1. Stellar Astrophysics with the Keck Interferometer PI: S. R. Kulkarni Co-I’s: D. Sasselov, M. Konacki, B. Lane

2. Motivation Current stellar models –Current models are good to ~10%. Not good enough even for cosmology. Problematic areas: Convection Helium abundance

3. Our Approach V 2 observations of Eclipsing Binaries –Radial Velocity provides all but distance –KI provides distance >> Derive all physical parameters Differential Phase for Bright Binaries –A range of targets, including G+M and Cepheid binaries

4. M-dwarf Eclipsing Binaries M-L-R relations for these stars are an issue of debate –Radius from eclipses –RV to set physical scale –Inteferometer for distance

5. YY Gem & CU Cnc (First two runs) KI observations resolved the systems

6. CM Dra Observations

7. CM Dra Model 21 V 2 points, 5.8% scatter.  2 = 1.2 Semi-Major Axis: 1.14  0.04 mas Parallax: 65.3±2.2 mas Systematic Plx Uncert: 0.2 mas (assuming 10 %  K, actually smaller)

8. CU Cnc  V 2 pts, 2% scatter.  2 = 0.3 Perhaps discrepant parallax from Hipparcos

9. Near-Term Prospects With scans over 1-2 more nights on CM Dra we will have a very interesting parallax measurement. With scans over 2 more nights we can solve the orbits of YY Gem and CU Cnc. We have applied for matching Caltech time (TAC is meeting today!)

10. Epilogue KI is now working very well for binary targets However, the slow speed of KI means that KI should be used sparingly for binary science Outrigger array would truly revolutionize stellar astrophysics

11. Distance to Pleiades via Atlas X-P Pan, M. Shao & S. Kulkarni (Nature, in negotiating phase) Pleiades is a gold standard for intermediate mass stars, brown dwarfs and Cepheid distance scale Hipparcos team published distance to Pleiades D = 118 +/- 4 pc Traditional distance (color-mag diagram) D = 131 +/- 3 pc Hipparcos result generated “lively” controversy.

12. Orbit of Atlas P(orbit)= 291 day a = 13 mas e = 0.245 Inclination=108d

13. Distance via Kepler’s 3rd law a 3 = d 3 a 3 = (m 1 +m 2 )P 2

14. Backup Slides

15. Additional Visibility Targets There are many more systems to choose from, e.g.: –UU Cnc, an eclipsing K4 II system thought to have mass transfer –Open cluster binaries ( vB22, attack issues of Y,  )

16. Predicted Mesurement Precision for CU Cnc (GJ 2069A)

17. Cepheid Binaries Binary companions hotter than primary, e.g. U Aql: F8Ib + B7V Very difficult to resolve (or even detect) with other methods Pulsation provides redundant signal

18. Predicted Differential Phase Signal for U Aql

19. PTI results We have ongoing work at PTI resolving binaries in open clusters such as the Hyades

20. Predicted Visibility Evolution for YY Gem

21. Predicted Measurement Precision for YY Gem