Stellar Coronagraphy: Study and Test of a Hybrid Interfero‐Coronagraph

Abstract

ABSTRACT. We present a device for high dynamic range imaging of faint structures in the close angular vicinity of stars. An advantage of this device is the capacity to explore the field of view both uniformly and as close (or near) to the parent star as allowed by the diffraction limit of the telescope. The design is adapted from the Achromatic Interfero-Coronagraph (AIC), which suppresses the light scattered by diffraction from an on-axis unresolved source, but yields two twin images of the stellar environment, displayed symmetrically in the focal plane (Gay & Rabbia 1996;Baudoz et al. 2000a). Our Hybrid Interfero-Coronagraph (HIC) avoids the 180Њ ambiguity and is therefore well suited for the study of extended objects distributed all around the star. Like the AIC, the on-axis extinction with HIC is based on destructive interference after amplitude division of the incident field from a single telescope. An achromatic p-dephasing and a spatial filtering of the wave front are performed on one arm of the interferometer. The interferometric process occurs between the wave front from the star and a spatially filtered wave front. Because of this spatial filtering, the destructive process no longer remains achromatic. However, the residual chromaticity is compatible with astrophysical applications on ground-based telescopes. Numerical simulations show that HIC performance does not suffer from telescope central obscuration. An appropriate size of the spatial filtering mask and a suitable apodization allow the nulling of an on-axis unresolved star at the level of 10 Ϫ6

Theoretical Limits on Extrasolar Terrestrial Planet Detection with Coronagraphs

“…The final image exhibits a 180 ambiguity, which may be removed at the expense of loosing achromaticity (Baudoz et al 2005). The Common Path Achromatic Interferometric Coronagraph (CPAIC) developed by Tavrov et al (2005) achieves the same achromatic -phase shifted and flipped nulling with a common path interferometer, and it is therefore optically more robust.…”

“…• AIC: The Achromatic Interferometric Coronagraph (Gay & Rabbia 1996;Baudoz et al 2000) uses a beam splitter to destructively combine 2 copies of the entrance pupil, one of them achromatically π-phase shifted and flipped. The final image exhibits a 180 degree ambiguity which may be removed at the expense of loosing achromaticity (Baudoz et al 2005). The Common Path Achromatic Interferometric Coronagraph (CPAIC) developed by Tavrov et al (2005) achieves the same achromatic π-phase shifted and flipped nulling with a common path interferometer, and is therefore optically more robust.…”

High performance coronagraphy for direct imaging of exoplanets

“…The two copies are identical for an on-axis point source (therefore producing a null at the output of the interferometer), but they are made to be different for an off-axis source (required to allow transmission of planet light through the nulling interferometer). In the Achromatic Interferometric Coronagraph (AIC) [23][24][25][26], one of the copies is rotated by 180 deg prior to nulling. In the visible nuller [27], a translation of the wavefront is used instead.…”

Super earth explorer: a coronagraphic off-axis space telescope

“…In two of them (diagonally opposed) the wavefront is phase shifted by π , resulting in an interferometric nulling of the stellar peak. The FQPM has been intensively benchmarked through numerous lab experiments, in the visible [2], near-infrared [22], mid-infrared for JWST/MIRI [1]. Three FQPMs have already been installed at the VLT's adaptive optics system [6] and an intensive research and development on the problem of achromatization is ongoing.…”