Protoplanetary Disks, Mid-Infrared Dips, and Disk Gaps

Details Protoplanetary Disks, Mid-Infrared Dips, and Disk Gaps Protoplanetary Disks, Mid-Infrared Dips, and Disk Gaps

Sep 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...469..366b&link_type=abstract

Astrophysical Journal v.469, p.366

Astronomy and Astrophysics

Astronomy

32

Infrared: Stars, Stars: Circumstellar Matter, Stars: Planetary Systems, Stars: Pre-Main-Sequence, Radiative Transfer, Stars: Individual Constellation Name: T Tauri

Scientific paper

The spectral energy distributions (SEDs) of pre-main-sequence (PM S) stars provide observational constraints on the physical properties of the protoplanetary disks that dominate PMS emission at wavelengths longer than a few microns. Many PMS stars have a peculiar signature: a relatively smooth SED from ˜1 μm to 100 μm, accompanied by a broad dip in the mid-infrared (˜10 μm). These mid-IR dips could be caused by gaps in a protoplanetary disk with a simple power-law structure, or they could arise in a continuous disk with a more realistic structure than the power-law assumption permits. A two-dimensional radiative hydrodynamics code has been used to construct a suite of detailed protoplanetary disk models, where the thermal structure is determined by the balance between radiative cooling and compressional or viscous heating (Boss 1996). Here we use a two-dimensional ray-tracing code (Yorke 1986) to compute the SEDs of these disk models for comparison with the nominal SED of the prototypical PMS star with a mid-IR dip, T Tauri. We have reproduced the SED of the same disk as that used by Boss & Yorke (1993), which yielded a good fit to the T Tau spectrum, and have extended the results to include models with varied disk masses, stellar masses, inclinations, opacities, mass accretion rates, α-viscosities, and midplane density profiles. For disks undergoing mass accretion from their envelopes at a rate of ˜10-6 to 10-5 Msun yr-1, disks with masses of ˜0.01-0.02 Msun orbiting a solar-mass star yield SEDs close to that of T Tau. Variations in the dust grain opacity have relatively little effect, but a steeper midplane profile (ρ0 ∝r-2, instead of ρ0 ∝r-3/2) leads to a mid-IR hump rather than a dip. For a disk mass of ˜0.02 Msun, disk mass accretion rates in the range of 10-7 to 10-5 Msun yr-1 are indicated for T Tau. When viscous heating is employed, a viscous α = 0.01 yields a good fit, whereas α = 0.1 produces a large mid-IR excess. These SEDs should be useful for interpreting the Infrared Space Observatory (ISO) and the Space Infrared Telescope Facility (SIRTF) observations of protoplanetary disks.

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