Search Publications
Density and brightness distribution of cometary dust tails
Keller, H. U.; Richter, K.
The density and brightness distributions of cometary dust tails are studied, assuming that the terminal velocity of a dust particle depends on emission time, particle size, and two angles defining the direction of emission. In the novel method, Keplerian trajectories are used for the particles rather than approximations. The corresponding Jacobian…
Upper limit to the boron abundance in the population II star HD 140283.
Molaro, P.
A high resolution IUE spectrum of the Population II star HD 140283 has been analyzed to search for the B I 2496 Å resonance doublet. No features attributable to this element have been found. An upper limit for the B abundance of B/H < 10-11, i.e. more than one order of magnitude less than the solar value has been derived. The presenc…
Hot Ions Observed by the Giotto Ion Mass Spectrometer at the Comet p/ Halley Contact Surface
Balsiger, H.; Young, D. T.; Goldstein, B. E. +6 more
Just inside the contact surface (∼ 4700 km) the High Energy Range Spectrometer (HERS) sensor of the Giotto Ion Mass Spectrometer (IMS) detected a sudden, intense burst of ions that lasted until the HERS sensor ceased transmitting data at a distance of ∼ 3000 km from comet P/Hallley. During this brief interval ions with M/Q = 1,2, 12, 14, 16-19,24,…
The stellar population in the Wolf-Rayet knot in NGC 5430.
Keel, W. C.
The barred spiral NGC 5430 contains an extremely luminous H II region showing very strong He II and N III Wolf-Rayet (WR) emission features. Spectrophotometry from 1200 - 7000 Å has been obtained. From these data, limits on the reddening and effective temperature of the stellar population are derived; Teff is between 25000 and 35000K. N…
Solar-type giants : new X-ray detections from EXOSAT observations.
Gondoin, P.; Mangeney, A.; Praderie, F.
The authors report new X-ray detections of HD 1671 (F5 III) and HD 12929 (K2 III). From an analysis of X-ray count rates in three broadband filters from HD 203387, they derive an estimate of its coronal temperature of T ≡ 3×106K. The data show that HD 12929 (K2 III) differs from the earlier type stars which the authors observed in the f…
Ultraviolet Doubly Excited Fe II Lines in the Laboratory and in the A-Type Star 21 Pegasi
Johansson, S.; Baschek, B.; Brage, T. +2 more
During a new investigation of the UV hollow-cathode spectrum of iron, some 120 lines were identified, among them strong lines around 1850 A, as transitions from doubly excited levels in Fe II. A combination of selective population by charge-transfer processes in the laboratory source and of a strong configuration interaction is probably the cause …
EXOSAT Observations of H2252-035 - Pulse Phase and Orbital Phase Dependent Low Energy Absorption and Iron Line Emission
Pietsch, W.; Pakull, M.; Kendziorra, E. +1 more
The 805 sec pulsing X-ray source H2252-035 has been observed for 7 h on September 14/15 and on September 17, 1983 in X-rays with the low energy telescope and the medium energy detectors of EXOSAT. While below 2 keV the semiamplitude of the 805 s pulses is ∼100% in the 2.3–7.9 keV band it is only ∼40%. X-ray dips that are more pronounced in low ene…
An archival study of IUE observations of low-redshift quasars.
Cheng, F. H.; Fang, L. Z.
The emission-line and continuum characteristics of a sample of 18 low-redshift quasars from the IUE archives are presented. The spectral index (Fν ∝ ν-α) is found to have a mean value of 1.10±0.11, which is considerably steeper than the index of the same spectral region for high-redshift objects. The line ratios Lα/…
The spectroscopic orbit of HD 128220.
Howarth, Ian D.
HD 128220 is a double-lined binary containing a subdwarf O star. A new orbital solution is presented, based principally on IUE spectroscopy. The implications of the solution for the physical parameters of the subdwarf are discussed, with the results that MOsin3i = 1.6±0.7 M_sun;; ROsin3/2i = 1.2±0.4 R_su…
EXOSAT observations of a broad absorption-line quasar : PHL 5200.
Singh, K. P.; Westergaard, N. J.; Schnopper, H. W.
Results are presented of broadband (0.05-10 keV) observations of the high-redshift quasar PHL 5200 using the EXOSAT Observatory. In observations of the 45-arcmin (FWHM) region centered on this broad-absorption-line quasar, performed with the medium-energy (ME) and low-energy (LE) experiments, X-ray emission has been detected in the 2-6 keV energy …