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WASP-12
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Title: The Apparently Decaying Orbit of WASP-12
Author: Kishore C. Patra, Joshua N. Winn, Matthew J. Holman, Liang Yu, Drake Deming, Fei Dai

We present new transit and occultation times for the hot Jupiter WASP-12b. The data are compatible with a constant period derivative: \dot{P}=-29±3 ms yr^-1 and P/ \dot{P}=3.2 Myr. However, it is difficult to tell whether we have observed orbital decay, or a portion of a 14-year apsidal precession cycle. If interpreted as decay, the star's tidal quality parameter Q* is about 2 x 10^5. If interpreted as precession, the planet's Love number is 0.44±0.10. Orbital decay appears to be the more parsimonious model: it is favored by delta_x˛=5.5 despite having two fewer free parameters than the precession model. The decay model requires the unlikely coincidence that WASP-12 was discovered within the final ~0.2% of its existence, but this harmonizes with independent evidence that the planet is nearing disruption. Precession does not invoke any temporal coincidence, but only if some unknown mechanism is maintaining an eccentricity of approx 0.002 in the face of rapid tidal circularization. A speculative possibility is Phinney's (1992) theory of eccentricity excitation by gravitational perturbations from the star's convective eddies. To distinguish unequivocally between decay and precession will probably require a few more years of monitoring. Particularly helpful will be occultation timing in 2019 and thereafter.

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RE: WASP-12b
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Title: A Detection of Water in the Transmission Spectrum of the Hot Jupiter WASP-12b and Implications for its Atmospheric Composition
Author: Laura Kreidberg, Michael R. Line, Jacob L. Bean, Kevin B. Stevenson, Jean-Michel Desert, Nikku Madhusudhan, Jonathan J. Fortney, Joanna K. Barstow, Gregory W. Henry, Michael Williamson, Adam P. Showman

Detailed characterisation of exoplanets has begun to yield measurements of their atmospheric properties that constrain the planets' origins and evolution. For example, past observations of the dayside emission spectrum of the hot Jupiter WASP-12b indicated that its atmosphere has a high carbon-to-oxygen ratio (C/O > 1), suggesting it had a different formation pathway than is commonly assumed for giant planets. Here we report a precise near-infrared transmission spectrum for WASP-12b based on six transit observations with the Hubble Space Telescope/Wide Field Camera 3. We bin the data in 13 spectrophotometric light curves from 0.84 - 1.67 µm and measure the transit depths to a median precision of 51 ppm. We retrieve the atmospheric properties using the transmission spectrum and find strong evidence for water absorption (7 sigma confidence). This detection marks the first high-confidence, spectroscopic identification of a molecule in the atmosphere of WASP-12b. The retrieved 1 sigma water volume mixing ratio is between 10-5 - 10-2, which is consistent with C/O > 1 to within 2 sigma. However, we also introduce a new retrieval parametrisation that fits for C/O and metallicity under the assumption of chemical equilibrium. With this approach, we constrain C/O to 0.5^{+0.2}_{-0.3} at 1 sigma and rule out a carbon-rich atmosphere composition (C/O>1) at >3 sigma confidence. Further observations and modelling of the planet's global thermal structure and dynamics would aid in resolving the tension between our inferred C/O and previous constraints. Our findings highlight the importance of obtaining high-precision data with multiple observing techniques in order to obtain robust constraints on the chemistry and physics of exoplanet atmospheres.

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Title: Hubble Space Telescope observations of the NUV transit of WASP-12b
Author: J. D. Nichols, G. A. Wynn, M. Goad, R. D. Alexander, S. L. Casewell, S. W. H Cowley, M. R. Burleigh, J. T. Clarke, D. Bisikalo

We present new observations of four closely-spaced NUV transits of the hot Jupiter-like exoplanet WASP-12b using HST/COS, significantly increasing the phase resolution of the observed NUV light curve relative to previous observations, while minimising the temporal variation of the system. We observe significant excess NUV absorption during the transit, with mean normalised in-transit fluxes of Fnormsimeq 0.97, i.e. simeq 2-5 sigma deeper than the optical transit level of simeq 0.986 for a uniform stellar disk (the exact confidence level depending on the normalisation method used). We further observe an asymmetric transit shape, such that the post-conjunction fluxes are overall simeq 2-3 sigma higher than pre-conjunction values, and characterised by rapid variations in count rate between the pre-conjunction and out of transit levels. We do not find evidence for an early ingress to the NUV transit as suggested by earlier HST observations. However, we show that the NUV count rate observed prior to the optical transit is highly variable, but overall simeq 2.2-3.0 sigma below the post-transit values and comparable in depth to the optical transit, possibly forming a variable region of NUV absorption from at least phase phi simeq 0.83, limited by the data coverage.

