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Multiperiodicities from the Hipparcos epoch photometry and possible pulsation in early A-type stars
Koen, Chris
A selection criterion based on the relative strength of the largest peaks in the amplitude spectra, and an information criterion are used in combination to search for multiperiodicities in Hipparcos epoch photometry. The method is applied to all stars which have been classified as variable in the Hipparcos catalogue: periodic, unsolved and microva…
Discovery of Associated Absorption Lines in an X-Ray Warm Absorber:Hubble Space Telescope Faint Object Spectrograph Observations of MR 2251-178
Elvis, Martin; Mathur, Smita; Wilkes, Belinda +1 more
The presence of a ``warm absorber'' was first suggested to explain spectral variability in an X-ray spectrum of the radio-quiet quasi-stellar object (QSO) MR 2251-178. A unified picture, in which X-ray warm absorbers and ``intrinsic'' UV absorbers are the same, offers the opportunity to probe the nuclear environment of active galactic nuclei. To t…
Optical-Near-Infrared Color Gradients in Early-Type Galaxies at z<=1.0
Hinkley, Sasha; Im, Myungshin
Recent studies based on line indices of nearby early-type galaxies suggest that stars in the galaxies' inner part may be younger and more metal-rich than stars in the outer part. If confirmed, the finding has a profound implication for the formation and evolution of early-type galaxies, since such age gradients naturally arise if merging played an…
A Comparative Study of the Atmospheric Composition of the DA White Dwarfs Feige 24 and G191-B2B
Vennes, Stéphane; Lanz, Thierry
We analyze Hubble Space Telescope Imaging Spectrograph spectra of two white dwarfs, Feige 24 and G191-B2B, and we compare the measured abundance patterns. Except for carbon, which appears overabundant in G191-B2B by 0.3-0.5 dex relative to Feige 24, the average heavy-element abundance in Feige 24 is 0.17 dex larger than in the cooler, hence older,…
The stellar composition of the star formation region CMa R1 - II. Spectroscopic and photometric observations of nine young stars
de Winter, D.; van den Ancker, M. E.; Tjin A Djie, H. R. E. +4 more
We present new high- and low-resolution spectroscopic and photometric data of nine members of the young association CMa R1. All the stars have circumstellar dust at some distance, as could be expected from their association with reflection nebulosity. Four stars (HD52721, HD53367, LkHα220 and LkHα218) show Hα emission and we argue that they are He…
Deep submillimeter images of NGC 7331; dust at the periphery of spiral disks
Bianchi, S.; Combes, F.; Lequeux, J. +3 more
We present deep 450 and 850 mu m SCUBA images of the nearby spiral galaxy NGC 7331. Using the submillimeter emissivity inferred from COBE observations of Milky Way dust, we convert our SCUBA images into maps of optical depth. The opacity derived in this way is quite low at the visible limit of NGC 7331 (tau B<= 0.22 at the R25
The B-type variable HD 131120 modelled by rotational modulation
Aerts, C.; Briquet, M.; De Cat, P. +1 more
We present ground-based multi-colour Geneva photometry and high-resolution spectra of the variable B-type star HD 131120. All sets of data reveal a monoperiodic star with a period of 1.569 days. We compare the variability of the star with a non-radial g-mode pulsation model and with a rotational modulation model. The latter model appears to be the…
The Rapid Burster in Liller 1: The Chandra X-Ray Position and a Search for an Infrared Counterpart
Anderson, Scott F.; Margon, Bruce; Deutsch, Eric W. +1 more
Despite the unique X-ray behavior of the compact bursting X-ray source MXB 1730-335, the ``Rapid Burster'' (RB) in the highly reddened globular cluster Liller 1, to date there has been no known optical/IR counterpart for the object, no precise astrometric solution that correlates X-ray, radio, and optical positions and thus restricts the number of…
Hubble Space Telescope Observations of the Gravitationally Lensed Cloverleaf Broad Absorption Line QSO H1413+1143: Imaging Polarimetry and Evidence for Microlensing of a Scattering Region
Turnshek, David A.; Rao, Sandhya M.; Schulte-Ladbeck, Regina E. +2 more
We report the results of Hubble Space Telescope Wide Field and Planetary Camera 2 broadband F555W and F702W photometric and F555W polarimetric observations of the ``Cloverleaf'' QSO H1413+1143. This is a four-component gravitationally-lensed broad absorption line (BAL) QSO. Observations were obtained at two epochs in 1999 March and 1999 June separ…
Dynamical Cycles in Charge and Energy for Iron Ions Accelerated in a Hot Plasma
Torsti, J.; Kocharov, L.; Kovaltsov, G. A.
We consider a unified model of Fe ion acceleration in the solar corona. The model comprises charge-changing processes, Coulomb energy losses, and both regular and stochastic acceleration. At a given acceleration scenario, the type of acceleration is found to have a minor effect on the mean charge states, but the shapes of the charge-state distribu…