The THESEUS space mission: science goals,requirements and mission concept

Experimental Astronomy - THESEUS, one of the two space mission concepts being studied by ESA as candidates for next M5 mission within its Comsic Vision programme, aims at fully exploiting Gamma-Ray...     

Mössbauer investigation of niningerite solid solutions (Mg,Fe)S

⁵⁷Fe Mössbauer spectra of (Mg,Fe)S solid solutions (niningerite) quenched from 1,000° C exhibit a singlet only within the composition range 8.4 to 50.0 mol. percent FeS. The isomer shift decreases progressively with increasing FeS content (from 0.99 to 0.95 mm/s) and extrapolates to a value of about 0.9 mm/s for FeS (halite structure), in close agreement with the isomer shift for FeS (troilite). Line width increases progressively with increasing FeS content (from 0.32 to 0.47 mm/s) and with decreasing temperature. The broadened singlet spectrum is interpreted as an unresolved composite quadrupole split doublet, which is attributed to local site distortion by next-nearest neighbor cation substitution. The ground state splitting is estimated to be 40 cm^?1 in (Mg_0.5Fe_0.5)S. The next-nearest neighbor effect in niningerite is anomalously small compared to that observed in spinel and (Mg,Fe)O compositions.     

The WASP Project and SuperWASP Camera

The WASP project and infrastructure supporting the SuperWASP Facility are described. As the instrument, reduction pipeline and archive system are now fully operative we expect the system to have a major impact in the discovery of bright exo-planet candidates as well in more general variable star projects.     

The unusual 2006 dwarf nova outburst of GK Persei

The 2006 outburst of GK Persei differed significantly at optical and ultraviolet (UV) wavelengths from typical outbursts of this object. We present multiwavelength (X-ray, UV and optical) Swift and AAVSO data, giving unprecedented broad-band coverage of the outburst, allowing us to follow the evolution of the longer-than-normal 2006 outburst across these wavelengths. In the optical and UV we see a triple-peaked morphology with maximum brightness ∼1.5 mag lower than in previous years. In contrast, the peak hard X-ray flux is the same as in previous outbursts. We resolve this dichotomy by demonstrating that the hard X-ray flux only accounts for a small fraction of the total energy liberated during accretion, and interpret the optical/UV outburst profile as arising from a series of heating and cooling waves traversing the disc, caused by its variable density profile.