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Title: Transmission Spectroscopy of the Hot-Jupiter WASP-12b from 0.7 to 5 microns
Author: Kevin B. Stevenson, Jacob L. Bean, Andreas Seifahrt, Jean-Michel Desert, Nikku Madhusudhan, Marcel Bergmann, Laura Kreidberg, Derek Homeier

Since the first report of a potentially non-solar carbon-to-oxygen ratio (C/O) in its dayside atmosphere, the highly irradiated exoplanet WASP-12b has been under intense scrutiny and the subject of many follow-up observations. Additionally, the recent discovery of stellar binary companions ~1" from WASP-12 has obfuscated interpretation of the observational data. Here we present new ground-based multi-object transmission-spectroscopy observations of WASP-12b that we acquired over two consecutive nights in the red optical with Gemini-N/GMOS. After correcting for the influence of WASP-12's stellar companions, we find that these data rule out a cloud-free, H2 atmosphere with no additional opacity sources. We detect features in the transmission spectrum that may be attributed to metal oxides (such as TiO and VO) for an O-rich atmosphere or to metal hydrides (such as TiH) for a C-rich atmosphere. We also reanalyzed NIR transit-spectroscopy observations of WASP-12b from HST/WFC3 and broadband transit photometry from Warm Spitzer. We attribute the broad spectral features in the WFC3 data to either H2O or CH4 and HCN for an O-rich or C-rich atmosphere, respectively. The Spitzer data suggest shallower transit depths than the models predict at infrared wavelengths, albeit at low statistical significance. A multi-instrument, broad-wavelength analysis of WASP-12b suggests that the transmission spectrum is well approximated by a simple Rayleigh scattering model with a planet terminator temperature of 1870 +/- 130 K. We conclude that additional high-precision data and isolated spectroscopic measurements of the companion stars are required to place definitive constraints on the composition of WASP-12b's atmosphere.

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Exoplanet WASP-12b was discovered on the 1st April 2008

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Title: Multi-site campaign for transit timing variations of WASP-12 b: possible detection of a long-period signal of planetary origin
Authors: G. Maciejewski, D. Dimitrov, M. Seeliger, St. Raetz, L. Bukowiecki, M. Kitze, R. Errmann, G. Nowak, A. Niedzielski, V. Popov, C. Marka, K. Gozdziewski, R. Neuhaeuser, J. Ohlert, T. C. Hinse, J. W. Lee, C.-U. Lee, J.-N. Yoon, A. Berndt, H. Gilbert, Ch. Ginski, M. M. Hohle, M. Mugrauer, T. Roell, T. O. B. Schmidt, N. Tetzlaff, L. Mancini, J. Southworth, M. Dall'Ora, S. Ciceri, R. Zambelli, G. Corfini, H. Takahashi, K. Tachihara, J. M. Benko, K. Sarneczky, Gy. M. Szabo, T. N. Varga, M. Vanko, Y. C. Joshi, W. P. Chen

The transiting planet WASP-12 b was identified as a potential target for transit timing studies because a departure from a linear ephemeris was reported in the literature. Such deviations could be caused by an additional planet in the system. We attempt to confirm the existence of claimed variations in transit timing and interpret its origin. We organised a multi-site campaign to observe transits by WASP-12 b in three observing seasons, using 0.5-2.6-metre telescopes. We obtained 61 transit light curves, many of them with sub-millimagnitude precision. The simultaneous analysis of the best-quality datasets allowed us to obtain refined system parameters, which agree with values reported in previous studies. The residuals versus a linear ephemeris reveal a possible periodic signal that may be approximated by a sinusoid with an amplitude of 0.00068±0.00013 d and period of 500±20 orbital periods of WASP-12 b. The joint analysis of timing data and published radial velocity measurements results in a two-planet model which better explains observations than single-planet scenarios. We hypothesize that WASP-12 b might be not the only planet in the system and there might be the additional 0.1 Jupiter mass body on a 3.6-d eccentric orbit. A dynamical analysis indicates that the proposed two-planet system is stable over long timescales.

