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Cluster observations of reconnection due to the Kelvin-Helmholtz instability at the dawnside magnetospheric flank
Balogh, A.; Lavraud, B.; Kistler, L. M. +4 more
On 3 July 2001, the four Cluster satellites traversed along the dawnside magnetospheric flank and observed large variations in all plasma parameters. The estimated magnetopause boundary normals were oscillating in the z-direction and the normal component of the magnetic field showed systematic 2-3 min bipolar variations for 1 h when the IMF had a …
Evidence for a Polar Ethane Cloud on Titan
Baines, K. H.; Jaumann, R.; Clark, R. +11 more
Spectra from Cassini's Visual and Infrared Mapping Spectrometer reveal the presence of a vast tropospheric cloud on Titan at latitudes 51° to 68° north and all longitudes observed (10° to 190° west). The derived characteristics indicate that this cloud is composed of ethane and forms as a result of stratospheric subsidence and the particularly coo…
An XMM-Newton view of the young open cluster NGC 6231 - II. The OB star population
Gosset, E.; Nazé, Y.; Rauw, G. +2 more
In this second paper of the series, we pursue the analysis of the 180-ks XMM-Newton campaign towards the young open cluster NGC 6231 and we focus on its rich OB star population. We present a literature-based census of the OB stars in the field of view with more than one hundred objects, among which 30 per cent can be associated with an X-ray sourc…
A Clathrate Reservoir Hypothesis for Enceladus' South Polar Plume
Spencer, John R.; Kieffer, Susan W.; Lu, Xinli +3 more
We hypothesize that active tectonic processes in the south polar terrain of Enceladus, the 500-kilometer-diameter moon of Saturn, are creating fractures that cause degassing of a clathrate reservoir to produce the plume documented by the instruments on the Cassini spacecraft. Advection of gas and ice transports energy, supplied at depth as latent …
Clues to Nuclear Star Cluster Formation from Edge-on Spirals
Seth, Anil C.; Dalcanton, Julianne J.; Hodge, Paul W. +1 more
We find nine nuclear cluster candidates in a sample of 14 edge-on, late-type galaxies observed with the Hubble Space Telescope Advanced Camera for Surveys. These clusters have magnitudes (MI~-11) and sizes (reff~3 pc) similar to those found in previous studies of face-on, late-type spirals and dE galaxies. However, three of t…
The Spiderweb Galaxy: A Forming Massive Cluster Galaxy at z ~ 2
Pentericci, Laura; Franx, Marijn; Illingworth, Garth D. +11 more
We present a deep image of the radio galaxy MRC 1138-262 taken with the Hubble Space Telescope (HST) at a redshift of z=2.2. The galaxy is known to have properties of a cD galaxy progenitor and be surrounded by a 3 Mpc-sized structure, identified with a protocluster. The morphology shown on the new deep HST ACS image is reminiscent of a spider's w…
Explaining the Color Distributions of Globular Cluster Systems in Elliptical Galaxies
Yoon, Suk-Jin; Lee, Young-Wook; Yi, Sukyoung Ken
The colors of globular clusters in most large elliptical galaxies are bimodal. This is generally taken as evidence for the presence of two cluster subpopulations that have different geneses. However, here we find that, because of the nonlinear nature of the metallicity-to-color transformation, a coeval group of old clusters with a unimodal metalli…
Mid-Infrared Spectral Diagnostics of Nuclear and Extranuclear Regions in Nearby Galaxies
Helou, G.; Moustakas, J.; Roussel, H. +19 more
Mid-infrared diagnostics are presented for a large portion of the Spitzer Infrared Nearby Galaxies Survey (SINGS) sample plus archival data from ISO and Spitzer. The SINGS data set includes low- and high-resolution spectral maps and broadband imaging in the infrared for over 160 nuclear and extranuclear regions within 75 nearby galaxies spanning a…
A Recalibration of Optical Photometry: Tycho-2, Strömgren, and Johnson Systems
Maíz Apellániz, J.
I use high-quality Hubble Space Telescope (HST) spectrophotometry to analyze the calibration of three popular optical photometry systems: Tycho-2 BT and VT, Strömgren uvby, and Johnson UBV. For Tycho-2, I revisit the analysis of an earlier paper to include the new recalibration of grating/aperture corrections, vignetting, and charge transfer ineff…
The Outburst of HST-1 in the M87 Jet
Cheung, C. C.; Sparks, W. B.; Wilson, A. S. +4 more
The X-ray intensity of knot HST-1, 0.85" from the nucleus of the radio galaxy M87, has increased by more than a factor of 50 during the last 5 yr. The optical increase is similar, and our more limited radio data indicate a commensurate activity. We give the primary results of our Chandra X-Ray Observatory monitoring program and consider some of th…