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Star Formation in the H I Bridge Between M81 and M82
Sabbi, E.; Gallagher, J. S.; Smith, L. J. +3 more
We present multiwavelength observations of stellar features in the H I tidal bridge connecting M81 and M82 in the region called Arp's loop. We identify eight young star-forming regions from Galaxy Evolution Explorer ultraviolet (UV) observations. Four of these objects are also detected at Hα. We determine the basic star-formation history of Arp's …
HST/WFPC2 Imaging of the Circumnuclear Structure of Low-Luminosity Active Galactic Nuclei. I. Data and Nuclear Morphology
Pérez, Enrique; Cid Fernandes, Roberto; González Delgado, Rosa M. +1 more
In several studies of low-luminosity active galactic nuclei (LLAGNs), we have characterized the properties of the stellar populations in LINERs and LINER/H II transition objects (TOs). We have found a populous class of galactic nuclei which stand out because of their conspicuous 0.1-1 Gyr populations. These nuclei are called "Young-TOs" since they…
Mid-Infrared Spectra of Optically-Selected Type 2 Quasars
Strauss, Michael A.; Zakamska, Nadia L.; Krolik, Julian H. +1 more
Type 2 quasars are luminous active galactic nuclei (AGNs) whose central engines are seen through large amounts of gas and dust. We present Spitzer spectra of 12 type 2 quasars selected on the basis of their optical emission line properties. Within this sample, we find a surprising diversity of spectra, from those that are featureless to those show…
Starbursts in the Local Universe: New Hubble Space Telescope Advanced Camera for Surveys Observations of the Irregular Galaxy NGC 4449
Leitherer, C.; Tosi, M.; van der Marel, R. P. +5 more
We present photometry with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope of stars in the Magellanic starburst galaxy NGC 4449. The galaxy has been imaged in the F435W (B), F555W (V), and F814W (I) broadband filters, and in the F658N (Hα) narrowband filter. Our photometry includes ≈300,000 objects in the (B, V) color-magnitude…
Revised Orbits of Saturn's Small Inner Satellites
Porco, C. C.; Cooper, N. J.; Murray, C. D. +4 more
We have updated the orbits of the small inner Saturnian satellites using additional Cassini imaging observations through 2007 March. Statistically significant changes from previously published values appear in the eccentricities and inclinations of Pan and Daphnis, but only small changes have been found in the estimated orbits of the other satelli…
The Population of Propellers in Saturn's A Ring
Porco, Carolyn C.; Hedman, Matthew M.; Burns, Joseph A. +1 more
We present an extensive data set of ~150 localized features from Cassini images of Saturn's A ring, a third of which are demonstrated to be persistent by their appearance in multiple images, and half of which are resolved well enough to reveal a characteristic "propeller" shape. We interpret these features as the signatures of small moonlets embed…
Deep Advanced Camera for Surveys Imaging in the Globular Cluster NGC 6397: the Binary Fraction
Anderson, J.; Stetson, P. B.; Rich, R. M. +5 more
Using Hubble Space Telescope observations of the globular cluster NGC 6397, we constrain the cluster's binary fraction. The observations consist of two fields: the primary science field, a single Advanced Camera for Surveys (ACS) pointing centered approximately 5' from the cluster center; and the parallel field, a single WFPC2 field centered on th…
Emerging Massive Star Clusters Revealed: High-Resolution Imaging of NGC 4449 from the Radio to the Ultraviolet
Johnson, Kelsey E.; Reines, Amy E.; Goss, W. M.
We present a multi-wavelength study of embedded massive clusters in the nearby (3.9 Mpc) starburst galaxy NGC 4449 in an effort to uncover the earliest phases of massive cluster evolution. By combining high-resolution imaging from the radio to the ultraviolet, we reveal these clusters to be in the process of emerging from their gaseous and dusty b…
Simulations of the Dynamical and Light-Scattering Behavior of Saturn's Rings and the Derivation of Ring Particle and Disk Properties
Dones, Luke; Porco, Carolyn C.; Weiss, John W. +3 more
We study the light-scattering behavior of Saturn's rings for the purpose of deducing the nature and distribution of the particles comprising them and the collisional and dynamical environments in which they reside. To this end, we have developed two complex numerical codes to apply to this objective. One is a geometric ray-tracing code that scatte…
L-Dwarf Binaries in the 20-Parsec Sample
Burgasser, Adam J.; Reid, I. Neill; Liu, Michael C. +1 more
We have used the NICMOS NIC1 camera on the Hubble Space Telescope to obtain high-resolution near-infrared images of 27 nearby ultracool dwarfs with formal distance estimates less than 20 parsecs. One target, 2MASS J22551861-5713056, is resolved as a binary system, with a 4:1 flux ratio in the F110W passband. The primary has spectral type L6, and t…