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skrap1r0n
2004-Apr-01, 03:49 AM
I am curious, I was out side tonight looking at the sky with some binocs. I was looking at the brightest star in ursa major and was curious about it, so I came in and fired up Cartes du Ciel, and looked it up. Turns out it is Dubhe.

In the info posted in Cartes du Ciel, it listed it as having a spectral class of K0IIIa. I know that spectrographic analysis can tell you a lot about that particular stars make up I began randomly clicking on stars.

Betelgeuse has a SC of M1-2Ia-Iab
Rigel has an SC of B8Ia

ad infenitum

Anyway I started trying to look up how to decipher how the spectral class is decoded so to speak and ended up with wither stuff I don't want to know (a list of star names and details about them) or stuff I was unable to understand, serious scientific gobbledygook I don't understand.

Any one know of a site that explains Spectral class in a way I may be able to understand it?

JohnOwens
2004-Apr-01, 04:06 AM
Personally, I always recommend Wikipedia (http://en.wikipedia.org/wiki/Stellar_classification) myself. :D

Brady Yoon
2004-Apr-01, 04:23 AM
Spectral classes are in definition what spectra stars produce, such as hydrogen lines, helium lines, etc. The main thing that the spectral class tells you is the star's surface temperature and color The spectral classes from hottest to coolest are WR, O, B, A, F, G, K, M, N, R, and S. WR, or wolf rayet stars, and N, R, and S stars, which are brown dwarves, are rarely used. This can be memorized by the well-known mnemonic-Oh Be A Fine Girl and Kiss Me Now Right this Second. :D
Some examples are
O: Alnitak electric blue
B: Spica, Rigel blue-white
A: Sirius, Deneb, Vega white
F: Canopus, Procyon yellowish-white
G: the sun, Alpha Centauri yellow
K: Arcturus, Aldebaran orange
M: Antares, Betelgeuse red

The letter/number designation after the spectral class is its luminosity class. For example, the blue supergiant Rigel has a spectral class of B8 and its luminosity class is Ia.
The different luminosity classes are:
Ia: Bright supergiant (Rigel, Deneb)
Ib: Supergiant (Polaris, Canopus)
II: Bright giant
III: Giant (Arcturus, Aldebaran)
IV: subgiant (Procyon)
V: dwarves-this refers to any small main sequence star, white dwarves, etc. (the sun, Sirius B, Barnard's Star)

The sun's designation is G2V, which makes it an average yellow main-sequence star (when I say average, I mean the sun is in the approximate middle of the brightest and dimmest stars. In fact, the sun is more luminous than 90% of the stars in our galaxy.

Here's a link with some more advice.
http://www.astro.uiuc.edu/~kaler/sow/class.html


In the info posted in Cartes du Ciel, it listed it as having a spectral class of K0IIIa.
Are you sure about this? There is no IIIa spectral class, as far as I know. :-?
Hope this helps.
Brady Yoon

Brady Yoon
2004-Apr-01, 04:26 AM
Personally, I always recommend Wikipedia myself.
Nice link there. :D

Ut
2004-Apr-01, 04:40 AM
The Universe and Beyond by Terry Dickenson has the best HR diagram I've seen to date for demonstrating colour temperature/spectral class relations. Much better than the one used on the wikipedia page. The description isn't as good, though.

JohnOwens
2004-Apr-01, 05:06 AM
The Universe and Beyond by Terry Dickenson has the best HR diagram I've seen to date for demonstrating colour temperature/spectral class relations. Much better than the one used on the wikipedia page. The description isn't as good, though.
Yeah, I see what you mean about the picture. Could be improved with some different colours & sizes for the dots. Maybe I'll add it to my list of things to do for Wikipedia.... :-k

AGN Fuel
2004-Apr-01, 06:32 AM
Just a further point of clarification: each of the spectral classes is further subdivided into 10 intermediate stages (0-9).

(This is why the sun is classed as a G2V and not simply a GV.)

Edited once due to a #-o error!

