A Resolved and Asymmetric Ring of PAHs within the Young Circumstellar Disk of IRS 48

Abstract

For one decade, the spectral type and age of the rho Oph object IRS-48 were subject to debate. and mystery. Modeling its disk with mid-infrared to millimeter observations led to various explanations to account for the complex intricacy of dust. holes and gas-depleted regions. We present multi-epoch high-angular-resolution interferometric near-infrared data of spatially resolved emissions in the first 15 au of IRS-48, known to have very strong polycyclic aromatic hydrocarbon (PAH) emissions within this dust-depleted region. We make use of new Sparse-Aperture-Masking data to instruct a revised radiative-transfer model, where spectral energy distribution fluxes and interferometry are jointly fitted. Neutral and ionized PAH, very small grains (VSG), and classical silicates are incorporated into the model; new stellar parameters and extinction laws are explored. A bright (42 L-circle dot) and. hence large (2.5 R-circle dot) central star with A(v) = 12.5 mag and R-v = 6.5 requires less near-infrared excess: the innermost disk at approximate to 1 au is incompatible with the interferometric data. The revised stellar parameters place this system on a 4 Myr evolutionary track,. four. times younger than the previous estimations, which. is. in better agreement with the surrounding rho Oph region and disk-lifetime. observations. The disk-structure solution converges to a classical-grain. outer. disk from 55 au combined with an unsettled and fully resolved VSG and PAH ring, between 11 and 26 au. We find two overluminosities in the PAH ring at color-temperatures consistent with the radiative transfer simulations; one follows a Keplerian circular orbit at 14 au. We show a depletion of a factor of approximate to 5 of classical dust grains up to 0.3 mm compared to very small particles: the IRS-48 disk is nearly void of dust grains in the first 55 au. A 3.5M(Jup) planet on a 40 au orbit can qualitatively explain the new disk. structure.