NICMOS Observations of the Transiting Hot Jupiter XO-1b

TL;DR

This study refines the physical parameters of the XO-1b exoplanet and its host star using HST NICMOS data, achieving high-precision transit timings and ruling out nearby Earth-mass resonant planets.

Contribution

First NICMOS-based detailed characterization of XO-1b, including improved transit timings and correction of instrumental noise, enhancing exoplanet parameter accuracy.

Findings

XO-1b radius measured as 1.21 RJup

Transit timings with 9-15 second precision

No Earth-mass planet in 2:1 resonance detected

Abstract

We refine the physical parameters of the transiting hot Jupiter planet XO-1b and its stellar host XO-1 using HST NICMOS observations. XO-1b has a radius Rp=1.21+/-0.03 RJup, and XO-1 has a radius Rs=0.94+/-0.02 RSun, where the uncertainty in the mass of XO-1 dominates the uncertainty of Rp and Rs. There are no significant differences in the XO-1 system properties between these broad-band NIR observations and previous determinations based upon ground-based optical observations. We measure two transit timings from these observations with 9 s and 15 s precision. As a residual to a linear ephemeris model, there is a 2.0 sigma timing difference between the two HST visits that are separated by 3 transit events (11.8 days). These two transit timings and additional timings from the literature are sufficient to rule out the presence of an Earth mass planet orbiting in 2:1 mean motion resonance coplanar with XO-1b. We identify and correct for poorly understood gain-like variations present in NICMOS time series data. This correction reduces the effective noise in time series photometry by a factor of two, for the case of XO-1.