FREQUENCY MODULATION OF DIRECTLY IMAGED EXOPLANETS: GEOMETRIC EFFECT AS A PROBE OF PLANETARY OBLIQUITY

ABSTRACT We consider the time-frequency analysis of a scattered light curve of a directly imaged exoplanet. We show that the geometric effect due to planetary obliquity and orbital inclination induce the frequency modulation of the apparent diurnal periodicity. We construct a model of the frequency...

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Bibliographic Details
Published in:The Astrophysical journal 2016-05, Vol.822 (2), p.112-112
Main Author: Kawahara, Hajime
Format: Article
Language:English
Subjects:
ALBEDO
AMPLITUDES
astrobiology
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
COMPARATIVE EVALUATIONS
Computer simulation
Earth
Extrasolar planets
FREQUENCY ANALYSIS
FREQUENCY MODULATION
INCLINATION
Light curve
Modulation
PERIODICITY
PLANETS
ROTATION
SCATTERING
SIMULATION
SPIN
techniques: photometric
Time-frequency analysis
VISIBLE RADIATION
WIGNER DISTRIBUTION
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Summary:ABSTRACT We consider the time-frequency analysis of a scattered light curve of a directly imaged exoplanet. We show that the geometric effect due to planetary obliquity and orbital inclination induce the frequency modulation of the apparent diurnal periodicity. We construct a model of the frequency modulation and compare it with the instantaneous frequency extracted from the pseudo-Wigner distribution of simulated light curves of a cloudless Earth. The model provides good agreement with the simulated modulation factor, even for the light curve with Gaussian noise comparable to the signal. Notably, the shape of the instantaneous frequency is sensitive to the difference between the prograde, retrograde, and pole-on spin rotations. While our technique requires the albedo map to be static, it does not need to solve the albedo map of the planet. The time-frequency analysis is complementary to other methods which utilize the amplitude modulation. This paper demonstrates the importance of the frequency domain of the photometric variability for the characterization of directly imaged exoplanets in future research.
ISSN:0004-637X
1538-4357
DOI:10.3847/0004-637X/822/2/112