10,771 research outputs found
The highly polarized open cluster Trumpler 27
We have carried out multicolor linear polarimetry (UBVRI) of the brightest
stars in the area of the open cluster Trumpler 27. Our data show a high level
of polarization in the stellar light with a considerable dispersion, from to . The polarization vectors of the cluster members appear to be
aligned. Foreground polarization was estimated from the data of some non-member
objects, for which two different components were resolved: the first one
associated with a dust cloud close to the Sun producing
and degrees, and a second component, the main source of
polarization for the cluster members, originated in another dust cloud, which
polarizes the light in the direction of degrees. From a detailed
analysis, we found that the two components have associated values for the first one, and for the other. Due the
difference in the orientation of both polarization vectors, almost 90 degrees
(180 degrees at the Stokes representation), the first cloud (
degrees) depolarize the light strongly polarized by the second one ( degrees).Comment: 12 Pages, 6 Figures, 2 tables (9 Pages), accepted for publication in
A
Millimeter observations and modeling of the AB Aurigae system
(Abriged) We present the results of millimeter observations and a suitable
chemical and radiative transfer model of the AB Aur (HD 31293) circumstellar
disk and surrounding envelope. The integral molecular content of this system is
studied by observing CO, CO, CS, HCO, DCO, HCO, 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 2D non-LTE line
radiative transfer code is applied to compute excitation temperatures of
several rotational transitions of HCO, CO, CO, and CS molecules. We
synthesize the HCO(1-0) interferometric map along with single-dish CO(2-1),
CO(2-1), HCO(1-0), HCO(3-2), CS(2-1), and CS(5-4) spectra and
compared 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 \iota=17^{+6}_{-3}\degr, (2) the
position angle \phi=80\pm30\degr, (3) the size AU,
(4) the mass M_\mathrm{disk}=1.3\cdot10^{-2} M_{\sun} (with a factor of
uncertainty), and (5) that the disk is in Keplerian rotation.
Furthermore, indirect evidence for a local inhomogeneity of the envelope at
\ga600 AU is found...Comment: 62 pages, 13 figures, 7 tables, accepted for publication in Ap
3D simulations of gas puff effects on edge plasma and ICRF coupling in JET
Recent JET (ITER-Like Wall) experiments have shown that the fueling gas puffed from different locations of the vessel can result in different scrape-off layer (SOL) density profiles and therefore different radio frequency (RF) coupling. To reproduce the experimental observations, to understand the associated physics and to optimize the gas puff methods, we have carried out three-dimensional (3D) simulations with the EMC3-EIRENE code in JET-ILW including a realistic description of the vessel geometry and the gas injection modules (GIMs) configuration. Various gas puffing methods have been investigated, in which the location of gas fueling is the only variable parameter. The simulation results are in quantitative agreement with the experimental measurements. They confirm that compared to divertor gas fueling, mid-plane gas puffing increases the SOL density most significantly but locally, while top gas puffing increases it uniformly in toroidal direction but to a lower degree. Moreover, the present analysis corroborates the experimental findings that combined gas puff scenarios-based on distributed main chamber gas puffing-can be effective in increasing the RF coupling for multiple antennas simultaneously. The results indicate that the spreading of the gas, the local ionization and the transport of the ionized gas along the magnetic field lines connecting the local gas cloud in front of the GIMs to the antennas are responsible for the enhanced SOL density and thus the larger RF coupling
Evolution of emission line activity in intermediate mass young stars
We present optical spectra of 45 intermediate mass Herbig Ae/Be stars.
Together with the multi-epoch spectroscopic and photometric data compiled for a
large sample of these stars and ages estimated for individual stars by using
pre-main sequence evolutionary tracks, we have studied the evolution of
emission line activity in them. We find that, on average, the H_alpha emission
line strength decreases with increasing stellar age in HAeBe stars, indicating
that the accretion activity gradually declines during the PMS phase. This would
hint at a relatively long-lived (a few Myr) process being responsible for the
cessation of accretion in Herbig Ae/Be stars. We also find that the accretion
activity in these stars drops substantially by ~ 3 Myr. This is comparable to
the timescale in which most intermediate mass stars are thought to lose their
inner disks, suggesting that inner disks in intermediate mass stars are
dissipated rapidly after the accretion activity has fallen below a certain
level. We, further find a relatively tight correlation between strength of the
emission line and near-infrared excess due to inner disks in HAeBe stars,
indicating that the disks around Herbig Ae/Be stars cannot be entirely passive.
We suggest that this correlation can be understood within the frame work of the
puffed-up inner rim disk models if the radiation from the accretion shock is
also responsible for the disk heating.Comment: 39 pages, accepted for publication in Ap
Mesonic Form Factors
We have started a program to compute the electromagnetic form factors of
mesons. We discuss the techniques used to compute the pion form factor and
present preliminary results computed with domain wall valence fermions on MILC
asqtad lattices, as well as Wilson fermions on quenched lattices. These methods
can easily be extended to rho-to-gamma-pi transition form factors.Comment: 7 pages, 6 figures, Workshop on Lattice Hadron Physics 2003 (LHP2003
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