Search Publications
A VLT/FORS2 spectroscopic survey in the HDF-S
Fontana, A.; Vanzella, E.; Grazian, A. +6 more
We report on low-resolution multi-object spectroscopy of 65 objects from I(AB) =~ 20 to I(AB) =~ 25 in the HDF-S obtained with the VLT Focal Reducer/low dispersion Spectrograph (FORS2). 18 objects belong to the HDF-S proper, i.e. the WFPC2 deep area. 15 high-redshift galaxies with 2.0 < z < 3.5 (10 in the HDF-S proper) have been identified. …
Subsurface structure of sunspots
Kosovichev, A. G.
The subsurface structure of sunspots is probed by measuring travel-time delays of acoustic waves propagating beneath the spots, and using a helioseismic inversion method to infer the internal sound-speed perturbations and mass flows. The initial results obtained from the MDI instrument on SOHO reveal under sunspots zones of the relatively low soun…
Resonance Line Profile Calculations Based on Hydrodynamical Models of Cataclysmic Variable Winds
Kallman, Timothy R.; Drew, Janet E.; Hartley, Louise E. +1 more
We describe a method of calculating synthetic line profiles using a generalized version of the Sobolev approximation. We apply this method to calculate line profiles predicted by the models of two-dimensional line-driven winds from luminous disks due to Proga, Stone, & Drew. We describe the main properties of the model line profiles and compar…
X-rays from the jet in 3C 273 : Clues from the radio-optical spectra
Meisenheimer, K.; Jester, S.; Röser, H. -J. +1 more
Using new deep VLA and HST observations of the large-scale jet in 3C 273 matched to 0.3 arcsec resolution, we have detected excess near-ultraviolet emission (lambda 300 nm) above a synchrotron cutoff spectrum accounting for the emission from radio through optical (lambda lambda 3.6 cm-620 nm). This necessitates a two-component model for the emissi…
Halo-coronal mass ejections near the 23rd solar minimum: lift-off, inner heliosphere, and in situ (1 AU) signatures
Plunkett, S. P.; Michels, D. J.; Thompson, B. J. +6 more
The extreme ultraviolet (EUV) signatures of a solar lift-off, decametric and kilometric radio burst emissions and energetic particle (EP) inner heliospheric signatures of an interplanetary shock, and in situ identification of its driver through solar wind observations are discussed for 12 isolated halo coronal mass ejections (H-CMEs) occurring bet…
Measurements of Three-dimensional Coronal Magnetic Fields from Coordinated Extreme-Ultraviolet and Radio Observations of a Solar Active Region Sunspot
Landi, Enrico; Brosius, Jeffrey W.; Gopalswamy, N. +3 more
We observed NOAA Active Region 8108 around 1940 UT on 1997 November 18 with the Very Large Array and with three instruments aboard the NASA/ESA Solar and Heliospheric Observatory satellite, including the Coronal Diagnostic Spectrometer, the EUV Imaging Telescope, and the Michelson Doppler Imager. We used the right-hand and left-hand circularly pol…
Analytic and Numerical Models for the Knots along the HH 111 Jet
Velázquez, P. F.; Raga, A. C.; Noriega-Crespo, A. +2 more
We consider a model for HH 111 as a jet ejected with a sawtooth, time-dependent ejection velocity. Such a variability is suggested by the position-velocity (PV) diagrams obtained from Hubble Space Telescope observations. We calculate both analytic and numerical models describing the flow resulting from such an ejection velocity time variability. A…
Hubble Space Telescope Imaging in the Chandra Deep Field-South. II. WFPC2 Observations of an X-Ray Flux-limited Sample from the 1 Million Second Chandra Catalog
Grogin, Norman A.; Koekemoer, Anton M.; Marconi, A. +10 more
We present Hubble Space Telescope/WFPC2 observations of a well-defined sample of 40 X-ray sources with X-ray fluxes above the detection threshold of the full 1 Ms Chandra Deep Field-South (CDF-S). The sensitivity and spatial resolution of our HST observations are sufficient to detect the optical counterparts of 37 of the X-ray sources, yielding in…
Transition-Region Blinkers - II. Active-Region Properties
Harrison, R. A.; Parnell, C. E.; Bewsher, D.
The distribution and general properties of events identified in an active region that have the same characteristics as quiet-Sun blinkers are discussed and named `active-region blinkers'. The events are identified using an automated scheme `BLinker Identification Program' (BLIP) which was designed for and tested on quiet-Sun blinkers. Like quiet-S…
The Oldest Stars of the Extremely Metal-Poor Local Group Dwarf Irregular Galaxy Leo A
Greggio, Laura; Hopp, Ulrich; Schulte-Ladbeck, Regina E. +2 more
We present deep Hubble Space Telescope (HST) single-star photometry of Leo A in B, V, and I. Our new field of view is offset from the centrally located field observed by Tolstoy et al. in order to expose the halo population of this galaxy. We report the detection of metal-poor red horizontal branch stars, which demonstrate that Leo A is not a youn…