This page describes some notes for Observers and Support Astronomers to bear in mind regarding operation of AO with NIRC2.

Guide Stars

The Guide Star Offset On-Line Planning Tool can The AO Natural Guide Star (NGS) system requires a guide star of suitable brightness (recommended brighter than V = 13m ) to correct for the atmospheric distortion. The NGS can be offset from the object of interest but the quality of correction degrades as the offset is increased. This quality varies from night to night with the isoplanatic angle. There are also hard limitations of the AO field steering mirror (FSM) system used to offset the guide star. The figure below shows the FSM limits relative to the NIRC2 wide field of view.

FSM control limits shown relative to the NIRC2 wide field of view (40 arcsec on a side). The figure depicts the case of the object being 10.0 arcsec away from the guide star at a position angle of 0.0°.

It is necessary to determine an optimum position angle (PA) setting for the rotator in order to allow for maximum guide star offset. The optimum PA should take into account the need to dither the object on the science detector. The NGS position needs to allow for this movement in FSM space. For NIRC2 the following simple formula is recommended for determining the PA :

    PA = Guide Star to Object PA
The figure above shows that the guide star is in a position that would allow for box dither pattern of 5 arcsec offsets.

Dome Open/Close Criteria

The Keck domes are typically closed when the sun is up. However, we recognize that this could prevent AO observers from opening in time to acquire twilight flats. Hence, the following modified dome opening policies apply for AO nights:

AO User Tools

From the pull down menu in the VNC session, select K2 AO User Tools.

The following options are available:


Note that when Guider Eavesdrop is launched, you will be viewing the ACAM guider.

Acquiring NIRC2 data in coordination with AO

Position Angle (PA)

Differential Atmospheric Refraction (DAR)


Imaging flat field frames can be acquired with dome flats or with twilight sky flats. Spectroscopy lamps will be installed on the AO bench at a later date.

Observing Overheads during an NGS-AO NIRC2 acquistion sequence