Context. This paper is the last in a series devoted to the analysis of the binary content of the Hipparcos Catalogue. Aims. The comparison of the proper motions constructed from positions spanning a short (Hipparcos) or long time (Tycho-2) makes it possible to uncover binaries with periods of the order of or somewhat larger than the short time span (in this case, the 3 yr duration of the Hipparcos mission), since the unrecognised orbital motion will then add to the proper motion. Methods. A list of candidate proper motion binaries is constructed from a carefully designed χ 2 test evaluating the statistical significance of the difference between the Tycho-2 and Hipparcos proper motions for 103 134 stars in common between the two catalogues (excluding components of visual systems). Since similar lists of proper-motion binaries have already been constructed, the present paper focuses on the evaluation of the detection efficiency of proper-motion binaries, using different kinds of control data (mostly radial velocities). The detection rate for entries from the Ninth Catalogue of Spectroscopic Binary Orbits (S B 9 ) is evaluated, as well as for stars like barium stars, which are known to be all binaries, and finally for spectroscopic binaries identified from radial velocity data in the Geneva-Copenhagen survey of F and G dwarfs in the solar neighbourhood. Results. Proper motion binaries are efficiently detected for systems with parallaxes in excess of ∼20 mas, and periods in the range 1000-30 000 d. The shortest periods in this range (1000-2000 d, i.e., once to twice the duration of the Hipparcos mission) may appear only as DMSA/G binaries (accelerated proper motion in the Hipparcos Double and Multiple System Annex). Proper motion binaries detected among S B 9 systems having periods shorter than about 400 d hint at triple systems, the proper-motion binary involving a component with a longer orbital period. A list of 19 candidate triple systems is provided. Binaries suspected of having low-mass (brown-dwarf-like) companions are listed as well. Among the 37 barium stars with parallaxes larger than 5 mas, only 7 exhibit no evidence for duplicity whatsoever (be it spectroscopic or astrometric). Finally, the fraction of proper-motion binaries shows no significant variation among the various (regular) spectral classes, when due account is taken for the detection biases.

We propose that the intermediate luminosity optical transient NGC 300 OT2008-1 was powered by a mass transfer episode from an extreme Asymptotic Giant Branch star to a Main Sequence companion. We find a remarkable similarity of the shapes of the light curves of the several months long NGC 300 OT2008-1 outburst, of the three months long 2002 enigmatic outburst of the B star V838 Mon, and the twenty-years long Great Eruption of the massive binary system Eta Carinae that occurred in the 19th century. Their similar decline properties hint to a common energy source: a gravitational energy that is released by accretion onto a main sequence star. These events populate a specific strip in the total energy vs. outburst duration diagram. The strip is located between novae and supernovae. We add recent transient events to that diagram and find them to occupy the same strip. This suggests that some intermediate luminosity optical transients are powered by accretion onto a compact object (not necessarily a main sequence star). These transients are expected to produce bipolar ejecta as a result of the geometry of the accretion process.

The single-mirror small-size telescope (SST-1M) is one of the three proposed designs for the small-size telescopes (SSTs) of the Cherenkov Telescope Array (CTA) project. The SST-1M will be equipped with a 4 m-diameter segmented reflector dish and an innovative fully digital camera based on silicon photo-multipliers. Since the SST subarray will consist of up to 70 telescopes, the challenge is not only to build telescopes with excellent performance, but also to design them so that their components can be commissioned, assembled and tested by industry. In this paper we review the basic steps that led to the design concepts for the SST-1M camera and the ongoing realization of the first prototype, with focus on the innovative solutions adopted for the photodetector plane and the readout and trigger parts of the camera. In addition, we report on results of laboratory measurements on real scale elements that validate the cama e-mail: matthieu.heller@cern.ch b e-mail: enrico.junior.schioppa@cern.ch c e-mail: alessio.porcelli@unige.ch era design and show that it is capable of matching the CTA requirements of operating up to high moonlight background conditions.

We study high-energy γ-rays observed from Cyg X-3 by the Fermi Large Area Telescope and the 15-GHz emission observed by the Ryle Telescope and the Arcminute Microkelvin Imager. We measure the γ-ray spectrum averaged over strong flares much more accurately than before, and find it well modelled by Compton scattering of stellar radiation by relativistic electrons with the power law index of 3.5 and a low-energy cutoff at the Lorentz factor of ∼ 10 3 . We find a weaker spectrum in the soft spectral state, but only upper limits in the hard and intermediate states. We measure strong orbital modulation during the flaring state, well modelled by anisotropic Compton scattering of blackbody photons from the donor by jet relativistic electrons. We discover a weaker orbital modulation of the 15 GHz radio emission, which is well modelled by free-free absorption by the stellar wind. We then study crosscorrelations between radio, γ-ray and X-ray emissions. We find the cross-correlation between the radio and γ-ray emissions peaks at a lag less than 1 d, while we detect a distinct radio lag of ∼50 d with respect to the soft X-rays in the soft spectral state.