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 θ = 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 Teff,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.