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.
MASCARA, the Multi-site All-Sky CAmeRA, consists of several fully-automated stations. Its goal is to find exoplanets transiting the brightest stars, in the mV = 4 to 8 magnitude range. Each station contains five wide- angle cameras monitoring the near-entire sky at each location. The five cameras are located in a temperature- controlled enclosure and look at the sky through five windows. A housing with a moving roof protects MASCARA from the environment. Here, we present the opto-mechanical design of the first MASCARA station.
MASCARA, the Multi-site All-Sky CAmeRA, will consist of several fully-automated stations distributed across the globe. Its goal is to find exoplanets transiting the brightest stars, in the mV = 4 to 8 magnitude range, currently probed neither by space- nor by ground-based surveys. The nearby transiting planet systems that MASCARA is expected to discover will be key targets for future detailed planet atmosphere observations. The target population for MASCARA consists mostly of hot Jupiters. The main requirement set on MASCARA to detect these planets around stars down to magnitude 8 is to reach a minimum Signal-to-Noise Ratio of 100 within one hour of observation.
Each MASCARA station consists of five low-noise off-the-shelf full-frame CCD cameras, fitted with standard Canon 24 mm , f/1.4 lenses, monitoring the near-entire sky down to magnitude 8 at that location. Measurements have demonstrated that the required Signal-to-Noise Ratio of 100, can be achieved in less than thirty minutes. MASCARA aims at deploying several stations world-wide to provide a nearly continuous coverage of the dark sky, at sub-minute cadence.
While at the faint end MASCARA is limited mainly by photon noise, at the bright end scintillation and red noise become the limiting factors. Instrumental noise sources are reduced by placing the cameras in a fixed orientation and in a temperature controlled environment. By defocusing and allowing stars to drift over the detector, the impact of pixel-to-pixel variations on the photometry are minimized, while taking exposures at fixed sidereal times allows accurate cross-calibration of consecutive nights. The exposure time of 6.4 seconds gives rise to a high data acquisition rate of a MASCARA station, around 500GB per night. In order to minimize data transport and data storage requirements, the raw images are reduced to produce accurate light curves in nearly real time.
The first MASCARA station will be integrated on La Palma during the summer of 2014. MASCARA test
data were taken in July 2013 with one camera targeting the transiting exoplanet HD 189733b. Its brightness of mV = 7:7 is close to the faint end of the MASCARA magnitude range. The 5 - σ detection of the 2.8% deep transit with a 5-minute binning of the data confirms that we will be able to detect 1% transit at the faint end within one hour.
MASCARA, the Multi-site All-Sky CAmeRA, consists of several fully-automated stations distributed across the globe. Its goal is to find exoplanets transiting the brightest stars, in the V = 4 to 8 magnitude range, currently probed neither by space- nor by ground-based surveys. The nearby transiting planet systems that MASCARA is expected to discover will be key targets for future detailed planet atmosphere observations. Each station contains five wide-angle cameras monitoring the near-entire sky at each location. Once fully deployed, MASCARA will provide a nearly continuous coverage of the dark sky, down to magnitude 8, at sub-minute cadence. Effectively taking an image of the full sky every 6.4 seconds, MASCARA will produce approximately 500 GB of raw data per night, per station. This data needs to be processed in order to produce calibrated light curves, for up to ~40,000 stars down to magnitude 8 and with a signal-to-noise-ratio of better than 100. The aim of the data reduction pipeline is to process the data locally and in real time, both to immediately have quality control, as well as to prevent a data back-log. Although the cameras are fixed and the stars are therefore drifting over the CCDs, MASCARA is a targeted mission. Data processing consists of three main steps: 1. Compute a complete astrometric solution to sub-pixel level for each exposure and extracting postage stamps for each of the stars in the field of view. 2. Perform accurate photometry on each of the postage stamps, including back-ground subtraction and identification of errors in the photometry due to bad pixels, satellites, air planes or Laser Guide Stars. 3. Remove fluctuations on time scales typical for transits, i.e., several hours, caused by for example the camera and atmospheric transmission, color variations in stars and pixel-to-pixel gain fluctuations. Photometry on short time scales already shows noise levels close to the photon noise limit, and using a combination of calibration and relative photometry the red-noise component can be reduced to close to this photon noise limit, allowing for semi-automated identification of exo-planet transits. This paper discusses the data handling, processing and calibration and shows the first results of the pipeline.
We designed and constructed a special instrument to enable the determination of the stellar's spin orientation. The
Differential image rotator for Stellar Spin Orientation, DeSSpOt, allows the simultaneous observations of two anti-parallel
orientations of the star on the spectrum. On a high resolution ´echelle spectrum, the stellar rotation causes a slight line tilt
visible in the spatial direction which is comparable to a rotation curve. We developed a new method, which exploits the
variations in these tilts, to estimate the absolute position angle of the rotation axis. The line tilt is retrieved by a spectroastrometric
extraction of the spectrum.
In order to validate the method, we observed spectroscopic binaries with known orbital parameters. The determination of
the orbital position angle is equivalent to the determination of the stellar position angle, but is easier to to detect.
DeSSpOt was successfully implemented on the high resolution Coud´e spectrograph of the Th¨uringer Landessternwarte
Tautenburg. The observations of Capella led to the determination of the orbital position angle. Our value of 37.2° is in
agreement with the values previously found in the literature. As such we verified that both method and instrument are valid.