Millimeter observations and modeling of the AB Aurigae system
Abstract
(Abriged) We present the results of millimeter observations and a suitable chemical and radiative transfer model of the AB Aur (HD 31293) circumstellar disk and surrounding envelope. The integral molecular content of this system is studied by observing CO, C18O, CS, HCO+, DCO+, H2CO, HCN, HNC, and SiO rotational lines with the IRAM 30-m antenna, while the disk is mapped in the HCO+(1-0) transition with the Plateau de Bure interferometer. Using a flared disk model with a vertical temperature gradient and an isothermal spherical envelope model with a shadowed midplane and two unshielded cones together with a gas-grain chemical network, time-dependent abundances of observationally important molecules are calculated. Then a 2D non-LTE line radiative transfer code is applied to compute excitation temperatures of several rotational transitions of HCO+, CO, C18O, and CS molecules. We synthesize the HCO+(1-0) interferometric map along with single-dish CO(2-1), C18O(2-1), HCO+(1-0), HCO+(3-2), CS(2-1), and CS(5-4) spectra and compared them with the observations. Our disk model successfully reproduces observed interferometric HCO+(1-0) data, thereby constraining the following disk properties: (1) the inclination angle =17+6-3, (2) the position angle φ=8030, (3) the size Rout=400200 AU, (4) the mass Mdisk=1.3·10-2 M (with a factor of 7 uncertainty), and (5) that the disk is in Keplerian rotation. Furthermore, indirect evidence for a local inhomogeneity of the envelope at 600 AU is found...
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