# CO Detected in CI Tau b: Hot Start Implied by Planet Mass and M$_K$

## TL;DR

This study confirms the existence of CI Tau b through direct CO detection, estimates its mass and brightness, and suggests it formed via a hot start mechanism, marking it as the youngest directly characterized exoplanet around a T Tauri star.

## Contribution

First direct spectroscopic detection of CO in CI Tau b's atmosphere, providing a model-independent mass estimate and insights into its formation mechanism.

## Key findings

- Confirmed CI Tau b's existence via CO detection
- Estimated planet's mass as 11.6 M_J
- Indicated a hot start formation process

## Abstract

We acquired high resolution IR spectra of CI Tau, the host star of one of the few young planet candidates amenable to direct spectroscopic detection. We confirm the planet's existence with a direct detection of CO in the planet's atmosphere. We also calculate a mass of 11.6 M$_J$ based on the amplitude of its radial velocity variations. We estimate its flux contrast with its host star to get an absolute magnitude estimate for the planet of 8.17 in the K band. This magnitude implies the planet formed via a "hot start" formation mechanism. This makes CI Tau b the youngest confirmed exoplanet as well as the first exoplanet around a T Tauri star with a directly determined, model-independent, dynamical mass.