We present the coronagraphic and adaptive optics performance of the Gemini-South Near-Infrared Coronagraphic Imager (NICI). NICI includes a dual-channel imager for simultaneous spectral difference imaging, a dedicated 85element curvature adaptive optics system, and a built-in Lyot coronagraph. It is specifically designed to survey for and image large extra-solar gaseous planets on the Gemini Observatory 8-meter telescope in Chile. We present the on-sky performance of the individual subsystems along with the end-to-end contrast curve. These are compared to our model predictions for the adaptive optics system, the coronagraph, and the spectral difference imaging.
The Gemini Planet Imager (GPI) entered on-sky commissioning and had its first-light at the Gemini South (GS) telescope in November 2013. GPI is an extreme adaptive optics (XAO), high-contrast imager and integral-field spectrograph dedicated to the direct detection of hot exo-planets down to a Jupiter mass. The performance of the apodized pupil Lyot coronagraph depends critically upon the residual wavefront error (design goal of 60 nm RMS with <5 mas RMS tip/tilt), and therefore is most sensitive to vibration (internal or external) of Gemini's instrument suite. Excess vibration can be mitigated by a variety of methods such as passive or active dampening at the instrument or telescope structure or Kalman filtering of specific frequencies with the AO control loop. Understanding the sources, magnitudes and impact of vibration is key to mitigation. This paper gives an overview of related investigations based on instrument data (GPI AO module) as well as external data from accelerometer sensors placed at different locations on the GS telescope structure. We report the status of related mitigation efforts, and present corresponding results.
Ground-based mid-infrared (mid-IR) observations appear to be widely perceived as esoteric and demanding, and very sensitive to observing conditions. Although the principles of observing in the background-limited regime are well-known, it is difficult for the non-specialist to find specific information on exactly how mid-IR data can be affected by environmental conditions. Understanding these effects is important for the efficiency of mid-IR queue observing, the ability of classical observers to adapt their programs to the prevailing conditions, and the standard of data being delivered. Through operating mid-IR instruments in the queue at Gemini we have amassed a considerable database of standard star observations taken under a wide range of atmospheric conditions and in a variety of instrumental configurations. These data can be used to illustrate the effect of factors such as water vapour column, airmass, cloud cover, etc. on observed quantities like raw sky background, residual background, atmospheric transmission and image FWHM. Here we present some preliminary results from this study, which we hope to be of use to observatory users and staff as a guide to which environmental conditions are truly important to mid-IR imaging observations, and which can safely be neglected.
Our team is carrying out a multi-year observing program to directly image and characterize young extrasolar planets using the Near-Infrared Coronagraphic Imager (NICI) on the Gemini-South 8.1-meter telescope. NICI is the first instrument on a large telescope designed from the outset for high-contrast imaging, comprising a high-performance curvature adaptive optics (AO) system with a simultaneous dual-channel coronagraphic imager. Combined with state-of-the-art AO observing methods and data processing, NICI typically achieves ≈2 magnitudes better contrast compared to previous ground-based or space-based planet-finding efforts, at separations inside of ≈2 ′′ . In preparation for the Campaign, we carried out efforts to identify previously unrecognized young stars as targets, to develop a rigorous quantitative method for constructing our observing strategy, and to optimize the combination of angular differential imaging and spectral differential imaging. The Planet-Finding Campaign is in its second year, with first-epoch imaging of 174 stars already obtained out of a total sample of 300 stars. We describe the Campaign's goals, design, target selection, implementation, on-sky performance, and preliminary results. The NICI Planet-Finding Campaign represents the largest and most sensitive imaging survey to date for massive ( ∼ >1 M Jup ) planets around other stars. Upon completion, the Campaign will establish the best measurements to date on the properties of young gas-giant planets at ∼ >5-10 AU separations. Finally, Campaign discoveries will be well-suited to long-term orbital monitoring and detailed spectrophotometric followup with next-generation planet-finding instruments.Keywords: Extrasolar planets; brown dwarfs; high contrast imaging; adaptive optics; near-IR instrumentation.Email: mliu@ifa.hawaii.edu Figure 1. Left: NICI at Mauna Kea Infrared in Hilo, Hawaii, prior to acceptance testing. Right: Block diagram of NICI optical configuration, including the 85-element curvature AO system, the focal & pupil plane mask mechanisms, and the two IR imaging channels. NICI is the first imager for a 8-10 meter telescope designed expressly for exoplanet imaging and is now in routine operation at the Gemini-South 8.1-meter Telescope.
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