Age and convective core overshooting calibrations in CPD-54 810 binary system

Statistical investigation on the solution robustness

¹ Dipartimento di Fisica “Enrico Fermi”, Università di Pisa, Largo Pontecorvo 3, 56127 Pisa, Italy
e-mail: valle@df.unipi.it
² INFN, Sezione di Pisa, Largo Pontecorvo 3, 56127 Pisa, Italy

Received: 11 March 2023
Accepted: 7 April 2023

Abstract

Aims. Relying on recent very precise observations for the CPD-54 810 binary system, we investigate the robustness of the estimated age and convective core overshooting for a system with both stars on the main sequence (MS). Our main aim is to assess the variability in the results, accounting for different statistical and systematic sources of uncertainty.

Methods. We adopt the SCEPtER pipeline, a well-established maximum likelihood technique, based on fine grids of stellar models computed for a different initial chemical composition and convective core overshooting efficiency.

Results. We performed different fits of the system, under different assumptions. The base fit suggests a common age of 3.02 ± 0.15 Gyr, in agreement with recent literature. This estimated convective core overshooting parameter is β = 0.09 ± 0.01, with a corresponding convective core mass $M_c=0.{059}_{-0.021}^{+0.017}$ M_⊙. The robustness of these estimates were tested assuming a narrow constraint on the helium-to-metal enrichment ratio, which is in agreement with the recently published results on the Hyades cluster. Under this constraint the chemical solution of the system changes, but the age and the overshooting parameter are almost unchanged ($3.{08}_{-0.14}^{+0.17}$ Gyr and 0.09 ± 0.01). In a further test, we halved the uncertainty as to the effective temperature of both stars and again the estimated parameter shows only small variations (3.02 ± 0.12 Gyr and 0.09 ± 0.01).

Conclusions. This low variability suggests that the age of the system with both stars in the MS can be reliably estimated at a 5% level, but it also indicates that the power of the investigation is probably low, because it is possible to find a satisfactory fit in several different configurations by only varying the initial chemical composition within its uncertainty. Despite the great increase in the observational constraints’ precision, the results support the conclusions of previous theoretical works on the stellar parameter calibration with double MS star binary systems.