Constraining Evolutionary Models with New Dynamical Masses:

1. Constraining Evolutionary Models with New Dynamical Masses: A Keck Laser Guide Star Adaptive-Optics Study of Very Low Mass (VLM) Binaries Quinn Konopacky, Andrea Ghez (UCLA) Travis Barman (Lowell) Emily Rice, Ian McLean (UCLA) Gaspard Duchêne (Grenoble)

2. Stellar Substellar Chabrier et al. 2000, Burrows et al. 1997 Evolutionary models can be distinguished with VLM binaries. Key Questions Is M/L transition where dust starts to become important in atmosphere? Is L/T transition when dust condenses out of atmosphere?  At what masses do these transitions occur? Requirement 1-3% accuracy in dynamical masses VLM = Very Low Mass

3. Currently, only four published mass estimates from very low mass binaries 2MASS J0746425+200032 - Bouy et al. 2004 2MASS J05352184-0546085 - Stassun et al. 2006, 2007 PPl 15 - Basri & Martín 1999 GJ 569 Bab - Zapatero Osorio et al. 2004

4. Laser guide star adaptive optics at Keck improves ability to get VLM dynamical masses. • Improvements • Increases accuracy for few that were measured • Dramatically expands possible sample • Sample • Define by Monte Carlo of all known VLM binaries (Mtot < 0.2 Mo) • Currently consists of ~20 tight visual binaries • Spectral Type range: M8 - T5.5 Keck Laser Guide Star Adaptive Optics (LGS-AO)

5. N N E 0.25” Laser guide star adaptive optics allow for improved (sub-milliarcsec) astrometric accuracy 2MASS J0746425+200032 pos = 0.5 mas Positional uncertainties are a factor of 2-16 smaller than earlier measurements

6. The first-ever combination of NIRSPEC with LGS-AO yield individual radial velocities. 2MASS J0746425+200032 CO bandhead Also first high spectral resolution (R~25,000), spatially resolved K-band spectrum of a binary Ldwarf

7. New data points lead to vast improvement in the uncertainties on all orbital parameters for 2MASS 0746+20. (factor of 4 improvement in mass, 2% accuracy)

8. Comparison to theoretical models shows the DUSTY are most consistent for a L0+L1.5 system

9. New mass also validates updated color estimates for the DUSTY models. This helps the well known problem with model transformations to filter colors (new models courtesy of T. Barman)

10. Secondary component is possibly sub-stellar

11. Atmospheric modeling of spectra will yield improvements in current tests and further tests. • Improved temperatures • Surface gravities (model courtesy of E. Rice & T. Barman)

12. A number of other systems in our sample are yielding orbital solutions and radial velocities. M8+M9 VLM Binary Radial Velocity ~9 km/s

13. 0.1” Conclusions • With the advent of LGS-AO at Keck • High precision measurement (~2%) of dynamical mass for 2MASS 0746+20 • Twenty more precision VLM masses are likely within 2 years • Using dynamical mass to test evolutionary models • DUSTY models most appropriate for L0+L1.5 system • Validates new color corrections in DUSTY model • Spatially resolved, high resolution K-band spectrum of L dwarf binary • Detailed atmospheric modeling • Temperatures • Surface gravities • One more for individual dynamical masses instead of total mass. New LGS-AO measurement from Sunday night yields one more dynamical mass