High-spatial-resolution CN and CS observation of two regions of massive star formation

Molecular line CN, CS and mm continuum observations of two intermediate- to high-mass star-forming regions - IRAS20293+3952 and IRAS19410+2336 - obtained with the Plateau de Bure Interferometer at high spatial resolution reveal interesting characteristics of the gas and dust emission. In spite of the expectation that the CN and CS morphology might closely follow the dense gas traced by the dust continuum, both molecules avoid the most central cores. Comparing the relative line strengths of various CN hyperfine components, this appears not to be an opacity effect but to be due to chemical and physical effects. The CN data also indicate enhanced emission toward the different molecular outflows in the region. Regarding CS, avoiding the central cores can be due to high optical depth, but the data also show that the CS emission is nearly always associated with the outflows of the region. Therefore, neither CS nor CN appear well suited for dense gas and disk studies in these two sources, and we recommend the use of different molecules for future massive disk studies. An analysis of the 1 and 3mm continuum fluxes toward IRAS20293+3952 reveals that the dust opacity index beta is lower than the canonical value of 2. Tentatively, we identify a decreasing gradient of beta from the edge of the core to the core center. This could be due to increasing optical depth toward the core center and/or grain growth within the densest cores and potential central disks. We detect 3mm continuum emission toward the collimated outflow emanating from IRAS20293+3952. The spectral index of alpha ~ 0.8 in this region is consistent with standard models for collimated ionized winds.Comment: 5 pages, 2 tables, 9 figures, accepted for Ap

Front propagation in geometric and phase field models of stratified media

We study front propagation problems for forced mean curvature flows and their phase field variants that take place in stratified media, i.e., heterogeneous media whose characteristics do not vary in one direction. We consider phase change fronts in infinite cylinders whose axis coincides with the symmetry axis of the medium. Using the recently developed variational approaches, we provide a convergence result relating asymptotic in time front propagation in the diffuse interface case to that in the sharp interface case, for suitably balanced nonlinearities of Allen-Cahn type. The result is established by using arguments in the spirit of $\Gamma$-convergence, to obtain a correspondence between the minimizers of an exponentially weighted Ginzburg-Landau type functional and the minimizers of an exponentially weighted area type functional. These minimizers yield the fastest traveling waves invading a given stable equilibrium in the respective models and determine the asymptotic propagation speeds for front-like initial data. We further show that generically these fronts are the exponentially stable global attractors for this kind of initial data and give sufficient conditions under which complete phase change occurs via the formation of the considered fronts

Kinematics of a hot massive accretion disk candidate

Characterizing rotation, infall and accretion disks around high-mass protostars is an important topic in massive star formation research. With the Australia Telescope Compact Array and the Very Large Array we studied a massive disk candidate at high angular resolution in ammonia (NH3(4,4) & (5,5)) tracing the warm disk but not the envelope. The observations resolved at ~0.4'' resolution (corresponding to ~1400AU) a velocity gradient indicative of rotation perpendicular to the molecular outflow. Assuming a Keplerian accretion disk, the estimated protostar-disk mass would be high, similar to the protostellar mass. Furthermore, the position-velocity diagram exhibits additional deviation from a Keplerian rotation profile which may be caused by infalling gas and/or a self-gravitating disk. Moreover, a large fraction of the rotating gas is at temperatures >100K, markedly different to typical low-mass accretion disks. In addition, we resolve a central double-lobe cm continuum structure perpendicular to the rotation. We identify this with an ionized, optically thick jet.Comment: 5 pages, 3 figures, accepted for Astrophysical Journal Letters, a high-resolution version of the draft can be found at http://www.mpia.de/homes/beuther/papers.htm

One-dimensional multi-agent optimal control with aggregation and distance constraints: Qualitative properties and mean-field limit

In this paper we consider an optimal control problem for a large population of interacting agents with deterministic dynamics, aggregating potential and constraints on reciprocal distances, in dimension 1. We study existence and qualitative properties of periodic in time optimal trajectories of the finite agents optimal control problem, with particular interest on the compactness of the solutions' support and on the saturation of the distance constraint. Moreover, we prove, through a \u393-convergence result, the consistency of the mean-field optimal control problemwith density constraintswith the corresponding underlying finite agent one and we deduce some qualitative results for the time periodic equilibria of the limit problem

