SkyViking
14-05-2012, 09:05 PM
Hi All,
Here is yet another globular image I took during near-full Moon conditions recently. This time of NGC 5286. This globular forms a beautiful duo with the 4.6 magnitude star M Centauri. This star has a funny pale yellow-orange colour (G8) which is an interesting contrast to the cluster.
Hi-res image is here: http://www.pbase.com/rolfolsen/image/143299725/original
Image details:
LRGB 27:15:15:15m
02/05/2012
10" f/5 Serrurier truss Newtonian
QSI 683wsg with Lodestar guider
I have also been busy creating a couple of colour-magnitude diagrams for some of the globular clusters I have imaged recently. I was surprised with how successful it turned out and how simple the process was, so I'll briefly describe what I did here:
To create these diagrams I downloaded the demo version of AstroArt. The demo lets you export a list of stars from an image, so that is perfect for this purpose.
I used the stacked B and R raw FITS images to generate the data. First I loaded the B image into Astro Art. Then from the Tools menu I selected 'Find Stars' and entered desired number of stars and FWHM criteria. For Omega Centauri I chose for example 30,000 stars. For the other clusters I chose a smaller number since they are more compact and crowded and there aren't as many stars available for selection.
Then I went to View -> Stars and a table with all the selected stars is displayed. I sorted the rows according to X coordinate and saved the star data as a .sta file via the right-click menu.
I then repeated the proces for the R file, using the same star selection criteria.
(The .sta format is simply tab/space separated values and can be opened in any text editor)
The main challenge was to somehow match each star in the two B/R .sta files and create one new file with correct magnitudes for the matched stars. Not all stars will be matched since AstroArt will not necessarily select the same stars in each image. So for this purpose I wrote a small Gosu (http://gosu-lang.org/) program that scans the two files and matches the entries by their coordinates. The program also calculates the magnitudes based on the ADU count. The result is a third file with the magnitudes for each star that was matched in the B and R file. This way I ended up with around 10,000 matched stars with magnitudes out of the 30,000 stars I selected for Omega Centauri.
Now I could open this new file in Excel and create a scatter plot for the data, and voila a textbook perfect colour-magnitude diagram emerged, complete with red giant branch and horizontal branch. Encouraged by this I repeated the process for some other globular clusters with equally effective results, allthough with fewer stars.
Click here to go to the gallery (http://www.pbase.com/rolfolsen/colourmagnitude_diagrams) with colour-magnitude diagrams for the globulars Omega Centauri, NGC 6752 and NGC5286.
I had great fun with this little exercise and will probably continue making more diagrams of any globulars I image in the future. Hmm, how about a diagram of UKS-1... :lol::P
Hope you enjoy the view. Comments and critique is welcome as usual.
Regards,
Rolf
Here is yet another globular image I took during near-full Moon conditions recently. This time of NGC 5286. This globular forms a beautiful duo with the 4.6 magnitude star M Centauri. This star has a funny pale yellow-orange colour (G8) which is an interesting contrast to the cluster.
Hi-res image is here: http://www.pbase.com/rolfolsen/image/143299725/original
Image details:
LRGB 27:15:15:15m
02/05/2012
10" f/5 Serrurier truss Newtonian
QSI 683wsg with Lodestar guider
I have also been busy creating a couple of colour-magnitude diagrams for some of the globular clusters I have imaged recently. I was surprised with how successful it turned out and how simple the process was, so I'll briefly describe what I did here:
To create these diagrams I downloaded the demo version of AstroArt. The demo lets you export a list of stars from an image, so that is perfect for this purpose.
I used the stacked B and R raw FITS images to generate the data. First I loaded the B image into Astro Art. Then from the Tools menu I selected 'Find Stars' and entered desired number of stars and FWHM criteria. For Omega Centauri I chose for example 30,000 stars. For the other clusters I chose a smaller number since they are more compact and crowded and there aren't as many stars available for selection.
Then I went to View -> Stars and a table with all the selected stars is displayed. I sorted the rows according to X coordinate and saved the star data as a .sta file via the right-click menu.
I then repeated the proces for the R file, using the same star selection criteria.
(The .sta format is simply tab/space separated values and can be opened in any text editor)
The main challenge was to somehow match each star in the two B/R .sta files and create one new file with correct magnitudes for the matched stars. Not all stars will be matched since AstroArt will not necessarily select the same stars in each image. So for this purpose I wrote a small Gosu (http://gosu-lang.org/) program that scans the two files and matches the entries by their coordinates. The program also calculates the magnitudes based on the ADU count. The result is a third file with the magnitudes for each star that was matched in the B and R file. This way I ended up with around 10,000 matched stars with magnitudes out of the 30,000 stars I selected for Omega Centauri.
Now I could open this new file in Excel and create a scatter plot for the data, and voila a textbook perfect colour-magnitude diagram emerged, complete with red giant branch and horizontal branch. Encouraged by this I repeated the process for some other globular clusters with equally effective results, allthough with fewer stars.
Click here to go to the gallery (http://www.pbase.com/rolfolsen/colourmagnitude_diagrams) with colour-magnitude diagrams for the globulars Omega Centauri, NGC 6752 and NGC5286.
I had great fun with this little exercise and will probably continue making more diagrams of any globulars I image in the future. Hmm, how about a diagram of UKS-1... :lol::P
Hope you enjoy the view. Comments and critique is welcome as usual.
Regards,
Rolf