Download Reflected Light From Extra Solar Planets

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.