Direct Detection of a (Proto)Binary-Disk System in IRAS 20126+4104

We report the direct detection of a binary/disk system towards the high-mass (proto)stellar object IRAS20126+4104 at infrared wavengths. The presence of a multiple system had been indicated by the precession of the outflow and the double jet system detected earlier at cm-wavelengths. Our new K, L' & M' band infrared images obtained with the UKIRT under exceptional seeing conditions on Mauna Kea are able to resolve the central source for the first time, and we identify two objects separated by ~ 0.5'' (850 AU). The K and L' images also uncover features characteristic of a nearly edge-on disk, similar to many low mass protostars with disks: two emission regions oriented along an outflow axis and separated by a dark lane. The peaks of the L' & M' band and mm-wavelength emission are on the dark lane, presumably locating the primary young star. The thickness of the disk is measured to be ~ 850 AU for radii < 1000 AU. Approximate limits on the NIR magnitudes of the two young stars indicate a high-mass system, although with much uncertainty. These results are a demonstration of the high-mass nature of the system, and the similarities of the star-formation process in the low-mass and high-mass regimes viz. the presence of a disk-accretion stage. The companion is located along the dark lane, consistent with it being in the equatorial/disk plane, indicating a disk-accretion setting for massive, multiple, star-formation.Comment: 12 pages, 3 figures (1 pseudo colour), 1 table; colour figure replaced with jpg file; to be published in ApJL; (back after temoprary withdrawal due to non-scientific reasons.

Nonlocal minimal clusters in the plane

We prove existence of partitions of an open set \u3a9 with a given number of phases, which minimize the sum of the fractional perimeters of all the phases, with Dirichlet boundary conditions. In two dimensions we show that, if the fractional parameter s is sufficiently close to 1, the only singular minimal cone, that is, the only minimal partition invariant by dilations and with a singular point, is given by three half-lines meeting at 120 degrees. In the case of a weighted sum of fractional perimeters, we show that there exists a unique minimal cone with three phases

Chemical Diversity in High-Mass Star Formation

Massive star formation exhibits an extremely rich chemistry. However, not much evolutionary details are known yet, especially at high spatial resolution. Therefore, we synthesize previously published Submillimeter Array high-spatial-resolution spectral line observations toward four regions of high-mass star formation that are in various evolutionary stages with a range of luminosities. Estimating column densities and comparing the spatially resolved molecular emission allows us to characterize the chemical evolution in more detail. Furthermore, we model the chemical evolution of massive warm molecular cores to be directly compared with the data. The four regions reveal many different characteristics. While some of them, e.g., the detection rate of CH3OH, can be explained by variations of the average gas temperatures, other features are attributed to chemical effects. For example, C34S is observed mainly at the core-edges and not toward their centers because of temperature-selective desorption and successive gas-phase chemistry reactions. Most nitrogen-bearing molecules are only found toward the hot molecular cores and not the earlier evolutionary stages, indicating that the formation and excitation of such complex nitrogen-bearing molecules needs significant heating and time to be fully developed. Furthermore, we discuss the observational difficulties to study massive accretion disks in the young deeply embedded phase of massive star formation. The general potential and limitations of such kind of dataset are discussed, and future directions are outlined. The analysis and modeling of this source sample reveals many interesting features toward a chemical evolutionary sequence. However, it is only an early step, and many observational and theoretical challenges in that field lie ahead.Comment: 14 pages, 9 figures, accepted for the Astronomical Journal, a high resolution version can be found at http://www.mpia.de/homes/beuther/papers.htm

Momentum-driven outflow emission from an O-type YSO: Comparing the radio jet with the molecular outflow

Aims: We want to study the physical properties of the ionized jet emission in the vicinity of an O-type young stellar object (YSO), and estimate how efficient is the transfer of energy and momentum from small- to large-scale outflows. Methods: We conducted Karl G. Jansky Very Large Array (VLA) observations, at both 22 and 45 GHz, of the compact and faint radio continuum emission in the high-mass star-forming region G023.01-00.41, with an angular resolution between 0.3" and 0.1", and a thermal rms of the order of 10 uJy/beam. Results: We discovered a collimated thermal (bremsstrahlung) jet emission, with a radio luminosity (L_rad) of 24 mJy kpc^2 at 45 GHz, in the inner 1000 AU from an O-type YSO. The radio thermal jet has an opening angle of 44 degrees and brings a momentum rate of 8 10^-3 M_sun yr^-1 km/s. By combining the new data with previous observations of the molecular outflow and water maser shocks, we can trace the outflow emission from its driving source through the molecular clump, across more than two order of magnitude in length (500 AU-0.2 pc). We find that the momentum-transfer efficiency, between the inner jet emission and the extended outflow of entrained ambient gas, is near unity. This result suggests that the large-scale flow is swept-up by the mechanical force of the radio jet emission, which originates in the inner 1000 AU from the high-mass YSO.Comment: 5 pages, 2 figures, 2 tables, accepted by Astronomy & Astrophysic