Calibrating Ultracool Dwarfs: Optical Template Spectra, Bolometric Corrections, and χ Values 1

• Published in: Publications of the Astronomical Society of the Pacific 2014-07, Vol.126 (941), p.642-659
• Main Authors: Schmidt, Sarah J., West, Andrew A., Bochanski, John J., Hawley, Suzanne L., Kielty, Collin
• Format: Article
• Language: English
• Subjects: Astronomical photometry; Bolometric correction; Colors; L dwarfs; Radial velocity; Spectrophotometry; Spectroscopy; Standard deviation; Stellar classification; Visible spectrum
• ISSN: 0004-6280; 1538-3873
• DOI: 10.1086/677403

We present optical template spectra, bolometric corrections, and χ 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 ∼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 thez-band andJ-band bolometric corrections for late-M and L dwarfs have a strong correlation withz–JandJ–K S colors, respectively. The new χ values, which can be used to convert Hα equivalent widths to activity strength, are based on spectrophotometrically calibrated SDSS spectra and the new bolometric fluxes. While the measured χ values have typical uncertainties of ∼20%, ultracool dwarf models show the continuum surrounding Hα can vary by up to an order of magnitude with changing surface gravity. Our semiempirical χ values are one to two orders of magnitude larger than previous χ values for mid-to-late L dwarfs, indicating that the upper limits for Hα activity strength on the coolest L dwarfs have been underestimated.