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The CO2/CO Abundance Ratio in 1P/Halley and Several Other Comets Observed by IUE and HST
Weaver, Harold A.; Feldman, Paul D.; Tozzi, Paolo +1 more
We report the detection of CO Cameron band emission in the ultraviolet spectra of four moderately active comets (including 1P/Halley) obtained by the International Ultraviolet Explorer (IUE) satellite. The motivation was the observation of Cameron band emission, a tracer of the CO2 production rate, in the spectra of two comets observed …
The Hipparcos distance determination of the Wolf-Rayet system γ2 Velorum (WC8+O) and its ramifications
van der Hucht, K. A.; Moffat, A. F. J.; van den Heuvel, E. P. J. +9 more
Hipparcos parallax measurements give a distance to the Wolf-Rayet WC8+O spectroscopic binary γ2 Vel of d = 258 -31+41 pc and a distance to the O4I(n)f star ξ Pup of d = 429 -77+120pc. Adopting for γ2 Vel an interstellar extinction of Aν = 0.06 mag, this implies an absolut…
GX17+2: X-ray spectral and timing behaviour of a bursting Z source
van Paradijs, J.; van der Klis, M.; Lewin, W. H. G. +2 more
We have investigated the properties of the Z pattern of the low-mass X-ray binary GX17+2 in the X-ray colour-colour diagrams (CDs) and hardness-intensity diagrams (HIDs), and of the power spectra as a function of position in the Z. We used all EXOSAT ME data on GX17+2, a total of six observations during 1983-86. We find that the Z pattern in the C…
Thermal Emission From The Dust Coma Of Comet Hale-Bopp And The Composition Of The Silicate Grains
Hayward, T. L.; Gehrz, R. D.; Hanner, M. S. +7 more
The dust coma of comet Hale-Bopp was observed in the thermal infrared over a wide range in solar heating (R = 4.9–0.9 AU) and over the full wavelength range from 3 µm to 160 µm. Unusual early activity produced an extensive coma containing small warm refractory grains; already at 4.9 AU, the 10 µm silicate emission feature was str…
Hipparcos, VLA, and CCD Observations of Cygnus OB2 No. 5: Solving the Mysteryof the Radio ``Companion''
Badiali, M.; Cardini, D.; Emanuele, A. +4 more
We present accurate optical and radio astrometry for the unresolved contact binary system Cyg OB2 No. 5 and its weaker component to the northeast. While the radio and optical positions of the primary component (taken to be the unresolved contact binary) agree within observational error (~70 mas), we find that the weaker radio component does not ag…
The Evolution of Ultraviolet Emission Lines From Circumstellar Material Surrounding SN 1987A
Cassatella, Angelo; Gilmozzi, Roberto; Fransson, Claes +5 more
The presence of narrow high-temperature emission lines from nitrogen-rich gas close to SN 1987A has been a principal observational constraint on the evolutionary status of the supernova's progenitor. A new analysis of the complete 5 year set of low- and high-resolution IUE ultraviolet spectra of SN 1987A (1987.2-1992.3) provides fluxes for the N V…
SWICS/Ulysses observations: The three-dimensional structure of the heliosphere in the declining/minimum phase of the solar cycle
Livi, S.; Woch, J.; Geiss, J. +5 more
The ESA/NASA spacecraft Ulysses provides the first in-situ observation of the solar wind at high solar latitudes. Data obtained with the Solar Wind Ion Composition Spectrometer (SWICS) during the first orbit of Ulysses around the Sun can be used to obtain a global view of the solar wind pattern within the heliosphere during the declining/minimum p…
HST observations of the field star population in the Large Magellanic Cloud
Elson, Rebecca A. W.; Gilmore, Gerard F.; Santiago, Basilio X.
We present V and I photometry, obtained with the Hubble Space Telescope, for ~15 800 stars in a field in the inner disc of the Large Magellanic Cloud. We confirm previous results indicating that an intense star formation event, probably corresponding to the formation of the LMC disc, occurred a few times 10^9 yr ago. We find a small but real diffe…
Observations and Theoretical Implications of GRB 970228
Reichart, Daniel E.
GRB 970228 is the first gamma-ray burst (GRB) for which prolonged postburst transient X-ray, optical, and infrared emission has been detected. Recent Hubble Space Telescope (HST) observations show that the transient consists of two components: a point source, which is known to be fading, and an extended source, which is possibly fading. I fit stan…
Electron Density Diagnostics for the Solar Upper Atmosphere from Spectra Obtained by SUMER/SOHO
Wilhelm, K.; Curdt, W.; Schühle, U. +3 more
We evaluate the electron density in various solar regions above the limb observed by the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) instrument on SOHO. We find in general good agreement among line ratios from Be-, B-, N-, and Mg-like ions, giving densities of order 108 cm-3.