1,150 research outputs found
The census of complex organic molecules in the solar type protostar IRAS16293-2422
Complex Organic Molecules (COMs) are considered crucial molecules, since they
are connected with organic chemistry, at the basis of the terrestrial life.
More pragmatically, they are molecules in principle difficult to synthetize in
the harsh interstellar environments and, therefore, a crucial test for
astrochemical models. Current models assume that several COMs are synthesised
on the lukewarm grain surfaces (30-40 K), and released in the gas
phase at dust temperatures 100 K. However, recent detections of COMs
in 20 K gas demonstrate that we still need important pieces to
complete the puzzle of the COMs formation. We present here a complete census of
the oxygen and nitrogen bearing COMs, previously detected in different ISM
regions, towards the solar type protostar IRAS16293-2422. The census was
obtained from the millimeter-submillimeter unbiased spectral survey TIMASSS.
Six COMs, out of the 29 searched for, were detected: methyl cyanide, ketene,
acetaldehyde, formamide, dimethyl ether, and methyl formate. The multifrequency
analysis of the last five COMs provides clear evidence that they are present in
the cold (30 K) envelope of IRAS16293-2422, with abundances 0.03-2
. Our data do not allow to support the hypothesis that the
COMs abundance increases with increasing dust temperature in the cold envelope,
as expected if COMs were predominately formed on the lukewarm grain surfaces.
Finally, when considering also other ISM sources, we find a strong correlation
over five orders of magnitude, between the methyl formate and dimethyl ether
and methyl formate and formamide abundances, which may point to a link between
these two couples of species, in cold and warm gas
Elastic and Raman scattering of 9.0 and 11.4 MeV photons from Au, Dy and In
Monoenergetic photons between 8.8 and 11.4 MeV were scattered elastically and
in elastically (Raman) from natural targets of Au, Dy and In.15 new cross
sections were measured. Evidence is presented for a slight deformation in the
197Au nucleus, generally believed to be spherical. It is predicted, on the
basis of these measurements, that the Giant Dipole Resonance of Dy is very
similar to that of 160Gd. A narrow isolated resonance at 9.0 MeV is observed in
In.Comment: 31 pages, 11 figure
Estimates in Beurling--Helson type theorems. Multidimensional case
We consider the spaces of functions on the
-dimensional torus such that the sequence of the Fourier
coefficients belongs to
. The norm on is defined by
. We study the rate of
growth of the norms as
for -smooth real
functions on (the one-dimensional case was investigated
by the author earlier). The lower estimates that we obtain have direct
analogues for the spaces
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
Shedding light on the formation of the pre-biotic molecule formamide with ASAI
Formamide (NH2CHO) has been proposed as a pre-biotic precursor with a key
role in the emergence of life on Earth. While this molecule has been observed
in space, most of its detections correspond to high-mass star-forming regions.
Motivated by this lack of investigation in the low-mass regime, we searched for
formamide, as well as isocyanic acid (HNCO), in 10 low- and intermediate-mass
pre-stellar and protostellar objects. The present work is part of the IRAM
Large Programme ASAI (Astrochemical Surveys At IRAM), which makes use of
unbiased broadband spectral surveys at millimetre wavelengths. We detected HNCO
in all the sources and NH2CHO in five of them. We derived their abundances and
analysed them together with those reported in the literature for high-mass
sources. For those sources with formamide detection, we found a tight and
almost linear correlation between HNCO and NH2CHO abundances, with their ratio
being roughly constant -between 3 and 10- across 6 orders of magnitude in
luminosity. This suggests the two species are chemically related. The sources
without formamide detection, which are also the coldest and devoid of hot
corinos, fall well off the correlation, displaying a much larger amount of HNCO
relative to NH2CHO. Our results suggest that, while HNCO can be formed in the
gas phase during the cold stages of star formation, NH2CHO forms most
efficiently on the mantles of dust grains at these temperatures, where it
remains frozen until the temperature rises enough to sublimate the icy grain
mantles. We propose hydrogenation of HNCO as a likely formation route leading
to NH2CHO.Comment: 26 pages, 9 figures. Accepted by Monthly Notices of the Royal
Astronomical Societ
Complex organics in IRAS 4A revisited with ALMA and PdBI: Striking contrast between two neighbouring protostellar cores
We used the Atacama Large (sub-)Millimeter Array (ALMA) and the IRAM Plateau
de Bure Interferometer (PdBI) to image, with an angular resolution of 0.5
(120 au) and 1 (235 au), respectively, the emission from 11 different
organic molecules in the protostellar binary NGC1333 IRAS 4A. We clearly
disentangled A1 and A2, the two protostellar cores present. For the first time,
we were able to derive the column densities and fractional abundances
simultaneously for the two objects, allowing us to analyse the chemical
differences between them. Molecular emission from organic molecules is
concentrated exclusively in A2 even though A1 is the strongest continuum
emitter. The protostellar core A2 displays typical hot corino abundances and
its deconvolved size is 70 au. In contrast, the upper limits we placed on
molecular abundances for A1 are extremely low, lying about one order of
magnitude below prestellar values. The difference in the amount of organic
molecules present in A1 and A2 ranges between one and two orders of magnitude.
