Context. We describe and benchmark two sophisticated chemical models developed by the Heidelberg and Bordeaux astrochemistry groups. Aims. The main goal of this study is to elaborate on a few well-described tests for state-of-the-art astrochemical codes covering a range of physical conditions and chemical processes, in particular those aimed at constraining current and future interferometric observations of protoplanetary disks. Methods. We considered three physical models: a cold molecular cloud core, a hot core, and an outer region of a T Tauri disk. Our chemical network (for both models) is based on the original gas-phase osu_03_2008 ratefile and includes gas-grain interactions and a set of surface reactions for the H-, O-, C-, S-, and N-bearing molecules. The benchmarking was performed with the increasing complexity of the considered processes: (1) the pure gas-phase chemistry, (2) the gas-phase chemistry with accretion and desorption, and (3) the full gas-grain model with surface reactions. The chemical evolution is modeled within 10 9 years using atomic initial abundances with heavily depleted metals and hydrogen in its molecular form. Results. The time-dependent abundances calculated with the two chemical models are essentially the same for all considered physical cases and for all species, including the most complex polyatomic ions and organic molecules. This result, however, required a lot of effort to make all necessary details consistent through the model runs, e.g., definition of the gas particle density, density of grain surface sites, or the strength and shape of the UV radiation field. Conclusions. The reference models and the benchmark setup, along with the two chemical codes and resulting time-dependent abundances are made publicly available on the internet. This will facilitate and ease the development of other astrochemical models and provide nonspecialists with a detailed description of the model ingredients and requirements to analyze the cosmic chemistry as studied, e.g., by (sub-) millimeter observations of molecular lines.

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 12 CO(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 . . . 1 Myr, comparable to the age of the system.

Aims. To constrain the ionization fraction in protoplanetary disks, we present new high-sensitivity interferometric observations of N 2 H + in three disks surrounding DM Tau, LkCa 15, and MWC 480. Methods. We used the IRAM PdBI array to observe the N 2 H + J = 1−0 line and applied a χ 2 -minimization technique to estimate corresponding column densities. These values are compared, together with HCO + column densities, to results of a steady-state disk model with a vertical temperature gradient coupled to gas-grain chemistry. Results. We report two N 2 H + detections for LkCa 15 and DM Tau at the 5σ level and an upper limit for MWC 480. The column density derived from the data for LkCa 15 is much lower than previously reported. The [N 2 H + /HCO + ] ratio is on the order of 0.02−0.03. So far, HCO + remains the most abundant observed molecular ion in disks. Conclusions. All the observed values generally agree with the modelled column densities of disks at an evolutionary stage of a few million years (within the uncertainty limits), but the radial distribution of the molecules is not reproduced well. The low inferred concentration of N 2 H + in three disks around low-mass and intermediate-mass young stars implies that this ion is not a sensitive tracer of the overall disk ionization fraction.

We studied several representative circumstellar disks surrounding the Herbig Ae star MWC 480 and the T Tauri stars LkCa 15 and DM Tau at (sub-)millimeter wavelengths in lines of CCH 1 . Our aim is to characterize photochemistry in the heavily UV-irradiated 1 Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

We present submillimeter (CSO 350µm) and millimeter (SEST 1.2 mm, OVRO 3 mm) photometry for 125 solar-type stars from the FEPS Spitzer Legacy program that have masses between ∼ 0.5 and 2.0 M ⊙ and ages from ∼ 3 Myr to 3 Gyr. Continuum emission was detected toward four stars with a signal to noise ratio ≥ 3: the classical T Tauri stars RX J1842.9−3532, RX J1852.3−3700, and PDS 66 with SEST, and the debris disk system HD 107146 with OVRO. RX J1842.9−3532 and RX J1852.3−3700 are located in projection nearby the R CrA molecular cloud with estimated ages of ∼ 10 Myr (Neuhäuser et al. 2000), while PDS 66 is a probable member of the ∼ 20 Myr old Lower Centaurus-Crux subgroup of the Scorpius-Centaurus OB association (Mamajek et al. 2004). The continuum emission toward these three sources is unresolved at the 24 ′′ SEST resolution and likely originates from circumstellar accretion disks, each with estimated dust masses of ∼ 5×10 −5 M ⊙ . Analysis of the visibility data toward HD 107146 (age ∼ 80-200 Myr) indicates that the 3 mm continuum emission is centered on the star -2within the astrometric uncertainties and resolved with a gaussian-fit FWHM size of (6.5 ′′ ± 1.4 ′′ ) × (4.2 ′′ ± 1.3 ′′ ), or 185 AU×120 AU. The results from our continuum survey are combined with published observations to quantify the evolution of dust mass with time by comparing the mass distributions for samples with different stellar ages. The frequency distribution of circumstellar dust masses around solar-type stars in the Taurus molecular cloud (age ∼ 2 Myr) is distinguished from that around 3-10 Myr and 10-30 Myr old stars at a significance level of ∼ 1.5σ and ∼ 3σ respectively. These results suggest a decrease in the mass of dust contained in small dust grains and/or changes in the grain properties by stellar ages of 10-30 Myr, consistent with previous conclusions. Further observations are needed to determine if the evolution in the amount of cold dust occurs on even shorter time scales.

