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The Variability and Spectrum of NGC 5548 in the Extreme Ultraviolet
Malkan, M. A.; Clavel, J.; Kriss, G. A. +8 more
We have measured the light curve and spectrum of NGC 5548 obtained with the Extreme Ultraviolet Explorer (EUVE) during a period when the galaxy was also intensively monitored with the Hubble Space Telescope, the International Ultraviolet Explorer, and ground-based telescopes. NGC 5548 was observed with EUVE for a total of about 20 days spread over…
Nuclear Spiral and Ring Star-forming Structures and the Starburst--Active Galactic Nucleus Connection in Barred Spirals NGC 3351 and NGC 4303
Colina, Luis; Alberdi, A.; Krabbe, A. +2 more
A high-resolution Hubble Space Telescope WFPC2 F218W UV image of the barred spiral NGC 4303 (classified as a LINER-type active galactic nucleus [AGN]) reveals for the first time the existence of a nuclear spiral structure of massive star-forming regions all the way down to the UV-bright unresolved core (size <= 8 pc) of an active galaxy.
T…Solar Wind Acceleration by Solitary Waves in Coronal Holes
Davila, J. M.; Ofman, L.
Coronal holes are well-known sources of the high-speed solar wind; however, the exact acceleration mechanism of the fast wind is still unknown. We solve numerically the time-dependent, nonlinear, resistive 2.5-dimensional MHD equations and find that solitary waves are generated in coronal holes nonlinearly by torsional Alfvén waves. The solitary w…
The Ionization Structure of the Narrow-Line Region of NGC 1068 and Its Relationship to the Extended Radio Emission
Macchetto, F. D.; Capetti, A.; Axon, D. J.
Hubble Space Telescope (HST)/WFPC2 imaging has been used to investigate the emission-line structure of the narrow-line region (NLR) of the Seyfert 2 galaxy NGC 1068 and its relationship to the extended radio emission. We find that the morphology and the ionization properties of the NLR of NGC 1068 are dominated by the interaction with the radio je…
S1040 in M67: A Post--Mass Transfer Binary with a Helium Core White Dwarf
Bergeron, P.; Stecher, T. P.; Di Stefano, R. +2 more
We have obtained spectra of the yellow giant S1040 in the open cluster M67 using the Goddard High-Resolution Spectrograph (GHRS) and the Faint Object Spectrograph on the Hubble Space Telescope. S1040 is a single-lined spectroscopic binary with a 42.8 day period that occupies a ``red straggler'' position in the M67 color-magnitude diagram (CMD), 0.…
The Intermediate-mass Stellar Population of the Large Magellanic Cloud Cluster NGC 1818 and the Universality of the Stellar Initial Mass Function
Grillmair, Carl J.; Holtzman, Jon A.; Light, Robert M. +1 more
We present stellar photometry from Hubble Space Telescope images of NGC 1818, a young populous star cluster in the Large Magellanic Cloud. The cluster stars in both the core and the outlying regions are well resolved, and the photometry extends to a V magnitude of 26, corresponding approximately to a K4 V star. With the use of isochrones, we compu…
Astrometric Detection of a Low-Mass Companion Orbiting the Star AB Doradus
White, G. L.; Arenou, F.; Lindegren, L. +19 more
We report submilliarcsecond-precise astrometric measurements for the late-type star AB Doradus via a combination of VLBI (very long baseline interferometry) and HIPPARCOS data. Our astrometric analysis results in the precise determination of the kinematics of this star, which reveals an orbital motion readily explained as caused by gravitational i…
Fundamental Stellar Parameters of γ2 Velorum from HIPPARCOS Data
Schaerer, Daniel; Schmutz, Werner; Grenon, Michel
We report parallax measurements by the HIPPARCOS satellite of γ2 Velorum and a few related objects. The distance of γ2 Vel is d = 258+41-31 pc, significantly smaller than the commonly adopted value to Vela OB2. For ζ Puppis d = 429+120-77 pc is in agreement with the canonical distan…
A Survey for Large-Image Separation Lensed Quasars
Maoz, Dan; Rix, Hans-Walter; Gould, Andrew +1 more
The statistics of gravitationally lensed quasars with multiple images in the 0.1"-7" range have been measured in various surveys. Little is known, however, about lensed-quasar statistics at larger image separations, which probe masses on the scale of galaxy clusters. We extend the results of the Hubble Space Telescope (HST) Snapshot Survey for Len…
The Star-grazing Extrasolar Comets in the HD 100546 System
Sitko, M. L.; Grady, C. A.; Bjorkman, Karen S. +4 more
Redshifted absorption profiles that resemble the high-velocity circumstellar gas features in the spectrum of β Pictoris have been detected in IUE data for the 10 Myr old Herbig Be star, HD 100546, on 1995 March 7. In addition to Mg II, Si II, and other refractory species similar to those seen in β Pic, the HD 100546 spectra are rich in accreting g…