ERRATUM: “PHYSICAL PROPERTIES OF THE 0.94 DAY PERIOD TRANSITING PLANETARY SYSTEM WASP-18” (2009, ApJ, 707, 167)

Abstract

The published version of this article presented high-precision observations of the transiting extrasolar planetary system WASP-18, which is of particular interest because accurate transit timings over a number of years may provide empirical constraints on the tidal quality factor of the host stars of gas giant planets. We have since discovered that the times recorded in the FITS headers of our observations were offset from the true values. This information was used to generate the timestamps in the photometric observations presented and analyzed in the published article, which are therefore also offset by an unknown amount.The problem has been traced back to a software "bug" (or "feature") which meant that the computer clock used in the generation of the FITS headers was only synchronized to an atomic clock when the computer was booted. WASP-18 was observed at the end of the season, when the computer had been running continuously for several months, and so was strongly affected by this problem. The timestamps in the light curve of WASP-18 are uniformly shifted to roughly 85 s later than the true values, calculated by comparison to the orbital ephemeris given by Hellier et al. (2009). A more precise value of the shift will be calculable in the future when an improved orbital ephemeris becomes available.The measured physical properties of the WASP-18 system in the published article are not affected by this problem, as they depend only on the relative values of the timestamps. However, the orbital ephemeris is significantly affected and should not be used in future analyses. For the purposes of planning further observations, we recommend that the orbital ephemeris given by Hellier et al. (2009) should be used.

Searching for Rapid Orbital Decay of WASP-18b

“…WASP: The Wide-Angle Search for Planets (WASP) Project (Pollacco et al 2006) announced the discovery and initial orbital solution of WASP-18b as observed in transit by the WASP-South Survey and in radial velocity with the CORALIE spectrograph (Hellier et al 2009), and confirmed with the Danish 1.5m telescope at ESO (Southworth et al 2009). The Southworth et al (2009) Warm Spitzer: Maxted et al (2013) observed two full phases of WASP-18b's orbit with warm Spitzer, one with the 3.6 µm channel on January 23, 2010, and the other with the 4.5 µm channel on August 23, 2010.…”

“…ephemeris was later found to be erroneous(Southworth et al 2010); we use only the Hellier et al (2009) ephemeris. Left: Two new transits of WASP-18 by its planet observed by TRAPPIST in 2015.…”

Transit timing variations in the WASP-4 planetary system

“…The 2009 season with the Danish Telescope suffered from a timing problem(Southworth et al 2009c(Southworth et al , 2010. We have investigated this further and found that it did not affect any observations of WASP-4 presented here.…”

Homogeneous studies of transiting extrasolar planets - IV. Thirty systems with space-based light curves

“…Some TEPs have a non‐circular orbit which changes the duration of the transit but has a negligible effect on the light‐curve shape (Kipping 2008). I account for this by adding published constraints on orbital eccentricity ( e ) and periastron longitude (ω), with the parameter combinations e cos ω and e sin ω when possible, using the approach outlined in Paper III and Southworth et al (2009c).…”