximum total system quantum efficiency of 1%), low background noise (order 0.01 counts s…
Ulysses: Interplanetary shocks between 1 and 4 AU
Balogh, A.; Forsyth, R. J.; Burton, M. E. +3 more
The complex solar events of March 1991 are evident as a large increase in the rate of occurrence of interplanetary shocks. Using Ulysses magnetic field and plasma measurements, 32 forward shocks and 7 reverse shocks have been identified in the 280 day interval from October 26, 1990 to August 1, 1991. The March events alone have produced 9 shocks, …