# Identification of Absorption Features in an Extrasolar Planet Atmosphere

## TL;DR

This paper detects water absorption in the atmosphere of exoplanet HD209458b by modeling its transmitted spectrum and comparing it with multi-wavelength eclipse measurements, providing insights into atmospheric composition and cloud effects.

## Contribution

It presents a cloud-free atmospheric model with solar abundances that matches observed eclipse depths across a broad wavelength range, offering new constraints on condensate removal and metallicity.

## Key findings

- Water absorption confirmed in HD209458b's atmosphere.
- Model agrees with eclipse measurements from ultraviolet to near-infrared.
- Constraints on condensate removal and metallicity established.

## Abstract

Water absorption is identified in the atmosphere of HD209458b by comparing models for the planet's transmitted spectrum to recent, multi-wavelength, eclipse-depth measurements (from 0.3 to 1 microns) published by Knutson et al. (2007). A cloud-free model which includes solar abundances, rainout of condensates, and photoionization of sodium and potassium is in good agreement with the entire set of eclipse-depth measurements from the ultraviolet to near-infrared. Constraints are placed on condensate removal by gravitational settling, the bulk metallicity, and the redistribution of absorbed stellar flux. Comparisons are also made to the Charbonneau et al. (2002) sodium measurements.