Extreme adaptive optics for the Thirty Meter Telescope

Abstract

Direct detection of extrasolar Jovian planets is a major scientific motivation for the construction of future extremely large telescopes such as the Thirty Meter Telescope (TMT). Such detection will require dedicated high-contrast AO systems. Since the properties of Jovian planets and their parent stars vary enormously between different populations, the instrument must be designed to meet specific scientific needs rather than a simple metric such as maximum Strehl ratio. We present a design for such an instrument, the Planet Formation Imager (PFI) for TMT. It has four key science missions. The first is the study of newly-formed planets on 5-10 AU scales in regions such as Taurus and Ophiucusthis requires very small inner working distances that are only possible with a 30m or larger telescope. The second is a robust census of extrasolar giant planets orbiting mature nearby stars. The third is detailed spectral characterization of the brightest extrasolar planets. The final targets are circumstellar dust disks, including Zodiacal light analogs in the inner parts of other solar systems. To achieve these, PFI combines advanced wavefront sensors, high-order MEMS deformable mirrors, a coronagraph optimized for a finely-segmented primary mirror, and an integral field spectrograph.

Mapping Directly Imaged Giant Exoplanets

“…Following the method described in the previous two sections, we calculate a J-band ADI rotation time requirement of ∼ 2 minutes and ∼ 10 minutes for a planet at a radial separation from the parent star of 1 ′′ and 0.2 ′′ respectively; here we present the results for the latter. Using the required characteristics of the GMT/TMT/ELT (GMT 2006; Macintosh et al 2006;Kasper et al 2010), we use a residual stellar PSF of 10 −8 at the radial separation of 0.2 ′′ to simulate the very high SNR (on the order of several thousands, using the ELT ETC provided by ESO) J-band lightcurve for model B2 in the lower panel of Figure 8. As was the case for the 8m ExAO systems, the residual stellar PSF is no longer the main culprit for systematic errors.…”

“…To estimate the achievable photometric accuracy of the different instruments we rely on the residual radial contrast curves provided by the instrument teams: VLT/NACO at 4 µm (Kasper et al 2007(Kasper et al , 2009), VLT/SPHERE in J-band (Vigan et al 2010;Mesa et al 2011), Gemini/GPI in H-band ), TMT/PFI in H-band (Macintosh et al 2006), ELT/EPICS in J-band and JWST/NIRCAM in K-band (Green et al 2005). All contrast limits are for coronographic images.…”

High-Contrast Imaging With an Arbitrary Aperture: Active Compensation of Aperture Discontinuities

“…ELTs will have to support a substantially heavier secondary than 8 meter class observatories do, and over larger lengths: as a consequence the relative area covered by the secondary support will increase by a factor of 10 (30 cm wide spiders, occupying ∼ 3% of the pupil diameter in the case of TMT). This will degrade the contrast of coronagraphs only designed for circularly obscured geometries by a factor ∼ 100, when the actual envisioned contrast for an ELT exo-planet imager can be as low as ∼ 10 −8 (Macintosh et al 2006). While the tradeoffs associated with minimization of spider width in the space-based case have yet to be explored, secondary support structures will certainly hamper the contrast depth of coronagraphic instruments of such observatories at levels that are well above the 10 10 contrast requirement.…”

“…1. As a consequence, a wavefront control system composed of two sequential Deformable Mirrors is currently the baseline architecture of currently envisioned coronagraphic space-based instruments Krist et al 2011) and ELT planet imagers (Macintosh et al 2006). One can thus naturally be motivated to investigate if such wavefront control systems can be used to cancel the light diffracted by secondary supports and segments in large telescopes, since such structures are amplitude errors, albeit large amplitude errors.…”

“…Such instruments will reach the contrast required to achieve their scientific goals by combining Extreme Adaptive Optics systems (Ex-AO, Poyneer & Véran (2005)), optimized coronagraphs Guyon 2003;Rouan et al 2000) and nanometer class wavefront calibration (Sauvage et al 2007;Wallace et al 2009;Pueyo et al 2010). In the future, highcontrast instruments on Extremely Large Telescopes will focus on probing planetary formation in distant star email: lap@pha.jhu.edu 1 Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD, USA forming regions (Macintosh et al 2006), characterizing both the spectra of cooler gas giants (Vérinaud et al 2010) and the reflected light of planets in the habitable zone of low mass stars. The formidable contrast necessary to investigate the presence of biomarkers at the surface of earth analogs (> 10 10 ) cannot be achieved from the ground beneath atmospheric turbulence and will require dedicated space-based instruments .…”