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Temperature and density diagnostics of quiet Sun and active regions observed with CDS NIS
Landini, M.; Landi, E.
We study the Differential Emission Measure distribution of two pairs of active and quiet regions of the solar atmosphere, observed by CDS Normal Incidence Spectrometer (NIS) on SOHO, and investigate their temperature and density structure . Use is made of the Arcetri Method (Landi & Landini 1997) for DEM and density diagnostics. An iterative m…
Isotopic Composition of Solar Wind Nitrogen: First In Situ Determination with the CELIAS/MTOF Spectrometer on board SOHO
Bochsler, P.; Geiss, J.; Ipavich, F. M. +6 more
Using the high-resolution Mass Time-of-Flight (MTOF) spectrometer of the Charge, Element, and Isotope Analysis System (CELIAS) experiment on board the Solar and Heliospheric Observatory (SOHO), we have determined the solar wind isotope abundance ratio 14N/15N = 200+/-55 (1 σ error), suggesting that the relative abundance of <…
Solar Wind at 6.8 Solar Radii from UVCS Observation of Comet C/1996Y1
Raymond, John C.; Ciaravella, A.; Fineschi, S. +10 more
The comet C/1996Y1, a member of the Kreutz family of Sun-grazing comets, was observed with the Ultraviolet Coronagraph Spectrometer (UVCS) aboard the Solar and Heliospheric Observatory (SOHO) satellite. The Lyα line profile and spatial distribution are interpreted in terms of the theory of bow shocks driven by mass-loading. At the time of the obse…
Is There a Difference in Luminosity between Field and Cluster RR Lyrae Variables?
Catelan, Marcio
Recent Hipparcos results have lent support to the idea that RR Lyrae variables in the halo field and in globular clusters differ in luminosity by ~0.2 mag. In this Letter, we study the pulsation properties of RR Lyrae variables in clusters with distances determined via main-sequence fitting to Hipparcos parallaxes for field subdwarfs and compare t…
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…