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Activity in late-type dwarfs. III. Chromospheric and transition region line fluxes for two dM stars.
Doyle, J. G.; Byrne, P. B.
Weak upper-chromospheric and transition-region emission from two dM stars (Gl 784 and Gl 825) has been observed using deep UV spectroscopy. Ly-alpha fluxes for the two stars were also determined for the first time. Using these results it is shown that the transition from weakly active dM to active dMe star is probably due to increasing surface cov…
On the Nature of Newly Formed Dust around the Hydrogen-deficient Star V348 Sagittarii
Drilling, J. S.; Schoenberner, D.
IUE spectra of V348 Sgr have been used to determine the extinction law from 1250 to 3080 A for circumstellar material recently ejected from it. This law differs from the standard extinction law in showing a bump at 2500 A rather than 2200 A, and in showing much lower extinction values for lambda less than 2000 A. These differences are attributed t…
A correlation between shape and (UV-V) color for early-type galaxies.
Bender, R.; Longo, G.; Capaccioli, M. +1 more
We present a correlation between the isophotal-shape parameter α_4_/α (Bender et al. 1989a) and the ultraviolet (UV) color index (1330 A-V) (Longo et al. 1989): boxy galaxies are found to be UV brighter than disky galaxies. The interpretation of the correlation between Mg_2_ and the UV color suggested by Burstein et al. (1988; hereafter BBBFL) is …
Revisited mass-loss rates for a sample of central stars of planetary nebulae.
Surdej, J.; Hutsemekers, D.
Using improved relations for the first order moment of a P Cygni line profile, mass-loss rates have been rederived for a sample of seventeen central stars of planetary nebulae observed with IUE in the low resolution mode. The average value of the mass-loss rates lies between 10 to the -7th and 10 to the -8th solar masses/yr. It is confirmed that t…
Energetic Ion Fluxes in the Inner Coma of Comet P/Halley
Balsiger, H.; Young, D. T.; Goldstein, R. +3 more
The particle phenomenon observed inside the magnetic field-free cavity near the nucleus of Comet P/Halley by the Giotto Ion Mass Spectrometer High-Energy Range Spectrometer sensor is studied. The question of access to the cavity of particles ionized farther out in the coma is addressed. A quantitative model of a mechanism for creating the observed…
Non--Equilibrium Ionization Effects in the Supernova Remnant RCW 86
Kaastra, J. S.; Smith, A.; Peacock, A. +2 more
X-ray images show that the SNR RCW 86 consists of two emission regions. The electron temperature of both two regions is 3.4 keV. The low-energy flux (0.2-2 keV) is strongly enhanced compared to a simple thermal bremsstrahlung spectrum with Te = 3.4 keV fitted to the 2-10 keV data. This enhancement is most likely caused by nonequilibrium ionization…
LMC X-2 : an extragalactic bulge-type source.
Parmar, A. N.; Motch, C.; Beuermann, K. +3 more
The X-ray source LMC X-2 was observed with EXOSAT for ~8 h on February 2, 1984 with simultaneous photometric and spectroscopic optical coverage. The source was seen at a luminosity of L_x_ ~1.5 10^38^ erg s^-1^ with a mean X-ray spectrum can be described equally well by either the superposition of thermal emission from an optically thin (T_th_ ~5 …
Small-Amplitude Coherent Signals in the X-Ray Emission of NGC 4151
Piro, L.; Perola, G. C.; Fiore, F. +1 more
We present the results of the temporal analysis performed on four EXOSAT medium-energy observations of the Seyfert galaxy NGC 4151, selected for their long duration and background stability. The light curves can be adequately described in terms of regular trends (representing variations on time scales >= 1 day) to which small-amplitude fluctuat…
X-Ray Bursts from 4U 1705-44: Another Case of Burst Properties Dependent on the Strength of the Persistent Emission
Haberl, F.; van Paradijs, J.; Lewin, W. H. G. +3 more
Three Exosat observations are reported of the low-mass X-ray binary 4U 1705-44 during which X-ray bursts are detected. Seventeen bursts are recorded in the low-intensity state and seven bursts in the medium-intensity state, of which 22 are suitable for a detailed analysis. Correlations between the burst properties and the strength of the persisten…
Broad emission line variability in 3C 273.
Zheng, W.; Wilson, R.; O'Brien, P. T.
We find that the broad Ly α H{BETA} and Fe II emission lines in the luminosity quasar 3C 273 vary by 10-30 per cent on time-scales less than a year. All the line variations occurred during approximately the same period. The line cores vary more than the wings, indicating that the line variability involves only pan of the BLR. The line variability …