Gas lines from the 5-Myr old optically thin disk around HD141569A. Herschel observations and modeling

TL;DR

This study combines Herschel and other observations with modeling to analyze the gas and dust properties of the transitional disk around HD141569A, revealing its structure, composition, and mass distribution.

Contribution

It provides the first detailed modeling of the gas and dust in HD141569A's disk using combined Herschel, Spitzer, VLT, and CO data, revealing the disk's structure and composition.

Findings

Oxygen lines originate from the inner disk.

CII emission is more extended than oxygen lines.

Disk gas mass is between 2.5 and 4.9E-4 solar masses.

Abstract

At the distance of 99-116 pc, HD141569A is one of the nearest HerbigAe stars that is surrounded by a tenuous disk, probably in transition between a massive primordial disk and a debris disk. We observed the fine-structure lines of OI at 63 and 145 micron and the CII line at 157 micron with the PACS instrument onboard the Herschel Space Telescope as part of the open-time large programme GASPS. We complemented the atomic line observations with archival Spitzer spectroscopic and photometric continuum data, a ground-based VLT-VISIR image at 8.6 micron, and 12CO fundamental ro-vibrational and pure rotational J=3-2 observations. We simultaneously modeled the continuum emission and the line fluxes with the Monte Carlo radiative transfer code MCFOST and the thermo-chemical code ProDiMo to derive the disk gas- and dust properties assuming no dust settling. The models suggest that the oxygen lines are emitted from the inner disk around HD141569A, whereas the [CII] line emission is more extended. The CO submillimeter flux is emitted mostly by the outer disk. Simultaneous modeling of the photometric and line data using a realistic disk structure suggests a dust mass derived from grains with a radius smaller than 1 mm of 2.1E-7 MSun and from grains with a radius of up to 1 cm of 4.9E-6 MSun. We constrained the polycyclic aromatic hydrocarbons (PAH) mass to be between 2E-11 and 1..4E-10 MSun assuming circumcircumcoronene (C150H30) as the representative PAH. The associated PAH abundance relative to hydrogen is lower than those found in the interstellar medium (3E-7) by two to three orders of magnitude. The disk around HD141569A is less massive in gas (2.5 to 4.9E-4 MSun or 67 to 164 MEarth) and has a flat opening angle (<10%). [abridged]