Search Publications
Circumstellar features in hot DA white dwarfs
Barstow, M. A.; Bruhweiler, F. C.; Holberg, J. B. +1 more
We present a phenomenological study of highly ionized, non-photospheric absorption features in high spectral resolution vacuum ultraviolet spectra of 23 hot DA white dwarfs. Prior to this study, four of the survey objects (Feige 24, REJ 0457-281, G191-B2B and REJ 1614-085) were known to possess these features. We find four new objects with multipl…
Proper Motions of Open Star Clusters and the Rotation Rate of the Galaxy
Beshenov, G. V.; Loktin, A. V.
The mean proper motions of 167 Galactic open clusters with radial-velocity measurements are computed from the data of the Tycho-2 catalog using kinematic and photometric cluster membership criteria. The resulting catalog is compared to the results of other studies. The new proper motions are used to infer the Galactic rotation rate at the solar ci…
Quasi-periodic Pulsations in a Solar Microwave Burst
Kundu, M. R.; White, S. M.; Grechnev, V. V.
Quasi-periodic pulsations in solar flares can provide important information on physical conditions in flaring regions. In this paper, we study a microwave burst that showed deep quasi-periodic pulsations. The most dramatic feature of this event has been discussed by Asai and coworkers. In the second of four bursts during the flare, strongly modula…
A Hubble Space Telescope WFPC2 Investigation of the Nuclear Morphology in the Toomre Sequence of Merging Galaxies
Böker, Torsten; van der Marel, Roeland P.; Zabludoff, Ann I. +4 more
We report on the properties of nuclear regions in the Toomre sequence of merging galaxies, based on imaging data gathered with the Hubble Space Telescope WFPC2 camera. We have imaged the 11 systems in the proposed evolutionary merger sequence in the F555W and F814W broadband filters, and in Hα+[N II] narrowband filters. The broadband morphology of…
The high frequency power spectrum of Markarian 766
Vaughan, S.; Fabian, A. C.
An analysis is presented of the power spectrum of X-ray variability of the bright Seyfert 1 galaxy Mrk 766 as observed by XMM-Newton. Over the 0.2-10 keV energy range the power spectral density (PSD) is well-represented by a power-law with a slope of αlow~ 1 at low frequencies, breaking to a slope of αhi= 2.8+0.2
Detection of strongly processed ice in the central starburst of NGC 4945
Lutz, D.; Pontoppidan, K. M.; Tielens, A. G. G. M. +4 more
The composition of ice grains provides an important tool for the study of the molecular environment of star forming regions. Using ISAAC at the VLT to obtain spectra around 4.65 mu m we have detected for the first time ``XCN'' and CO ice in an extragalactic environment: the nuclear region of the nearby dusty starburst/AGN galaxy NGC 4945. The prof…
Balmer Lines as Diagnostics of Physical Conditions in Active Galactic Nuclei Broad Emission Line Regions
Popović, L. Č.
Using a well-known method for laboratory plasma diagnostics, the Boltzmann plot, we discuss the physical properties in the broad-line regions (BLRs) of active galactic nuclei (AGNs). We apply the Boltzmann plot method to Balmer lines on a sample of 14 AGNs and find that it may indicate the existence of ``case B'' recombination or partial local the…
Statistical Flux Tube Properties of 3D Magnetic Carpet Fields
Priest, E. R.; Parnell, C. E.; Mackay, D. H. +1 more
The quiet-Sun photosphere consists of numerous magnetic flux fragments of both polarities that evolve with granular and supergranular flow fields. These concentrations give rise to a web of intermingled magnetic flux tubes which characterise the coronal magnetic field. Here, the nature of these flux tubes is studied. The photosphere is taken to be…
Internal structure and dynamics of the kiloparsec-scale jet in M87
Lobanov, Andrei; Hardee, Philip; Eilek, Jean
Detailed analysis of HST and VLA observations enables quantitative modeling of the internal structure of the kiloparsec-scale jet in M87. The jet transverse profiles can be modeled by double-Gaussian profiles. The jet structure is dominated by two threads resembling closely a double helix visible until about 20″ distance. It is produced by a combi…
The temporal and spatial evolution of the starburst in ESO 338-IG04 as probed by its star clusters
Östlin, G.; Zackrisson, E.; Bergvall, N. +1 more