Photometric detection of the starlight reflection by a “Pegasi” planet Martin Vannier (1), Tristan Guillot (2), Suzanne Aigrain (1) (1) ESO, Chile (2) OCA, France (3) Institute of Astronomy, Cambridge, UK Corot Week 2005Ubatuba, Brazil, 2-6 Oct. A description of two proposals in the Corot Additional Programme

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 Photometric detection of the starlight reflection by a “Pegasi” planet Corot Week 2005Ubatuba, Brazil, 2-6 Oct.

Corot Week 2005Ubatuba, Brazil, 2-6 Oct. Photometry of Star+Planet varies with planetary phase Principle In a perfect simple world : ⇨ Periodical variations of the photometry Photometric variation (ppm)

Planetary signal Corot Week 2005Ubatuba, Brazil, 2-6 Oct. Amplitude of the signal (homogeneous reflection, circular orbit): S=1/2 A sin(i) (R pl /a) 2 A: Albedo i: orbital inclination Rpl: planetary radius a: orbital distance ⇨ Degeneracy between A, i, (R) ⇨ constrains the parameters space

Signal / fundamental noise Corot Week 2005Ubatuba, Brazil, 2-6 Oct. ● Amplitude of the signal: S=1/2 A sin(i) (R pl /a) 2 ➢ “Pegasi” are much favored E.g.: HD46375 (target for Prop. II), a=0.04 AU, R pl =1.3 Rj up ⇨ S= a few ● Photon Noise: B=1/sqrt(N ph ) with N ph photons per sample. E.g.: m V =7.9 Sample =3h ⇨ B= , SNR=30 ● Instrumental (white) noise also nulls out Photometric variation (ppm)

Stellar activity Corot Week 2005Ubatuba, Brazil, 2-6 Oct. E.g.: simulations of HD46375 (S. Aigrain) : A fairly quiet K1 IV star, RMS=170 ppm Planet (i=  /6, A=0.5) (Dotted: Star alone) Planet + Star + photon noise

Spectral Analysis with known orbital period and phase (Prop. I) Corot Week 2005Ubatuba, Brazil, 2-6 Oct. ➢ 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 ⇨ <10% for a 150-days run Sine fit Planetary signal Measured signal, including stellar activity

Field of View and Target (Prop. I) Corot Week 2005Ubatuba, Brazil, 2-6 Oct. HD46375: - in FOV - K1 IV type-star - a=0.04 AU - m V =7.94 Favorable planet-host stars and the Corot “eyes”

Field of View and Target (Prop. I) Corot Week 2005Ubatuba, Brazil, 2-6 Oct. HD46375: - K1 IV type-star - a=0.04 AU - mv= in FOV Together with short-run primary target HD46558 in seismo field ➢ Phase B Pegasi-planet target HD46375(cross) together with primary target HD46558

Proposal II Potential for new detections Corot Week 2005Ubatuba, Brazil, 2-6 Oct. Number of detection = Number of objects observed 60 (10 per season) ×Proportion hosting a Pegasi planet1% ×Fraction of these for which the planetary reflection signal can be distinguished from the stellar activity. Largely unknown... 1/3 ?? 0.2 ?? ⇨ Not much, but potentially high value result at a free cost !

Corot Week 2005Ubatuba, Brazil, 2-6 Oct. Orbital frequency Sine fit (frequency, amplitude, phase) on a HD46375-type star: ⇨ Precision over 150 days: <10% on the amplitude of the planetary reflection 5% on its period Spectral Analysis with unknown orbital elements

Coping with stellar activity for new detections Corot Week 2005Ubatuba, Brazil, 2-6 Oct. ● 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 (P=40 d) ➢ strongly degraded precision for fast rotators (prohibitive for P≤15 d) ➢ a number of local minima ⇨ fake alarms or dubious cases (*) Orbital period and phase. A fixed ⇨ amplitude = f(period)

Corot Week 2005Ubatuba, Brazil, 2-6 Oct. ⇨ 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

Corot Week 2005Ubatuba, Brazil, 2-6 Oct. For a circular orbit and a homogeneous albedo: S=1/4 A (R pl /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 Planetary signal as a function of time

Planetary signal + Fundamental Noise ??? Corot Week 2005Ubatuba, Brazil, 2-6 Oct. Dominated by photon noise: B=1/sqrt(N ph ) with N ph : stellar flux, time E.g.: HD46375 SNR =