Search Publications
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…
First Results from SWAN Lyman α solar wind mapper on SOHO
Schmidt, W.; Bertaux, J. L.; Lallement, R. +7 more
After one year of almost flawless operation on board the SOHO spacecraft poised at L1 Lagrange point, we report the main features of SWAN observations. SWAN is mainly dedicated to the monitoring of the latitude distribution of the solar wind by the Lα method. Maps of sky Lα emissions were recorded througout the year. The region of maximum emission…
The Electron Drift Instrument for Cluster
Simpson, D.; Baumjohann, W.; Torbert, R. B. +20 more
Kinematic ages of OB associations
Brown, A. G. A.; de Zeeuw, P. T.; Dekker, G.
Astrometric data from the HIPPARCOS mission include measurements of early-type stars in nearly all OB associations within 1kpc from the Sun, and are available as of 1996. In anticipation thereof we studied the determination of kinematic ages and initial sizes of OB associations. These studies have traditionally been done using proper motion data. …
Active Regions Observed in Extreme Ultraviolet Light by the Coronal Diagnostic Spectrometer on SOHO
Young, P. R.; Mason, H. E.; Harrison, R. A. +4 more
We present observations of five active regions made by the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO). CDS observes the Sun in the extreme ultraviolet range 150-780 Å. Examples of active region loops seen in spectral lines emitted at various temperatures are shown. Several classes of loops are identified…
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…