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Abstract
Context. The radius of an exoplanet may be affected by various factors, including irradiation received from the host star, the mass of the planet and its heavy element content. A significant number of transiting exoplanets have now been discovered for which the mass, radius, semimajor axis, host star metallicity and stellar effective temperature are known.
Aims. We use multivariate regression models to determine the powerlaw dependence of planetary radius on planetary equilibrium temperature Teq, planetary mass Mp, stellar metallicity [Fe/H], orbital semimajor axis a, and tidal heating rate Htidal, for 119 transiting planets in three distinct mass regimes.
Methods. We fit models initially to all 119 planets, resulting in fairly high scatter between fitted and observed radii, and subsequently to three subsets of these planets: Saturnmass planets, Jupitermass planets, and highmass planets.
Results. We find models for each subset that fit the observed planetary radii well and show the importance of the various environmental parameters on each subset.
Conclusions. We determine that heating leads to larger planet radii, as expected, increasing mass leads to increased or decreased radii of lowmass (<0.5 RJ) and highmass (>2.0 RJ) planets, respectively (with no mass effect on Jupitermass planets), and increased hoststar metallicity leads to smaller planetary radii, indicating a relationship between hoststar metallicity and planet heavy element content. For Saturnmass planets, a good fit to the radii may be obtained from log(Rp/RJ) = –0.077 + 0.450 log(Mp/MJ) – 0.314 [Fe/H] + 0.671 log(a/AU) + 0.398 log(Teq/K). The radii of Jupitermass planets may be fit by log(Rp/RJ) = − 2.217 + 0.856 log(Teq/K) + 0.291 log(a/AU). Highmass planets’ radii are best fit by log(Rp/RJ) = –1.067 + 0.380 log(Teq/K) – 0.093 log(Mp/MJ) – 0.057 [Fe/H] + 0.019 log(Htidal/1 × 1020). These equations produce a very good fit to the observed radii, with a mean absolute difference between fitted and observed radius of 0.11 RJ, compared to the mean reported uncertainty in observed radius of 0.07 RJ. A clear distinction is seen between the coredominated Saturnmass (0.1–0.5 MJ) planets, whose radii are determined almost exclusively by their mass and heavy element content, and the gaseous envelopedominated Jupitermass (0.5–2.0 MJ) planets, whose radii increase strongly with irradiating flux, partially offset by a powerlaw dependence on orbital separation.
Aims. We use multivariate regression models to determine the powerlaw dependence of planetary radius on planetary equilibrium temperature Teq, planetary mass Mp, stellar metallicity [Fe/H], orbital semimajor axis a, and tidal heating rate Htidal, for 119 transiting planets in three distinct mass regimes.
Methods. We fit models initially to all 119 planets, resulting in fairly high scatter between fitted and observed radii, and subsequently to three subsets of these planets: Saturnmass planets, Jupitermass planets, and highmass planets.
Results. We find models for each subset that fit the observed planetary radii well and show the importance of the various environmental parameters on each subset.
Conclusions. We determine that heating leads to larger planet radii, as expected, increasing mass leads to increased or decreased radii of lowmass (<0.5 RJ) and highmass (>2.0 RJ) planets, respectively (with no mass effect on Jupitermass planets), and increased hoststar metallicity leads to smaller planetary radii, indicating a relationship between hoststar metallicity and planet heavy element content. For Saturnmass planets, a good fit to the radii may be obtained from log(Rp/RJ) = –0.077 + 0.450 log(Mp/MJ) – 0.314 [Fe/H] + 0.671 log(a/AU) + 0.398 log(Teq/K). The radii of Jupitermass planets may be fit by log(Rp/RJ) = − 2.217 + 0.856 log(Teq/K) + 0.291 log(a/AU). Highmass planets’ radii are best fit by log(Rp/RJ) = –1.067 + 0.380 log(Teq/K) – 0.093 log(Mp/MJ) – 0.057 [Fe/H] + 0.019 log(Htidal/1 × 1020). These equations produce a very good fit to the observed radii, with a mean absolute difference between fitted and observed radius of 0.11 RJ, compared to the mean reported uncertainty in observed radius of 0.07 RJ. A clear distinction is seen between the coredominated Saturnmass (0.1–0.5 MJ) planets, whose radii are determined almost exclusively by their mass and heavy element content, and the gaseous envelopedominated Jupitermass (0.5–2.0 MJ) planets, whose radii increase strongly with irradiating flux, partially offset by a powerlaw dependence on orbital separation.
Original language  English 

Article number  A99 
Number of pages  11 
Journal  Astronomy & Astrophysics 
Volume  540 
DOIs  
Publication status  Published  1 Apr 2012 
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Dive into the research topics of 'Factors affecting the radii of closein transiting exoplanets'. Together they form a unique fingerprint.Projects
 2 Finished

Astrophysics at St Andrews:2012  2014: Astrophysics at St Andrews: 2012  2014
Horne, K. D. (PI)
Science & Technology Facilities Council
1/10/11 → 31/03/12
Project: Standard

Wide Area Search for Planets: Project support for the Wide Area Search for Planets
Cameron, A. C. (PI)
Science & Technology Facilities Council
1/08/08 → 31/07/11
Project: Standard