Our results suggest that the optical depth of dust emission at these
wavelengths is unlikely to be sufficiently high to completely hide a hot corino
in A1 similar in size to that in A2. Thus, the significant contrast in
molecular richness found between the two sources is most probably real. We
estimate that the size of a hypothetical hot corino in A1 should be less than
12 au. Our results favour a scenario in which the protostar in A2 is either
more massive and/or subject to a higher accretion rate than A1, as a result of
inhomogeneous fragmentation of the parental molecular clump. This naturally
explains the smaller current envelope mass in A2 with respect to A1 along with
its molecular richness.Comment: Accepted in Astronomy and Astrophysic
Hormones and temporal components of speech: sex differences and effects of menstrual cyclicity on speech
Voice onset time (VOT) is a salient acoustic parameter of speech which signals the âvoicedâ and âvoicelessâ status of plosives in English (e.g. the initial sound in âbatâ vs. the initial sound in âpatâ). As a micro-temporal acoustic parameter, VOT may be sensitive to changes in hormones which may affect the neuromuscular systems involved in speech production. This study adopted a novel approach by investigating the effects of menstrual cycle phase and sex on VOT. VOT data representing the 6 plosives of English (/p b t d k g/) were examined for 7 women (age 20-23 years) at two phases of the menstrual cycle (day 18-25: High Estrogen and Progesterone; day 2-5: Low Estrogen and Progesterone). Results indicated that menstrual cycle phase had a significant interaction with the identity of the plosive (F (5,30) = 5.869, P .05), or the contrast between voiced and voiceless cognates (F (1,10) = .407, P > .05). In contrast, the high hormone phase VOT samples displayed significant plosive by sex interactions (F (5,50) = 4.442, P < .005). In addition, significant sex differences were found for the contrasts between cognate voiced and voiceless plosives (F (1,10) = 5.019, P < .05); the women displayed a more marked voiced/voiceless contrast. The findings suggest that ovarian hormones play some role in shaping some temporal components of speech
Vertical Structure of the Transition Zone from Infalling Rotating Envelope to Disk in the Class 0 Protostar, IRAS04368+2557
We have resolved for the first time the radial and vertical structure of the
almost edge-on envelope/disk system of the low-mass Class 0 protostar L1527.
For that, we have used ALMA observations with a spatial resolution of
0.250.13 and
0.370.23 at 0.8 mm and 1.2 mm,
respectively. The L1527 dust continuum emission has a deconvolved size of 78 au
21 au, and shows a flared disk-like structure. A thin
infalling-rotating envelope is seen in the CCH emission outward of about 150
au, and its thickness is increased by a factor of 2 inward of it. This radius
lies between the centrifugal radius (200 au) and the centrifugal barrier of the
infalling-rotating envelope (100 au). The gas stagnates in front of the
centrifugal barrier and moves toward vertical directions. SO emission is
concentrated around and inside the centrifugal barrier. The rotation speed of
the SO emitting gas is found to be decelerated around the centrifugal barrier.
A part of the angular momentum could be extracted by the gas which moves away
from the mid-plane around the centrifugal barrier. If this is the case, the
centrifugal barrier would be related to the launching mechanism of low velocity
outflows, such as disk winds
Lognormal scale invariant random measures
In this article, we consider the continuous analog of the celebrated
Mandelbrot star equation with lognormal weights. Mandelbrot introduced this
equation to characterize the law of multiplicative cascades. We show existence
and uniqueness of measures satisfying the aforementioned continuous equation;
these measures fall under the scope of the Gaussian multiplicative chaos theory
developed by J.P. Kahane in 1985 (or possibly extensions of this theory). As a
by product, we also obtain an explicit characterization of the covariance
structure of these measures. We also prove that qualitative properties such as
long-range independence or isotropy can be read off the equation.Comment: 31 pages; Probability Theory and Related Fields (2012) electronic
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