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

Interactions between unidirectional quantized vortex rings

We have used the vortex filament method to numerically investigate the interactions between pairs of quantized vortex rings that are initially traveling in the same direction but with their axes offset by a variable impact parameter. The interaction of two circular rings of comparable radii produce outcomes that can be categorized into four regimes, dependent only on the impact parameter; the two rings can either miss each other on the inside or outside, or they can reconnect leading to final states consisting of either one or two deformed rings. The fraction of of energy went into ring deformations and the transverse component of velocity of the rings are analyzed for each regime. We find that rings of very similar radius only reconnect for a very narrow range of the impact parameter, much smaller than would be expected from geometrical cross-section alone. In contrast, when the radii of the rings are very different, the range of impact parameters producing a reconnection is close to the geometrical value. A second type of interaction considered is the collision of circular rings with a highly deformed ring. This type of interaction appears to be a productive mechanism for creating small vortex rings. The simulations are discussed in the context of experiments on colliding vortex rings and quantum turbulence in superfluid helium in the zero temperature limit

Simplified Quantum Process Tomography

We propose and evaluate experimentally an approach to quantum process tomography that completely removes the scaling problem plaguing the standard approach. The key to this simplification is the incorporation of prior knowledge of the class of physical interactions involved in generating the dynamics, which reduces the problem to one of parameter estimation. This allows part of the problem to be tackled using efficient convex methods, which, when coupled with a constraint on some parameters allows globally optimal estimates for the Kraus operators to be determined from experimental data. Parameterising the maps provides further advantages: it allows the incorporation of mixed states of the environment as well as some initial correlation between the system and environment, both of which are common physical situations following excitation of the system away from thermal equilibrium. Although the approach is not universal, in cases where it is valid it returns a complete set of positive maps for the dynamical evolution of a quantum system at all times.Comment: Added references to interesting related work by Bendersky et a

The Nature of the Molecular Environment within 5 pc of the Galactic Center

We present a detailed study of molecular gas in the central 10pc of the Galaxy through spectral line observations of four rotation inversion transitions of NH3 made with the VLA. Updated line widths and NH3(1,1) opacities are presented, and temperatures, column densities, and masses are derived. We examine the impact of Sgr A East on molecular material at the Galactic center and find that there is no evidence that the expansion of this shell has moved a significant amount of the 50 km/s GMC. The western streamer, however, shows strong indications that it is composed of material swept-up by the expansion of Sgr A East. Using the mass and kinematics of the western streamer, we calculate an energy of E=(2-9)x10^{51} ergs for the progenitor explosion and conclude that Sgr A East was most likely produced by a single supernova. The temperature structure of molecular gas in the central ~20pc is also analyzed in detail. We find that molecular gas has a ``two-temperature'' structure similar to that measured by Huttemeister et al. (2003a) on larger scales. The largest observed line ratios, however, cannot be understood in terms of a two-temperature model, and most likely result from absorption of NH3(3,3) emission by cool surface layers of clouds. By comparing the observed NH3 (6,6)-to-(3,3) line ratios, we disentangle three distinct molecular features within a projected distance of 2pc from Sgr A*. Gas associated with the highest line ratios shows kinematic signatures of both rotation and expansion. The southern streamer shows no significant velocity gradients and does not appear to be directly associated with either the circumnuclear disk or the nucleus. The paper concludes with a discussion of the line-of-sight arrangement of the main features in the central 10pc.Comment: 51 pages, 16 figures, accepted for publication in ApJ. Due to size limitations, some of the images have been cut from this version. A complete, color PS or PDF version can be downloaded from http://www.astro.columbia.edu/~herrnstein/NH3/paper

Characterization of Infrared Dark Clouds -- NH3_3 Observations of an Absorption-contrast Selected IRDC Sample

Despite increasing research in massive star formation, little is known about its earliest stages. Infrared Dark Clouds (IRDCs) are cold, dense and massive enough to harbour the sites of future high-mass star formation. But up to now, mainly small samples have been observed and analysed. To understand the physical conditions during the early stages of high-mass star formation, it is necessary to learn more about the physical conditions and stability in relatively unevolved IRDCs. Thus, for characterising IRDCs studies of large samples are needed. We investigate a complete sample of 218 northern hemisphere high-contrast IRDCs using the ammonia (1,1)- and (2,2)-inversion transitions. We detected ammonia (1,1)-inversion transition lines in 109 of our IRDC candidates. Using the data we were able to study the physical conditions within the star-forming regions statistically. We compared them with the conditions in more evolved regions which have been observed in the same fashion as our sample sources. Our results show that IRDCs have, on average, rotation temperatures of 15 K, are turbulent (with line width FWHMs around 2 km s$^{-1}$), have ammonia column densities on the order of $10^{14}$ cm$^{-2}$ and molecular hydrogen column densities on the order of $10^{22}$ cm$^{-2}$. Their virial masses are between 100 and a few 1000 M$_\odot$. The comparison of bulk kinetic and potential energies indicate that the sources are close to virial equilibrium. IRDCs are on average cooler and less turbulent than a comparison sample of high-mass protostellar objects, and have lower ammonia column densities. Virial parameters indicate that the majority of IRDCs are currently stable, but are expected to collapse in the future.Comment: 21 pages, 11 figures, 7 tables. Paper accepted for publication in Astronomy & Astrophysic

