117,138 research outputs found
Spectroscopic reassignment and ground state dissociation energy of molecular iodine
Spectroscopic reassignment and ground state dissociation energy of molecular iodin
Permeability of a one-dimensional potential barrier
Permeability of one dimensional potential barrie
Dissociation energy and long-range potential of diatomic molecules from vibrational spacings - The halogens
Dissociation energy and long-range potential of diatomic molecules from vibrational spacings, halogen
Shape resonances and rotationally predissociating levels - The atomic collision time delay functions and quasibound level properties of H2 /Chi /1 Sigma g plus//
Atomic collision time delay functions and quasibound level properties of ground state of molecular hydroge
Sticky Particles and Stochastic Flows
Gaw\c{e}dzki and Horvai have studied a model for the motion of particles
carried in a turbulent fluid and shown that in a limiting regime with low
levels of viscosity and molecular diffusivity, pairs of particles exhibit the
phenomena of stickiness when they meet. In this paper we characterise the
motion of an arbitrary number of particles in a simplified version of their
model
Foot-operated cell-counter
Cell-counter for cell indices consists of a footboard with four pressure sensitive switches and an enclosure for the components and circuitry. This device increases the operators efficiency by reducing the number of required hand movements
Very High-Redshift Lensed Galaxies
We review in this paper the main results recently obtained on the
identification and study of very high-z galaxies usinglensing clusters as
natural gravitational telescopes. We present in detail our pilot survey with
ISAAC/VLT, aimed at the detection of z>7 sources. Evolutionary synthesis models
for extremely metal-poor and PopIII starbursts have been used to derive the
observational properties expected for these high-z galaxies, such as expected
magnitudes and colors, line fluxes for the main emission lines, etc. These
models have allowed to define fairly robust selection criteria to find z~7-10
galaxies based on broad-band near-IR photometry in combination with the
traditional Lyman drop-out technique. The first results issued from our
photometric and spectroscopic survey are discussed, in particular the
preliminary confirmation rate, and the global properties of our high-z
candidates, including the latest results on the possible z=10.0 candidate
A1835-1916. The search efficiency should be significantly improved by the
future near-IR multi-object ground-based and space facilities. However, strong
lensing clusters remain a factor of ~5-10 more efficient than blank fields in
this redshift domain, within the FOV of a few arcminutes around the cluster
core, for the typical depth required for this survey project.Comment: 14 pages, 7 figures, Proceedings of IAU Symposium No. 225: The Impact
of Gravitational Lensing on Cosmology, Y. Mellier and G. Meylan, Ed
The ionization fraction gradient across the Horsehead edge: An archetype for molecular clouds
The ionization fraction plays a key role in the chemistry and dynamics of
molecular clouds. We study the H13CO+, DCO+ and HOC+ line emission towards the
Horsehead, from the shielded core to the UV irradiated cloud edge, i.e., the
Photodissociation Region (PDR), as a template to investigate the ionization
fraction gradient in molecular clouds. We analyze a PdBI map of the H13CO+
J=1-0 line, complemented with IRAM-30m H13CO+ and DCO+ higher-J line maps and
new HOC+ and CO+ observations. We compare self-consistently the observed
spatial distribution and line intensities with detailed depth-dependent
predictions of a PDR model coupled with a nonlocal radiative transfer
calculation. The chemical network includes deuterated species, 13C
fractionation reactions and HCO+/HOC+ isomerization reactions. The role of
neutral and charged PAHs in the cloud chemistry and ionization balance is
investigated. The detection of HOC+ reactive ion towards the Horsehead PDR
proves the high ionization fraction of the outer UV irradiated regions, where
we derive a low [HCO+]/[HOC+]~75-200 abundance ratio. In the absence of PAHs,
we reproduce the observations with gas-phase metal abundances, [Fe+Mg+...],
lower than 4x10(-9) (with respect to H) and a cosmic-rays ionization rate of
zeta=(5+/-3)x10(-17) s(-1). The inclusion of PAHs modifies the ionization
fraction gradient and increases the required metal abundance. The ionization
fraction in the Horsehead edge follows a steep gradient, with a scale length of
~0.05 pc (or ~25''), from [e-]~10(-4) (or n_e ~ 1-5 cm(-3)) in the PDR to a few
times ~10(-9) in the core. PAH^- anions play a role in the charge balance of
the cold and neutral gas if substantial amounts of free PAHs are present ([PAH]
>10(-8)).Comment: 13 pages, 7 figures, 6 tables. Accepted for publication in A&A
(english not edited
Adaptive Optics observations of LBQS 0108+0028: K-band detection of the host galaxy of a radio-quiet QSO at z=2
We report the first unambiguous detection of the host galaxy of a normal
radio-quiet QSO at high-redshift in K-band. The luminosity of the host
comprises about 35% of the total K-band luminosity. Assuming the average colour
of QSOs at z=2, the host would be about 5 to 6 mag brighter than an unevolved
L* galaxy placed at z=2, and 3 to 4 mag brighter than a passively evolved L*
galaxy at the same redshift. The luminosity of the host galaxy of the QSO would
thus overlap with the highest found in radio-loud QSOs and radio-galaxies at
the same redshift.Comment: Accepted to be published in MNRAS. 4 pages, 2 postscript figures.
Also available at http://www.mpa-garching.mpg.de/~itzia
- …