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The nature of isolated T Tauri stars
Henning, Thomas; Hoff, Wilhelm; Pfau, Werner
We present the results of a search for young stellar objects around the two isolated T Tauri stars (TTSs) TW Hya and CoD-29degr 8887. From the spectroscopic properties of these two objects, it is obvious that they are T Tauri stars, although they are not associated with a star-forming region as it is the case for most of the known TTSs. Especially…
Unveiling the nature of the Cloverleaf lens-system: HST/NICMOS-2 observations
Kneib, J. -P.; Alloin, D.; Pello, R.
We present new elements in the identification of the Cloverleaf lens-system based on recent NICMOS-2/F160W observations. After a careful PSF subtraction of the 4 images of the quasar, the residual HF160W image reveals the presence of a faint object (H ~ 20.5) amid the 4 quasars. This object corresponds to a single galaxy that we identif…
Photometric Evolution of Galaxies in Cosmological Scenarios
Steinmetz, Matthias; Contardo, Gertrud; Fritze-von Alvensleben, Uta
The photometric evolution of galaxies in a hierarchically clustering universe is investigated. The study is based on high-resolution numerical simulations that include the effects of gasdynamics, shock heating, radiative cooling, and a heuristic star formation scheme. The outcome of the simulations is convolved with photometric models, which enabl…
Radial heliospheric magnetic fields detected by Ulysses
Balogh, A.; Jones, G. H.; Forsyth, R. J.
The magnetometer aboard the Ulysses spacecraft has recorded numerous examples of heliospheric magnetic fields orientated in near-radial directions for periods of several hours or more. These fields are unusual, as their existence is contrary to the predictions of classical theories concerning solar wind production and propagation. The magnetic fie…
The ASCA X-Ray Spectrum of η Carinae
Koyama, K.; Davidson, K.; Corcoran, M. F. +9 more
We have obtained high signal-to-noise ratio 0.5-10 keV band X-ray spectra of the peculiar, extremely luminous star η Carinae with the Advanced Satellite for Cosmology and Astrophysics (ASCA) X-ray observatory during Cycle 4 observations in mid-1996. These data comprise the best X-ray spectra to date of the cool source (kT ~ 0.3 keV) surrounding th…
Boron in Lithium- and Beryllium-deficient F Stars
Deliyannis, Constantine P.; Lambert, David L.; Boesgaard, Ann Merchant +1 more
The Goddard High Resolution Spectrograph (GHRS) has been used with the Hubble Space Telescope (HST) to observe the B I region at 2497 Å in nine F and G dwarfs of approximately solar metallicity. The stars were selected because they have a variety of Li and Be deficiencies. Most of the nine stars were newly observed at high spectral resolution and …
Galactic planetary nebulae with Wolf-Rayet nuclei. I. Objects with [WC]-early type stars
Koesterke, L.; Esteban, C.; Pena, M. +3 more
Spatially resolved long-slit spectrophotometric data for the planetary nebulae PB 6, NGC 2452, NGC 2867, NGC 6905 and He 2-55 are presented. Different knots were observed in each nebula. All the nebulae are ionized by [WC 2-3] type nuclei. For the five objects, we calculated photoionization models using the ionizing radiation field from models of …
HIPPARCOS Parallaxes of Eclipsing Binaries and the Radiative Flux Scale
Popper, Daniel M.
Eclipsing binaries with Hipparcos parallaxes are found to define a radiative flux relation for main-sequence stars in the B6-F0 range about as well as stars with angular diameters and to extend the range to F8. The fluxes of components of binaries showing large intrinsic variations fall well below the curve for other stars and its extension to low…
Heating Events in the Quiet Solar Corona
Krucker, Säm; Benz, Arnold O.
Sensitive observations of the quiet Sun observed by EIT on the SOHO satellite in high-temperature iron-line emission originating in the corona are presented. The thermal radiation of the quiet corona is found to fluctutate significantly, even on the shortest time scale of 2 min and in the faintest pixels. The power spectrum of the emission measure…
The helium isotopic ratio in the solar wind and ion fractionation in the corona by inefficient Coulomb drag
Bochsler, Peter; Bodmer, Roland
Using data obtained between 1991 and 1996 with the SWICS instrument (Solar Wind Ion Composition Spectrometer) aboard the Ulysses spacecraft, a long time average of the ((4) He / (3) He ) isotopic ratio of 2450 +/- 460 in coronal hole dominated solar wind is derived. To assess the influence of inefficient Coulomb friction in the inner corona and to…