Joe Filippazzo edited untitled.tex  almost 10 years ago

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Figure 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 NYMG 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; Liu et al. 2013; Zapaterio Osario et al. 2014; Gizis et 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., 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 using evolutionary models  while minimizing our assumptions about the source. source (See Filippazzo et al., in prep). The plot of $L_{bol}$ versus spectral type shows most low-g, young, and field objects all lie along the same sequence.  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.