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A comparison of ground-based stellar positions and proper motions with provisional HIPPARCOS results
Lattanzi, M. G.; Lindegren, L.; Mignard, F. +9 more
Preliminary positions and proper motions derived from the first 30 months of the Hipparcos mission are compared with some of the best ground-based catalogues and optical measurements. Comparison with FK5 and PPM very clearly brings out the zonal and regional errors of these catalogues. The proper motion system of PPM is found to have magnitude dep…
Discovery of a white dwarf companion (EUVE J0254-053) to the K0 IV star HD18131
Doyle, J. G.; Mathioudakis, M.; Byrne, P. B. +2 more
New ultraviolet (UV) observations of late-type stars detected in the Extreme Ultraviolet Explorer (EUVE) all-sky survey revealed an unsuspected white dwarf companion to the K0 star HD18131. The International Ultraviolet Explorer (IUE) spectrum show a composite of a white dwarf and a late-type star. The white dwarf dominates the emission below 2000…
Non-LTE line formation for iron group elements. II. Fe VI.
Butler, K.; Becker, S. R.
A non-LTE line formation calculation for Fevi is presented. The data for radiative bound-bound transitions which have been derived as part of this work are described and their accuracy is evaluated. The theoretical non-LTE spectrum of Fevi is compared to an IUE spectrum of Feige 67. An iron abundance of approximately ten times the solar value is d…
The gamma-ray burst GB 920622.
Greiner, J.; Hurley, K.; Fishman, G. J. +12 more
We have analyzed the Ulysses, BATSE, and COMPTEL spectral data from the γ-ray burst of June 22, 1992 (GB 920622). COMPTEL data reveal a hard to soft evolution within the first pulse of the burst, while the mean hardness ratios of the three pulses are the same. Unlike the single instrument spectra, the composite spectrum of GB 920622 averaged over …
Evidence on sizes and fragmentation of the nuclei of comet Shoemaker-Levy 9 from Hubble Space Telescope images.
Sekanina, Z.
Digital maps of the central regions of 13 nuclear condensations of Comet Shoemaker-Levy 9, obtained with the Wide Field Planetary Camera-2 of the Hubble Space Telescope on January 24-25, March 28-30, and July 4, 1994, were analyzed with the aim to identify the presence of distinct, major fragments in each condensation, to deconvolve their contribu…
A study of systematic positional errors in the SPM plates
Lindegren, L.; Crifo, F.; Platais, I. +4 more
The high-precision reference system defined by the Hipparcos 30-month solution is used to evaluate the presence of potential systematic errors in star positions on the Southern Proper Motion program (SPM) plates. The SPM plates modeled into the Hipparcos positions show a consistent magnitude equation which can be explained by lens decentering. Not…
Near-infrared imaging of the Seyfert 2 galaxy NGC 5252.
Prieto, M. A.; Kotilainen, J. K.
We present near-infrared (JHK) imaging of the Seyfert 2 galaxy NGC 5252, taken with the IRAC2 array on the 2.2m telescope at ESO, La Silla. The unresolved and galactic components to the nuclear emission are separated by a multicomponent fitting of the light profiles in the optical and near-infrared bands. The nuclear flux in a 3" aperture is found…
Optical identification of EUV sources: the secrets of EUVE J2056-17.1.
Doyle, J. G.; Mathioudakis, M.; Dupuis, J. +7 more
We present optical, ultraviolet (UV), and extreme ultraviolet (EUV) results for a new active late-type dwarf star discovered by the Extreme Ultraviolet Explorer (EUVE). A large flare with an energy in excess of 10^35^erg and duration of ~1.1 days was detected in the EUVE Lex/B band (60-200A). The energetics of the event indicate that radiative los…
HST imaging of the planetary nebula K 648 in M 15.
Bianchi, L.; Paresce, F.; de Marchi, G. +2 more
Two images of the Planetary Nebula K 648 in M 15 were taken in the PC mode of the WFPC1 camera on HST in the narrow [OIII] and Halpha_ filters, and an image in [OIII] light with the FOC. This object, never resolved before in ground-based data, is resolved in the HST images. It shows a bipolar structure: a spherical shell containing a br…
A Method for Determining the Individual Accuracy of Astrometric Catalogues
Wielen, R.
We present a method for determining empirically the actual accuracy (external errors) of proper motions and positions given in astrometric catalogues. The method is based on a comparison of a sufficient number of independent proper motions and positions. The method can be applied, for example, to a comparison of the basic FK5 and the future Hippar…