Search Publications
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…
The ISOPHOT far-infrared serendipity north ecliptic pole minisurvey
Kessler, M. F.; Burgdorf, M.; Lemke, D. +11 more
The ISOPHOT Serendipity Survey fills the otherwise unused slew time between ISO's fine pointings with measurements in an unexplored wavelength regime near 200 microns. In order to test point source extraction software, the completeness of the detected objects as well as the astrophysical content we investigate a 100 sq degr field near the North ec…
Photospheric metals in hot DA white dwarfs
Dreizler, S.; Wolff, B.; Koester, D. +1 more
Previous observations of the soft X-ray and EUV region with the Einstein, EXOSAT, and ROSAT satellites have indicated the presence of photospheric absorbers in most DA white dwarfs with {T_eff} ga 40000K. Several of these objects have now been observed with the Extreme Ultraviolet Explorer (EUVE). Since the detection of individual metal lines is r…
Global warming on Triton
Olkin, C. B.; Franz, O. G.; Buie, M. W. +11 more
Triton, Neptune's largest moon, has been predicted to undergo significant seasonal changes that would reveal themselves as changes in its mean frost temperature. But whether this temperature should at the present time be increasing, decreasing or constant depends on a number of parameters (such as the thermal properties of the surface, and frost m…
Molecular gas phase counterparts to solid state grain mantles features: implication for gas/grain chemistry
Boulanger, F.; Puget, J. -L.; Dartois, E. +4 more
We present ISO SWS (AOT6) observations of the protostellar object RAFGL 7009S. This source is particularly interesting for the characterisation of chemistry arising from grain surfaces and mantles, since the solid state features of many simple molecules such as H_2O, CO, CO_2, (13) CO_2 and CH_4 are detected, together with weaker features not yet …