Search Publications
Barred Galaxies in the Abell 901/2 Supercluster with Stages
Bell, Eric F.; Wisotzki, Lutz; Wolf, Christian +22 more
We present a study of bar and host disk evolution in a dense cluster environment, based on a sample of ~800 bright (M V <= -18) galaxies in the Abell 901/2 supercluster at z~ 0.165. We use Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) F606W imaging from the STAGES survey, and data from Spitzer, XMM-Newton, and COMBO-…
Imaging of star clusters in unperturbed spiral galaxies with the Advanced Camera for Surveys. II. A comparison of star cluster systems in five late type spirals
Larsen, S. S.; Kissler-Patig, M.; Richtler, T. +2 more
Aims: Our goal is to investigate the formation of star clusters in relatively unperturbed environments. To do this, we studied the five nearby spiral galaxies: NGC 45, NGC 1313, NGC 4395, NGC 5236, and NGC 7793.
Methods: We obtained images of the galaxies and their star cluster systems in {UBVI} using the Advanced Camera for Surveys (ACS) and …
The source of Saturn's periodic radio emission
Kivelson, Margaret G.; Southwood, David J.
This paper proposes a model of the link between the pulsing radio signals from Saturn (Saturn kilometric radiation), known to be most intense on the morningside, and the rotating magnetic (cam) field structure identified on low-latitude orbits. On the high-inclination orbits of the Cassini spacecraft in late 2006, large-scale azimuthal deviations …
Unabsorbed Seyfert 2 galaxies: the case of `naked' AGN
Bianchi, S.; Gastaldello, F.; Barcons, X. +6 more
Hawkins reported on a class of `naked' active galactic nuclei (AGN) characterized by strong amplitude optical brightness variability and the complete absence of broad emission lines in the optical spectrum. The variability suggests that the nucleus is seen directly, however the absence of broad lines contradicts the simple formulation of Unified M…
The Cycles of α Centauri
Ayres, Thomas R.
The main AB pair of the nearby α Centauri triple system has one of the most extensive X-ray records of any cosmic object, stretching over 30 years. The primary, α Cen A (G2 V), is a near twin of the Sun, with a similarly soft (1-2 MK) corona. The secondary, α Cen B (K1 V), is more active than the Sun, with a generally harder coronal spectrum. Here…
MHD model of the flapping motions in the magnetotail current sheet
Kubyshkin, I. V.; Semenov, V. S.; Erkaev, N. V. +2 more
A new kind of magnetohydrodynamic waves is analyzed for a current sheet in the presence of a small normal magnetic field component (B z ) varying along the sheet. For the initial undisturbed state, a simplified model of the current sheet is considered with a Harris-like current density distribution across the sheet. Within the framewor…
Mass Outflow in the Seyfert 1 Galaxy NGC 5548
Kaastra, J. S.; Arav, N.; Kraemer, S. B. +4 more
We present a study of the intrinsic UV absorption and emission lines in an historically low-state spectrum of the Seyfert 1 galaxy NGC 5548, which we obtained in 2004 February at high spatial and spectral resolution with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. We isolate a component of emission with a width of 680 k…
Plasma electrons in Saturn's magnetotail: Structure, distribution and energisation
Lewis, G. R.; Coates, A. J.; Russell, C. T. +11 more
In this paper Saturn's nightside and pre-dawn electron (0.5 eV-28 keV) plasma sheet is studied using Cassini plasma electron and magnetic field data from 2006. Case studies are presented which exemplify the typical and atypical states of the plasma sheet, and are complemented by a statistical study of the plasma sheet. It will be shown that Saturn…
Storm clouds on Saturn: Lightning-induced chemistry and associated materials consistent with Cassini/VIMS spectra
Nicholson, Philip D.; Baines, Kevin H.; Buratti, Bonnie J. +4 more
Thunderstorm activity on Saturn is associated with optically detectable clouds that are atypically dark throughout the near-infrared. As observed by Cassini/VIMS, these clouds are ~20% less reflective than typical neighboring clouds throughout the spectral range from 0.8 µm to at least 4.1 µm. We propose that active thunderstorms origi…
Spectroscopic Confirmation of Faint Lyman Break Galaxies Near Redshift Five in the Hubble Ultra Deep Field
Dickinson, Mark; Hathi, Nimish; Cohen, Seth +17 more
We present the faintest spectroscopically confirmed sample of z ~ 5 Lyman break galaxies (LBGs) to date. The sample is based on slitless grism spectra of the Hubble Ultra Deep Field region from the Grism ACS Program for Extragalactic Science (GRAPES) and Probing Evolution and Reionization Spectroscopically (PEARS) projects, using the G800L grism o…