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HSTUV measurements of wind structure and velocities in Local Group OB stars
Crowther, Paul A.; Prinja, Raman K.
Archival HST FOS and GHRS data sets have been used to collect ultraviolet evidence for large- and small-scale stellar wind structure in extragalactic Local Group OB stars (i.e. SMC, LMC including R136, M31, M33 and NGC 6822). By comparison with previous studies of Galactic OB stars, wind activity is principally diagnosed in individual spectrograms…
Electron temperature in the solar wind: Generic radial variation from kinetic collisionless models
Issautier, Karine; Meyer-Vernet, Nicole
We calculate analytically the radial profile of the average electron temperature in the solar wind with a kinetic collisionless model. The electron temperature profile at large distances r is the sum of a term ~r-4/3 plus a constant, with both terms of the same order of magnitude near r~1AU. This result is generic as it is weakly depend…
A New Look at Carbon Abundances in Planetary Nebulae. III. DDDM1, IC 3568, IC 4593, NGC 6210, NGC 6720, NGC 6826, and NGC 7009
Henry, R. B. C.; Kwitter, K. B.
This paper is the third in a series reporting on a study of carbon abundances in a carefully chosen sample of planetary nebulae representing a large range in progenitor mass and metallicity. We make use of the IUE Final Archive database containing consistently reduced spectra to measure line strengths of C III] λ1909 along with numerous other UV l…
Far-infrared emission of intracluster dust in the Coma galaxy cluster
Lemke, D.; Haas, M.; Mattila, K. +2 more
The ISOPHOT C200 camera aboard ISO has been used to observe the extended far infrared (FIR) emission from the Coma cluster of galaxies. Two scans with 48arcmin length across the cluster, each at 120 microns and 185 microns , were obtained at crossing position angles. The profiles of the surface brightness ratio I_120 microns / I_185 microns along …
On the rotation-activity correlation for active binary stars
Doyle, J. G.; Mitrou, C. K.; Gunn, A. G.
We present an investigation of rotation-activity correlations using International Ultraviolet Explorer (IUE) SWP measurements of the Civ emission line at 1550Angstroms for 72 active binary systems. We use a standard stellar evolution code to derive non-empirical Rossby numbers, R_0, for each star in our sample and compare the resulting Civ rotatio…
Mass determination of astrometric binaries with Hipparcos. II. Selection of candidates and results
Mignard, F.; Martin, C.
In a previous paper (\cite{Mar97}) we have shown that for double stars with orbital periods smaller than about 25 years, it was possible to determine from the Hipparcos data, the mass ratio B of the components or the difference between the mass and intensity ratios, beta -B, provided the orbital elements of the relative orbit are available. From a…
Evidence for a Physically Compact Narrow-Line Region in the Seyfert 1 Galaxy NGC 5548
Peterson, Bradley M.; Filippenko, Alexei V.; Crenshaw, D. Michael +1 more
We have combined Hubble Space Telescope/Faint Object Spectrograph and ground-based spectra of the Seyfert 1 galaxy NGC 5548 to study the narrow emission lines over the 1200-10000 Å region. All of the spectra were obtained when the broad emission line and continuum fluxes were at a historically low level, allowing us to determine accurately the con…
Dynamic Behavior of the Upper Solar Atmosphere: Sumer/ Solar and Heliospheric Observatory Observations of Hydrogen Lyman Lines
Heinzel, Petr; Curdt, Werner
We present first observations of the temporal evolution of hydrogen Lyman lines, made by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory. A time series of about 33 minutes was obtained on 1997 June 5. The entrance slit has crossed a quiet-Sun region of 115.3" with two internetw…
Automatic Noise Estimation from the Multiresolution Support
Starck, Jean-Luc; Murtagh, Fionn
We describe an automated approach for determining the noise associated with astronomical images. Detector noise is ever present and must be determined for high-quality image filtering or compression. We also show that the method can be used for very high quality cosmic-ray hit removal. Our method is based on a multiresolution transform of the imag…
The evolutionary status of activity-selected solar-type stars and of T Tauri stars as derived from HIPPARCOS parallaxes: evidence for long-lived T Tauri disks?
D'Antona, F.; Micela, G.; Favata, F. +1 more
We have used the Hipparcos parallaxes to study the evolutionary status of a sample of stars with spectral types from late F to M0 (hereafter ``solar-type stars''), selected on the basis of their activity, mainly from Einstein-based surveys. The parallaxes have been used to place the objects in the H-R diagram, determining their age by comparison w…