Search Publications
Oxygen abundances in nearby stars. Clues to the formation and evolution of the Galactic disk
Allende Prieto, C.; Lambert, D. L.; Ramírez, I.
The abundances of iron and oxygen are homogeneously determined in a sample of 523 nearby (d<150 pc) FGK disk and halo stars with metallicities in the range -1.5<[Fe/H]<0.5. Iron abundances were obtained from an LTE analysis of a large set of Fe I and Fe II lines with reliable atomic data. Oxygen abundances were inferred from a restricted …
Dissipation in Turbulent Plasma due to Reconnection in Thin Current Sheets
Retinò, Alessandro; Sundkvist, David; Vaivads, Andris +1 more
We present in situ measurements in a space plasma showing that thin current sheets the size of an ion inertial length exist and are abundant in strong and intermittent plasma turbulence. Many of these current sheets exhibit the microphysical signatures of reconnection. The spatial scale where intermittency occurs corresponds to the observed struct…
EUV Emission Lines and Diagnostics Observed with Hinode/EIS
Del Zanna, Giulio; Landi, Enrico; Harra, Louise K. +9 more
Quiet Sun and active region spectra from the Hinode/EIS instrument are presented, and the strongest lines from different temperature regions discussed. A list of emission lines recommended to be included in EIS observation studies is presented based on analysis of blending and diagnostic potential using the CHIANTI atomic database. In addition we …
A Wide-Field Survey of Two z ~ 0.5 Galaxy Clusters: Identifying the Physical Processes Responsible for the Observed Transformation of Spirals into S0s
Smith, Graham P.; Treu, Tommaso; Smail, Ian +3 more
We present new results from our comparative survey of two massive, intermediate-redshift galaxy clusters, Cl 0024+17 (z=0.39) and MS 0451-03 (z=0.54). Combining optical and UV imaging with spectroscopy of member galaxies, we identify and study several key classes of ``transition objects'' whose stellar populations or dynamical states indicate a re…
Geoeffectiveness of halo coronal mass ejections
Gopalswamy, N.; Yashiro, S.; Akiyama, S.
We studied the geoeffectiveness, speed, solar source, and flare association of a set of 378 halo coronal mass ejections (CMEs) of cycle 23 (1996-2005, inclusive). We compiled the minimum Dst values occurring within 1-5 days after the CME onset. We compared the distributions of such Dst values for the following subsets of halo CMEs: disk halos (wit…
Optical Spectroscopy and X-Ray Detections of a Sample of Quasars and Active Galactic Nuclei Selected in the Mid-Infrared from Two Spitzer Space Telescope Wide-Area Surveys
Armus, L.; Canalizo, G.; Sajina, A. +5 more
We present optical spectroscopy of a sample of 77 luminous active galactic nuclei (AGNs) and quasars selected on the basis of their mid-infrared colors. Our objects are selected from the Spitzer Extragalactic First Look Survey and the SWIRE XMM-Newton Large-Scale Structure Survey (XMM-LSS) fields, with a typical 24 µm flux density of 5 mJy. …
The Multiplicity of the Subgiant Branch of ω Centauri: Evidence for Prolonged Star Formation
Recio-Blanco, A.; Anderson, J.; Cool, A. M. +9 more
We combine spectroscopic and photometric data for subgiant stars of ω Cen to extract results that neither data set could have provided on its own. GIRAFFE@VLT spectra of 80 stars at R=6400 give metallicities for all of them and abundances of C, N, Ca, Ti, and Ba for a subset of them. The photometric data, which have unusually high accuracy, come f…
INTEGRAL observations of the cosmic X-ray background in the 5-100 keV range via occultation by the Earth
Sunyaev, R.; Revnivtsev, M.; Sazonov, S. +32 more
Aims: We study the spectrum of the cosmic X-ray background (CXB) in energy range ~5-100 keV.
Methods: Early in 2006 the INTEGRAL observatory performed a series of four 30 ks observations with the Earth disk crossing the field of view of the instruments. The modulation of the aperture flux due to occultation of extragalactic objects by the Eart…
Preplanetary Nebulae: A Hubble Space Telescope Imaging Survey and a New Morphological Classification System
Sahai, Raghvendra; Sánchez Contreras, Carmen; Morris, Mark +1 more
Using the Hubble Space Telescope (HST), we have carried out a survey of candidate preplanetary nebulae (PPNs). We report here our discoveries of objects having well-resolved geometric structures, and we use the large sample of PPNs now imaged with HST (including previously studied objects in this class) to devise a comprehensive morphological clas…
The Compact, Conical, Accretion-Disk Warm Absorber of the Seyfert 1 Galaxy NGC 4051 and Its Implications for IGM-Galaxy Feedback Processes
Elvis, Martin; Nicastro, Fabrizio; Mathur, Smita +4 more
Using a 100 ks XMM-Newton exposure of NGC 4051, we show that the time evolution of the ionization state of the X-ray absorbers in response to the rapid and highly variable X-ray continuum constrains all the main physical and geometrical properties of an AGN ``warm absorber'' wind. The absorber consists of two different ionization components, with …