Search Publications
HST/ACS color-magnitude diagrams of candidate intermediate-age M 31 globular clusters. The role of blue horizontal branches
Bellazzini, M.; Galleti, S.; Federici, L. +3 more
We present deep (V ≃ 28.0) BV photometry obtained with the wide field channel of the Advanced Camera for Surveys on board HST for four M 31 globular clusters that were identified as candidate intermediate-age (age ~ 1-9 Gyr) by various authors, based on their integrated spectra and/or broad/intermediate-band colors. Two of them (B292 and B350) dis…
Methane on Mars: Current observations, interpretation, and future plans
Forget, Francois; Atreya, Sushil K.; Witasse, Olivier +5 more
Hubble Space Telescope survey of the Perseus cluster - III. The effect of local environment on dwarf galaxies
Conselice, Christopher J.; Penny, Samantha J.; de Rijcke, Sven +3 more
We present the results of a Hubble Space Telescope (HST) study of dwarf galaxies in the outer regions of the nearby rich Perseus cluster, down to MV=-12, and compare these with the dwarf population in the cluster core from our previous HST imaging. In this paper, we examine how properties such as the colour-magnitude relation, structure…
Constraints on Quasar Lifetimes and Beaming from the He II Lyα Forest
Furlanetto, Steven R.; Lidz, Adam
We show that comparisons of He II Lyα forest lines of sight to nearby quasar populations can strongly constrain the lifetimes and emission geometry of quasars. By comparing the He II and H I Lyα forests along a particular line of sight, one can trace fluctuations in the hardness of the radiation field (which are driven by fluctuations in the He II…
High-altitude charged aerosols in the atmosphere of Titan
Coates, Andrew; Young, David T.; Wellbrock, Anne +3 more
Observations by several instruments onboard the Cassini spacecraft revealed the existence of heavy hydrocarbon and nitrile species with masses of several thousand atomic mass units in the ionosphere of Titan. These very large molecules are in fact aerosols. The goal of this paper is to compute the concentrations of the charged aerosols in the uppe…
Retrieving optical depth from shadows in orbiter images of Mars
Keller, H. U.; Thomas, N.; Hoekzema, N. M. +6 more
The difference in brightness between shadowed and sunlit regions in space images of Mars is a measure of the optical depth of the atmosphere. The translation of this difference into optical depth is what we name the "shadow method". Our analysis of two HRSC data-sets and a HiRISE data-set indicates that it is possible to estimate the optical depth…
A multi-epoch XMM-Newton campaign on the core of the massive Cygnus OB2 association
Rauw, G.
Context. Cyg OB2 is one of the most massive associations of O-type stars in our Galaxy. Despite the large interstellar reddening towards Cyg OB2, many studies, spanning a wide range of wavelengths, have been conducted to more clearly understand this association. X-ray observations provide a powerful tool to overcome the effect of interstellar abso…
Fast acceleration of "killer" electrons and energetic ions by interplanetary shock stimulated ULF waves in the inner magnetosphere
Zong, QuiGang; Wang, YongFu; Yang, Biao +3 more
Energetic electrons and ions in the Van Allen radiation belt are the number one space weather threat. Understanding how these energetic particles are accelerated within the Van Allen radiation belt is one of the major challenges in space physics. This paper reviews the recent progress on the fast acceleration of "killer" electrons and energetic io…
Solar total irradiance in cycle 23
Solanki, S. K.; Schmutz, W.; Krivova, N. A.
Context. The most recent minimum of solar activity was deeper and longer than the previous two minima as indicated by different proxies of solar activity. This is also true for the total solar irradiance (TSI) according to the PMOD composite.
Aims: The apparently unusual behaviour of the TSI has been interpreted as evidence against solar surf…
Chandra and ROSAT Observations of A194: Detection of an X-Ray Cavity and Mapping the Dynamics of the Cluster
Baum, Stefi A.; O'Dea, Christopher P.; Churazov, Eugene +6 more
Based on Chandra and ROSAT observations, we investigated the nearby poor cluster A194, which hosts two luminous radio galaxies, NGC 547 (3C 40B) and NGC 541 (3C 40A). We demonstrated the presence of a large X-ray cavity (r ~ 34 kpc) formed by the giant southern radio lobe arising from 3C 40B in NGC 547. The estimated age of the cavity is t = 7.9 ×…