Abstract
We present Warm Spitzer/IRAC secondary eclipse time series photometry of three short-period transiting exoplanets, HAT-P-3b, HAT-P-4b and HAT-P-12b, in both the available 3.6 and 4.5 micron bands. HAT-P-3b and HAT-P-4b are Jupiter-mass, objects orbiting an early K and an early G dwarf stars, respectively. For HAT-P-3b we find eclipse depths of 0.112%+0.015%-0.030% (3.6 micron) and 0.094%+0.016%-0.009% (4.5 micron). The HAT-P-4b values are 0.142%+0.014%-0.016% (3.6 micron) and 0.122%+0.012%-0.014% (4.5micron). The two planets' photometry is consistent with inefficient heat redistribution from their day to night sides (and low albedos), but it is inconclusive about possible temperature inversions in their atmospheres. HAT-P-12b is a Saturn-mass planet and is one of the coolest planets ever observed during secondary eclipse, along with hot Neptune GJ 436b and hot Saturn WASP-29b. We are able to place 3$\sigma$ upper limits on the secondary eclipse depth of HAT-P-12b in both wavelengths: < 0.042% (3.6 micron) and <0.085% (4.5 micron). We discuss these results in the context of the {\it Spitzer} secondary eclipse measurements of GJ 436b and WASP-29b. It is possible that we do not detect the eclipses of HAT-P-12b due to high eccentricity, but find that weak planetary emission in these wavelengths is a more likely explanation. We place 3 sigma upper limits on the |e cos(omega)| quantity (where e is eccentricity and omega is the argument of periapsis) for HAT-P-3b (<0.0081) and HAT-P-4b (<0.0042), based on the secondary eclipse timings.
Highlights
There are about 177 confirmed exoplanets with orbital periods of less than 10 days and masses greater than 0.1 Jupiter mass, which are often referred to as “hot Jupiters.” About 145 of them transit their host stars.17 Hot Jupiters have high equilibrium temperatures, often over 1000 K, due to their proximity to their parent stars
In a previous paper (Todorov et al 2012), we focused on Warm Spitzer secondary eclipse photometry of three planets (XO-4b, HAT-P-6b and HAT-P-8b) with masses comparable to Jupiter’s orbiting F dwarfs
In principle, possible to use this code to analyze all available Spitzer secondary eclipse data sets in a single investigation, but we find that every data set has peculiarities that need to be addressed on an individual basis
Summary
There are about 177 confirmed exoplanets with orbital periods of less than 10 days and masses greater than 0.1 Jupiter mass, which are often referred to as “hot Jupiters.” About 145 of them transit their host stars. Hot Jupiters have high equilibrium temperatures, often over 1000 K, due to their proximity to their parent stars. Zahnle et al (2009) suggested that sulfur compounds may account for the stratospheric opacity in some hot Jupiter atmospheres Another hypothesis is that the presence or absence of temperature inversions is correlated with the magnetic activity and related UV flux from the host star (Knutson et al 2010). The increased UV flux received by planets orbiting active stars destroys the molecule responsible for the formation of temperature inversions We can test these hypotheses by building up a large sample of hot Jupiters with secondary eclipse measurements and searching for correlations with other system parameters, such as stellar activity or a Ti abundance in the stellar photosphere.
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