Information for observers proposing to use AO in semester 2003 August-January (JTR 06 March 03)

AO is being offered on a shared risk basis in semester August 2003 to January 2004. One user program per month will be supported Since AO is still undergoing testing we can't guarantee performance. AO is only being offered with NSFCAM this semester. Observers should keep in mind the following capabilities and restrictions when preparing proposals.

  • NSFCAM 0.056 "/pixel scale only (FOV 14.3"x14.3"). All listed filters, CVFs, and grisms are available, but no polarimetry. Observing in the L and L' filters is possible although the background with the AO relay in the beam is much higher due to the additional warm mirrors and baffles in the beam. NSFCAM uses a cold 0.95um IR transmitting/visible reflecting dichroic to direct the visible beam into the wavefront sensor. This means that the short wavelength side of the IJH (asteroid) grism is now blocked (although this type of program is best done with SpeX).

  • When using AO the position angle of the instrument rotator will be fixed at 0 degrees. Rotating to other position angles is not possible because this changes the mapping between the deformable mirror in the AO relay (above the instrument rotator) and the lenslet array (below the instrument rotator). Therefore it will not be possible to align the grism slit in NSFCAM to do both components in a binary for example.

  • AO observations will be restricted to < 1.6 airmasses and hour angles to < |+/- 2 hrs|).

  • The FOV available to the wavefront sensor is 75" x 75" (square). The science object and guide star must lie within this FOV. The closer the guide star to the object the better the correction of course. Note that for reasons we do not yet understand the available FOV is about half this value. We hope to fix this following further engineering tests.

  • Guide stars should be brighter than R=12. Guiding on extended objects with diameters < 5" (e.g. Uranus and Neptune) is acceptable.

  • Guiding on objects moving at different rates to the science object is acceptable (e.g. guiding on Tethys for Saturn). This mode isn't working yet but we plan to have it ready for this semester.

  • Dithering on the guide star by up to 5" is acceptable.

  • Object-sky sequences are acceptable, i.e. nodding to blank sky and and resuming AO guiding when the telescope nods back to the object.

  • The best performance achieved so far is a strehl ratio of about 30% at 2 micron when the uncorrected 2 micron seeing is better than about 0.6 arcsec FWHM.

    Questions about AO proposals should be directed to John Rayner. Technical questions about AO should be sent to Doug Toomey.