Optical Support of the NASAStanford Gravity Probe B Mission

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Optical Supportof the NASA/Stanford Gravity
Probe B Mission

• General Relativity tests
• Gravity Probe B mission
• Our participation in the mission

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General Relativity 1916
ETH 1896-1901, 1912-1914
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General Relativity

• Theory of gravitation
• curvature of space-time

• Predictions
• perihelion precession
• starlight deflection
• gravitational redshift
• gravitational radiation
• frame-dragging

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Perihelion precession

• Mercury 43/century
• Taylor-Hulse binary pulsar PSR 191316
  4.2/year

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Gravitational radiation

• Taylor-Hulse binary pulsar orbit shrinks
  3.1mm/7.75h
• Nobel prize 1993

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Light deflection

• Solar eclipse 1919 1.75
• Agreement with GR 20

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Light deflection

• Solar eclipse 1919 1.75
• Gravitational lensing

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Light deflection

• Solar eclipse 1919 1.75
• Gravitational lensing
• Shapiro radar experiments in 1960s
• Cassini experiment 2002
• Agreement in signal delay 210-7

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Gravitational redshift

• WD z2.510-4 (1924)
• Agreement with GR 20
• Pound Rebka (1960) 14.4 keV X-rays up 21.6 m
  z2.5610-15
• Agreement with GR 10
• Sun z210-6 (1962)
• Agreement with GR 20

57Fe
57Fe
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Gravitational redshift

• Gravity Probe A 1976 maser clocks, 10 km, 2h
• Agreement with GR 210-4

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Gravity Probe B

• Curvature of space-time geodetic effect
• Frame-dragging gravitomagnetic effect
• Lense Thirring (1918)
• Gyroscopes on a polar orbit L. Shiff (1960)
• PI F. Everitt (1964-now)

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GP-B launch 20 Apr 2004

• 48 weeks on the orbit
• 30 weeks of data collection
• 10 months science phase

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Gravity Probe B

• Geodetic effect spin-orbit
  accuracy 10-40.7mas (R)
• Frame-dragging spin-spin accuracy
  10-20.4mas (½R)
• Ciufolini Pavlis (Oct 2004) LAGEOS 2m/yr (10)

• Guide star IM Peg
• bright (optical radio)
• convenient for tracking
• with known motion
• near the reference quasar

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GP-B experiment
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IM Peg binary

• Spectroscopic binary, d96pc
• Primary K2 III, R13R?(0.7mas)
• Circular orbit P24.64878 d, a118R?(1mas)
  (Berdyugina et al. 1999)

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IM Peg secondary

• 1999 K0 V, M20.8M?
• 2004 M1/M20.55
• a233R?(1.8mas) (Berdyugina et al. 2005)

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IM Peg starspots

• Spotted star
• Spots 0.5 mas
• Offset 0.1R 0.07mas

1996.8
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IM Peg Doppler Imaging

• Telescopes
• NOT, La Palma
• AST, TSU, Arizona
• Lick Obs.
• Crimean Obs.
• AAT
• Monitoring 2003/5
• Two DI methods

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IM Peg Doppler Imaging
1996.7
1996.9
1997.6
1997.9
1998.7
1998.9
1999.6
1999.7
Method Occamian Approach (Berdyugina
1998) Images Berdyugina et al. (2000)
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IM Peg Doppler Imaging
2003.7
2003.9
2004.0
2004.3
2004.5
2004.6
2004.7
2004.8
Method LSD Maximum Entropy method (Donati et
al. 1997) Images Berdyugina et al. (2005)
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IM Peg long-term trends
Mean spottedness variations 30 yr cycle Active
longitudes and flip-flops 11 yr cycle
(Berdyugina et al. 2005)
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IM Peg third companion?

• Possible solution
• P4.8 yr
• ab8R?(0.45mas)
• a37.6 AU (90 mas)
• M30.09M?
• M8-9 V

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In conclusion

• GP-B is a high-tech gravity test
• First practical application of the stellar
  activity research
• Both agreement and disagreement with GR are of
  great value

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Summary

• Our contribution to GP-B
• Precise orbit of IM Peg
• Optical centroid shifts due to spots
• Estimates of systematic trends
• Scientific outputs
• Starspot evolution
• Differential rotation
• Activity cycles