We estimate the parameters of the donor of the accreting black hole binary MAXI J1820+070. The measured values of the binary period, rotational and radial velocities, and constraints on the orbital inclination imply the donor is a subgiant with the mass of M 2 ≈ 0.49 − 0.10 + 0.10 M ☉ and the radius of R 2 ≈ 1.19 − 0.08 + 0.08 R ☉ . We reanalyze the previously obtained optical spectrum from the Gran Telescopio Canarias and found it yields a strict lower limit on the effective temperature of T > 4200 K. We compile optical and infrared fluxes observed during the quiescence of this system. From the minima r - and i -band fluxes found in Pan-STARSS1 Data Release 2 prediscovery imaging and for a distance of D ≈ 3 kpc, reddening of E ( B – V ) = 0.23, and R 2 ≈ 1.11 R ⊙ , we find T ≲ 4230 K, very close to the above lower limit. For a larger distance, the temperature can be higher, up to about 4500 K (corresponding to a K5 spectral type, preferred by previous studies) at D = 3.5 kpc, allowed by the Gaia parallax. We perform evolutionary calculations for the binary system and compare them to the observational constraints. Our model fitting the above temperature and radius constraints at D ≈ 3 kpc has a mass of 0.4 M ⊙ , T ≈ 4200 K, and solar metallicity. Two alternative models require D ≳ 3.3–3.4 kpc at 0.4 M ⊙ , T ≈ 4500 K and half-solar metallicity, and 0.5 M ⊙ , T ≈ 4300 K, and solar metallicity. These models yield mass-transfer rates of ∼10 −10 M ⊙ yr −1 , compatible with those based on the estimated accreted mass of ≈2 × 10 25 g and the time between the 2018 discovery and the 1934 historical outburst.
CITATION STYLE
Mikołajewska, J., Zdziarski, A. A., Ziółkowski, J., Torres, M. A. P., & Casares, J. (2022). The Donor of the Black Hole X-Ray Binary MAXI J1820+070. The Astrophysical Journal, 930(1), 9. https://doi.org/10.3847/1538-4357/ac6099
Mendeley helps you to discover research relevant for your work.