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Collisional consequences of big interstellar grains
Grün, Eberhard; Landgraf, Markus
Identification by the Ulysses spacecraft of interstellar grains inside the planetary system provides a new window for the study of diffuse interstellar matter. Dust particles observed by Ulysses and confirmed by Galileo are more massive (>=10-13g) than the ``classical'' interstellar grains. Even bigger grains (~10-7g) were…
Stellar Structure and Evolution: Deductions from Hipparcos
Lebreton, Yveline
During the last decade, the understanding of fine features of the structure and evolution of stars has become possible as a result of enormous progress made in the acquisition of high-quality observational and experimental data, and of new developments and refinements in the theoretical description of stellar plasmas. The confrontation of high-qua…
Molecular Gas in the Powerful Radio Galaxies 3C 31 and 3C 264: Major or Minor Mergers?
Combes, Françoise; Lim, Jeremy; Leon, Stephane +1 more
We report the detection of 12CO (1-->0) and 12CO (2-->1) emission from the central regions (<~5-10 kpc) of the two powerful radio galaxies 3C 31 and 3C 264. Their individual CO emission exhibits a double-horned line profile that is characteristic of an inclined rotating disk with a central depression at the rising pa…
Modeling the Dynamics of Cometary Fragments: Application to Comet C/1996 B2 Hyakutake
Jones, G. H.; Levasseur-Regourd, A. C.; Klinger, J. +1 more
A tridimensional model for the dynamics of cometary fragments is presented, using a direct integration of the vectorial sum of forces. This model is validated with a complete set of images of Comet C/1996 B2 Hyakutake, between March 22 and April 6, 1996, UT, by making the assumption that the bright condensations visible in the near-nucleus coma we…
Charge state distributions of iron in impulsive solar flares: Importance of stripping effects
Ruffolo, D.; Kocharov, L.; Kartavykh, Y. Y. +2 more
A model of stochastic acceleration of heavy ions by Alfvén wave turbulence has been developed. It takes into account spatial diffusion, Coulomb losses, and the possibility of charge changes for ions during stochastic acceleration. The main processes influencing the ionic charge states are the stripping by thermal electrons and protons as constitue…
Interstellar and Circumstellar Optical and Ultraviolet Lines Toward SN 1998S
Bowen, David V.; Meyer, David M.; Roth, Katherine C. +1 more
We have observed SN 1998S which exploded in NGC 3877, with the Utrecht Echelle Spectrograph (6-7 km s-1 FWHM) at the William Herschel Telescope and with the E230M echelle of the Space Telescope Imaging Spectrograph (8 km s-1 FWHM) aboard the Hubble Space Telescope. Both data sets were obtained at two epochs, separated by 19 (…
A Near-Infrared Stellar Census of Blue Compact Dwarf Galaxies: NICMOS Detection of Red Giant Stars in the Wolf-Rayet Galaxy Markarian 178
Greggio, Laura; Hopp, Ulrich; Schulte-Ladbeck, Regina E. +1 more
We observed the blue compact dwarf/Wolf-Rayet galaxy Mrk 178 with the NICMOS camera aboard Hubble Space Telescope. The galaxy is well resolved into individual stars in the near-IR photometry in J and H yields color-magnitude diagrams containing 791 individual point sources. We discuss the stellar content, drawing particular attention to the interm…
Ultraviolet fluorescence lines of Fe II observed in satellite spectra of the symbiotic star RR Telescopii
Johansson, S.; Hartman, H.
By examining all emission lines of Fe II in high resolution satellite spectra of the symbiotic star RR Tel we have made a systematic study of fluorescence lines in the ultraviolet wavelength region 1200-3000 Ä. We list 33 energy levels of Fe II that are selectively excited in the stellar system by photons from strong lines of H, He II, Si III, O I…
Ca II activity and rotation in F-K evolved stars
Pasquini, L.; de Medeiros, J. R.; Girardi, L.
Ca II H and K high resolution observations for 60 evolved stars in the field and in 5 open clusters are presented. From these spectra chromospheric fluxes are derived, and a homogeneous sample of more than 100 giants is built adding data from the literature. In addition, for most stars, rotational velocities were derived from CORAVEL observations.…
Photometric Recovery of Crowded Stellar Fields Observed with HST/WFPC2 and the Effects of Confusion Noise on the Extragalactic Distance Scale
Freedman, Wendy L.; Stetson, Peter B.; Ferrarese, Laura +4 more
We explore the limits of photometric reductions of crowded stellar fields observed with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope. Two photometric procedures, based on the DoPHOT and DAOPHOT/ALLFRAME programs, are tested, and the effects of crowding, complex sky background, and cosmic-ray contamination are discussed…