Search Publications
The Specific Globular Cluster Frequencies of Dwarf Elliptical Galaxiesfrom the Hubble Space Telescope
Ferguson, Henry C.; Stiavelli, Massimo; Whitmore, Bradley C. +2 more
The specific globular cluster frequencies (SN) for 24 dwarf elliptical (dE) galaxies in the Virgo and Fornax Clusters and the Leo Group that were imaged with the Hubble Space Telescope are presented. Combining all available data, we find that for nucleated dE (dE, N) galaxies, which are spatially distributed like giant elliptical galaxi…
Late Spectral Evolution of SN 1987A. II. Line Emission
Fransson, Claes; Kozma, Cecilia
Using the temperature and ionization calculated in our previous paper, we model the spectral evolution of SN 1987A. We find that the temperature evolution is directly reflected in the time evolution of the lines. In particular, the IR catastrophe is seen in the metal lines as a transition from thermal to nonthermal excitation, seen most clearly in…
The Ages of the Globular Clusters in the Fornax Dwarf Galaxy
Suntzeff, N. B.; Buonanno, R.; Corsi, C. E. +3 more
From observations with the Hubble Space Telescope, color-magnitude diagrams (CMDs) have been constructed for the four most metal-poor globular clusters in the Fornax dSph galaxy. These diagrams confirm that cluster 1 has a redder horizontal-branch (HB) morphology than the other three clusters despite its similarity in metallicity (the second param…
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…
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…
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…
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…
Are Seyfert Narrow-Line Regions Powered by Radio Jets?
Dopita, Michael A.; Sutherland, Ralph S.; Tsvetanov, Zlatan I. +1 more
We argue that the narrow-line regions (NLRs) of Seyfert galaxies are powered by the transport of energy and momentum by the radio-emitting jets. This implies that the ratio of the radio power to jet energy flux is much smaller than is usually assumed for radio galaxies. This can be partially attributed to the smaller ages (~106 yr) of S…
Thermal Water Vapor Emission from Shocked Regions in Orion
Neufeld, David A.; Kaufman, Michael J.; Melnick, Gary J. +1 more
Using the Long Wavelength Spectrometer on board the Infrared Space Observatory, we have observed thermal water vapor emission from a roughly circular field of view approximately 75" in diameter centered on the Orion BN-KL region. The Fabry-Perot line strengths, line widths, and spectral line shifts observed in eight transitions between 71 and 125 …
Systematics of RR Lyrae Statistical Parallax. III. Apparent Magnitudes and Extinctions
Gould, Andrew; Popowski, Piotr
We sing the praises of the central limit theorem. Having previously removed all other possible causes of significant systematic error in the statistical-parallax determination of RR Lyrae absolute magnitudes, we investigate systematic errors from two final sources of input data: apparent magnitudes and extinctions. We find corrections due to each …