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Oscillating Blue Stragglers in the Core of 47 Tucanae
Bono, Giuseppe; Gilliland, Ronald L.; Saha, Abhijit +5 more
Six SX Phe variables detected in a 39 hr time series of Hubble Space Telescope Planetary Camera exposures in the F336W (U) filter are discussed. Two of these stars show both the fundamental and first-overtone modes and are among the first double-mode SX Phe stars reported in globular clusters. One of the double-mode stars shows evidence for a thir…
HST images of a galaxy group at z=2.81, and the sizes of damped Lyalpha galaxies
Møller, P.; Warren, S. J.
We present Hubble Space Telescope (HST) WFPC2 observations in three bands (F450W=B, F467M and F814W=I) of a group of three galaxies at z=2.8 discovered in a ground-based narrow-band search for Lyalphaemission near the z=2.8 quasar PKS 0528-250. One of the galaxies is a damped Lyalpha(DLA) absorber and these observations bear on the relation betwee…
Measurement of the Abundance of Helium-3 in the Sun and in the Local Interstellar Cloud with SWICS on ULYSSES
Gloeckler, George; Geiss, Johannes
The abundance of 3He in the present day local interstellar cloud (LIC) and in the sun has important implications for the study of galactic evolution and for estimating the production of light nuclei in the early universe. Data from the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses is used to measure the isotopic ratio of helium (3He/4…
Numerical Simulations of Triggered Star Formation. I. Collapse of Dense Molecular Cloud Cores
Vanhala, Harri A. T.; Cameron, A. G. W.
Results from numerical simulations of shock waves impacting molecular cloud cores are presented. The three-dimensional smoothed particle hydrodynamics code used in the calculations includes effects from a varying adiabatic exponent, molecular, atomic, and dust cooling, as well as magnetic pseudofluid. The molecular cloud cores are assumed to be em…
The dynamical evolution of stellar superclusters
Kroupa, Pavel
Recent images taken with the Hubble Space Telescope (HST) of the interacting disc galaxies NGC 4038/4039 (the Antennae) reveal clusters of many dozens and possibly hundreds of young compact massive star clusters within projected regions spanning about 100 to 500 pc. It is shown here that a large fraction of the individual star clusters merge withi…
Testing CNO Enrichment Scenarios in Metal-poor Galaxies with Hubble Space Telescope Spectroscopy
Kobulnicky, Henry A.; Skillman, Evan D.
Using Hubble Space Telescope ultraviolet and ground-based optical spectroscopy, we measure the C/O and N/O ratios of three metal-poor galaxies with similar metallicity but differing N/O. These observations, in conjunction with photoionization models, indicate that the C/O ratios estimated from C III] λ1909 and [O III] λ5007 lines are consistent wi…
Ice segregation toward massive protostars
Ehrenfreund, P.; Dartois, E.; Demyk, K. +1 more
Recent ISO results allow new insights into the evolution of interstellar ices in the vicinity of massive protostars. The presence of CO2 ice has recently been confirmed with the SWS (Short Wavelength Spectrometer) on-board ISO as a dominant ice component of interstellar grain mantles. The bending mode of CO2 ice, currently ob…
Ultraviolet Diagnostics for the Emission-Line Gas in Active Galaxies
Dopita, Michael A.; Allen, Mark G.; Tsvetanov, Zlatan I.
Optical diagnostic diagrams are frequently ambiguous as tests of the photoionization or fast-shock models of the narrow-line regions of active galaxies. Here, we present a set of UV line ratio diagrams that can discriminate between pure shock and photoionization modes of excitation and can, to some extent, also discriminate shocks with ionized pre…
Determination of the temperatures of selected ISO flux calibration stars using the Infrared Flux Method
Lynas-Gray, A. E.; Blackwell, D. E.
Effective temperatures for 420 stars with spectral types between A0 and K3, and luminosity classes between II and V, selected for a flux calibration of the Infrared Space Observatory, ISO, have been determined using the Infrared Flux Method (IRFM). The determinations are based on narrow and wide band photometric data obtained for this purpose, and…
The Radio Properties of NGC 5253 and Its Unusual H II Regions
Turner, Jean L.; Beck, Sara C.; Ho, Paul T. P.
We present VLA images of the radio continuum emission of the starburst in NGC 5253 at wavelengths of 6, 3.6, and 2 cm, with resolutions of 1"-2", and at 20 cm with resolution of ~9". A spectral index map constructed from the 6 and 2 cm images indicates that thermal free-free emission from ionized gas, most of it from a single source, dominates the…