Search

Detailed models of αCen A and B based on new seismological data for αCen B by Carrier & Bourban ([CITE]) have been computed using the Geneva evolution code including atomic diffusion. Taking into account the numerous observational constraints now available for the αCen system, we find a stellar model which is in good agreement with the astrometric, photometric, spectroscopic and asteroseismic data. The global parameters of the αCen system are now firmly constrained to an age of $t=6.52 \pm 0.30$Gyr, an initial helium mass fraction $Y_{\mathrm{i}}=0.275 \pm 0.010$and an initial metallicity $(Z/X)_{\mathrm{i}}=0.0434 \pm 0.0020$. Thanks to these numerous observational constraints, we confirm that the mixing-length parameter αof the B component is larger than the one of the A component, as already suggested by many authors (Noels et al. [CITE]; Fernandes & Neuforge [CITE]; Guenther & Demarque [CITE]): $\alpha_{\mathrm{B}}$is about 8% larger than $\alpha_{\mathrm{A}}$($\alpha_{\mathrm{A}}=1.83 \pm 0.10$and $\alpha_{\mathrm{B}}=1.97 \pm 0.10$). Moreover, we show that asteroseismic measurements enable to determine the radii of both stars with a very high precision (errors smaller than 0.3%). The radii deduced from seismological data are compatible with the new interferometric results of Kervella et al. ([CITE]) even if they are slightly larger than the interferometric radii (differences smaller than 1%).

INTEGRALhas observed the bright quasar 3C 273 on 3 epochs in January 2003 as one of the first observations of the open programme. The observation on January 5 was simultaneous with RXTEand XMM-Newtonobservations. We present here a first analysis of the continuum emission as observed by these 3 satellites in the band from $\simeq$3 keV to $\simeq$500 keV. The continuum spectral energy distribution of 3C 273 was observed to be weak and steep in the high energies during this campaign. We present the actual status of the cross calibrations between the instruments on the three platforms using the calibrations available in June 2003.

We describe the INTEGRAL reference catalog which classifies previously known bright X-ray and gamma-ray sources before the launch of INTEGRAL. These sources are, or have been at least once, brighter than ~1 mCrab above 3 keV, and are expected to be detected by INTEGRAL. This catalog is being used in the INTEGRAL Quick Look Analysisto discover new sources or significantly variable sources. We compiled several published X-ray and gamma-ray catalogs, and surveyed recent publications for new sources. Consequently, there are 1122 sources in our INTEGRAL reference catalog. In addition to the source positions, we show an approximate spectral model and expected flux for each source, based on which we derive expected INTEGRAL counting rates. Assuming the default instrument performances and at least ~ 105s exposure time for any part of the sky, we expect that INTEGRAL will detect at least ~700 sources below 10 keV and ~400 sources above 20 keV over the mission life.

The K1 dwarf αCen B was observed with the Coraliespectrograph on the 1.2-m Swiss telescope at La Silla in April 2003. Thirteen nights of observations have made it possible to collect 3626 radial velocity measurements with a standard deviation of 1.4 m s-1exhibiting a mean noise level in the amplitude spectrum of only 3.75 cm s-1. Twelve oscillation modes have been identified in the power spectrum between 3 and 4.6 mHz with amplitudes in the range 8.7 to 13.7 cm s-1and showing a regularity with a large separation of 161.1 μHz. A preliminary discussion on the physical parameters of the αCen binary system is presented.