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K dwarfs and the chemical evolution of the solar cylinder
Chiappini, Cristina; Matteucci, Francesca; Flynn, Chris +1 more
K dwarfs have lifetimes older than the present age of the Galactic disc, and are thus ideal stars for investigating the chemical evolution of the disc. We have developed several photometric metallicity indicators for K dwarfs, based on a sample of accurate spectroscopic metallicities for 34 disc and halo G and K dwarfs. The photometric metalliciti…
Multiple magnetic clouds in interplanetary space
Wang, S.; Wang, Y. M.; Ye, P. Z.
An interplanetary magnetic cloud (MC) is usually considered the byproduct of a coronal mass ejection (CME). Due to the frequent occurrence of CMEs, multiple magnetic clouds (multi-MCs), in which one MC catches up with another, should be a relatively common phenomenon. A simple flux rope model is used to get the primary magnetic field features of m…
The physical structure of Magellanic Cloud H II regions. II. Elemental abundances
van der Hulst, J. M.; Vermeij, R.
Based on a new data set of optical and infrared spectra described in Vermeij et al. (\cite{Ronald}), we analyse the gas-phase elemental abundances of a sample of H Ii regions in the Large and Small Magellanic Cloud. The combined optical and infrared data set gives us access to all the ionization stages of astrophysically important elements such as…
Element abundances in cool white dwarfs. II. Ultraviolet observations of DZ white dwarfs
Wolff, B.; Koester, D.; Liebert, J.
We present a small data base of homogeneously derived photospheric element abundances of DZ white dwarfs and related objects. Our previous investigations are supplemented with the analysis of ultraviolet spectra for nine white dwarfs. Of particular interest is the detection of Lalpha absorption in van Maanen 2 and a determination of the effective …
The Embedded Super-Star Cluster of SBS 0335-052
Sauvage, Marc; Plante, Stéphanie
We analyze the infrared (6-100 µm) spectral energy distribution of the blue compact dwarf and metal-poor (Z=Zsolar/41) galaxy SBS 0335-052. With the help of DUSTY, a program that solves the radiation transfer equations in a spherical environment, we evaluate that the infrared emission of SBS 0335-052 is produced by an embedded sup…
Mass segregation in young compact star clusters in the Large Magellanic Cloud - I. Data and luminosity functions
de Grijs, R.; Gilmore, G. F.; Johnson, R. A. +1 more
We have undertaken a detailed analysis of HST/WFPC2 and STIS imaging observations, and of supplementary wide-field ground-based observations obtained with the ESO New Technology Telescope (NTT) of two young (~10-25Myr) compact star clusters in the LMC, NGC 1805 and 1818. The ultimate goal of our work is to improve our understanding of the degree o…
Hubble Space Telescope STIS Observations of the Kinematics of Emission-Line Nebulae in Three Compact Steep-Spectrum Radio Sources
Koekemoer, Anton M.; Baum, Stefi A.; O'Dea, Christopher P. +8 more
We have obtained Hubble Space Telescope Space Telescope Imaging Spectrograph long-slit spectroscopy of the aligned emission-line nebulae in three compact steep-spectrum radio sources: 3C 67, 277.1, and 303.1. We find systematic offsets (~300-500 km s-1) of the emission-line velocities on one or both sides of the radio sources. We also s…
Echoes in X-ray binaries
Horne, Keith; O'Brien, K.; Chen, W. +3 more
We present a method of analysing the correlated X-ray and optical/UV variability in X-ray binaries, using the observed time delays between the X-ray driving light curves and their reprocessed optical echoes. This allows us to determine the distribution of reprocessing sites within the binary. We model the time-delay transfer functions by simulatin…
Constraining the cosmological parameters using strong lensing
Kneib, J. -P.; Soucail, G.; Golse, G.
We investigate the potential of using strong lensing clusters to constrain the cosmological parameters Omegam and Omegalambda. The existence of a multiple image system with known redshift allows, for a given (Omegam, Omegalambda) cosmology, absolute calibration of the total mass deduced from lens modelli…
Phase-steepened Alfvén waves, proton perpendicular energization and the creation of magnetic holes and magnetic decreases: The ponderomotive force
Lakhina, G. S.; Tsurutani, B. T.; Goldstein, B. E. +6 more
Solar wind protons detected within Magnetic Holes (MHs) and Magnetic Decreases (MDs) are found to be preferentially heated perpendicular to B0. The MHs/MDs are associated with the phase-steepened edges of nonlinear Alfvén waves. The proton anisotropies can lead to the proton cyclotron and mirror mode plasma instabilities. We examine the…