The Circumstellar Disc of Beta Pictoris
Imaging the Circumstellar Disc around Beta Pictoris with Amateur Equipment
This image shows the famous circumstellar disc of debris and dust orbiting the star Beta Pictoris 63.4 light years away. This is a very young system thought to be only around 12 million years old and is essentially similar to how our own Solar System must have formed some 4.5 billion years ago. The disc is seen edge-on from our perspective and appears in professional images as thin wedges or lines protruding radially from the central star in opposite directions.
For the last couple of years I have been wondering if it was possible for amateurs to capture this special target but have never come across any such images. The main difficulty is the overwhelming glare from Beta Pictoris itself which completely drowns out the dust disc that is circling very close to the star. Images of the disc taken by the Hubble Space Telescope, and from big observatories, are usually made by physically blocking out the glare of Beta Pictoris itself within the optical path. But I then found this excellent 1993 paper 'Observation of the central part of the beta Pictoris disk with an anti-blooming CCD' (Lecavelier des Etangs, A., Perrin, G., Ferlet, R., Vidal-Madjar, A., Colas, F., et al., 1993, A&A, 274, 877) Full article available here: http://adsabs.harvard.edu/abs/1993A%26A...274..877L
I realised that with this technique it might not be entirely impossible to also record the debris disc with relatively modest equipment. I followed the technique described in the paper above, which basically consists of imaging Beta and then taking another image of a similar reference star under the same conditions. The two images are subtracted from each other to eliminate the stellar glare, and the dust disc should then hopefully reveal itself. However, since the two stars have different magnitudes I needed to calculate how long to expose Alpha for in order to get a similar image which I could subtract from the Beta image:
The magnitude difference between the stars is 3.86(Beta) - 3.30(Alpha) = 0.56
Due to the logarithmic nature of the magnitude scale we know that a difference of 1 magnitude equals a brightness ratio of 2.512. Therefore 2.512 to the power of the numerical magnitude difference then equals the variation in brightness.
2.5120.56 = 1.67, so it appears Alpha is 1.67 times brighter than Beta. This means that exposure for Alpha should be 1/1.67 = 0.597 times that of Beta.
With this approach I managed to capture the first amateur image of the debris disc on 16th November 2011. This image generated a lot of attention from both professional and amateur astronomers and was reported in the media all over the world.
After the initial success of capturing the disc I was contacted by several people in the astronomy community, among which were Dr Grant Christie of Auckland's Stardome Observatory. Following his suggestions I had a go at imaging it again using shorter exposures. This was to minimise the area saturated by Beta Pictoris itself and potentially reveal more of the debris disc closer to the star. The ICX098BQ chip in the ToUCam saturates fairly quickly for bright stars, even at very short exposures. Since long exposures with my ToUCam can only be controlled in 0.5s increments I decided to use 7.0s and 4.0s for Beta and Alpha respectively, which translates to a factor of 0.571. This was very close to the calculated brightness factor of 0.597 and still significantly shorter than the 30.0s I used for the first image on 16/11/2011.
So for this second image I collected 344 images of Beta Pictoris at 7.0 seconds each and 299 images of Alpha Pictoris at 4.0s each. Both sets of images were dark subtracted and stacked separately in Registax. I then subtracted the Alpha image from the Beta image in PixInsight LE, and also created the absolute difference between the two.
The absolute difference image is simply easier to work with, but the subtraction image was important as a reference to examine which of the stars had contributed the various parts of the difference. Below are both the subtraction result (left) and the absolute difference (right):
In the subtraction image on the left contributions from Alpha Pictoris are dark, while contributions from Beta Pictoris are light. It is clear that there is a fairly strong signal corresponding to the exact location of the debris disc and that it is coming from the Beta image.
I created a more natural looking final image by taking the original stacked Beta image and then blending in the central parts from a stretched version of the absolute difference image that showed the dust disc. I decided to also keep the black spot of the central glare from the difference image since the contrast with the protruding disc just seems better this way. So there is no occulting disc involved, it is simply for the sake of presentation. I created a couple of versions which can be seen in the gallery below. This is a vastly better image than the first one taken on 16/11/2011. I believe the higher number of subframes (344 versus 55) coupled with the shorter exposure times are responsible for the improvement.
