Search Publications
WFPC2 Studies of the Crab Nebula. II. Ionization Structure of the Crab Filaments
Ballester, Gilda E.; Crisp, David; Holtzman, Jon A. +15 more
Narrowband images of the Crab Nebula taken with the Hubble Space Telescope (HST) WFPC2 show the morphology and ionization structure of the filaments in great detail. At HST resolution, low- and high-ionization emission from filaments in the Crab differ in two complementary respects. First, low-ionization emission is found to be concentrated in ver…
The Problem of HIPPARCOS Distances to Open Clusters. II. Constraints from Nearby Field Stars
Stauffer, John R.; Pinsonneault, Marc H.; Soderblom, David R. +4 more
This paper examines the discrepancy between distances to nearby open clusters as determined by parallaxes from Hipparcos compared to traditional main-sequence fitting. The biggest difference is seen for the Pleiades, and our hypothesis is that if the Hipparcos distance to the Pleiades is correct, then similar subluminous zero-age main-sequence (ZA…
Models of the ISO 3-µm Reflection Spectrum of Jupiter
Feuchtgruber, H.; Drossart, P.; Knacke, R. F. +3 more
A spectrum of Jupiter in the 3-µm region obtained with the Infrared Space Observatory (ISO) shows evidence for the long-sought spectral signature of NH3ice particles in the jovian atmosphere. We calculated Jupiter 3-µm reflection spectrum, including multiple scattering by spherical cloud particles. Models containing reflecti…
A Hubble Space Telescope Study of Extragalactic OB Associations
Macri, Lucas M.; Gibson, Brad K.; Stetson, Peter B. +9 more
We present a study of OB associations, identified by objective means, in seven spiral galaxies observed with the Hubble Space Telescope as part of the Key Project on the distance scale. The properties of the associations, including their size distribution and average diameter, and the luminosity function of their brightest stars, do not vary signi…
An Asymmetric Arcsecond Radio Jet from Circinus X-1
Wu, Kinwah; van Paradijs, Jan; Fender, Robert +4 more
In observations with the Australia Telescope Compact Array, we have resolved the radio counterpart of the unusual X-ray binary Circinus X-1 into an asymmetric, extended structure on arcsecond scales. In order to quantify the asymmetry, we have redetermined as accurately as possible both the optical and radio coordinates of the source. The extended…
The Intervening and Associated O VI Absorption-Line Systems in the Ultraviolet Spectrum of H1821+643
Tripp, Todd M.; Savage, Blair D.; Lu, Limin
GHRS and FOS ultraviolet spectra of the bright QSO H1821+643 (m_V = 14.2, z_em = 0.297) reveal the presence of strong O vi lambdalambda1031.93, 1037.62 absorption systems at z_abs = 0.225 and 0.297, the latter being at the redshift of the QSO itself. Ground-based galaxy redshift measurements by us and others reveal two emission-line galaxies near …
Physical Conditions in the Inner Narrow-Line Region of the Seyfert 2 Galaxy NGC 1068
Crenshaw, D. Michael; Kraemer, Steven B.; Ruiz, José R.
The physical conditions in the inner narrow-line region (NLR) of the Seyfert 2 galaxy NGC 1068 are examined using ultraviolet and optical spectra and photoionization models. The spectra are Hubble Space Telescope archive data obtained with the Faint Object Spectrograph (FOS). We selected spectra of four regions, taken through the 0.3" FOS aperture…
``Baade's Red Sheet'' Resolved into Stars with Hubble Space Telescope in the Blue Compact Dwarf Galaxy VII Zw 403
Hopp, Ulrich; Schulte-Ladbeck, Regina E.; Crone, Mary M.
Hubble Space Telescope Wide Field Planetary Camera 2 observations of the nearby blue compact dwarf galaxy VII Zw 403 (=UGC 6456) resolve single stars down to MI~-2.5, deep enough to identify red giants. This population has a more uniform spatial distribution than the young main-sequence stars and supergiants, forming the structure known…
Hubble Space Telescope Wide Field Planetary Camera 2 Observations of HH 1-2
Hester, J. Jeff; Stapelfeldt, Karl R.; Scowen, Paul A.
We present Hubble Space Telescope Wide Field Planetary Camera 2 images of the bipolar Herbig-Haro complex HH 1-2 in three emission lines (Hα, [S ii], and [O iii]) and one continuum band (F702W). In addition to showing the complex morphology of these objects, the WFPC2 data allow us to resolve the cooling and recombination regions behind radiative …
A Cepheid distance to the Fornax cluster and the local expansion rate of the Universe
Illingworth, Garth D.; Madore, Barry F.; Freedman, Wendy L. +13 more
Both galaxy distances and velocities are required for the determination of the expansion rate of the Universe, as described by the Hubble constant H0. The radial velocities of galaxies arise not just from this expansion but also from random components and large-scale flows. To reach out to distances dominated by the overall cosmic expan…