Talk:V391 Pegasi

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[edit] Luminosity?

What's the source for the luminosity value of 15.4 times solar? If I do the calculation assuming the star and the Sun are spherical blackbodies, the equation for bolometric luminosity is:

\frac { L_\ast } { L_\odot } = \left ( \frac { T_\ast } { T_\odot } \right )^4 \left ( \frac { r_\ast } { r_\odot } \right )^2

Using the values given in the article for radius and temperature, I obtain a bolometric luminosity of 35 times solar. However I'm not sure how well the blackbody approximation holds for subdwarf B stars.

On the other hand, if I use the absolute magnitude, the visual luminosity (I'm going to use the symbol l here rather than L to avoid confusion) is given by:

\frac { l_\ast } { l_\odot } = 100^{((M_\odot - M_\ast)/5)}

Using an absolute visual magnitude of +3.84 for V391 Peg and +4.83 gives a visual luminosity 2.5 times solar.

So what's the source of the 15.4? Chaos syndrome 20:24, 16 September 2007 (UTC)

I calculated the bolometric luminosity using the temperature and radius as in the equation above. The temperature and radius come from the Extrasolar Planets Encyclopaedia. BlueEarth 21:24, 16 September 2007 (UTC)