Search Publications
Speckle interferometry of nearby multiple stars
Weigelt, G.; Hofmann, K. -H.; Schertl, D. +5 more
We present the results of diffraction-limited optical speckle interferometry and infrared bispectrum speckle interferometry of 111 double and 10 triple systems performed in 1998-1999 with the 6-m telescope of the Special Astrophysical Observatory in Zelenchuk. The observations concentrated on nearby close binaries discovered during the Hipparcos m…
X-ray observations of a large-scale solar coronal shock wave
Aurass, H.; Khan, J. I.
We report observations of a propagating disturbance in the solar corona observed in emission in soft X-ray images from the Yohkoh Soft X-ray Telescope (SXT). The disturbance was associated with a flare which began at about 09:04 UT on 1997 November 03. This flare was associated with a type II radio burst observed at decimetric-dekametric wavelengt…
Dynamical masses of young star clusters in NGC 4038/4039
Genzel, R.; Lehnert, M. D.; Mengel, S. +1 more
In order to estimate the masses of the compact, young star clusters in the merging galaxy pair, NGC 4038/4039 (``the Antennae''), we have obtained medium and high resolution spectroscopy using ISAAC on VLT-UT1 and UVES on VLT-UT2 of five such clusters. The velocity dispersions were estimated using the stellar absorption features of CO at 2.29 mu m…
Astrometric radial velocities. III. Hipparcos measurements of nearby star clusters and associations
Lindegren, Lennart; Madsen, Søren; Dravins, Dainis
Radial motions of stars in nearby moving clusters are determined from accurate proper motions and trigonometric parallaxes, without any use of spectroscopy. Assuming that cluster members share the same velocity vector (apart from a random dispersion), we apply a maximum-likelihood method on astrometric data from Hipparcos to compute radial and spa…
Flare waves observed in Helium I 10 830 Å. A link between Hα Moreton and EIT waves
Vršnak, B.; Hanslmeier, A.; Warmuth, A. +1 more
Three traveling disturbances recorded in the absorption line of Helium I at 10 830 Å, (He I), analogous to Hα Moreton waves, are analyzed. The morphology and kinematics of the wavefronts are described in detail. The He I wave appears as an expanding arc of increased absorption roughly corresponding to the Hα disturbance, although not as sharply de…
XMM-Newton observation of the distant (z=0.6}) galaxy cluster RX J1120.1+4318
Aghanim, N.; Arnaud, M.; Giard, M. +11 more
We report on a 20 ks XMM observation of the distant cluster RX J1120.1+4318, discovered at z=0.6 in the SHARC survey. The cluster has a regular spherical morphology, suggesting it is in a relaxed state. The combined fit of the EPIC/MOS&pn camera gives a cluster mean temperature of kT= 5.3+/-0.5 kev with an iron abundance of 0.47+/-0.19. The te…
The profiles of the aromatic infrared bands explained with molecular carriers
Joblin, C.; Boissel, P.; Pech, C.
Using a compilation of the photophysical properties of molecules such as coronene, C24H12, we have constructed a numerical model to calculate the IR emission spectrum of a population of polycyclic aromatic hydrocarbon (PAH) species subjected to UV photons. The model enables us to calculate not only the energy emitted in the I…
High-resolution X-ray spectroscopy of Procyon by Chandra and XMM-Newton
Kaastra, J. S.; Raassen, A. J. J.; Mewe, R. +6 more
We report the analysis of the high-resolution soft X-ray spectrum of the nearby F-type star Procyon in the wavelength range from 5 to 175 Å obtained with the Low Energy Transmission Grating Spectrometer (LETGS) on board Chandra and with the Reflection Grating Spectrometers (RGS) and the EPIC-MOS CCD spectrometers on board XMM-Newton. Line fluxes h…
The blue compact dwarf galaxy I Zw 18: A comparative study of its low-surface-brightness component
Thuan, T. X.; Izotov, Y. I.; Green, R. F. +4 more
Using HST and ground-based optical and NIR imaging data we investigate whether the blue compact dwarf (BCD) galaxy I Zw 18 possesses an extended low-surface-brightness (LSB) old stellar population underlying its star-forming regions, as is the case in the majority of BCDs. This question is central to the long-standing debate on the evolutionary st…
Spectroscopic diagnostics of stellar transition regions and coronae in the XUV: AU Mic in quiescence
Mason, H. E.; Landini, M.; Del Zanna, G.
In this paper we review the spectroscopic diagnostic techniques that can be applied to XUV observations of active stars. In particular, we discuss methods for the determination of electron densities, emission measures and the chemical composition of the stellar transition regions and coronae. We pay particular attention to the atomic data used and…