It was an important week for the Gemini Planet Imager Consortium. Several of us met at SPIE Astro in Montreal, Quebec, Canada to present our work on GPI. Katie Morzinski wrote a blog post describing the GPI -focused events at the conference, so I will briefly give my perspective.
Yesterday, we submitted simultaneously 18 proceedings summarizing the analysis of data collected during the first light runs. I attached at the bottom of this post the complete list of proceedings. I recommend you check them if you want to know more about the first sky-results with this fantastic instrument.
The conference was also an opportunity for several members of the consortium to meet again, and for some of us to meet for the first time after several years communicating by emails. The Dunlap Institute, one of the partners of the consortium, invited the GPI team to a dinner in a fantastic Italian restaurant. Thanks Quinn for coordinating this memorable GPI event.
Thanks to the entire team for this great work.
See you in September at Chicago for the GPI Science meeting.
The Gemini Planet Imager (GPI) is a complex optical system designed to directly detect the self-emission of young planets within two arcseconds of their host stars. After suppressing the starlight with an advanced AO system and apodized coronagraph, the dominant residual contamination in the focal plane are speckles from the atmosphere and optical surfaces. Since speckles are diffractive in nature their positions in the field are strongly wavelength dependent, while an actual companion planet will remain at fixed separation. By comparing multiple images at different wavelengths taken simultaneously, we can freeze the speckle pattern and extract the planet light adding an order of magnitude of contrast. To achieve a bandpass of 20%, sufficient to perform speckle suppression, and to observe the entire two arcsecond field of view at diffraction limited sampling, we designed and built an integral field spectrograph with extremely low wavefront error and almost no chromatic aberration. The spectrograph is fully cryogenic and operates in the wavelength range 1 to 2.4 microns with five selectable filters. A prism is used to produce a spectral resolution of 45 in the primary detection band and maintain high throughput. Based on the OSIRIS spectrograph at Keck, we selected to use a lenslet-based spectrograph to achieve an rms wavefront error of approximately 25 nm. Over 36,000 spectra are taken simultaneously and reassembled into image cubes that have roughly 192×192 spatial elements and contain between 11 and 20 spectral channels. The primary dispersion prism can be replaced with a Wollaston prism for dual polarization measurements. The spectrograph also has a pupil-viewing mode for alignment and calibration.
Pascale Hibon, Sandrine Thomas, Jennifer Dunn, Jenny Atwood, Les Saddlemyer, Naru Sadakuni, Stephen Goodsell, Bruce Macintosh, James Graham,Marshall Perrin, Fredrik Rantakyrö, Vincent Fesquet, Andrew Serio, Carlos Quiroz, Andrew Cardwell, Gaston Gausachs, Dmitry Savransky, Dan Kerley,Markus Hartung, Ramon Galvez, Kayla Hardie
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.
Naru Sadakuni, Bruce A. Macintosh, David W. Palmer, Lisa A. Poyneer, Claire E. Max, Dmitry Savransky, Sandrine J. Thomas, Andrew Cardwell, Stephen Goodsell, Markus Hartung, Pascale Hibon,Fredrik Rantakyrö, Andrew Serio, with the GPI team
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.