Overview of WASP-42 b and WASP-49 b: Discovery and Characteristics of Two Transiting Sub-Jupiters
The paper presents the discovery and subsequent analysis of two new transiting exoplanets, WASP-42 b and WASP-49 b, resulting from observations conducted under the WASP (Wide Angle Search for Planets) survey. These objects are characterized as sub-Jupiters, with masses and radii considerably smaller than the giant planets traditionally associated with the classification of Hot Jupiters.
WASP-42 b
WASP-42 b orbits a K1 star located approximately 160 parsecs from Earth and possesses a mass of $0.500 \pm 0.035$ $M_{J}$, consistent with other low-mass gas giants. Its radius of $1.080 \pm 0.057$ $R_{J}$ indicates a somewhat inflated size relative to its mass, though not exceptionally so compared to similar planets. This object demonstrates a non-zero eccentricity of $0.060 \pm 0.013$, suggesting an interaction history potentially involving migration and circularization processes as outlined in planet formation theories. The equilibrium temperature of WASP-42 b is estimated at 995 K, aligning with expected values for close-in exoplanets. In examining the host star's properties, the authors derive a possible older age using gyrochronological methods and isochrone placements, though the precise age remains uncertain.
WASP-49 b
Orbiting a G6 star roughly 170 parsecs away, WASP-49 b presents contrasting characteristics. It has an even lower mass of $0.378 \pm 0.027$ $M_{J}$ coupled with a slightly bloated radius of $1.115 \pm 0.047$ $R_{J}$, suggesting significant inflation mechanisms despite its age. Unlike WASP-42 b, WASP-49 b's orbit is found to be nearly circular, with no significant eccentricity within measurement limits. The equilibrium temperature is estimated at 1369 K. This planet is remarkable for its metal-poor stellar environment and is more akin to HD149026 b in terms of mass, yet notably differing in terms of density and radius.
Observational Methods and Analysis
The discovery was enabled by extensive photometric monitoring via WASP-South and follow-up observations using EulerCam, TRAPPIST, and Faulkes South telescopes. Radial velocity measurements supporting these findings were obtained with the CORALIE and HARPS spectrographs. Both planets have been subjected to rigorous analysis, including determining fundamental planet properties and constraints on eccentricity and stellar rotation. The study also utilized Bayesian models to assess radial velocity solutions, offering substantial evidence for the identification of these planets' orbital parameters.
Implications and Future Work
The detection and characterization of WASP-42 b and WASP-49 b contribute valuable data to the population of sub-Jovian planets, particularly those orbiting within small separations (< 0.1 AU) of their host stars. These findings bolster understanding of the mass-radius relationship and the role of stellar radiation in inflating planetary envelopes. Both planets serve as intriguing subjects for future research, particularly with regard to their atmospheric characteristics and potential migration histories.
The study exemplifies the importance of thorough follow-up observations in confirming planetary characteristics and understanding dynamic orbital histories. As planet discovery methods improve, further attention to similar systems may unravel insights into planet formation pathways and the diversity observed within the exoplanet catalog. Continued advancements in observational technology and analysis techniques are crucial for expanding the database of known exoplanets and refining theoretical models on planet characterization.