by Ann » Fri Oct 27, 2017 8:07 am
Yes, NGC 404 sounds like an error message.
What is most interesting about the picture to me is that it shows how much redder the star is than the galaxy. Mirach is an M-type giant, which makes it a quite red star in the sky, but not record red by any means. It is (probably) less red than Betelgeuse, whose B-V is 1.500 ± 0.500, versus 1.576 ± 0.010 for Mirach. Betelgeuse is definitely more infrared than Mirach, with a V-I index of 2.32 ± 0.02, versus 1.74 ± 0.03 for Mirach. That is actually not so red.
The only truly red stars are carbon stars like T Lyra or R Leporis. The B-V of R Leporis is 2.70 ± 0.510, and the B-V of T Lyra is 5.460 ± 0.510. Now we're talking red.
Visible and UV image of Mirach and NGC 404.
NGC 404, the galaxy that is "The Ghost of Mirach", is an S0-type galaxy and therefore made up almost exclusively of old "red" stars. But the overall light of the stars of typical S0 and elliptical galaxies is not so red. The B-V of NGC 404 is 0.940, which is a very normal B-V index for galaxies that have mostly stopped forming stars. It corresponds to a color redder than the Sun, but bluer than Pollux.
As the GALEX image at right shows, NGC 404 does have a faint ring of young stars that surrounds it.
One minute astronomer wrote:
Lenticular galaxies tend to have little star-forming activity. But astronomers have discovered NGC 404 is ringed by newly-formed stars and excited hydrogen gas. Studies suggest the little galaxy was jostled by the gravity of another galaxy about a billion years ago, an event which triggered a wave of star formation from the last remnants of gas within this tiny star group.
Ann
Yes, NGC 404 sounds like an error message.
[float=left][img2]https://farm2.staticflickr.com/1614/25185079004_951aefcfec_b.jpg[/img2][c][size=85]Red carbon star T Lyrae, much redder than Mirach.
Source: http://picssr.com/photos/9885064@N05?nsid=9885064@N05[/size][/c][/float] [float=right][img2]http://en.es-static.us/upl/2009/06/Pollux.jpeg[/img2][c][size=85]Yellow star Pollux, yellower than NGC 404.
Source: http://earthsky.org/brightest-stars/pollux-not-castor-is-geminis-brightest-star[/size][/c][/float]
What is most interesting about the picture to me is that it shows how much redder the star is than the galaxy. Mirach is an M-type giant, which makes it a quite red star in the sky, but not record red by any means. It is (probably) less red than Betelgeuse, whose B-V is 1.500 ± 0.500, versus 1.576 ± 0.010 for Mirach. Betelgeuse is definitely more infrared than Mirach, with a V-I index of 2.32 ± 0.02, versus 1.74 ± 0.03 for Mirach. That is actually not so red.
The only truly red stars are carbon stars like T Lyra or R Leporis. The B-V of R Leporis is 2.70 ± 0.510, and the B-V of T Lyra is 5.460 ± 0.510. Now we're talking red.
[float=right][img2]http://astronomer.wpengine.netdna-cdn.com/wp-content/uploads/2013/11/glx2008-02r_img01_small.jpg[/img2][c][size=85]Visible and UV image of Mirach and NGC 404.[/size][/c][/float] NGC 404, the galaxy that is "The Ghost of Mirach", is an S0-type galaxy and therefore made up almost exclusively of old "red" stars. But the overall light of the stars of typical S0 and elliptical galaxies is not so red. The B-V of NGC 404 is 0.940, which is a very normal B-V index for galaxies that have mostly stopped forming stars. It corresponds to a color redder than the Sun, but bluer than Pollux.
As the GALEX image at right shows, NGC 404 does have a faint ring of young stars that surrounds it.
[quote][url=http://oneminuteastronomer.com/9300/the-ghost-of-mirach/]One minute astronomer[/url] wrote:
Lenticular galaxies tend to have little star-forming activity. But astronomers have discovered NGC 404 is ringed by newly-formed stars and excited hydrogen gas. Studies suggest the little galaxy was jostled by the gravity of another galaxy about a billion years ago, an event which triggered a wave of star formation from the last remnants of gas within this tiny star group.[/quote]
Ann