(Submitted January 25, 2007)
While self-teaching in astronomy (amateur stargazer class), I've come accross
spectra marked R,N,C & S.(The reference is in an online version of Hipparcos).
While I've become well-aquainted with the usual OBAFGKM system, these leave me
a little puzzled. After a look on the web, I've found about 7,000 files that
describe the details (lots of research papers), but not the basics (such as
where they are on the HR diagram or even their names such as "an R star is
better known as a Jones Star") without which the later information isn't much
Thanks for your question. The R, N, C & S classification for stars are reserved
for a special class of stars known as carbon stars, stars with a rather high
carbon content. Most carbon stars are variable stars and many are thought to be
in the red giant/AGB phase on the H-R diagram. A very good description can be
found at the following website:
Hope this helps,
Georgia & Mike
For "Ask a Astrophysicist"