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AO-assisted NIFS IFU spectroscopy with ALTAIR

Observations made with NIFS+ALTAIR adaptive optics are the most common observing mode. Typically, the adaptive optics correction with ALTAIR on a bright star gives a best-fit FWHM value of 90 - 110 mas. The FWHM is limited by the rectangular 0."1 x 0."04 pixels in the NIFS spectrograph, so the ALTAIR PSF is sub-sampled by the NIFS spectral pixels. We found that guiding with NIFS+ALTAIR yields correction results that are largely consistent with the performance described on the ALTAIR pages, resulting in image quality of around 0.1-0.15" FWHM.

An upgrade to the ALTAIR adaptive optics system during late 2005 made available a Field Lens for ALTAIR AO observations. The field lens allows ALTAIR to deliver a higher and more uniform Strehl ratio across a larger field of view, and consequently improves the correction from ALTAIR in the NIFS field when guiding off-axis. The field lens MUST be used for NIFS+ALTAIR observations with the Laser Guide Star. For ALTAIR NGS, the field lens is recommended when the guide source is more than 5" off axis. More information concerning the field lens can be found on the ALTAIR field lens web-page.

Required ALTAIR Guide Star Characteristics: See the table on the main guiding options page for useful guide star separations and brightnesses for ALTAIR guide sources. See the ALTAIR pages for more detailed information on the guide performance vs. stellar magnitude for wavefront sensor stars. Also, the NIFS OT Details page has information on guide fields of view and configurations for NIFS+ALTAIR stars.