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Title: Near-UV Absorption, Chromospheric Activity, and Star-Planet Interactions in the WASP-12 system
Authors: C. A. Haswell, L. Fossati, T. Ayres, K. France, C. S. Froning, S. Holmes, U. C. Kolb, R. Busuttil, R. A. Street, L. Hebb, A. Collier Cameron, B. Enoch, V. Burwitz, J. Rodriguez, R. G. West, D. Pollacco, P. J. Wheatley, A. Carter

We observed the extreme close-in hot Jupiter system, WASP-12, with HST. Near-UV transits up to three times deeper than the optical transit of WASP-12b reveal extensive diffuse gas, extending well beyond the Roche lobe. The distribution of absorbing gas varies between visits. The deepest NUV transits are at wavelength ranges with strong photospheric absorption, implying the absorbing gas may have temperature and composition similar to the stellar photosphere. Our spectra reveal significantly enhanced absorption (greater than 3 \sigma below the median) at ~200 wavelengths on each of two HST visits; 65 of these wavelengths are consistent between the two visits, using a strict criterion for velocity matching which excludes matches with velocity shifts exceeding ~20 km/s. Excess transit depths are robustly detected throughout the inner wings of the MgII resonance lines independently on both HST visits. We detected absorption in FeII 2586A, the heaviest species yet detected in an exoplanet transit. The MgII line cores have zero flux, emission cores exhibited by every other observed star of similar age and spectral type are conspicuously absent. WASP-12 probably produces normal MgII profiles, but the inner portions of these strong resonance lines are likely affected by extrinsic absorption. The required Mg+ column is an order of magnitude greater than expected from the ISM, though we cannot completely dismiss that possibility. A more plausible source of absorption is gas lost by WASP-12b. We show that planetary mass loss can produce the required column. Our Visit 2 NUV light curves show evidence for a stellar flare. We show that some of the possible transit detections in resonance lines of rare elements may be due instead to non-resonant transitions in common species. We present optical observations and update the transit ephemeris.

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Title: Re-evaluating Hot Jupiter WASP-12b: An Update
Authors: Ian J. M. Crossfield, Travis Barman, Brad M. S. Hansen, Ichi Tanaka, Tadayuki Kodama

The hot Jupiter WASP-12b is one of the largest, hottest, and best-studied extrasolar planets. We revisit our recent analysis of WASP-12b's emission spectrum in light of near-infrared spectroscopic measurements which have been claimed to support either a hydride-dominated or carbon-rich atmospheric composition. We show that this new spectrum is still consistent with a featureless blackbody, indicating a nearly isothermal photosphere on the planet's day side. Thus the ensemble of occultation measurements for WASP-12b is still insufficient to constrain the planet's atmospheric composition.

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Title: 3D Gas Dynamic Simulation of the Interaction Between the Exoplanet WASP-12b and Its Host Star
Authors: D. Bisikalo, P. Kaygorodov, D. Ionov, V. Shematovich, H. Lammer, L. Fossati

HST transit observations in the near-UV performed in 2009 made WASP-12b one of the most "mysterious" exoplanets; the system presents an early-ingress, which can be explained by the presence of optically thick matter located ahead of the planet at a distance of 4-5 planet radii. This work follows previous attempts to explain this asymmetry with an exospheric outflow or a bow shock, induced by a planetary magnetic field, and provides a numerical solution of the early-ingress, though we did not perform any radiative transfer calculation. We performed pure 3D gas dynamic simulations of the plasma interaction between WASP-12b and its host star, and describe the flow pattern in the system. In particular, we show that the overfilling of the planet's Roche lobe leads to a noticeable outflow from the upper atmosphere in the direction of the L1 and L2 points. Due to the conservation of the angular momentum, the flow to the L1 point is deflected in the direction of the planet's orbital motion, while the flow towards L2 is deflected in the opposite direction, resulting in a non-axisymmetric envelope, surrounding the planet. The supersonic motion of the planet inside the stellar wind leads to the formation of a bow shock with a complex shape. The existence of the bow shock slows down the outflow through the L1 and L2 points, allowing us to consider a long-living flow structure which is in the steady-state.

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Giant Planet Being Blown Away Behind a Cloudy Veil

A star is slowly snuffing the life out of an alien planet. But in a macabre twist, material stripped out of the dying world's atmosphere has become a death shroud enveloping the gas giant and its star.
First discovered in 2008, WASP-12b is a so-called hot Jupiter - a gas giant planet orbiting extremely close to its parent star.

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