Joe Filippazzo edited untitled.tex  almost 10 years ago

Commit id: 6a6b048adc360bafc504cb1d73d00d8ef2eccf26

deletions | additions      

       

We construct 175 near-complete SEDs 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 (MIR) 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 $L_{bol}$ 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(a,b,c) 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 surface gravity (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 low-g  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. The plot of $L_{bol}$ versus spectral type (Figure 1d) 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. 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 (See Filippazzo et al., in prep).