Abstract
We present a method that employs the secondary eclipse light curves of transiting extrasolar planets to probe the spatial variation of their thermal emission. This technique permits an observer to resolve the surface of the planet without the need to spatially resolve its central star. We evaluate the feasibility of this technique for the HD 209458 system [..]. We consider two representations of the planetary thermal emission; a simple model parameterized by a sinusoidal dependence on longitude and latitude, as well as the results of a three-dimensional dynamical simulation of the planetary atmosphere previously published by Cooper & Showman. We find that observations of the secondary eclipse light curve are most sensitive to a longitudinal offset in the geometric and photometric centroids of the hemisphere of the planet visible near opposition. To quantify this signal, we define a new parameter, the ``uniform time offset,'' which measures the time lag between the observed secondary eclipse and that predicted by a planet with a uniform surface flux distribution. We compare the predicted amplitude of this parameter for HD 209458 with the precision with which it could be measured with IRAC. We find that IRAC observations at 3.6um a single secondary eclipse should permit sufficient precision to confirm or reject the Cooper & Showman model of the surface flux distribution for this planet. We quantify the signal-to-noise ratio for this offset in the remaining IRAC bands (4.5um, 5.8um, and 8.0um), and find that a modest improvement in photometric precision (as might be realized through observations of several eclipse events) should permit a similarly robust detection.
Highlights
The identification of the first transiting extrasolar planet, HD 209458b (Charbonneau et al 2000; Henry et al 2000; Mazeh et al 2000), initiated a flurry of investigations into the properties of the planetary body that are not possible for nontransiting objects
We found that an observation of a zero uniform time offset in the 3.6 m Infrared Array Camera (IRAC) bandpass would already put the CS05 model in doubt, since this would be expected to occur by chance in less than 1% of such data sets
In this paper, we have explored how the secondary eclipse light curves of an extrasolar planet may be used to learn about the spatial variation of its emission
Summary
The identification of the first transiting extrasolar planet, HD 209458b (Charbonneau et al 2000; Henry et al 2000; Mazeh et al 2000), initiated a flurry of investigations into the properties of the planetary body that are not possible for nontransiting objects. From the known system parameters (namely the orbital period, phase, inclination, and radii of the planet and star), it is possible to invert the observed light curve to recover some aspects of the flux distribution across the dayside of the planet This technique is not new; a similar approach has been used, for example, to produce surface maps of Pluto and Charon (for a review for such observations, see Stern 1992). Only with the Spitzer detections of the past year has it been feasible to consider applying this technique to extrasolar planets This possibility is interesting because several recent dynamical simulations have predicted the presence of a large flux contrast across the dayside of a hot Jupiter planet. That our technique can be applied to other instruments and transiting extrasolar planets
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