29 research outputs found
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-
contrast sensitivity of at . 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 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
POLARIMETRY WITH THE GEMINI PLANET IMAGER: METHODS, PERFORMANCE AT FIRST LIGHT, AND THE CIRCUMSTELLAR RING AROUND HR 4796A
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 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&T STAGES OF THE GEMINI PLANET FINDER
Abstract. The Gemini Planet Imager (GPI) is currently in its final Acceptance & Testing stages. GPI is an XAO system based on a tweeter & woofer architecture (43 & 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'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 , and 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