Apsidal motion and TESS light curves of two southern eclipsing binaries with high eccentricity: V1647 Sgr and V2283 Sgr

TL;DR

The paper analyzes apsidal motion in two eccentric eclipsing binaries, V1647 Sgr and V2283 Sgr, by combining ground-based photometry, four-sector TESS data, and archival spectroscopy to derive eclipse timings, light curves, and radial velocities. Light-curve modeling with PHOEBE separates the Newtonian and relativistic contributions to periastron advance, yielding apsidal-motion periods of $U\approx580$ yr for V1647 Sgr and $U\approx533$ yr for V2283 Sgr, with relativistic fractions of about $13.8\%$ and $11.7\%$, respectively. The authors obtain refined absolute parameters, with V1647 Sgr having $M_1\!=\!2.184\,M_\odot$, $M_2\!=\!1.957\,M_\odot$, $R_1\!=\!1.839\,R_\odot$, $R_2\!=\!1.716\,R_\odot$, and V2283 Sgr having $M_1\!=\!2.178\,M_\odot$, $M_2\!=\!1.547\,M_\odot$, $R_1\!=\!1.796\,R_\odot$, $R_2\!=\!1.544\,R_\odot$, with mean internal-structure constants $\log k_{2,obs}\approx -2.39$ for both components. The results broadly agree with theoretical models, contributing valuable data to the ISC statistics for early-type stars and supporting the absence of a detectable third body in either system.

Abstract

The study of apsidal motion rates in eccentric eclipsing binaries provides an important observational test of theoretical models of stellar structure and evolution. Precise physical parameters of the stellar components together with systematic measurements of the periastron advance are needed. We present new results of our long-term observational project to analyze the apsidal motion in early-type eccentric eclipsing binaries. New ground and space-based photometric data were obtained, and archival spectroscopic measurements were used in this study of two detached southern-hemisphere eclipsing binaries: V1647 Sgr (P=3.28 d, e=0.41), and V2283 Sgr (3.47, 0.49). Their TESS observations in four sectors have also been included and the corresponding light curves were solved using the Phoebe code. The newly completed O-C diagrams were analyzed using all reliable timings found in the literature and calculated using the TESS light curves. New or improved values were obtained for the elements of apsidal motion. Using archival spectroscopy for V1647 Sgr, the precise absolute parameters were improved: M1 = 2.184(0.035) M$_\odot$, M2 = 1.957(0.035) M$_\odot$, and R1 = 1.839(0.015) R$_\odot$, R2 = 1.716(0.015) R$_\odot$. For V2283 Sgr the absolute dimensions were newly estimated: M1 = 2.178(0.10) M$_\odot$, M2 = 1.547(0.10) M$_\odot$, and R1 = 1.796(0.01) R$_\odot$, R2 = 1.544(0.01) R$_\odot$. We improved relatively long periods of apsidal motion of about 580 and 530 years, together with the corresponding internal structure constants, log k2, -2.394, and -2.418, for V1647 Sgr and V2283 Sgr, respectively. The relativistic contribution to apsidal motion is not negligible, making about 12 resp. 14% of the total rate of apsidal motion. No signs of the presence of an additional body were revealed in the light curves or in the O-C diagrams of both eccentric systems.

Figures (8)

• Figure 1: Example of our photometric observations of V2283 Sgr obtained at FRAM observatory, Argentina, during two consecutive nights in July 2025. Differential photometry in $R$ filter and its fit in Phoebe. The secondary minimum of V2283 Sgr falls close to phase 0.75.
• Figure 2: Complete $O\!-\!C$ diagram of V1647 Sgr spanning almost one century. Primary minima are denoted by blue circles, secondary by orange triangles. The curves correspond to our best-fit apsidal motion model. All TESS data represents four clusters of points at the end of both curves.
• Figure 3: Historical $O\!-\!C$ diagram of V2283 Sgr since the beginning of 20th century together with our best-fit apsidal motion model. See legend to Fig. \ref{['1647oc']}.
• Figure 4: TESS light curve of V1647 Sgr obtained in Sector 66 (June 2023, orange dots, binning 300) and its Phoebe solution (black curve).
• Figure 5: Radial velocity curve for V1647 Sgr obtained by 1985AA...145..206A and its current solution in Phoebe. Blue color denotes primary component, orange for secondary. The $\gamma$-velocity (--17 km/s) is plotted as a dotted line. The residuals are given in the bottom panel.