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Title: 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 ρ 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 {sub ⊙}) and hence large (2.5 R {sub ⊙}) central star with A {sub v} = 12.5 mag and R {sub v} = 6.5 requires less near-infrared excess: the inner-most disk at ≈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 ρ Oph region and disk-lifetimemore » 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 ≈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 3.5 M {sub Jup} planet on a 40 au orbit can qualitatively explain the new disk structure.« less

Authors:
; ;  [1];  [2]; ;  [3];  [4];  [5];  [6]
  1. LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universits, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité (France)
  2. Dpto. Astrofísica, Centro de Astrobiología (INTA-CSIC), ESAC Campus, P.O. Box 78, E-28691, Villanueva de la Cañada (Spain)
  3. Univ. Grenoble Alpes, IPAG, F-38000 Grenoble, France CNRS, IPAG, F-38000 Grenoble (France)
  4. Observatoire de l’Université de Genève, 51 chemin des Maillettes, 1290 Versoix (Switzerland)
  5. European Southern Observatory, Alonso de Cordova 3107, Casilla 19001 Vitacura, Santiago 19 (Chile)
  6. Sydney Institute for Astronomy, School of Physics, The University of Sydney, NSW 2006 (Australia)
Publication Date:
OSTI Identifier:
22663496
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 842; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; APERTURES; ASYMMETRY; COMPARATIVE EVALUATIONS; DUSTS; EMISSION; ENERGY SPECTRA; INTERFEROMETRY; INTERSTELLAR SPACE; LIFETIME; ORBITS; PLANETS; POLYCYCLIC AROMATIC HYDROCARBONS; PROTOPLANETS; RADIANT HEAT TRANSFER; RESOLUTION; RINGS; SIMULATION; STARS

