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HIPPARCOS results for ROSAT-discovered young stars
Brandner, Wolfgang; Neuhauser, Ralph
Out of ~ 500 Lithium-rich ROSAT counterparts, which were presumed to be low-mass pre-main sequence stars, 21 stars have been observed by HIPPARCOS. We study their parallaxes, proper motions, and photometric data. For 7 out of 10 Taurus and Lupus stars in our sample, proper motions and parallaxes are not inconsistent with membership to these associ…
HST and ground-based eclipse observations of V2051 Ophiuchi: binary parameters
Horne, Keith; Baptista, Raymundo; Catalan, M. S. +1 more
We report on high-speed eclipse photometry of the dwarf nova V2051 Oph while it was in a low brightness state, at B~=16.2 mag. In comparison with the average IUE spectra, the ultraviolet continuum and emission lines appear reduced by factors of, respectively, ~=4 and ~=5. Flickering activity is mostly suppressed and the light curve shows the eclip…
Near-IR images of the torus and micro-spiral structure in NGC 1068 using adaptive optics
Rouan, D.; Doyon, R.; Gendron, E. +5 more
We present diffraction-limited near-IR images in J, H and K of the nucleus of NGC 1068, obtained with the Adaptive Optics system Pueo at CFHT. The achieved resolution (0.12") reveals several components, particularly prominent on the [J-K] image: a) an unresolved, conspicuous core (size < 9 pc); b) an elongated structure at P.A. ~ 102°, beginnin…
The Far-Field Hubble Constant
Lauer, Tod R.; Ajhar, Edward A.; Postman, Marc +2 more
We used the Hubble Space Telescope to obtain surface brightness fluctuation (SBF) observations of four nearby brightest cluster galaxies (BCGs) to calibrate the BCG Hubble diagram of Lauer & Postman. This BCG Hubble diagram contains 114 galaxies covering the full celestial sphere and is volume-limited to 15,000 km s-1, providing exc…
Solar Cycle Onset Seen in SOHO Michelson Doppler Imager Seismic Data
Kosovichev, A. G.; Schou, J.; Dziembowski, W. A. +2 more
We have analyzed time changes in centroid frequencies and multiplet frequency splittings of solar oscillations determined with the Michelson Doppler Imager instrument (MDI) on SOHO. The data were divided into five consecutive 72 day sets covering the period from 1996 May 1 through 1997 April 25. We have detected a significant trend in the a4<…
Do SI stars undergo any rotational braking?
North, P.
The old question of rotational braking of Ap Si stars is revisited on the empirical side, taking advantage of the recent Hipparcos results. Field stars with various evolutionary states are considered, and it is shown that the loose correlation between their rotational period and their surface gravity is entirely compatible with conservation of ang…
The large-scale distribution of X-ray active stars
Schmitt, J. H. M. M.; Motch, C.; Guillout, P. +4 more
We analyse the large-scale sky distribution of 8593 X-ray emitting stars from the cross-correlation of the ROSAT All-Sky Survey sources with the Tycho catalog. We detect a density gradient from the galactic plane to the galactic pole which is attributed to the scale height of the young late type star population of the galactic disc. The data also …
Goddard High-Resolution Spectrograph Observations of Cool Low-Gravity Stars. IV. A Comparison of the K5 III stars α Tauri and γ Draconis
Brown, Alexander; Robinson, Richard D.; Carpenter, Kenneth G.
The Goddard High-Resolution Spectrograph (GHRS) has observed the K5 III star α Tau in the 2330 Å region on three separate occasions. These spectra show marked changes with time, with the UV continuum varying by a factor of 2, and with the emission lines changing in flux by 30% or more, with the amount of change dependent upon the opacity of the li…
The Cassini CAPS Electron Spectrometer
Coates, A. J.; Linder, D. R.; Grande, M. +6 more
One of the major aims of the Cassini spacecraft is to characterize in detail the interaction of the solar wind with the Saturnian system. The Cassini Plasma Spectrometer (CAPS) addresses this aim by measuring the plasma particles, ions and electrons, with a suite of three complementary sensors. One of these, the Electron Spectrometer (ELS), will m…
On the mass-loss of PG1159 stars
Rauch, T.; Dreizler, S.; Koesterke, L.
The winds of the four PG1159 stars NGC7094, NGC246, K1-16 and RXJ2117.1+3412 are investigated by means of non-LTE models for spherically expanding atmospheres. Based on the results of recent plane-parallel non-LTE analyses, several individual models with various mass-loss rates are calculated. Synthetic profiles of the C Iv resonance line are comp…