A Flaring L5 Dwarf: The Nature of H\alpha Emission in Very Low Mass (Sub)Stellar Objects

Abstract

Time series spectrophotometry of the L5 dwarf 2MASS 01443536-0716142 showed strong H\alpha emission which declined by nearly 75% in four consecutive exposures. The line was not detected in emission on a spectrum obtained eleven months later. This behavior constrasts with that of 2MASSI J1315309-264951, an L5 dwarf which has shown even stronger H\alpha 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 of order 1%. In contrast, the few, continuously-strong H\alpha emitters, including PC 0025+0447 and 2MASSI J1237392+652615, must either be (1) objects no older than 10-100 Myrs 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 and unknown mechanism for the H\alpha energy.