by Chris Peterson » Mon Jul 29, 2013 3:05 pm
geckzilla wrote:Some of those might be single stars. Or they might be multi-star systems. I don't understand how you can say with any certainty that any of them are single stars.
I'm not saying it with certainty. I simply suspect that some of the brighter, star-colored spots in that region are, in fact, stars. There's no reason they couldn't be. I'm not sure what the expected distribution of globular clusters is in the case of a ring galaxy like this.
Is it even possible to look at just one and make that determination? I still wonder if the dots around the central nebula are something like globular clusters or if they are massive stars. They seem blurry so I'm guessing they are clusters.
At that distance, I don't think clusters would be optically resolved as anything other than point sources, the same as stars. So geometrically, there is no way to distinguish the two. That could only be done by other methods, such as spectroscopically or photometrically. In either case, diffraction will make the objects larger than single pixels, and will make them "fuzzy".
Also, there are some single pixel anomalies that do happen across channels. I'm not saying I see any of them here but I'd have to go get the FITS files and spend a lot more time on it to try to make that argument. Usually those are stark white, though.
Right. Hot, warm, cool, and cold pixels are always present. Warm and cool pixels are usually eliminated by calibration, but hot and cold ones may not be. If they aren't taken care of by some sort of bad pixel mapping, they usually show up as either white or black dots. They can usually be distinguished from actual signal because they are only one pixel in extent. That can't be seen in JPEG images, but is usually not hard to see in the released TIFFs, and of course in the original FITS files.
[quote="geckzilla"]Some of those [i]might[/i] be single stars. Or they might be multi-star systems. I don't understand how you can say with any certainty that any of them are single stars.[/quote]
I'm not saying it with certainty. I simply suspect that some of the brighter, star-colored spots in that region are, in fact, stars. There's no reason they couldn't be. I'm not sure what the expected distribution of globular clusters is in the case of a ring galaxy like this.
[quote]Is it even possible to look at just one and make that determination? I still wonder if the dots around the central nebula are something like globular clusters or if they are massive stars. They seem blurry so I'm guessing they are clusters.[/quote]
At that distance, I don't think clusters would be optically resolved as anything other than point sources, the same as stars. So geometrically, there is no way to distinguish the two. That could only be done by other methods, such as spectroscopically or photometrically. In either case, diffraction will make the objects larger than single pixels, and will make them "fuzzy".
[quote]Also, there are some single pixel anomalies that do happen across channels. I'm not saying I see any of them here but I'd have to go get the FITS files and spend a lot more time on it to try to make that argument. Usually those are stark white, though.[/quote]
Right. Hot, warm, cool, and cold pixels are always present. Warm and cool pixels are usually eliminated by calibration, but hot and cold ones may not be. If they aren't taken care of by some sort of bad pixel mapping, they usually show up as either white or black dots. They can usually be distinguished from actual signal because they are only one pixel in extent. That can't be seen in JPEG images, but is usually not hard to see in the released TIFFs, and of course in the original FITS files.