21,719 research outputs found
Detection of chloronium and measurement of the 35Cl/37Cl isotopic ratio at z=0.89 toward PKS1830-211
We report the first extragalactic detection of chloronium (H2Cl+), in the
z=0.89 absorber in front of the lensed blazar PKS1830-211. The ion is detected
through its 1_11-0_00 line along two independent lines of sight toward the
North-East and South-West images of the blazar. The relative abundance of H2Cl+
is significantly higher (by a factor ~7) in the NE line of sight, which has a
lower H2/H fraction, indicating that H2Cl+ preferably traces the diffuse gas
component. From the ratio of the H2^35Cl+ and H2^37Cl+ absorptions toward the
SW image, we measure a 35Cl/37Cl isotopic ratio of 3.1 (-0.2; +0.3) at z=0.89,
similar to that observed in the Galaxy and the solar system.Comment: Accepted for publication in A&A Lette
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Evidence for product-specific active sites on oxide-derived Cu catalysts for electrochemical CO2 reduction
Carbon dioxide electroreduction in aqueous media using Cu catalysts can generate many different C2 and C3 products, which leads to the question whether all products are generated from the same types of active sites or if product-specific active sites are responsible for certain products. Here, by reducing mixtures of 13CO and 12CO2, we show that oxide-derived Cu catalysts have three different types of active sites for C–C coupled products, one that produces ethanol and acetate, another that produces ethylene and yet another that produces 1-propanol. In contrast, we do not find evidence of product-specific sites on polycrystalline Cu and oriented (100) and (111) Cu surfaces. Analysis of the isotopic composition of the products leads to the prediction that the adsorption energy of *COOH (the product of the first step of CO2 reduction) may be a descriptor for the product selectivity of a given active site. These new insights should enable highly selective catalysts to be developed
Herschel observations of interstellar chloronium. II - Detections toward G29.96-0.02, W49N, W51, and W3(OH), and determinations of the ortho-to-para and Cl/Cl isotopic ratios
We report additional detections of the chloronium molecular ion, HCl,
toward four bright submillimeter continuum sources: G29.96, W49N, W51, and
W3(OH). With the use of the HIFI instrument on the Herschel Space Observatory,
we observed the transition of ortho-HCl at 781.627
GHz in absorption toward all four sources. Much of the detected absorption
arises in diffuse foreground clouds that are unassociated with the background
continuum sources and in which our best estimates of the ratio lie in the range .
These chloronium abundances relative to atomic hydrogen can exceed the
predictions of current astrochemical models by up to a factor of 5. Toward
W49N, we have also detected the transition of
ortho-HCl at 780.053 GHz and the transition of
para-HCl at 485.418 GHz. These observations imply column density ratios that are consistent with the
solar system Cl/Cl isotopic ratio of 3.1, and chloronium
ortho-to-para ratios consistent with 3, the ratio of spin statistical weights.Comment: 31 pages, including 7 figures. Accepted for publication in the Ap
A spectral line survey in the 2 mm and 1.3 mm windows toward the carbon rich envelope of IRC +10216
We present the results of our spectral line surveys in the 2 mm and 1.3 mm
windows toward the carbon rich envelope of IRC +10216. Totally 377 lines are
detected, among which 360 lines are assigned to 57 known molecules (including
29 rare isotopomers and 2 cyclic isomers). Only 17 weak lines remain
unidentified. Rotational lines of isotopomers 13CCH and HN13C are detected for
the first time in IRC +10216. The detection of the formaldehyde lines in this
star is also confirmed. Possible abundance difference among the three 13C
substituted isotopic isomers of HC3N is reported. Isotopic ratios of C and O
are confirmed to be non-solar while those of S and Si to be nearly solar.
Column densities have been estimated for 15 molecular species. Modified
spectroscopic parameters have been calculated for NaCN, Na13CN, KCN and SiC2.
Transition frequencies from the present observations were used to improve the
spectroscopic parameters of Si13CC, 29SiC2 and 30SiC2.Comment: 17 pages of text, 18 pages of 14 tables, 35 pages of 4 figures, a
typo corrected in Abstrac
A lambda=3 mm molecular line survey of NGC1068. Chemical signatures of an AGN environment
We aimed to study the molecular composition of the interstellar medium (ISM)
surrounding an Active Galactic Nucleus (AGN), by making an inventory of
molecular species and their abundances, as well as to establish a chemical
differentiation between starburst galaxies and AGN. We used the IRAM-30 m
telescope to observe the central 1.5-2 kpc region of NGC1068, covering the
frequencies between 86.2 GHz and 115.6 GHz. Using Boltzmann diagrams, we
calculated the column densities of the detected molecules. We used a chemical
model to reproduce the abundances found in the AGN, to determine the origin of
each detected species, and to test the influence of UV fields, cosmic rays, and
shocks on the ISM. We identified 24 different molecular species and
isotopologues, among which HC3N, SO, N2H+, CH3CN, NS, 13CN, and HN13C are
detected for the first time in NGC1068. We obtained the upper limits to the
isotopic ratios 12C/13C=49, 16O/18O=177 and 32S/34S=5. Our chemical models
suggest that the chemistry in the nucleus of NGC1068 is strongly influenced by
cosmic rays, although high values of both cosmic rays and far ultraviolet (FUV)
radiation fields also explain well the observations. The gas in the nucleus of
NGC1068 has a different chemical composition as compared to starburst galaxies.
