Monthly Notices of the Royal Astronomical Society, 2020
The binary nature of the M8.5 dwarf DENIS J063001.4−184014AB (DE0630−18) was discovered with astr... more The binary nature of the M8.5 dwarf DENIS J063001.4−184014AB (DE0630−18) was discovered with astrometric monitoring from the ground, which determined the unresolved photocentric orbit and the trigonometric parallax of the system. Here we present radial velocity monitoring and resolved observations in the near-infrared with Keck aperture masking that allows us to measure the system’s relative separation and brightness. By combining all available information, we determine the individual dynamical masses of the binary components to be $M_1 = 0.052^{+0.009}_{-0.008}$MSun and $M_2 = 0.052^{+0.005}_{-0.004}$MSun, both firmly in the substellar regime. These masses are surprising, given the object’s M8.5 optical spectral type and equivalent absolute magnitude, and the significant difference in brightness between the components (ΔK = 1.74 ± 0.06 mag). Our results suggest that DE0630−18 is a relatively young system (∼200 Myr) with a secondary component that is itself a potentially unresolved ...
ABSTRACT Physical parameters such as effective temperature, surface gravity, metallicity, and dus... more ABSTRACT Physical parameters such as effective temperature, surface gravity, metallicity, and dust and clouds muddle the characteristics of brown dwarf atmospheres. To disentangle the effects of these components we construct nearly complete absolute spectral energy distributions (SEDs) for a large sample of brown dwarfs by combining SDSS, 2MASS, IRAC and WISE photometry with our extensive database of optical and near-infrared spectra and parallaxes. We fit PHOENIX model atmospheres to the SEDs to constrain radii and calculate bolometric luminosities for comparison of objects with the same spectral type. We also use model atmospheres to identify colors indicative of youth and compare to our sample of brown dwarf SEDs using both survey and synthetic photometry. Our extended SEDs provide a powerful spectroscopic and photometric tool for characterizing the atmospheres of brown dwarfs and identifying new young candidates.
We combine optical, near-infrared, and mid-infrared spectra and photometry to construct expanded ... more We combine optical, near-infrared, and mid-infrared spectra and photometry to construct expanded spectral energy distributions for 145 field age (>500 Myr) and 53 young (lower age estimate <500 Myr) ultracool dwarfs (M6-T9). This range of spectral types includes very low mass stars, brown dwarfs, and planetary mass objects, providing fundamental parameters across both the hydrogen and deuterium burning minimum masses for the largest sample assembled to date. A subsample of 29 objects have well constrained ages as probable members of a nearby young moving group. We use 182 parallaxes and 16 kinematic distances to determine precise bolometric luminosities (L bol) and radius estimates from evolutionary models give semi-empirical effective temperatures (T eff) for the full range of young and field age late-M, L, and T dwarfs. We construct age-sensitive relationships of luminosity, temperature, and absolute magnitude as functions of spectral type and absolute magnitude to disentangle the effects of degenerate physical parameters such as T eff , surface gravity, and clouds on spectral morphology. We report bolometric corrections in J for both field age and young objects and find differences of up to a magnitude for late-L dwarfs. Our correction in Ks shows a larger dispersion but not necessarily a different relationship for young and field age sequences. We also characterize the NIR–MIR reddening of low gravity L dwarfs and identify a systematically cooler T eff of up to 300 K from field age objects of the same spectral type and 400 K cooler from field age objects of the same M H magnitude.
ABSTRACT Physical parameters such as effective temperature, surface gravity, metallicity, and dus... more ABSTRACT Physical parameters such as effective temperature, surface gravity, metallicity, and dust and clouds muddle the characteristics of brown dwarf atmospheres. To disentangle the effects of these components we construct nearly complete absolute spectral energy distributions (SEDs) for a large sample of brown dwarfs by combining SDSS, 2MASS, IRAC and WISE photometry with our extensive database of optical and near-infrared spectra and parallaxes. We fit PHOENIX model atmospheres to the SEDs to constrain radii and calculate bolometric luminosities for comparison of objects with the same spectral type. We also use model atmospheres to identify colors indicative of youth and compare to our sample of brown dwarf SEDs using both survey and synthetic photometry. Our extended SEDs provide a powerful spectroscopic and photometric tool for characterizing the atmospheres of brown dwarfs and identifying new young candidates.
