2018年4月

# Radiation Hydrodynamics Simulations of Photoevaporation of Protoplanetary Disks by Ultraviolet Radiation: Metallicity Dependence

The Astrophysical Journal

DOI
10.3847/1538-4357/aab70b

Protoplanetary disks are thought to have lifetimes of several million yr in the solar neighborhood, but recent observations suggest that the disk lifetimes are shorter in a low-metallicity environment. We perform a suite of radiation hydrodynamics simulations of photoevaporating protoplanetary disks to study their long-term evolution of ̃10,000 yr and the metallicity dependence of mass-loss rates. Our simulations follow hydrodynamics, extreme and far-ultraviolet (FUV) radiative transfer, and nonequilibrium chemistry in a self-consistent manner. Dust-grain temperatures are also calculated consistently by solving the radiative transfer of the stellar irradiation and grain (re-)emission. We vary the disk metallicity over a wide range of {10}&lt;SUP&gt;-4&lt;/SUP&gt; {Z}&lt;SUB&gt;☉ &lt;/SUB&gt;≤slant Z≤slant 10 {Z}&lt;SUB&gt;☉ &lt;/SUB&gt;. The photoevaporation rate is lower with higher metallicity in the range of {10}&lt;SUP&gt;-1&lt;/SUP&gt; {Z}&lt;SUB&gt;☉ &lt;/SUB&gt;≲ Z≲ 10 {Z}&lt;SUB&gt;☉ &lt;/SUB&gt;, because dust shielding effectively prevents FUV photons from penetrating and heating the dense regions of the disk. The photoevaporation rate sharply declines at even lower metallicities in {10}&lt;SUP&gt;-2&lt;/SUP&gt; {Z}&lt;SUB&gt;☉ &lt;/SUB&gt;≲ Z≲ {10}&lt;SUP&gt;-1&lt;/SUP&gt; {Z}&lt;SUB&gt;☉ &lt;/SUB&gt;, because FUV photoelectric heating becomes less effective than dust-gas collisional cooling. The temperature in the neutral region decreases, and photoevaporative flows are excited only in an outer region of the disk. At {10}&lt;SUP&gt;-4&lt;/SUP&gt; {Z}&lt;SUB&gt;☉ &lt;/SUB&gt;≤slant Z≲ {10}&lt;SUP&gt;-2&lt;/SUP&gt; {Z}&lt;SUB&gt;☉ &lt;/SUB&gt;, H I photoionization heating acts as a dominant gas heating process and drives photoevaporative flows with a roughly constant rate. The typical disk lifetime is shorter at Z = 0.3 {Z}&lt;SUB&gt;☉ &lt;/SUB&gt; than at Z={Z}&lt;SUB&gt;☉ &lt;/SUB&gt;, being consistent with recent observations of the extreme outer galaxy....

リンク情報
DOI
https://doi.org/10.3847/1538-4357/aab70b
URL
http://orcid.org/0000-0003-3127-5982