Hybrid Shaped Pupil Design Apodized Pupil Lyot Coronagraphs for Imaging Earth-like Planets with Future Space Observatories

Apodized pupil Lyot coronagraphs for arbitrary apertures. V. Hybrid Shaped Pupil designs for imaging Earth-like planets with future space observatories

Authors:

N'Diaye et al

Abstract:

We introduce a new class of solutions for Apodized Pupil Lyot Coronagraphs (APLC) with segmented aperture telescopes to remove broadband diffracted light from a star with a contrast level of 1010. These new coronagraphs provide a key advance to enabling direct imaging and spectroscopy of Earth twins with future large space missions. Building on shaped pupil (SP) apodization optimizations, our approach enables two-dimensional optimizations of the system to address any aperture features such as central obstruction, support structures or segment gaps. We illustrate the technique with a design that could reach 1010 contrast level at 34\,mas for a 12\,m segmented telescope over a 10\% bandpass centered at a wavelength λ0=500\,nm. These designs can be optimized specifically for the presence of a resolved star, and in our example, for stellar angular size up to 1.1\,mas. This would allow probing the vicinity of Sun-like stars located beyond 4.4\,pc, therefore fully retiring this concern. If the fraction of stars with Earth-like planets is $\eta_{\Earth}=0.1$, with 18\% throughput, assuming a perfect, stable wavefront and considering photon noise only, 12.5 exo-Earth candidates could be detected around nearby stars with this design and a 12\,m space telescope during a five-year mission with two years dedicated to exo-Earth detection (one total year of exposure time and another year of overheads). Our new hybrid APLC/SP solutions represent the first numerical solution of a coronagraph based on existing mask technologies and compatible with segmented apertures, and that can provide contrast compatible with detecting and studying Earth-like planets around nearby stars. They represent an important step forward towards enabling these science goals with future large space missions.

Hunting for Gas Giant Exoplanets Around A & F Class Stars

Searching for gas giant planets on Solar System scales - A NACO/APP L'-band survey of A- and F-type Main Sequence stars

Authors:

Meshkat et al

Abstract:

We report the results of a direct imaging survey of A- and F-type main sequence stars searching for giant planets. A/F stars are often the targets of surveys, as they are thought to have more massive giant planets relative to solar-type stars. However, most imaging is only sensitive to orbital separations greater than 30 AU, where it has been demonstrated that giant planets are rare. In this survey, we take advantage of the high-contrast capabilities of the Apodizing Phase Plate coronagraph on NACO at the Very Large Telescope. Combined with optimized principal component analysis post-processing, we are sensitive to planetary-mass companions (2 to 12 MJup) at Solar System scales (≤30 AU). We obtained data on 13 stars in L'-band and detected one new companion as part of this survey: an M6.0±0.5 dwarf companion around HD 984. We re-detect low-mass companions around HD 12894 and HD 20385, both reported shortly after the completion of this survey. We use Monte Carlo simulations to determine new constraints on the low-mass (less than 80 MJup) companion frequency, as a function of mass and separation. Assuming solar-type planet mass and separation distributions, normalized to the planet frequency appropriate for A-stars, and the observed companion mass-ratio distribution for stellar companions extrapolated to planetary masses, we derive a truncation radius for the planetary mass companion surface density of less than 135 AU at 95% confidence.

The Capabilities of a 2M Space Coronagraphs to Characterize Rocky and Gaseous Exoplanets

Characterizing Rocky and Gaseous Exoplanets with 2-meter Class Space-based Coronagraphs: General Considerations

Authors:

Robinson et al

Abstract:

