Source-linked AI summary
WASP-3b: a strongly-irradiated transiting gas-giant planet
D. Pollacco, I. Skillen, A. Collier Cameron, B. Loeillet, H. C. Stempels, F. Bouchy, N. P. Gibson, L. Hebb, G. Hebrard, Y. C. Joshi, I. McDonald, B. Smalley, A. M. S. Smith, R. A. Street, S. Udry, R. G. West, D. M. Wilson, P. J. Wheatley, S. Aigrain, C. R. Benn, V. A. Bruce, D. J. Christian, W. I. Clarkson, B. Enoch, A. Evans, A. Fitzsimmons, C. A. Haswell, C. Hellier, S. Hickey, S. T. Hodgkin, K. Horne, M. Hrudkova, J. Irwin, S. R. Kane, F. P. Keenan, T. A. Lister, P. Maxted, M. Mayor, C. Moutou, A. J. Norton, J. P. Osborne, N. Parley, F. Pont, D. Queloz, R. Ryans, E. Simpson
TL;DR
The paper addresses the need to identify and characterize strongly irradiated transiting gas giants. It combines transit photometry, radial-velocity spectroscopy, and joint modelling, finding that WASP-3b has a mass of 1.76 +0.08 -0.14 M_J and radius 1.31 +0.07 -0.14 R_J and is among the hottest known exoplanets.
Problem
Transiting exoplanets are valuable because their geometry permits direct mass and radius measurements for testing planetary structure and evolution models.
Method
The study combines SuperWASP and follow-up transit photometry with SOPHIE radial velocities and simultaneous transit-reflex-motion modelling.
Results
1.76 +0.08 -0.14 M_J and 1.31 +0.07 -0.14 R_J are derived for WASP-3b, whose host-star properties and close orbit place it among the hottest known exoplanets.
Takeaways & Limitations
WASP-3b is an excellent candidate for future observational tests of the hot-stratosphere hypothesis.
Takeaways & Limitations
Higher-precision photometry contains uncorrected systematic noise estimated at 2 millimag, with periodicities of 2 and approximately 20 minutes.
Abstract
from arXiv · showhide
We report the discovery of WASP-3b, the third transiting exoplanet to be discovered by the WASP and SOPHIE collaboration. WASP-3b transits its host star USNO-B1.0 1256-0285133 every 1.846834+-0.000002 days. Our high precision radial-velocity measurements present a variation with amplitude characteristic of a planetary-mass companion and in-phase with the light-curve. Adaptive optics imaging shows no evidence for nearby stellar companions, and line-bisector analysis excludes faint, unresolved binarity and stellar activity as the cause of the radial-velocity variations. We make a preliminary spectroscopic analysis of the host star finding it to have Teff = 6400+-100 K and log g = 4.25+-0.05 which suggests it is most likely an unevolved main sequence star of spectral type F7-8V. Our simultaneous modelling of the transit photometry and reflex motion of the host leads us to derive a mass of 1.76 +0.08 -0.14 M_J and radius 1.31 +0.07-0.14 R_J for WASP-3b. The proximity and relative temperature of the host star suggests that WASP-3b is one of the hottest exoplanets known, and thus has the potential to place stringent constraints on exoplanet atmospheric models.
1 INTRODUCTION
Transiting exoplanets provide unusually direct constraints on planetary masses and radii, enabling tests of internal-structure and evolution models. Against this context, the WASP and SOPHIE collaboration reports the discovery of the strongly irradiated gas giant WASP-3b.
- Transit geometry constrains orbital inclination, allowing exoplanet masses and radii to be determined directly.
- Mass-radius measurements provide probes of exoplanet internal structure through comparison with planetary structure and evolution models.
- The limited sample of studied transiting exoplanets already shows remarkable diversity in physical parameters.
- Radial-velocity surveys discovered most known exoplanetary systems, while wide-field photometric imaging was expected to become a dominant detection method.
- The WASP and SOPHIE collaboration announces WASP-3b as a relatively high-mass, strongly irradiated gas-giant exoplanet.
2 OBSERVATIONS AND DATA REDUCTION
The study combines wide-field survey photometry, higher-precision follow-up light curves, and SOPHIE spectroscopy to characterize WASP-3. These observations establish the transit signal, refine its ephemeris, and provide radial-velocity measurements with quantified uncertainties and instrumental limitations.
