The Gemini Planet Imager has been successfully obtaining images and spectra of exoplanets, brown dwarfs, and debris and protoplanetary circumstellar disks using its integral field spectrograph and polarimeter. GPI observations are transformed from raw data into high-quality astrometrically and photometrically calibrated datacubes using the GPI Data Reduction Pipeline, an open-source software framework continuously developed by our team and available to the community. It uses a flexible system of reduction recipes composed of individual primitive steps, allowing substantial customization of processing depending upon science goals. This paper provides a broad overview of the GPI pipeline, summarizes key lessons learned, and describes improved calibration methods and new capabilities available in the latest version. Enhanced automation better supports observations at the telescope with streamlined and rapid data processing, for instance through real-time assessments of contrast performance and more automated calibration file processing. We have also incorporated the GPI Data Reduction Pipeline as one component in a larger automated data system to support the GPI Exoplanet Survey campaign, while retaining its flexibility and stand-alone capabilities to support the broader GPI observer community. Several accompanying papers describe in more detail specific aspects of the calibration of GPI data in both spectral and polarimetric modes.
We present on-sky polarimetric observations with the Gemini Planet Imager (GPI) obtained at straight Cassegrain focus on the Gemini South 8-m telescope. Observations of polarimetric calibrator stars, ranging from nearly un- polarized to strongly polarized, enable determination of the combined telescope and instrumental polarization. We find the conversion of Stokes I to linear and circular instrumental polarization in the instrument frame to
be I → (QIP, UIP, PIP, VIP) = (-0.037 ± 0.010%, +0.4338 ± 0.0075%, 0.4354 ± 0.0075%, -6.64 ± 0.56%). Such
precise measurement of instrumental polarization enables ~0.1% absolute accuracy in measurements of linear
polarization, which together with GPI’s high contrast will allow GPI to explore scattered light from circumstellar
disk in unprecedented detail, conduct observations of a range of other astronomical bodies, and potentially even study polarized thermal emission from young exoplanets. Observations of unpolarized standard stars also let us quantify how well GPI's differential polarimetry mode can suppress the stellar PSF halo. We show that GPI polarimetry achieves cancellation of unpolarized starlight by factors of 100-200, reaching the photon noise limit for sensitivity to circumstellar scattered light for all but the smallest separations at which the calibration for instrumental polarization currently sets the limit.
The Gemini Planet Imager (GPI) is an instrument designed to directly image planets and circumstellar disks
from 0.9 to 2.5 microns (the YJHK infrared bands) using high contrast adaptive optics with a lenslet-based
integral field spectrograph. We develop an extraction algorithm based on a least-squares method to disentangle
the spectra and systematic noise contributions simultaneously. We utilize two approaches to adjust for the effect
of flexure of the GPI optics which move the position of light incident on the detector. The first method is
to iterate the extraction to achieve minimum residual and the second is to cross-correlate the detector image
with a model image in iterative extraction steps to determine an offset. Thus far, this process has made clear
qualitative improvements to the cube extraction by reducing the Moiré pattern. There are also improvements
to the automated routines for finding flexure offsets which are reliable to with ~ 0.5 pixel accuracy compared to
pixel accuracy prior. Further testing and optimization will follow before implementation into the GPI pipeline.
The newly commissioned Gemini Planet Imager (GPI) combines extreme adaptive optics, an advanced coronagraph, precision wavefront control and a lenslet-based integral field spectrograph (IFS) to measure the spectra of young extrasolar giant planets between 0.9-2.5 μm. Each GPI detector image, when in spectral model, consists
of ~37,000 microspectra which are under or critically sampled in the spatial direction. This paper demonstrates
how to obtain high-resolution microlens PSFs and discusses their use in enhancing the wavelength calibration,
flexure compensation and spectral extraction. This method is generally applicable to any lenslet-based integral field spectrograph including proposed future instrument concepts for space missions.
The Gemini Planet Imager (GPI) has as its science instrument an infrared integral field spectrograph/polarimeter (IFS). Integral field spectrographs are scientificially powerful but require sophisticated data reduction systems. For GPI to achieve its scientific goals of exoplanet and disk characterization, IFS data must be reconstructed into high quality astrometrically and photometrically accurate datacubes in both spectral and polarization modes, via flexible software that is usable by the broad Gemini community. The data reduction pipeline developed by the GPI instrument team to meet these needs is now publicly available following GPI’s commissioning.
This paper, the first of a series, provides a broad overview of GPI data reduction, summarizes key steps, and presents the overall software framework and implementation. Subsequent papers describe in more detail the algorithms necessary for calibrating GPI data. The GPI data reduction pipeline is open source, available from planetimager.org, and will continue to be enhanced throughout the life of the instrument. It implements an extensive suite of task primitives that can be assembled into reduction recipes to produce calibrated datasets ready for scientific analysis. Angular, spectral, and polarimetric differential imaging are supported. Graphical tools automate the production and editing of recipes, an integrated calibration database manages reference files, and an interactive data viewer customized for high contrast imaging allows for exploration and manipulation of data.
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