American Association of Variable Star Observers (AAVSO)
Mon, 08/03/2020 - 01:36


I'm pretty much new here although I've been working on SRc Alf Ori for quite some time. Specifically delving around its Luminosity/Mass Loss relationship as coined by new researches about stars in the RSB [e.g. Beasor (2020)]. Anyways, I'm entailed to utilize the light curve generated by Vstar and may I ask if there's an available code/program that does 'sort of' converts it onto luminosity?

Looking forward for your responses (and may as well be suggestions/recommendations).

Best regards,

CGHA | Ad Astra

American Association of Variable Star Observers (AAVSO)
I cannot offer a full answer...

Dear CGHA, I cannot offer a full answer, but perhaps my comments will be helpful.  I think what you are asking, is how to convert a star's magnitude, to its true energy output in physical units, e.g. watts.  So you want to determine the "absolute bolometric luminosity", where "bolometric" means the total output, across the entire spectrum (even though the magnitude value you have is for a specific wavelength band).  Saying it is "absolute" means it has been corrected for the distance from the star to the observer.

If you do a google search on on "convert star's magntude to bolometric luminosity", there are some useful hits.  E.g.

You might also try searching on things like "relative power output of stars", "stellar luminosity" etc.

The things I've found, including the above web page, don't seem to cover the important step of accounting for stars of different effective temperatures.  Two stars might have the same magnitude in one spectral band, but have different total outputs because they differ from each other in other bands.

I don't personally know of any program that does the calculation you want, but I've never looked in to this before.

I hope this helps,    Gary Billings


American Association of Variable Star Observers (AAVSO)
Mbol for SRc

I don't know of a good way to translate visual, or optical band photometric magnitudes into luminosity for these types of stars, although one may exist. 

The thing to remember about stars like Alpha Ori is that most of their energy is being radiated in the IR, so measurements in the optical regions don't really capture the amount of energy output coming from these stars.

A research group studied SRc (same classification as Alpha Ori) type stars in the Magellanic clouds and found a relationship between bolometric luminosity (at maximum) and period. 

Mbol = -8.6Log(P) + 16.4.

American Association of Variable Star Observers (AAVSO)
physical vs numerical

In brief: one needs either (1) to integrate the energy physically, for example bolometrically; or (2) to integrate energy numerically, that is, model the spectrum somehow (known? or from similar stars?), take enough measurements (possibly including magnitudes in standard passbands like V & I or the Sloans) to put spectral parameters on absolute scales, then integrate the derived absolute spectrum.

Then make atmospheric corrections. And corrections for interstellar reddening--an expert in the field could advise you whether this latter is important to absolute luminosity of very red stars.

(& mustn't forget: one needs an accurate distance to the star.)

I know of no off-the-shelf software to do this; others might.