Citation Formats

Schworer, Guillaume, Lacour, Sylvestre, Du Foresto, Vincent Coudé, Huélamo, Nuria, Pinte, Christophe, Chauvin, Gaël, Ehrenreich, David, Girard, Julien, and Tuthill, Peter. A Resolved and Asymmetric Ring of PAHs within the Young Circumstellar Disk of IRS 48. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA74B7.
Schworer, Guillaume, Lacour, Sylvestre, Du Foresto, Vincent Coudé, Huélamo, Nuria, Pinte, Christophe, Chauvin, Gaël, Ehrenreich, David, Girard, Julien, & Tuthill, Peter. A Resolved and Asymmetric Ring of PAHs within the Young Circumstellar Disk of IRS 48. United States. doi:10.3847/1538-4357/AA74B7.
Schworer, Guillaume, Lacour, Sylvestre, Du Foresto, Vincent Coudé, Huélamo, Nuria, Pinte, Christophe, Chauvin, Gaël, Ehrenreich, David, Girard, Julien, and Tuthill, Peter. Tue . "A Resolved and Asymmetric Ring of PAHs within the Young Circumstellar Disk of IRS 48". United States. doi:10.3847/1538-4357/AA74B7.
@article{osti_22663496,
title = {A Resolved and Asymmetric Ring of PAHs within the Young Circumstellar Disk of IRS 48},
author = {Schworer, Guillaume and Lacour, Sylvestre and Du Foresto, Vincent Coudé and Huélamo, Nuria and Pinte, Christophe and Chauvin, Gaël and Ehrenreich, David and Girard, Julien and Tuthill, Peter},
abstractNote = {For one decade, the spectral type and age of the ρ 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 {sub ⊙}) and hence large (2.5 R {sub ⊙}) central star with A {sub v} = 12.5 mag and R {sub v} = 6.5 requires less near-infrared excess: the inner-most disk at ≈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 ρ 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 ≈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 3.5 M {sub Jup} planet on a 40 au orbit can qualitatively explain the new disk structure.},
doi = {10.3847/1538-4357/AA74B7},
journal = {Astrophysical Journal},
number = 2,
volume = 842,
place = {United States},
year = {Tue Jun 20 00:00:00 EDT 2017},
month = {Tue Jun 20 00:00:00 EDT 2017}
}
  • We present the first resolved near-infrared imagery of the transition disk Oph IRS 48 (WLY 2-48), which was recently observed with ALMA to have a strongly asymmetric submillimeter flux distribution. H-band polarized intensity images show a ∼60 AU radius scattered light cavity with two pronounced arcs of emission, one from northeast to southeast and one smaller, fainter, and more distant arc in the northwest. K-band scattered light imagery reveals a similar morphology, but with a clear third arc along the southwestern rim of the disk cavity. This arc meets the northwestern arc at nearly a right angle, revealing the presence ofmore » a spiral arm or local surface brightness deficit in the disk, and explaining the east-west brightness asymmetry in the H-band data. We also present 0.8-5.4 μm IRTF SpeX spectra of this object, which allow us to constrain the spectral class to A0 ± 1 and measure a low mass accretion rate of 10{sup –8.5} M {sub ☉} yr{sup –1}, both consistent with previous estimates. We investigate a variety of reddening laws in order to fit the multiwavelength spectral energy distribution of Oph IRS 48 and find a best fit consistent with a younger, higher luminosity star than previous estimates.« less
  • The physical processes leading to the disappearance of disks around young stars are not well understood. A subclass of transitional disks, the so-called cold disks with large inner dust holes, provides a crucial laboratory for studying disk dissipation processes. IRS 48 has a 30 AU radius hole previously measured from dust continuum imaging at 18.7 {mu}m. Using new optical spectra, we determine that IRS 48 is a pre-main-sequence A0 star. In order to characterize this disk's gas distribution, we obtained AO-assisted Very Large Telescope CRIRES high-resolution (R {approx} 100,000) spectra of the CO fundamental rovibrational band at 4.7 {mu}m. Allmore » CO emission, including that from isotopologues and vibrationally excited molecules, is off-source and peaks at 30 AU. The gas is thermally excited to a rotational temperature of 260 K and is also strongly UV pumped, showing a vibrational excitation temperature of {approx}5000 K. We model the kinematics and excitation of the gas and posit that the CO emission arises from the dust hole wall. Prior imaging of UV-excited polycyclic aromatic hydrocarbon molecules, usually a gas tracer, within the hole makes the large CO hole even more unexpected.« less
  • The processes that form transition disks-disks with depleted inner regions-are not well understood; possible scenarios include planet formation, grain growth, and photoevaporation. Disks with spatially resolved dust holes are rare, but, in general, even less is known about the gas structure. The disk surrounding the A0 star Oph IRS 48 in the nearby {rho} Ophiuchus region has a 30 AU radius hole previously detected in the 18.7 {mu}m dust continuum and in warm CO in the 5 {mu}m fundamental rovibrational band. We present here Submillimeter Array 880 {mu}m continuum imaging resolving an inner hole. However, the radius of the holemore » in the millimeter dust is only 13 AU, significantly smaller than measured at other wavelengths. The nesting structure of the disk is counter intuitive, with increasingly large radius rings of emission seen in the millimeter dust (12.9{sup +1.7}{sub -3.4} AU), 5 {mu}m CO (30 AU), and 18.7 {mu}m dust (peaking at 55 AU). We discuss possible explanations for this structure, including self-shadowing that cools the disk surface layers, photodissociation of CO, and photoevaporation. However, understanding this unusual disk within the stringent multi-wavelength spatial constraints will require further observations to search for cold atomic and molecular gas.« less
  • We report on the {lambda} = 5-36 {mu}m Spitzer Infrared Spectrograph (IRS) spectra of 79 young stellar objects in the very young nearby cluster NGC 1333. NGC 1333's youth enables the study of early protoplanetary disk properties, such as the degree of settling and the formation of gaps and clearings. We construct spectral energy distributions (SEDs) using our IRS data as well as published photometry and classify our sample into SED classes. Using 'extinction-free' spectral indices, we determine whether the disk, envelope, or photosphere dominates the spectrum. We analyze the dereddened spectra of objects that show disk-dominated emission using spectralmore » indices and properties of silicate features in order to study the vertical and radial structure of protoplanetary disks in NGC 1333. At least nine objects in our sample of NGC 1333 show signs of large (several AU) radial gaps or clearings in their inner disk. Disks with radial gaps in NGC 1333 show more nearly pristine silicate dust than their radially continuous counterparts. We compare properties of disks in NGC 1333 to those in three other well-studied regions, Taurus-Auriga, Ophiuchus, and Chamaeleon I, and find no difference in their degree of sedimentation and dust processing.« less
  • A global disk oscillation implemented in the viscous decretion disk (VDD) model has been used to reproduce most of the observed properties of the well known Be star ζ Tau. 48 Librae shares several similarities with ζ Tau—they are both early-type Be stars, display shell characteristics in their spectra, and exhibit cyclic V / R variations—but has some marked differences as well, such as a much denser and more extended disk, a much longer V / R cycle, and the absence of the so-called triple-peak features. We aim to reproduce the photometric, polarimetric, and spectroscopic observables of 48 Librae withmore » a self-consistent model, and to test the global oscillation scenario for this target. Our calculations are carried out with the three-dimensional NLTE radiative transfer code HDUST. We employ a rotationally deformed, gravity-darkened central star surrounded by a disk whose unperturbed state is given by the VDD model. A two-dimensional global oscillation code is then used to calculate the disk perturbation and superimpose it on the unperturbed disk. A very good, self-consistent fit to the time-averaged properties of the disk is obtained with the VDD. The calculated perturbation has a period P = 12 years, which agrees with the observed period, and the behavior of the V / R cycle is well reproduced by the perturbed model. The perturbed model improves the fit to the photometric data and reproduces some features of the observed spectroscopic data. Some suggestions to improve the synthesized spectroscopy in a future work are given.« less