IRSF SIRIUS JHKs Simultaneous Transit Photometry of GJ1214b

TL;DR

This study presents simultaneous JHKs band transit photometry of GJ1214b, finding consistent radius ratios with previous work and supporting a flat atmosphere, but also noting discrepancies that require further investigation.

Contribution

First simultaneous JHKs band transit observations of GJ1214b using IRSF/SIRIUS, providing new constraints on its atmospheric properties.

Findings

Radius ratios consistent with previous studies within 1σ.

Results support a flat transmission spectrum, indicating water-dominated or cloudy/hazy atmosphere.

Discrepancy in Ks band measurements suggests need for further observations.

Abstract

We report high precision transit photometry of GJ1214b in JHKs bands taken simultaneously with the SIRIUS camera on the IRSF 1.4m telescope at Sutherland, South Africa. Our MCMC analyses show that the observed planet-to-star radius ratios in JHKs bands are R_{\rm p}/R_{\rm s,J} = 0.11833 \pm 0.00077, R_{\rm p}/R_{\rm s,H} = 0.11522 \pm 0.00079, R_{\rm p}/R_{\rm s,Ks} = 0.11459 \pm 0.00099, respectively. The radius ratios are well consistent with the previous studies by Bean et al. (2011) within 1\sigma, while our result in Ks band is shallower than and inconsistent at 4\sigma\ level with the previous measurements in the same band by Croll et al. (2011). We have no good explanation for this discrepancy at this point. Our overall results support a flat transmission spectrum in the observed bands, which can be explained by a water-dominated atmosphere or an atmosphere with extensive high-altitude clouds or haze. To solve the discrepancy of the radius ratios and to discriminate a definitive atmosphere model for GJ1214b in the future, further transit observations around Ks band would be especially important.