SIMBAD references

We show that for a wide range of stellar masses, from 0.3 to 20 M_☉, and for evolutionary phases from the main sequence to the beginning of the red giant stage, the stellar flux-weighted gravity, g_F ≡ g/T_eff⁴, is tightly correlated with absolute bolometric magnitude M_bol. 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 M_bol = 9.0 to -8.0 mag with a scatter of 0.17 mag above M_bol = -3.0 and 0.29 mag below this value. We then test the relation with 2.2 million stars with 6.5 mag >= M_bol >= 0.5 mag, where "mass-produced" but robust logg, T_eff, and M_bol 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%.