Ya. N. Pavlyuchenkov

Millimeter Observations and Modeling of the AB Aurigae System

We present the results of millimeter observations and a suitable chemical and radiative transfer model of the AB Aurigae (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 two-dimensional 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 compare 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 i=17+6-3 deg, (2) the position angle φ=80deg+/-30deg, (3) the size Rout=400+/-200 AU, (4) the mass Mdisk=1.3×10-2 Msolar (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. The single-dish spectra are synthesized for three different cases, namely, for the disk model, for the envelope model, and for their combination. An overall reasonable agreement between all modeled and acquired line intensities, widths, and profiles is achieved for the latter model, with the exception of the CS (5-4) data that require the presence of high-density clumpy structures in the model. This allows us to constrain the physical structure of the AB Aur inner envelope: (1) its mass-average temperature is about 35+/-14 K; (2) the density goes inversely down with the radius, ρ~r-1.0+/-0.3, starting from an initial value n0~3.9×105 cm-3 at 400 AU; and (3) the mass of the shielded region within 2200 AU is about 4×10-3 Msolar (the latter two quantities are uncertain by a factor of ~7). In addition, evolutionary nature and lifetime for dispersal of the AB Aur system and Herbig Ae/Be systems in general are discussed.

Rotating molecular outflows: the young T Tauri star in CB 26 ⋆

Context: The disk-outflow connection is thought to play a key role in extracting excess angular momentum from a forming proto-star. Although jet rotation has been observed in a few objects, no rotation of molecular outflows has been unambiguously reported so far. Aims: We report new millimeter-interferometric observations of the edge-on T Tauri star - disk system in the isolated Bok globule CB 26. The aim of these observations was to study the disk-outflow relation in this 1 Myr old low-mass young stellar object. Methods: The IRAM PdBI array was used to observe 12CO(2-1) at 1.3 mm in two configurations, resulting in spectral line maps with 1.5´´ resolution. We use an empirical parameterized steady-state outflow model combined with 2-D line radiative transfer calculations and χ^2-minimization in parameter space to derive a best-fit model and constrain parameters of the outflow. Results: The data reveal a previously undiscovered collimated bipolar molecular outflow of total length ≈2000 AU, escaping perpendicular to the plane of the disk. We find peculiar kinematic signatures that suggest that the outflow is rotating with the same orientation as the disk. However, we could not ultimately exclude jet precession or two misaligned flows as possible origins of the observed peculiar velocity field. There is indirect indication that the embedded driving source is a binary system, which, together with the youth of the source, could provide a clue to the observed kinematic features of the outflow. Conclusions: CB 26 is so far the most promising source in which to study the rotation of a molecular outflow. Assuming that the outflow is rotating, we compute and compare masses, mass flux, angular momenta, and angular momentum flux of the disk and outflow and derive disk dispersal timescales of 0.5 ldots 1 Myr, comparable to the age of the system. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). Also based on observations collected at the Centro Astronomico Hispano Aleman (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut fur Astronomie and the Instituto de Astrofisica de Andalucia (CSIC). A complete set of channel maps is available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/494/147.

Molecular Emission Line Formation in Prestellar Cores

We investigate general aspects of molecular line formation under conditions typical of prestellar cores. Focusing on simple linear molecules, we study the formation of their rotational lines with radiative transfer simulations. We present a thermalization diagram to show the effects of collisions and radiation on the level excitation. We construct a detailed scheme (contribution chart) to illustrate the formation of emission-line profiles. This chart can be used as an efficient tool to identify which parts of the cloud contribute to a specific line profile. We show how molecular line characteristics for uniform model clouds depend on hydrogen density, molecular column density, and kinetic temperature. The results are presented in a two-dimensional plane to illustrate mutual effects of the physical factors. We also use a core model with a nonuniform density distribution and chemical stratification to study the effects of cloud contraction and rotation on spectral line maps. We discuss the main issues that should be taken into account when dealing with interpretation and simulation of observed molecular lines.

Gas-phase CO depletion and N2H+ abundances in starless cores

Context. In the dense and cold interiors of starless molecular cloud cores, a number of chemical processes allow for the formation of complex molecules and the deposition of ice layers on dust grains. Dust density and temperature maps of starless cores derived from Herschel continuum observations constrain the physical structure of the cloud cores better than ever before. We use these to model the temporal chemical evolution of starless cores. Aims: We derive molecular abundance profiles for a sample of starless cores. We then analyze these using chemical modeling based on dust temperature and hydrogen density maps derived from Herschel continuum observations. Methods: We observed the

Dust dynamics and evolution in expanding H ii regions. I. Radiative drift of neutral and charged grains

^{12}

Determining the Parameters of Massive Protostellar Clouds via Radiative Transfer Modeling

CO (2-1),

Polycyclic aromatic hydrocarbons in spatially resolved extragalactic star-forming complexes

^{13}

A method for molecular-line radiative-transfer computations and its application to a two-dimensional model for the starless core L1544

CO (2-1), C

Influence of luminosity bursts on properties of protostellar disks

^{18}

Modeling of Protostellar Clouds and Their Observational Properties

O (2-1) and N