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

Guillaume Schworer, Sylvestre Lacour, Nuria Huélamo, Christophe Pinte, Gaël Chauvin, Vincent Coudé du Foresto, David Ehrenreich, Julien Girard, Peter Tuthill. 2017. A Resolved and Asymmetric Ring of PAHs within the Young Circumstellar Disk of IRS 48. Astrophysical Journal 842, 2 DOI: 10.3847/1538-4357/aa74b7

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.

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