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Exoplanets in Reflection and Shadow
Exoplanets Exoplanets in Reflection in Reflection and Shadowand Shadow
Penny D. SackettPenny D. Sackett RSAA, Mt Stromlo RSAA, Mt Stromlo
ObservatoryObservatory
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Ulyana Dyudina (ANU Caltech)PDS (ANU)Daniel Bayliss (ANU)Sara Seager (DTM)Carolyn Porco (Space Science Inst)Henry Throop (Southwest Research Inst)Luke Dones (Southwest Research Inst)
ApJ 2004, in press (astro-ph/0406390)
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ELT: Lots of photons possibility for ultra-precise relative photometry
What could we learn about exoplanets with ultra-precise photometry if:
1. adequate time resolution was possible
2. star light could be adequately separated from light associated with the planet (in reflection or
i i )
Precise, Time-series Photometry
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State of Play
Searches for modulated reflected light around such planets have yielded:
No detections.Upper limits have placed the albedo of three exoplanets. Collier Cameron et al 2002, MNRAS
Leigh et al 2003, MNRAS
Size of modulated signal strongest for planets in orbit with small semi-major axis a.
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Reflections and Shadows
ϑ = 0At opposition
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Basic Geometry
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Use Pioneer- and Voyager-measured anisotropic scattering functions of Jupiter, Saturn and its rings at 0.6 - 0.7 micron
Construct phase light curves. Vary orbital inclination, planet oblateness, ring obliquity, ring viewing angle, orbit size, orbit eccentricity, and orbit viewing angle
Extract detectability (contrast). Compare to Lambertian scattering and ELT capabilities
Not included: ring size, planetary thermal emission
Our Approach
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Ring size
Arnold & Schneider 2004,
A&A, 420, 1153
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Comparison to Pioneer Data
Forw
ard
Bac
kwar
d
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Model Scattering Properties
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Ringless Albedos
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Ring Effects (Edge-on)
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45 Degrees Orientation
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Top View Orientation
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Great Variety in Reflected
Light Curves
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Elliptical Orbits Observer-Orbit Orientation now ImportantArgument of Pericentre ω
=
90 deg if viewing from pericentre
-90 deg if viewing from apocentre
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Exo Test Case: HD 108147b
Discovered by Pepe, Major et al(2002, A&A, 388, 632)
Properties:Semi-major axis = 0.104 AUPeriod = 10.9 daysEccentricity = 0.498Argument of pericentre = ω
= -41°
Inclination = ?
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Worked Example:
HD108147b
Peric
entr
e
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HD108147b with
different viewing angle
Argument of pericentre = 60 deg,
not -41 deg Con
tras
t
T-shift
Peric
entr
e
Opp
ositi
on
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Temporal shift is measurable if orbital phase known. How large is shift?
% of Period:
Red 50%Green 25%Blue 10%
Can be used to determine inclination
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Can we detect the effect for, say, Jupiter with a = 5 AU?
Contrast:
Dyudina, Sackett, Bayliss etal, 2004, ApJ accepted,
astro-ph/0406390
Red 10-7
Green 10-8
Blue 10-9
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Conclusions
With precise photometry (high dynamic range) of 105 to 109:Study planets as distant as 5 AU from solar type starsDetect planet morphology (rings)Draw inferences atmospheric scattering propertiesCan determine orbital inclination if Vrad knownDifficult systematics at these levels
If contrast can be achieved at relevant distance from host:Get orbit automaticallyGet all planets automaticallyLow resolution spectra yield more info RE: atmospheres