by Ann » Sat Oct 09, 2010 4:09 am
Chris Peterson wrote:Ann wrote:HD 224037 is a quite red star, almost as red as Betelgeuse. But it is a far cry from the really red stars, the carbon stars. When I observed Betelgeuse, I thought it's color wasn't even orange, but golden. So the color balance in today's APOD may be slightly red. On the other hand, it is interesting to note that the brighter stars in the image almost all seem slightly red, while the fainter stars seem to be neutral-colored. Either this is a photographic effect, or else we are in a part of the sky where the brighter-looking stars are almost all red giants and the fainter-looking stars are more neutral main sequence stars. The latter scenario is definitely a possibility.
Other considerations: the image was made with a DSLR, so it is likely to be a bit color challenged to begin with. When the exposure was made, this region was at an altitude of only 35° above the horizon, which is low enough that atmospheric extinction effects were present, including some reddening.
Well, I checked the stars with my astronomy software. Many of them are faint enough that my software has no information about them, but of the faint ones which had had their "vital statistics" taken, all had color indexes between 0.25 and 0.55. Those are all non-red stars. They are in fact blue enough that they may be early A-type stars that suffer some reddening, or they may be unreddened late A-type stars or F-type stars. The reddish K5 star that you identified for me had a luminosity of 85 times the Sun (plus/minus 50 Suns or so), and despite the uncertainty this shows quite well that HD 224037 is no brighter than Arcturus, which is 110 times brighter than the Sun. So HD 224037 is no supergiant star. Since it is redder than Arcturus and of a later spectral class but no brighter, I take it that HD 224037 is, if anything, less massive than Arcturus, or when it was less massive than Arcturus when both were main sequence stars.
But all the brighter stars in the vicinity of HD 224037 that are of a slightly similar distance from us (about a thousand light years) are all of spectral class K, although none are as red or have a similarly late spectral type as HD 224037. I find it quite interesting that this photograph might be showing us a few red giants and a larger number of A and F-type main sequence stars at moderately the same distance.
Ann
[quote="Chris Peterson"][quote="Ann"]HD 224037 is a quite red star, almost as red as Betelgeuse. But it is a far cry from the really red stars, the carbon stars. When I observed Betelgeuse, I thought it's color wasn't even orange, but golden. So the color balance in today's APOD may be slightly red. On the other hand, it is interesting to note that the brighter stars in the image almost all seem slightly red, while the fainter stars seem to be neutral-colored. Either this is a photographic effect, or else we are in a part of the sky where the brighter-looking stars are almost all red giants and the fainter-looking stars are more neutral main sequence stars. The latter scenario is definitely a possibility.[/quote]
Other considerations: the image was made with a DSLR, so it is likely to be a bit color challenged to begin with. When the exposure was made, this region was at an altitude of only 35° above the horizon, which is low enough that atmospheric extinction effects were present, including some reddening.[/quote]
Well, I checked the stars with my astronomy software. Many of them are faint enough that my software has no information about them, but of the faint ones which had had their "vital statistics" taken, all had color indexes between 0.25 and 0.55. Those are all non-red stars. They are in fact blue enough that they may be early A-type stars that suffer some reddening, or they may be unreddened late A-type stars or F-type stars. The reddish K5 star that you identified for me had a luminosity of 85 times the Sun (plus/minus 50 Suns or so), and despite the uncertainty this shows quite well that HD 224037 is no brighter than Arcturus, which is 110 times brighter than the Sun. So HD 224037 is no supergiant star. Since it is redder than Arcturus and of a later spectral class but no brighter, I take it that HD 224037 is, if anything, less massive than Arcturus, or when it was less massive than Arcturus when both were main sequence stars.
But all the brighter stars in the vicinity of HD 224037 that are of a slightly similar distance from us (about a thousand light years) are all of spectral class K, although none are as red or have a similarly late spectral type as HD 224037. I find it quite interesting that this photograph might be showing us a few red giants and a larger number of A and F-type main sequence stars at moderately the same distance.
Ann