Detection of FeO towards SgrB2

We have observed the J=5-4 ground state transition of FeO at a frequency of 153 GHz towards a selection of galactic sources. Towards the galactic center source SgrB2, we see weak absorption at approximately the velocity of other features towards this source (62 km s$^{-1}$ LSR). Towards other sources, the results were negative as they were also for MgOH(3-2) and FeC(6-5). We tentatively conclude that the absorption seen toward SgrB2 is due to FeO in the hot ($\sim$ 500 K) relatively low density absorbing gas known to be present in this line of sight. This is the first (albeit tentative) detection of FeO or any iron--containing molecule in the interstellar gas. Assuming the observed absorption to be due to FeO, we estimate [FeO]/[SiO] to be of order or less than 0.002 and [FeO]/[H$_{2}$] of order $3 10^{-11}$. This is compatible with our negative results in other sources. Our results suggest that the iron liberated from grains in the shocks associated with SgrB2 remains atomic and is not processed into molecular form.Comment: 1 postscrit figure,10 page

Carbon recombination lines in the Orion Bar

We have carried out VLA D-array observations of the C91alpha carbon recombination line as well as Effelsberg 100-m observations of the C65alpha line in a 5 arcmin square region centered between the Bar and the Trapezium stars in the Orion Nebula with spatial resolutions of 10 arcsec and 40 arcsec, respectively. The results show the ionized carbon in the PDR associated with the Orion Bar to be in a thin, clumpy layer sandwiched between the ionization front and the molecular gas. From the observed line widths we get an upper limit on the temperature in the C+ layer of 1500 K and from the line intensity a hydrogen density between 5 10^4 and 2.5 10^5 cm-3 for a homogeneous medium. The observed carbon level population is not consistent with predictions of hydrogenic recombination theory but could be explained by dielectronic recombination. The layer of ionized carbon seen in C91alpha is found to be essentially coincident with emission in the v=1-0 S(1) line of vibrationally excited molecular hydrogen. This is surprising in the light of current PDR models and some possible explanations of the discrepancy are discussed.Comment: 9 pages, 3 Postscript figures, uses aaspp4 and psfig, To Appear in ApJ Letters (accepted Jul. 24, 1997

Evolution and excitation conditions of outflows in high-mass star-forming regions

Theoretical models suggest that massive stars form via disk-mediated accretion, with bipolar outflows playing a fundamental role. A recent study toward massive molecular outflows has revealed a decrease of the SiO line intensity as the object evolves. The present study aims at characterizing the variation of the molecular outflow properties with time, and at studying the SiO excitation conditions in outflows associated with massive YSOs. We used the IRAM30m telescope to map 14 massive star-forming regions in the SiO(2-1), SiO(5-4) and HCO+(1-0) outflow lines, and in several dense gas and hot core tracers. Hi-GAL data was used to improve the spectral energy distributions and the L/M ratio, which is believed to be a good indicator of the evolutionary stage of the YSO. We detect SiO and HCO+ outflow emission in all the sources, and bipolar structures in six of them. The outflow parameters are similar to those found toward other massive YSOs. We find an increase of the HCO+ outflow energetics as the object evolve, and a decrease of the SiO abundance with time, from 10^(-8) to 10^(-9). The SiO(5-4) to (2-1) line ratio is found to be low at the ambient gas velocity, and increases as we move to high velocities, indicating that the excitation conditions of the SiO change with the velocity of the gas (with larger densities and/or temperatures for the high-velocity gas component). The properties of the SiO and HCO+ outflow emission suggest a scenario in which SiO is largely enhanced in the first evolutionary stages, probably due to strong shocks produced by the protostellar jet. As the object evolves, the power of the jet would decrease and so does the SiO abundance. During this process, however, the material surrounding the protostar would have been been swept up by the jet, and the outflow activity, traced by entrained molecular material (HCO+), would increase with time.Comment: 31 pages, 10 figures and 5 tables (plus 2 figures and 3 tables in the appendix). Accepted for publication in A&A. [Abstract modified to fit the arXiv requirements.

Turbulent Vortex Flow Responses at the AB Interface in Rotating Superfluid 3He-B

In a rotating two-phase sample of 3He-B and magnetic-field stabilized 3He-A the large difference in mutual friction dissipation at 0.20 Tc gives rise to unusual vortex flow responses. We use noninvasive NMR techniques to monitor spin down and spin up of the B-phase superfluid component to a sudden change in the rotation velocity. Compared to measurements at low field with no A-phase, where these responses are laminar in cylindrically symmetric flow, spin down with vortices extending across the AB interface is found to be faster, indicating enhanced dissipation from turbulence. Spin up in turn is slower, owing to rapid annihilation of remanent vortices before the rotation increase. As confirmed by both our NMR signal analysis and vortex filament calculations, these observations are explained by the additional force acting on the B-phase vortex ends at the AB interface.Comment: 6 pages, 6 figure