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Searching for heavily obscured post-AGB stars and planetary nebulae. II. Near-IR observations of IRAS sources
Guerrero, M. A.; Ramos-Larios, G.; Gómez, J. F. +2 more
The most massive AGB stars are expected to result in heavily obscured post-AGB stars, proto-PNe and PNe with highly axisymmetric morphologies. To investigate this evolutionary connection, we have selected a sample of 165 presumably obscured IRAS post-AGB star and PN candidates and obtained near-IR JHK images for 164 of them. These images, in conju…
HST/COS Observations of Thirteen New He II Quasars
Anderson, Scott F.; Schneider, Donald P.; York, Donald G. +3 more
The full reionization of intergalactic helium was a major event in the history of the intergalactic medium (IGM), and UV observations of the He II Gunn-Peterson trough allow us to characterize the end of this process at z ~ 3. Due to intervening hydrogen absorption, quasars allowing such study are rare, with only 33 known in the literature, and mo…
Deep Chandra and XMM-Newton X-ray observations of AWM 7 - I. Investigating X-ray surface brightness fluctuations
Fabian, A. C.; Sanders, J. S.
We investigate the levels of small-scale structure in surface brightness images of the core of the X-ray bright cool-core galaxy cluster AWM 7. After subtraction of a model of the smooth cluster emission, we find a number of approximately radial surface brightness depressions which are not present in simulated images and are seen in both the Chand…
Oscillations in Active Region Fan Loops: Observations from EIS/ Hinode and AIA/SDO
Banerjee, D.; Krishna Prasad, S.; Singh, Jagdev
Active region fan loops in AR 11076 were studied, in search of oscillations, using high cadence spectroscopic observations from Extreme-ultraviolet Imaging Spectrometer (EIS) on board Hinode combined with imaging sequences from the Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO). Spectra from EIS were analyzed in two s…
Quasi full-disk maps of solar horizontal velocities using SDO/HMI data
Roudier, Th.; Malherbe, J. M.; Gizon, L. +6 more
Aims: For the first time, the motion of granules (solar plasma on the surface on scales larger than 2.5 Mm) has been followed over the entire visible surface of the Sun, using SDO/HMI white-light data.
Methods: Horizontal velocity fields are derived from image correlation tracking using a new version of the coherent structure tracking al…
H I content, metallicities and spin temperatures of damped and sub-damped Lyα systems in the redshift desert (0.6 < zabs < 1.7)★
Ellison, Sara L.; Prochaska, J. Xavier; Kanekar, Nissim +2 more
The H I 21-cm absorption optical depth and the N(H I) column density derived from Lyα absorption can be combined to yield the spin temperature (Ts) of intervening damped Lyα systems (DLAs). Although spin temperatures have been determined for samples of DLAs with zabs < 0.6 and zabs > 1.7, the intermediate reg…
BD-22°3467, a DAO-type star exciting the nebula Abell 35
Rauch, T.; Werner, K.; Kruk, J. W. +2 more
Context. Spectral analyses of hot, compact stars with non-local thermodynamical equilibrium (NLTE) model-atmosphere techniques allow the precise determination of photospheric parameters such as the effective temperature (Teff), the surface gravity (log g), and the chemical composition. The derived photospheric metal abundances are cruci…
Photocentric variability of quasars caused by variations in their inner structure: consequences for Gaia measurements
Jovanović, P.; Popović, L. Č.; Stalevski, M. +4 more
Context. We study the photocenter position variability caused by variations in the quasar inner structure. We consider the variability in the accretion disk emissivity and torus structure variability caused by the different illumination by the central source. We discuss the possible detection of these effects by Gaia. Observations of the photocent…
The XMM-Newton view of supergiant fast X-ray transients: the case of IGR J16418-4532
Mereghetti, S.; Sidoli, L.; Sguera, V. +1 more
We report on a 40 ks long, uninterrupted X-ray observation of the candidate supergiant fast X-ray transient (SFXT) IGR J16418-4532 performed with XMM-Newton on 2011 February 23. This high-mass X-ray binary lies in the direction of the Norma arm, at an estimated distance of 13 kpc. During the observation, the source showed strong variability exceed…
Hydrogen Fluoride in High-mass Star-forming Regions
Ceccarelli, C.; Lis, D. C.; Phillips, T. G. +5 more
Hydrogen fluoride (HF) has been established to be an excellent tracer of molecular hydrogen in diffuse clouds. In denser environments, however, the HF abundance has been shown to be approximately two orders of magnitude lower. We present Herschel/HIFI observations of HF J = 1-0 toward two high-mass star formation sites, NGC 6334 I and AFGL 2591. I…