A Simple Unified Spectroscopic Indicator of Stellar Luminosity: the
  Extended Flux Weighted Gravity-Luminosity Relationship
  We show that for a wide range of stellar masses, from 0.3 to 20 Msun, and for
evolutionary phases from the main sequence to the beginning of the red giant
stage, the stellar flux weighted gravity, g_F ~ g/Teff^4, is tightly correlated
with absolute bolometric magnitude Mbol. Such a correlation is predicted by
stellar evolution theory. We confirm this relation observationally, using a
sample of 445 stars with precise stellar parameters. It holds over 17 stellar
magnitudes from Mbol = 9.0 mag to -8.0 mag with a scatter of 0.17 mag above
Mbol = -3.0 and 0.29 mag below this value. We then test the relation with 2.2
million stars with 6.5 mag > Mbol > 0.5 mag, where 'mass-produced' but robust
log g, Teff and Mbol from LAMOST DR5 and Gaia DR2 are available. We find that
the same relation holds with a scatter of ~0.2 mag for single stars offering a
simple spectroscopic distance estimate good to ~10 percent.
