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Center-to-limb line width measurements of solar chromospheric, transition region and coronal lines
Doyle, J. G.; Wilhelm, K.; Erdelyi, R. +1 more
Line widths derived from observational data obtained by SUMER onboard SOHO in August 1996 at disk center and at the limb are used to confront those derived via assuming Alfven and/or magneto-acoustic wave heating. The observational data clearly shows a center-to-limb variation in the upper chromospheric and transition region lines, with only a mar…
Long-lived giant cells detected at the surface of the Sun
Scherrer, P. H.; Duvall, T. L.; Beck, J. G.
Giant convective cells have been predicted to exist in the Sun. Such cells should span the entire zone unstable to convective motions - now known to cover the outer 29 per cent of the Sun's radius - and could be dredging up the magnetic flux that is thought to be the source of solar activity (sunspots). Several studies have failed to detect these …
Wide Field Planetary Camera 2 Observations of the Brown Dwarf Gliese 229B: Optical Colors and Orbital Motion
Kulkarni, S. R.; Golimowski, D. A.; Burrows, C. J. +2 more
Three-epoch observations of the M1 V-plus-brown dwarf system Gliese 229AB using the Hubble Space Telescope's Wide Field Planetary Camera 2 (WFPC2) are reported. Relative astrometric measurements spanning 1 year confirm the common proper motion of the pair and reveal the first evidence of orbital motion. The radial and azimuthal components of Gl 22…
The equatorial disc of the Be star X Persei
Waters, L. B. F. M.; de Martino, D.; Boogert, A. C. A. +4 more
We study the long-term behaviour of the equatorial disc of the Be/X-ray binary X Persei (X Per), combining new low-resolution IUE spectra and IR photometry with UV, optical and IR observations collected from the literature. We find that the near-UV continuum level of X Per varies along with the optical brightness. From the UV observations, we also…
The absolute magnitude of the early type MK standards from HIPPARCOS parallaxes
Gomez, A. E.; Jaschek, C.
We analyse the standards of the MK system with the help of Hipparcos parallaxes, using only stars for which the error of the absolute magnitude is <= 0.3 mag. We find that the main sequence is a wide band and that, although in general giants and dwarfs have different absolute magnitudes, the separation between luminosity classes V and III is no…
On the Association of Gamma-Ray Bursts with Supernovae
Galama, T. J.; Hurley, K.; Kouveliotou, C. +7 more
The recent discovery of a supernova (SN 1998bw) seemingly associated with GRB 980425 adds a new twist to the decades-old debate over the origin of gamma-ray bursts. To investigate the possibility that some (or all) bursts are associated with supernovae, we performed a systematic search for temporal/angular correlations using catalogs of BATSE and …
High-Resolution Near-Infrared Imaging of the Orion 114-426 Silhouette Disk
Schneider, Glenn; Rieke, Marcia; Bally, John +6 more
We present the first high-resolution near-infrared images of the edge-on silhouette circumstellar disk, Orion 114-426, made using NICMOS on the Hubble Space Telescope. Images taken against the bright nebular background of the ionized hydrogen Paα line at 1.87 µm show the major axis of the disk to be approximately 20% smaller than at 0.6 &mic…
The shock structure in the protoplanetary nebula M1-92: imaging of atomic and H_2 line emission
Sahai, R.; Alcolea, J.; Bujarrabal, V. +2 more
We present HST imaging of continuum (5500 Angstroms) and atomic line (Hα , [OI] 6300 Angstroms, [SII] 6717 and 6731 Angstroms, and [OIII] 5007 Angstroms) emissions in the protoplanetary nebula M 1-92. Ground based imaging of 2$() µm continuum and H_2 ro-vibrational (S(1) v=3D1-0 and v=3D2-1 lines) emission has been also performed. The 5500 A…
The Coronae of Moderate-Mass Giants in the Hertzsprung Gap and the Clump
Ayres, Thomas R.; Brown, Alexander; Wood, Brian E. +3 more
We have used the Röentgensatellit (ROSAT), the Extreme Ultraviolet Explorer (EUVE), and the Hubble Space Telescope (HST) to measure X-ray and ultraviolet emissions of moderate-mass (~2-3 M⊙) giants in the Hertzsprung gap (spectral types early F to mid-G) and the post-helium flash ``clump'' (~G8-K0). Our motivation was to document the ev…
Non-parametric reconstruction of cluster mass distribution from strong lensing: modelling Abell 370.
Saha, Prasenjit; Williams, Liliya L. R.; Abdelsalam, Hanadi M.
The authors describe a new non-parametric technique for reconstructing the mass distribution in galaxy clusters with strong lensing, i.e. from multiple images of background galaxies. The observed positions and redshifts of the images are considered as rigid constraints, and through the lens (ray-trace) equation they provide us with linear constrai…