54 research outputs found
Search for methylamine in high mass hot cores
We aim to detect methylamine, CHNH, in a variety of hot cores and
use it as a test for the importance of photon-induced chemistry in ice mantles
and mobility of radicals. Specifically, CHNH cannot be formed from atom
addition to CO whereas other NH-containing molecules such as formamide,
NHCHO, can. Submillimeter spectra of several massive hot core regions were
taken with the James Clerk Maxwell Telescope. Abundances are determined with
the rotational diagram method where possible. Methylamine is not detected,
giving upper limit column densities between 1.9 6.4 10
cm for source sizes corresponding to the 100 K envelope radius. Combined
with previously obtained JCMT data analyzed in the same way, abundance ratios
of CHNH, NHCHO and CHCN with respect to each other and
to CHOH are determined. These ratios are compared with Sagittarius B2
observations, where all species are detected, and to hot core models. The
observed ratios suggest that both methylamine and formamide are overproduced by
up to an order of magnitude in hot core models. Acetonitrile is however
underproduced. The proposed chemical schemes leading to these molecules are
discussed and reactions that need further laboratory studies are identified.
The upper limits obtained in this paper can be used to guide future
observations, especially with ALMA.Comment: 14 pages, 5 figures, accepted for publication in A&
Interstellar bromine abundance is consistent with cometary ices from Rosetta
Cometary ices are formed during star and planet formation, and their
molecular and elemental makeup can be related to the early solar system via the
study of inter- and protostellar material. The first cometary abundance of the
halogen element bromine (Br) was recently made available by the Rosetta
mission. Its abundance in protostellar gas is thus far unconstrained, however.
We set out to place the first observational constraints on the interstellar
gas-phase abundance of bromine (Br). We further aim to compare the protostellar
Br abundance with that measured by Rosetta in the ices of comet
67P/Churyumov-Gerasimenko. Archival Herschel data of Orion KL, Sgr B2(N), and
NGC 6334I are examined for the presence of HBr and HBr emission or
absorption lines. A chemical network for modelling HBr in protostellar
molecular gas is compiled to aid in the interpretation. HBr and HBr were
not detected towards any of our targets. However, in the Orion KL Hot Core, our
upper limit on HBr/HO is a factor of ten below the ratio measured in
comet 67P. This result is consistent with the chemical network prediction that
HBr is not a dominant gas-phase Br carrier. Cometary HBr is likely
predominantly formed in icy grain mantles which lock up nearly all elemental
Br.Comment: Accepted for publication in A&A. 9 pages, 6 figure
Interstellar bromine abundance is consistent with cometary ices from Rosetta
Cometary ices are formed during star and planet formation, and their
molecular and elemental makeup can be related to the early solar system via the
study of inter- and protostellar material. The first cometary abundance of the
halogen element bromine (Br) was recently made available by the Rosetta
mission. Its abundance in protostellar gas is thus far unconstrained, however.
We set out to place the first observational constraints on the interstellar
gas-phase abundance of bromine (Br). We further aim to compare the protostellar
Br abundance with that measured by Rosetta in the ices of comet
67P/Churyumov-Gerasimenko. Archival Herschel data of Orion KL, Sgr B2(N), and
NGC 6334I are examined for the presence of HBr and HBr emission or
absorption lines. A chemical network for modelling HBr in protostellar
molecular gas is compiled to aid in the interpretation. HBr and HBr were
not detected towards any of our targets. However, in the Orion KL Hot Core, our
upper limit on HBr/HO is a factor of ten below the ratio measured in
comet 67P. This result is consistent with the chemical network prediction that
HBr is not a dominant gas-phase Br carrier. Cometary HBr is likely
predominantly formed in icy grain mantles which lock up nearly all elemental
Br.Comment: Accepted for publication in A&A. 9 pages, 6 figure
The formation of CO through consumption of gas-phase CO on vacuum-UV irradiated water ice
[Abridged] Observations of protoplanetary disks suggest that they are
depleted in gas-phase CO. It has been posed that gas-phase CO is chemically
consumed and converted into less volatile species through gas-grain processes.
