Search results for "Individual stars"
showing 4 items of 4 documents
Wind accretion in the massive X-ray binary 4U 2206+54: abnormally slow wind and a moderately eccentric orbit
2006
Massive X-ray binaries are usually classified depending on the properties of the donor star in classical, supergiant and Be X-ray binaries. The massive X-ray binary 4U 2206+54 does not fit in any of these groups, and deserves a detailed study to understand how the transfer of matter and the accretion on to the compact object take place. To this end we study an IUE spectrum of the donor and obtain a wind terminal velocity (v_inf) of ~350 km/s, which is abnormally slow for its spectral type. We also analyse here more than 9 years of available RXTE/ASM data. We study the long-term X-ray variability of the source and find it to be similar to that observed in the wind-fed supergiant system Vela …
INTEGRAL/RXTE Observations of Cygnus X-1
2003
We present first results from contemporaneous observations of Cygnus X-1 with INTEGRAL and RXTE, made during INTEGRAL's performance verification phase in 2002 November and December. Consistent with earlier results, the 3-250 keV data are well described by Comptonization spectra from a Compton corona with a temperature of kT~50-90 keV and an optical depth of tau~1.0-1.3 plus reflection from a cold or mildly ionized slab with a covering factor of Omega/2pi~0.2-0.3. A soft excess below 10 keV, interpreted as emission from the accretion disk, is seen to decrease during the 1.5 months spanned by our observations. Our results indicate a remarkable consistency among the independently calibrated de…
Does GRS 1915+105 exhibit "canonical" black-hole states?
2003
We have analysed RXTE data of the superluminal source GRS 1915+105 in order to investigate if, despite its extreme variability, it also exhibits the canonical source states that characterise other black-hole candidates. The phenomenology of GRS 1915+105 has been described in terms of three states (named A, B and C) based on their hardness ratios and position in the colour-colour diagram. We have investigated the connection between these states and the canonical behaviour and found that the shape of the power spectral continuum and the values of the best-fit model parameters to the noise components in all three states indicate that the source shows properties similar to the canonical very hi…
The kinematics of water masers in the stellar molecular outflow source, IRAS 19134+2131
2004
Using the Very Large Array (VLA) and the Very Long Baseline Array (VLBA), we have observed water maser emission in the proto-planetary nebula candidate IRAS 19134+2131, in which the water maser spectrum has two groups of emission features separated in radial velocity by ∼100 km s^−1. The blue-shifted and red-shifted clusters of maser features are clearly separated spatially by ∼150 mas, indicative of a fast collimated flow. However, not all of the maser features are aligned along the axis of the flow, as is seen in the similar high-velocity water maser source, W43A. Comparing the VLA and VLBA maps of the water maser source, we find 4 maser features that were active for 2 years. Using only V…