Search Publications
The Nature and Origin of Substructure in the Outskirts of M31. I. Surveying the Stellar Content with the Hubble Space Telescope Advanced Camera for Surveys
Chapman, S. C.; Tanvir, N. R.; Ferguson, A. M. N. +8 more
We present the largest and most detailed survey to date of the stellar populations in the outskirts of M31 based on the homogeneous analysis of 14 deep Hubble Space Telescope Advanced Camera for Surveys (HST/ACS) pointings spanning the range 11.5 kpc lsim R proj lsim 45 kpc. Many of these pointings sample coherent substructure discovere…
Structural Properties of Ultra-Compact Dwarf Galaxies in the Fornax and Virgo Clusters
Peng, C. Y.; Hilker, M.; Evstigneeva, E. A. +6 more
We present a detailed analysis of high-resolution two-band Hubble Space Telescope Advanced Camera for Surveys imaging of 21 ultra-compact dwarf (UCD) galaxies in the Virgo and Fornax Clusters. The aim of this work is to test two formation hypotheses for UCDs—whether they are bright globular clusters (GCs) or stripped ("threshed") early-type dwarf …
Masses of Nix and Hydra
Buie, Marc W.; Grundy, William M.; Tholen, David J. +1 more
A four-body orbit solution for the Pluto system yields GM values of 870.3 ± 3.7, 101.4 ± 2.8, 0.039 ± 0.034, and 0.021 ± 0.042 km3 s-2 for Pluto, Charon, Nix, and Hydra, respectively. Assuming a Charon-like density of 1.63 gm cm-3, the implied diameters for Nix and Hydra are 88 and 72 km, leading to visual geometri…
The Stellar Mass Distribution in the Giant Star Forming Region NGC 346
Tosi, M.; Sabbi, E.; Nota, A. +8 more
Deep F555W and F814W Hubble Space Telescope (HST ) Advanced Camera for Survey (ACS) images are the basis for a study of the present-day mass function (PDMF) of NGC 346, the largest active star-forming region in the Small Magellanic Cloud (SMC). We find a PDMF slope of Γ = -1.43 ± 0.18 in the mass range 0.8-60 Msun, in excellent agreemen…
V838 Monocerotis: A Geometric Distance from Hubble Space Telescope Polarimetric Imaging of its Light Echo
White, Richard L.; Sparks, William B.; Bond, Howard E. +10 more
Following the outburst of the unusual variable star V838 Monocerotis in 2002, a spectacular light echo appeared. A light echo provides the possibility of direct geometric distance determination, because it should contain a ring of highly linearly polarized light at a linear radius of ct, where t is the time since the outburst. We present imaging p…
Deep Advanced Camera for Surveys Imaging in the Globular Cluster NGC 6397: Reduction Methods
Anderson, Jay; Rich, R. Michael; Stetson, Peter B. +6 more
We describe here the reduction methods that we developed to study the faintest red dwarfs and white dwarfs in an outer field of NGC 6397, which was observed by HST for 126 orbits in 2005. The particular challenge of this data set is that the faintest stars are not readily visible in individual exposures, so special care must be taken to combine th…
Charge-Coupled Device Speckle Observations of Binary Stars with the WIYN Telescope. V. Measures During 2001-2006
Horch, Elliott P.; van Altena, William F.; Cyr, William M., Jr. +3 more
A total of 1067 speckle observations of 345 binary stars are presented. Of these, 161 are double stars first resolved by Hipparcos, 17 are resolved for the first time in the observations presented here, and 21 are stars previously discovered by our program and reported in earlier papers in the series. In 947 cases, a magnitude difference is report…
Main-Sequence Fitting Distance to the σ Ori Cluster
Walter, F. M.; Wolk, S. J.; Sherry, W. H. +1 more
The σ Ori cluster is an unbound aggregate of a few hundred young, low-mass stars centered on the multiple system σ Ori. This cluster is of great interest because it is at an age when roughly half of the stars have lost their protoplanetary disks, and the cluster has a very large population of brown dwarfs. One of the largest sources of uncertainty…
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…