Eroica
2004-Apr-01, 07:19 AM
The different luminosity classes are:
Ia: Bright supergiant (Rigel, Deneb)
Ib: Supergiant (Polaris, Canopus)
II: Bright giant
III: Giant (Arcturus, Aldebaran)
IV: subgiant (Procyon)
V: dwarves-this refers to any small main sequence star, white dwarves, etc. (the sun, Sirius B, Barnard's Star)


Three rarely used luminosity classes:

VI: Subdwarfs
VII: White Dwarfs
IX: Brown Dwarfs (there's no VIII because of Ia and Ib)

Eroica
2004-Apr-01, 07:23 AM
The spectral classes from hottest to coolest are WR, O, B, A, F, G, K, M, N, R, and S. WR, or wolf rayet stars, and N, R, and S stars, which are brown dwarves, are rarely used. This can be memorized by the well-known mnemonic-Oh Be A Fine Girl and Kiss Me Now Right this Second. :D
Brown dwarfs are classified as L and T.
R and N stars are now called C (or Carbon) stars. Neither they nor S stars are brown dwarfs. These three classes are not cooler than M stars.

AGN Fuel
2004-Apr-01, 07:30 AM
The spectral classes from hottest to coolest are WR, O, B, A, F, G, K, M, N, R, and S. WR, or wolf rayet stars, and N, R, and S stars, which are brown dwarves, are rarely used. This can be memorized by the well-known mnemonic-Oh Be A Fine Girl and Kiss Me Now Right this Second. :D
Brown dwarfs are classified as L and T.
R and N stars are now called C (or Carbon) stars. Neither they nor S stars are brown dwarfs. These three classes are not cooler than M stars.

Yes, the mnemonic has become "Oh Be A Fine Girl, Kiss My Lips Tenderly" with the addition of the Brown Dwarf classes.

Ut
2004-Apr-01, 07:48 AM
...
*blink*
There's a harassment suit in there somewhere.

AstroSmurf
2004-Apr-01, 10:33 AM
I daresay female astronomers would speak of Guys for the G class stars :P

Kullat Nunu
2004-Apr-01, 10:54 AM
R and N stars are now called C (or Carbon) stars. Neither they nor S stars are brown dwarfs. These three classes are not cooler than M stars.

Indeed. Former class R stars have temperatures similar to G and K stars, and N stars overlap class M.

C stars, as opposed to normal stars, have more carbon than oxygen. In S stars carbon and oxygen abundances are similar.

White dwarf are of type D#, where # is C, A, B, O, Z, Q, or K. Note that these letters have nothing to do with the main sequence classification.

skrap1r0n
2004-Apr-01, 04:26 PM
I daresay female astronomers would speak of Guys for the G class stars :P

This statement is SCREAMING for a response, however, I will refrain.

tracer
2004-Apr-01, 10:20 PM
In the info posted in Cartes du Ciel, it listed it as having a spectral class of K0IIIa.
Are you sure about this? There is no IIIa spectral class, as far as I know. :-?
All the luminosity classes can theoretically be subdivided into "a" and "b." "Ia" and "Ib" are just the most famous examples. I've seen bright main sequence stars listed with a spectral class of "Va", for example.

"IIIa" would be the upper end of Luminosity Class III, i.e. a somewhat-brighter-than-average Giant star that isn't bright enough to make it into the Bright Giant category (Luminosity Class II).

skrap1r0n
2004-Apr-01, 10:33 PM
In the info posted in Cartes du Ciel, it listed it as having a spectral class of K0IIIa.
Are you sure about this? There is no IIIa spectral class, as far as I know. :-?
All the luminosity classes can theoretically be subdivided into "a" and "b." "Ia" and "Ib" are just the most famous examples. I've seen bright main sequence stars listed with a spectral class of "Va", for example.

"IIIa" would be the upper end of Luminosity Class III, i.e. a somewhat-brighter-than-average Giant star that isn't bright enough to make it into the Bright Giant category (Luminosity Class II).

