Emily Rice edited untitled.tex  almost 10 years ago

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Unable to sustain nuclear fusion in their cores due to insufficient mass, all brown dwarfs are about the radius of Jupiter, emit primarily in the infrared, and are degenerate across effective temperature, mass mass,  and radius. age.  These observational challenges make stellar direct detection measurement  methods such as interferometry and asteroseismology unfeasible and dynamical mass measurements very difficult for a large number of objects. However, with the groundswell of optical and near-infrared (NIR) spectra from the BDNYC Data Archive combined with mid-infrared data from the Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010) and the Spitzer Space Telscope (Fazio et al. 2004; Houck et al. 2004), we construct 175 near-complete spectral energy distributions (SED) for the entire sequence of late-M, L and T dwarfs. Objects with optical signatures of low surface gravity ($\beta$ or $\gamma$; Kirkpatrick et al. 2005, Cruz et al. 2009) or membership in nearby young (10-150 Myr) moving groups (Reidel et al. in prep) are identified as 24 percent of the sample to investigate the effects of temperature, gravity, and dust and clouds on spectral morphology. We determine bolometric luminosities ($L_{bol}$) for our sample by integration of the SEDs, flux calibrated using parallax measurements from the Brown Dwarf Kinematics Project (Faherty et al. 2012) and the literature (Dupuy et al. 2013, Tinney et al. 2003, Vrba et al. 2004) or published kinematic distances (Cruz et al. 2003/2007, Faherty et al. 2009, Schmidt et al. 2006/2010, Reid et al. 2006, Delorme et al. 2012, Naud et al. 2014). INSERT SENTENCE HERE ABOUT WHAT SEDs AND BOLOMETRIC LUMINOSITIES PROVIDE.  We construct 175 near-complete spectral energy distributions (SED) for the entire sequence of late-M, L and T dwarfs with optical and near-infrared (NIR) spectra from the BDNYC Data Archive combined with mid-infrared data from the Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010) and the Spitzer Space Telscope (Fazio et al. 2004; Houck et al. 2004). Objects with optical signatures of low surface gravity ($\beta$ or $\gamma$; Kirkpatrick et al. 2005, Cruz et al. 2009) or membership in nearby young (10-150 Myr) moving groups (NYMGs, Faherty et al. in prep) are identified as 24 percent of the sample to investigate the effects of temperature, gravity, and dust/clouds on spectral morphology. We calculate bolometric luminosities ($L_{bol}$) for our sample by integration of the SEDs, flux calibrated using parallax measurements from the Brown Dwarf Kinematics Project (Faherty et al. 2012) and the literature (Dupuy et al. 2013, Tinney et al. 2003, Vrba et al. 2004) or published kinematic distances (Cruz et al. 2003, 2007; Faherty et al. 2009; Schmidt et al. 2006, 2010; Reid et al. 2006; Delorme et al. 2012; Naud et al. 2014).  Figure 1. 1  shows $L_{bol}$ versus selected absolute magnitudes $M_J$, $M_{Ks}$ and $M_{W2}$ for the 59 field age, 27 low-g, and 11 young moving group member L dwarfs of our sample. The flux of low-g L dwarfs appears to be redistributed from the NIR into the MIR, primarily from J to W2, as compared to field age Ls of the same luminosity (Faherty et al. 2012/2013, 2012, 2013;  Liu et al. 2013, 2013;  Zapaterio Osario et al. 2014, 2014;  Gizis et al. al.,  submitted). Indeed we find low gravity Ls are 0.5-1 magnitudes dimmer in $M_J$ and 0.3-0.6 magnitudes brighter in $M_{W2}$ (Filippazzo et al. al.,  in prep). This is probably due to absorption and scattering of light to longer wavelengths by diffuse, unsettled dust in the atmospheres of young objects. Additionally, $M_{Ks}$ magnitudes appear to be largely unaffected by surface gravity making it an ideal band from which to determine age-independent bolometric corrections for L dwarfs. Bolometric luminosities are one of the few direct measurements we can make for brown dwarfs for identification of substellar touchstones, however, effective temperatures ($T_{eff}$) can also be tightly constrained while minimizing our assumptions about the source. Qualitatively, low-g L dwarfs have larger radii than their field age counterparts of the same $L_{bol}$ so they must have cooler photospheres according to the Stefan-Boltzmann Law. We use the DUSTY evolutionary models of Baraffe et al. (2002) and assume the full range of posible radii for field age (0.5-10 Gyr) dwarfs of 1.0 +/- 0.21 $R_{Jup}$. For young moving group members, we interpolate between isochrones to retrieve the uncertainty in radius at a given $L_{bol}$. And for low-g objects, we... (Assuming the entire range of 10-150 Myr radii but don't plot points?)  Preliminary results suggest that confirmed young objects are 100-400 K cooler than field age L dwarfs of the same spectral type. While the uncertainties on the radii of low-g (but not necessarily young) objects are large, they still fall below the track of "normal" Ls on the $T_{eff}$ versus spectral type plot (Filippazzo et al. in prep). Consequently, surface gravity must be taken into account when using spectral type as a proxy for $T_{eff}$. The reliance on an age insensitive temperature-spectral type relationship (Golimowski et al. 2004, Stephens et al. 2009) might explain why young objects appear underluminous as compared to older L dwarfs of the same temperature.  MAYBE JUST PLOT L_BOL VERSUS SPECTRAL TYPE AND DISCUSS QUALITATIVELY INSTEAD OF USING EVOLUTIONARY MODELS  Though the complex nature of their cool atmospheres obscures the fundamental parameters of brown dwarfs, the picture of substellar touchstones becomes clearer as larger age-calibrated samples are assembled and detection methods improve.