Indirect Detection of Planets and Brown Dwarfs

Spectroscopic Signatures

• Brown dwarfs
  • Lithium at 670.8 nm
  • water vapor, methane in very cool ones
• Planets
  • auroral lines
  • oxygen, water, carbon dioxide

Photometric Variations

• planetary eclipses would be very weak effects
• observationally intensive because statistically rare
• must distinguish from stellar activity and spot transits

Gravitational Perturbations

• proper motion
  • get low amplitude wobble in the star's path
  • detectability depends on mass. brightness difference, period
  • a Jupiter @ 5 AU around 0.15 solar mass dM has wobble of about 1 mas with 28 year period
• radial velocity (Doppler effect)
  • get low amplitude wobble in line of sight velocity
  • detectability depends on mass, period (shorter better) , orbital orientation
  • Jupiter causes the sun to wobble with amplitude 13 m/s
    Saturn @ 0.05 AU induces wobble of 37 m/s
    Neptune @ 0.05 AU induces wobble of 6.8 m/s
  • precision now reduced to 2 m/s (~1/1000 pixel)

Gravitational Lensing