We present the results of both laboratory and on sky astrometric characterization of the Gemini Planet Imager (GPI). This characterization includes measurement of the pixel scale* of the integral field spectrograph (IFS), the position of the
detector with respect to north, and optical distortion. Two of these three quantities (pixel scale and distortion) were
measured in the laboratory using two transparent grids of spots, one with a square pattern and the other with a random pattern. The pixel scale in the laboratory was also estimate using small movements of the artificial star unit (ASU) in the
GPI adaptive optics system. On sky, the pixel scale and the north angle are determined using a number of known binary or multiple systems and Solar System objects, a subsample of which had concurrent measurements at Keck Observatory. Our current estimate of the GPI pixel scale is 14.14 ± 0.01 millarcseconds/pixel, and the north angle is -1.00 ± 0.03°. Distortion is shown to be small, with an average positional residual of 0.26 pixels over the field of view, and is corrected using a 5th order polynomial. We also present results from Monte Carlo simulations of the GPI Exoplanet Survey (GPIES) assuming GPI achieves ~1 milliarcsecond relative astrometric precision. We find that with this precision, we
will be able to constrain the eccentricities of all detected planets, and possibly determine the underlying eccentricity
distribution of widely separated Jovians.
The Project 1640 instrument on the 200-inch Hale telescope at Palomar Observatory is a coronagraphic instru- ment with an integral eld spectrograph at the back end, designed to nd young, self-luminous planets around nearby stars. To reach the necessary contrast for this, the PALM-3000 adaptive optics system corrects for fast atmospheric speckles, while CAL, a phase-shifting interferometer in a Mach-Zehnder con guration, measures the quasistatic components of the complex electric eld in the pupil plane following the coronagraphic stop. Two additional sensors measure and control low-order modes. These eld measurements may then be combined with a system model and data taken separately using a white-light source internal to the AO system to correct for both phase and amplitude aberrations. Here, we discuss and demonstrate the procedure to maintain a half-plane dark hole in the image plane while the spectrograph is taking data, including initial on-sky performance.
P1640 high contrast imaging system on the Palomar 200 inch Telescope consists of an apodized-pupil Lyot coronagraph, the PALM-3000 adaptive optics (P3K-AO), and P1640 Calibrator (CAL). Science images are recorded by an integral field spectrograph covering J-H bands for detecting and characterizing stellar companions. With aberrations from atmosphere corrected by the P3K-AO, instrument performance is limited mainly by the quasi-static speckles due to noncommon path wavefront aberrations for the light to propagate to the P3K-AO wavefront sensor and to the coronagraph mask. The non-common path wavefront aberrations are sensed by CAL, which measures the post-coronagraph E-field using interferometry, and can be effectively corrected by offsetting the P3K-AO deformable mirror target position accordingly. Previously, we have demonstrated using CAL measurements to correct high order wavefront aberrations, which is directly connected to the static speckles in the image plane. Low order wavefront, on the other hand, usually of larger amplitudes, causes light to leak through the coronagraph making the whole image plane brighter. Knowledge error in low order wavefront aberrations can also affect the estimation of the high order wavefront. Even though, CAL is designed to sense efficiently high order wavefront aberrations, the low order wavefront front can be inferred with less sensitivity. Here, we describe our method for estimating both low and high order wavefront aberrations using CAL measurements by propagating the post-coronagraph E-field to a pupil before the coronagraph. We present the results from applying this method to both simulated and experiment data.
P1640 calibrator is a wavefront sensor working with the P1640 coronagraph and the Palomar 3000 actuator
adaptive optics system (P3K) at the Palomar 200 inch Hale telescope. It measures the wavefront by interfering
post-coronagraph light with a reference beam formed by low-pass filtering the blocked light from the coronagraph
focal plane mask. The P1640 instrument has a similar architecture to the Gemini Planet Imager (GPI) and its
performance is currently limited by the quasi-static speckles due to non-common path wavefront errors, which
comes from the non-common path for the light to arrive at the AO wavefront sensor and the coronagraph mask.
By measuring the wavefront after the coronagraph mask, the non-common path wavefront error can be estimated
and corrected by feeding back the error signal to the deformable mirror (DM) of the P3K AO system. Here, we
present a first order wavefront estimation algorithm and an instrument calibration scheme used in experiments
done recently at Palomar observatory. We calibrate the P1640 calibrator by measuring its responses to poking
DM actuators with a sparse checkerboard pattern at different amplitudes. The calibration yields a complex
normalization factor for wavefront estimation and establishes the registration of the DM actuators at the pupil
camera of the P1640 calibrator, necessary for wavefront correction. Improvement of imaging quality after feeding
back the wavefront correction to the AO system demonstrated the efficacy of the algorithm.
Project 1640, a high-contrast spectral-imaging effort involving a coordinated set of instrumentation and software, built at
AMNH, JPL, Cambridge and Caltech, has been commissioned and is fully operational. This novel suite of
instrumentation includes a 3388+241-actuator adaptive optics system, an optimized apodized pupil Lyot coronagraph, an
integral field spectrograph, and an interferometric calibration wave front sensor. Project 1640 is the first of its kind of
instrumentation, designed to image and characterize planetary systems around nearby stars, employing a variety of
techniques to break the speckle-noise barrier. It is operational roughly one year before any similar project, with the goal
of reaching a contrast of 10-7 at 1 arcsecond separation. We describe the instrument, highlight recent results, and
document on-sky performance at the start of a 3-year, 99-night survey at the Palomar 5-m Hale telescope.
A non-redundant pupil mask placed in front of a low-resolution integral field spectrograph (IFS) adds a spectral dimension to high angular resolution imaging behind adaptive optics systems. We demonstrate the first application of this technique, using the spectroscopic binary star system β CrB as our target. The mask and IFS combination enabled us to measure the first low-resolution spectrum of the F3-F5 dwarf secondary component of β CrB, at an angular separation 141 mas from its A5-A7Vp primary star. To record multi-wavelength closure phases, we collected interferograms simultaneously in 23 spectral channels spanning the J and H bands (1.1 μm-1.8 μm), using the Project 1640 IFS behind the 249-channel PalAO adaptive optics system on the Hale telescope at Palomar Observatory. In addition to providing physical information about the source, spectrally resolved mask fringes have the potential to enhance detection limits over single filter observations. While the overall dynamic range of our observation suffers from large systematic calibration errors, the information gleaned from the full channel range improves the dynamic range by a factor of 3 to 4 over the best single channel.
In July 2008, a new integral field spectrograph and a diffraction limited, apodized-pupil Lyot coronagraph was installed behind the adaptive optics system at the Hale 200-inch telescope at Palomar. This instrument serves as the basis of a long-term observational program in high-contrast imaging. The technical goal is to utilize the spectral nature of speckle noise to overcome it. The coronagraph alone will achieve an initial dynamic range of 10-5 at 1", with first light in mid-2008, without speckle noise suppression. Initial work indicates that spectral speckle suppression will provide a factor of 10 to 100 improvement over this. Such sensitivity provides detection and low resolution spectra of young planets of several Jupiter masses around young stars within 25 pc. The spectrograph obtains 32 images across the J and H bands (1.05 - 1.75 &mgr;m), with a spectral resolution of 30-100. The image plane is subdivided by a 200 x 200 element micro-lenslet array with a plate scale of 21 mas per lenslet, diffraction-limited at 1.0 &mgr;m. Data is collected with a 2048 x 2048 pixel Rockwell Hawaii-II HgCdTe infrared detector cooled with liquid Nitrogen. This system is the first of a new generation of apodized pupil coronagraphs combined with high-order adaptive optics and integral field spectrographs.