SharpCap Forums

I've been pushing the little Mak 127 a little further, instead of planets around our own star, this is a lightcurve detection of the extrasolar planet TrES-3b orbiting the star TrES-3 (V1434 Hercules)
The planet has about twice the mass of Jupiter and an orbital period of 31 hours.

Equipment used:
Mak 127 + 0.5 FR.
ZWO 178MM
Baader 610 filter
Software Sharpcap, Skysafari, MaxIm DL

Clear skies
Doug

Hi Doug,

that's very nice - impressive to see how clear the dip is in the graph in spite of only being 0.04 magnitudes or so. We have had some previous discussions on here about monitoring this sort of variability, and I seem to recall that one idea that came up was deliberately being a bit out-of-focus. The idea behind this was that it spread the star out on the image and allowed longer exposures without saturating (and the longer exposures meant less noise). No idea if you have already been using tricks like this or not, but thought I would mention it.

cheers,

Robin

Hi Doug,

Nice capture!

I can't remember where I first came across the de-focusing technique. I think I saw it first done by an Italian amateur, then I brought the topic up with Robin who described the physics of it. I was attracted to it for the reason that my Atik 314E CCD doesn't have a very deep well (about 13k electrons) so instead of buying a new, expensive camera I de-focused to allow a longer exposure which leads to less noise by integrating over a larger aperture. It works!

Here is a plot of a DSCT variable Cze V627 in Cygnus. The peak-to-peak magnitude difference is identical to yours, about 0.05 mags: And here is a single frame, so you can see the out-of-focus stars: I used a William Optics 71mm f/5.9 with a Wratten #12 filter (Red + Green) and 90s exposure.

I know you are doing exoplanets, so the one reason I can think of why you wouldn't want a longer exposure is that it affects transit ingress and egress timing.

Brian

Thanks Robin,

Yes I've tried that method, even slightly trailed images seem to work too, anything really to push the SNR and increase the signal.

Cheer's,
Doug

Hi Brian,

Yes I try to run the shortest exposure with the best SNR I can achieve. Out of focus images certainly work. To get the ingress and egress timing certainly is the goal.
Also I've found shorter exposures, while giving up some signal are great also for Flare star imaging. Here's a light curve of a recent run on the star CR Dra. Exposures are 15 seconds.

Doug

Hi Doug,

It is really impressive to see measurements like these and the level of accuracy - research paper stuff less than 30 years ago - now accessible to amateurs. Well done and thanks for writing it up here.

Tim