Search Publications
Hyades dynamics from N-body simulations: Accuracy of astrometric radial velocities from Hipparcos
Madsen, Søren
The internal velocity structure in the Hyades cluster as seen by Hipparcos is compared with realistic N-body simulations using the NBODY6 code, which includes binary interaction, stellar evolution and the Galactic tidal field. The model allows to estimate reliably the accuracy of astrometric radial velocities in the Hyades as derived by Lindegren …
Propagation velocities of gas rings in collisional ring galaxies
Bizyaev, D.; Vorobyov, E. I.
The propagation velocity of the first gas ring in collisional ring galaxies, i.e. the velocity at which the maximum in the radial gas density profile propagates radially in the galactic disk, is usually inferred from the radial expansion velocity of gas in the first ring. Our numerical hydrodynamics modeling of ring galaxy formation however shows …
Line shape diagnostics of Galactic 26Al
Hartmann, D. H.; Diehl, R.; Kretschmer, K.
The shape of the gamma-ray line from radioactive 26Al, at 1808.7 keV energy in the frame of the decaying isotope, is determined by its kinematics when it decays, typically 106 y after its ejection into the interstellar medium from its nucleosynthesis source. Three measurements of the line width exist: HEAO-C's 1982 value of (…
A weak lensing analysis of a STIS dark-lens candidate
Schirmer, M.; Fosbury, R. A. E.; Schneider, P. +6 more
We perform a weak lensing analysis on a previously reported dark-lens candidate on STIS Parallel data \citep{meh02}. New VLT-data indicate that the reported signal originates from a small number of galaxies tangentially aligned towards the center of the STIS field but no signature for an extended mass distribution is found. We argue that we should…
The INTEGRAL ground segment and its science operations centre
Parmar, A. N.; Schmidt, M.; Kuulkers, E. +10 more
The INTEGRAL ground segment is divided into operational and scientific components. The operational component consists of the Mission Operations Centre, the ground stations and communications lines while the scientific component comprises of a Science Operations Centre and Science Data Centre. The overall architecture of the ground segment is descr…
IBIS Veto System. Background rejection, instrument dead time and zoning performance
Bird, A. J.; Ubertini, P.; Bazzano, A. +7 more
IBIS is the high energy imager on board the INTEGRAL satellite. The gamma-ray instruments on board will take advantage of the long uninterrupted observation made possible by the very eccentric orbit (10 000 km perigee and 152 000 km apogee). A disadvantage for orbits outside the protection of the van Allen belts is the exposure to cosmic and solar…
Visual orbit for the low-mass binary Gliese 22 AC from speckle interferometry
Leinert, Ch.; Docobo, J. A.; Woitas, J. +1 more
Based on 14 data points obtained with near-infrared speckle interferometry and covering an almost entire revolution, we present a first visual orbit for the low-mass binary system Gliese 22 AC. The quality of the orbit is largely improved with respect to previous astrometric solutions. The dynamical system mass is 0.592+/- 0.065 Msun, w…
XMM-Newton observations of the Seyfert 1 galaxy ESO 141-G55
Gondoin, P.; Orr, A.; Lumb, D.
We report on an observation of the Seyfert 1 galaxy ESO 141-G55 performed in October 2001 with the EPIC MOS cameras and Reflection Grating Spectrometers (RGS) on board the XMM-Newton observatory. We find the hard (3-10 keV) continuum slope, including reflection, to be somewhat flatter (Gamma = 1.72 +/- 0.06) than that of a typical broad-line Seyfe…
Grey extinction in the solar neighbourhood?
Galazutdinov, G. A.; Strobel, A.; Skórzyński, W.
Some of the close O and B dwarfs appear to be fainter than indicated by their Hipparcos distances, intrinsic absolute magnitudes attributed to their spectral types, and estimated selective interstellar extinction. This discrepancy is explained in the paper by the grey (neutral) interstellar extinction in the visual range of spectrum. The measure o…
A study of the causal relationship between the emergence of a twisted magnetic flux rope and a small Hα two-ribbon flare
Brooks, D. H.; Kurokawa, H.; Berger, T. E. +2 more
We present results from an analysis of a small two-ribbon flare which occurred above emerging flux in solar active region NOAA 8218 on 1998, May 13th and which was observed by the Swedish Vacuum Solar Telescope (SVST) on the island of La Palma, Spain. The relatively simple magnetic morphology and small size of the flare together with the high qual…