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Post-Voyager brightness variations on Io
McGrath, Melissa A.; Spencer, John R.; McEwen, Alfred S. +1 more
Imaging of Io with the faint object and planetary cameras of the Hubble space telescope in 1992 and 1993 at wavelengths of ~3450, 3700, and 4100 Å shows two surface areas that have undergone significant, large-scale change in reflectivity since the 1979 Voyager encounters. The first is located in Colchis Regio and covers ~106 km2
Eclipse Timings of the Low-Mass X-Ray Binary EXO 0748-676: Statistical Arguments against Orbital Period Changes
Wood, Kent S.; Hertz, Paul; Cominsky, Lynn
EXO 0748-676, an eclipsing low-mass X-ray binary, is one of only about four or five low-mass X-ray binaries for which orbital period evolution has been reported. We observed a single eclipse egress with ROSAT . The time of this egress is consistent with the apparent increase in Porb previously reported on the basis of EXOSAT and Ginga o…
A Radio-Optical Reference Frame.VIII.CCD Observations from KPNO and CTIO: Internal Calibration and First Results
Zacharias, N.; Winter, L.; de Vegt, C. +1 more
In this pilot investigation, precise optical positions in the FK5 system are presented for a set of 16 compact extragalactic radio sources, which will be part of the future radio-optical reference frame. The 0.9 m KPNO and CTIO telescopes equipped with 2 K CCDs have been used for this project. The astrometric properties of these instruments are in…
A comparison between the Hercules X-1 pre-eclipse and anomalous dips.
Parmar, A. N.; Reynolds, A. P.
We report the properties of three pre-eclipse and two anomalous dips from Hercules X-1 using data from the EXOSAT Observatory. The anomalous dips are shorter, lasting ~1hr compared to lower limits of ~3hr for the pre-eclipse dips, and shallower, never resulting in more than 91+/-4% of the 2-17keV flux being obscured, compared to the pre-eclipse di…
Star Counts from the HST Snapshot Survey. II. Wide Binaries
Maoz, Dan; Gould, Andrew; Yanny, Brian +1 more
We report on a study of the first sample of wide binaries whose members are primarily in the old component of the Galactic disk. The binaries were discovered in 446 fields imaged with the Hubble Space Telescope (HST) Planetary Camera to an average magnitude limit of V = 2.13, as part of the Snapshot Survey for gravitational lenses. Most of the fie…
Identification of Emission-Line Stars in 30 Doradus Using HST Observations
Parker, Joel Wm.; Heap, Sara R.; Malumuth, Eliot M.
Using broadband (F439W) and narrowband (F469N) Hubble Space Telescope archive images of the R136 central cluster of 30 Doradus, we have identified candidate Wolf-Rayet stars from the strength of their He II λ4686 emission lines. The number ratio of Wolf-Rayet to O stars found in our data is 0.11±0.03. Our results are more consistent with an instan…
Ultraviolet Temporal Variability of the Peculiar Star R Aquarii
Kafatos, M.; Meier, S. R.
This paper is a comprehensive study of all far-UV spectra obtained with the International Ultraviolet Explorer (IUE) satellite of the symbiotic star R Aquarii (R Aqr) covering a 13 yr period between 1979 and 1992. We have analyzed the ultraviolet emission for the compact H II region and the NE and SW extended "jetlike" filamentary structures. The …
The singularity of Tau Scorpii
Stickland, D. J.; Lloyd, C.
UV Spectra of the Eclipsing LMC X-Ray Binary CAL 87
Hutchings, J. B.; Crampton, D.; Cowley, A. P. +1 more
UV spectra of the supersoft x-ray binary CAL 87 have been obtained with the Faint Object Spectrograph of the HST. Eight spectra were obtained in 1995 January in a continuous observation covering the eclipse, from orbital phase 0.65 to 0.02. Interstellar extinction is modeled and removed to measure the system luminosity. The disk bolometric luminos…
The Ulysses south polar pass: Anomalous component of cosmic rays
Klecker, B.; Bothmer, V.; Sanderson, T. R. +4 more
We have expanded our previous study of latitudinal gradients of anomalous cosmic ray oxygen (8 to 12 MeV/n and 12 to 16 MeV/n) by using also helium (11 to 20 MeV/n) as an additional component and a larger ULYSSES/LET data set including the segment up to the maximum southern latitude and the pole-to-equator segment of the mission down to 38°S. The …