The Different Evolution of Gas and Dust in Disks around Sun-like and Cool Stars

TL;DR

This study compares the dust and gas properties of disks around sun-like and cool stars, revealing differences in molecular composition, silicate features, and disk evolution, with implications for planet formation.

Contribution

It provides the first comprehensive comparative analysis of disks around sun-like and cool stars using Spitzer/IRS data, highlighting key differences in their evolution and composition.

Findings

Detection of organic molecules in brown dwarf disks

Significant under-abundance of HCN relative to C2H2 in cool star disks

Cool stars have more processed silicate grains and longer disk lifetimes

Abstract

We present the first comprehensive, comparative Spitzer/IRS study of the dust and gas properties of disks around young sun-like stars (K1-M5) and cool stars/brown dwarfs (M5-M9). The comparison of these two large samples of over 60 sources reveal major differences in the evolution of both the dust and gas components.We report the first detections of organic molecules in disks around brown dwarfs. The detection rate statistics and the line flux ratios of HCN and C2H2 show a striking diference between the two samples, demonstrating a significant under-abundance of HCN relative to C2H2 in the disk surface of cool stars. We propose this to originate from the large difference in the UV-irradiation around the two types of sources. The statistical comparison of the 10 micron silicate emission features also reveals a significant difference between the two samples. Cool stars and brown dwarfs show weaker features arising from more processed silicate grains in the disk atmosphere. These findings complement previous indications of flatter disk structures and longer disk lifetimes around cool stars.