Fundamental effective temperature measurements for eclipsing binary stars -- V. The circumbinary planet system EBLM J0608-59

EBLM J0608-59 / TOI-1338 / BEBOP-1 is a 12th-magnitude, F9V star in an eclipsing binary with a much fainter M-dwarf companion on a wide, eccentric orbit (P=14. 6 d). The binary is orbited by two circumbinary planets: one transiting on a 95-day orbit and one non-transiting on a 215-day orbit. We have used high-precision photometry from the TESS mission combined with direct mass measurements for the two stars published recently to measure the following model-independent radii: R₁ = 1. 32 0. 02 R_, R₂ = 0. 309 0. 004 R_. Using R₁ and the parallax from Gaia EDR3 we find that this star's angular diameter is = 0. 0309 0. 0005 mas. The apparent bolometric flux of the primary star corrected for both extinction and the contribution from the M-dwarf (<0. 4%) is F, ₀ = (0. 417 0. 005) 10^-9 \, erg\, cm^-2 \, s^-1. Hence, this F9V star has an effective temperature T ₄₅₅, ₁ = 6031\, K 46 \, K\, (rnd. ) 10 \, K\, (sys. ). EBLM J0608-59 is an ideal benchmark star that can be added to the sample of such systems we are establishing for "end-to-end" tests of the stellar parameters measured by large-scale spectroscopic surveys.