Search Publications
Virgo's Intracluster Globular Clusters as Seen by the Advanced Camera for Surveys
Ferguson, Henry C.; Williams, Benjamin F.; Freeman, Ken C. +11 more
We report the discovery of four candidate intracluster globular clusters (IGCs) in a single deep HST ACS field of the Virgo Cluster. We show that each cluster is roughly spherical, has a magnitude near the peak of the Virgo globular cluster luminosity function, has a radial profile that is best fitted by a King model, and is surrounded by an exces…
Surface Brightness Fluctuations from Archival ACS Images: A Stellar Population and Distance Study
Blakeslee, John; Cantiello, Michele; Raimondo, Gabriella +2 more
We derive surface brightness fluctuations (SBF) and integrated magnitudes in the V and I bands using Advanced Camera for Surveys (ACS) archival data. The sample includes 14 galaxies covering a wide range of physical properties: morphology, total absolute magnitude, and integrated color. We take advantage of the latter characteristic of the sample …
Bimodal Infrared Colors of the M87 Globular Cluster System: Peaks in the Metallicity Distribution
Kundu, Arunav; Zepf, Stephen E.
The globular cluster (GC) systems of many galaxies reveal bimodal optical color distributions. Based on stellar evolutionary models and the bimodal colors and metallicities of Galactic GCs, this is thought to reflect an underlying bimodal metallicity distribution. However, stars at many different phases of stellar evolution contribute to optical l…
The Magnetar Nature and the Outburst Mechanism of a Transient Anomalous X-Ray Pulsar
Kouveliotou, Chryssa; Göǧüş, Ersin; Güver, Tolga +1 more
Anomalous X-ray pulsars (AXPs) belong to a class of neutron stars believed to harbor the strongest magnetic fields in the universe, as indicated by their energetic bursts and their rapid spin-downs. However, an unambiguous measurement of their surface field strengths has not been made to date. It is also not known whether AXP outbursts result from…
Hubble Space Telescope and Spitzer Observations of the Afterglow and Host Galaxy of GRB 050904 at z = 6.295
Gladders, M. D.; Cenko, S. B.; Peterson, B. A. +11 more
We present deep Hubble Space Telescope (HST) and Spitzer Space Telescope observations of GRB 050904 at z=6.295. We detect the afterglow in the H band more than 3 weeks after the burst and confirm the presence of a jet break at t~2.1 days. This leads to an estimated opening angle of about 4° and a beaming-corrected energy of about 1051 e…
The Preshock Gas of SN 1006 from Hubble Space Telescope Advanced Camera for Surveys Observations
Raymond, J. C.; Korreck, K. E.; Blair, W. P. +3 more
We derive the preshock density and scale length along the line of sight for the collisionless shock from a deep HST image that resolves the Hα filament in SN 1006 and updated model calculations. The very deep ACS high-resolution image of the Balmer line filament in the northwest quadrant shows that 0.25 cm-3<=n0<=0.4 cm…
Ion Charge States in the Fast Solar Wind: New Data Analysis and Theoretical Refinements
Laming, J. Martin; Lepri, Susan T.
We present a further investigation into the increased ionization observed in element charge states in the fast solar wind compared to its coronal hole source regions. Once ions begin to be perpendicularly heated by ion cyclotron waves and execute large gyro-orbits, density gradients in the flow can excite lower hybrid waves that then damp by heati…
Solar Models with Revised Abundances and Opacities
Yang, W. M.; Bi, S. L.
Using reconstructed opacities, we construct solar models with low heavy-element abundance. Rotational mixing and enhanced diffusion of helium and heavy elements are used to reconcile the recently observed abundances with helioseismology. The sound speed and density of models in which the relative and absolute diffusion coefficients for helium and …
Flux Pile-up Magnetic Reconnection in the Solar Photosphere
Chae, Jongchul; Litvinenko, Yuri E.; Park, So-Young
Magnetic reconnection in the temperature minimum region of the solar photosphere, observationally manifested as canceling magnetic features, is considered. Flux pile-up reconnection in the Sweet-Parker current sheet is analyzed. It is shown that the standard Sweet-Parker reconnection rate in the photosphere is too slow to explain the observed canc…
Effect of Suppressed Excitation on the Amplitude Distribution of 5 Minute Oscillations in Sunspots
Kosovichev, A. G.; Parchevsky, K. V.
Five minute oscillations on the Sun (acoustic and surface gravity waves) are excited by subsurface turbulent convection. However, in sunspots the excitation is suppressed because a strong magnetic field inhibits convection. We use three-dimensional simulations to investigate how the suppression of excitation sources affects the distribution of the…