Variable Star near M20?

[avandonk]

Noticed this while comparing data collected months apart. The star is far brighter a few months ago.

Bert

[AlexN]

hard to tell due to the big difference in either focus or resolution, not to mention different processing and colouring.. It seems to me that all the stars in that image have erupted into super novae, :)

[Terry B]

I think the answer is yes. There is a mira variable called V1951 Sgr that is very close to the area you ar looking at. It is a bit blurry to be certain and it is a very busy field. Your image is oriented west up and south to the right.
The mira ranges from about mag 8 to 15 over a 510 day cycle.
Curiously it is not exactly where it is catalogued. I have looked in the catalogues an dcompared them to the DSS filed and one of my images. The star you have seen is on the DSS images and on my image (marked) but the catalogued position is not on the DSS image or my image. I assume it is either an error or the star has a high propper motion.
I have rotated my image to match your one.
The DSS image with the variable marked is here (http://mira.aavso.org/cgi-bin/vsp.pl?action=render&name=V1951+Sgr&ra=&dec=&charttitle=&chartcomment=&aavsoscale=F&fov=18.5&resolution=100&maglimit=18.5&north=down&east=right&dss=on&othervars=all&chartid=&Submit=Plot+Chart).

[avandonk]

Thanks Terry. Here is an animated gif with images aligned with Registar. 1.6MB

http://d1355990.i49.quadrahosting.com.au/2009_10/var2.gif

The variable is more obvious now as it was when I blinked both large images.

Bert

[DavidU]

How did you spot that Bert? Amazing find. Were you nova searching?

[Terry B]

Very good.
You can see how red it is.
It seems to be in the correct place.This means that it is too dim on my image to be seen. Mine was taken in May 08.
Still doesn't explain why the other star I marked is missing from the AAVSO charts.

[avandonk]

David if you have two images that have the same exact field and size by alternating or blinking as it is called, any difference just jumps out. You must then check to see if the difference is real. It was a bit more difficult with these two images as one was taken with a 300mm lens and the other with an FSQ106.

Here is part of the two images in an animated gif 1.3MB

http://d1355990.i49.quadrahosting.com.au/2009_10/ab.gif

Here is Terryb's image alternating with the FSQ image. 1MB

http://d1355990.i49.quadrahosting.com.au/2009_10/varD.gif

I use Registar to produce these images. I always try to compare images taken at different times to see if anything is changing. The great thing about dslr images is they have a timestamp so if anything turns up you have the info.

I don't do any systematic searches but keep an eye on the images I do take in case something obvious turns up. In this case I guessed it was a variable and I was sure someone on IIS would know more than me to identify it correctly. Terryb has done just that.

Bert