2025MNRAS.544.1361H

We present a comprehensive photometric and spectroscopic analysis of the Algol-type binary Gaia DR3 1892576067672499328. We identified the system as a spectroscopic binary based on medium-resolution LAMOST spectra. Combined with TESS photometry, we determine an orbital period of $ P = 2.47757 (1)$ d, a low mass ratio of $ q = 0.098 \pm 0.002$, and an orbital inclination of $ i = 46.934^{+2.613}_{-1.11}$ deg. The orbit is consistent with being circular ($ e = 0$). The binary comprises a $ M_1 = 1.817 ^{ +0.106}_{-0.202} \, \mathrm{ M}_\odot$, $ R_1 = 1.265^{+0.121}_{-0.160}\, \mathrm{ R}_\odot$ A-type primary and a Roche lobe-filling secondary of $ M_2 = 0.179 ^{ +0.011}_{-0.020} \, \mathrm{ M}_\odot$, $ R_2 = 1.994 ^{ +0.041}_{-0.077} \, \mathrm{ R}_\odot$. The double-peak H $\alpha$ emission line indicates the possible existence of a Keplerian accretion disc. We established a simple standard accretion disc model and modelled the geometric and dynamical properties of the accretion disc. The obtained outer disc radius $R_{\mathrm{out}} \approx 3.36 \pm 0.43\, \mathrm{ R}_\odot$ is consistent with the values inferred from the emission velocity of H $\alpha$. Systemic velocity variations observed over time suggest the possible presence of a tertiary companion, with a minimum mass of $M_3 > 0.369 \pm 0.024 \, \mathrm{ M}_\odot$. Given the low mass ratio, the secondary may evolve into a proto-helium white dwarf, forming an EL CVn-type system in the future. This system offers valuable insights into accretion dynamics and the formation of binaries.