Search

Near-UV (NUV) Hubble Space Telescope (HST) observations of the extreme hot-Jupiter WASP-12b revealed the presence of diffuse exospheric gas extending beyond the planet's Roche lobe. Furthermore the NUV observations showed a complete lack of the normally bright core emission of the Mg ii h&k resonance lines, in agreement with the measured anomalously low stellar activity index (log R′). Comparisons with other distant and inactive stars, and the analysis of radio and optical measurements of the intervening interstellar medium (ISM), led us to the conclusion that the system is surrounded by a circumstellar gas cloud, likely formed of material lost by the planet. Similar anomalous log R′ index deficiencies might therefore signal the presence of translucent circumstellar gas around other stars hosting evaporating planets; we identified five such systems and WASP-18 is one of them. Both radio and optical observations of the region surrounding WASP-18 point towards a negligible ISM absorption along the WASP-18 line of sight. Excluding the unlikely possibility of an intrinsic anomalously low stellar activity, we conclude that the system is probably surrounded by a circumstellar gas cloud, presumably formed of material lost by the planet. Nevertheless only a far-UV spectrum of the star would provide a definite answer. Theoretical modelling suggests WASP-18b undergoes negligible mass loss, in contrast to the probable presence of a circumstellar gas cloud formed of material lost by the planet. The solution might be the presence either of an extra energy source driving mass loss (e.g., the reconnection of the stellar and planetary magnetic fields inside the planet atmosphere) or of an evaporating third body (e.g., moon). [ABSTRACT FROM AUTHOR]

The success of the International Ultraviolet Explorer (IUE) first and then of the STIS and COS spectrographs on-board the Hubble Space Telescope (HST) demonstrate the impact that observations at UV wavelengths had and are having on modern astronomy. Several discoveries in the exoplanet field have been done at UV wavelengths. Nevertheless, the amount of data collected in this band is still limited both in terms of observed targets and time spent on each of them. For the next decade, the post-HST era, the only large (2-m class) space telescope capable of UV observations will be the World Space Observatory-UltraViolet (WSO-UV). In its characteristics, the WSO-UV mission is similar to that of HST, but all observing time will be dedicated to UV astronomy. In this work, we briefly outline the major prospects of the WSO-UV mission in terms of exoplanet studies. To the limits of the data and tools currently available, here we also compare the quality of key exoplanet data obtained in the far-UV and near-UV with HST (STIS and COS) to that expected to obtain with WSO-UV. [ABSTRACT FROM AUTHOR]

The results of study of the classical symbiotic star Z And during the recent activity period that began in 2000 are presented. Up to now series of six outbursts took place. Comparison of observational data with the results of gasdynamic modeling allow us to suggest the possible scenario for activity in this system describing all stages of an outburst development-from the mechanism of transition to the outburst and outburst development to the behavior of the system during all the activity period. Particularly, the proposed scenario explains the principal difference between outbursts-the presence of high-velocity bipolar collimated optical outflows in strong recurring outbursts. We have not found contradictions with the available data for previous outbursts of Z And. We assume that the proposed scenario could be also typical for other classic symbiotic stars. In order to check and improve our model additional observations are highly desirable and the UV spectral range could provide us with very useful data. [ABSTRACT FROM AUTHOR]

The results of gasdynamic modeling allowed us to propose the new mechanism of transition to active state in classical symbiotics and explain the step-by-step rise to the light maximum during the outburst. Good agreement with available observational data for Z And supports our model. Existing observations of symbiotic stars indicate the presence of winds from both components at active stages in these systems. We have carried out the gasdynamic modeling of the outburst development process in the classic symbiotic star Z And in the framework of the colliding winds model. It is shown that contribution from the system of shocks that forms in the area of wind collision is rather significant especially at short wavelengths. [ABSTRACT FROM AUTHOR]

The review of gasdynamic models used for the description of the mass exchange in close binaries is presented. Main features of the flow structure are summarized. Special attention is paid to physics of accretion discs in binary systems. It is shown that in self-consistent considerations of gas dynamics of mass transfer in close binaries the interaction of the stream fromL1 with the forming accretion disc is shock-free, and, hence, a “hot spot” does not form at the outer edge of the disc. To explain the presence of the observed zones of high luminosity in semidetached binaries a self-consistent “hot line” model is proposed. According to this model the excess energy is released in a shock wave formed due to interaction of the circumdisc halo and the gas stream flowing out of the donor-star through the vicinity of the inner Lagrangian point. [ABSTRACT FROM AUTHOR]

I review the current knowledge on binarity accompanying intrinsic variability of different types, according to the existing classification scheme. In many cases, binary nature not only accompanies but causes intrinsic variability. [ABSTRACT FROM AUTHOR]