3,353 research outputs found
O2 signature in thin and thick O2-H2O ices
Aims. In this paper we investigate the detectability of the molecular oxygen
in icy dust grain mantles towards astronomical objects. Methods. We present a
systematic set of experiments with O2-H2O ice mixtures designed to disentangle
how the molecular ratio affects the O2 signature in the mid- and near-infrared
spectral regions. All the experiments were conducted in a closed-cycle helium
cryostat coupled to a Fourier transform infrared spectrometer. The ice mixtures
comprise varying thicknesses from 8 10 to 3 m. The
absorption spectra of the O2-H2O mixtures are also compared to the one of pure
water. In addition, the possibility to detect the O2 in icy bodies and in the
interstellar medium is discussed. Results. We are able to see the O2 feature at
1551 cm even for the most diluted mixture of H2O : O2 = 9 : 1,
comparable to a ratio of O2/H2O = 10 % which has already been detected in situ
in the coma of the comet 67P/Churyumov-Gerasimenko. We provide an estimate for
the detection of O2 with the future mission of the James Webb Space Telescope
(JWST).Comment: 11 pages, 10 figures, article in press, to appear in A&A 201
Thermal transport driven by charge imbalance in graphene in magnetic field, close to the charge neutrality point at low temperature: Non local resistance
Graphene grown epitaxially on SiC, close to the charge neutrality point
(CNP), in an orthogonal magnetic field shows an ambipolar behavior of the
transverse resistance accompanied by a puzzling longitudinal magnetoresistance.
When injecting a transverse current at one end of the Hall bar, a sizeable non
local transverse magnetoresistance is measured at low temperature. While Zeeman
spin effect seems not to be able to justify these phenomena, some dissipation
involving edge states at the boundaries could explain the order of magnitude of
the non local transverse magnetoresistance, but not the asymmetry when the
orientation of the orthogonal magnetic field is reversed. As a possible
contribution to the explanation of the measured non local magnetoresistance
which is odd in the magnetic field, we derive a hydrodynamic approach to
transport in this system, which involves particle and hole Dirac carriers, in
the form of charge and energy currents. We find that thermal diffusion can take
place on a large distance scale, thanks to long recombination times, provided a
non insulating bulk of the Hall bar is assumed, as recent models seem to
suggest in order to explain the appearance of the longitudinal resistance. In
presence of the local source, some leakage of carriers from the edges generates
an imbalance of carriers of opposite sign, which are separated in space by the
magnetic field and diffuse along the Hall bar generating a non local transverse
voltage.Comment: 25 pages, 12 figure
The observed chemical structure of L1544
Prior to star formation, pre-stellar cores accumulate matter towards the
centre. As a consequence, their central density increases while the temperature
decreases. Understanding the evolution of the chemistry and physics in this
early phase is crucial to study the processes governing the formation of a
star. We aim at studying the chemical differentiation of a prototypical
pre-stellar core, L1544, by detailed molecular maps. In contrast with single
pointing observations, we performed a deep study on the dependencies of
chemistry on physical and external conditions. We present the emission maps of
39 different molecular transitions belonging to 22 different molecules in the
central 6.25 arcmin of L1544. We classified our sample in five families,
depending on the location of their emission peaks within the core. Furthermore,
to systematically study the correlations among different molecules, we have
performed the principal component analysis (PCA) on the integrated emission
maps. The PCA allows us to reduce the amount of variables in our dataset.
Finally, we compare the maps of the first three principal components with the
H column density map, and the T map of the core. The results of
our qualitative analysis is the classification of the molecules in our dataset
in the following groups: (i) the -CH family (carbon chain
molecules), (ii) the dust peak family (nitrogen-bearing species), (iii) the
methanol peak family (oxygen-bearing molecules), (iv) the HNCO peak family
(HNCO, propyne and its deuterated isotopologues). Only HCO and
CS do not belong to any of the above mentioned groups. The principal
component maps allow us to confirm the (anti-)correlations among different
families that were described in a first qualitative analysis, but also points
out the correlation that could not be inferred before.Comment: 29 pages, 19 figures, 2 appendices, accepted for publication in A&A,
arXiv abstract has been slightly modifie
Investigation of HNCO isomers formation in ice mantles by UV and thermal processing: an experimental approach
Current gas phase models do not account for the abundances of HNCO isomers
detected in various environments, suggesting a formation in icy grain mantles.
We attempted to study a formation channel of HNCO and its possible isomers by
vacuum-UV photoprocessing of interstellar ice analogues containing HO,
NH, CO, HCN, CHOH, CH, and N followed by warm-up, under
astrophysically relevant conditions. Only the HO:NH:CO and HO:HCN
ice mixtures led to the production of HNCO species. The possible isomerization
of HNCO to its higher energy tautomers following irradiation or due to ice
warm-up has been scrutinized. The photochemistry and thermal chemistry of
HO:NH:CO and HO:HCN ices was simulated using the Interstellar
Astrochemistry Chamber (ISAC), a state-of-the-art ultra-high-vacuum setup. The
ice was monitored in situ by Fourier transform mid-infrared spectroscopy in
transmittance. A quadrupole mass spectrometer (QMS) detected the desorption of
the molecules in the gas phase. UV-photoprocessing of
HO:NH:CO/HO:HCN ices lead to the formation of OCN as main
product in the solid state and a minor amount of HNCO. The second isomer HOCN
has been tentatively identified. Despite its low efficiency, the formation of
HNCO and the HOCN isomers by UV-photoprocessing of realistic simulated ice
mantles, might explain the observed abundances of these species in PDRs, hot
cores, and dark clouds
Robust and efficient generator of almost maximal multipartite entanglement
Quantum chaotic maps can efficiently generate pseudo-random states carrying
almost maximal multipartite entanglement, as characterized by the probability
distribution of bipartite entanglement between all possible bipartitions of the
system. We show that such multipartite entanglement is robust, in the sense
that, when realistic noise is considered, distillable entanglement of
bipartitions remains almost maximal up to a noise strength that drops only
polynomially with the number of qubits.Comment: 4 pages, 4 figures. Published versio
A study of the -/- ratio in low-mass star forming regions
We use the deuteration of - to probe the physical
parameters of starless and protostellar cores, related to their evolutionary
states, and compare it to the -deuteration in order to
study possible differences between the deuteration of C- and N-bearing species.
We observed the main species -, the singly and doubly
deuterated species - and -, as
well as the isotopologue - toward 10 starless
cores and 5 protostars in the Taurus and Perseus Complexes. We examined the
correlation between the
(-)/(-) ratio and the dust
temperature along with the column density and the CO depletion
factor. The resulting
(-)/(-) ratio is within the
error bars consistent with in all starless cores with detected
-. This also accounts for the protostars except for the
source HH211, where we measure a high deuteration level of . The
deuteration of follows the same trend but is considerably
higher in the dynamically evolved core L1544. Toward the protostellar cores the
coolest objects show the largest deuterium fraction in
-. We show that the deuteration of
- can trace the early phases of star formation and is
comparable to that of . However, the largest
- deuteration level is found toward protostellar cores,
suggesting that while - is mainly frozen onto dust
grains in the central regions of starless cores, active deuteration is taking
place on ice
- …