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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…
Dust Spirals and Acoustic Noise in the Nucleus of the Galaxy NGC 2207
Elmegreen, B. G.; Brinks, E.; Elmegreen, D. M. +6 more
Observations with the Hubble Space Telescope reveal an irregular network of dust spiral arms in the nuclear region of the interacting disk galaxy NGC 2207. The spirals extend from ~50 to ~300 pc in galactocentric radius, with a projected width of ~20 pc. Radiative transfer calculations determine the gas properties of the spirals and the inner disk…
The ISO-SWS 2.4-45.2 Micron Spectrum Toward Orion IR c2
Cernicharo, José; Vandenbussche, Bart; van Dishoeck, Ewine F. +4 more
The complete infrared spectrum from 2.4 to 45.2 µm toward the prototypical massive star-forming region Orion IRc2 is presented, obtained with the Short Wavelength Spectrometer (SWS) on board the Infrared Space Observatory (ISO) at a resolving power λ/Δλ~1300-2500. A wealth of emission and absorption features is found, including H2…
Infrared array photometry of bulge globular clusters. I. Combined ground based JK and HST VI photometry of NGC 6553
Moneti, A.; Montegriffo, P.; Bica, E. +4 more
JK infrared photometry for the bulge globular cluster NGC 6553, combined with high resolution visual VI observations are presented and discussed in connection with the bulge metal rich population. The infrared data were taken with IRAC2 at ESO 2.2m telescope while the optical counterparts are from Hubble Space Telescope (HST). We find a mean magni…
HIPPARCOS and the age of the Galactic disc
Jimenez, Raul; Flynn, Chris; Kotoneva, Eira
We use the Hipparcos colour-magnitude diagram of field stars with Tycho colours to make a new minimum age estimate for the Galactic disc. The method is based on fits to the red envelope of subgiants in the Hipparcos colour-magnitude diagram with synthetic isochrones covering the range of disc metal abundance. The colours and luminosities of the is…