A flaring L5 dwarf:: The nature of Hα emission in very low mass (sub)stellar objects

Time series spectrophotometry of the L5 dwarf 2MASS J01443536-0716142 showed strong H emission that declined by nearly 75% in four consecutive exposures. The line was not detected in emission on a spectrum obtained 11 months later. This behavior contrasts with that of 2MASSI J1315309-264951, an L5 dwarf that has shown even stronger Halpha emission on four separate occasions. The observational database suggests that L dwarfs can be found in such strong flares only occasionally, with a duty cycle on the order of 1%. In contrast, the few, continuously strong Halpha emitters, including PC 0025+ 0447 and 2MASSI J1237392+ 652615, must either be (1) objects no older than 10-100 Myr with continuously active accretion and/or chromospheres, but which apparently formed in isolation from known young stellar clusters and associations, or (2) objects empowered by a different but unknown mechanism for the Halpha energy.