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Hubble Space Telescope Proper Motions and Stellar Dynamics in the Core of the Globular Cluster 47 Tucanae
Anderson, Jay; Gebhardt, Karl; Minniti, Dante +4 more
We have used HST imaging of the central regions of the globular cluster 47 Tucanae (=NGC 104), taken with the WFPC2 and ACS instruments between 1995 and 2002, to derive proper motions and U- and V-band magnitudes for 14,366 stars within 100" (about 5 core radii) of the cluster center. This represents the largest set of member velocities collected …
Supernova remnant energetics and magnetars: no evidence in favour of millisecond proto-neutron stars
Vink, Jacco; Kuiper, Lucien
It is generally accepted that anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) are magnetars, i.e. neutron stars with extremely high surface magnetic fields (B > 1014 G). The origin of these high magnetic fields is uncertain, but a popular hypothesis is that magnetars are born with an initial spin period not much ex…
Giant Ringlike Radio Structures Around Galaxy Cluster Abell 3376
Paul, Surajit; Durret, Florence; Bagchi, Joydeep +1 more
In the current paradigm of cold dark matter cosmology, large-scale structures are assembling through hierarchical clustering of matter. In this process, an important role is played by megaparsec (Mpc)-scale cosmic shock waves, arising in gravity-driven supersonic flows of intergalactic matter onto dark matter-dominated collapsing structures such a…
Hubble Space Telescope ACS Multiband Coronagraphic Imaging of the Debris Disk around β Pictoris
Ford, H. C.; Demarco, R.; Infante, L. +40 more
We present F435W (B), F606W (broad V), and F814W (broad I) coronagraphic images of the debris disk around β Pictoris obtained with the Hubble Space Telescope's Advanced Camera for Surveys. These images provide the most photometrically accurate and morphologically detailed views of the disk between 30 and 300 AU from the star ever recorded in scatt…
The XMM Cluster Survey: A Massive Galaxy Cluster at z = 1.45
Conselice, Christopher J.; Hilton, Matt; Stanford, S. A. +14 more
We report the discovery of XMMXCS J2215.9-1738, a massive galaxy cluster at z=1.45, which was found in the XMM Cluster Survey. The cluster candidate was initially identified as an extended X-ray source in archival XMM data. Optical spectroscopy shows that six galaxies within a ~60" diameter region lie at z=1.45+/-0.01. Model fits to the X-ray spec…
Associations of Dwarf Galaxies
Dolphin, A. E.; Rizzi, L.; Tully, R. Brent +6 more
The Hubble Space Telescope Advanced Camera for Surveys has been used to determine accurate distances for 20 galaxies from measurements of the luminosity of the brightest red giant branch stars. Five associations of dwarf galaxies that had originally been identified based on strong correlations on the plane of the sky and in velocity are shown to b…
The Detailed Star Formation History in the Spheroid, Outer Disk, and Tidal Stream of the Andromeda Galaxy
Ferguson, Henry C.; Brown, Thomas M.; Rich, R. Michael +5 more
Using HST ACS, we have obtained deep optical images reaching stars well below the oldest main-sequence turnoff in the spheroid, tidal stream, and outer disk of Andromeda. We have reconstructed the star formation history in these fields by comparing their color-magnitude diagrams to a grid of isochrones calibrated to Galactic globular clusters obse…
Tip of the Red Giant Branch Distances. I. Optimization of a Maximum Likelihood Algorithm
Dolphin, Andrew E.; Shaya, Edward J.; Tully, R. Brent +4 more
Accurate distances to galaxies can be determined from the luminosities of stars at the tip of the red giant branch (TRGB). We use a maximum likelihood algorithm to locate the TRGB in galaxy color-magnitude diagrams. The algorithm is optimized by introducing reliable photometric errors and a completeness characterization determined with artificial …
Coronal prominence structure and dynamics: A magnetic flux rope interpretation
Gibson, S. E.; Fan, Y.
The solar prominence is an example of a space physics phenomenon that can be modeled as a twisted magnetic flux tube or magnetic flux "rope." In such models the prominence is one observable part of a larger magnetic structure capable of storing magnetic energy to drive eruptions. We show how a flux rope model explains a range of observations of pr…
Direct x-ray constraints on sterile neutrino warm dark matter
Beacom, John F.; Watson, Casey R.; Yüksel, Hasan +1 more
Warm dark matter might more easily account for small scale clustering measurements than the heavier particles typically invoked in Λ cold dark matter (ΛCDM) cosmologies. In this paper, we consider a ΛWDM cosmology in which sterile neutrinos νs, with a mass ms of roughly 1 100 keV, are the dark matter. We use the diffuse x-ray…