ABSTRACT We present medium resolution optical and NIR spectral data for components of the newly d... more ABSTRACT We present medium resolution optical and NIR spectral data for components of the newly discovered WISE J104915.57-531906.1AB (Luhman 16AB) brown dwarf binary. The optical spectra reveal strong 6708 A Li I absorption in both Luhman 16A (8.0+/-0.4 A) and Luhman 16B (3.8+/-0.4 A). Interestingly, this is the first detection of Li I absorption in a T dwarf. Combined with the lack of surface gravity features, the Li I detection constrains the system age to 0.1 - 3 Gyr. In the NIR data, we find strong KI absorption at 1.168, 1.177, 1.243, and 1.254 {\mu}m in both components. Compared to the strength of KI line absorption in equivalent spectral subtype brown dwarfs, Luhman 16A is weaker while Luhman 16B is stronger. Analyzing the spectral region around each doublet in distance scaled flux units and comparing the two sources, we confirm the J band flux reversal and find that Luhman 16B has a brighter continuum in the 1.17 {\mu}m and 1.25 {\mu}m regions than Luhman 16A. Converting flux units to a brightness temperature we interpret this to mean that the secondary is ~ 50 K warmer than the primary in regions dominated by condensate grain scattering. One plausible explanation for this difference is that Luhman 16B has thinner clouds or patchy holes in its atmosphere allowing us to see to deeper, hotter regions. We also detect comparably strong FeH in the 0.9896 {\mu}m Wing-Ford band for both components. Traditionally, a signpost of changing atmosphere conditions from late-type L to early T dwarfs, the persistence and similarity of FeH at 0.9896 {\mu}m in both Luhman 16A and Luhman 16B is an indication of homogenous atmosphere conditions. We calculate bolometric luminosities from observed data supplemented with best fit models for longer wavelengths and find the components are consistent within 1{\sigma} with resultant Teffs of 1310+/-30 K and 1280+/-75 K for Luhman 16AB respectively.
Monthly Notices of the Royal Astronomical Society, 2020
The binary nature of the M8.5 dwarf DENIS J063001.4−184014AB (DE0630−18) was discovered with astr... more The binary nature of the M8.5 dwarf DENIS J063001.4−184014AB (DE0630−18) was discovered with astrometric monitoring from the ground, which determined the unresolved photocentric orbit and the trigonometric parallax of the system. Here we present radial velocity monitoring and resolved observations in the near-infrared with Keck aperture masking that allows us to measure the system’s relative separation and brightness. By combining all available information, we determine the individual dynamical masses of the binary components to be $M_1 = 0.052^{+0.009}_{-0.008}$MSun and $M_2 = 0.052^{+0.005}_{-0.004}$MSun, both firmly in the substellar regime. These masses are surprising, given the object’s M8.5 optical spectral type and equivalent absolute magnitude, and the significant difference in brightness between the components (ΔK = 1.74 ± 0.06 mag). Our results suggest that DE0630−18 is a relatively young system (∼200 Myr) with a secondary component that is itself a potentially unresolved ...
ABSTRACT Physical parameters such as effective temperature, surface gravity, metallicity, and dus... more ABSTRACT Physical parameters such as effective temperature, surface gravity, metallicity, and dust and clouds muddle the characteristics of brown dwarf atmospheres. To disentangle the effects of these components we construct nearly complete absolute spectral energy distributions (SEDs) for a large sample of brown dwarfs by combining SDSS, 2MASS, IRAC and WISE photometry with our extensive database of optical and near-infrared spectra and parallaxes. We fit PHOENIX model atmospheres to the SEDs to constrain radii and calculate bolometric luminosities for comparison of objects with the same spectral type. We also use model atmospheres to identify colors indicative of youth and compare to our sample of brown dwarf SEDs using both survey and synthetic photometry. Our extended SEDs provide a powerful spectroscopic and photometric tool for characterizing the atmospheres of brown dwarfs and identifying new young candidates.
