Five New Transits of the Super-Neptune HD 149026

TL;DR

This study presents new transit observations of the super-Neptune HD 149026, refining its planetary radius, transit timing, and orbital parameters, confirming high metallicity consistent with theoretical models.

Contribution

The paper provides five new transit measurements that improve the accuracy of the planet's radius and orbital parameters, and refines stellar and planetary characteristics.

Findings

Planet-to-star radius ratio: 0.0491^{+0.0018}_{-0.0005}

Planetary radius: 0.71 +/- 0.05 R_Jup

Orbital eccentricity constraint: e cos(omega) = -0.0014 +/- 0.0012

Abstract

We present new photometry of HD 149026 spanning five transits of its "super-Neptune" planet. In combination with previous data, we improve upon the determination of the planet-to-star radius ratio: R_p/R_star = 0.0491^{+0.0018}_{-0.0005}. We find the planetary radius to be 0.71 +/- 0.05 R_Jup, in accordance with previous theoretical models invoking a high metal abundance for the planet. The limiting error is the uncertainty in the stellar radius. Although we find agreement among four different ways of estimating the stellar radius, the uncertainty remains at 7%. We also present a refined transit ephemeris and a constraint on the orbital eccentricity and argument of pericenter, e cos(omega) = -0.0014 +/- 0.0012, based on the measured interval between primary and secondary transits.