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Infrared, radio and optical variability of the BL Lacertae object 2007+777
Quirrenbach, A.; Wagner, S. J.; Zensus, J. A. +8 more
We present infrared observations at wavelengths of 60 and 100 mu m and contemporaneous radio (five frequencies) and optical (R band) monitoring of the BL Lac object 2007+777. During a three-week campaign with the ISO, the VLA, the Effelsberg 100 m radio telescope, and optical telescopes in Heidelberg and on Calar Alto, Spain, we observed variabili…
A detailed spectroscopic analysis of varepsilon Per. I. Determination of the orbital parameters and of the frequencies
Mathias, P.; Aerts, C.; De Cat, P. +1 more
We present the analysis of 445 high signal-to-noise spectra of the Si III triplet at 4553 Ä, 4568 Ä, 4575 Ä of the line-profile variable star varepsilon Persei. The data were gathered during 14 consecutive nights and fully cover the orbital cycle of the binary. The orbital parameters that we derive from our data for the close binary are in full ag…
Hubble Space Telescope Observations of the Hubble Clusters in NGC 6822: Ages and Structure
Zucker, Daniel B.; Hodge, Paul W.; Wyder, Ted K.
We present Hubble Space Telescope observations of four cluster candidates in NGC 6822 originally identified by Hubble. One of them, Hubble IV, is an H II region while Hubble VI, VII, and VIII are confirmed as rich star clusters. Based upon cluster color-magnitude diagrams from which the field star contamination has been subtracted, we derive ages …
Dynamical Characteristics of Small-Scale Hα Upflow Events on the Quiet Sun
Wang, Haimin; Chae, Jongchul; Lee, Chik-Yin
Studies of small-scale dynamical features on the quiet Sun are crucial for understanding the energetics and mass supply in the chromosphere and corona. Recent works by Wang and coworkers revealed the existence of numerous short-lived upflow events in Hα on the quiet Sun. In this paper we examine in detail the dynamical characteristics of these Hα …
Kinematical trends among the field horizontal branch stars
de Boer, Klaas S.; Altmann, Martin
Horizontal branch (HB) stars in the field of the Milky Way can be used as tracers for the study of early stages of the evolution of our galaxy. Since the age of individual HB stars is not known a priori, we have studied the kinematics of a sample of field HB stars measured with Hipparcos to look for signs of age and population nature. Our sample c…
Heliospheric Latitude Variations of Properties of Cometary Plasma Tails: A Test of the Ulysses Comet Watch Paradigm
Brandt, John C.; Snow, Martin
Images of comets de Vico in 1995, Hyakutake in 1996, and Hale-Bopp in 1997 taken by observers in the Ulysses Comet Watch clearly show plasma tail properties reflecting the demarcation of the solar wind into distinct equatorial and polar regions with the boundary determined by the maximum extent of the heliospheric current sheet (HCS). Generally, (…
Numerical Simulations of Oscillation Modes of the Solar Convection Zone
Kosovichev, A. G.; Georgobiani, D.; Nigam, R. +2 more
We use the three-dimensional hydrodynamic code of Stein & Nordlund to realistically simulate the upper layers of the solar convection zone in order to study physical characteristics of solar oscillations. Our first result is that the properties of oscillation modes in the simulation closely match the observed properties. Recent observations fr…
A Multiwavelength Campaign on γ Cassiopeiae. IV. The Case for Illuminated Disk-enhanced Wind Streams
Smith, Myron A.; Cranmer, Steven R.; Robinson, Richard D.
On 1996 March 14-15 we conducted a campaign with the Hubble Space Telescope GHRS to observe the Si IV λλ1394, 1403 lines of the B0.5e star γ Cas at high temporal and spectral resolution. As a part of this ~22 hr campaign, the Rossi X-Ray Timing Explorer (RXTE) was also used to monitor this star's copious and variable X-ray emission. In this fourth…
Hubble Space Telescope Observations of the Luminous Blue Variable/W-R Eclipsing Binary System HD 5980
Walborn, Nolan R.; Morrell, Nidia; Niemela, Virpi S. +5 more
We report the results of Hubble Space Telescope STIS observations of the intriguing luminous blue variable/Wolf-Rayet binary system HD 5980 in the Small Magellanic Cloud. Although its spectral characteristics (WN6) are currently very similar to those observed in 1995 in the FUV, some of the line fluxes continue with the increasing trend observed s…
Deep far infrared ISOPHOT survey in ``Selected Area 57". I. Observations and source counts
Nørgaard-Nielsen, H. U.; Ábrahám, P.; Lemke, D. +7 more
We present here the results of a deep survey in a 0.4 deg2 blank field in Selected Area 57 conducted with the ISOPHOT instrument aboard ESAs Infrared Space Observatory (ISO at both 60 mu m and 90 mu m. The resulting sky maps have a spatial resolution of 15 x 23 arcsec2 per pixel which is much higher than the 90 x 90 arcsec