Search Publications
Discovery of Another Peculiar Radial Distribution of Blue Stragglers in Globular Clusters: The Case of 47 Tucanae
Ferraro, Francesco R.; Sills, Alison; Sabbi, Elena +3 more
We have used the high-resolution Wide Field Planetary Camera (WFPC2) on the Hubble Space Telescope (HST) and wide-field ground-based observations to construct a catalog of blue straggler stars (BSSs) in the globular cluster 47 Tuc spanning the entire radial extent of the cluster. The BSS distribution is highly peaked in the cluster center, rapidly…
Photometric Redshifts for Galaxies in the GOODS Southern Field
Cimatti, A.; Daddi, E.; Wolf, C. +19 more
We use extensive multiwavelength photometric data from the Great Observatories Origins Deep Survey to estimate photometric redshifts for a sample of 434 galaxies with spectroscopic redshifts in the Chandra Deep Field-South. Using the Bayesian method, which incorporates redshift/magnitude priors, we estimate photometric redshifts for galaxies in th…
The Structure of the Local Interstellar Medium. II. Observations of D I, C II, N I, O I, Al II, and Si II toward Stars within 100 Parsecs
Redfield, Seth; Linsky, Jeffrey L.
Moderate- and high-resolution measurements (λ/Δλ>~40,000) of interstellar resonance lines of D I, C II, N I, O I, Al II, and Si II (hereafter called light ions) are presented for all available observed targets located within 100 pc that also have high-resolution observations of interstellar Fe II or Mg II (heavy ions) lines. All spectra were ob…
The Association of Big Flares and Coronal Mass Ejections: What Is the Role of Magnetic Helicity?
Andrews, M. D.; Nindos, A.
Recently, M. D. Andrews found that approximately 40% of M-class flares between 1996 and 1999, classified according to GOES X-ray flux, are not associated with coronal mass ejections (CMEs). Using 133 events from his data set for which suitable photospheric magnetograms and coronal images were available, we studied the preflare coronal helicity of …
The Origin of Postflare Loops
Warren, H. P.; Sheeley, N. R., Jr.; Wang, Y. -M.
We apply a tracking technique, previously developed to study motions in the outer corona by Sheeley, Walters, Wang, and Howard, to 195 Å filtergrams obtained with the Transition Region and Coronal Explorer (TRACE) satellite and obtain height-time maps of the motions in the hot (10-20 MK) plasma clouds above postflare loop systems. These maps indic…
A New Probe of the Planet-forming Region in T Tauri Disks
Herczeg, Gregory J.; Russell, Ray W.; Qi, Chunhua +9 more
We present new observations of the far-ultraviolet (FUV; 1100-2200 Å) radiation field and the near- to mid-IR (3-13.5 µm) spectral energy distribution (SED) of a sample of T Tauri stars selected on the basis of bright molecular disks (GM Aur, DM Tau, and LkCa 15). In each source we find evidence for Lyα-induced H2 fluorescence and…
E+A Galaxies and the Formation of Early-Type Galaxies at z~0
Lauer, Tod R.; Zabludoff, Ann I.; Zaritsky, Dennis +2 more
E+A galaxies, whose spectra have deep Balmer absorption lines but no significant [O II] emission, are the best candidates for an evolutionary link between star-forming, gas-rich galaxies and quiescent, gas-poor galaxies. However, their current morphologies are not well known. We present Hubble Space Telescope WFPC2 observations of the five bluest …
Coronal Heating through Braiding of Magnetic Field Lines
Peter, Hardi; Gudiksen, Boris V.; Nordlund, Åke
Cool stars such as our Sun are surrounded by a million degree hot outer atmosphere, the corona. For more than 60 years, the physical nature of the processes heating the corona to temperatures well in excess of those on the stellar surface have remained puzzling. Recent progress in observational techniques and numerical modeling now opens a new win…
Imaging X-Ray, Optical, and Infrared Observations of the Transient Anomalous X-Ray Pulsar XTE J1810-197
Gotthelf, E. V.; Halpern, J. P.; Buxton, M. +1 more
We report X-ray imaging, timing, and spectral studies of XTE J1810-197, a 5.54 s pulsar discovered by Ibrahim and coworkers in recent Rossi X-Ray Timing Explorer (RXTE) observations. In a set of short exposures with the High Resolution Camera on board the Chandra X-Ray Observatory, we detect a strongly modulated signal (55%+/-4% pulsed fraction) w…
Ultraviolet Emission from the Millisecond Pulsar J0437-4715
Pavlov, George G.; Kargaltsev, Oleg; Romani, Roger W.
We observed PSR J0437-4715 with the FUV-MAMA detector of the Space Telescope Imaging Spectrometer (STIS) to measure the pulsar's spectrum and pulsations. For the first time, UV emission from a millisecond pulsar has been detected. The measured flux, (2.0+/-0.2)×10-15 ergs s-1 cm-2 in the 1150-1700 Å range, correspo…