We combine optical, near-infrared, and mid-infrared spectra and photometry to construct expanded ... more We combine optical, near-infrared, and mid-infrared spectra and photometry to construct expanded spectral energy distributions for 145 field age (>500 Myr) and 53 young (lower age estimate <500 Myr) ultracool dwarfs (M6-T9). This range of spectral types includes very low mass stars, brown dwarfs, and planetary mass objects, providing fundamental parameters across both the hydrogen and deuterium burning minimum masses for the largest sample assembled to date. A subsample of 29 objects have well constrained ages as probable members of a nearby young moving group. We use 182 parallaxes and 16 kinematic distances to determine precise bolometric luminosities (L bol) and radius estimates from evolutionary models give semi-empirical effective temperatures (T eff) for the full range of young and field age late-M, L, and T dwarfs. We construct age-sensitive relationships of luminosity, temperature, and absolute magnitude as functions of spectral type and absolute magnitude to disentangle the effects of degenerate physical parameters such as T eff , surface gravity, and clouds on spectral morphology. We report bolometric corrections in J for both field age and young objects and find differences of up to a magnitude for late-L dwarfs. Our correction in Ks shows a larger dispersion but not necessarily a different relationship for young and field age sequences. We also characterize the NIR–MIR reddening of low gravity L dwarfs and identify a systematically cooler T eff of up to 300 K from field age objects of the same spectral type and 400 K cooler from field age objects of the same M H magnitude.
ABSTRACT Physical parameters such as effective temperature, surface gravity, metallicity, and dus... more ABSTRACT Physical parameters such as effective temperature, surface gravity, metallicity, and dust and clouds muddle the characteristics of brown dwarf atmospheres. To disentangle the effects of these components we construct nearly complete absolute spectral energy distributions (SEDs) for a large sample of brown dwarfs by combining SDSS, 2MASS, IRAC and WISE photometry with our extensive database of optical and near-infrared spectra and parallaxes. We fit PHOENIX model atmospheres to the SEDs to constrain radii and calculate bolometric luminosities for comparison of objects with the same spectral type. We also use model atmospheres to identify colors indicative of youth and compare to our sample of brown dwarf SEDs using both survey and synthetic photometry. Our extended SEDs provide a powerful spectroscopic and photometric tool for characterizing the atmospheres of brown dwarfs and identifying new young candidates.
ABSTRACT We present medium resolution optical and NIR spectral data for components of the newly d... more ABSTRACT We present medium resolution optical and NIR spectral data for components of the newly discovered WISE J104915.57-531906.1AB (Luhman 16AB) brown dwarf binary. The optical spectra reveal strong 6708 A Li I absorption in both Luhman 16A (8.0+/-0.4 A) and Luhman 16B (3.8+/-0.4 A). Interestingly, this is the first detection of Li I absorption in a T dwarf. Combined with the lack of surface gravity features, the Li I detection constrains the system age to 0.1 - 3 Gyr. In the NIR data, we find strong KI absorption at 1.168, 1.177, 1.243, and 1.254 {\mu}m in both components. Compared to the strength of KI line absorption in equivalent spectral subtype brown dwarfs, Luhman 16A is weaker while Luhman 16B is stronger. Analyzing the spectral region around each doublet in distance scaled flux units and comparing the two sources, we confirm the J band flux reversal and find that Luhman 16B has a brighter continuum in the 1.17 {\mu}m and 1.25 {\mu}m regions than Luhman 16A. Converting flux units to a brightness temperature we interpret this to mean that the secondary is ~ 50 K warmer than the primary in regions dominated by condensate grain scattering. One plausible explanation for this difference is that Luhman 16B has thinner clouds or patchy holes in its atmosphere allowing us to see to deeper, hotter regions. We also detect comparably strong FeH in the 0.9896 {\mu}m Wing-Ford band for both components. Traditionally, a signpost of changing atmosphere conditions from late-type L to early T dwarfs, the persistence and similarity of FeH at 0.9896 {\mu}m in both Luhman 16A and Luhman 16B is an indication of homogenous atmosphere conditions. We calculate bolometric luminosities from observed data supplemented with best fit models for longer wavelengths and find the components are consistent within 1{\sigma} with resultant Teffs of 1310+/-30 K and 1280+/-75 K for Luhman 16AB respectively.
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