A 12CO (J = 1 -> 0) study towards the Ara OB1 region

Intermediate angular resolution (HPBW = 8. 0 7) carbon monoxide (12CO J = 1→0) line observations towards the OB association Ara OB1 are reported. The molecular line observations cover an area of 2. ◦75 × 3. ◦00, and disclose a rich and complex distribution of the molecular line emission. The molecular features likely to be associated with the OB-association Ara OB1 span the velocity range from −28 to −20 km s−1. The most negative radial velocities are observed along NGC 6188 (≡Rim nebula). This nebula marks the interface between the H region RCW 108 and the highly absorbing molecular material located westwards of the ionised region. The dominant CO structures, labeled E and F, have a radial velocity of about −23.5 and −21.8 km s−1, respectively. The former harbours a bright optical knot, the infrared cluster RCW-108 and the strong IRAS source 16362−4845. IRAS point sources are also seen in projection onto 12CO concentrations F and H. This may indicate that the star forming process is a widespread phenomenon in this molecular complex. Extended continuum emission, having a high degree of spatial correlation with both the infrared and molecular emission, is observed in the region. We believe that this emission, thermal in nature, arises from the ionised surface layers of the molecular complex. The ionising agents are the high mass stars of NGC 6193, the nucleus of Ara OB1. The total amount of molecular gas related to Ara OB1 is about ∼1.4×104 M .Fil: Arnal, Edmundo Marcelo. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: May, J.. Universidad de Chile; ChileFil: Romero, Gisela Andrea. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentin

Experimental analysis of the boundary layer transition with zero and positive pressure gradient

The influence of a positive pressure gradient on the boundary layer transition is studied. The mean velocity and turbulence profiles of four cases are examined. As the intensity of the pressure gradient is increased, the Reynolds number of the transition onset and the length of the transition region are reduced. The Tollmein-Schlichting waves disturb the laminar regime; the amplification of these waves is in good agreement with the stability theory. The three dimensional deformation of the waves leads finally to the appearance of turbulence. In the case of zero pressure gradient, the properties of the turbulent spots are studied by conditional sampling of the hot-wire signal; in the case of positive pressure gradient, the turbulence appears in a progressive manner and the turbulent spots are much more difficult to characterize

NANTEN 12CO (J=1-0) observations around the star WR 55

Context: A complete study of the molecular and ionized gas in the environs of the nebula RCW 78 around WR 55 is presented. Aims: The aim of this work is to investigate the spatial distribution, physical characteristics, and kinematical properties of the molecular gas linked to the galactic nebula RCW 78 to achieve a better understanding of its interaction with the star and with the ionized gas. Methods: This study was based on 12CO(1-0) fully sampled observations of a region of ~0.45{\deg} in size around the star WR 55 and the nebula RCW 78 obtained with the 4-m NANTEN telescope, radio continuum archival data at 1.4 and 4.85 GHz, obtained from SGPS and PMNRAO Southern Radio Survey, respectively, and available infrared MIPSGAL images at 24 microns. Results: A molecular gas component in the velocity range from ~ -58 to -45 km s-1, compatible with the velocity of the ionized gas, was found to be associated with the optical nebula. Adopting a distance of ~ 5 kpc, the mass of this molecular component is about 3.4 x 10^4 Msun. The analysis of the molecular data revealed the presence of a velocity gradient, in agreement with the Halpha line. New radiocontinuum flux density determinations confirm the thermal nature of RCW 78. This indicates that the ionized gas in RCW 78 arises from photoionization of the molecular gas component in the velocity range from -58 km s-1 to -45 km s-1. A molecular concentration at a velocity of -56.1 km s-1 (identified as C1) is very likely associated with the star HD 117797 and with a collection of candidate YSOs, lying at a distance of 3.9 kpc, while the rest of the molecular gas at velocities between -56 and -46 km s-1 constitute an incomplete ring-like structure which expands around WR 55 at a velocity of about ~ 5 km s-1. Mechanical energy and time requirements indicate that WR 55 is very capable of sustaining the expansion of the nebula.Comment: 14 pages, 10 figures.Accepted for publication in A&

Experimental analysis and computation of the onset and development of the boundary layer transition

The transition of an incompressible boundary layer, with zero pressure gradient and low free-stream turbulence is studied. Mean velocity, turbulence and Reynolds shear stress profiles are presented. The development of the Tollmien-Schlichting waves is clearly shown until the turbulent spots appear. The intermittency phenomenon is studied by conditional sampling of the hotwire signal. The comparison with calculation results obtained by resolution of a set of transport equations shows a good agreement for the mean characteristics of the flow; discrepancies observed for the turbulent quantities evolution are due to the intermittency phenomenon

La convexité de l'application moment d'un groupe de Lie

AbstractLet π be a unitary representation of a Lie group G. The moment mapping Ψπ of π assigns to every C∞ vector ξ in the Hilbert space H of π the linear functional Ψπ(ξ) of the Lie algebra g of G by the rule ψπ(ξ)(X)=1i〈dπ(X)ξ, ξ〉H, X ϵ g In this paper, we study the moment set Iπ of π, i.e., the closure of the image of Ψπ. It is shown that for solvable G, Iπ is always convex and that if furthermore π is irreducible, then Iπ is the closure (in g∗) of the convex hull of the Kirillov-Pukanszky orbit of π. If G is compact and if π is irreducible, then we show that Iπ is the convex hull of the orbit of the highest weight Λ of π, if and only if the number Πi = 1n 〈2Λ − αi, αi〉 is different from 0. Here α1, …, αn denote the simple roots of g

Ultrarobust calibration of an optical lattice depth based on a phase shift

We report on a new method to calibrate the depth of an optical lattice. It consists in triggering the intrasite dipole mode of the cloud by a sudden phase shift. The corresponding oscillatory motion is directly related to the intraband frequencies on a large range of lattice depths. Remarkably, for a moderate displacement, a single frequency dominates this oscillation for the zeroth and first order interference pattern observed after a sufficiently long time-of-flight. The method is robust against atom-atom interactions and the exact value of the extra external confinement of the initial trapping potential.Comment: 7 pages, 6 figure