How to get a light curve from my observations?

[rogerg (Roger)]

Originally Posted by AstroJunk

5 seconds is pretty good for that magnitude

Out of interest, seeing as I've been reminded about this thread.. I've done some more testing and definitely should have used shorter exposures than 5 seconds. For the upcoming June 4 occultation I'll be using 1 second exposures. At that exposure time I get 18 images per minute.

Roger.

[higginsdj]

I take it that you haven't done done photometry before.... How linear is the CCD for your target and comp stars for the exposure time you have chosen? Linearity falls off at both ends (over and under exposure) of most CCD camera's. Can I assume you used the 12"? 5 seconds in a 12" scope isn't going to produce a very high SNR for a magnitude 14 target meaning that whatever occultation you may record will be well inside the noise and linearity for such exposures is also questionable.

You have an option to stack your images (say 5-6 consecutive images) and then re-measure. Yes, your timing of the occultation will suffer but you should be able to get 0.05mag accuracy (or close to it) in the photometry and get around the extensive noise in your data.

(To achieve 2% photometry in my 14" I have to integrate for ~ 60 seconds on mag 14 minor planets)

[rogerg (Roger)]

Thanks for replying David ...

Originally Posted by higginsdj

How linear is the CCD for your target and comp stars for the exposure time you have chosen?

I don't understand sorry ... an indication of my level of experience yes I have briefly about linearity of CCD's, seems from what you say I need to understand it.

Originally Posted by higginsdj

Can I assume you used the 12"? 5 seconds in a 12" scope isn't going to produce a very high SNR for a magnitude 14 target meaning that whatever occultation you may record will be well inside the noise and linearity for such exposures is also questionable.

12" @ ~F/7.5 yes, 5 second exposures gave the target (Pluto) an ADU of about 1150 (varies between exposures of course). That's compared to a backgorund noise level that I'd estimate to be about 200 ADU.

Originally Posted by higginsdj

You have an option to stack your images (say 5-6 consecutive images) and then re-measure. Yes, your timing of the occultation will suffer but you should be able to get 0.05mag accuracy (or close to it) in the photometry and get around the extensive noise in your data.

Yeap, stacking, sure... but if 5 seconds isn't sufficient I'd just increase the exposure time, I'd think at these "short" exposure times increasing the exposure time would be more suitable than stacking?

Originally Posted by higginsdj

(To achieve 2% photometry in my 14" I have to integrate for ~ 60 seconds on mag 14 minor planets)

Wow, OK ... not the impression I was getting from the occultation people out there that use video cameras for these things! (not even 5 second exposures). Interesting.

Thanks,
Roger.

[AstroJunk (Jonathan)]

Originally Posted by rogerg

Wow, OK ... not the impression I was getting from the occultation people out there that use video cameras for these things! (not even 5 second exposures). Interesting.

I think the thread has begun to stray away from occultation timing and into photometry. Two very different outcomes...