AB Aur, a Rosetta stone for studies of planet formation

Abstract

Context. The sulfur abundance is poorly known in most environments. Yet, deriving the sulfur abundance is key to understanding the evolution of the chemistry from molecular clouds to planetary atmospheres. We present observations of H 2 S 1 10 − 1 01 at 168.763 GHz toward the Herbig Ae star AB Aur. Aims. We aim to study the abundance of sulfuretted species toward AB Aur and to constrain how different species and phases contribute to the sulfur budget. Methods. We present new NOrthern Extended Millimeter Array (NOEMA) interferometric observations of the continuum and H 2 S 1 10 − 1 01 line at 168.763 GHz toward AB Aur. We derived radial and azimuthal profiles and used them to compare the geometrical distribution of different species in the disk. Assuming local thermodynamical equilibrium (LTE), we derived column density and abundance maps for H 2 S, and we further used Nautilus to produce a more detailed model of the chemical abundances at different heights over the mid-plane at a distance of r=200 au. Results. We have resolved H 2 S emission in the AB Aur protoplanetary disk. The emission comes from a ring extending from 0.67 (∼109 au) to 1.69 (∼275 au). Assuming T=30 K, n H =10 9 cm −3 , and an ortho-to-para ratio of three, we derived a column density of (2.3±0.5)×10 13 cm −2 . Under simple assumptions, we derived an abundance of (3.1±0.8)×10 −10 with respect to H nuclei, which we compare with Nautilus models to deepen our understanding of the sulfur chemistry in protoplanetary disks. Chemical models indicate that H 2 S is an important sulfur carrier in the solid and gas phase. We also find an important transition at a height of ∼12 au, where the sulfur budget moves from being dominated by ice species to being dominated by gas species. Conclusions. We confirm that present-day models still struggle to simultaneously reproduce the observed column densities of the different sulfuretted species, and the observed abundances are still orders of magnitude away from the cosmic sulfur abundance. Studying sulfuretted species in detail in the different phases of theinterstellar medium is key to solving the issue.

AB Aur: A Rosetta stone for planet formation theories

“…We assumed a gas-to-dust ratio of 40, no sulfur depletion ([S/H] = 1.5 ⇥ 10 −5 ), and C/O=0.7. The details of the model can be found in the original papers [8,15]. Our model results in an H 2 S column density of 3.5⇥10 13 cm −2 , in good agreement, given the uncertainties, with the value derived assuming LTE.…”

“…We observed the H 2 S 1 10 -1 01 transition with NOEMA (see the velocity integrated intensity map in Fig. 1 bottom right panel) with an angular resolution of 1.19" ⇥ 0.97" [15]. This is the second time that resolved observations of H 2 S towards a protoplanetary disk were performed after the observations toward GG Tau [16].…”

The vibronic state dependent predissociation of H2S: determination of all fragmentation processes

“…[4][5][6][7] For example, the estimated abundances of S-containing species in the outer layers of the photodissociation region in the Horsehead nebula are only ∼25% of the cosmic value 8 and orders of magnitude lower abundances have been suggested in cold molecular clouds. [9][10][11] This apparent depletion is explained by assuming that much of the (undetected) sulfur is locked up in solids, i.e. in dust grains and in icy mantles.…”

Formation of H2CO and CH3OH in the Protoplanetary Disks

“…Planets are formed among the protoplanetary disks (PPDs) [1] while protoplanetary disks are formed from the molecular cloud core collapse. Protoplanetary disks are composed of gas and dust particles [2].…”