# Low albedos of hot to ultra-hot Jupiters in the optical to near-infrared transition regime

## TL;DR

This study measures the optical to near-infrared albedo of hot Jupiters, finding low reflectivity and providing the first z' band albedo constraint for HAT-P-32b, indicating minimal influence of silicate clouds.

## Contribution

First z' band albedo measurement for HAT-P-32b and application of a consistent method to multiple hot Jupiters revealing generally low optical reflectivity.

## Key findings

- HAT-P-32b has an albedo A_g < 0.2 in the z' band.
- Hot to ultra-hot Jupiters exhibit low optical to near-infrared reflectivity.
- The results disfavor large silicate cloud influence on planetary daysides.

## Abstract

The depth of a secondary eclipse contains information of both the thermally emitted light component of a hot Jupiter and the reflected light component. If the dayside atmosphere of the planet is assumed to be isothermal, it is possible to disentangle both. In this work, we analyze 11 eclipse light curves of the hot Jupiter HAT-P-32b obtained at 0.89 $\mu$m in the z' band. We obtain a null detection for the eclipse depth with state-of-the-art precision, -0.01 +- 0.10 ppt. We confirm previous studies showing that a non-inverted atmosphere model is in disagreement to the measured emission spectrum of HAT-P-32b. We derive an upper limit on the reflected light component, and thus, on the planetary geometric albedo $A_g$. The 97.5%-confidence upper limit is $A_g$ < 0.2. This is the first albedo constraint for HAT-P-32b, and the first z' band albedo value for any exoplanet. It disfavors the influence of large-sized silicate condensates on the planetary day side. We inferred z' band geometric albedo limits from published eclipse measurements also for the ultra-hot Jupiters WASP-12b, WASP-19b, WASP-103b, and WASP-121b, applying the same method. These values consistently point to a low reflectivity in the optical to near-infrared transition regime for hot to ultra-hot Jupiters.