Reducing precipitable water vapor effects on SAINT-EX lightcurves by harnessing satellite weather data

Variations in precipitable water vapor (PWV) have been shown to cause significant fluctuations in stellar lightcurves. These changes can happen on short (hour or less) timescales mimicking transits or on longer timescales causing jumps in the global lightcurves. Differential photometry does not easily correct for these changes in the lightcurves of cool M or L class stars, where most stars in the field are bluer than the target. When direct measurements of water vapor are available at an observatory site, these changes can be modeled and accounted for; however in many locations this information is unavailable. The SAINT-EX telescope, located in San Pedro Martir, Mexico is a member of the SPECULOOS group and specializes in finding transits around cool stars. As an in situ PWV sensor is not present at the site, we develop a model to use satellite-derived PWV estimates combined with local weather information to model the PWV values above the observatory. These estimates are then applied to archive data to improve photometric variability.