Search Publications
Large-Scale Dynamics of Active Regions and Small Photospheric Magnetic Features
Meunier, N.
This paper presents an analysis of the dynamics of magnetic features within and outside active regions using full-disk magnetograms obtained by the MDI (Michelson Doppler Imager) instrument on the SOHO spacecraft. The absence of distortion and the short time interval (96 minutes) between images allow us to calculate high-quality cross-correlations…
A Stellar Population Gradient in VII ZW 403: Implications for the Formation of Blue Compact Dwarf Galaxies
Greggio, Laura; Hopp, Ulrich; Schulte-Ladbeck, Regina E. +1 more
We present evidence for the existence of an old stellar halo in the blue compact dwarf galaxy VII Zw 403. VII Zw 403 is the first blue compact dwarf galaxy for which a clear spatial segregation of the resolved stellar content into a core-halo structure is detected. Multicolor Hubble Space Telescope WFPC2 (HST/WFPC2) observations indicate that acti…
The Mini-Active Galactic Nucleus at the Center of the Elliptical Galaxy NGC 4552 with Hubble Space Telescope
Cappellari, Michele; Renzini, Alvio; Greggio, Laura +4 more
The complex phenomenology shown by the UV-bright, variable spike first detected with the Hubble Space Telescope (HST) at the center of the otherwise normal galaxy NGC 4552 is further investigated with both HST imaging (FOC) and spectroscopy (FOS). HST/FOC images taken in 1991, 1993, and 1996 in the near-UV have been analyzed in a homogeneous fashi…
Multiple Velocity Components in the C IV Absorption Line of NGC 5548
Elvis, Martin; Mathur, Smita; Wilkes, Belinda
We have observed the much-studied Seyfert 1 galaxy NGC 5548 with the Goddard High-Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST). Our 14 ks observation covers the C IV emission line at a resolution of greater than 20,000. Our purpose was to study the absorption line found at lower resolution by IUE and the HST Faint Object Spec…
Helioseismic Images of an Active Region Complex
Braun, D. C.; Lindsey, C.
Helioseismic images of a large active region complex at a frequency of 5 mHz show a prominent halo of acoustic emission, which we call the ``acoustic glory,'' surrounding the active region. This feature is remarkably intense and contains small-scale elements of concentrated seismic emission which cluster in strings in nonmagnetic regions. Subsurfa…
Heating and Jet Formation by Hydrodynamic Cumulation in the Solar Atmosphere
Fludra, A.; Tarbell, T.; Ryutova, M. +1 more
The solar transition region is the site of supersonic plasma jets and sporadic radiative events, whose origin and physical nature have not been understood. Here we show that ubiquitous small-scale magnetic flux ``tubes,'' constantly emerging from subsurface layers, may cause the formation of plasma jets and a sporadic excess of temperature near th…
The Dusty Starburst Nucleus of M33
Gordon, Karl D.; Rieke, G. H.; Clayton, Geoffrey C. +2 more
We have thoroughly characterized the ultraviolet to near-infrared (0.15-2.2 µm) spectral energy distribution (SED) of the central parsec of the M33 nucleus through new infrared photometry and optical/near-infrared spectroscopy, combined with ultraviolet/optical observations from the literature and the Hubble Space Telescope archive. The SED …
A Highly Collimated Bipolar Outflow in a Proto-planetary Nebula: Hubble Space Telescope Imaging of HEN 401
Bujarrabal, V.; Sahai, Raghvendra; Zijlstra, A.
We have obtained high-resolution wide- and narrowband images of the bipolar proto-planetary nebula Hen 401 with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. Two very long (14.5"), cylindrical-shaped bipolar outflow lobes are seen in reflected light, each with a length/width ratio of ~7, probably the largest seen in a prot…
Hubble Space Telescope Observations of the Optical Jets of PKS 0521-365, 3C 371, and PKS 2201+044
Urry, C. Megan; Scarpa, Riccardo; Treves, Aldo +1 more
Hubble Space Telescope (HST) observations have led to the discovery of the optical counterpart of the radio jet of PKS 2201+044 and to a detailed analysis of the optical jets of PKS 0521-365 and 3C 371. At HST spatial resolution these jets are well resolved, displaying knotty morphologies. When compared with radio maps of appropriate resolution, a…
The Hubble Space Telescope Survey of BL Lacertae Objects: Gravitational Lens Candidates and Other Unusual Sources
Urry, C. Megan; O'Dowd, Matthew; Scarpa, Riccardo +4 more
We present Hubble Space Telescope (HST) observations of seven unusual objects from the HST ``snapshot survey'' of BL Lacertae objects, of which four are gravitational lens candidates. In three cases a double point source is observed: 0033+595, with 1.58" separation, and 0502+675 and 1440+122, each with ~0.3" separation. The last two also show one …