Search Publications
Optically thin H Lyman alpha production on outer planets: Low-energy proton acceleration in parallel electric fields and neutral H atom precipitation from ring current
Bhardwaj, A.; Singhal, R. P.
A Monte Carlo model has been constructed to describe the energization and energy degradation of low-energy protons in an H2 atmosphere in the presence of parallel electric field. The energy spectrum of Ly α collision events is employed to determine the volume emission rate (VER) of H Ly α emissions. Numerical experiments have been perfo…
Intergalactic and galactic clouds on the line of sight to SN 1993J in M 81 seen in IUE spectra.
Bomans, D. J.; Fransson, C.; Kirshner, R. P. +4 more
High resolution IUE spectra of SN 1993J in M81 show the existence of several clouds on the line of sight. These include local galactic gas at 0 km s^-1^, gas in M81 at -130 km s^-1^, a cloud in the halo of the Milky Way near -45 km s^-1^, and an intergalactic cloud near +140 km s^-1^. Arguments for each of these locations are given. There is littl…
Mass loading and velocity diffusion models for heavy pickup ions at comet Grigg-Skjellerup
Coates, A. J.; Neubauer, Fritz M.; Johnstone, A. D. +1 more
We compare model predictions of cometary water group ion densities and the solar wind slow down with measurements made by the Giotto Johnstone plasma analyzer implanted ion sensor at the encounter with comet Grigg-Skjellerup (G-S) on July 10, 1992. The observed slope of the ion density profile on approach to the comet is unexpectedly steep. Possib…
Core sub-structure of elliptical galaxies : the core resolution technique applied to NGC 1399.
Stiavelli, M.; Zeilinger, W. W.; Moller, P.
UBRJK' images, obtained with subarcsecond seeing, are presented and used to derive the core light profile of the elliptical galaxy NGC 1399. These data, combined with an HST PC V band exposure, and high- resolution velocity dispersion data obtained by us are used to show that NGC 1399 is likely to possess a central dark mass concentration. Models …
Hubble Space Telescope Ultraviolet Spectroscopy of the Highly Polarized but Quiescent Quasar OI 287
Kinney, Anne L.; Antonucci, Robert; Hurt, Todd
The quasar OI 287 has a unique combination of properties, including a high and constant optical polarization oriented parallel to the radio axis, a quiescent optical flux, and a lobe-dominant radio source. The polarization suggests a relationship to the broad absorption line quasars. It is a possible transition object which could illuminate the ge…
Optical and Hubble Space Telescope Ultraviolet Spectropolarimetry of 3C 273 and PG 1114+445
Schmidt, Gary D.; Smith, Paul S.; Allen, Richard G.
Ultraviolet polarization measurements of 3C 273 made with the Faint Object Spectrograph of the Hubble Space Telescope are combined with new optical spectropolarimetry and broad-band measurements made during occasions when the linear polarization of the quasar was <=1%. The HST measurements exhibit very weak UV polarization during the epoch of o…
Spectral analysis of LSE 78 : an extreme helium star similar to BD -9 4395 and DY Centauri.
Jeffery, C. S.
LSE 78 is a hydrogen-deficient early-B supergiant, spectroscopically similar to the pulsating extreme helium star BD - 9 deg 4395 and the hot R CrB star DY Cen. The photospheric parameters of LSE 78 have been derived from optical high-resolution spectra by the method of fine analysis. The principal results are Teff = 18000 K, log g = 2.…
The Optical Jet in Markarian 463
Ford, H. C.; Cohen, Ross D.; Evans, I. N. +4 more
Hubble Space Telescope images of Markarian 463, an interacting Seyfert 2 galaxy, reveal an optical jet 0.84 arcsec long at position angle PA~182^deg^ originating at the Seyfert nucleus. The jet terminates at a radio point source 1.2 arcsec from the nucleus. Previous polarization observations and our filter photometry suggests that the jet may be t…
Periodic Low Amplitude Variations in the Brightness of Proxima Centauri
Benedict, G. F.; Franz, O. G.; Hemenway, P. D. +10 more
Using data acquired with Fine Guidance Sensor #3 on board the Hubble Space Telescope we find that the brightness of Proxima Centauri varies with an amplitude of 0.01 magnitude and a period P=41.6 +/- 0.6 days. We interpret this variation as rotational modulation of star spots or bright regions in the photosphere of Proxima Centauri. In a total of …
Variability of the Seyfert galaxy MKN 766 in the ROSAT all sky survey.
Molendi, S.; Maccacaro, T.; Schaeidt, S.
Results are presented from the ROSAT All Sky Survey (RASS) observation of the Seyfert galaxy Mkn 766. Using a technique specifically developed for the analysis of point sources in the RASS we show that Mkn 766 is highly variable. Comparison of the soft X-ray spectrum (0.1-2 keV) with EXOSAT Medium Energy archive data (2-10 keV) clearly shows that …