Search Publications
Fine-Scale Temperature Fluctuations in the Orion Nebula and the t2 Problem
O'Dell, C. R.; Peimbert, Antonio; Peimbert, Manuel
We present a high spatial resolution map of the columnar electron temperature (Tc) of a region to the southwest of the Trapezium in the Orion Nebula. This map was derived from Hubble Space Telescope images that isolated the primary lines of H I for determination of the local extinction and of the [O III] lines for determination of T
The [Fe II] 1.644 Micron Emission in M82 and NGC 253: Is It a Measure of the Supernova Rate?
Rieke, George H.; Alonso-Herrero, Almudena; Rieke, Marcia J. +1 more
We present Hubble Space Telescope NICMOS [Fe II] 1.644 µm, Paα (1.87 µm), and continuum images of the starburst galaxies M82 and NGC 253 at an unprecedented spatial resolution. In both galaxies we detect [Fe II] compact sources superposed on a diffuse background in the disk of the galaxies, together with a component above and below the…
Observability of Scattered-Light Echoes around Variable Stars and Cataclysmic Events
Sugerman, Ben E. K.
Scattered-light echoes from variable and cataclysmic stars offer one of the most effective means to probe the structure and composition of circumstellar and interstellar media. I build a simple model of light-echo surface brightness by considering the source spectrum and the dust density, geometry, and scattering efficiency. I use this model to in…
NICMOS Coronagraphic Observations of the GM Aurigae Circumstellar Disk
Schneider, G.; Wood, K.; Silverstone, M. D. +5 more
We present Hubble Space Telescope Near Infrared Camera and Multi-Object Spectrometer (NICMOS) coronagraphic observations of the environment in the region of the young star-disk system GM Aurigae. Scattered near-infrared light in two spectral bands (F110W=1.1 µm and F160W=1.6 µm) trace the morphology of circumstellar dust to a distance …
Space Velocities of Southern Globular Clusters. IV. First Results for Inner Galaxy Clusters
Girard, Terrence M.; van Altena, William F.; López, Carlos E. +1 more
We have measured the absolute proper motions of four low-latitude, inner Galaxy globular clusters. These clusters are NGC 6266 (M62), NGC 6304, NGC 6316, and NGC 6723. The proper motions are on the Hipparcos system, since no background extragalactic objects are found in these high-extinction regions. The proper-motion uncertainties range between 0…
Local Surface Density of the Galactic Disk from a Three-Dimensional Stellar Velocity Sample
Girard, T. M.; Korchagin, V. I.; van Altena, W. F. +2 more
We have reestimated the surface density of the Galactic disk in the solar neighborhood within +/-0.4 kpc of the Sun using the parallaxes and proper motions of a kinematically and spatially unbiased sample of 1476 old bright red giant stars from the Hipparcos catalog with measured radial velocities from Barbier-Brossat & Figon. We determine the…
The 100 Brightest X-Ray Stars within 50 Parsecs of the Sun
Makarov, Valeri V.
Based on the Hipparcos and Tycho-2 astrometric catalogs and the ROSAT surveys, a sample of 100 stars most luminous in X-rays within or around a distance of 50 pc is culled. The smallest X-ray luminosity in the sample, in units of 1029 ergs s-1, is LX=9.8 the strongest source in the solar neighborhood is II Peg, a R…
Mapping the Circumstellar Environment of T Tauri with Fluorescent H2 Emission
Valenti, Jeff A.; Brown, Alexander; Walter, Frederick M. +6 more
We have obtained three long-slit, far-UV spectra of the pre-main-sequence system T Tauri. These Hubble Space Telescope STIS spectra show a strong and variable on-source spectrum composed of both fluoresced H2 and stellar chromospheric lines. Extended H2 emission is seen up to 10" from the T Tau system. The on-source and exten…
Deep Hubble Space Telescope Imaging of Sextans A. II. Cepheids and Distance
Dolphin, Andrew E.; Skillman, Evan D.; Saha, A. +6 more
We have identified 82 short-period variable stars in Sextans A from deep Wide Field Planetary Camera 2 observations. All the periodic variables appear to be short-period Cepheids, with periods as small as 0.8 days for fundamental mode Cepheids and 0.5 days for first-overtone Cepheids. These objects have been used, along with measurements of the re…
The Star Formation History of NGC 1705: A Poststarburst Galaxy on the Verge of Activity
Leitherer, Claus; Greggio, L.; Tosi, M. +2 more
We infer the star formation history in different regions of the blue compact dwarf NGC 1705 by comparing synthetic color-magnitude diagrams with the Hubble Space Telescope optical and near-infrared photometry. We find that NGC 1705 is not a young galaxy, because its star formation commenced at least 5 Gyr ago. On the other hand, we confirm the exi…