I used MaximDL to produce some more in-depth illustrations of what is going on in the difference image. First a area plot of the intensity immediately around Beta Pictoris. The circular plateau in the centre corresponds to the saturated area caused by Beta Pictoris itself (The narrow trough immediately surrounding it is an artifact of the image processing). The debris disc is visible as the elevated red areas on each side of the star:
And profile plots taken both through the debris disc plane and perpendicular to it. The horizontal scale is Astronomical Units and the area saturated by Beta itself is highlighted on the plots:
The visible part of the debris disc seems to extend to roughly 250-300AU before it falls below the background noise levels. I have found that the limiting magnitude with the ToUCam from my location is around 20.0. So how far out should the debris disc theoretically be visible in my image? This is a plot of the magnitude pr. square arcsecond for the debris disc (Smith, B. A. & Terrile, R. J. 1984, Science, 226, 1421 A Circumstellar Disk around Beta Pictoris):
It seems from the figure above that if a limiting magnitude of approximately 20.0 is assumed, then the debris disc should be visible out to somewhere around 250-300AU. This corresponds with what is seen in the profile plots above.
This annotated crop of the final image shows the extent of the debris disc on both sides of Beta itself:
Some notes on ToUCam and IR sensitivity
The disc is most prominent in IR and fortunately the ICX098BQ CCD chip is very good at picking up signals in IR, probably on par with or even better than some modern CCD's in this aspect.
Another property of the ICX098BQ that helps here is actually the Bayer colour matrix. This is because each pixel either receives only red, green or blue light due to the overlaid Bayer matrix. But since the matrix dyes are practically transparent to IR light, every pixel therefore receives signal from the IR band. So the IR S/N ratio in the final image can be assumed to be correspondingly higher than the RGB S/N. This could easily explain why the ToUCam seems to pick up IR light so well; the Bayer matrix effectively acts like a IR pass filter and allows a proportionally higher number of pixels to be IR illuminated than RGB illuminated.
While I have not tested this in practice it could mean that the limiting magnitude of the ToUCam is higher in IR than in RGB.
Rolf Wahl Olsen, 04th December 2011
Comments:I received a lot of kind and encouraging comments on my old site (http://www.pbase.com/rolfolsen) about this image, so I have copied these comments below:
(If you would like to leave a new comment please feel free to do so via the button at the very bottom of this page)
ikkaisei 09-Aug-2012 21:15
This is encouraging work - what an effort.
Rob Craftsman 01-Aug-2012 21:39
For a self-proclaimed first amateur (are you sure?? this is really good) pic of another solar system, this is really stunning. You are rightfully special to have accomplished this. Heck, I feel special at having witnessed it here.
Guest email@example.com 16-Jul-2012 07:41
Yep - that is pretty impressive alright :) Say hello to Takapuna beach and Rangitoto for me - I miss that place :)
New Forest Observatory
Guest 27-Jun-2012 08:43
air ambulance 20-Jun-2012 20:40
Guest 12-Jun-2012 06:30
Well done.That is very impressive.
Judd Niemann 20-Dec-2011 12:05
Rolf - this is one of the most inspirational amateur shots I have ever seen ! The subtraction technique is a great idea. I wonder if you could get even better results with an ICX618 chip, which has greater sensitivity as well as being harder to saturate ! It may reveal even more of the disk...
I love your presentation, too. The 3-d plot with the axes in au's is really cool.
Guest firstname.lastname@example.org 12-Dec-2011 11:22
Congrats...Awesome..being from the northern hemisphere in Istanbul the view is different...great capture from the southern hemisphere ...I will keep an eye on your site...dont stop! :-)
Guest email@example.com 09-Dec-2011 10:00
great work... very very inspiring...i am interested in astronomy for years but you gave me the drive of motivation to take astro pictures...i have a Mak 6" and neximage and Canon 550 and will be working hard these nights...
Guest 08-Dec-2011 20:27
OOOH MYYY GOOOOOD that is awesom
Guest 08-Dec-2011 19:12
As a "professional" (what a weird word to use) having worked on this object for the past 10 years, I can only sit back and applaude: this is really amazing. congratulations!