Several concepts now exist for small, space-based missions to directly characterize exoplanets in reflected light. Here, we develop an instrument noise model suitable for studying the spectral characterization potential of a coronagraph-equipped, space-based telescope. We adopt a baseline set of telescope and instrument parameters, including a 2 m diameter primary aperture, an operational wavelength range of 0.4-1.0 um, and an instrument spectral resolution of 70, and apply our baseline model to a variety of spectral models of different planet types, including Earth twins, Jupiter twins, and warm and cool Jupiters and Neptunes. With our exoplanet spectral models, we explore wavelength-dependent planet-star flux ratios for main sequence stars of various effective temperatures, and discuss how coronagraph inner and outer working angle constraints will influence the potential to study different types of planets. For planets most favorable to spectroscopic characterization---cool Jupiters and Neptunes as well as nearby Earth twins and super-Earths---we study the integration times required to achieve moderate signal-to-noise ratio spectra. We also explore the sensitivity of the integration times required to detect the base of key absorption bands (for methane, water vapor, and molecular oxygen) to coronagraph raw contrast performance, exozodiacal light levels, and the distance to the planetary system. Most modeled observations have noise dominated by dark current, indicating that improving CCD performance could substantially drive down requisite integration times. Finally, we briefly discuss the extension of our models to a more distant future Large UV-Optical-InfraRed (LUVOIR) mission.

Can WFIRST With an Optical Coronagraph Directly Image Jupiter Analogs?

The Direct Detectability of Giant Exoplanets in the Optical

Authors:

Greco et al

Abstract:

Motivated by the possibility that an optical coronagraph will be put on WFIRST/AFTA, we present an exploration of the general character of the direct detectability of extrasolar giant planets (EGPs) in the optical. We quantify a planet's direct detectability by the fraction of its orbit for which it is in an observable configuration--defined to be its observability fraction (fobs). Using a suite of Monte Carlo experiments, we study the dependence of fobs upon various technological and astrophysical parameters, including the inner working angle (IWA) and minimum achievable contrast (Cmin) of the direct-imaging observatory; the planet's scattering phase function, geometric albedo, single-scattering albedo, radius, and distance from Earth; and the semi-major axis distribution of EGPs. We assume cloud-free, homogeneous atmospheres and calculate phase functions for a given geometric or single-scattering albedo, assuming various scattering mechanisms. We find that the often-assumed Lambertian phase function can predict significantly larger fobs values with respect to the more physically motivated Rayleigh phase function. For observations made with WFIRST/AFTA's baseline coronagraphic capabilities (Cmin∼10−9, IWA∼0.2″), Jupiter-like planets orbiting stars within 10, 30, and 50 pc from Earth have volume-averaged (assuming a uniform distribution of stars) observability fractions of ∼12%, 3%, and 0.5%, respectively. Using a plausible estimate for the occurrence rate of EGPs, we find that, in all but the most optimistic configurations, the probability a blind search will lead to a detection is low (less than 5%). However, with orbital parameter constraints from long-term radial-velocity campaigns and Gaia astrometry, the tools we develop in this work can be used to determine both the most promising systems to target and when to observe them.

Coronagraphic Exoplanet Imaging and Spectroscopy Using WFIRST

Scientific Return of Coronagraphic Exoplanet Imaging and Spectroscopy Using WFIRST

Author:

Burrows

Abstract:

In this study, we explore and review the scientific potential for exoplanet characterization by a high-contrast optical coronagraph on WFIRST/AFTA. We suggest that the heterogeneity in albedo spectra and planet/star flux ratios as a function of orbital distance, planet mass, and composition expected for the giant exoplanets at separations from their primaries accessible to WFIRST will provide unique constraints on giant planet atmospheres, evolution, aerosol and cloud properties, and general theory. Such exoplanets are not merely extrapolations of Jupiter and Saturn, but are likely to occupy a rich continuum of varied behaviors. Each in themselves and jointly, optical spectra, photometry, and polarization measurements of a diverse population of giant exoplanets in the solar neighborhood has the potential to reveal a multitude of fundamental features of their gas-giant chemistry, atmospheres, and formation. Such a campaign will enrich our understanding of this class of planets beyond what is possible with even a detailed exploration of the giants in our own solar system, and will compliment ongoing studies of exoplanets in the infrared and on close-in orbits inaccessible to coronagraphy.

