Search

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. For the purpose of the site testing campaign, we gathered photometric and seeing measurements utilizing different instruments available at the site. As in any search for new locations for astronomical observations, 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 the V-band is not dissimilar from that of other sites. The median seeing over the period of in situ observations is found to be ?1.7?. 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 of 2009 May-August 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 ?ph? 3 mmag (rms) in several nights for bright stars (R? 11 mag). A median performance ?ph? 6 mmag during the observing period is obtained for stars with R? 13 mag. A by-product of the significant amount of photometric data collected in the stellar fields of WASP-3 and HAT-P-7 was the identification of a handful of new variable stars, four of which are presented and discussed here. Our results demonstrate that the OAVdA site is well poised to conduct an upcoming long-term photometric survey for transiting low-mass, small-size planets around a well-defined sample of M dwarfs in the solar neighborhood.