Guest firstname.lastname@example.org 08-Dec-2011 18:47
An inspiration to professional astronomers too!
Guest Willemsf001@hawaii.rr.com 05-Dec-2011 19:58
Outstanding work !
Guest 04-Dec-2011 20:38
I am totally inspired by your work, this is a great work, a break-through in
Very well presented, congratulations!
Mert de Vries
Guest 04-Dec-2011 19:26
Congratulations on another great observation.
This is truly one of the finest observations I've seen in a long time. A huge inspiration to all amateur astronomers.
Guest email@example.com 03-Dec-2011 19:30
Congratulations. While I am not an amateur astronomer, I appreciate all of you watching the skies for us. I love looking at the images. Truly specatacular. Keep up the good work.
Guest firstname.lastname@example.org 03-Dec-2011 04:59
amazing, absolutely stunning, thanx for this work...
Guest email@example.com 03-Dec-2011 04:33
This is even better than seeing Russia from my house!
Guest firstname.lastname@example.org 03-Dec-2011 01:04
Very well done Rolf !! Truly amazing with a 10"
Guest 03-Dec-2011 01:01
congrats on a great catch
KEL 02-Dec-2011 15:11
Congratulations and Thank you!
I am posting the photo with it's frame on my blog thecleverevolutionproject.blogspot.com with some information about you/the photo and links to this page and also some information about Alain Lecavelier des Etangs "call" to aamateurs..
If it is not ok to post the photo please email me email@example.com.
Guest 02-Dec-2011 09:37
This is so cool, I have no astronomy experience, but this just wants me to run to a store and buy a beginners telescope! ;-) Great job! KR, Ronald
Guest 02-Dec-2011 04:55
I’m a die hard visual astronomer and this is the first time I seriously consider experimenting with astrophotography. Congratulations on such impressive achievement. (Jose from Mexico)
Guest firstname.lastname@example.org 01-Dec-2011 17:12
Hey Rolf, I'd like permission to use your photo in a gallery I'm doing for Yahoo! News about amateur astronomy. If you could get back to me ASAP that would be fantastic. Thanks so much!
Guest email@example.com 01-Dec-2011 01:30
great work!!!! I am impressed that amateur astronomer can today reach the imaging capability that we had in the 1990s. One small correction though. You did not image another "solar system" but another "planetary system" or "stellar system". There is only one Sun and that's the one we see nearby Earth.
Guest firstname.lastname@example.org 30-Nov-2011 20:26
Fantastisk! Et stort tillykke fra Danmark.
Guest 30-Nov-2011 20:24
Amazing work - Congrats
Guest email@example.com 30-Nov-2011 19:23
Very cool! Great work!
Guest firstname.lastname@example.org 30-Nov-2011 17:19
Extraordinary work. Congratulations from a mere enthusiast to a very impressive amateur astronomer. Keep up the good work and I wouldn't be surprised to see your title shift from amatuer to professional astronomer!
Guest email@example.com 30-Nov-2011 07:43
After Gliese 581g and Proxima Centuri, Beta Pictoris should be a priorty destination when humanity masters interstellar travel:)
Guest firstname.lastname@example.org 29-Nov-2011 23:47
You are an inspiration to fellow amateur, great work!
Guest email@example.com 29-Nov-2011 23:01
Congratulations, I'm amazed by people like you. By the way, is there an observatory in NZ that you would recommend to visit?
Guest 29-Nov-2011 21:37
Congratulations Rolf. Outstanding achievement. Must be quite a thrill!
Guest 29-Nov-2011 21:26
Great Work Rolf. This is unbelievable.
Being an amateur and finding/imaging a solar system is way too cool.
Guest firstname.lastname@example.org 29-Nov-2011 18:48
Be proud of that. You really set a mark!!! Thanks for that great picture. Greetings from germany.
Guest 29-Nov-2011 16:32
Abolutely stunning! Brilliant!
Guest 29-Nov-2011 16:04
Awesome! Spectacular work! T. Peige Wise
Guest email@example.com 29-Nov-2011 15:47
Yeahhhhhhh great, feeling must be amazing
Guest 29-Nov-2011 13:51
Dear Mr Olsen,
First: CONGRATULATION for this great image of the Beta Pictoris dust disk !!
