Reflected Light FromExtra 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 d=planet-star separation
=phase function 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.
MOST
Kepler
Elliptical Orbits
Semi-major axis
Apocentre Pericentre
Eccentricities of Extra Solar PlanetsE
ccen
tric
ity
Semi-major axis (AU)
Inclination: i=0° (face on)
Orientation of the orbital plane - Inclination
Inclination: i=10°
Inclination: i=45°
Inclination: i~90° (edge on)
Argument of pericentre: ω=0°
To observer
Orientation of the orbital plane - Argument of Pericentre
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
TimeP days
8 x 10-6
0
Example Light Curve
i=90o (Edge on)
LP
/ L
*
Pericentre Apocentre
Time
8 x 10-6
i=75o
0
LP
/ L
*
P days
Time
8 x 10-6
i=60o
0
LP
/ L
*
P days
Time
8 x 10-6
i=45o
0
LP
/ L
*
P days
Time
8 x 10-6
i=30o
0
LP
/ L
*
P days
Time
8 x 10-6
i=15o
0
LP
/ L
*
P days
Time
8 x 10-6
i=0o (Face on)
0
LP
/ L
*
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 = ?
Time10.9 days
40 x 10-6
HD 108147b
0
LP
/ L
*
Time10.9 days
10 x 10-6
Contrast
contrast
0
LP
/ L
*
Contrast for e=0In
clin
atio
n (i
)
90
0-90
Scale at 0.1 AU (x10-6)
100
10
1
0.1
Argument of pericentre (ω)
090
Kepler
Contrast for e=0.6In
clin
atio
n (i
)
90
0-90
Scale at 0.1 AU (x10-6)
Argument of pericentre (ω)
090
100
10
1
0.1
Contrast for various e
Argument of pericentre (ω)
Scale at 0.1 AU (x10-6)
Incl
inat
ion
(i)
e=0.6 e=0.7 e=0.8
e=0 e=0.1 e=0.2
e=0.3 e=0.4 e=0.5
100
10
1
0.1
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.