Quote:
Originally Posted by middy
Hi Chris. Awesome result. I tried my hand at asteroid occultations several times, but that was a bit too 'real-time' and I couldn't get fast enough video frame rates and still have a decent amount of signal. Exoplanet transits look to be a bit more of a relaxed pace with no need to video.
What exposure times did you use? And how often did you take images?
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Thanks Andrew.
It was a pretty relaxed pace, just like any other imaging I've done, with just a few different concepts and setup considerations.
For this transit I used 147 sec exposures at 200 gain, and imaged continuously for transit and an hour before and after, however, these values are determined by the length of the transit and the magnitude of the target star, so every target will be different.
The imaging time (1 hour before transit to 1 hour after) was 3.5 hours. I wanted to get around 30 images per hour to give me enought data points, so I aimed for somewhere around 120 sec. exposures. That would give me about 100 images in total. Thats a nice starting point for processing.
Another thing to consider is the camera gain. I aimed to get the brightest pixel in the target star image to be around 66% of the camera full well value. The target star brightness is going to change during the night, not just from the transit but as you track through different atmospheric thicknesses. 66% of max pixel value gives you some headroom because if any pixels saturate in the target star you're going to be losing data. You don't want that. However, if you see the max pixel value increasing too high during imaging you can try decreasing focus to spread the flux out and this will lower the individual pixel values of the target star. Anyway, I adjust the gain to get the initial pixel value to around 66%.
Don't forget to shoot flats and darks with these setting also, you need them too.
Chris