Ooooh cool, some astro contoversy ....interesting discussion guys, you both make some valid points, lets get to the bottom of it, adds even more interest and intrigue
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 BetaPictoris.
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.
I provided my opinion on what I could see in your image, based on the information you posted. I don't think it amounts to discounting anything.
The main problem, as I see it, is still that your diffraction spikes lie very close to the dust disc plane. I have attached an image which shows my image overlaid on yours. Notice how the diffraction spikes in your image nearly covers the area where the dust disc appears in mine. Surely that will not help with detecting it.
Reducing the glare is paramount, and I also believe the wire spider I'm using makes a big difference. I don't know what kind of spider you are using but there just seem to be more glare in the images you posted than what I saw in mine.
The second image attached (Kalas & Jewitt, 2000) is a good reference, it's upside down though.
Nice work Rolf. I am very impressed by your dedication to squeezing the maximum performance out of your set up; the clip-less mirror along with a skinny spider are the hallmark of an obsessive striving for perfection. I just love reading about this stuff.
Brilliant Rob, this is an outstanding effort and you actually blown out my mind, I would never -ever- imagined it was possible to take such an image with an amateur equipment (and a webcam!) !!
Very nice work indeed - congrats! I am working on a project trying to detect a bow shock very near a bight star.
One thing you can do is remove the PSF of the star itself using an AstroFractool. This is heavy reading but the results are pretty cool. there is a link towards the bottom to download the tool.
I provided my opinion on what I could see in your image, based on the information you posted. I don't think it amounts to discounting anything.
The main problem, as I see it, is still that your diffraction spikes lie very close to the dust disc plane. I have attached an image which shows my image overlaid on yours. Notice how the diffraction spikes in your image nearly covers the area where the dust disc appears in mine. Surely that will not help with detecting it.
Reducing the glare is paramount, and I also believe the wire spider I'm using makes a big difference. I don't know what kind of spider you are using but there just seem to be more glare in the images you posted than what I saw in mine.
The second image attached (Kalas & Jewitt, 2000) is a good reference, it's upside down though.
The larger the secondary the heaver the spiders but some of that is light scatter. I have some on my excellent 20" RC optics. You can get extra scatter from an unmasked edge on the primary, a field flattener or even dirt on the optics. Also poor seeing can cause the star halo area to expand.
If you can use thinner spiders that is excellent but my secondary is almost 8" across (larger than my first 6" reflector) so one cannot use wire to be stable. I fght bright stars with longer exposures so sometimes I will cut my subs down to just overwhelming the read noise.
Even with an expensive excellent system bright stars can be an issue to get a clean star profile. It seems no matter what you pay you have to tweak and modify to get things right.
This is good discussion as it helps us understand how to better utilize our imaging systems.
Thank you very much for your comments everyone, Dave, H, Brian, Ken, Bart, Rick, Louie, Greg, Ron, Ric, Dennis, Alex, Marc, John, Mike, Marcus, Steve, Steven, Tom, Rich, Dave, Ross, Marco and KenC. This certainly created a bit of buzz, much more than I expected!
Quote:
Originally Posted by Ken Crawford
One thing you can do is remove the PSF of the star itself using an AstroFractool. This is heavy reading but the results are pretty cool. there is a link towards the bottom to download the tool.
Thanks for that link Ken, it looks very promising I'll have to look into that.
Hi Everyone, thanks again for your comments and greetings. This story has certainly gone around the world, I had no idea it would create such a buzz!
I've lost count of the places it has been published now, and it's been a crazy day today! Just this evening I've had crews from 3News, Dominion Post and Western Leader at the house. Probably spent a good 1 1/2 hour giving interviews and explaning how my telescope works Also managed to mention IceInSpace, so hopefully they'll include that somewhere.
It's supposed to run tonight on TV3 Nightline 11:10pm NZST. And be repeated tomorrow morning on Firstline from 6am. Don't know how it'll turn out yet
And many others have contacted me, including Dr Grant Christie of the Stardome Observatory in Auckland with whom I had a very enjoyable chat this afternoon.
And here I thought astronomy was a peaceful quiet passtime
....interesting discussion guys, you both make some valid points, lets get to the bottom of it, adds even more interest and intrigue 
Well done with your efforts Rolf!
