Magnetic Activity of Pre-main Sequence Stars near the Stellar-Substellar Boundary

TL;DR

This study investigates magnetic activity in very low-mass pre-main sequence stars near the stellar-substellar boundary using X-ray observations, finding no decline in X-ray emission up to 30 million years of age.

Contribution

It provides new X-ray observational data for 10-30 Myr old pre-MS stars, exploring magnetic activity evolution near the stellar-substellar boundary.

Findings

No decline in fractional X-ray luminosity up to 30 Myr

X-ray activity does not depend on spectral type or age within this range

Results suggest magnetic activity decline occurs after 30 Myr

Abstract

X-ray observations of pre-main sequence (pre-MS) stars of M-type probe coronal emission and offer a means to investigate magnetic activity at the stellar-substellar boundary. Recent observations of main sequence (MS) stars at this boundary display a decrease in fractional X-ray luminosity ($L_{X}$/$L_{bol}$) by almost two orders of magnitude for spectral types M7 and later. We investigate magnetic activity and search for a decrease in X-ray emission in the pre-MS progenitors of these MS stars. We present XMM-Newton X-ray observations and preliminary results for ~10 nearby (30-70 pc), very low mass pre-MS stars in the relatively unexplored age range of 10-30 Myr. We compare the fractional X-ray luminosities of these 10-30 Myr old stars to younger (1-3 Myr) pre-MS brown dwarfs and find no dependence on spectral type or age suggesting that X-ray activity declines at an age later than ~30 Myr in these very low-mass stars.