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The young Sun and the atmosphere and photochemistry of the early Earth
Giampapa, M. S.; Imhoff, C. L.; Canuto, V. M. +2 more
The origin and evolution of the Earth's early atmosphere depend crucially on the dissipation time tN of the primitive solar nebula, SN. Using different theories of turbulence, we estimate that for a 0.1 Msolar SN, tN is 2.5-8.3Myr. Because accretion times are usually much longer, we conclude that most planetary acc…
Spectral fine analysis of the extreme helium star BD +10 2179.
Heber, U.
Line blanketed linear transfer of energy (LTE) model atmospheres were used to analyze UV and visual spectra of the extreme He star BD +10.2179. Model inputs included a temperature within 600 K of 16,000 K, an He component totaling 0.989, and a microturbulent velocity within 1.5 km/sec of 7 km/sec. Hydrogen abundance was calculated to be 0.1% by nu…
Ultraviolet interstellar absorption toward HD 5980 in the Small Magellanic Cloud.
Savage, B. D.; Fitzpatrick, E. L.
Individual high-dispersion International Ultraviolet Explorer (IUE) spectra of extragalactic stars are noisy because of the long exposure times required and the inherent limitations of the IUE detectors. A program has, therefore, been undertaken to obtain multiple ultraviolet spectra of the brightest Magellanic Cloud stars in order to produce comp…
Ultraviolet spectroscopic observations of some Be stars of later typeand A-F type shell stars.
Carpenter, K. G.; Slettebak, A.
High-dispersion IUE spectra of 18 later type Be and A-F type shell stars as well as eight standard nonemission line stars have been analyzed for anomalous ionization and mass loss effects. It is found that superionization in the Be stars extends to the latest spectral subtypes but does not seem to be present in the A-F type stars. The superionized…
MR 2251-178 : a nearby QSO embedded in a giant H II envelope.
Tarenghi, M.; Boksenberg, A.; Bergeron, J. +1 more
Spectra of MR 2251-178 and surrounding galaxies were obtained and analyzed. The kinematics of the extended region, the spectra of the QSO and nebulosity, and the galaxies of the surrounding cluster are discussed. The QSO lies in the nucleus of a galaxy having a gaseous component of very high ionization, high temperature and relatively low abundanc…
Redshifts of high-temperature emission lines in the far-ultraviolet spectra of late-type stars.
Jordan, C.; Stencel, R. E.; Linsky, J. L. +4 more
High-dispersion IUE spectra of six late-type stars exhibit small but statistically significant differential redshifts of high-temperature emission lines, like Si IV and C IV, with respect to low-temperature lines like S I and O I. A well-exposed, small-aperture spectrum of the active chromosphere binary Capella (Alpha Aurigae A: G6 II+F9 III) esta…
Star formation in blue galaxies. I. Ultraviolet, optical, and infrared observations of NGC 4214 and NGC 4670.
Gallagher, J.; Fabbiano, G.; Huchra, J. P. +4 more
NGC 4214 and NGC 4760 have been observed between 1150 A and 1950 A with the IUE satellite, and new infrared and optical broad-band photometry have been obtained. The spectra of both galaxies are dominated by O stars, and, in the spectrum of NGC 4214, the C IV 1550 A line exhibits a P Cygni profile indicative of hot stars with large mass-loss rates…
Observations of active chromosphere stars.
Stencel, R. E.; Bopp, B. W.; Africano, J. L. +2 more
It is pointed out that spectroscopic signatures of stellar chromospheric activity are readily observable. The present study is concerned with new photometric and spectroscopic observations of active-chromosphere RS CVn, BY Dra, and FK Com stars. Attention is given to the first results of a synoptic monitoring program of many active chromosphere st…
Far-ultraviolet emission lines in U Cephei : evidence for a hot, turbulent circumstellar envelope.
Plavec, M. J.
U Cephei is a classical semidetached eclipsing binary of the Algol type, whose unusually high level of activity in the optical spectrum has long been recognized. This paper reports detection of numerous emission lines in the far-ultraviolet spectrum. For the first time, the line-emitting region has been studied both in emission and in absorption. …
UV and visible spectrophotometry of nine LMC Wolf-Rayet stars.
Willis, A. J.; Smith, L. J.
The first combined UV and visible spectrophotometric measurements of Large-Magellanic-Cloud Wolf-Rayet stars (6 of the WN subclass and 3 of the WC) are presented. The strengths of the He II 4686 A and 1640 A emission lines in the LMC WN stars are about twice as strong as those of their galactic counterparts. Expansion velocities and properties of …