A Two-limb Explanation for the Optical-to-infrared Transmission Spectrum of the Hot Jupiter HAT-P-32Ab

Abstract

We present a new optical transmission spectrum of the hot Jupiter HAT-P-32Ab acquired with the Carnegie Observatories Spectrograph and Multiobject Imaging Camera (COSMIC) on the Palomar 200 inch Hale Telescope (P200). The P200/COSMIC transmission spectrum, covering a wavelength range of 3990–9390 Å, is composed of 25 spectrophotometric bins with widths ranging from 200 to 400 Å and consistent with previous transit measurements obtained in the common wavelength range. We derive a combined optical transmission spectrum based on measurements from five independent instruments, which, along with the 1.1–1.7 μm spectrum acquired by the Hubble Space Telescope and two Spitzer measurements, exhibits an enhanced scattering slope blueward of a relatively flat optical continuum, a water absorption feature at 1.4 μm, and a carbon dioxide feature at 4.4 μm. We perform Bayesian spectral retrieval analyses on the 0.3–5.1 μm transmission spectrum and find that it can be well explained by a two-limb approximation of solar metallicity, with a strongly hazy morning limb of K and a haze-free evening limb of K. This makes HAT-P-32Ab a promising target for James Webb Space Telescope to look for asymmetric signatures directly in the light curves.