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HST/ACS Observations of RR Lyrae Stars in Six Ultra-deep Fields of M31
Ferguson, H. C.; Rich, R. M.; Kalirai, J. S. +6 more
We present HST/ACS observations of RR Lyrae variable stars in six ultra-deep fields of the Andromeda galaxy (M31), including parts of the halo, disk, and giant stellar stream. Past work on the RR Lyrae stars in M31 has focused on various aspects of the stellar populations that make up the galaxy's halo, including their distances and metallicities.…
Structured ionospheric outflow during the Cassini T55-T59 Titan flybys
Coates, A. J.; Dougherty, M. K.; Wahlund, J. -E. +7 more
During the final three of the five consecutive and similar Cassini Titan flybys T55-T59 we observe a region characterized by high plasma densities (electron densities of 1-8 cm-3) in the tail/nightside of Titan. This region is observed progressively farther downtail from pass to pass and is interpreted as a plume of ionospheric plasma e…
Pitch angle evolutions of oxygen ions driven by storm time ULF poloidal standing waves
Zong, Q. -G.; Reme, H.; Fu, S. Y. +9 more
We present the first systematic observational study on the pitch angle evolutions of O+ ions associated with ULF Pc5 poloidal standing waves excited during geomagnetic storms. The O+ ion measurements are made on board the CLUSTER satellites with the Composition Distribution Function (CODIF) instrument, which covers energies f…
Emission geometry, radiation pattern and magnetic topology of the magnetar XTE J1810-197 in its quiescent state
Stella, L.; Rea, N.; Gotthelf, E. V. +3 more
The return to the quiescent state of the anomalous X-ray pulsar (AXP) XTE J1810-197 following its 2003 outburst represents a unique opportunity to probe the surface emission properties of a magnetar. The quiescent emission of XTE J1810-197 is composed of two thermal components, one arising from the whole star surface and the other from a small war…
Millimeter Imaging of the β Pictoris Debris Disk: Evidence for a Planetesimal Belt
Hughes, A. Meredith; Wilner, David J.; Andrews, Sean M.
We present observations at 1.3 mm wavelength of the β Pictoris debris disk with beam size 4farcs3 × 2farcs6 (83 × 50 AU) from the Submillimeter Array. The emission shows two peaks separated by ~7'' along the disk plane, which we interpret as a highly inclined dust ring or belt. A simple model constrains the belt center to 94 ± 8 AU, close to the p…
On the Lx - L6 µm ratio as a diagnostic for Compton-thick AGN
Vignali, C.; Gilli, R.; Ranalli, P. +6 more
As the mid-IR luminosity represents a good isotropic proxy of the AGN power, a low X-ray to mid-IR luminosity ratio is often claimed to be a reliable indicator of Compton-thick AGN. We assess the efficiency of the X-ray to mid-IR luminosity ratio diagnostic by examining the 12 µm IRAS AGN sample (intrinsic L2-10 keV > 1042…
Spatially Resolving the HK Tau B Edge-on Disk from 1.2 to 4.7 µm: A Unique Scattered Light Disk
Pinte, C.; Ménard, F.; Duchêne, G. +3 more
We present spatially resolved scattered light images of the circumstellar disk around HK Tau B at 3.8 and 4.7 µm taken with the Keck Telescope Laser Guide Star Adaptive Optics (AO) system, and 1.6-2.12 µm images taken with the Very Large Telescope/NACO AO system. Combined with previously published optical Hubble Space Telescope data, w…
Time-dependent cosmic ray modulation
Ferreira, S. E. S.; Potgieter, M. S.; Engelbrecht, N. E. +2 more
Time-dependent cosmic ray modulation is calculated over multiple solar cycles using our well established two-dimensional time-dependent modulation model. Results are compared to Voyager 1, Ulysses and IMP cosmic ray observations to establish compatibility. A time-dependence in the diffusion and drift coefficients, implicitly contained in recent ex…
Resolving the Baryon-fraction Profile in Lensing Galaxies
Saha, Prasenjit; Ferreras, Ignacio; Falco, Emilio E. +1 more
The study of the distribution of baryonic matter within dark halos enriches our understanding of galaxy formation. We show the radial dependence of stellar baryon-fraction curves derived for 21 lensing galaxies from the CfA-Arizona Space Telescope LEns Survey (CASTLES) by means of stellar population synthesis and pixel-based mass reconstruction. T…
Intense plasma wave emissions associated with Saturn's moon Rhea
Schippers, P.; Gurnett, D. A.; Russell, C. T. +7 more
Measurements by the Cassini spacecraft during a close flyby of Saturn's moon Rhea on March 2, 2010, show the presence of intense plasma waves in the magnetic flux tube connected to the surface of the moon. Three types of waves were observed, (1) bursty electrostatic waves near the electron plasma frequency, (2) intense whistler-mode emissions belo…