I am trying to compile a list of bright Red Supergiants (RSGs), and it is proving to be a bit of a challenge. My understanding of the general criteria is that RSGs have mass 8x that of the sun or greater, radius 100-1000x that of the sun, temperature 3500-4500K, and B-V from 1.5 to 2 for spectral types K through M5 (I'm a little unclear if the color index criteria does not apply past M5, or if RSGs are not found past M5.
Soooo...., I perform a Simbad search for stars with V<7.0 of luminosity class I (and its variants) and filter out stars earlier than K. I am left with 29 stars (csv list attached). Of these, Simbad identifies 9 as RSGs (119 Tau, NO AUr, alf Ori, psi1 Aur, omi1 CMa, KQ Pup, VX Sgr, mu Cep, and 5 Lac). Example, 119 Tau:
http://simbad.u-strasbg.fr/simbad/sim-id?Ident=119+tau&submit=submit+id
Antares is curiously *not* flagged RSG:
http://simbad.u-strasbg.fr/simbad/sim-id?Ident=antares&submit=submit+id
I think the reason is that "double or multiple star" supercedes "red supergiant" for the description. This would mean that all the binaries in my supergiant list that are in fact RSGs will not be flagged as such. I don't see where in the other object information fields I could pick out RSG. Does anyone know?
The question also arises, who decides what is an RSG and what isn't (the Simbad RSG designation has to come from *somewhere*)? I perused the web site of Jim Kahler, who is an expert on stellar evolution:
http://stars.astro.illinois.edu/sow/sowlist.html
Of the RSG stars in my list, he notes the following (grrr... tables don't seem to be working)
star
radius
mass
K
alf Ori
~700x
18x
3650
sig CMa
360x
12x
3750
119 Tau
12-18x
525-800x
3500-3700
omi1 CMa
530x
18x
4000
Of my non-RSG stars, he notes:
star
radius
mass
K
notes
eta Per
210x
9-11x
4300
"supergiant"
pi Pup
290x
13-14x
4000
"supergiant","orange"
lam Vel
207x
9-12x
4000
"supergiant","orange"
eps Peg
150x
10x
4460
"supergiant","orange"
omi2 Cyg
230x
10x
3500-3900
"supergiant"
alf Her
400x
7-8x
3300
"red supergiant"
alf Sco
15-18x
~800x
3600
Except for alf Her, which he explicitly calls an RSG, all these stars fall in the B-V range to qualify as RSG. So are they or not? It feels like membership in the RSG club is not really well defined.
Tom
[I've had to pick out a lot of information by hand, here, so there may be errors on my part.]
There is an easy way to get a list of red supergiant stars.
Most if not all are variable so they are in VSX.
The type SRC is reserved for red supergiants so making a search by type (click on the "More" button twice to get the extended search options) and typing %SRC% in the Var type field will work. You will get 96 results.
Do the same for LC, the irregular supergiants (likely poorly studied SRC objects). 116 additional objects will come up.
You can also add the spectral type M% to the search if you want to exclude some K-type supergiants from the list. Most will be M-type anyway.
Cheers,
Sebastian
Sebastian:
Thankyou, that turned up (or confirmed) many candidates. However, the question remains as to how it was determined that a given star was SRC or LC. For instance, sig CMa is listed as LC. There are two references: one to the Hipparcos catalog, the other to a 1963 paper by Cousins (attached). The latter makes no claims for the type of variability. It alludes to a method for screening supergiants in a color-color diagram, but that method depends upon U-B photometry, which the paper does not have for this star. Where did the LC designation come from?
Types are inherited from the GCVS and continuously being updated (along with other information) in VSX with data from surveys or publications. Check the star's revision history to see what changes were made in VSX. The range was updated with Hipparcos and Tycho data.
The type comes from the light curve (irregular) plus the luminosity class found in the majority of papers in the literature. There are discrepant types, ranging from K4III to M1.5Iab that's why the intermediate K7Ib, also published in several sources, was chosen.
A normal K-giant usually does not have such a variety of spectral types published so that fact already justifies the LC classification.
So, in principle, if there is at least one published spectral type showing a supergiant nature, the star is likely to be added the C suffix.
Cheers,
Sebastian
Consider V959 Her and V395 Aur, both SRC in VSX. I don't see anything in either their VSX or GCVS histories to indicate why they should be considered supergiants. VSX, itself, lists V959 Her and V394 Aur as class III, which is internally inconsistent. Of the SRC and LC variables I turned up in VSX (that were not in my supergiant list from Simbad), fully half were luminosity class II or III in Simbad (I didn't check all the VSX designations).
My problem is that I need to know if a star is *actually* a supergiant, not just if an untraceable someone once said so.
Welcome to the catalogue business!
There are multiple sources for spectra (and for classification too). There are stars with very different types or luminosity classes depending on the source you choose.
SIMBAD is not necessarily the bible regarding spectral types. They are taken from specific papers and maybe there are other papers that could be more reliable. Who knows. And SIMBAD is also not complete in all regards so I wouldn't trust it blindly.
The VSX examples you gave are indeed inconsistent so I will check them and revise the classification or the spectral type if needed.
Thanks.
And I'm sorry that what there is available doesn't fill your needs.
Cheers,
Sebastian