Occultation of Chariklo 12th May

[deanm (Dean)]

Many thanks, Tony & Jonathan - your comments are appreciated.

I guess someone could come up with an algorithm (an App!) that optimises sampling rate versus magnitude for a given aperture + stellar magnitude.

Cheers!

Dean

[tonybarry (Tony)]

Hi Dean,

The aperture of the scope and the magnitude of the star are important. Also the "seeing" or the transparency of the sky; all these things go into the determination of frame rate.

The optimisation also has to use signal to noise ratio as an input, because sometimes for an occultation the target star is much brighter than the occulting body, so it's just an on / off signal; but other times it's a step change in brightness (because the two objects have similar brightness levels).

In the case of PHEMU observations (mutual occultations by Jupiter's satellites) the light curve is a very gradual diminution over tens of seconds to minutes, rather than a step change.

The gain of the camera can be an influencer - at high gain, the light curve is noisier than at lower gain (pretty obvious), so dropping gain, and reducing frame rate may provide a cleaner output, with a reduction in temporal accuracy as a trade off.

The last thing in the mix is the tiredness of the operator. I've found that at 3am my mind is working at about 50%, and my rig has to be **very** easy to use, and hard to get wrong. So anything that gets done easily is good.

Regards,
Tony Barry
WSAAG

[Blue Skies (Jacquie)]

Originally Posted by deanm

I guess someone could come up with an algorithm (an App!) that optimises sampling rate versus magnitude for a given aperture + stellar magnitude.

I've thought about something similar, a graphical representation, for several years, being keeper of the observing manual, and I've had someone else suggest similar to me as well. But as Tony has explained, it just ain't that easy. I've kept a log of my settings for each event I've monitored and conditions vary greatly from night to night. Sometimes I can get a mag 12 star with only x4 integration, other times I've needed x24 on a night of bad seeing and the Full Moon within 5 degrees of the target star! Nonetheless I think there some "rules of thumb" that could be formulated, such as the timing needed to clearly detect the passage of the rings of Chariklo, and I'll ruminate on them a bit more for next update of the manual, I think. The best thing at the moment is to observe frequently and get to know how your current set-up performs, and what it can and can't do - and write it down so you don't forget!