Search Publications
Blue Straggler Stars: A Direct Comparison of Star Counts and Population Ratios in Six Galactic Globular Clusters
Ferraro, Francesco R.; Sills, Alison; Paltrinieri, Barbara +2 more
The central regions of six Galactic globular clusters (GGCs) (M3, M80, M10, M13, M92, and NGC 288) have been imaged using HST-WFPC2 and the ultraviolet filters (F255W and F336W). The selected sample covers a large range in both central density (logρ0) and metallicity ([Fe/H]). In this paper, we present a direct cluster-to-cluster compar…
The INTEGRAL Burst Alert System
Götz, D.; Mereghetti, S.; Pedersen, H. +2 more
We describe the INTEGRAL Burst Alert System (IBAS): the automatic software for the rapid distribution of the coordinates of the Gamma-Ray Bursts detected by INTEGRAL. IBAS is implemented as a ground based system, working on the near-real time telemetry stream. During the first six months of operations, six GRB have been detected in the field of vi…
Continuous magnetic reconnection at Earth's magnetopause
Fuselier, S. A.; Mende, S. B.; Frey, H. U. +1 more
The most important process that allows solar-wind plasma to cross the magnetopause and enter Earth's magnetosphere is the merging between solar-wind and terrestrial magnetic fields of opposite sense-magnetic reconnection. It is at present not known whether reconnection can happen in a continuous fashion or whether it is always intermittent. Solar …
High-Resolution Spectroscopy of FU Orionis Stars
Herbig, G. H.; Duemmler, R.; Petrov, P. P.
High-resolution spectroscopy was obtained of the FU orionis stars FU Ori and V1057 Cyg between 1995 and 2002 with the SOFIN spectrograph at the Nordic Optical Telescope and with HIRES at Keck I. During these years FU Ori remained about 1 mag (in B) below its 1938-39 maximum brightness, but V1057 Cyg (B~10.5 at peak in 1970-1971) faded from about 1…
Gamma-ray emission from Wolf-Rayet binaries
Romero, G. E.; Benaglia, P.
In the colliding wind region of early-type binaries, electrons can be accelerated up to relativistic energies displaying power-law spectra, as demonstrated by the detection of non-thermal radio emission from several WR+OB systems. The particle acceleration region, located between the stars, is exposed to strong photon fields in such a way that inv…
Discovery of Early Optical Emission from GRB 021211
Peterson, B. A.; Price, P. A.; Harrison, F. A. +11 more
We report our discovery and early-time optical, near-infrared, and radio wavelength follow-up observations of the afterglow of the gamma-ray burst GRB 021211. Our optical observations, beginning 21 minutes after the burst trigger, demonstrate that the early afterglow of this burst is roughly 3 mag fainter than the afterglow of GRB 990123 at simila…
The Host Galaxies of Narrow-Line Seyfert 1 Galaxies: Evidence for Bar-Driven Fueling
Kraemer, S. B.; Crenshaw, D. M.; Gabel, J. R.
We present a study of the host galaxy morphologies of narrow- and broad-line Seyfert 1 galaxies (NLS1's and BLS1's) based on broadband optical images from the Hubble Space Telescope archives. We find that large-scale stellar bars, starting at ~1 kpc from the nucleus, are much more common in NLS1's than BLS1's. Furthermore, the fraction of NLS1 spi…
Low-Redshift Damped Lyα Galaxies toward the Quasars B2 0827+243, PKS 0952+179, PKS 1127-145, and PKS 1629+120
Turnshek, David A.; Rao, Sandhya M.; Bergeron, Jacqueline +3 more
We present optical and near-infrared ground-based imaging results on four low-redshift damped Lyα (DLA) galaxies. The corresponding DLA systems were discovered in our Hubble Space Telescope spectroscopic surveys for DLA lines in known strong Mg II absorption-line systems toward the quasars B2 0827+243 (zDLA=0.525), PKS 0952+179 (zD…
The remarkable rapid X-ray, ultraviolet, optical and infrared variability in the black hole XTE J1118+480
Chaty, S.; Cui, W.; Horne, Keith +6 more
The transient black-hole binary XTE J1118+480 exhibited dramatic rapid variability at all wavelengths which were suitably observed during its 2000 April-July outburst. We examine time-resolved X-ray, ultraviolet, optical and infrared data spanning the plateau phase of the outburst. We find that both X-ray and infrared bands show large amplitude va…
Weak-Field Magnetogram Calibration using Advanced Stokes Polarimeter Flux Density Maps - II. SOHO/MDI Full-Disk Mode Calibration
Lites, B. W.; Berger, T. E.
Cotemporal Ni i 676.8 nm full-disk magnetograms from the Michelson Doppler Interferometer (MDI) instrument on SOHO and the Advanced Stokes Polarimeter (ASP) are quantitatively compared using observations of active region AR 8218, a large negative polarity sunspot group observed at S20 W22 on 13 May 1998. MDI produces flux density estimates based o…