Laurent Pueyo

DETECTION AND CHARACTERIZATION OF EXOPLANETS AND DISKS USING PROJECTIONS ON KARHUNEN-LOÈVE EIGENIMAGES

We describe a new method to achieve point-spread function (PSF) subtractions for high-contrast imaging using principal component analysis that is applicable to both point sources or extended objects (disks). Assuming a library of reference PSFs, a Karhunen–Lo` eve transform of these references is used to create an orthogonal basis of eigenimages on which the science target is projected. For detection this approach provides comparable suppression to the Locally Optimized Combination of Images (LOCI) algorithm, albeit with increased robustness to the algorithm parameters and speed enhancement. For characterization of detected sources, the method enables forward modeling of astrophysical sources. This alleviates the biases in the astrometry and photometry of discovered faint sources, which are usually associated with LOCI-based PSF subtractions schemes. We illustrate the algorithm performance using archival Hubble Space Telescope images, but the approach may also be considered for ground-based data acquired with angular differential imaging or integral-field spectrographs.

First light of the Gemini Planet Imager

Bruce Macintosh a , James R. Graham , Patrick Ingraham b , Quinn Konopacky , Christian Marois , Marshall Perrin f , Lisa Poyneer a , Brian Bauman a , Travis Barman , Adam Burrows , Andrew Cardwell , Jeffrey Chilcote j , Robert J. De Rosa , Daren Dillon , Rene Doyon , Jennifer Dunn e , Darren Erikson e , Michael Fitzgerald j , Donald Gavel l , Stephen Goodsell i , Markus Hartung i , Pascale Hibon i , Paul G. Kalas c , James Larkin j , Jerome Maire d , Franck Marchis , Mark Marley , James McBride c , Max Millar-Blanchaer d , Katie Morzinski , Andew Norton l B. R. Oppenheimer , Dave Palmer a , Jennifer Patience k , Laurent Pueyo f , Fredrik Rantakyro i , Naru Sadakuni i , Leslie Saddlemyer e , Dmitry Savransky , Andrew Serio i , Remi Soummer f Anand Sivaramakrishnan f , q Inseok Song , Sandrine Thomas , J. Kent Wallace , Sloane Wiktorowicz l , and Schuyler Wolff vSignificance Direct detection—spatially resolving the light of a planet from the light of its parent star—is an important technique for characterizing exoplanets. It allows observations of giant exoplanets in locations like those in our solar system, inaccessible by other methods. The Gemini Planet Imager (GPI) is a new instrument for the Gemini South telescope. Designed and optimized only for high-contrast imaging, it incorporates advanced adaptive optics, diffraction control, a near-infrared spectrograph, and an imaging polarimeter. During first-light scientific observations in November 2013, GPI achieved contrast performance that is an order of magnitude better than conventional adaptive optics imagers. The Gemini Planet Imager is a dedicated facility for directly imaging and spectroscopically characterizing extrasolar planets. It combines a very high-order adaptive optics system, a diffraction-suppressing coronagraph, and an integral field spectrograph with low spectral resolution but high spatial resolution. Every aspect of the Gemini Planet Imager has been tuned for maximum sensitivity to faint planets near bright stars. During first-light observations, we achieved an estimated H band Strehl ratio of 0.89 and a 5-σ contrast of 106 at 0.75 arcseconds and 105 at 0.35 arcseconds. Observations of Beta Pictoris clearly detect the planet, Beta Pictoris b, in a single 60-s exposure with minimal postprocessing. Beta Pictoris b is observed at a separation of 434 ± 6 milliarcseconds (mas) and position angle 211.8 ± 0.5°. Fitting the Keplerian orbit of Beta Pic b using the new position together with previous astrometry gives a factor of 3 improvement in most parameters over previous solutions. The planet orbits at a semimajor axis of 9.0−0.4+0.8 AU near the 3:2 resonance with the previously known 6-AU asteroidal belt and is aligned with the inner warped disk. The observations give a 4% probability of a transit of the planet in late 2017.

Discovery and spectroscopy of the young jovian planet 51 Eri b with the Gemini Planet Imager

An exoplanet extracted from the bright Direct imaging of Jupiter-like exoplanets around young stars provides a glimpse into how our solar system formed. The brightness of young stars requires the use of next-generation devices such as the Gemini Planet Imager (GPI). Using the GPI, Macintosh et al. discovered a Jupiter-like planet orbiting a young star, 51 Eridani (see the Perspective by Mawet). The planet, 51 Eri b, has a methane signature and is probably the smallest exoplanet that has been directly imaged. These findings open the door to understanding solar system origins and herald the dawn of a new era in next-generation planetary imaging. Science, this issue p. 64; see also p. 39 The Gemini Planet Imager detects a Jupiter-like exoplanet orbiting the young star 51 Eridani. [Also see Perspective by Mawet] Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric compositions and luminosities, which are influenced by their formation mechanisms. Using the Gemini Planet Imager, we discovered a planet orbiting the ~20-million-year-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water-vapor absorption. Modeling of the spectra and photometry yields a luminosity (normalized by the luminosity of the Sun) of 1.6 to 4.0 × 10−6 and an effective temperature of 600 to 750 kelvin. For this age and luminosity, “hot-start” formation models indicate a mass twice that of Jupiter. This planet also has a sufficiently low luminosity to be consistent with the “cold-start” core-accretion process that may have formed Jupiter.

