Quote:
Originally Posted by SkyViking
Hi Steve, I must say it does feel like a bit of a dig even though you say it isn't. Particularly because it's not the first time you doubt my credibility and I'm really not sure what you're implying by your statements.
But since you've had a go yourself and tried to replicate my results then I'll comment on it:
The literature gives the brightness for the dust disc as 15 magnitudes per square arcsecond. I don't know if that's an average, or only for the brightest part (I suspect the latter), but in any case that is well within the capabilities of amateur equipment. I have captured galaxies of magnitude 21.00 in the past. The challenge here is the overwhelming glare from Beta Pictoris.
Have you read the paper that I linked to? This dust disc was imaged with a Thomson THX 7852 CCD, which is now over 20 years old (Imaging area of 208x144 pixels...) Although I don't know the specs of that particular CCD I wouldn't think a modern webcam is particularly inferior in any way, except when it comes to sensitivity.
I also image with the RAW modification so I'm using the full resolution and am therefore not limited by the Bayer matrix other than when it comes to sensitivity.
Remember that what you see in my processed image is not what it looked like in my raw diff image. As I said, I blended in the parts from the diff image that showed the dust disc onto the normal image of Beta. This was after very careful processing, stretching, noise reduction etc. As a result my dust disc is nothing but a diffuse blur, it was indeed very faint in the raw data. I'm not sure what processing has been done to your diff image, but there seems to be a lot more glare and spikes than I had in mine.
Most importantly your diffraction spikes seem to lie very close to the plane of the dust disc. The position angle you have indicated is actually a little off, I have drawn the correct angle in the attached image which is even closer to the spikes. These spikes would probably put a severe limitation to what can be squeezed out of your data.
Also be aware that I have deliberately removed mirror holding clips and anything else that can produce excess diffraction patterns in my system. I'm using a wire spider with 0.08mm wires, which drastically reduces the amount of diffraction glare (see image of the spider here: http://www.pbase.com/rolfolsen/image/134140252). In your image I notice quite a bit of spikes and glare also around some of the other bright stars - I have also marked these in the attachment. There must have been quite a lot around Beta itself and this would again limit the possibilities of detecting the dust disc I think.
Your diff image also doesn't quite seem to line up, I can see quite large signals from the diffraction spikes that seem to have been different for Alpha and Beta and there is also a difference apparent in the stellar discs.
In addition there could be other reasons for the lack of detection in your images. I don't know what exposure time you used. You CCD is more sensitive than mine, so you'd need shorter exposures than I used, probably a lot shorter. Another complication could be if your skies are light polluted, but I don't know if that's the case.
I hope that answers your questions.
Edit: Can't seem to upload images at the moment, will add it later. |
Rolf,
firstly, I did read the article, in full.
I did doubt you in the past. I did make that admission to you, in full,
in a pm to that effect, even pasting the content of what my doubts were to a very
experienced imager in the pm to you.
You seemed to be gracious about it back then.
Secondly, you seem to discount about 5 aspects of how I obtained my
result. You may be totally correct in that assessment.
I do , however, have a bit of faith in my ability to image at hi res and
down to a reasonable sensitivity to be within the ballpark of a
similar setup like yours.
If you feel like my scrutiny or discussion is not welcome I'll remove it in full.
If you would like to have a go at aligning/processing my raw FITS to see
how you go with them, you are welcome to do so.
On the subject of the initial alignment being slightly off and the disks of
the stars being not equal, I can tell you that perfect align with a 2x upsample
had them exact, before post processing the 'dark' result.
Slightly mis-aligning the difference image made almost no noticeable
difference to the flares that you see.
There are several flares, none any more prominent than the other.
I have stars resolved very close to Beta and Alpha too.
My exposures were 10s for Beta and 6s for Alpha.
Do you think that was too much? I'd like to know how you can estimate
what would be a good exposure for this PP imaging?
The article mentions way different exposures. It was also done with a
very big scope.
Finally, my sentiment at that end of my post stands.
'I sincerely hope I am wrong, I have admired your extreme imaging for years.'
Rolf if I am totally wrong in doubting your result I would be the first
to apologise in this thread.
regards,
Steve