PLANET DETECTION IN HIGH MAGNIFICATION MICROLENSING EVENTS

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PLANET DETECTION IN HIGH MAGNIFICATION
MICROLENSING EVENTS

• Philip Yock
• Nicholas Rattenbury
• Ian Bond
• MOA group
• MNRAS 335, 159-169 (2002)

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Maximum possible magnification-Max mag ? (2?rE
? rS)/?rS2 rE/rs ? 1000(S. Liebes, Phys. Rev.
133B, 835, 1964)

• Observer Lens
  Source (moving)

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Event rates-

• 10 events with magnification 100 were found
  in 2001
• similar event rates occurred in 2002 and 2003
• I. Bond et al, MNRAS, 331, L19, 2002
• http//www.roe.ac.uk/iab/alert/alert.html

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The primary effect of planetary deflectors bound
to stars will be to slightly perturb the lens
action of these stars Liebes (Phys. Rev.
133B, 835, 1964)

• Planet orbiting the lens star-

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Calculations of planetary perturbations-
Griest Safizadeh, ApJ 500, 37, 1998 Computed
planetary perturbations in events with Amax
10 Rattenbury et al, MNRAS 335, 159, 2002
Computed planetary perturbations in events with
Amax 100
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• Amax 80, sep 0.8rE, ice giant at 30

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• Amax 80, sep 0.8 rE, ice giant at 60º

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Amax80, sep 0.8 rE, ice giant at 90

• Amax 80, sep 0.8 rE, ice giant at 90

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planet
Lens star
?
Source track
ll
?
theta
?
?
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Planets in the lower hemsiphere produce mirror
image perturbations-

• Amax 80, sep 0.8 rE, ice giant at 210

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Terrestrial planets-

• Amax 80, sep 0.8 rE, Earth mass planet at 60

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Regions of detectability-

• If Amax ? 100, then-
• Terrestrial planets detectable from 0.8-1.3 rE
• Ice giants at gt 0.4 rE
• Gas giants anywhere
• (Further details at MNRAS 335, 159, 2002)

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Exceptional regions-

• Loss of sensitivity at 0 and 180-

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Multiplanets-

• Planets at 120 and 150, both 4? Earth mass

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Three planets-

• Earth at 150, 4? Earth at 60, Neptune at 300

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Mass-separation and reflection degeneracies-

• Planet at 1.5rE, mass ratio 5?10-4

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• Conclusion - High magnification microlensing
  events are promising for studying extrasolar
  planets-
• Sensitivity to gas giants is 100
• Sensitivity to ice-giants is substantial
• Sensitivity to terrestrial planets is
  significant

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Abundance measurements-

• In a few years-
• Significant measurements possible for ice-giants
  in the Galaxy
• Rudimentary measurements may be possible for
  terrestrial planets

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Requirement-

• The peaks of high magnification events need to be
  monitored intensively