the structure rotates to keep the
GMOS slit mask aligned on the
stars.) The origin of this effect is
unknown and is currently being
investigated. However, we found
that it can be modeled (black lines
in the top two panels of Figure 1)
and removed from the data.
In Figure 2, we show the corrected high-precision spectroscopic
light curves that we obtained with
GMOS-N by binning the data for
the first night over 15-nm-wide
spectral channels. The measured
transit depths vary as a function
of wavelength; this gives us the
planet’s transmission spectrum,
which in turn, tells us about its atmospheric composition.
Because WASP-12b’s orbital period is clo ͔