In the Hertzsprung-Russel diagram, there are a class of pulsators located in the intersection region between the instability strip of δ Scuti stars and that of the γ Dor stars. They are very important and promising objects for the study of the stellar structure, since presence of p- and g-modes allow us probe properties of the star from the envelope to the core.

In a study published in The Astrophysical Journal on Dec. 26, CHEN Xinghao and LI Yan from Yunnan Observatories of the Chinese Academy of Sciences (CAS) and ZHANG Xiaobin from National Astronomical Observatories of CAS studied the hybrid pulsator CoRoT 100866999 in eclipsing binary system and determined precisely the size of the convective core of CoRoT 100866999 with asteroseismology.

The researchers constructed a grid of theoretical models with different size of convective core overshooting to reproduce the observed modes. They found that the frequency spectra of CoRoT 100866999 can be well identified with the method of the rotational splitting, and their fundamental parameters determined by asteroseismic fit match well with those obtained from the eclipsing light curve analysis.

Moreover, the researchers investigated propagating characters of the oscillation modes inside the star in details. They found that most of the nonradial δ Scuti frequencies behave distinct mixed characters. Those modes have substantial amplitudes near the edge of the convective core and the surface of the star, providing strong constraints on conditions of the deep interior of the star.

Finally, the researchers obtained the size of the convective core of CoRoT 100866999 to be 9.3% of the stellar radius.

"It is the fascination of asteroseismology. Asteroseismology is the only technique that can be used to probe interiors of stars via reproducing oscillation modes,” said Dr. CHEN.