J. Ong | Searcharxiv

arXiv2022

KIC 7955301: a hierarchical triple system with eclipse timing variations and an oscillating red giant

KIC 7955301 is a hierarchical triple system with eclipse timing and depth variations discovered by the Kepler mission. It is composed of a non-eclipsing primary star at the bottom of the red giant branch on a 209-day orbit with a K/G-type main-sequence inner eclipsing binary, orbiting in 15.3 days. This system was noted for the large amplitude of its eclipse timing variations (4 hours), and the clear solar-like oscillations of the red-giant component, including p-modes of degree up to l=3 and mixed l=1 modes. The system is a single-lined spectroscopic triple. We perform a dynamical model by combining the Kepler photometric data, eclipse timing variations, and radial-velocity data obtained at Apache Point (ARCES) and Haute Provence (SOPHIE) observatories. The dynamical mass of the red-giant is determined with a 2% precision at 1.30 (+0.03,-0.02) solar mass. We perform asteroseismic modeling based on the global seismic parameters and on the individual frequencies. Both methods lead to a mass of the red giant that matches the dynamical mass within the uncertainties. Asteroseismology also reveals the rotation rate of the core (15 days), the envelope (150 days), and the inclination (75 deg) of the red giant. Three different approaches lead to an age between 3.3 and 5.8 Gyr, which highlights the difficulty of determining stellar ages despite the exceptional wealth of available information. On short timescales, the inner binary exhibits eclipses with varying depths during a 7.3-year long interval, and no eclipses during the consecutive 11.9 years. This is why Kepler could detect its eclipses, TESS will not, and the future ESA PLATO mission should. Over the long term, the system owes its evolution to the evolution of its individual components. It could end its current smooth evolution by merging by the end of the red giant or the asymptotic giant branch of the primary star.

astro-ph.SR↗

arXiv2021

PLATO Hare-and-Hounds exercise: Asteroseismic model fitting of main-sequence solar-like pulsators

Asteroseismology is a powerful tool to infer fundamental stellar properties. The use of these asteroseismic-inferred properties in a growing number of astrophysical contexts makes it vital to understand their accuracy. Consequently, we performed a hare-and-hounds exercise where the hares simulated data for 6 artificial main-sequence stars and the hounds inferred their properties based on different inference procedures. To mimic a pipeline such as that planned for the PLATO mission, all hounds used the same model grid. Some stars were simulated using the physics adopted in the grid, others a different one. The maximum relative differences found (in absolute value) between the inferred and true values of the mass, radius, and age were 4.32 per cent, 1.33 per cent, and 11.25 per cent, respectively. The largest systematic differences in radius and age were found for a star simulated assuming gravitational settling, not accounted for in the model grid, with biases of -0.88 per cent (radius) and 8.66 per cent (age). For the mass, the most significant bias (-3.16 per cent) was found for a star with a helium enrichment ratio outside the grid range. Moreover, a ~7 per cent dispersion in age was found when adopting different prescriptions for the surface corrections or shifting the classical observations by $\pm 1σ$. The choice of the relative weight given to the classical and seismic constraints also impacted significantly the accuracy and precision of the results. Interestingly, only a few frequencies were required to achieve accurate results on the mass and radius. For the age the same was true when at least one $l=2$ mode was considered.

astro-ph.SR↗