Segmented Pupil Experiment for Exoplanet Detection

SPEED: the Segmented Pupil Experiment for Exoplanet Detection

Authors:

Patrice et al

Abstract:

Searching for nearby exoplanets with direct imaging is one of the major scientific drivers for both space and ground-based programs. While the second generation of dedicated high-contrast instruments on 8-m class telescopes is about to greatly expand the sample of directly imaged planets, exploring the planetary parameter space to hitherto-unseen regions ideally down to Terrestrial planets is a major technological challenge for the forthcoming decades. This requires increasing spatial resolution and significantly improving high contrast imaging capabilities at close angular separations. Segmented telescopes offer a practical path toward dramatically enlarging telescope diameter from the ground (ELTs), or achieving optimal diameter in space. However, translating current technological advances in the domain of high-contrast imaging for monolithic apertures to the case of segmented apertures is far from trivial. SPEED (the segmented pupil experiment for exoplanet detection) is a new instrumental facility in development at the Lagrange laboratory for enabling strategies and technologies for high-contrast instrumentation with segmented telescopes. SPEED combines wavefront control including precision segment phasing architectures, wavefront shaping using two sequential high order deformable mirrors for both phase and amplitude control, and advanced coronagraphy struggled to very close angular separations (PIAACMC). SPEED represents significant investments and technology developments towards the ELT area and future spatial missions, and will offer an ideal cocoon to pave the road of technological progress in both phasing and high-contrast domains with complex/irregular apertures. In this paper, we describe the overall design and philosophy of the SPEED bench.

Using a High-contrast Coronagraph to Directly Image Earth-like Exoplanets

A high-contrast coronagraph for earth-like exoplanets direct imaging: design and test

Authors:

Liu et al

Abstract:

The high-contrast coronagraph for direct imaging earth-like exoplanets at the visible needs a contrast of 10^(-10) at a small angular separation of 4 lambda/D or less. Here we report our recent laboratory experiment that is close to the limits. The test of the high-contrast imaging coronagraph is based on our step-transmission apodized filter. To achieve the goal, we use a liquid crystal array (LCA) as a phase corrector to create a dark hole based on our dedicated focal dark algorithm. We have suppressed the diffracted and speckle noise near the star point image to a level of 1.68 x 10^(-9) at 4 lambda/D, which can be immediately used for the direct imaging of Jupiter like exoplanets. This demonstrates that high-contrast coronagraph telescope in space has the potentiality to detect and characterize earth-like planets.

Using Spectroscopic Cornography for Exoplanet Detection

Spectroscopic Coronagraphy for Planetary Radial Velocimetry of Exoplanets

Authors:

Kawahara et al

Abstract:

We propose to apply the coronagraphic techniques to the spectroscopic direct detection of exoplanets via the Doppler shift of planetary molecular lines. Even for unresolved close-in planetary system, we show that a combination of a visible nuller and an extreme adaptive optics system can reduce photon noise of a main star and increases total signal-to-noise ratio of the molecular absorptions of exoplanetary atmosphere: it works as spectroscopic coronagraph. Assuming a 30 m telescope, we demonstrate the benefit of these high-contrast instruments for nearby close-in planets that mimic 55 Cnc b (0.6λ/D of the angular separation in the K-band). We find that the tip-tilt error is the most crucial factor, however, low-order speckles also contribute to the noise. Assuming relatively conservative estimates for future wavefront control technique, the spectroscopic coronagraph can increase the contrast to ∼50−130 times and enable us to obtain a ∼3−6 times larger S/N for warm Jupiters and Neptunes at 10 pc than that without it. If the tip-tilt error can be reduced to ≲0.3 mas (rms), it gains a ∼10−30 times larger S/N and enables to detect warm super Earths with an extremely large telescope. This paper demonstrates the concept of spectroscopic coronagraphy for the future spectroscopic direct detection. Further studies of selection of coronagraphs and tip-tilt sensors will extend the range of application of the spectroscopic direct detection beyond the photon correcting area limit.