Search Publications
Doppler tracking of spacecraft with multi-frequency links
Comoretto, G.; Iess, L.; Bertotti, B.
We discuss the use of multi-frequency microwave links in Doppler tracking of interplanetary spacecraft for scientific purposes, especially in relation to the measurement and the elimination of the contribution due to the plasma in the solar wind and the ionosphere. We show how the two contributions in the up- and the down-link can be separately me…
SAO 244567 : a post-AGB star which has turned into a planetarey nebula within the last 40 years.
Pottasch, S. R.; Clavel, J.; de Martino, D. +5 more
SAO 244567 (Hen 1357 = CPD -59 deg 6926 = IRAS 17119-5926) is an IRAS source with far infrared colors and flux distribution similar to those of planetary nebulae. The IUE ultraviolet spectra obtained in July 1988 and April 1992 show nebular emission lines, and also the changes in the spectra suggest the formation of the planetary nebula and the ra…
Lyman-alpha emission in spectra of Herbig AE stars. an indication of accretion ?
Talavera, A.; Blondel, P. F. C.; Djie, H. R. E. T. A.
Lyman-alpha emission lines have been detected in the IUE spectra of several Herbig Ae stars, but not in those of Herbig Be stars. The shapes and positions of these lines are not consistent with those expected from a chromosphere and transition region (TR), which may be the origin of the other FUV emission lines in the spectra of these stars. The c…
Environment dependence of interstellar extinction curves.
Greenberg, J. M.; Jenniskens, P.
The IUE interstellar extinction curves published by Aiello et al. (1988) are decomposed into a bump, linear rise and FUV non-linear rise, in the parameterization scheme of Fitzpatrick & Massa (1990). The parameters of the 115 extinction curves are given. The lines of sight are characterized from the IRAS Skyflux and Point Source Catalogue data…
Analysis of the DA white dwarf HZ 43A and its companion star.
Werner, K.; Jordan, S.; Barstow, M. A. +3 more
The DA white dwarf HZ 43 A (WD 1314+293) is analyzed based on a newly obtained optical spectrogram. We demonstrate that the derived parameters Teff = 49.000 K and log g = 7.7 are in agreement with the observed Ly-alpha line, the slope of the UV continuum, and the measured trigonometric parallax. The EXOSAT spectrograms of Paerels et al.…
UES and IUE observations of the O9.5V star HD 93521 : non-radial pulsatutions, wind and distance.
Howarth, Ian D.; Reid, Andy H. N.
We have obtained time-series spectroscopy of the rapidly rotating O9.5 V star HD 93521 during commissioning of the Utrecht Echelle Spectrograph (UES) on the William Herschel Telescope. The He I lines show 'wiggles' at the approximately 1% level, which move systematically from blue to red across the profile; by contrast, the He II lines do not show…
Polarimetric investigatio, on interstellar dust within 50 PC from the sun.
Leroy, J. L.
We have analyzed the polarization catalogue, for 1000 stars closer than 50 Pc, which has been presented in a companion paper. Although the accuracy of the measurements is generally very good (better than 0.02% for more than 700 stars), the catalogue contains essentially unpolarized stars, which is to be related to the well known depletion of dust …
Cyclotron and Zeeman spectroscopy of MR Serpentis in low and high states of accretion.
Beuermann, K.; Jordan, S.; Schwope, A. D. +1 more
Phase-resolved low-resolution spectrophotometry of the polar MR Ser obtained during states of low and high accretion reveals cyclotron line emission as well as Balmer line Zeeman absorption. At both occasions the cyclotron lines move with phase. The whole system of cyclotron lines appears wavelength- and phase-shifted when the system switches from…
Spectral analysis of DY Centauri, a hot R Coronae Borealis star with an unusually high hydrogen content.
Heber, U.; Jeffery, C. S.
The photospheric parameters of DY Cen, an H-deficient early-B supergiant that is spectroscopically similar to the pulsating, extreme-He star BD-9 deg 4395, have been derived from high-resolution spectra via atomic data and line-blanketed model atmospheres. DY Cen is shown to be a metal-poor EHe star whose composition supports an anticorrelation be…
UV spectral variability in the Herbig AE star HR 5999. 11: The accretion interpretation
Grady, C. A.; Perez, M. R.; The, P. S.
We report recent IUE high- and low-dispersion observations with the IUE long wavelength camera (LWP) and short wavelength camera (SWP) of the Herbig Ae star HR 5999. We have found a dramatic change in the structure of the Mg II h and k lines (2795.5, 2802.7 Å) along with some continuum flux excesses especially at the short end of the SWP camera. L…