A New Algol-type Binary with an Accretion disk

Abstract

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

Figures (10)

• Figure 1: The color--magnitude diagram shows our target star (red star) in comparison to the LAMOST sample (blue dots). The horizontal axis represents the color index $G_\mathrm{BP} - G_\mathrm{RP}$, while the vertical axis indicates the absolute magnitude $M_\mathrm{G}$. All photometric measurements are taken from Gaia DR3.
• Figure 2: Phase-folded observational data and best-fit model for binary $Gaia$ DR3 1892576067672499328. Top panel: Radial velocity curves. Green and blue symbols represent the observed RVs of the primary and secondary stars, respectively. The dashed and dotted lines show the corresponding model predictions. middle panel: Phase-folded light curves. Black and blue points represent flux measurements from TESS and ZTF, respectively, while the red line indicates the best-fitting model. Bottom panel: Residuals between the observed light curves and the fitted model.
• Figure 3: Dynamical spectrum constructed from red-arm spectra centered on the H$\alpha$ region, phase-folded using the orbital period derived from the TESS light curve. The horizontal axis shows radial velocity (km/s), and the vertical axis represents orbital phase. Dark blue bands correspond to absorption features, while yellow regions indicate relative emission or continuum enhancement.
• Figure 4: The central panel illustrates the Roche geometry and stellar configurations of the semi-detached binary, while the surrounding panels present the evolution of the H$\alpha$ line profiles across various orbital phases.
• Figure 5: Model visualization of the binary system Gaia DR3 1892576067672499328 at selected orbital phases. The primary is the accreting star surrounded by an accretion disc, while the secondary acts as the donor star that fills its Roche lobe. The color bar indicates luminosity, with the deep red region marking the location of the hotspot on the disc. For visual clarity, the system is rendered at an inclination angle of $80^\circ$, whereas the actual inclination derived from our modeling is $46.934^\circ$.