I'll check it out again. if any of you have it handy (I don't ATM) look up the entry for for Dubhe.

tracer
2004-Apr-01, 10:44 PM
The short answer to your question(s) posed in the OP:

"K0" is reddish-orangish, "IIIa" is giant, so Dubhe is a "red giant."
"M1-2" is red, "Ia-Iab" is supergiant, so Betelgeuse is a "red supergiant."
"B8" is blue, "Ia" is supergiant, so Rigel is a "blue supergiant."
"G2" is yellow, "V" is main-sequence or dwarf, so the sun is a "yellow dwarf."

skrap1r0n
2004-Apr-01, 10:56 PM
The short answer to your question(s) posed in the OP:

"K0" is reddish-orangish, "IIIa" is giant, so Dubhe is a "red giant."
"M1-2" is red, "Ia-Iab" is supergiant, so Betelgeuse is a "red supergiant."
"B8" is blue, "Ia" is supergiant, so Rigel is a "blue supergiant."
"G2" is yellow, "V" is main-sequence or dwarf, so the sun is a "yellow dwarf."

Thanks Tracer, there no NEED for me to know this right now, I was just curious. after I inepret a few on my own I'll get the hang of it.

Eroica
2004-Apr-02, 10:59 AM
This site gives Dubhe as K0-IIIa:

http://www.tcaep.co.uk/astro/constell/11030125.htm

tracer
2004-Apr-02, 07:06 PM
Yeah, but they don't mention that that spectrum's only for Dubhe A. Dubhe B is a plain old F7-V, the kind of star you wouldn't feel ashamed taking home to show your parents.

themiller
2004-Apr-29, 02:33 PM
White dwarf are of type D#, where # is C, A, B, O, Z, Q, or K. Note that these letters have nothing to do with the main sequence classification.

Im trying to plot a H-R diagram of the stars within 7 parsecs for a university essay and was wondering if there is a way to convert these classifications to OBAFGKM values so i can add them to the diagram

any help would be greatly appreciated

Eroica
2004-May-03, 08:30 AM
These letters refer to spectroscopic peculiarities of white dwarfs. I don't think there is a simple correlation between them and the surface temperature (which is indicated by the OBAFGKM system).

DA ................... Only Balmer lines; no He I or metals present

DB ................... He I lines; no H or metals present

DC ................... Continuous spectrum, no lines deeper than 5% in any part of the electromagnetic spectrum

DO ................... He II strong; He I or H present

DZ .................... Metal lines only; no H or He lines

DQ ................... Carbon features, either atomic or molecular in any part of the electromagnetic spectrum

I'm not familiar with DK.

tracer
2004-May-03, 02:31 PM
Eroica is right. The temperature classification for a white dwarf is not found in the letter after the D, but in the number following the letter-after-the-D.

In other words, in the world of spectral classes for ordinary stars, F0 through F9 are just a way to divide spectral class F on the OBAFGKM series into ten little fine-grained subdivisions for extra precision. But, in the world of white dwarf spectral classes, that number after the letters means something else entirely. A spectral designation like "DA" or "DQ" only tells you the chemical composition of the white dwarf, not its surface temperature. The number after the "DA" or "DQ", on the other hand, is determined directly from the star's effective blackbody temperature. A DA0 white dwarf is the same temperature as a DQ0 white dwarf, and is the hottest kind of white dwarf. A DA9 or DQ9 white dwarf would be the coolest kind of white dwarf.

Specifically, the number at the end of the white dwarf's spectral class is calculated by dividing 50,400K by the star's temperature, and rounding off to the nearest integer. So a D_0 white dwarf would have a surface temperature in excess of 100,800K, while a D_9 white dwarf would have a surface temperature of less than 5,929K. For comparison, the sun's surface temperature is a little less than 5,800K. Thus far, no white dwarfs have been detected that are as cool as the sun -- and with good reason. It would take longer than the currently estimated age of the universe for a white dwarf to cool off to that low a temperature!

Russ
2004-May-04, 10:23 PM
Please excuse this post. I will have to read this thread a few more times to get all the information through my thick skull, so I'm bumping it back to the top of the list for my own convenience. :oops:

Bob
2004-May-05, 05:13 PM
I daresay female astronomers would speak of Guys for the G class stars :P

There are alternative mnemonics:

Only Boys Accepting Feminism Get Kissed Meaningfully

Eroica
2004-May-06, 02:57 PM
There are alternative mnemonics:

Only Boys Accepting Feminism Get Kissed Meaningfully
Yeah, but you need another mnemonic to help you remember this one. :D