Compatibility of a Diffractive Pupil and Coronagraphic Imaging

et al. 2017

ApJ

Direct imaging of exoplanets represents a challenge for astronomical instrumentation due to the high-contrast ratio and small angular separation between the host star and the faint planet. Multi-star systems pose additional challenges for coronagraphic instruments due to the diffraction and aberration leakage caused by companion stars. Consequently, many scientifically valuable multi-star systems are excluded from direct imaging target lists for exoplanet surveys and characterization missions. Multi-star wavefront control (MSWC) is a technique that uses a coronagraphic instrument's deformable mirror (DM) to create high-contrast regions in the focal plane in the presence of multiple stars. Our previous paper introduced the Super-Nyquist Wavefront Control (SNWC) technique that uses a diffraction grating to enable the DM to generate high-contrast regions beyond the nominal region correctable by the DM. These two techniques can be combined to generate high-contrast regions for multi-star systems at any angular separation. As a case study, a high-contrast wavefront control (WC) simulation that applies these techniques shows that the habitable region of the Alpha Centauri system can be imaged reaching at least 8 × 10 −9 mean contrast in 10% broadband light in one-sided dark holes from 1.6-5.5λ/D.

Section: Super-nyquist Multi-star Wavefront Controlmentioning

confidence: 99%

Techniques for High-contrast Imaging in Multi-star Systems. II. Multi-star Wavefront Control

Sirbu

Thomas

et al. 2017

ApJ

“…Finally, this multi-star imaging scenario uses the starshade alignment as designed with the LOWFS sensor performing position sensing. To enable observation of binary stars with Super-Nyquist angular separations, the only requirement is that a diffraction grating be available at an appropriate location within the CGI (for example could take the form of a diffractive pupil 19 ). SNWC is otherwise a purely an algorithmic solution.…”

Section: On-axis Starshade With Super Nyquist Wavefront Controlmentioning

confidence: 99%

Prospects for exoplanet imaging in multi-star systems with starshades

Sirbu

Techniques and Instrumentation for Detection of Exoplanets VIII

Bendek

et al. 2017

Self Cite

We explore the capabilities of a starshade mission to directly image multi-star systems. In addition to the diffracted and scattered light for the on-axis star, a multi-star system features additional starlight leakage from the off-axis star that must also be controlled. A basic option is for additional starshades to block the offaxis stars. An interesting option takes the form of hybrid operation of a starshade in conjunction with an internal starlight suppression. Two hybrid scenarios are considered. One such scenario includes the coronagraph instrument blocking the on-axis star, with the starshade blocking off-axis starlight. Another scenario uses the wavefront control system in the coronagraph instrument and using a recent Super-Nyquist Wavefront Control (SNWC) technique can remove the off-axis stars leakage to enable a region of high-contrast around the on-axis star blocked by the starshade. We present simulation results relevant for the WFIRST telescope.

“…The diffractive pupil spacing can be adjusted to create PSF replicas to run the SNWC, and also to obtain high-precision astrometry on wide-field images. A description of the optimal hexagonal geometry for combining these two techniques has been published by (Bendek et al 2013).…”

Section: Snwc Implementation With a Gratingmentioning

confidence: 99%

Techniques for High-Contrast Imaging in Multi-Star Systems. I. Super-Nyquist Wavefront Control

Thomas

Bendek

2015

ApJ

Extra-solar planets direct imaging is now a reality with the deployment and commissioning of the first generation of specialized ground-based instruments (GPI, SPHERE, P1640 and SCExAO). These systems allow of planets 10 7 times fainter than their host star. For space-based missions (EXCEDE, EXO-C, EXO-S, WFIRST), various teams have demonstrated laboratory contrasts reaching 10 −10 within a few diffraction limits from the star. However, all of these current and future systems are designed to detect faint planets around a single host star or unresolved multiples, while most non M-dwarf stars such as Alpha Centauri belong to multi-star systems. Direct imaging around binaries/multiple systems at a level of contrast allowing Earth-like planet detection is challenging because the region of interest is contaminated by the hosts star companion as well as the host Generally, the light leakage is caused by both diffraction and aberrations in the system. Moreover, the region of interest usually falls outside the correcting zone of the deformable mirror (DM) for the companion. Until now, it has been thought that removing the light of a companion star is too challenging, leading to the exclusion of binary systems from target lists of direct imaging coronographic missions.In this paper, we will show different new techniques for high-contrast imaging of planets around multi-star systems and detail the Super-Nyquist Wavefront Control (SNWC) method, which allows to control wavefront errors beyond nominal control region of the DM. Using the SNWC we reached contrasts around 5 × 10 −9 in a 10% bandwidth.