A New High Contrast Imaging Program at Palomar Observatory

We describe a new instrument that forms the core of a long-term high contrast imaging program at the 200 inch (5 m) Hale Telescope at Palomar Observatory. The primary scientific thrust is to obtain images and low-resolution spectroscopy of brown dwarfs and young exoplanets of several Jupiter masses in the vicinity of stars within 50 pc of the Sun. The instrument is a microlens-based integral field spectrograph integrated with a diffraction-limited, apodized-pupil Lyot coronagraph. The entire combination is mounted behind the Palomar adaptive optics (AO) system. The spectrograph obtains imaging in 23 channels across the J and H bands (1.06–1.78 μm). The image plane of our spectrograph is subdivided by a 200 × 200 element microlens array with a plate scale of 19.2 mas per microlens, critically sampling the diffraction-limited point-spread function at 1.06 μm. In addition to obtaining spectra, this wavelength resolution allows suppression of the chromatically dependent speckle noise, which we describe. In addition, we have recently installed a novel internal wave front calibration system that will provide continuous updates to the AO system every 0.5–1.0 minutes by sensing the wave front within the coronagraph. The Palomar AO system is undergoing an upgrade to a much higher order AO system (PALM-3000): a 3388-actuator tweeter deformable mirror working together with the existing 241-actuator mirror. This system, the highest-resolution AO corrector of its kind, will allow correction with subapertures as small as 8.1 cm at the telescope pupil using natural guide stars. The coronagraph alone has achieved an initial dynamic range in the H band of 2 × 10^(-4) at 1″, without speckle noise suppression. We demonstrate that spectral speckle suppression provides a factor of 10–20 improvement over this, bringing our current contrast at 1″ to ~2 × 10^(-5). This system is the first of a new generation of apodized-pupil coronagraphs combined with high-order adaptive optics and integral field spectrographs (e.g., GPI, SPHERE, HiCIAO), and we anticipate that this instrument will make a lasting contribution to high-contrast imaging in the Northern Hemisphere for years.

Reconnaissance of the HR 8799 Exosolar System. I. Near-infrared Spectroscopy

We obtained spectra in the wavelength range λ = 995-1769 nm of all four known planets orbiting the star HR 8799. Using the suite of instrumentation known as Project 1640 on the Palomar 5 m Hale Telescope, we acquired data at two epochs. This allowed for multiple imaging detections of the companions and multiple extractions of low-resolution (R ~ 35) spectra. Data reduction employed two different methods of speckle suppression and spectrum extraction, both yielding results that agree. The spectra do not directly correspond to those of any known objects, although similarities with L and T dwarfs are present, as well as some characteristics similar to planets such as Saturn. We tentatively identify the presence of CH_4 along with NH_3 and/or C_2H_2, and possibly CO_2 or HCN in varying amounts in each component of the system. Other studies suggested red colors for these faint companions, and our data confirm those observations. Cloudy models, based on previous photometric observations, may provide the best explanation for the new data presented here. Notable in our data is that these presumably co-eval objects of similar luminosity have significantly different spectra; the diversity of planets may be greater than previously thought. The techniques and methods employed in this paper represent a new capability to observe and rapidly characterize exoplanetary systems in a routine manner over a broad range of planet masses and separations. These are the first simultaneous spectroscopic observations of multiple planets in a planetary system other than our own.

Asymmetric features in the protoplanetary disk MWC 758

Context. The study of dynamical processes in protoplanetary disks is essential to understand planet formation. In this context, transition disks are prime targets because they are at an advanced stage of disk clearing and may harbor direct signatures of disk evolution. Aims. We aim to derive new constraints on the structure of the transition disk MWC 758, to detect non-axisymmetric features and understand their origin. Methods. We obtained infrared polarized intensity observations of the protoplanetary disk MWC 758 with SPHERE/VLT at 1.04 m to resolve scattered light at a smaller inner working angle (0.093 00 ) and a higher angular resolution (0.027 00 ) than previously achieved. Results. We observe polarized scattered light within 0.53 00 (148 au) down to the inner working angle (26 au) and detect distinct nonaxisymmetric features but no fully depleted cavity. The two small-scale spiral features that were previously detected with HiCIAO are resolved more clearly, and new features are identified, including two that are located at previously inaccessible radii close to the star. We present a model based on the spiral density wave theory with two planetary companions in circular orbits. The best model requires a high disk aspect ratio (H=r 0.20 at the planet locations) to account for the large pitch angles which implies a very warm disk. Conclusions. Our observations reveal the complex morphology of the disk MWC 758. To understand the origin of the detected features, the combination of high-resolution observations in the submillimeter with ALMA and detailed modeling is needed.

