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

ABSTRACT EBLM J0608-59/TOI-1338/BEBOP-1 is a 12^ th-magnitude, F9 V 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-d orbit and one non-transiting on a 215-d 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 per cent) is {F}, 0 = (0. 417 0. 005) 10^-9 erg cm^-2 s^-1. Hence, this F9 V 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.