- SuperWASP-N Photometry: 3969 SuperWASP-N data points were collected over 118 days, identifying WASP-3 as a high-priority transit candidate.
- SuperWASP-N Photometry: 17 transits were observed in the original SuperWASP-N photometry, with more than half a transit captured on 10 occasions.
- SuperWASP-N Photometry: The survey transit had a depth of 0.013 mag and a duration of 137 minutes, yielding an initial ephemeris with P = 1.846800 days.
- Higher precision photometric observations: Follow-up photometry used the IAC 80 cm telescope in V and I bands and the Keele 60 cm telescope in R band.
- Higher precision photometric observations: The IAC observations comprised 327 images, while the Keele run obtained 644 20-second R-band observations.
- OHP 1.9 m and SOPHIE: SOPHIE spectroscopy provided seven usable spectra from eight observing nights, with simultaneous stellar and sky spectra acquired at R = 40000.
- OHP 1.9 m and SOPHIE: Moonlight contamination was corrected using the sky-fibre cross-correlation function before Gaussian fitting of the stellar signal.
- OHP 1.9 m and SOPHIE: The radial-velocity measurements had an average photon-noise uncertainty of 14 m/s, with an additional approximately 10 m/s component added in quadrature.
3 RESULTS AND ANALYSES
The analysis combines SOPHIE spectroscopy, transit photometry, radial velocities, and MCMC modelling to characterize WASP-3 and its planetary system. Spectral fitting constrains the host star, while simultaneous transit–reflex-motion modelling determines system parameters and tests their consistency.
- Stellar parameters: The SOPHIE radial-velocity table reports measurements with uncertainties combining photon noise and 10 m/s of added jitter.The table also records CCF width, contrast, and signal-to-noise ratio.
- Stellar parameters: SME spectral synthesis uses five wavelength regions to constrain Teff, log g, metallicity, and lithium abundance, although the combined spectrum cannot support detailed abundance analysis.The regions include Hα, Na I D, Mg I b, metal lines, and Li I.
- MCMC analysis: The transit and reflex-velocity signals are modelled simultaneously with nine parameters describing the light curve and stellar radial-velocity orbit.The model includes transit timing, period, duration, depth, impact parameter, stellar mass, velocity amplitude, eccentricity, and periastron longitude.
- MCMC analysis: The transit model uses the Mandel–Agol small-planet approximation with nonlinear limb darkening, while the orbital semi-major axis follows from Kepler’s third law and stellar mass.Photometric and radial-velocity offsets and a combined χ2 quantify the fit.
- MCMC analysis: The fitted parameters are consistent with the earlier spectroscopic analysis, while the preferred stellar surface gravity is 4.25 < log g < 4.35 and the impact parameter is 0.4 < b < 0.6.Lower gravities produce unsatisfactory ingress and egress fits and implausibly inflated stellar and planetary radii.
4 DISCUSSION
WASP-3b is a relatively massive, strongly irradiated transiting gas giant whose measured properties place it among the hottest known exoplanets. The updated comparisons also examine relationships between planetary and stellar properties, though the radius–host-mass correlation remains weak.
- System properties: 1.76 +0.08 −0.14 M_J and 1.31 +0.07 −0.14 R_J are the derived mass and radius of WASP-3b.Its host star has Teff = 6400 ± 100 K and log g = 4.25 ± 0.05, consistent with spectral type F7-8V.
- System properties: WASP-3b is among the most massive known transiting exoplanets.The paper marks WASP-3b in the updated mass–radius comparisons.
- Population comparisons: The updated comparisons consider planet radius versus host mass, planet mass versus orbital period, and surface gravity versus orbital period.The radius–host-mass correlation remains weak even after adding newly discovered systems and excluding the two most massive objects.
- Irradiation and atmosphere: WASP-3b is one of the most strongly irradiated and hottest known exoplanets, second only to OGLE-TR-56b and comparable to OGLE-TR-132.Its close orbit, large planetary radius, and host-star effective temperature contribute to this assessment.
- Irradiation and atmosphere: Its irradiation may permit TiO and VO to remain gaseous above the temperature minimum, producing a strongly absorbing hot stratosphere.The paper links this possibility to an anomalously high infrared brightness temperature.