Quote:
Originally Posted by SkyViking
Cheers Steve,
My thoughts are as follows: I can see you used ~70 frames, I think that's too few. I tried a couple of weeks ago using a NIR filter but like you I came up empty handed (more on that below). I did use 500 frames on each though and it really makes a difference for the background noise. My conclusion so far is that the disc is not very bright in IR at all, contrary to what I've always thought. At least it's not bright in the NIR range, but maybe at longer wavelengths.
I did some further reading on it and as far as I can gather the disc is optically neutral, meaning that it simply reflects the same colour of light that hits it. So there wouldn't be any wavelength that offers a particular advantage in contrast between the star and the disc.
I think the best option is to just use no filter at all, so for me I'll need to have another go witout the NIR filter.
Apart from number of subframes you do seem to have some star trailing (the bright double star in the 2 o'clock position looks close to an 8), but I'm not sure if or how that amount of blurring will impact the detectability of the disk.
Also, the disk gets exponentially brighter closer to the star, and the saturated area is quire large. Maybe try shorter subframes and many more of them.
The diffraction pattern is also visibly different between the two stars, though only slightly. But maybe still enough to overpower the faint signal from the disk in the difference image? I think more subframes will help here too. I don't think it's due to collimation changes but it's my experience that all the small diffraction spikes slightly change shape and size under atmospheric influence so it does need to be averaged out over a large number of frames to get a true image of the PSF of your system.
That's what I can think of at this stage. I'll probably try myself again once I get a break in the clouds that coincides with a new Moon.
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Thanks for the comments Rolf,
Here is a result from 27 Nov.
details: exposures for Beta: 5 sec, exposures for Alpha 3 sec.
(that is still a a ratio of 0.6, same as 10sec vs 6 sec for previous attempts)
You state that 0.591 is ideal and your successful attempt was 0.571 with
the critical Beta exposures at 7 secs.
So I'm happy that I'm close to the ideal. Maybe closer to the ideal than you were
Difference align was done with 4x resize raws
I've also shown an inset with a deliberate misalign using the same raws.
You can see the same resultant flare pattern after a curve manipulation shows up with both alignments.
Conclusions:
I might have something resembling the PP disk in the correct P.A of the disk.
However, curve adjustment of the difference layer should show anything
'different' in a 'brighter' layer as a brighter feature.
My artifact is darker.
Shorter exposures than 10s/6s and other ratios have shown
a different flare pattern.
Now what has also changed?
I remade the spider with 0.25mm vanes, and made a secondary vane holder and screw adjustment assembly on the lathe.
Laser collimation was spot on. Collimator was also collimated in a vee block as previous.
Also, 27 Nov was a brilliant night, way superior to many recent nights.
You can see how good it was by the 'star' curve I have applied to
the close double star, inset.
Another plus was that all subs were obtained with the CCD sitting at 10.3C for over two hours, both lights and darks.
That is very stable imaging.
I'm confident that this is a fairly tight set of data to use as a benchmark
for future nights.
Confident though
regards,
Steve