Search Publications
Internal Properties of Ultracompact Dwarf Galaxies in the Virgo Cluster
Hilker, M.; Evstigneeva, E. A.; Drinkwater, M. J. +1 more
We present new imaging and spectroscopic observations of six ultracompact dwarf (UCD) galaxies in the Virgo Cluster, along with reanalyzed data for five Fornax Cluster UCDs. These are the most luminous UCDs: -14 mag < MV < -12 mag. Our Hubble Space Telescope imaging shows that most of the UCDs have shallow or steep cusps in their …
Structural Parameters for Globular Clusters in M31 and Generalizations for the Fundamental Plane
Forbes, Duncan A.; Barmby, Pauline; Harris, William E. +2 more
The structures of globular clusters (GCs) reflect their dynamical states and past histories. High-resolution imaging allows the exploration of morphologies of clusters in other galaxies. Surface brightness profiles from new Hubble Space Telescope observations of 34 GCs in M31 are presented, together with fits of several different structural models…
Visual Binaries in the Orion Nebula Cluster
Bally, John; Reipurth, Bo; Connelley, Michael S. +1 more
We have carried out a major survey for visual binaries toward the Orion Nebula Cluster, using images obtained with the Advanced Camera for Surveys on the Hubble Space Telescope through an Hα filter. From 1051 stars more than 60″ from θ1 Ori C, we have selected 781 that fulfill the criteria for membership in the Orion Nebula Cluster. Amo…
Trigonometric Parallaxes of Central Stars of Planetary Nebulae
Harris, Hugh C.; Vrba, Frederick J.; Leggett, S. K. +11 more
Trigonometric parallaxes of 16 nearby planetary nebulae are presented, including reduced errors for seven objects with previous initial results and results for six new objects. The median error in the parallax is 0.42 mas, and 12 nebulae have parallax errors of less than 20%. The parallax for PHL 932 is found here to be smaller than was measured b…
Past and Present Star Formation in the SMC: NGC 346 and its Neighborhood
Tosi, M.; Sabbi, E.; Nota, A. +8 more
In the quest to understand how star formation occurs and propagates in the low-metallicity environment of the Small Magellanic Cloud (SMC), we acquired deep F555W (~V) and F814W (~I) Hubble Space Telescope ACS images of the young and massive star-forming region NGC 346. These images and their photometric analysis provide us with a snapshot of the …
The Three-Dimensional Morphology of VY Canis Majoris. I. The Kinematics of the Ejecta
Humphreys, Roberta M.; Jones, Terry J.; Helton, L. Andrew
Images of the complex circumstellar nebula associated with the famous red supergiant VY CMa show evidence for multiple and asymmetric mass-loss events over the past 1000 yr. Doppler velocities of the arcs and knots in the ejecta show that they are not only spatially distinct but also kinematically separate from the surrounding diffuse material. In…
Proper Motions of Dwarf Spheroidal Galaxies from Hubble Space Telescope Imaging. V. Final Measurement for Fornax
Minniti, Dante; Mateo, Mario; Piatek, Slawomir +5 more
The measured proper motion of Fornax, expressed in the equatorial coordinate system, is (µα,µδ)=(47.6+/-4.6,-36.0+/-4.1) mas century-1. This proper motion is a weighted mean of four independent measurements for three distinct fields. Each measurement uses a quasi-stellar object as a reference point. Rem…
Self-Gravity Wake Structures in Saturn's A Ring Revealed by Cassini VIMS
Nicholson, Philip D.; Hedman, Matthew M.; Baines, Kevin H. +5 more
During the summer of 2005, the Visual and Infrared Mapping Spectrometer onboard the Cassini spacecraft observed a series of occultations of the star o Ceti (Mira) by Saturn's rings. These observations revealed pronounced variations in the optical depth of the A ring with longitude, which can be attributed to oriented structures in the rings known …
Space Velocities of Southern Globular Clusters. V. A Low Galactic Latitude Sample
Casetti-Dinescu, Dana I.; Girard, Terrence M.; van Altena, William F. +3 more
We have measured the absolute proper motions of globular clusters NGC 2808, 3201, 4372, 4833, 5927, and 5986. The proper motions are on the Hipparcos system, and they are the first determinations ever made for these low Galactic latitude clusters. The proper-motion uncertainties range from 0.3 to 0.5 mas yr-1. The inferred orbits indica…
Proper Motions of the Jets in the Region of HH 30 and HL/XZ Tau: Evidence for a Binary Exciting Source of the HH 30 Jet
Anglada, Guillem; Masegosa, Josefa; Estalella, Robert +3 more
We present [S II] images of the HH 30 and HL/XZ Tau region obtained at two epochs, as well as long-slit optical spectroscopy of the HH 30 jet. We measured proper motions of ~100-300 km s-1 for the HH 30 jet and counterjet and of ~120 km s-1 for the HL Tau jet. Inclination angles with respect to the plane of the sky are 0°-40°…