A 0535 + 26/HDE 245770: A typical X-ray/Be system

Among the X-ray/Be systems, A 0535 + 26/HDE 245770 has been noted, since its discovery, for its peculiar features in several respects, in a wide energy range. For this reason and for a series of concomitant favorable causes, this system has been one of the most studied among the massive X-ray binary systems. The most remarkable incident was that its optical identification with an early-type-emission-line star (O9.7IIIe) has led to a deep studies on Be stars and their interactions with neutron stars, which have allowed to discover, without unbiguity, the presence of optical indicators of consequent X-ray flares, as well as that Be stars in X-ray/Be systems behave just as normal Be stars. Overmore, thanks to the multifrequency coordinated observations of this system, the X-ray emissions from binary companion of the Be stars are best explained by assuming the presence of a thick equatorial disk with low expansion velocity and a thin polar region with high expansion velocity. This picture reconciled the strong discrepancy in mass loss rate evaluations coming from IR and from UV measurements, assuming that the observed regions are enterely distinct from each other, one being a high-density, low-velocity region, and the other being a low-density, very hot, rapidly-expanding disk-like zone.Since, this picture seems to be the best up-to-date frame to cuckold all the experimental panorama available on X-ray/Be systems, we would like to paint in this paper the multifrequency behaviour of A 0535 + 26/HDE 245770, which is the best studied among such systems, in order to stimulate future coordinated experimental-theoretical works on this very interesting class of objects.     

The cataclysmic variable SS Cygni

In this work we will try to give the most general panorama, comparatively with the conciseness, on SS Cygni which is the brightest dwarf nova.The dwarf novae form a sub-class of the more vaste panorama of the Cataclysmic Variables (CVs). For this reason firstly we will describe in general the CVs and the current theories which attempt to describe their physical behaviour (Sections 2 and 3). The up-to-date observational properties of SS Cygni (Section 4) and a discussion on their explanation within the framework of theories (Section 5) will allow us to draw the conclusions (Section 6) and to argue the most convenient line of investigation (Section 7) both experimental and theoretical for a better understanding of the underlying physics of these systems.     

The Pre-Main-Sequence Star RU Lupi: An Extreme T Tauri star

In this work I will try to give the most general complete view, comparatively with the conciseness, on RU Lupi, which is an Extreme Classical T Tauri star.T Tauri stars (TTSs) form a class of low luminosity stars which are going to the Main Sequence. They are young contracting objects that are in a particular Pre-Main-Sequence (PMS) evolutionary phase. The study of the Pre-Main-Sequence Stars (PMSSs) can provide crucial information on stellar evolution and formation of planetary systems, and therefore also indirect information on the processes occurred in the primeval solar system.For this reason, firstly I will briefly comment a sort of classification of stars in PMS phases (Section 2); then I will emphasize the main characteristics of TTSs and the current theories (Section 3). The up-to-date observational properties of RU Lupi (Section 4) and a discussion on their explanation within the framework of theories (Section 5) will allow me to draw the conclusions (Section 6) and to argue the most convenient line of investigation (Section 7) both experimental and theoretical for a better understanding of the underlying physics of these systems. Finally (Section 8), I will comment in general on the methodology of investigation of highly variable cosmic sources.An original result has been obtained in this work: the flare-like events (FLEs) of RU Lupi, occurring in all wavelength regions, are periodic with aP _FLE=27.686±0.002 days. This periodicity could be the rotational period of the star.     

Gamma rays from accreting matter onto collapsed objects

In the spherical accretion onto massive objects, the matter may be heated up to temperatures as high as 10¹² °K. In such a hot plasma, the thermal bremsstrahlung (e-e and e-p) and π° decay from inelastic collisions of protons are the main γ-ray sources. We determined the γ -ray production spectra from the π° decay and from bremsstrahlung for different temperatures. The expected γ-ray spectra were evaluated too in order to fit experimental data. We have fitted COS B data from 3C 273 using a two temperatures plasma model. The best fit is for

Full-size image (1K)

(M₈ is the black hole mass in 10⁸ M) which gives . The hard X-ray measurements do not contradict the bremsstrahlung spectrum.     

Rapid oscillations in SS Cygni

High speed photometry of the dwarf nova SS Cygni during an outburst reveals the presence of rapid oscillations detected over an interval of four days. The period of the oscillations ranged from a maximum of 9.91 s to a minimum of 8.96 s. The results are discussed from the view point of several current models.     

Ultraviolet and optical observations of HDE 245770/ A 0535+26 system during an X-ray flare

We present high and low dispersion UV spectra of HDE 245770, which is the optical counterpart of the recurrent transient X-ray pulsar A 0535+26,during a decay of an X-ray flare. UBV photometric measurements and medium dispersion optical spectra were simultaneously obtained.The energy distribution of the star in the 12 – 10 micron range is compared with the models of Kurucz and Poeckert and Marlborough.In this phase, HDE 245770 does not show evaluable variations with respect to the quiescent X-ray phase.