HAT-P-2 - Phase variations and additional companion?

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HAT-P-2 - Phase variations and additional companion?

Post by Sirius_Alpha on 20th February 2013, 10:48 pm

Orbital Phase Variations of the Eccentric Giant Planet HAT-P-2b
http://arxiv.org/abs/1302.5084

We present the first secondary eclipse and phase curve observations for the highly eccentric hot Jupiter HAT-P-2b in the 3.6, 4.5, 5.8, and 8.0 \mu m bands of the Spitzer Space Telescope. The 3.6 and 4.5 \mu m data sets span an entire orbital period of HAT-P-2b, making them the longest continuous phase curve observations obtained to date and the first full-orbit observations of a planet with an eccentricity exceeding 0.2. We present an improved non-parametric method for removing the intrapixel sensitivity variations in Spitzer data at 3.6 and 4.5 \mu m that robustly maps position-dependent flux variations. We find that the peak in planetary flux occurs at 4.39+/-0.28, 5.84+/-0.39, and 4.68+/-0.37 hours after periapse passage with corresponding maxima in the planet/star flux ratio of 0.1138%+/-0.0089%, 0.1162%+/-0.0080%, and 0.1888%+/-0.0072% in the 3.6, 4.5, and 8.0 \mu m bands respectively. We compare our measured secondary eclipse depths to the predictions from a one-dimensional radiative transfer model, which suggests the possible presence of a transient day side inversion in HAT-P-2b's atmosphere near periapse. We also derive improved estimates for the system parameters, including its mass, radius, and orbital ephemeris. Our simultaneous fit to the transit, secondary eclipse, and radial velocity data allows us to determine the eccentricity and argument of periapse of HAT-P-2b's orbit with a greater precision than has been achieved for any other eccentric extrasolar planet. We also find evidence for a long-term linear trend in the radial velocity data. This trend suggests the presence of another substellar companion in the HAT-P-2 system, which could have caused HAT-P-2b to migrate inward to its present-day orbit via the Kozai mechanism.


Last edited by Sirius_Alpha on 23rd February 2013, 10:53 am; edited 1 time in total (Reason for editing : Made title more accurate)

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Re: HAT-P-2 - Phase variations and additional companion?

Post by Lazarus on 23rd February 2013, 8:29 am

Way too early to call the second object a planet...

We know the orbital period of c must be significantly longer than six years since we do not detect any significant curvature in our long term RV trend, so we set a lower limit of Mc sin ic ~ 15 MJ and ac ~ 10 AU based on an orbital period for c of 24 years.
and
Using HAT-P-2s parallax distance of 119 8 pc and estimated age of 2.6 0.5 Gyr as determined by Pl et al. (2010) through a combined isochrone, light curve, and spectroscopic analysis, we find that our diffraction-limited observations are sensitive to companions on the hydrogen-fusing boundary for separations beyond ≈ 1″. Interior to this region, the combination of imaging and RV data eliminates most low-mass stars, though late-type M-dwarf tertiaries located at ~ 40 AU could cause the long-term Doppler drift yet simultaneously evade direct detection (Figure 11)
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Re: HAT-P-2 - Phase variations and additional companion?

Post by Sirius_Alpha on 23rd February 2013, 10:53 am

Excellent point. Thread title modified.

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Re: HAT-P-2 - Phase variations and additional companion?

Post by Led_Zep on 8th May 2013, 5:51 am

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Re: HAT-P-2 - Phase variations and additional companion?

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