Search Publications
The Host Galaxy of GRB 990123
Piro, L.; Frontera, F.; Harrison, F. A. +20 more
We present deep images of the field of GRB 990123 obtained in a broadband UV/visible bandpass with the Hubble Space Telescope (HST) and deep near-infrared images obtained with the Keck I 10 m telescope. The HST image reveals that the optical transient (OT) is offset by 0.67" (5.8 kpc in projection) from an extended, apparently interacting galaxy. …
Faint, Moving Objects in the Hubble Deep Field: Components of the Dark Halo?
Ibata, Rodrigo A.; Gilliland, Ronald L.; Richer, Harvey B. +1 more
The deepest optical image of the sky, the Hubble Deep Field, obtained with the Hubble Space Telescope in 1995 December, has been compared to a similar image taken in 1997 December. Two very faint, blue, isolated, and unresolved objects are found to display a substantial apparent proper motion, 23+/-5 and 26+/-5 mas yr-1 a further three …
Filament Eruptions near Emerging Bipoles
Sheeley, N. R., Jr.; Wang, Y. -M.
It has been suggested in previous studies that quiescent prominences and filaments erupt preferentially in the vicinity of emerging magnetic flux. We describe three such filament eruptions observed during 1998 with the Extreme-ultraviolet Imaging Telescope on the Solar and Heliospheric Observatory. Comparison with magnetograms and with potential f…
CO Band Head Spectroscopy of IC 342: Mass and Age of the Nuclear Star Cluster
Böker, Torsten; van der Marel, Roeland P.; Vacca, William D.
We have used the NASA Infrared Telescope Facility (IRTF) to observe the nuclear stellar cluster in the nearby, face-on, giant Scd spiral IC 342. From high-resolution (lambda/Deltalambda=21,500) spectra of the ^12CO (2-0) band head at 2.3 mum, we derive a line-of-sight stellar velocity dispersion sigma=(33+/-3) km s^-1. To interpret this observatio…
Detection of moving groups among early type stars
Figueras, F.; Torra, J.; Chen, B. +1 more
Our procedure to detect moving groups in the solar neighbourhood \cite{chen} in the four-dimensional space of the stellar velocity components and age has been improved. The method, which takes advantadge of non-parametric estimators of density distribution to avoid any a priori knowledge of the kinematic properties of these stellar groups, now inc…
Stellar Populations at the Center of IC 1613
Cole, Andrew A.; Ballester, Gilda E.; Krist, John E. +18 more
We have observed the center of the Local Group dwarf irregular galaxy IC 1613 with the WFPC2 aboard the Hubble Space Telescope in the F439W, F555W, and F814W filters. We analyze the resulting color-magnitude diagrams (CMDs) using the main-sequence and giant-branch luminosity functions and comparisons with theoretical stellar models to derive a pre…
Discovery of a massive equatorial torus in the η Carinae stellar system
de Graauw, Th.; Waters, L. B. F. M.; Mutschke, H. +10 more
The enigmatic object η Carinae is believed to represent an important, but short-lived, unstable phase in the life of the most massive stars, occurring shortly before they explode as supernovae or collapse directly to black holes. The putative binary system believed to constitute η Carinae survived an outburst in the previous century that lasted 20…
Self-consistent Alfvén-wave transmission and test-particle acceleration at parallel shocks
Vainio, R.; Schlickeiser, R.
The transmission of Alfvén waves at parallel shocks is treated self-consistently, i.e., taking the pressure and energy flux exerted by the waves into account when determining the shock's gas compression ratio. The resulting test-particle acceleration and transport parameters at the shock are shown to be functions of five parameters: the Alfvénic M…
Speckle Interferometry of New and Problem HIPPARCOS Binaries
Mason, Brian D.; ten Brummelaar, Theo; Barry, Donald J. +7 more
The ESA Hipparcos satellite made measurements of over 12,000 double stars and discovered 3406 new systems. In addition to these, 4706 entries in the Hipparcos Catalogue correspond to double star solutions that did not provide the classical parameters of separation and position angle (rho,theta) but were the so-called problem stars, flagged ``G,'' …
The Interaction of New and Old Magnetic Fluxes at the Beginning of Solar Cycle 23
Kosovichev, A. G.; Benevolenskaya, E. E.; Hoeksema, J. T. +1 more
The 11 yr cycle of solar activity follows Hale's law by reversing the magnetic polarity of leading and following sunspots in bipolar regions during the minima of activity. In the 1996-1997 solar minimum, most solar activity emerged in narrow longitudinal zones--``active longitudes'' but over a range in latitude. Investigating the distribution of s…