Performance of the Gemini Planet Imager Non-Redundant Mask and spectroscopy of two close-separation binaries HR 2690 and HD 142527

The Gemini Planet Imager (GPI) contains a 10-hole non-redundant mask (NRM), enabling interferometric resolution in complement to its coronagraphic capabilities. The NRM operates both in spectroscopic (integral field spectrograph, henceforth IFS) and polarimetric configurations. NRM observations were taken between 2013 and 2016 to characterize its performance. Most observations were taken in spectroscopic mode with the goal of obtaining precise astrometry and spectroscopy of faint companions to bright stars. We find a clear correlation between residual wavefront error measured by the AO system and the contrast sensitivity by comparing phase errors in observations of the same source, taken on different dates. We find a typical 5-$\sigma$ contrast sensitivity of $2-3~\times~10^{-3}$ at $\sim\lambda/D$. We explore the accuracy of spectral extraction of secondary components of binary systems by recovering the signal from a simulated source injected into several datasets. We outline data reduction procedures unique to GPI's IFS and describe a newly public data pipeline used for the presented analyses. We demonstrate recovery of astrometry and spectroscopy of two known companions to HR 2690 and HD 142527. NRM+polarimetry observations achieve differential visibility precision of $\sigma\sim0.4\%$ in the best case. We discuss its limitations on Gemini-S/GPI for resolving inner regions of protoplanetary disks and prospects for future upgrades. We summarize lessons learned in observing with NRM in spectroscopic and polarimetric modes.Comment: Accepted to AJ, 22 pages, 14 figure

GPI Spectra of HR8799 C, D, and E in H-K Bands with KLIP Forward Modeling

We demonstrate KLIP forward modeling spectral extraction on Gemini Planet Imager coronagraphic data of HR8799, using PyKLIP. We report new and re-reduced spectrophotometry of HR8799 c, d, and e from H-K bands. We discuss a strategy for choosing optimal KLIP PSF subtraction parameters by injecting fake sources and recovering them over a range of parameters. The K1/K2 spectra for planets c and d are similar to previously published results from the same dataset. We also present a K band spectrum of HR8799e for the first time and show that our H-band spectra agree well with previously published spectra from the VLT/SPHERE instrument. We compare planets c, d, and e with M, L, and T-type field objects. All objects are consistent with low gravity mid-to-late L dwarfs, however, a lack of standard spectra for low gravity late L-type objects lead to poor fit for gravity. We place our results in context of atmospheric models presented in previous publications and discuss differences in the spectra of the three planets

On-sky low order non-common path correction of the GPI calibration unit

The Gemini Planet Imager (GPI) entered on-sky commissioning phase, and had its First Light at the Gemini South telescope in November 2013. Meanwhile, the fast loops for atmospheric correction of the Extreme Adaptive Optics (XAO) system have been closed on many dozen stars at different magnitudes (I=4-8), elevation angles and a variety of seeing conditions, and a stable loop performance was achieved from the beginning. Ultimate contrast performance requires a very low residual wavefront error (design goal 60 nm RMS), and optimization of the planet finding instrument on different ends has just begun to deepen and widen its dark hole region. Laboratory raw contrast benchmarks are in the order of 10^-6 or smaller. In the telescope environment and in standard operations new challenges are faced (changing gravity, temperature, vibrations) that are tackled by a variety of techniques such as Kalman filtering, open-loop models to keep alignment to within 5 mas, speckle nulling, and a calibration unit (CAL). The CAL unit was especially designed by the Jet Propulsion Laboratory to control slowly varying wavefront errors at the focal plane of the apodized Lyot coronagraph by the means of two wavefront sensors: 1) a 7x7 low order Shack-Hartmann SH wavefront sensor (LOWFS), and 2) a special Mach-Zehnder interferometer for mid-order spatial frequencies (HOWFS) - atypical in that the beam is split in the focal plane via a pinhole but recombined in the pupil plane with a beamsplitter. The original design goal aimed for sensing and correcting on a level of a few nm which is extremely challenging in a telescope environment. This paper focuses on non-common path low order wavefront correction as achieved through the CAL unit on sky. We will present the obtained results as well as explain challenges that we are facing.Comment: 9 pages, 7 figures, Proc. SPIE 9148 (2014

