FUV Irradiation and the Heat Signature of Accretion in Protoplanetary Disk Atmospheres
- National Optical Astronomical Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)
- Astronomy Department, 501 Campbell Hall, University of California, Berkeley, CA 94720 (United States)
Although stars accrete mass throughout the first few million years of their lives, the physical mechanism that drives disk accretion in the T Tauri phase is uncertain, and diagnostics that probe the nature of disk accretion have been elusive, particularly in the planet formation region of the disk. Here we explore whether an accretion process such as the magnetorotational instability (MRI) could be detected through its “heat signature,” the energy it deposits in the disk atmosphere. To examine this possibility, we investigate the impact of accretion-related mechanical heating and energetic stellar irradiation (FUV and X-rays) on the thermal-chemical properties of disk atmospheres at planet formation distances. We find that stellar FUV irradiation (Lyα and continuum), through its role in heating and photodissociation, affects much of the upper warm (400–2000 K) molecular layer of the atmosphere, and the properties of the layer are generally in good agreement with the observed molecular emission features of disks at UV, near-infrared, and mid-infrared wavelengths. At the same time, the effect of FUV irradiation is restricted to the upper molecular layer of the disk, even when irradiation by Lyα is included. The region immediately below the FUV-heated layer is potentially dominated by accretion-related mechanical heating. As cooler (90–400 K) CO, water, and other molecules are potential diagnostics of the mechanically heated layer, emission line studies of these diagnostics might be used to search for evidence of the MRI in action.
- OSTI ID:
- 22875798
- Journal Information:
- Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 847; ISSN ASJOAB; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
SURFACE LAYER ACCRETION IN CONVENTIONAL AND TRANSITIONAL DISKS DRIVEN BY FAR-ULTRAVIOLET IONIZATION
Shielding by water and OH in FUV and X-ray irradiated protoplanetary disks