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We present optical template spectra, bolometric corrections, and $\chi$values for ultracool dwarfs. The templates are based on spectra from the SloanDigital Sky Survey (SDSS) and the Astrophysical Research Consortium 3.5-mtelescope. The spectral features and overall shape of the L dwarf templates areconsistent with previous spectroscopic standards and the templates have aradial velocity precision of $\sim$10--20 km s$^{-1}$. We calculate bolometricfluxes (accurate to 10--20\%) for 101 late-M and L dwarfs from SDSS, 2MASS, andWISE photometry, SDSS spectra, and BT-Settl model spectra. We find that the$z$- and $J$-band bolometric corrections for late-M and L dwarfs have a strongcorrelation 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 newbolometric fluxes. While the measured $\chi$ values have typical uncertaintiesof $\sim$20\%, ultracool dwarf models show the continuum surrounding H$\alpha$can vary by up to an order of magnitude with changing surface gravity. Oursemi-empirical $\chi$ values are one to two orders of magnitude larger thanprevious $\chi$ values for mid- to late-L dwarfs, indicating that the upperlimits for H$\alpha$ activity strength on the coolest L dwarfs have beenunderestimated.

Calibrating Ultracool Dwarfs: Optical Template Spectra, Bolometric Corrections, and $\chi$ Values