High precision astrometry with a diffractive pupil telescope

Abstract

Astrometric detection and mass determination of Earth-mass exoplanets requires sub-microarcsec accuracy, which is theoretically possible with an imaging space telescope using field stars as an astrometric reference. The measurement must however overcome astrometric distortions which are much larger than the photon noise limit. To address this issue, we propose to generate faint stellar diffraction spikes using a two-dimensional grid of regularly spaced small dark spots added to the surface of the primary mirror (PM). Accurate astrometric motion of the host star is obtained by comparing the position of the spikes to the background field stars. The spikes do not contribute to scattered light in the central part of the field and therefore allow unperturbed coronagraphic observation of the star's immediate surrounding. Because the diffraction spikes are created on the PM and imaged on the same focal plane detector as the background stars, astrometric distortions affect equally the diffraction spikes and the background stars, and are therefore calibrated. We describe the technique, detail how the data collected by the wide-field camera are used to derive astrometric motion, and identify the main sources of astrometric error using numerical simulations and analytical derivations. We find that the 1.4 m diameter telescope, 0.3 sq.deg field we adopt as a baseline design achieves 0.2 microarcsec single measurement astrometric accuracy. The diffractive pupil concept thus enables sub-microarcsec astrometry without relying on the accurate pointing, external metrology or high stability hardware required with previously proposed high precision astrometry concepts.

23 pages, 15 figures. This first paper describes the diffractive pupil telescope concept for single aperture absolute astrometry (to measure exoplanets orbits and masses), compatible with high contrast imaging (to acquire exoplanet spectra / colors in reflected light)

References in corpus (5)

• Parallactic Motion for Companion Discovery: An M-Dwarf Orbiting Alcor
• Astrometry and photometry with HST WFC3. II. Improved geometric-distortion corrections for 10 filters of the UVIS channel
• Astrometry and Photometry with Coronagraphs
• Accurate Astrometry and Photometry of Saturated and Coronagraphic Point Spread Functions
• Micro-pixel accuracy centroid displacement estimation and detector calibration

Cited by in corpus (18)

• Gemini multi-conjugate adaptive optics system review II: Commissioning, operation and overall performance
• VLT/SPHERE robust astrometry of the HR8799 planets at milliarcsecond-level accuracy Orbital architecture analysis with PyAstrOFit
• Astrometric performance of the Gemini multi-conjugate adaptive optics system in crowded fields
• Techniques for High Contrast Imaging in Multi-Star Systems I: Super-Nyquist Wavefront Control
• Simultaneous Exoplanet Characterization and deep wide-field imaging with a diffractive pupil telescope
• Discovery of a low-mass companion around HR3549
• Astrometric detection of exoplanets from the ground
• Phase Retrieval and Design with Automatic Differentiation
• Light propagation in the gravitational field of N arbitrarily moving bodies in 1PN approximation for high-precision astrometry
• Light propagation in the gravitational field of N arbitrarily moving bodies in the 1.5PN approximation for high-precision astrometry
• Kernel Phase and Coronagraphy with Automatic Differentiation
• Light propagation in 2PN approximation in the field of one moving monopole II. Boundary value problem
• Differentiable Optics with dLux I: Deep calibration of Flat Field and Phase Retrieval with Automatic Differentiation
• Light propagation in 2PN approximation in the monopole and quadrupole field of a body at rest: Initial value problem
• Astrometric and photometric characterization of $\eta$ Tel B combining two decades of observations
• Simulation of a method to directly image exoplanets around multiple stars systems
• Periodic Astrometric Signal Recovery through Convolutional Autoencoders
• A method to directly image exoplanets in multi-star systems such as Alpha-Centauri