The distinct physical processes dominating galaxy nuclei (e.g. C-shocks, UV
fields, X-rays, cosmic rays) leave clear imprints in the chemistry of the gas,
which allow to characterise the nucleus activity by its molecular abundances.Comment: 16 pages, 6 figures, 7 tables. Accepted for publication in Astronomy
and Astrophysic
Neutron-rich Chromium Isotope Anomalies in Supernova Nanoparticles
Neutron-rich isotopes with masses near that of iron are produced in Type Ia and II supernovae (SNeIa and SNeII). Traces of such nucleosynthesis are found in primitive meteorites in the form of variations in the isotopic abundance of ^(54)Cr, the most neutron-rich stable isotope of chromium. The hosts of these isotopic anomalies must be presolar grains that condensed in the outflows of SNe, offering the opportunity to study the nucleosynthesis of iron-peak nuclei in ways that complement spectroscopic observations and can inform models of stellar evolution. However, despite almost two decades of extensive search, the carrier of ^(54)Cr anomalies is still unknown, presumably because it is fine grained and is chemically labile. Here, we identify in the primitive meteorite Orgueil the carrier of ^(54)Cr anomalies as nanoparticles (3.6 × solar). Such large enrichments in ^(54)Cr can only be produced in SNe. The mineralogy of the grains supports condensation in the O/Ne-O/C zones of an SNII, although a Type Ia origin cannot be excluded. We suggest that planetary materials incorporated different amounts of these nanoparticles, possibly due to late injection by a nearby SN that also delivered ^(26)Al and ^(60)Fe to the solar system. This idea explains why the relative abundance of ^(54)Cr and other neutron-rich isotopes vary between planets and meteorites. We anticipate that future isotopic studies of the grains identified here will shed new light on the birth of the solar system and the conditions in SNe
Maser emission from SiO isotopologues traces the innermost 100 AU around Radio Source I in Orion BN/KL
We have used the Very Large Array (VLA) at 7 mm wavelength to image five
rotational transitions (J=1-0) from three SiO isotopologues towards Orion
BN/KL: 28SiO v=0,1,2; and 29SiO and 30SiO v=0. For the first time, we have
mapped the 29SiO and 30SiO J=1-0 emission, established the maser nature of the
emission, and confirmed association with the deeply embedded high-mass young
stellar object commonly denoted radio Source I. The 28SiO v=0 maser emission
shows a bipolar structure that extends over ~700 AU along a northeast-southwest
axis, and we propose that it traces a bipolar outflow driven by Source I. The
high-brightness isotopic SiO maser emission imaged with a ~0.2 arcsec
resolution has a more compact distribution, generally similar to that of the
28SiO v=1,2 emission, and it probably traces bulk gas flows in a region of
diameter <100 AU centered on Source I. On small scales of <10 AU, however,
compact 29SiO/30SiO v=0 and 28SiO v=1,2 emission features may be offset from
one another in position and line-of-sight velocity.
From a radiative transfer analysis based on a large velocity gradient (LVG)
pumping model, we derive similar temperatures and densities for the optimum
excitation of both 29SiO/30SiO v=0 and 28SiO v=1,2 masers, significantly higher
than required for 28SiO v=0 maser excitation. In order to account for the
small-scale differences among the isotopologues (v=0) and the main species
(v=1,2), follow-up radiative transfer modeling that incorporates non-local line
overlap among transitions of all SiO isotopic species may be required.Comment: 10 pages, 3 figures, accepted for publication by Ap
Ground-State SiO Maser Emission Toward Evolved Stars
We have made the first unambiguous detection of vibrational ground-state
maser emission from SiO toward six evolved stars. Using the Very Large Array,
we simultaneously observed the v=0, J=1-0, 43.4-GHz, ground-state and the v=1,
J=1-0, 43.1-GHz, first excited-state transitions of SiO toward the oxygen-rich
evolved stars IRC+10011, o Ceti, W Hya, RX Boo, NML Cyg, and R Cas and the
S-type star chi Cyg. We detected at least one v=0 SiO maser feature from six of
the seven stars observed, with peak maser brightness temperatures ranging from
10,000 K to 108,800 K. In fact, four of the seven v=0 spectra show multiple
maser peaks, a phenomenon which has not been previously observed. Ground-state
thermal emission was detected for one of the stars, RX Boo, with a peak
brightness temperature of 200 K. Comparing the v=0 and the v=1 transitions, we
find that the ground-state masers are much weaker with spectral characteristics
different from those of the first excited-state masers. For four of the seven
stars the velocity dispersion is smaller for the v=0 emission than for the v=1
emission, for one star the dispersions are roughly equivalent, and for two
stars (one of which is RX Boo) the velocity spread of the v=0 emission is
larger. In most cases, the peak flux density in the v=0 emission spectrum does
not coincide with the v=1 maser peak. Although the angular resolution of these
VLA observations were insufficient to completely resolve the spatial structure
of the SiO emission, the SiO spot maps produced from the interferometric image
cubes suggest that the v=0 masers are more extended than their v=1
counterparts
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