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 ${134}_{-33}^{+45}\times $ solar metallicity, with a strongly hazy morning limb of ${1134}_{-194}^{+232}$ K and a haze-free evening limb of ${1516}_{-44}^{+33}$ K. This makes HAT-P-32Ab a promising target for James Webb Space Telescope to look for asymmetric signatures directly in the light curves.