Observations of interstellar ices reveal a CO component within HO ice
suggesting co-formation. The aim of this work is to experimentally verify the
interaction of gas-phase CO with solid-state OH radicals above the sublimation
temperature of CO. Amorphous solid water (ASW) is deposited at 15 K and
followed by vacuum-UV (VUV) irradiation to dissociate HO and create OH
radicals. Gas-phase CO is simultaneously admitted and only adsorbs with a short
residence time on the ASW. Products in the solid state are studied with
infrared spectroscopy and once released into the gas phase with mass
spectrometry. Results show that gas-phase CO is converted into CO, with an
efficiency of 7-27%, when interacting with VUV irradiated ASW. Between 40 and
90 K, CO production is constant, above 90 K, O production takes over.
In the temperature range of 40-60 K, the CO remains in the solid state,
while at temperatures 70 K the formed CO is released into the gas
phase. We conclude that gas-phase CO reacts with solid-state OH radicals above
its sublimation temperature. This gas-phase CO and solid-state OH radical
interaction could explain the observed CO embedded in water-rich ices. It
may also contribute to the observed lack of gas-phase CO in planet-forming
disks, as previously suggested. Our experiments indicate a lower water ice
dissociation efficiency than originally adopted in model descriptions of
planet-forming disks and molecular clouds. Incorporation of the reduced water
ice dissociation and increased binding energy of CO on a water ice surfaces in
these models would allow investigation of this gas-grain interaction to its
full extend.Comment: Accepted for publication in Astronomy & Astrophysic
A major asymmetric ice trap in a planet-forming disk IV. Nitric oxide gas and a lack of CN tracing sublimating ices and a C/O ratio
[Abridged] Most well-resolved disks observed with ALMA show signs of dust
traps. These dust traps set the chemical composition of the planet forming
material in these disks, as the dust grains with their icy mantles are trapped
at specific radii and could deplete the gas and dust of volatiles at smaller
radii. In this work we analyse the first detection of nitric oxide (NO) in a
protoplanetary disk. We aim to constrain the nitrogen chemistry and the
gas-phase C/O ratio in the highly asymmetric dust trap in the Oph-IRS 48 disk.
We use ALMA observations of NO, CN, CH, and related molecules and model the
effect of the dust trap on the physical and chemical structure using the
thermochemical code DALI. Furthermore, we explore how ice sublimation
contributes to the observed emission lines. NO is only observed at the location
of the dust trap but CN and CH are not detected in the Oph-IRS 48 disk.
This results in an CN/NO column density ratio of and thus a low C/O
ratio at the location of the dust trap. The main gas-phase formation pathways
to NO through OH and NH in the fiducial model predict NO emission that is an
order of magnitude lower than is observed. The gaseous NO column density can be
increased by factors ranging from 2.8 to 10 when the HO and NH gas
abundances are significantly boosted by ice sublimation. However, these models
are inconsistent with the upper limits on the HO and OH column densities
derived from observations. We propose that the NO emission in the Oph-IRS 48
disk is closely related to the nitrogen containing ices sublimating in the dust
trap. The non-detection of CN constrains the C/O ratio both inside and outside
the dust trap to be if all nitrogen initially starts as N and , consistent with the Solar value, if (part of) the nitrogen initially
starts as N or NH.Comment: Accepted for publication in Astronomy and Astrophysic
The formation of peptide-like molecules on interstellar dust grains
Molecules with an amide functional group resemble peptide bonds, the
molecular bridges that connect amino acids, and may thus be relevant in
processes that lead to the formation of life. In this study, the solid state
formation of some of the smallest amides is investigated in the laboratory. To
this end, CH:HNCO ice mixtures at 20 K are irradiated with far-UV
photons, where the radiation is used as a tool to produce the radicals required
for the formation of the amides. Products are identified and investigated with
infrared spectroscopy and temperature programmed desorption mass spectrometry.
