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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…
An XMM-Newton observation of the narrow-line Seyfert 1 galaxy Markarian 896
O'Brien, P. T.; Reeves, J. N.; Page, K. L. +1 more
We present XMM-Newton observations of the narrow-line Seyfert 1 galaxy Markarian 896. Over the 2-10 keV band, an iron emission line, close to 6.4 keV, is seen. The line is just resolved and has an equivalent width of ~170 eV. The broad-band spectrum is well modelled by a power-law slope of Γ~ 2.03, together with two blackbody components to fit the…
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…
Fragmentation of Globules in H II Regions: Hubble Space Telescope Images of Thackeray's Globules
Reipurth, Bo; Heathcote, Steve; Raga, Alex
We present Hubble Space Telescope WFPC2 images through an Hα filter of Thackeray's globules in the southern H II region IC 2944. The images document the state of the globule complex during its current highly dynamical phase of breakup. A population of very small and short-lived splinters suggests that continuous fragmentation must play an importan…
Stellar collisions in galactic centres: black hole growth and colour gradients
Yu, Qingjuan
We study the effects of stellar collisions, particularly on feeding massive black holes (BHs) and colour gradients, in realistic galactic centres. We find that the mass released by stellar collisions is not sufficient to account for the present BH mass in galactic centres, especially in bright galaxies. This study, together with the study by Magor…
Structural analysis of periodic surface waves on the magnetospheric boundary
Roth, M.; De Keyser, J.
In situ observations of the flanks of the magnetospheric boundary (magnetopause and boundary layer) sometimes show periodic surface waves to be present. We propose a straightforward but powerful technique for analyzing such periodic boundary waves. The result of this analysis is a two-dimensional picture of the structure of the wave in a reference…
The global heliospheric magnetic field polarity distribution as seen at Ulysses
Balogh, A.; Jones, G. H.
The Ulysses spacecraft is in a near-polar solar orbit with a period of 6.2 years. The heliospheric magnetic field polarity detected by Ulysses from its 1992 Jupiter encounter to the current time is presented, following ballistic mapping of the polarity information to the solar wind source surface, at approximately 2.5 solar radii. The spacecraft's…
Consequences of the Solar System passage through dense interstellar clouds
Fahr, H. J.; Yeghikyan, A. G.
Several consequences of the passage of the solar system through dense interstellar molecular clouds are discussed. These clouds, dense (more than 100 cm-3), cold (10-50 K) and extended (larger than 1 pc), are characterized by a gas-to-dust mass ratio of about 100, by a specific power grain size spectrum (grain radii usually cover the range 0.001-3…
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…