Altair at Gemini North: Full Sky Coverage Laser AO Correction at Visible Wavelengths
Abstract
We present two recent upgrades to the Gemini North Adaptive Optics(AO) system, Altair. These two upgrades provide 100% sky coverage forlow performance AO suitable for improving the natural seeing byfactors of 2 to 3 from blue visible wavelengths (350 nm) through thenear infrared (2.5 micron wavelengths). The first upgrade, dubbed LGS + P1 "Super Seeing" mode allowscorrection of high order aberrations with an on-axis Laser Guide Star(LGS) while tip/tilt correction is performed with a more distantperipheral wavefront sensor (P1). Most currently operating LGS AOsystems are limited in their sky coverage, primarily due to tip/tiltstar availability. Although P1 provides sub-optimal tip/tiltcorrection due to its distance from the science source, its patrolradius allows operation in LGS + P1 mode anywhere in the sky fromdeclinations of +70 degrees to -30 degrees. This mode was offered forscience use at Gemini North in 2013A. We will present typicalperformance and use from its first semester in science operation,where we expect to improve image quality by a factor 2 to 3 overseeing limited images. The second upgrade is the commissioning of the AO system to correct atvisible wavelengths, which is expected to be completed in late 2013.In this mode, Altair will feed the Gemini Multi-Object Spectrograph(GMOS), which is an optical imager as well as a long-slit, multi-slitand integral field unit spectrograph. We intend to replace thecurrent Altair science dichroic with a sodium notch filter, passingonly the 589nm wavelength light from the LGS to the AO system. Therest of the spectrum from 400 nm to the GMOS red cutoff at 1.1 micronsis intended as science capable light. Tip/tilt correction will beperformed close to the science target with the GMOS on-instrumentwavefront sensor or with P1 as in the P1+LGS mode discussed above. Weexpect an image quality improvement of roughly a factor 2 in this modeover seeing limited observations. Since exposure time to reach a given signal-to-noise ratio scalesroughly as the square of the image quality, these two upgradesrepresent a substantial efficiency improvement which is available tonearly all targets normally observed at Gemini North.
- Publication:
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Proceedings of the Third AO4ELT Conference
- Pub Date:
- December 2013
- DOI:
- 10.12839/AO4ELT3.13288
- Bibcode:
- 2013aoel.confE..51T
- Keywords:
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- Laser guide star systems