Abstract
ArielRad, the Ariel radiometric model, is a simulator developed to address the challenges in optimising the space mission science payload and to demonstrate its compliance with the performance requirements. Ariel, the Atmospheric Remote-Sensing Infrared Exoplanet Large-survey, has been selected by ESA as the M4 mission in the Cosmic Vision programme and, during its 4 years primary operation, will provide the first unbiased spectroscopic survey of a large and diverse sample of transiting exoplanet atmospheres. To allow for an accurate study of the mission, ArielRad uses a physically motivated noise model to estimate contributions arising from stationary processes, and includes margins for correlated and time-dependent noise sources. We show that the measurement uncertainties are dominated by the photon statistic, and that an observing programme with about 1000 exoplanetary targets can be completed during the primary mission lifetime.
Highlights
The lower photon conversion efficiency (PCE) observed in VISPhot and FGS1 with respect to FGS2 and NIRSpec is caused by a lower detector QE at short wavelengths, while a similar PCE reduction at Ariel Infrared Spectrometer (AIRS) wavelengths is mainly a consequence of the refractive materials used in the mid-infrared
In this work we have discussed the algorithmic implementation of ArielRad, the Ariel radiometric simulator, used for the optimisation of the payload design and to evaluate the science performance of the ESA M4 space mission
ArielRad accounts for all relevant sources of uncertainties on the detection of exoplanetary atmospheres with Ariel, that are: photon noise, detector noise and electronic noise, and jitter noise
Summary
In the past 20 years more than 4000 exoplanets have been detected using space and ground based surveys, and many more are expected to be discovered in the coming years thanks to space missions such as TESS [1], CHEOPS [2], PLATO [3] and GAIA. ExoSim is a end-to-end, time-domain simulator of Ariel observations It evaluates photometric and spectroscopic light curves implementing a detailed description of the instrument design, source of uncertainties, and systematics of instrument and astrophysical origin. AERM overcomes this limitation implementing a simplified approach based on a radiometric modelling of the detection and of the uncertainties. These simplifications mean it is capable of assessing the confidence limit on the detection of emission and transmission spectra of hundreds of exoplanet targets. ArielRad overcomes the limitations of AERM by implementing a detailed payload model, similar to that used by ExoSim, capable of describing all major instrument components. In this work we describe ArielRad, the models implemented, their validation, and provide examples of how ArielRad can be used to support the Ariel mission development, leaving to a future work a detailed assessment of the Ariel mission performance
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