Hi All

I couldn't leave it sit, so I ferreted around for data on Gl876. Jean Schneider's site has the basics, but the luminosity needs to be worked out from the Colour Index.

Here's a web-site with a bolometric correction calculator...

BC Calculator

...plug-in any old radius and Temp and you get luminosity , colour index and the BC. Same Temp gives the same B-V and BC, so radius doesn't matter and ignore the luminosity etc. Working back from his referenced equations and you can easily get Teff in terms of the (B-V) value. For Gl 876 (B-V) = 1.58, so Teff ~ 3318 K, and the BC ~ -2.36. Its V = 10.17 and distance is 4.72 psc, so M = 11.8. Thus the bolometric magnitude is 9.44.

Hence L = 0.01318 L(sol) and since Gl876 is orbitting at 0.021 AU that's an insolation of ~ 30 times Earth's. That seems a bit hot. Sort of between Mercury and the Sun kind of hot. With a hefty albedo (~ 0.5) and averaged over the planet then temperatures might be ~ 200-400 C. Either that or I need a more recent source on Gl 876's absolute luminosity.

Adam