PhD student SHI Xiangdong, Prof. QIAN Shengbang et al., from Yunnan Observatories of the Chinese Academy of Sciences, revealed that  HL Draconis (HL Dra) is an oscillating eclipsing binary of Algol type (oEA), whose secondary component is almost filling its critical Roche lobe. They also found that the primary component oscillates in different pulsating modes and the secondary component has spots and flares and a cycle of magnetic activities. This result was published in Monthly Notices of the Royal Astronomical Society recently.

Binary systems are the most reliable object to derive absolute stellar parameters and to create stellar evolutionary models. If a pulsator is a component of binary system, it can be studied by using the analysis method of binary systems. oEA is an Algol type binary system in which the primary component shows δ Sct-like oscillations.

By analyzing the light curves observed with the Transiting Exoplanet Survey Satellite (TESS), it has been detected that HL Dra is Algol binary system with a mass ratio of 0.361, where the radius filling factor of the primary and secondary component is 87% and 98%, respectively. The secondary component is almost filling its critical Roche lobe, but not entirely.

During TESS observation, both the variable O’Connell effect and the existence of superflares indicate that the secondary of HL Dra should have strong magnetic activities. Researchers collected the sky survey data of more than 100 years and discovered that the O-C curve shows a sinusoidal variation with a period of 129.88 years, which might be caused by a cool red dwarf third body.

After removal of the binary model, a total of 252 pulsation frequencies are detected from the TESS light curves, including 28 multiplets of tidally split frequencies. They identify 2 radial modes, 21 non-radial p-modes and 3 non-radial f-modes from the possible independent frequencies.

All of these features reveal that HL Dra is a very interesting system for further investigations of binary formation and evolutions and for tidal interactions on stellar pulsations and on magnetic activities.

Contact:

SHI Xiangdong, sxd@ynao.ac.cn

Yunnan Observatories, CAS