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Stellar Astrophysics with the Keck Interferometer

VIEWS: 8 PAGES: 21

									 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




• 29 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 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.
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

								
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