Search

Aims.We present the first results of an asteroid photo-polarimetry program started at Asiago-Cima Ekar Observatory. The aim of our survey is to estimate diversity in polarimetric properties of asteroids belonging to different taxonomic and dynamical classes.

Extensive optical and infrared photometry as well as low and high resolution spectroscopy are used as inputs in deriving robust estimates of the reddening, distance and nature of the progenitor of V838 Mon, the 2002 outbursting event that produced a most spectacular light-echo. The reddening affecting V838 Mon is found to obey the RV=3.1 law and amounts to (i) $E_{B-V}=0.86$from the interstellar NaI and KI lines; (ii) $E_{B-V}=0.88$from the energy distribution of the B3 V component; and (iii) $E_{B-V}=0.87$from the progression of extinction along the line of sight. The adopted $E_{B-V}=0.87\pm0.01$is also the amount required by fitting the progenitor with theoretical isochrones of appropriate metallicity. The distance is estimated from (a) the galactic kinematics of the three components of the interstellar lines; (b) the amount of extinction vs. the HI column density and vs. the dust emission through the whole Galaxy in that direction; from (c) spectrophotometric parallax to the B3 V companion; from (d) comparison of the observed color-magnitude diagram of field stars with 3D stellar population models of the Galaxy; from (e) comparison of theoretical isochrones with the components of the binary system in quiescence and found to be around 10 kpc. Pre-outburst optical and IR energy distributions show that the component erupting in 2002 was brighter and hotter than the B3 V companion. The best fit is obtained for a 50 000 K source, 0.5 mag brighter than the B3 V companion. The latter passed unaffected through the outburst, which implies an orbital separation wide enough to avoid mass exchange during the evolution of the binary system, and to allow a safe comparison with theoretical isochrones for single stars. Such a comparison suggests that the progenitor of the outbursting component had an initial mass ~65 $M_\odot$, that it was approaching the carbon ignition stage in its core at the time it erupted in 2002 and that the age of the V838 Mon binary system is close to 4 million yr. The 2002 event is probably just a shell thermonuclear event in the outer envelope of the star.

We present the results of our polarimetric and spectropolarimetric monitoring of V838 Monocerotis, performed at the Asiago and Crimean observatories during and after the multiple outbursts that occurred in January-March 2002. The polarization of the object is mainly due to interstellar polarization ($P\sim 2.48$%). Intrinsic polarization up to ∼0.7% at 5000 Å  is present during the second maximum of the object (February 2002). This intrinsic component increases toward shorter wavelengths but our limited spectral coverage (5000-7500 Å) does not allow conclusive inferences about its origin. A strong depolarization across the Hαprofile is observed. The interstellar polarization gives a lower limit to the reddening of $E(B-V) >0.28$, with $E(B-V)\sim 0.5$being the most probable value. A normal ratio of total to selective absorption ($R_{V}=3.22\pm0.17$) was derived from the wavelength of maximum interstellar polarization. This suggests a low (if any) contribution by circumstellar material with a peculiar dust to gas ratio. A polarimetric map of a portion of the light echo shows a complex polarization distribution reaching $P_{\max}=45$%.

V838 Mon is marking one of the most mysterious stellar outbursts on record. The spectral energy distribution of the progenitor resembles an under-luminous F main sequence star (at $V=15.6$mag), that erupted into a cool supergiant following a complex and multi-maxima lightcurve (peaking at $V=6.7$mag). The outburst spectrum show BaII, LiI and lines of several $s-$elements, with wide P-Cyg profiles and a moderate and retracing emission in the Balmer lines. A light-echo discovered expanding around the object helped to constrain the distance ($d=790 \pm 30$pc), providing MV=+4.45 in quiescence and MV=-4.35 at optical maximum (somewhat dependent on the still uncertain $E_{B-V}=0.5$reddening). The general outburst trend is toward lower temperatures and larger luminosities, and continuing so at the time of writing. The object properties conflict with a classification within already existing categories: the progenitor was not on a post-AGB track and thus the similarities with the born-again AGB stars FG Sge, V605 Aql and Sakurai's object are limited to the cool giant spectrum at maximum; the cool spectrum, the moderate wind velocity (500 km s-1and progressively reducing) and the monotonic decreasing of the low ionization condition argues against a classical nova scenario. The closest similarity is with a star that erupted into an M-type supergiant discovered in M 31 by Rich et al. ([CITE]), that became however much brighter by peaking at MV=-9.95, and with V4332 Sgr that too erupted into an M-type giant (Martini et al. [CITE]) and that attained a lower luminosity, closer to that of V838 Mon. M 31-RedVar, V4332 Sgr and V838 Mon could be all manifestations of a new class of astronomical objects.

Context. A new extremely high speed photon-counting photometer, Iqueye, has been installed and tested at the New Technology Telescope, in La Silla.Aims. This instrument is the second prototype of a ?quantum? photometer being developed for future Extremely Large Telescopes of 30?50?m aperture.Methods. Iqueye divides the telescope aperture into four portions, each feeding a single photon avalanche diode. The counts from the four channels are collected by a time-to-digital converter board, where each photon is appropriately time-tagged. Owing to a rubidium oscillator and a GPS receiver, an absolute rms timing accuracy better than 0.5?ns during one-hour observations is achieved. The system can sustain a count rate of up to 8?MHz uninterruptedly for an entire night of observation.Results. During five nights of observations, the system performed smoothly, and the observations of optical pulsar calibration targets provided excellent results.

Aims.We present simulations of the perfomances of the future SPHERE IFS instrument designed for imaging extrasolar planets in the near infrared (Y, J, and Hbands).