Search Publications
Ultra-compact Dwarfs in the Core of the Coma Cluster
Ferguson, Henry C.; Spitler, Lee R.; Forbes, Duncan A. +6 more
We have discovered both a red and a blue subpopulation of ultra-compact dwarf (UCD) galaxy candidates in the Coma galaxy cluster. We analyzed deep F475W (Sloan g) and F814W (I) Hubble Space Telescope images obtained with the Advanced Camera for Surveys Wide Field Channel as part of the Coma Cluster Treasury Survey and have fitted the light profile…
Radioheliograph Observations of Metric Type II Bursts and the Kinematics of Coronal Mass Ejections
Kartha, Sreeja S.; Ramesh, R.; Kathiravan, C. +1 more
Assuming that metric type II radio bursts from the Sun are due to magnetohydrodynamic shocks driven by coronal mass ejections (CMEs), we estimate the average CME acceleration from its source region up to the position of the type II burst. The acceleration values are in the range ≈600-1240 m s^{-2}, which are consistent with values obtained using n…
Coronal Fuzziness Modeled with Pulse-heated Multi-stranded Loop Systems
Reale, Fabio; Peres, Giovanni; Guarrasi, Massimiliano
Coronal active regions are observed to get increasingly fuzzy (i.e., increasingly confused and uniform) in increasingly hard energy bands or lines. We explain this as evidence of fine multi-temperature structure of coronal loops. To this end, we model bundles of loops made of thin strands, each heated by short and intense heat pulses. For simplici…
Equations of state in collisionless magnetic reconnection
Egedal, J.; Daughton, W.; Drake, J. F. +4 more
Kinetic simulation as well as in situ measurement of reconnecting current sheets in the Earth's magnetosphere show strong electron temperature anisotropy, with the parallel electron temperature becoming several times greater than the perpendicular temperature. This anisotropy is accounted for in a solution of the Vlasov equation recently derived f…
A dynamo model for axisymmetrizing Saturn's magnetic field
Stanley, S.
Magnetic field measurements demonstrate that Saturn's internally generated magnetic field has an extremely small dipole tilt. The nearly-perfect axisymmetry of Saturn's dipole is troubling because of Cowling's theorem which states that an axisymmetric magnetic field cannot be maintained by a dynamo. A possible mechanism to axisymmetrize the observ…
Spatial and Temporal Distributions of Transient Horizontal Magnetic Fields with Deep Exposure
Tsuneta, Saku; Ishikawa, Ryohko
We obtained a long-exposure vector magnetogram of the quiet Sun photosphere at the disk center with a wide field of view of 51'' × 82''. The observation was performed at Fe I 525.0 nm with the shutterless mode of the Narrow Band Filter Imager of the Solar Optical Telescope (SOT) on board the Hinode satellite. We summed the linear polarization (LP)…
Spitzer, Very Large Telescope, and Very Large Array Observations of the Galactic Luminous Blue Variable Candidate HD 168625
Umana, G.; Hora, J. L.; Trigilio, C. +2 more
We present mid-IR and radio observations of the Galactic luminous blue variables (LBVs) candidate HD 168625 and its associated nebula. We obtained mid-IR spectroscopic observations using the Infrared Spectrograph on board the Spitzer Space Telescope, and performed mid-IR and radio imaging observations using VISIR on the Very Large Telescope and th…
Non-thermal radio emission from O-type stars. IV. Cygnus OB2 No. 8A
Blomme, R.; Rauw, G.; Volpi, D. +1 more
Context. Several early-type colliding-wind binaries are known to emit synchrotron radiation due to relativistic electrons, which are most probably accelerated by the Fermi mechanism. By studying such systems we can learn more about this mechanism, which is also relevant in other astrophysical contexts. Colliding-wind binaries are furthermore impor…
Ancient Stars Beyond the Local Group: RR Lyrae Variables and Blue Horizontal Branch Stars in Sculptor Group Dwarf Galaxies
Rejkuba, M.; Da Costa, G. S.; Grebel, E. K. +1 more
We have used Hubble Space Telescope Advanced Camera for Surveys images to generate color-magnitude diagrams that reach below the magnitude of the horizontal branch in the Sculptor Group dwarf galaxies ESO294-010 and ESO410-005. In both diagrams, blue horizontal branch stars are unambiguously present, a signature of the existence of an ancient stel…
Host galaxy colour gradients and accretion disc obscuration in AEGIS z ~ 1 X-ray-selected active galactic nuclei
Faber, S. M.; Lotz, J. M.; Coil, A. L. +7 more
We describe the effect of active galactic nucleus (AGN) light on host galaxy optical and UV-optical colours, as determined from X-ray-selected AGN host galaxies at z ~ 1, and compare the AGN host galaxy colours to those of a control sample matched to the AGN sample in both redshift and stellar mass. We identify as X-ray-selected AGNs 8.7+4