Effects of differential wavefront sensor bias drifts on high contrast imaging

The Gemini Planet Imager (GPI) is a new facility, extreme adaptive optics (AO), coronagraphic instrument, currently being integrated onto the 8-meter Gemini South telescope, with the ultimate goal of directly imaging extrasolar planets. To achieve the contrast required for the desired science, it is necessary to quantify and mitigate wavefront error (WFE). A large source of potential static WFE arises from the primary AO wavefront sensor (WFS) detector's use of multiple readout segments with independent signal chains including on-chip preamplifiers and external amplifiers. Temperature changes within GPI's electronics cause drifts in readout segments' bias levels, inducing an RMS WFE of 1.1 nm and 41.9 nm over 4.44 degrees Celsius, for magnitude 4 and 11 stars, respectively. With a goal of $<$2 nm of static WFE, these are significant enough to require remedial action. Simulations imply a requirement to take fresh WFS darks every 2 degrees Celsius of temperature change, for a magnitude 6 star; similarly, for a magnitude 7 star, every 1 degree Celsius of temperature change. For sufficiently dim stars, bias drifts exceed the signal, causing a large initial WFE, and the former periodic requirement practically becomes an instantaneous/continuous one, making the goal of $<$2 nm of static WFE very difficult for stars of magnitude 9 or fainter. In extreme cases, this can cause the AO loops to destabilize due to perceived nonphysical wavefronts, as some of the WFS's Shack-Hartmann quadcells are split between multiple readout segments. Presented here is GPI's AO WFS geometry, along with detailed steps in the simulation used to quantify bias drift related WFE, followed by laboratory and on sky results, and concluded with possible methods of remediation.Comment: 8 pages, 7 figures. Proceedings of the SPIE, 9148-21

Automated alignment and on-sky performance of the Gemini planet imager coronagraph

The Gemini Planet Imager (GPI) is a next-generation, facility instrument currently being commissioned at the Gemini South observatory. GPI combines an extreme adaptive optics system and integral field spectrograph (IFS) with an apodized-pupil Lyot coronagraph (APLC) producing an unprecedented capability for directly imaging and spectroscopically characterizing extrasolar planets. GPI's operating goal of $10^{-7}$ contrast requires very precise alignments between the various elements of the coronagraph (two pupil masks and one focal plane mask) and active control of the beam path throughout the instrument. Here, we describe the techniques used to automatically align GPI and maintain the alignment throughout the course of science observations. We discuss the particular challenges of maintaining precision alignments on a Cassegrain mounted instrument and strategies that we have developed that allow GPI to achieve high contrast even in poor seeing conditions.Comment: 11 pages, 7 figures. Proceedings of the SPIE, 9147-15

FINAL A&amp;T STAGES OF THE GEMINI PLANET FINDER

Abstract. The Gemini Planet Imager (GPI) is currently in its final Acceptance &amp; Testing stages. GPI is an XAO system based on a tweeter &amp; woofer architecture (43 &amp; 9 actuators respectively across the pupil), with the tweeter being a Boston Michromachines 64 2 MEMS device. The XAO AO system is tightly integrated with a Lyot apodizing coronagraph. Acceptance testing started in February 2013 at the University of California, Santa Cruz. A conclusive acceptance review was held in July 2013 and the instrument was found ready for shipment to the Gemini South telescope on Cerro Pachon, Chile. Commissioning at the telescope will take place by the end of 2013, matching the summer window of the southern hemisphere. According to current estimates the 3 year planet finding campaign (890 allocated hours) might discover, image, and spectroscopically analyze 20 to 40 new exo-planets. Final acceptance testing of the integrated instrument can always bring up surprises when using cold chamber and flexure rig installations. The latest developments are reported. Also, we will give an overview of GPI&apos;s lab performance, the interplay between subsystems such as the calibration unit (CAL) with the AO bench. We report on-going optimizations on the AO controller loop to filter vibrations and last but not least achieved contrast performance applying speckle nulling. Furthermore, we will give an outlook of possible but challenging future upgrades as the implementation of a predictive controller or exchanging the conventional 48x48 SH WFS with a pyramid. With the ELT era arising, GPI will proof as a versatile and path-finding testbed for AO technologies on the next generation of ground-based telescopes

Characterization of the atmospheric dispersion corrector of the Gemini planet imager

An Atmospheric Dispersion Corrector (ADC) uses a double-prism arrangement to nullify the vertical chromatic dispersion introduced by the atmosphere at non-zero zenith distances. The ADC installed in the Gemini Planet Imager (GPI) was first tested in August 2012 while the instrument was in the laboratory. GPI was installed at the Gemini South telescope in August 2013 and first light occurred later that year on November 11th. In this paper, we give an overview of the characterizations and performance of this ADC unit obtained in the laboratory and on sky, as well as the structure of its control software.Comment: 16 pages, 12 figures. Proceedings of the SPIE, 9147-18

Gemini planet imager observational calibrations X: non-redundant masking on GPI

The Gemini Planet Imager (GPI) Extreme Adaptive Optics Coronograph contains an interferometric mode: a 10-hole non-redundant mask (NRM) in its pupil wheel. GPI operates at $Y, J, H$, and $K$ bands, using an integral field unit spectrograph (IFS) to obtain spectral data at every image pixel. NRM on GPI is capable of imaging with a half resolution element inner working angle at moderate contrast, probing the region behind the coronagraphic spot. The fine features of the NRM PSF can provide a reliable check on the plate scale, while also acting as an attenuator for spectral standard calibrators that would otherwise saturate the full pupil. NRM commissioning data provides details about wavefront error in the optics as well as operations of adaptive optics control without pointing control from the calibration system. We compare lab and on-sky results to evaluate systematic instrument properties and examine the stability data in consecutive exposures. We discuss early on-sky performance, comparing images from integration and tests with the first on-sky images, and demonstrate resolving a known binary. We discuss the status of NRM and implications for future science with this mode.Comment: 14 pages, 14 figures. Proceedings of the SPIE, 9147-13