We present optical template spectra , bolometric corrections , and \chi values for ultracool dwarfs .
The templates are based on spectra from the Sloan Digital Sky Survey ( SDSS ) and the Astrophysical Research Consortium 3.5-m telescope .
The spectral features and overall shape of the L dwarf templates are consistent with previous spectroscopic standards and the templates have a radial velocity precision of \sim 10–20 km s ^ { -1 } .
We calculate bolometric fluxes ( accurate to 10–20 % ) for 101 late-M and L dwarfs from SDSS , 2MASS , and WISE photometry , SDSS spectra , and BT-Settl model spectra .
We find that the z - and J -band bolometric corrections for late-M and L dwarfs have a strong correlation with z - J and J - K _ { S } colors respectively .
The new \chi values , which can be used to convert H \alpha equivalent widths to activity strength , are based on spectrophotometrically calibrated SDSS spectra and the new bolometric fluxes .
While the measured \chi values have typical uncertainties of \sim 20 % , ultracool dwarf models show the continuum surrounding H \alpha can vary by up to an order of magnitude with changing surface gravity .
Our semi-empirical \chi values are one to two orders of magnitude larger than previous \chi values for mid- to late-L dwarfs , indicating that the upper limits for H \alpha activity strength on the coolest L dwarfs have been underestimated .