The laboratory data show that NHCHO, CHNCO, NHC(O)NH,
CHC(O)NH and CHNH can simultaneously be formed. The
NHCO radical is found to be key in the formation of larger amides. In
parallel, ALMA observations towards the low-mass protostar IRAS 16293-2422B are
analysed in search of CHNHCHO (N-methylformamide) and
CHC(O)NH (acetamide). CHC(O)NH is tentatively detected
towards IRAS 16293-2422B at an abundance comparable with those found towards
high-mass sources. The combined laboratory and observational data indicates
that NHCHO and CHC(O)NH are chemically linked and form in the
ice mantles of interstellar dust grains. A solid-state reaction network for the
formation of these amides is proposed.Comment: Accepted for publication in MNRA
Molecular complexity on disc scales uncovered by ALMA: Chemical composition of the high-mass protostar AFGL 4176
Context. The chemical composition of high-mass protostars reflects the physical evolution associated with different stages of star formation. In addition, the spatial distribution and velocity structure of different molecular species provide valuable information on the physical structure of these embedded objects. Despite an increasing number of interferometric studies, there is still a high demand for high angular resolution data to study chemical compositions and velocity structures for these objects. Aims. The molecular inventory of the forming high-mass star AFGL 4176, located at a distance of ∼3.7 kpc, is studied in detail at a high angular resolution of ∼0.35′′, equivalent to ∼1285 au at the distance of AFGL 4176. This high resolution makes it possible to separate the emission associated with the inner hot envelope and disc around the forming star from that of its cool outer envelope. The composition of AFGL 4176 is compared with other high- and low-mass sources, and placed in the broader context of star formation. Methods. Using the Atacama Large Millimeter/submillimeter Array (ALMA) the chemical inventory of AFGL 4176 has been characterised. The high sensitivity of ALMA made it possible to identify weak and optically thin lines and allowed for many isotopologues to be detected, providing a more complete and accurate inventory of the source. For the detected species, excitation temperatures in the range 120-320 K were determined and column densities were derived assuming local thermodynamic equilibrium and using optically thin lines. The spatial distribution of a number of species was studied. Results. A total of 23 different molecular species and their isotopologues are detected in the spectrum towards AFGL 4176. The most abundant species is methanol (CH3OH) with a column density of 5.5
7 1018 cm-2 in a beam of ∼0.3″, derived from its 13C-isotopologue. The remaining species are present at levels between 0.003 and 15% with respect to methanol. Hints that N-bearing species peak slightly closer to the location of the peak continuum emission than the O-bearing species are seen. A single species, propyne (CH3C2H), displays a double-peaked distribution. Conclusions. AFGL 4176 comprises a rich chemical inventory including many complex species present on disc scales. On average, the derived column density ratios, with respect to methanol, of O-bearing species are higher than those derived for N-bearing species by a factor of three. This may indicate that AFGL 4176 is a relatively young source since nitrogen chemistry generally takes longer to evolve in the gas phase. Taking methanol as a reference, the composition of AFGL 4176 more closely resembles that of the low-mass protostar IRAS 16293-2422B than that of high-mass, star-forming regions located near the Galactic centre. This similarity hints that the chemical composition of complex species is already set in the cold cloud stage and implies that AFGL 4176 is a young source whose chemical composition has not yet been strongly processed by the central protostar
Compactification near and on the light front
We address problems associated with compactification near and on the light
front. In perturbative scalar field theory we illustrate and clarify the
relationships among three approaches: (1) quantization on a space-like surface
close to a light front; (2) infinite momentum frame calculations; and (3)
quantization on the light front. Our examples emphasize the difference between
zero modes in space-like quantization and those in light front quantization. In
particular, in perturbative calculations of scalar field theory using
discretized light cone quantization there are well-known ``zero-mode induced''
interaction terms. However, we show that they decouple in the continuum limit
and covariant answers are reproduced. Thus compactification of a light-like
surface is feasible and defines a consistent field theory.Comment: 24 pages, 4 figure
Recommended from our members
Toward Detecting Polycyclic Aromatic Hydrocarbons on Planetary Objects with ORIGIN
Polycyclic aromatic hydrocarbons (PAHs) are found on various planetary surfaces in the solar system. They are proposed to play a role in the emergence of life, as molecules that are important for biological processes could be derived from them. In this work, four PAHs (pyrene, perylene, anthracene, and coronene) were measured using the ORganics Information Gathering INstrument system (ORIGIN), a lightweight laser desorption ionization-mass spectrometer designed for space exploration missions. In this contribution, we demonstrate the current measurement capabilities of ORIGIN in detecting PAHs at different concentrations and applied laser pulse energies. Furthermore, we show that chemical processing of the PAHs during measurement is limited and that the parent mass can be detected in the majority of cases. The instrument achieves a 3σ detection limit in the order of femtomol mm−2 for all four PAHs, with the possibility of further increasing this sensitivity. This work illustrates the potential of ORIGIN as an instrument for the detection of molecules important for the emergence or presence of life, especially when viewed in combination with previous results by the instrument, such as the identification of amino acids. ORIGIN could be used on a lander or rover platform for future in situ missions to targets in the solar system, such as the icy moons of Jupiter or Saturn
The Generalized Gell-Mann--Low Theorem for Relativistic Bound States
The recently established generalized Gell-Mann--Low theorem is applied in
lowest perturbative order to bound-state calculations in a simple scalar field
theory with cubic couplings. The approach via the generalized Gell-Mann--Low
Theorem retains, while being fully relativistic, many of the desirable features
of the quantum mechanical approaches to bound states. In particular, no
abnormal or unphysical solutions are found in the model under consideration.
Both the non-relativistic and one-body limits are straightforward and
consistent. The results for the spectrum are compared to those of the
Bethe-Salpeter equation (in the ladder approximation) and related equations.Comment: 24 pages, 6 pspicture diagrams, 4 postscript figure
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