Search Publications
High-Resolution Ultraviolet Observations of the Interstellar Diffuse Clouds toward MU Columbae
Savage, Blair D.; Sofia, Ulysses J.; Cardelli, Jason A.
Data obtained from the Goddard High Resolution spectrograph (GHRS) are used to study differences in gas-phase abundances of ions occurring in the diffuse neutral clouds toward mu Col. The sight-line characteristics determined in previous studies are reviewed and results for the cloud velocities, absorption equivalent widths, ion column densities, …
Variability of [O I] 6300-Å emission near Io
Smyth, W. H.; Scherb, F.
Observations of [O I] 6300-Å emission near Io have been obtained in 1990, 1991, and 1992 by the National Solar Observatory staff using the solar-stellar spectrograph on the McMath-Pierce telescope at Kitt Peak. High-resolution spectra with a resolving power of about 1.2×105 were obtained with an integration time of 10-15 min each. The v…
The discovery and properties of the ultra-soft X-ray transient EXO 1846-031.
Parmar, A. N.; White, N. E.; Angelini, L. +1 more
We report the discovery of a previously uncataloged ultra-soft X-ray transient EXO 1846-031 which was in outburst during 1985 April to September. The X-ray spectrum consists of an ultra-soft component and a high-energy power-law tail that extends to at least 25 keV. The ultra-soft component may be modeled by either a cutoff power-law or a multicol…
Metal-Line Blanketing and the Peculiar H beta Line Profile in the DAO Star Feige 55
Chayer, P.; Bergeron, P.; Wesemael, F. +1 more
A detailed analysis of the optical spectrum of the DAO white dwarf Feige 55 is presented. We show that the atmospheric parameters obtained from fits to the H-beta line and to higher Balmer lines, respectively, are discrepant. This problem is akin to that reported in previous analyses of hot DAO central stars of planetary nebulae. Model atmosphere …
Prediction of the heliospheric current sheet tilt: 1992 - 1996
Hoeksema, J. T.; McComas, D. J.; Suess, S. T.
Heliospheric current sheet tilt evolves systematically over the solar cycle. Here we show that this evolution is different than the sunspot cycle and that tilt for the period 1992 - 1996 can be predicted using persistence. That is, the tilt over the coming cycle will be the same as for the past cycle. The Ulysses spacecraft has passed Jupiter and …
The Drift of Saturn's North Polar Spot Observed by the Hubble Space Telescope
Caldwell, J.; Hua, X. -M.; Turgeon, B. +2 more
Polar projections of 50 images of Saturn at 889 nanometers and 25 images at 718 nanometers taken by the Hubble Space Telescope in November 1990, as well as 3 images at each wavelength taken in June 1991, have been examined. Among them, 31 show the north polar spot, which is associated with Saturn's polar hexagon, in locations suitable for measurem…
Ultraviolet Continuum Variability and Visual Flickering in the Peculiar Object MWC 560
Sonneborn, G.; Michalitsianos, A. G.; Shore, S. N. +8 more
High-speed U-band photometry of the peculiar emission object MWC 560 obtained with the ground-based instrumentation, and V-band photometry obtained with the International Ultraviolet Explorer-Fine Error Sensor indicates irregular brightness variations are quasi-periodic. Multiple peaks of relative brightness power indicate statistically significan…
Spectroscopic Observations of V443 Herculis: A Symbiotic Binary With Low Mass White Dwarfs
Mikolajewska, Joanna; Kenyon, Scott J.; Dobrzycka, Danuta
We present an analysis of new and existing photometric and spectroscopic observations of the symbiotic binary V443 Herculis. This binary system consists of a normal M5 giant and a hot compact star. These two objects have comparable luminosities: about 1500 solar for the M5 giant and about 1000 solar for the compact star. We identify three nebular …
Absolute Proper Motion and Space Motion of the Globular Cluster M15
Le Campion, J. -F.; Odenkirchen, M.; Geffert, M. +1 more
We have separated cluster members and field stars for stars in a region around the globular cluster M 15. The membership of ultraviolet bright stars of M 15 is discussed. The absolute proper motion of M 15 has been determined with respect to the PPM catalogue. An extragalactic calibration of the proper motions has been performed. The calibration w…
Cosmic-abundance absorption dips in X1755-33.
Church, M. J.; Balucinska-Church, M.
Results of spectral analysis for the source X1755-33 using the 1984 EXOSAT/ME data are presented, with spectral fitting made to the complete 18-h observation by dividing it into 314 consecutive 400-s timebins. It is found that spectral changes take place on time scales of this order and that analysis of longer sections of data can lead to errors. …