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Galactic Interior Motions Derived from HIPPARCOS Proper Motions. I. Young Disk Population
Zhu, Zi; Miyamoto, Masanori
Analyzing Hipparcos proper motions of 1352 O-B5 stars other than the Gould belt stars, which are representative of the young disk population, we have found a clear stellar warping motion that is a systematic rotation +3.8 +/- 1.1 km s^-1 kpc^-1 of stars about the axis pointing to the Galactic center in the sense of increasing the inclination of th…
The edge-on spiral gravitational lens B1600+434
Koopmans, L. V. E.; Jackson, N.; de Bruyn, A. G.
We present new observations of the gravitational lens (GL) system B1600+434, strongly suggesting that the lens is an edge-on spiral galaxy. These observations are used to constrain the mass model of the system, in particular the oblateness and velocity dispersion of the dark matter halo around the lensing galaxy. From an analytical model we find a…
Jet-induced Shocks in 3C 171: An Intermediate-Redshift Analog of High-Redshift Radio Galaxies
Tadhunter, C. N.; Axon, D. J.; Robinson, A. +2 more
We present spectroscopic observations of the extended emission-line region (EELR) aligned with the radio axis of the powerful radio galaxy 3C 171. The results obtained from a detailed analysis of the observational data show that shocks induced by jet-cloud interactions have a dramatic effect on the extended line-emitting gas. The evidence for shoc…
Evidence for water ice and estimate of dust production rate in comet Hale-Bopp at 2.9 AU from the Sun
Altieri, B.; Keller, H. U.; Lellouch, E. +7 more
We report observational evidence for water ice in comet C/1995 O1 (Hale-Bopp) when it was at 2.9 AU from the Sun, from emission features at 44 and 65 mu m, and possibly an absorption feature at 3.1 mu m, observed with ISO/LWS and PHT. We find that icy grains have mean radii of 15 mu m within a factor of 2, lifetimes of ~ 2 days, a temperature of ~…
Hyperfine Induced Transitions as Diagnostics of Isotopic Composition and Densities of Low-Density Plasmas
Judge, Philip G.; Jönsson, Per; Brage, Tomas +5 more
The J = 0 --> J' = 0 radiative transitions, usually viewed as allowed through two-photon decay, may also be induced by the hyperfine (HPF) interaction in atoms or ions having a nonzero nuclear spin. We compute new and review existing decay rates for the nsnp 3PoJ --> ns2 1SJ'=0
Reobservation of Close QSO Groups: The Size Evolution and Shape of Lyα Forest Absorbers
Crotts, Arlin P. S.; Fang, Yihu
In order to study the size and shape of the absorbers that lie in front of the QSOs, in particular the Lyα forest, we present an analysis of 785 absorption lines in the spectra of five QSOs in close groupings: a pair (LB 9605: 1517+2357 at z = 1.834 and LB 9612: 1517+2356 at z = 1.903, with a separation of 102" between them) and a triplet (KP 76: …
OH in Saturn's magnetosphere: Observations and implications
Richardson, J. D.; McGrath, M. A.; Eviatar, A. +1 more
The discovery of OH in Saturn's inner magnetosphere changed our view of this region from one where plasma dominated the physics to one where neutrals are dominant. We revisit Hubble Space Telescope observations of OH and derive revised OH brightnesses for observations in 1992, 1994, and 1995. These OH observations as well as Voyager observations a…
The Local ISM and Its Interaction with the Winds of Nearby Late-Type Stars
Wood, Brian E.; Linsky, Jeffrey L.
We present new Goddard High-Resolution Spectrograph (GHRS) observations of the Lyα and Mg II absorption lines seen toward the nearby stars 61 Cyg A and 40 Eri A. We use these data to measure interstellar properties along these lines of sight and to search for evidence of circumstellar hydrogen walls, which are produced by collisions between the st…
The absolute magnitude of field metal-poor horizontal branch stars
Gratton, Raffaele G.
Hipparcos satellite parallaxes for 22 metal-poor field horizontal branch stars with V_0<9 are used to derive their absolute magnitude. The weighted mean value is M_V=+0.69+/-0.10 for an average metallicity of [Fe/H]=-1.41 a somewhat brighter average magnitude of M_V=+0.60+/-0.12 for an average metallicity of [Fe/H]=-1.51 is obtained by eliminat…
Hubble Space Telescope Detection of Optical Companions of WR 86, WR 146, and WR 147: Wind Collision Model Confirmed
Zurek, David R.; Moffat, Anthony F. J.; Wallace, Debra J. +2 more
Hubble Space Telescope (HST) Wide Field Planetary Camera 2 images of the rado-binary Wolf-Rayet stars WR 146 and WR 147, as well as the 0.2" visual binary WR 86, resolve each of them into two very close optical components. The colors of these optical pairs are similar, indicating that they are likely to be physically bound WR + OB systems at the s…