I had heard the term Carbon Star many times over the past few years, and it finally sunk down to the level of my conciousness that stars are made up of hydrogen and a bit of helium. But finally, I got to asking the question "What is a carbon star?" And why is it red? I applied a bit of logic and came up with one red reason, and it went something like this. Obviously if carbon is in the star, then the star is more than just a little old. It must be cooking Helium and who knows knows what else to produce carbon. Than means old, and old means red. But I had heard that carbon stars are really red. So I went on a mission.
One of my great discoveries has been the AAVSO. Now this is measured against, in my opinion, a lifetime of really wonderful discoveries. But what can you say to a group who, if you ask a question like "What is a Carbon Star", you will get the kind of answers that will just make you shake your head in awe. I asked the question yesterday, and by this morning, I had gotten not only the definitive definition of the term Carbon Star, but a host of other supporting opinions, sources, and even a table of over 5000 of these wonderful objects. All sent to me using e-mail. Folks like Rik Hill, Wayne Warren, Brian Skiff, make the AAVSO a truely rewarding experience. During my internet travels, I found a web page that described in some detail the sequence of stellar evolutionary steps leading to the formation of Carbon Stars.
Cool carbon stars are defined as stars whose spectra at low dispersion (say a resolution no better than 1-2 angstroms) are known to show bands of the Swan system of the C2 molecule; or, if the spectral region of the Swan system is inadequately observed, they show the red or infrared bands of CN in strength adequate to infer that the Swan bands almost certainly would be seen if their presence could be tested. The ADC provides access to almost 6000 stars that are considered cool carbon stars.
Two things are interesting about these stars. The first is that the C2 line is produced not only by carbon, but by the C2 molecule. The stars are cool enough to permit formation of molecules. The second thing about these stars is their redness. The redness is actually enhanced in these stars because C2 absorbes blue from the spectrum thereby increasing the red color of the star.
Cool huh? If you would like to check out some of these stars, I have extracted about 400 from the archive by limiting the selection to stars above -20 degrees in declination, and stars brighter than 11th magnitude.
(Note! your browser may complain about this link being script intensive. It may ask if you want to terminate the script. Just respond NO)
The list can be found here.
For those interested in binocular objects, 8th magnitude or brighter stars (about 50) can be found here.