Fast computation of Lyot-style coronagraph propagation

We present a new method for numerical propagation through Lyot-style coronagraphs using finite occulting masks. Standard methods for coronagraphic simulations involve Fast Fourier Transforms (FFT) of very large arrays, and computing power is an issue for the design and tolerancing of coronagraphs on segmented Extremely Large Telescopes (ELT) in order to handle both the speed and memory requirements. Our method combines a semi-analytical approach with non-FFT based Fourier transform algorithms. It enables both fast and memory-efficient computations without introducing any additional approximations. Typical speed improvements based on computation costs are of about ten to fifty for propagations from pupil to Lyot plane, with thirty to sixty times less memory needed. Our method makes it possible to perform numerical coronagraphic studies even in the case of ELTs using a contemporary commercial laptop computer, or any standard commercial workstation computer.

Fundamental Limitations of High Contrast Imaging Set by Small Sample Statistics

In this paper, we review the impact of small sample statistics on detection thresholds and corresponding confidence levels (CLs) in high-contrast imaging at small angles. When looking close to the star, the number of resolution elements decreases rapidly toward small angles. This reduction of the number of degrees of freedom dramatically affects CLs and false alarm probabilities. Naively using the same ideal hypothesis and methods as for larger separations, which are well understood and commonly assume Gaussian noise, can yield up to one order of magnitude error in contrast estimations at fixed CL. The statistical penalty exponentially increases toward very small inner working angles. Even at 5-10 resolution elements from the star, false alarm probabilities can be significantly higher than expected. Here we present a rigorous statistical analysis that ensures robustness of the CL, but also imposes a substantial limitation on corresponding achievable detection limits (thus contrast) at small angles. This unavoidable fundamental statistical effect has a significant impact on current coronagraphic and future high-contrast imagers. Finally, the paper concludes with practical recommendations to account for small number statistics when computing the sensitivity to companions at small angles and when exploiting the results of direct imaging planet surveys.

Broadband wavefront correction algorithm for high-contrast imaging systems

Great strides have been made in recent years toward the goal of high-contrast imaging with a sensitivity adequate to detect earth-like planets around nearby stars. It appears that the hardware − optics, coronagraph masks, deformable mirrors, illumination systems, thermal control systems − are up to the task of obtaining the required 10-10 contrast. But in broadband light (e.g., 10% bandpass) the wavefront control algorithms have been a limiting factor. In this paper we describe a general correction methodology that works in broadband light with one or multiple deformable mirrors by conjugating the electric field in a predefined region in the image where terrestrial planets would be found. We describe the linearized approach and demonstrate its effectiveness through laboratory experiments. This paper presents results from the Jet Propulsion Laboratory High Contrast Imaging Testbed (HCIT) for both narrow-band light (2%) and broadband light (10%) correction.

APODIZED PUPIL LYOT CORONAGRAPHS FOR ARBITRARY APERTURES. III. QUASI-ACHROMATIC SOLUTIONS

Direct imaging and spectroscopy of young giant planets from the ground requires broadband starlight suppression with coronagraphy. It is important to minimize the coronagraph chromatic sensitivity to help remove residual speckles through post-processing of images at multiple wavelengths. The coronagraph must also be able to mitigate the effects of ground-based telescopes with central obstruction. We present new properties of the Apodized Pupil Lyot Coronagraph (APLC) that enable quasi-achromatic starlight suppression over a broad bandpass (20%) and with central obstructions. We discuss the existence of these quasi-achromatic solutions using the properties of the generalized prolate spheroidal functions, which are used to define the apodizer profile. We discuss a broadband optimization method and illustrate its parameter space in terms of inner working angle and contrast. These new APLC solutions are implemented in the Gemini Planet Imager (GPI), a new facility instrument to detect and characterize young giant planets and disks, which will be commissioned in 2011. The coronagraph design delivers a contrast better than 10–7 beyond a separation of 0.2 arcsec in the presence of Geminis central obstruction over a 20% bandpass. The science camera is an integral field spectrograph observing in one of the Y, J, or H, or in about two-thirds of the K bandpass, at a single time. Similar solutions have also been used for the Palomar 1640 coronagraphic integral field spectrograph.