This image remembers me when (with Guy Perrin, Alfred Vidal-Madjar, François Colas and others) we obtained very similar images in 1992. It was a great time. I have no doubt that this is really the disk of Beta Pic that you have in your image: its looks so similar to what we obtained. Captured with a 10" telescope, your image represents a very nice achievement and a technical exploit. CONGRATULATION!!
As I wrote to a journalist asking me, I feel that it is unlikely that your image can be used to learn something new about this Beta Pictoris system. But this is not the most important: the most important is that your image is impressive and beautiful. A beautiful image of a young planetary system 62 light-years away, a beautiful image among other beautiful images in your pbase galleries.
Nonetheless, your work shows that amateur can obtain results which are potentially useful for scientists. In particular, I think about transit of exoplanets some of which can be surveyed by amateur astronomers. By the way, this gives me the opportunity to send a call for photometric survey of Beta Pictoris, which can be done by (expert) amateurs. Indeed, in 1994 we discovered that a planet likely transited in front of Beta Pictoris in 1981. In 1994, the claim for the observation of a transiting exoplanet was regarded as very suspicious. But the things have changed, and since 2008 we know that a planet orbits around Beta Pictoris (Lagrange et al. 2008), moreover the imaged planet is very consistent with a transit in 1981 (Lecavelier & Vidal-Madjar 2009). To predict when the next transit will happen a survey of Beta Pictoris photometry is needed. In that regard, the help from amateur can be useful.
A comment: in contrary to the title of the photo, the Beta Pictoris disk is not "protoplanetary", this is a "debris disk". The dust seen in the image is not massive enough for a new planet to form. This dust is produced by collision between asteroids and/or evaporation of comets: the dusty grains captured in your photo are the debris of minor bodies orbiting in a young and active planetary system, similar to our own solar system when it was a few million years old.
Congratulation again !
Alain Lecavelier des Etangs
Guest firstname.lastname@example.org 29-Nov-2011 13:05
Guest 29-Nov-2011 10:11
I take my hat off to you sir! Fantastic picture and great achievement!
Guest 29-Nov-2011 08:55
Superb work. More please!
Guest email@example.com 29-Nov-2011 02:33
Great work. How does it feel to be immortal on the Internet? I saw you on Channel 3 from up here in Slidell, Louisiana, USA after watching the news. Tell everyone that NZ is a terrible place, so more lights don't go up.
Guest 29-Nov-2011 01:39
Guest firstname.lastname@example.org 28-Nov-2011 22:41
Congratulations Mr Olsen! Today the amateur astronomers make importante jobs at astrophotography...!
Fernando Gois (from Madeira Islands/Portugal)
Guest 28-Nov-2011 21:57
dear mr. olsen, i would like to ask for your kind permission to show your images in a report about your achievement in my blog (grenzwissenschaft-aktuell.de). please could you get in contact with my - as i was unable to find out a contact-adress to you.
many thanks and best wishes
Guest email@example.com 28-Nov-2011 19:17
Real great job!! I placed it on Facebook
Guest firstname.lastname@example.org 28-Nov-2011 18:16
From the Netherlands,
Great job! keep the good work going!
Guest email@example.com 28-Nov-2011 17:54
From Spain, my most sincere congratulations...
Desde España, mi mas sincera enhorabuena...
Guest 28-Nov-2011 17:16
Read about your achievement in detecting and photographing the far away solar system.
Your photos are amazing
Guest firstname.lastname@example.org 28-Nov-2011 16:48
Felicidades desde España, es un gran trabajo.
Congratulations from Spain. It is a great job.
Guest email@example.com 28-Nov-2011 16:45
I´m very happy for you.. thanks,,, and,, continue!!.. Felicidades, compañero,, !!!-..
Guest firstname.lastname@example.org 28-Nov-2011 15:48
Enhorabuena y a seguir!
Congratulations and follow on with it!
Guest news@LPRRI.ORG 28-Nov-2011 13:31
Muy bien, LPR News. www.lprri.org
Guest 28-Nov-2011 13:24
Congratulations mate. What a great achievment... you know you've done well when Phil Plait congratulates you... Keep up the good work!
Guest email@example.com 28-Nov-2011 13:04
Congrats for this wonderful pic! It's amazing.
