Probing Convective Dynamo Activity in Young Suns with the Chandra X-ray Observatory

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Abstract
Our analysis of Chandra X-ray data for over 27,000 pre-main sequence (PMS) stellar members of various young Galactic star-forming regions and open clusters suggests that, compared to the present-day Sun, the convective dynamo responsible for generating magnetic fields in PMS stars demonstrates much higher levels of surface activity: large spot areas, magnetic fluxes, baseline and flare X-ray luminosities, and magnetic loop sizes. The convective dynamo mechanism enables the production of X-ray super-flares (with X-ray energies E x ranging from 10 34 to 10 36 erg) and mega-flares ( Ex> 10 36 erg) in fully convective (Hayashi track) PMS stars, far surpassing the capabilities of the contemporary Sun. Moreover, it leads to frequent weaker X-ray flares ( Ex< 10 34 erg) with an occurrence rate more than a million times higher than in older solar-type main sequence stars. Furthermore, we present two other PMS dynamo-related findings. First, we find no observational evidence of strong, long-term cyclical activity in PMS stars driven by convective dynamos. Second, our research offers tentative evidence for a transition from a convective dynamo to a solar-type tachoclinal dynamo as radiative cores develop in solar-mass stars at ages between 10 and 25 million years.

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