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Reflected Light From Extra Solar Planets Modeling light curves of planets with highly elliptical orbits Daniel Bayliss, Summer Student, RSAA, ANU Ulyana Dyudina, RSAA, ANU Penny Sackett, RSAA, ANU Introduction • 119 extra solar planets detected. – 118 found by precise radial velocity measurements. – 1 by found by transit photometry. • No reflected light from extra solar planets detected to date, however the albedo of τ Boo constrained by lack of signal (Charbonneau et al.,1999, ApJ, 522, L145). Reflected light • Amount of reflected light given by: p=albedo =phase function d=planet-star separation Rp=planet radius Space Photometry • Current photometric precision limited by atmosphere to around LP/L* ~50 x 10-6. • Canadian micro satellite MOST target list includes 3 stars with planets (close-in, circular). • NASA’s Kepler satellite (2007) with 100,000+ target stars. • Predicted to achieve precision of LP/L*< 10 x 10-6. Kepler MOST Elliptical Orbits Apocentre Pericentre Semi-major axis Eccentricity Eccentricities of Extra Solar Planets Semi-major axis (AU) Orientation of the orbital plane - Inclination Inclination: i=0° (face on) Inclination: i=10° Inclination: i=45° Inclination: i~90° (edge on) Orientation of the orbital plane Argument of Pericentre To observer Argument of pericentre: ω=0° To observer Argument of pericentre: ω=90° To observer Argument of pericentre: ω=-90° Model • Reflective properties of planets based on Pioneer data of Jupiter. • Planetary radius assumed to be 1 Jupiter radius. • Example light curve properties: – Semi-major axis = 0.1 AU – Argument of pericentre = 60° – Eccentricity = 0.5 Example Light Curve 8 x 10-6 LP / L* i=90o (Edge on) 0 Pericentre Apocentre Time P days 8 x 10-6 LP / L* i=75o 0 Time P days 8 x 10-6 LP / L* i=60o 0 Time P days 8 x 10-6 LP / L* i=45o 0 Time P days 8 x 10-6 LP / L* i=30o 0 Time P days 8 x 10-6 LP / L* i=15o 0 Time P days 8 x 10-6 LP / L* i=0o (Face on) 0 Time P days Example - HD 108147b • Extra solar planet discovered by Pepe, Mayor, et al (2002, A&A , 388, 632). • Properties: – Semi-major axis = 0.104 AU – Period = 10.9 days – Eccentricity = 0.498 – Argument of pericentre = -41° – Inclination = ? HD 108147b LP / L* 40 x 10-6 0 Time 10.9 days Contrast 10 x 10-6 LP / L* contrast 0 Time 10.9 days Contrast for e=0 Scale at 0.1 AU (x10-6) 90 100 Inclination (i) Kepler 10 1 0 90 0.1 0 -90 Argument of pericentre (ω) Contrast for e=0.6 Scale at 0.1 AU (x10-6) 90 Inclination (i) 100 10 1 0 90 0.1 0 -90 Argument of pericentre (ω) Contrast for various e Scale at 0.1 AU (x10-6) Inclination (i) 100 e=0 e=0.1 e=0.2 e=0.3 e=0.4 e=0.5 10 1 0.1 e=0.6 e=0.7 e=0.8 Argument of pericentre (ω) Conclusions 1. A low inclination (face on) orientation can show strong contrast if it has a high eccentricity orbit. 2. Light curves from elliptical orbits may help constrain a systems inclination. 3. Favourable pericentric orientation can dramatically increase the contrast.