Guest firstname.lastname@example.org 28-Nov-2011 12:37
Fantastic work on that Beta Pictoris project! Your astroimages are top rate and all that from a Toucam!
Guest 28-Nov-2011 10:02
Nice. Well done
Guest email@example.com 28-Nov-2011 09:58
Felicidades por ese logro un saludo desde argentina
Guest 28-Nov-2011 09:18
Greetings from Sydney!
Like many, I have come to your site after seeing an article on your photo of beta pictoris. Congratulations on that, and on your wonderful site, which showcases so many wonderful photographs.
Guest firstname.lastname@example.org 28-Nov-2011 03:40
Pure Talent! I Love it - good one you ;)
Guest 28-Nov-2011 03:12
..that is eff-ing awesome work. Please consider contacting the '93 authors, and see if they'll co-author a p-reviewed paper with you!
Guest email@example.com 28-Nov-2011 01:19
Extraordinary. An outstanding achievement, well done!
Guest firstname.lastname@example.org 27-Nov-2011 23:06
Guest 27-Nov-2011 22:34
Great work mate
Guest 27-Nov-2011 22:16
Beautiful. I'm in love
Guest email@example.com 27-Nov-2011 22:07
Hi Rolf, my name is Dave Owen from the Hamilton Astronomical Society. I'd like to include your photo and quote some material from your website in our monthly bulletin, along with the photo of you that appeared in the stuff.co.nz article. I hope that's okay with you - if not could you please let me know: firstname.lastname@example.org
Thanks and congratulations on your achievement.
Guest Aaron79@yahoo.com 27-Nov-2011 21:39
Your work based around Beta Pictoris is Phenomenal - good work mate
Guest email@example.com 27-Nov-2011 21:34
This is amazing and so inspiring. I am keen on starting out in astrophotography. And sdeeing this just makes it more exciting :D Thanks for sharing
Guest firstname.lastname@example.org 27-Nov-2011 21:13
incredible! wow and thanks!!!
Guest email@example.com 27-Nov-2011 20:01
Congratulations! That's really special. Thanks for sharing it :D
Guest firstname.lastname@example.org 27-Nov-2011 19:56
Hi Rolf, great work. I'm keen to have a chat with you about it if you could contact me on 044740527 or at email@example.com. Thanks, Michelle Cooke (journalist for Fairfax NZ)
Guest firstname.lastname@example.org 27-Nov-2011 16:05
Fantastic work, congratulations! You're an inspiration to amateur astrophotographers everywhere.
Guest email@example.com 27-Nov-2011 15:47
All this done without adaptive optics! I'm fllored.
Guest 27-Nov-2011 14:31
Wow! Spectacular! Now only if we can contact some intelligent life there! Our planet desperately needs it!
Guest firstname.lastname@example.org 27-Nov-2011 09:35
What if you applied the same image processing techniques to images from Hubble? Could you not refine the already amazing picture you have here? And I assume the image above is the highest resolution you have? Saving the image to my PC and zooming in on it just fills my imagination with the details that aren't there.
Guest 27-Nov-2011 04:04
I LOVE THE STANDARD OF THE ACOMPLISHMENT
Guest 26-Nov-2011 23:09
Inspiring work Rolf….congratulations
Guest email@example.com 26-Nov-2011 21:59
really nice... you'll remain in History for doing this!
Try to nail more photos like this!
Guest firstname.lastname@example.org 26-Nov-2011 21:17
Guest email@example.com 26-Nov-2011 21:04
I would say you are an unpaid astronomer, not an amateur astronomer. Absolutely stunning work.
Guest 26-Nov-2011 20:26
A very impressive endeavour - well done.
Guest firstname.lastname@example.org 26-Nov-2011 19:09
Heck yeah! A fantastic accomplishment! Congrats!
jm 26-Nov-2011 05:33
Think outside the box, and you'll get this kind of outcome. Well done mate.
Guest 26-Nov-2011 04:56
Outstanding work Rolf!!!! Glad to see work like this from the ranks of us amateurs.
Patrick Harrold - a.k.a. Astrodude
strongmanmike2002 20-Nov-2011 04:37
Well that's pretty special Rolf! great project, congratulations!