Stellar Astrophysics with the Keck Interferometer

PI: S. R. Kulkarni

Co-I’s: D. Sasselov, M. Konacki, B. Lane

Motivation

• Current stellar models– Current models are good to ~10% . Not good

enough even for cosmology.

• Problematic areas:• Convection• Helium abundance

Our Approach• V2 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

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

YY Gem & CU Cnc (First two runs)

KI observations resolved the systems

CM Dra Observations

CM Dra Model

• 21 V2 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)

CU Cnc

• V2 pts, 2% scatter.• 2 = 0.3• Perhaps discrepant parallax

from Hipparcos

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!)

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

Distance to Pleiades via AtlasX-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.

Orbit of Atlas

P(orbit)= 291 day

a = 13 mas

e = 0.245

Inclination=108d

Distance via Kepler’s 3rd law

a3 = d3 a3= (m1+m2)P2

Backup Slides

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,)

Predicted Mesurement Precision for CU Cnc (GJ 2069A)

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

Predicted Differential Phase Signal for U Aql

PTI results

• We have ongoing work at PTI resolving binaries in open clusters such as the Hyades

Predicted Visibility Evolution for YY Gem

Predicted Measurement Precision for YY Gem