Exoplanets and Stellar Physics

Abstract:

The planned launch of the James Webb Space Telescope (JWST) in 2018 will herald a new era of exoplanet spectroscopy. JWST will be the first telescope sensitive enough to potentially characterize terrestrial planets from their transmission spectra. In this work, we explore the possibility that terrestrial planets with Venus-type and Earth-type atmospheres could be distinguished from each other using spectra obtained by JWST. If we find a terrestrial planet close to the liquid water habitable zone of an M5 star within a distance of 10 parsec, it would be possible to detect atmospheric ozone if present in large enough quantities, which would enable an oxygen-rich atmosphere to be identified. However, the cloudiness of a Venus-type atmosphere would inhibit our ability to draw firm conclusions about the atmospheric composition, making any result ambiguous. Observing small, temperate planets with JWST requires significant investment of resources, with single targets requiring of the order of 100 transits to achieve sufficient signal to noise. The possibility of detecting a crucial feature such as the ozone signature would need to be carefully weighed against the likelihood of clouds obscuring gas absorption in the spectrum.

Abstract:

MASCARA, the Multi-site All-Sky CAmeRA, is a project aimed at finding exoplanets transiting the brightest stars, in the V = 4 to 8 magnitude range, currently probed neither by space- nor by ground-based surveys. The target population for MASCARA consists mostly of hot Jupiters, for which the average transit depth is around 1%, and hot Neptunes. In order to achieve consistently a signal-To-noise-ratio of better than 100 per hour at magnitude 8, MASCARA is based on three main concepts; simplicity stability and calibration. MASCARA was designed with a minimum number of moving components. Five fixed, shutter-less, Peltier-cooled cameras, fitted with standard Canon 24 mm f/1.4 lenses are operating in a temperature controlled environment. Each camera constantly stares at the same patch of the sky. The exposure time is set to 6.4 seconds, keeping trailing of stars and saturation to a minimum while allowing for continuous exposures. Each camera is connected to its own control-And data processing computer, allowing for fully independent operation of each of the cameras. Each camera takes between 4,000 and 7,000 exposures per night, which are reduced locally to produce un-calibrated light curves for the up to 40,000 pre-selected stars, as well as image stacks of 50 images. For each set of 50 images, astrometry of the solution is verified to monitor drifts in the station. Currently both reduced data as well as raw data (500 GB/night) are transferred to a central data repository, but for stations with less bandwidth, potentially only the reduced data could be transferred. MASCARA currently only permanently stores the reduced light curves and binned image stacks, deleting the raw images after one month. After transfer, the raw light curves are self-calibrated in batches of 2-4 weeks, removing the spatially-varying transmission of the camera, the impact of crowding and spatially-variable PSF, and the time-variable transmission of the atmosphere. Using a combination of SysRem and flagging of data points that are impacted by known artifacts (moon, sun, clouds, etc), we have demonstrated a photometric stability of MASCARA down to 0.3% at magnitude V=7.7 within 5.3 minutes.