Abstract: Enhanced direct Imaging exoplanet detection with astrometric mass determination

Eduardo Bendek/NASA Ames Research Center

Enhancing direct imaging by adding high-precision astrometry capabilities on a single mission is a valuable and cost effective approach to enable high-performance coronagraphs to detect and fully characterize exoplanets. Sub-microarcsecond astrometry would allow measuring the masses and orbital parameters of Earth-mass planets within 10pc. This proposal aims to perform a laboratory demonstration of the combined operation of a high performance coronagraph and a wide field camera for astrometric measurements. The goal is to augment a high-performance coronagraph by wide-field astrometry and provide an end-to-end laboratory testbed to demonstrate this technology. This concept can deliver 1 microarcsecond (μas) (2.35x10-5 #/D) or better astrometric accuracy on a 2.4m wide-field telescope. When equipped with a coronagraph, this would allow measurement of both the spectra and masses of Super-Earth and sub-Neptune planets (~2 Rearth), the most common found by the Kepler mission. Simultaneously, we aim to show that no diffractive contamination exists within the coronagraph's field, and that the telescope's wide field imaging capabilities are preserved. In order to achieve sub microarcsecond imaging astrometry a Diffractive Pupil (DP) concept was proposed in 2012. The approach has been validated at the University of Arizona with a previous APRA grant, which achieved TRL3. This proposal will combine an astrometric camera with the PIAA coronagraph at the Ames Coronagraphy Experiment (ACE) laboratory at NASA Ames. We will design and build a new astrometric wide-field camera that is compatible with the ACE experiment. This new instrument includes a star simulator that will feed the astrometry arm and the coronagraph and it has field selection optics that will send the light to each instrument, as it will be performed on the real spacecraft. The proposed work is a medium to high fidelity demonstration of the concept that would increase its TRL level from 3 to late TRL4. We will advance the technology towards achieving 1μas (2.35x10-5 #/D), for a 2.4m telescope at 500nm, astrometric accuracy using a (DP) while performing simultaneous high-contrast imaging. Our demonstration milestone will be limited to 5μas (1.17x10-4 #/D), for D=2.4m at 500nm, accuracy due to practical laboratory limitations such as instabilities of the star simulator, detector size and cost, and telescope roll. We will produce a detailed error budget that will allow us to validate our simulations with experimental data, and create performance models that can predict the system astrometric accuracy as a function of telescope aperture and FoV. The significance of this work is to demonstrate the feasibility of performing combined astrometry and direct imaging for exoplanet detection, mitigating risks associated with the implementation of this approach on a real mission. This work will extend the capabilities of ACE to deliver a unique laboratory for NASA that will allow evaluating the performance of adding the astrometry capability for any exoplanet detection focused future mission such as EXO- C and EXO-S, as well as scientific trade-off for general astrophysics missions that combines wide-field imaging and high-performance coronagraphy, such as WFIRST-AFTA. Finally, we will also assess the DP ability to calibrate field distortions that can benefit other astrometry related general astrophysics science cases, such as improve Near Earth Objects (NEOs) orbit characterization, dynamical studies of galaxies and weak lensing measurements that could be obtained with the addition of wide-field astrometry. Therefore, this work will advance exoplanet detection technologies that will also help to address other objectives of the decadal survey and the NASA Strategic plan.