Photometric detection

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Photometric detection of the starlight
reflection by a Pegasi planet
A description of two proposals in the Corot
Additional Programme
Martin Vannier(1), Tristan Guillot(2), Suzanne
Aigrain(1) (1) ESO, Chile (2) OCA, France (3)
Institute of Astronomy, Cambridge, UK
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• 2 proposals in the Corot Additional Programme
• (M. Vannier, T. Guillot, S. Aigrain)
• I Observation of the starlight reflected by a
  Pegasi planet
• ?Phase B
• II Photometric detection of Pegasi planets in
  the seismo field
• ?Accepted

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Photometry of StarPlanet varies with planetary
phase
In a perfect simple world ? Periodical
variations of the photometry
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Amplitude of the signal (homogeneous reflection,
circular orbit) S1/2 A sin(i) (Rpl/a)2 A
Albedo i orbital inclination Rpl planetary
radius a orbital distance ?Degeneracy between
A, i, (R) ?constrains the parameters space

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• Amplitude of the signal
• S1/2 A sin(i) (Rpl/a)2
• ? Pegasi are much favored
• E.g. HD46375 (target for Prop. II), a0.04
  AU, Rpl1.3 Rjup
• ? S a few 10-5

• Photon Noise B1/sqrt(Nph) with Nph photons per
  sample.
• E.g. mV7.9
• Sample 3h ? B4 10-6, SNR30
• Instrumental (white) noise also nulls out

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E.g. simulations of HD46375 (S. Aigrain) A
fairly quiet K1 IV star, RMS170 ppm


Planet Star photon noise
(Dotted Star alone)
Planet (ip/6, A0.5)
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? Stellar activity exceeds the signal in
amplitude, including at the (known) orbital
frequency
? Fit with a sine, to best match both the
amplitude and phase at the orbital frequency. In
the case of HD46375, the precision on the
amplitude of the planetary reflection would be ?
30 for a 20-days short run ? lt10 for a 150-days
run
Measured signal, including stellar activity
Sine fit
Planetary signal
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HD46375 - in FOV - K1 IV type-star - a0.04
AU - mV7.94

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HD46375 - K1 IV type-star - a0.04 AU -
mv7.94 - in FOV Together with short-run primary
target HD46558 in seismo field ? Phase B

Pegasi-planet target HD46375(cross) together
with primary target HD46558
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Sine fit (frequency, amplitude, phase) on a
HD46375-type star ? Precision over 150 days
lt10 on the amplitude of the planetary
reflection 5 on its period
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• Depends on rotational velocity, colour index and
  age of the star
• Used simulations for MS stars with type F5 to
  K5, rotational period 5 to 40 days
• Sine fit on a 150-days serie with two free
  parameters() yields
• ? a precision on the amplitude ranging from 20
  to a few (depending on S.T) for slow-rotating
  stars (P40 d)
• ? strongly degraded precision for fast rotators
  (prohibitive for P15 d)
• ? a number of local minima ? fake alarms or
  dubious cases

() Orbital period and phase. A fixed ?
amplitude f(period)
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• ?A potential for new detection of Pegasi planets
  around low-activity stars of the seismo field.
• But...
• Further work to be done...
• Need for
• A better simulation including
• - eccentric orbit, albedo depending on the
  planetary phase (? peaked Mercury-type
  reflection)
• - estimated stellar activity representative of
  the actually observed population
• - a smarter fit algorithm
• RV follow-up to raise the ambiguity on the
  dubious cases

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For a circular orbit and a homogeneous
albedo S1/4 A (Rpl/a)2 (1-sin(i)cos(2 pi t/P))
But the variations or not sine in case of
?eccentric orbit ?surface albedo depends on the
orbital configuration
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Dominated by photon noise B1/sqrt(Nph) with
Nph stellar flux, time E.g. HD46375 SNR