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Turbulence is thought to be a key driver of the evolution of protoplanetary disks, regulating the mass accretion process, the transport of angular momentum, and the growth of dust particles. We intend to determine the magnitude of the turbulent motions in the outer parts (> 100 AU) of the disk surrounding DM Tau. Turbulent motions can be constrained by measuring the nonthermal broadening of line emission from heavy molecules. We used the IRAM Plateau de Bure interferometer to study emission from the CS molecule in the disk of DM Tau. High spatial (1.4 x 1 ) and spectral resolution (0.126 km/s) CS J=3-2 images provide constraints on the molecule distribution and velocity structure of the disk. A low sensitivity CS J=5-4 image was used in conjunction to evaluate the excitation conditions. We analyzed the data in terms of two parametric disk models, and compared the results with detailed time-dependent chemical simulations. The CS data confirm the relatively low temperature suggested by observations of other simple molecules. The intrinsic linewidth derived from the CS J=3-2 data is much larger than expected from pure thermal broadening. The magnitude of the derived nonthermal component depends only weakly on assumptions about the location of the CS molecules with respect to the disk plane. Our results indicate turbulence with a Mach number around 0.4 - 0.5 in the molecular layer. Geometrical constraints suggest that this layer is located near one scale height, in reasonable agreement with chemical model predictions.
M-stars are the most common hosts of planetary systems in the Galaxy. Protoplanetary disks around M-stars thus offer a prime opportunity to study the chemistry of planet-forming environments. We present an ALMA survey of molecular line emission towar
The volatile composition of a planet is determined by the inventory of gas and ice in the parent disk. The volatile chemistry in the disk is expected to evolve over time, though this evolution is poorly constrained observationally. We present ALMA ob
Context. Several sulfur-bearing molecules are observed in the interstellar medium and in comets, in strong contrast to protoplanetary disks where only CS, H$_2$CS and SO have been detected so far. Aims. We combine observations and chemical models to
(abridged) We used the IRAM 30-m to perform a sensitive wideband survey of 30 protoplanetary disks in the Taurus Auriga region. We simultaneously observed HCO$^+$(3-2), HCN(3-2), C$_2$H(3-2), CS(5-4), and two transitions of SO. We combine the results
Molecular line emission from protoplanetary disks is a powerful tool to constrain their physical and chemical structure. Nevertheless, only a few molecules have been detected in disks so far. We take advantage of the enhanced capabilities of the IRAM