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 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 .
A byproduct 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 were presented and discussed here .
Our results demonstrate 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 .