Photometric transit search for planets around cool stars from the Western Italian Alps: a site characterization study

Abstract

We present the results of a site characterization study carried out at the Astronomical Observatory of the Autonomous Region of the Aosta Valley (OAVdA), in the Western Italian Alps, aimed at establishing its potential to host a photometric transit search for small-size planets around a statistically significant sample of nearby cool M dwarfs. [abridged] we gauged site-dependent observing conditions such as night-sky brightness, photometric precision, and seeing properties. Public meteorological data were also used in order to help in the determination of the actual number of useful observing nights per year. The measured zenithal $V$-band night-sky brightness is typical of that of very good, very dark observing sites. The extinction registered at $V$ band is not dissimilar from that of other sites. The median seeing over the period of in situ observations is found to be $\sim 1.7^{\prime \prime }$. Given the limited duration of the observations, we did not probe any possible seeing seasonal patterns, or the details of its possible dependence on other meteorological parameters, such as wind speed and direction. Moreover, our data show that the seeing at the observatory was reasonably stable during most of the nights. The fraction of fully clear nights per year amounts to 39\%, while the total of useful nights increases to 57\% assuming a (conservative) cloud cover of not more than 50\% of the night. Based on the analysis of photometric data collected over the period May-August 2009 for three stellar fields centered on the transiting planet hosts WASP-3, HAT-P-7, and Gliese 436, we achieve seeing-independent best-case photometric precision ${\sigma }_{\mathrm{ph}}\lesssim 3$ mmag (rms) in several nights for bright stars ($R\lesssim 11$ mag). A median performance ${\sigma }_{\mathrm{ph}}\sim 6$ mmag during the observing period is obtained for stars with $R\lesssim 13$ mag. [abridged]

42 Pages, 18 figures, 2 tables. Accepted for publication in PASP

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• Five Planets Orbiting 55 Cancri
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• Two new variable stars observed in the field of the extrasolar planet host star WASP-3

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• TASTE. III. A homogeneous study of transit time variations in WASP-3b
• Photometric transit search for planets around cool stars from the western Italian Alps: A pilot study
• Global Analysis of the TRAPPIST Ultra-Cool Dwarf Transit Survey
• Photometric rotation periods for 107 M dwarfs from the APACHE survey