by Ann » Fri May 18, 2012 6:55 am
I really like today's APOD! It is so beautiful!
As for the ring-like structures that are seen in ultraviolet by GALEX in today's APOD, they have been seen infrared light, too. This WISE image shows how the cool, starforming dust in Andromeda forms ring-like structures.
A few details are very interesting in the GALEX image. Note that one of Andromeda's satellite galaxies, M32, is barely visible here. Note, too, that although Andomeda's other bright satellite, NGC 205, is easy to spot, it is yellower in color than any part of M31. In visual light, NGC 205 is actually somewhat bluer than the Andromeda galaxy, but apparently ultraviolet light is produced by very many sources all over the disk of M31, whereas NGC 205 is "quiet". (There are actually a few young stars near the center of NGC 205, and you can just barely spot their bluish color in this picture.)
Finally, I find myself scratching my head over the color of the foreground stars. At three o'clock and five o'clock, there are two blue stars that might possibly be two ninth magnitude A-type stars. At ten o'clock, there is a blue source which actually corresponds to a cool M-type star, EG Andromedae! Yes, but the M-type primary apparently has a white dwarf companion, whose ultraviolet light is detected by GALEX.
And then at seven o'clock there is a bright blue star. The only match I have tentatively found for it is an A-type star, seventh magnitude HD 3431. How strange to see this visually unimpressive star shine so brightly in an ultraviolet image.
Ann
I really like today's APOD! It is so beautiful!
[float=left][img]http://upload.wikimedia.org/wikipedia/commons/thumb/0/0e/WISE-_Andromeda.jpg/220px-WISE-_Andromeda.jpg[/img][/float]As for the ring-like structures that are seen in ultraviolet by GALEX in today's APOD, they have been seen infrared light, too. This WISE image shows how the cool, starforming dust in Andromeda forms ring-like structures.
A few details are very interesting in the GALEX image. Note that one of Andromeda's satellite galaxies, M32, is barely visible here. Note, too, that although Andomeda's other bright satellite, NGC 205, is easy to spot, it is yellower in color than any part of M31. In visual light, NGC 205 is actually somewhat bluer than the Andromeda galaxy, but apparently ultraviolet light is produced by very many sources all over the disk of M31, whereas NGC 205 is "quiet". (There are actually a few young stars near the center of NGC 205, and you can just barely spot their bluish color in this picture.)
Finally, I find myself scratching my head over the color of the foreground stars. At three o'clock and five o'clock, there are two blue stars that might possibly be two ninth magnitude A-type stars. At ten o'clock, there is a blue source which actually corresponds to a cool M-type star, EG Andromedae! Yes, but the M-type primary apparently has a white dwarf companion, whose ultraviolet light is detected by GALEX.
And then at seven o'clock there is a bright blue star. The only match I have tentatively found for it is an A-type star, seventh magnitude HD 3431. How strange to see this visually unimpressive star shine so brightly in an ultraviolet image.
Ann