Astronomy questions.

[gridlore]

I'm still loving the Astrogator's Handbook, but I have a question or three for those of you on my friends list with more formal astronomy training.

I'm a little confused by some of the information on the star tables. I understand basic stellar classifications, but there are notations on some of the stars I don't get. Many of the stars have extra letters after the basic type and size classification. For example, Proxima Centauri is listed as "dM5 e" I know that dM5 means that this is a dwarf M5, but what does the "e" indicate? "e" seems to be a pretty common modifier, but I also see "p" and "J" used after regular . Also, many stars are listed only by a letter. "k", "m", and "0" seem to be used in this role. what does this mean?

There's also some confusion with binary systems. Take UV Ceti. The remarks section for the companion includes the following a=5.57" P=200 years. It's obvious that P is the companion's orbital period, but what is a? Is there a good on-line source for known binaries?

Comments

[pompe.livejournal.com]

a is the separation between the stars as apparent from Earth in arcseconds.
e is the presence of emission lines in the spectrum.
p means "peculiar", so there is something unusual with it.
If the star just says "k" or "m" I believe the spectrum isn't sufficiently typed.

You might want to check NStars data if available if the book you use isn't already based upon it if there's a specific star you need to check. Gliese 3 is what, 15 years old and Hipparcos didn't catch a lot of dim stars. Nor did Gliese, new ones turn up all the time.

caveat

[pompe.livejournal.com]

...but then again, I don't know if NStars have been updated since 2001.

[pompe.livejournal.com]

...and about the emission lines. Red dwarf stars with "e"'s are likely to be flare stars. The "J", however, I don't know much about but I think it might have to do with how the spectrum was measured.

FWIW, I've been hearing that a LOT of stars ...

[capplor.livejournal.com]

are variable in intensity. One of your markings ought to be about that.

Re: FWIW, I've been hearing that a LOT of stars ...

[pauldrye.livejournal.com]

That would be a small letter "v" or "var.", if noted.

Re: FWIW, I've been hearing that a LOT of stars ...

[pompe.livejournal.com]

And that is sometimes not put on the spectral type code but on the magnitude.

[pauldrye.livejournal.com]

And just to add a bit of actual meaning to the "e" notation, an emission feature in the spectrum normally means that there's something hot -- dust or gas around the star, usually -- chipping some light into the mix.

"J" is an spectrum as well -- emission or absorption, I don't know which -- one where carbon silicate is the culprit. Stars are normally too hot for any compound substances to survive in their atmospheres, but if it's sufficiently dim and cool, carbon and SiO-related compounds are the first to form (and so muck up the spectrum by getting in the way).