Aims. We study the content in S-bearing molecules of protoplanetary disks around low-mass stars. Methods. We used the new IRAM 30-m receiver EMIR to perform simultaneous observations of the 1 10 −1 01 line of H 2 S at 168.8 GHz and 2 23 −1 12 line of SO at 99.3 GHz. We compared the observational results with predictions coming from the astrochemical code NAUTILUS, which has been adapted to protoplanetary disks. The data were analyzed together with existing CS J = 3−2 observations. Results. We fail to detect the SO and H 2 S lines, although CS is detected in LkCa15, DM Tau, and GO Tau but not in MWC 480. However, our new upper limits are significantly better than previous ones and allow us to put some interesting constraints on the sulfur chemistry. Conclusions. Our best modeling of disks is obtained for a C/O ratio of 1.2, starting from initial cloud conditions of H density of 2 × 10 5 cm −3 and age of 10 6 yr. The results agree with the CS data and are compatible with the SO upper limits, but fail to reproduce the H 2 S upper limits. The predicted H 2 S column densities are too high by at least one order of magnitude. H 2 S may remain locked onto grain surfaces and react with other species, thereby preventing the desorption of H 2 S.

Einc schr wichtigc Eigeiiscliaft selir junger iiiassereiclicr Sternc (BN-Objckte) 1st ilir intcnsivcr Massenvcrlust. Wir geben die wichtigsten Mcthoden a n , uin dic Mnssciiverlustratcii abzuleitcn. Bcobachtungsergcbiiissc wcrdcn vcrwcndct, uni die ionisicrtcn Sternwindc und dic CO-Fliisse zu charakterisieren. Dic Ergebnisse wcrden niit bestellenden Tlieoricn zuin Masscnverlust konfronticrt.A vcry important property of very young and massive stars (BN objects) is their iiitcnsive mass loss. We describe the main mcthods to derive tlie mass loss rates. Available observations arc used to characterize thc ionizcd stellar winds and the CO flows. The rcsults arc confronted with theories describing the anisotropic inass loss.

Our search for the earliest stages of massive star formation turned up 12 massive pre-protocluster candidates plus a few protoclusters. For this search, we selected 47 FIR-bright IRAS sources in the outer Galaxy. We mapped regions of several square arcminutes around the IRAS source in the millimeter continuum in order to find massive cold cloud cores possibly being in a very early stage of massive star formation. Masses and densities are derived for the 128 molecular cloud cores found in the obtained maps. We present these maps together with near-infrared, mid-infrared, and radio data collected from the 2MASS, MSX, and NVSS catalogs. Further data from the literature on detections of high-density tracers, outflows, and masers are added. The multiwavelength data sets are used to characterize each observed region. The massive cloud cores (M > 100 M ) are placed in a tentative evolutionary sequence depending on their emission at the investigated wavelengths. Candidates for the youngest stages of massive star formation are identified by the lack of detections in the above-mentioned near-infrared, mid-infrared, and radio surveys. Twelve massive cores prominent in the millimeter continuum fulfill this requirement. Since neither FIR nor radio emission have been detected from these cloud cores, massive protostars must be very deeply embedded in these cores. Some of these objects may actually be pre-protocluster cores: an up to now rare object class, where the initial conditions of massive star formation can be studied.