Search Publications
Evidence for a Physically Compact Narrow-Line Region in the Seyfert 1 Galaxy NGC 5548
Peterson, Bradley M.; Filippenko, Alexei V.; Crenshaw, D. Michael +1 more
We have combined Hubble Space Telescope/Faint Object Spectrograph and ground-based spectra of the Seyfert 1 galaxy NGC 5548 to study the narrow emission lines over the 1200-10000 Å region. All of the spectra were obtained when the broad emission line and continuum fluxes were at a historically low level, allowing us to determine accurately the con…
Dynamic Behavior of the Upper Solar Atmosphere: Sumer/ Solar and Heliospheric Observatory Observations of Hydrogen Lyman Lines
Heinzel, Petr; Curdt, Werner
We present first observations of the temporal evolution of hydrogen Lyman lines, made by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory. A time series of about 33 minutes was obtained on 1997 June 5. The entrance slit has crossed a quiet-Sun region of 115.3" with two internetw…
High-Frequency Peaks in the Power Spectrum of Solar Velocity Observations from the GOLF Experiment
García, R. A.; Pallé, P. L.; Turck-Chièze, S. +9 more
The power spectrum of more than 630 days of full-disk solar velocity data, provided by the GOLF spectrophotometer aboard the Solar and Heliospheric Observatory, has revealed the presence of modelike structure well beyond the acoustic cutoff frequency for the solar atmosphere (νac~5.4 mHz). Similar data produced by full-disk instruments …
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…
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…
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…
The Opacity of Nearby Galaxies from Colors and Counts of Background Galaxies. I. The Synthetic Field Method and Its Application to NGC 4536 and NGC 3664
Ferguson, Henry C.; Calzetti, Daniela; Panagia, Nino +3 more
We describe a new direct method for determining the opacity of foreground galaxies that does not require any a priori assumptions about the spatial distribution or the reddening law of the obscuring material. The method is to measure the colors and counts of background galaxies that can be identified through the foreground system. The method is ca…
On Chromospheric Heating Mechanisms of ``Basal Flux'' Stars
Judge, P. G.; Carpenter, K. G.
Several pieces of evidence have been pieced together over recent years to support the notion that the chromospheric emission measured from stars with convection zones results in part from the upward propagation and dissipation of acoustic waves. One argument, based on a statistical analysis of available UV data of such stars across the H-R diagram…