[en] The Italian satellite for X-Ray Astronomy to be launched in late 1990 will be devoted to the study of galactic and extragalactic X-Ray sources in the energy interval 0.1-200 KeV. The unique characteristics of SAX are its ability to image X-Ray sources with moderate angular resolution (about 1 arcmin) over the energy range 1-10 keV including the Fe lines complex, the very wide simultaneous spectral coverage from 0.1 to 200 keV and, finally, the ability to detect and position transient phenomena and perform long term monitoring of variable sources. The instrumentation of SAX consists of four X-Ray imaging concentrators (nested double cones, approximation to Wolter I type grazing optics), a high pressure gas scintillation proportional counter, a phoswich detector and two wide field cameras. SAX is put in a quasi equatorial low altitude orbit by the Italian upper stage IRIS on board of the NASA Space Shuttle. The satellite is three-axis stabilized, has a total mass of 900 kg and the expected lifetime is two years. The SAX Program, presently in phase B, is carried out by Italy in collaboration with the Netherlands

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[en] It is known from Copernicus ultraviolet observations that all O type stars are losing mass by stellar wind. The ionized expanding circumstellar envelope formed by the stellar wind is emitting through free-free and bound-free radiation processes. This radiation is detectable at the infrared wavelengths where the stellar continuum is negligible. The measurement of the IR excess (defined as the difference between the total flux and the stellar continuum at a given wavelength) and the knowledge of the terminal velocity of the envelope, allow one to derive for OB stars the mass loss rate. From the analysis of Ir observations of two O stars, HDE 226868 and HDE 245770, identified as optical counterpart of X-ray sources, an estimate is given of their mass loss rate. (Auth.)

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[en] The transient X-ray pulsar A0535 + 26 was observed on Oct. 4, 1980 during a high level intensity outburst with a balloon-borne hard X-ray detector. High statistical quality source spectra were determined up to 100 keV. Both blackbody and Wien laws fit well the data. Pulse phase spectroscopy shows variation of temperature index between 7.5 and 8.5 keV in the off source spectra and between 7.4 and 10.5 keV in the off pulse spectra. The time-averaged luminosity above 30 keV is about 8 x 10 to the 36th erg/s. 11 references

[en] The X-ray source A0535+26 is well established as a recurrent transient. During its activity it shows long period pulsations (Papprox.=104 sec) with a relevant and variable rate of decrease of the pulse period. On the basis of its peak luminosity and pulsation features, the source has been suggested (see e.g. Elsner and Lamb, 1976) as an accreting neutron star in a binary system. In September-October 1980 the source showed a very high level outburst. Oda and the Hakucho Team (1980) gave a flux level in the 1-12 keV energy range of about 1 Crab on October 2nd, and 2 Crab on October 7th. We observed the source in the hard X-ray energy range on October 5th. Thanks to high signal from A0535+26 the observation resulted to be very effective to study its time variability and energy spectrum. (orig.)

[en] A derivation is presented of the optical-infrared energy distribution of the OBe star HDE 245770, the optical counterpart of the transient X-ray source A 0535 + 26, using infrared observations made in the period 1976 November - 1977 March and UBV photometry obtained by other workers in 1976 November. An infrared excess is evident with flux density Ssub(ν) varies as νsup(approximately 0.6). The excess is explained in terms of thermal free-free emission from an ionized gaseous envelope around the OBe star. Assuming a matter outflow through the envelope with uniform velocity of a few hundred km/s, a value is obtained for the mass loss rate in HDE 245770 of about 10^-6 solar masses/yr. (author)

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[en] A long observation of the recurrent transient X-ray pulsar A0535+26 was performed when the source was near the maximum of its high intensity level outburst occurred on October 1980. A light curve quite different from those observed in previous outbursts is found. The time averaged pulsed spectrum is well fitted both by a blackbody (kT = 9.0 +- 0.1 keV) and a Wien law (kT = 9.1 +- 0.1 keV). Spectral variability with pulse phase has also been observed. (Auth.)