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DDO 44 and UGC 4998: Distances, Metallicities, and Star Formation Histories

Mateo, Mario; Aparicio, Antonio; Alonso-García, Javier

We have obtained deep HST imaging of two candidate dwarf systems in the nearby M81 Group, DDO 44 and UGC 4998. Both are isolated, low surface brightness systems, but with likely very different star formation histories based on their mean colors and color fluctuations. The color-magnitude diagrams of these galaxies have been used to estimate their …

UV Capabilities to Probe the Formation of Planetary Systems: From the ISM to Planets

Cernicharo, José; Gómez de Castro, Ana I.; Linsky, Jeffrey L. +2 more

Planetary systems are angular momentum reservoirs generated during star formation. Solutions to three of the most important problems in contemporary astrophysics are needed to understand the entire process of planetary system formation: The physics of the ISM. Stars form from dense molecular clouds that contain ∼ 30% of the total interstellar medi…

Is V899 Herculis an unsolved quadruple system containing double close binary stars?

Qian, S. -B.; Liao, W. -P.; He, J. -J. +2 more

Orbital period variation of the W UMa-type eclipsing binary, V899 Herculis, discovered by the Hipparcos satellite was investigated based on all available photoelectric and CCD times of light minimum. It is discovered that the orbital period of the binary shows a cyclic change with an amplitude of 0.0117 days. The cyclic period change can be explai…

Instabilities driven by ion shell distributions observed by Cluster in the midaltitude plasma sheet boundary layer

Fazakerley, A. N.; Marchaudon, A.; Cornilleau-Wehrlin, N. +5 more

Cluster observations in the near-Earth plasma sheet boundary layer (PSBL) region have shown the presence of ion shell distributions related to velocity-dispersed ion structures (VDIS) coincident with electrostatic emissions. We have examined ion shell instabilities in the presence of a cold ion and electron background using linear theory and parti…

On the Nature of the Hard X-Ray Source IGR J2018+4043

Kennea, J. A.; Terrier, R.; Rauw, G. +13 more

We found a very likely counterpart to the recently discovered hard X-ray source IGR J2018+4043 in the multiwavelength observations of the source field. The source, originally discovered in the 20-40 keV band, is now confidently detected also in the 40-80 keV band, with a flux of (1.4+/-0.4)×10^-11 ergs cm^-2 s^-1. A 5…

Energisation of O⁺ and O⁺ ₂ Ions at Mars: An Analysis of a 3-D Quasi-Neutral Hybrid Model Simulation

Kallio, E.; Fedorov, A.; Janhunen, P. +12 more

We have studied the loss of O⁺ and O⁺₂ ions at Mars with a numerical model. In our quasi-neutral hybrid model ions (H⁺, He⁺⁺, O⁺, O⁺₂) are treated as particles while electrons form a massless charge-neutralising fluid. The employed model version does not includ…

A Blue Straggler Binary with Three Progenitors in the Core of a Globular Cluster?

Knigge, C.; Long, K. S.; Gilliland, R. L. +3 more

We show that the X-ray source W31 in the core of the globular cluster 47 Tucanae is physically associated with the bright blue straggler BSS 7. The two sources are astrometrically matched to 0.061", with a chance coincidence probability of less than 1%. We then analyze optical time-series photometry obtained with the Hubble Space Telescope (HST) a…

Short-term changes in the belt/zone structure of Saturn's Southern Hemisphere (1996-2004)

Sánchez-Lavega, A.; Pérez-Hoyos, S.; French, R. G.

Aims.The main goal of this paper is to study the reflectivity changes that affect Saturn's global belt/zone pattern on time-scales from weeks to a few months, and to determine their frequency and intensity, as well as the variations of the vertical cloud structure that cause such changes.
Methods: .We have used 177 images from Hubble Space Tel…

The dark clump near Abell 1942: dark matter halo or statistical fluke?

Castander, F. J.; von der Linden, A.; Schneider, P. +1 more

Using HST WFPC2 mosaic imaging, deep Chandra observations, and the

original CFHT imaging, we investigate the case for the dark clump candidate originally presented by (Erben et al. 2000, A&A, 355, 23). We show that the original detection is well reproducible in the CFHT data, and can confirm the presence of an alignment signal at the dark…

X-Ray Pulsations in the Supersoft X-Ray Binary CAL 83

Cowley, A. P.; Schmidtke, P. C.

Chandra and XMM-Newton X-ray data reveal that the supersoft X-ray binary CAL 83 exhibits 38.4 minute pulsations at some epochs. These X-ray variations are similar to those found in some novae and are likely to be caused by nonradial pulsations of the white dwarf. This is the first detection of pulsations in a classical supersoft X-ray binary.