Terry B
29-08-2011, 10:37 PM
Dear All
I had a request to take some images of the dim mira variable GT Sgr to attempt to make a visual sequence for the star. It is quite close to M28. As it turned out this was a bit unneccesary as there had been a typo in the original request and a different variable star was actually needed.
Before I knew this I had taken a series of images throught B,Vand R filters.
Exposures were 120 sec x 3 for the V and R and a single 300sec exposure for B.
I decided to measure the region anyway. I used a modified all sky photometry technique with comparison stars from nearby standard regions at 2 different airmasses and measured the magnitude of a selection of stars near GT Sgr. These are marked on the image below. It is a V image inverted to show the stars more clearly.
I have also made a colour image using the photometry filter images as BGR. These are pretty close to the normal imaging colour filters but have more overlap. It has produced a reasonable image of M28. It is a very busy region of the sky. The Mira variable is clearly a very red star and the colour of the comparison stars can be seen as well. There are quite a few blue artifacts from cosmic ray hits that I'm too lazy to try and remove. The other colours have less because the stacking method removed them.
The images were taken with my VC200L at 1800mm with a ST10XME. The field is about 30arcmin x 20arcmin.
I had a request to take some images of the dim mira variable GT Sgr to attempt to make a visual sequence for the star. It is quite close to M28. As it turned out this was a bit unneccesary as there had been a typo in the original request and a different variable star was actually needed.
Before I knew this I had taken a series of images throught B,Vand R filters.
Exposures were 120 sec x 3 for the V and R and a single 300sec exposure for B.
I decided to measure the region anyway. I used a modified all sky photometry technique with comparison stars from nearby standard regions at 2 different airmasses and measured the magnitude of a selection of stars near GT Sgr. These are marked on the image below. It is a V image inverted to show the stars more clearly.
I have also made a colour image using the photometry filter images as BGR. These are pretty close to the normal imaging colour filters but have more overlap. It has produced a reasonable image of M28. It is a very busy region of the sky. The Mira variable is clearly a very red star and the colour of the comparison stars can be seen as well. There are quite a few blue artifacts from cosmic ray hits that I'm too lazy to try and remove. The other colours have less because the stacking method removed them.
The images were taken with my VC200L at 1800mm with a ST10XME. The field is about 30arcmin x 20arcmin.