WASP-12b: The hottest transiting planet yet discovered (0812.3240v2)

Abstract: We report on the discovery of WASP-12b, a new transiting extrasolar planet with $R_{\rm pl}=1.79 \pm 0.09 R_J$ and $M_{\rm pl}=1.41 \pm 0.1 M_J$. The planet and host star properties were derived from a Monte Carlo Markov Chain analysis of the transit photometry and radial velocity data. Furthermore, by comparing the stellar spectrum with theoretical spectra and stellar evolution models, we determined that the host star is a super-solar metallicity ([M/H]$=0.3^{+0.05}_{-0.15}$), late-F (T${\rm eff}=6300^{+200}{-100}$ K) star which is evolving off the zero age main sequence. The planet has an equilibrium temperature of T$_{\rm eq}$=2516 K caused by its very short period orbit ($P=1.09$ days) around the hot, 12th magnitude host star. WASP-12b has the largest radius of any transiting planet yet detected. It is also the most heavily irradiated and the shortest period planet in the literature.

• The paper presents the discovery and detailed characterization of WASP-12b, identified as the hottest transiting exoplanet known at the time, notable for its exceptionally large radius (1.79 R_J) and low density orbiting very close to its star.
• Its extremely short 1.09-day orbital period results in intense stellar irradiation from its late-F type host star, driving its equilibrium temperature up to approximately 2516 K, making it one of the most irradiated exoplanets.
• The planet's unusually large radius challenges current planetary formation models, suggesting potential roles for intense stellar irradiation, atmospheric opacity, or tidal heating in maintaining its expanded size.

WASP-12b: The Hottest Transiting Extra-Solar Planet Yet Discovered

The paper on WASP-12b presents a comprehensive paper of this distinctive transiting extrasolar planet. The discovery was made using transit photometry and radial velocity methods, which revealed a planet with a notably large radius and high equilibrium temperature. WASP-12b stands out due to its exceptional characteristics, such as its 1.79 ± 0.09 R_J radius and its orbit around a hot host star with a super-solar metallicity.

Key Findings

• Planetary Characteristics: WASP-12b is notable for its large size, with a radius of 1.79 R_J, making it the largest transiting planet discovered at the time of the paper. The planet has a mass of 1.41 M_J, indicating a low density of 0.24 ρ_J.
• Orbital Dynamics: The planet's very short orbital period of 1.09 days leads to an intense irradiation from its host star, resulting in an equilibrium temperature of approximately 2516 K. This positions WASP-12b among the most heavily irradiated exoplanets on record.
• Host Star Properties: The host star of WASP-12b, identified as a late-F type star with a temperature of 6300 K, showcases a super-solar metallicity of [M/H] = 0.3, and it is evolving off the zero-age main sequence.

Observational Techniques

The paper utilizes a variety of observational methods:

• SuperWASP-N Photometry: This provided the initial identification and photometry of the planet through transit light curve analysis.
• SOPHIE Spectroscopy: Used to obtain radial velocity measurements, helping confirm the mass of the planet and detect any possible eccentricity in its orbit.
• Follow-up Photometry: Conducted in multiple bands using higher resolution telescopes to refine the transit models and confirm the planetary nature of the body detected.

Implications and Future Work

The discovery and analysis of WASP-12b have significant implications for theories of planetary formation and evolution, particularly:

• The unusually large radius of WASP-12b challenges existing models of planet formation and contraction, suggesting that additional factors, such as intense stellar irradiation and possibly high atmospheric metallicity, might play a role in maintaining large radii for some hot Jupiters.
• The potential for enhanced atmospheric opacities or tidal heating could warrant further exploration through theoretical modeling, which might help explain anomalous radius inflations.
• The paper suggests that continued observations, especially those measuring eclipse depths and atmospheric compositions, could provide deeper insights into the atmospheric physics and evolution of such highly irradiated exoplanets.

Conclusion

WASP-12b contributes significantly to the catalog of known exoplanets due to its extreme properties. The findings challenge current theoretical models and call for further paper into the environmental and internal conditions contributing to the development of gas giants in such severe proximity to their host stars. Future observations and modeling efforts are essential to improving understanding of planetary atmospheres, core compositions, and the role of stellar irradiation in the morphological evolution of exoplanets.