Stellar Parameters and Evolutionary Pathways of the Subgiant system HIP 72217

TL;DR

This study applies Al-Wardat's spectrophotometric method to the hierarchical triple system HIP 72217 to derive precise stellar parameters for the AB sub-system and its faint companion C. The authors integrate photometric/SED fitting with a refined orbital solution from Tokovinin's ORBITX to obtain $M_A \approx 1.14\,M_\odot$, $M_B \approx 1.12\,M_\odot$, and $M_{dyn} \approx 2.26\,M_\odot$, with an age of $3.548$ Gyr placing A and B in the early subgiant phase. The AB pair exhibits Teff of $6125$ K and $5950$ K, radii around $1.47$ and $1.39\,R_\odot$, and luminosities of $\sim2.7$ and $\sim2.2\,L_\odot$, while C is a $\sim0.17\,M_\odot$ red dwarf ($T_{\text{eff}} \approx 3250$ K). A stability and habitability analysis using Holman & Wiegert criteria and Kopparapu HZ coefficients indicates narrow S-type stability close to the stars and a circumbinary HZ extending roughly 1–3 AU, informing the prospects for planets in this system. Overall, the results validate Al-Wardat's method for binary evolution studies and contribute to understanding subgiant binary evolution and planetary stability in multiple-star environments.

Abstract

In this study, we applied Al-Wardat's method to analyze the subgiant system HIP72217 for which we obtained accurate parameters including stellar masses, effective temperatures ($T_{\text{eff}}$) and system age.For the primary component we determined a stellar mass of $M_A = 1.14 \pm 0.15\,M_{\odot}$ and effective temperature $T_{\text{eff,A}} = 6125 \pm 50$\,K while for the secondary component we obtained the values of $M_B = 1.12 \pm 0.14\,M_{\odot}$ and $T_{\text{eff,2}} = 5950 \pm 50$\,K. The system's age was estimated to be $3.548 Gyr$, which is consistent with the predicted evolutionary period of a subgiant binary. The evolutionary timeline of HIP\,72217 becomes clearer through our study, which also demonstrates Al-Wardat's approach as an effective approach for binary star system characterization. These findings contribute to a better understanding of the physical mechanisms that control subgiant binary evolution and their broader role in stellar evolutionary processes.

Figures (7)

• Figure 1: Left: Pictorial representation of the three components A, B and C of the system HIP 72217 with their magnitudes( $m_{vA}$=7.08, $m_{vB}$ = 7.30, $m_{vC}$=16.84) and magnitude differencesESA1997 Their separation in mas is also denoted in the picture. Right: Hierarchical chart showing the combinations of the three components.
• Figure 2: Spectral Energy Distribution (SED) of HIP 72217, showing the combined synthetic SED of the binary system along with individual flux contributions from each component. Observed magnitudes from Gaia2022yCat.1355....0G, 2MASS2003yCat.2246....0C and Tycho2002AA...384..180F are overlaid for comparison.
• Figure 3: Component A and B of HIP 72217 placed on the Evolutionary Track and Isochrone of $Z=0.03$ taken from Girardi 2000AAS..141..371G2000yCat..41410371G. The HR diagram shows a plot of $\log$ of effective temperature plotted against $\log(L/L_{\odot})$, the logarithm of the ratio of the stellar luminosity to the Solar Luminosity
• Figure 4: Orbit of HIP72217 (solid curve) with observations (circles; 1951--2023). The bottom left panel displays fit residuals that indicate the differences between observed and modeled angular separation ($\Delta\rho$) and position angle ($\Delta\theta$) measurements of the orbit. The bottom right panel shows a box plot that summarizes data distribution by displaying minimum and maximum values, first ($Q1$) and third ($Q3$) quartiles, median, and any detected outliers.
• Figure 5: Habitability (green area) and Stability (dashed line) for the HD72217 entire binary system. Using analytical models, this figure illustrates the potential habitable zones (green shaded areas) for HD 72217. It is entirely based on calculated criteria (Holman & Wiegert, 1999; Kopparapu et al., 2013), without any direct observations. In this figure, no residuals are plotted since no empirical data are used. Within the system, it provides a conceptual map for evaluating potential planetary stability and habitability.