Search Publications
The Abundance of Mg in the Interstellar Medium
Fitzpatrick, Edward L.
An empirical determination of the f-values of the far-UV Mg II λλ1239, 1240 lines is reported. The strong near-UV Mg II λλ2796, 2803 lines are generally highly saturated along most interstellar sight lines outside the local interstellar medium (ISM) and usually yield extremely uncertain estimates of Mg+ column densities in interstellar …
The modelling of the latitude dependence of cosmic ray protons and electrons in the inner heliosphere
Potgieter, M. S.; Heber, B.; Ferrando, P. +1 more
Observations during the fast latitude scan of Ulysses show that the latitude dependence of cosmic ray protons is significantly less than predicted by drift models which were based on the Parker geometry for the heliospheric magnetic field (HMF) and diffusion coefficients ~ 1/B_p. Recent modeling with a modified HMF and enhanced turbulence in the p…
Damped Lyalpha Absorption Associated with an Early-Type Galaxy at Redshift z=0.16377.
Meyer, David M.; Chen, Hsiao-Wen; Savaglio, Sandra +8 more
We report new HST and ground-based observations of a damped Lyα absorption system toward the QSO 0850+4400. The redshift of the absorption system is ζ=0.l63770±0.000054 and the neutral hydrogen column density of the absorption system is log N=19.81±0.04 cm-2. The absorption system is by far the lowest redshift confirmed damped Lyα absor…
Pulsations and Accretion Geometry in YY Draconis: A Study Based on Hubble Space Telescope Observations
Thorstensen, John R.; Hellier, Coel; Haswell, Carole A. +2 more
We present 1 Å resolution fast ultraviolet spectroscopy of YY Dra, coordinated U, B, V, R, and I photometry, and Hα spectroscopy. The UV continuum is strongly pulsed: we found 16% semiamplitude pulses with period 264.7(1) s; there was no evidence for power at twice this period. The UBV pulses are in phase with the UV continuum pulsation. A color t…
The Hourglass Nebulae of Sher 25 and SN 1987A: Two of a Kind? 1
Grebel, Eva K.; Brandner, Wolfgang; Chu, You-Hua +2 more
We have performed a detailed study of the morphology and kinematics of the hourglass-shaped nebula around the blue supergiant Sher 25 in the galactic giant H II region NGC 3603. Near-infrared high-resolution adaptive optics images in the Br gamma line and HST/NICMOS images in the He I 1.08 mu m line were compared with isovelocity maps in the H alp…
Deep HST V- and I-Band Observations of Two Globular Clusters in the Halo of M31.
Richer, Harvey B.; Fahlman, Gregory G.; Holland, Stephen
We present deep (V∼=27) V- and I-band stellar photometry of G302 and G312, two globular star clusters in the halo of M31. These data were obtained using the Hubble Space Telescope's Wide Field/Planetary Camera 2. We find iron abundances of [Fe/H]= -1.85±0.12 for G302 and [Fe/H]=-0.56±0.03 for G312, consistent with spectroscopic measurements. The c…
Association of Extreme-Ultraviolet Imaging Telescope (EIT) Polar Plumes with Mixed-Polarity Magnetic Network
Michels, D. J.; Gurman, J. B.; Delaboudinière, J. -P. +18 more
SOHO EIT spectroheliograms showing the polar coronal holes during the present sunspot minimum are compared with National Solar Observatory (Kitt Peak) magnetograms taken in Fe I λ8688 and Ca II λ8542. The chromospheric λ8542 magnetograms, obtained on a routine, near-daily basis since 1996 June, reveal the Sun's strong polar fields with remarkable …
The Nuclear Region of NGC 1068: High-Accuracy Alignment of the Optical and Radio Emission
Macchetto, F. D.; Capetti, A.; Lattanzi, M. G.
We present the results of a campaign to obtain an accurate registration of Hubble Space Telescope (HST) and MERLIN images of NGC 1068, the prototypical Seyfert 2 galaxy. The final registration is accurate to 100 mas.
A strong anticorrelation between radio and optical emission is revealed; in particular, the radio jet lies on a region of relat…Titan's North-South Asymmetry from HST and Voyager Imaging: Comparison with Models and Ground-Based Photometry
Karkoschka, Erich; Lorenz, Ralph D.; Lemmon, Mark T. +3 more
New measurements of Titan's hemispheric brightness asymmetry from HST images from 260 to 1040 nm show that the contrast is strongest near 450 nm (blue) and, with the opposite sign, at 889 nm (methane band). Comparison with a full Titan year of disk-integrated albedo data indicates that the seasonal cycle in asymmetry is smooth, but is insufficient…
The morphological segregation of galaxies in clusters. III. The distant cluster CL 0939+4713 (Abell 851).
Andreon, S.; Davoust, E.; Heim, T.
We have performed an isophotal analysis of galaxies in the distant (z=0.4) cluster Cl0939+4713 (Abell 851), using post-refurbished Hubble Space Telescope images. Morphological type estimates for the galaxies are given. A rigorous comparison of the properties of the types shows that early-type galaxies in Cl0939+4713 are, within the present statist…