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 mi
cron 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]
Circumstellar disc evolution is paramount for the understanding of planet formation. The GASPS program aims at determining the circumstellar gas and solid mass around ~250 pre-main-sequence Herbig Ae and TTauri stars. We aim to understand the origin
and nature of the circumstellar matter orbiting 51 Oph, a young (<1 Myr) luminous B9.5 star. We obtained continuum and line observations with the PACS instrument on board the Herschel Space Observatory and continuum data at 1.2 mm with the IRAM 30m telescope. The SED and line fluxes were modelled using the physico-chemo radiative transfer code ProDiMo. We detected a strong emission by OI at 63 microns using the Herschel Space Observatory. The [OI] emission at 145 microns, the [CII] emission at 158 microns, the high-J CO emissions, and the warm water emissions were not detected. Continuum emission was detected at 1.2 mm. The continuum from the near- to the far-infrared and the [OI] emission are well explained by the emission from a compact hydrostatic disc model with a gas mass of 5E-6 MSun, 100 times that of the solid mass. However, this model fails to match the continuum millimeter flux, which hints at a cold outer disc with a mass in solids of 1E-6 MSun or free-free emission from a photoevaporative disc wind. This outer disc can either be devoid of gas and/or is to cold to emit in the [OI] line. A very flat extended disc model (Rout=400 AU) with a fixed vertical structure and dust settling matches all photometric points and most of the [O I] flux. The observations can be explained by an extended flat disc where dust grains have settled. However, a flat gas disc cannot be reproduced by hydrostatic disc models. The low mass of the 51 Oph inner disc in gas and dust may be explained either by the fast dissipation of an initial massive disc or by a very small initial disc mass.
The carbon monoxide rovibrational emission from discs around Herbig Ae stars and T Tauri stars with strong ultraviolet emissions suggests that fluorescence pumping from the ground X1 Sigma+ to the electronic A1 Pi state of CO should be taken into acc
ount in disc models. We implemented a CO model molecule that includes up to 50 rotational levels within nine vibrational levels for the ground and A excited states in the radiative photochemical code ProDiMo. We took CO collisions with hydrogen molecules, hydrogen atoms, helium, and electrons into account. We estimated the missing collision rates using standard scaling laws and discussed their limitations. UV fluorescence and IR pumping impact on the population of ro-vibrational v > 1 levels. The v = 1 rotational levels are populated at rotational temperatures between the radiation temperature around 4.6 micron and the gas kinetic temperature. The UV pumping efficiency increases with decreasing disc mass. The consequence is that the vibrational temperatures, which measure the relative populations between the vibrational levels, are higher than the disc gas kinetic temperatures (suprathermal population). Rotational temperatures from fundamental transitions derived using optically thick 12CO lines do not reflect the gas kinetic temperature. CO pure rotational levels with energies lower than 1000 K are populated in LTE but are sensitive to a number of vibrational levels included in the model. The 12CO pure rotational lines are highly optically thick for transition from levels up to Eupper=2000 K. (abridged)
