To investigate the potential connection between the intense X-ray emission from young , low-mass stars and the lifetimes of their circumstellar , planet-forming disks , we have compiled the X-ray luminosities ( L _ { X } ) of M stars in the \sim 8 Myr-old TW Hya Association ( TWA ) for which X-ray data are presently available .
Our investigation includes analysis of archival Chandra data for the TWA binary systems TWA 8 , 9 , and 13 .
Although our study suffers from poor statistics for stars later than M3 , we find a trend of decreasing L _ { X } / L _ { bol } with decreasing T _ { eff } for TWA M stars wherein the earliest-type ( M0–M2 ) stars cluster near \log { ( L _ { X } / L _ { bol } ) } \approx - 3.0 and then \log { ( L _ { X } / L _ { bol } ) } decreases , and its distribution broadens , for types M4 and later .
The fraction of TWA stars that display evidence for residual primordial disk material also sharply increases in this same ( mid-M ) spectral type regime .
This apparent anticorrelation between the relative X-ray luminosities of low-mass TWA stars and the longevities of their circumstellar disks suggests that primordial disks orbiting early-type M stars in the TWA have dispersed rapidly as a consequence of their persistent large X-ray fluxes .
Conversely , the disks orbiting the very lowest-mass pre-MS stars and pre-MS brown dwarfs in the Association may have survived because their X-ray luminosities and , hence , disk photoevaporation rates are very low to begin with , and then further decline relatively early in their pre-MS evolution .