ARCSAT Prototype off axis auto-guider

APO has implemented a prototype guide camera for the 0.5-m Telescope. It uses a Meade DSI II camera on a 5 inch finder scope on the side of the 0.5-m. Guiding is done automatically though MaximDL and Astronomers Control Program (ACP).

There is no user interaction with the autoguider. The only thing a user needs to know is that ACP will initiate guiding if an exposure (or any exposure in an observing script) is >60s. As an example, if a user specifies a 45s exposure and a 120s exposure of the same object in a script, ACP will turn auto-guiding on for both exposures (even the 45s). Guiding will continue unless a guide star is lost (clouds, high background from moon or twilight, or the telescope is slewed to another field). There is no control given to the user.

There is approximately a maximum 1 minute overhead in field set-up time (if the software can not find a suitable guide star on the first attempt). This overhead is only initially. ACP maintains the guiding for the same field and will not re-acquire a guide star unless the field moves (example excessive tracking jumps) or ACP needs to re-center the object.

The following screen shot describes the additions a remote user will see on the ACP System Status screen. A postage stamp of the guide camera subframed field showing the guide star (1), A Guider section (2) with exposure times and reported Ex and Ey errors (pixels) from the guider, and graphical plots of those errors (Ex and Ey) with time in the section labelled Tracking Errors (3). It is worth noting, because of the optics in the finder scope, there are large diffraction spikes on the guide stars.

The auto-guiding can be disabled by the 3.5-m observing specialist per request but by default it is on. The prototype guider is in shared-risk mode. A known failure mode requires human interaction to go out to the dome and disconnect/reconnect the guide camera. Hopefully this problem happens infrequently. Feedback is welcome and appreciated.