Guide star faded message in MaximDL using SX AO

[naskies (Dave)]

Question for anyone else using MaximDL and (Starlight Xpress) Adaptive Optics:

I often get the "guide star faded" message when MaximDL tries to re-acquire the guide star at the end of an exposure (when it dithers).

As far as I can tell, the guide star hasn't actually disappeared (it's still quite bright). Rather, Maxim seems to lock onto the star during a moment of seeing when it's particularly bright - resulting in the normal ADUs being seemingly too low.

All I have to do to fix it is to stop AO tracking, and then immediately restart AO tracking - and it all works perfectly again. While this isn't difficult, having to do it *every* exposure becomes very tedious - especially when I'm trying to sleep!

Has anyone seen this before? Any suggestions on how to fix it?

[cfranks (Charles)]

My experience was if I had set up to do multiple exposures, Maxim always re-acquired the guide star very easily. It was always the first guide star selection that had to be done manually. As you implied, no sleep! The no-sleep bit is why I have never been able to use any Automation software when I use the Sx-AO. Otherwise it worked great.
I must say that every time I had a 'guide star faded' was either clouds or I hadn't chosen a bright enough star. Every time!

Charles

[RickS (Rick)]

Dave,

There are regular complaints about the "dreaded guide star faded message" on the MaximDL group on Yahoo from AO and non-AO users. I haven't seen any magic bullet solutions proposed. Using calibration frames with the guide scope seems to help, especially with a Lodestar. I have seen this error occasionally (without cloud or any other obvious cause) but not often. Others seem to have a lot more problems.

Cheers,
Rick.

[naskies (Dave)]

Thanks gents. I've noticed that it's not related to smearing / larger FWHMs in poor seeing or windy conditions, but rather to do with the total ADU count fluctuating between exposures.

Some nights the guide image and ADU count will be rock steady, and others (such as last night)will fluctuate wildly - e.g. with a baseline of 30,000 I've seen it sometimes drop down to 500 and as high as 60,000 in the tracking panel. If it "locks on" during the 60,000 sample, then guiding is screwed.

This is a very weird bug. I would imagine that the simplest fix would be for the software to reset the target total ADU count when it attempts to re-acquire the guide star (or if it's failed for a certain amount of time).

The good news - I managed to capture 8 hrs worth of data last night. The bad news - I had to wake up every 40 mins or so during the night to reset the guiding. Very sleepy today!