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ABSTRACT: New centimeter-wave (7–80 GHz) and submillimeter-wave (580–661 GHz) spectra of a deuterated species of methyl formate (DCOOCH 3) have been measured. Transitions with a maximum value of J = 64 and K = 36 have been assigned and fitted together with previous measurements. The internal rotation of this compound was treated using the so-called rho axis method. A total of 1703 transitions were fitted using this method. Only 24 parameters were employed in the final fit, which has an rms deviation of 94.2 kHz. The dipole moment and the nuclear quadrupole coupling constants of the deuterated specie have also been obtained. This new study has permitted a tentative detection of DCOOCH 3 in Orion with the IRAM 30 m telescope based on the observation of more than 100 spectral features with low blending effects among the 400 lines expected in the observed frequency domain (for which over 300 are heavily blended with other species). These 100 transitions are above noise and confusion limited without heavy blending and cannot be assigned to any other species. Moreover, none of the strongest unblended transitions is missing. The derived source-averaged total column density for DCOOCH 3 is 7.8 × 10 14 cm −2 and the DCOOCH 3 /HCOOCH 3 column density ratio varies between 0.02 and 0.06 in the different cloud components of Orion. This value is consistent with the deuteration enhancement found for other species in this cloud.
The Astrophysical Journal. 10/2015; 714:1120-1132.
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ABSTRACT: We report on the discovery of methyl acetate, CH3COOCH3, through the
detection of a large number of rotational lines from each one of the spin
states of the molecule: AA species (A1 or A2), EA species (E1), AE species
(E2), EE species (E3 or E4). We also report the detection, for the first time
in space, of the $gauche$ conformer of ethyl formate, CH3CH2OCOH, in the same
source. The trans conformer is also detected for the first time outside the
galactic center source SgrB2. From the derived velocity of the emission of
methyl acetate we conclude that it arises mainly from the compact ridge region
with a total column density of (4.2+-0.5)E15 cm(-2). The derived rotational
temperature is 150 K. The column density for each conformer of ethyl formate,
trans and gauche, is (4.5+-1.0)E14 cm(-2). Their abundance ratio indicates a
kinetic temperature of 135 K for the emitting gas and suggests that gas phase
reactions could participate efficiently in the formation of both conformers in
addition to cold ice mantle reactions on the surface of dust grains.
05/2013;
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ABSTRACT: We present a study of the Silicon-bearing species detected in a line confusion limited survey towards Orion KL performed with the IRAM 30-m telescope, which ranges from 80 to 280 GHz. Our aim is to derive physical and chemical conditions for each family taking into account all observed lines from all isotopologues of each species. We have modeled the lines of the detected molecules using a radiative transfer code, which permit us to choose between LVG and LTE approximations depending on the physical conditions of the gas. We have used appropriate collisional rates for the LVG calculations. For the v=1 state of SiO we have detected the J=2-1 line and, for the first time in this source, emission in the J=4-3 transition, both of them showing strong masering effect. For SiO v=0, we have detected 28SiO, 29SiO, and 30SiO; in addition, we have mapped the J = 5-4 SiO line. For SiS, we have detected the main species, 29SiS, and SiS v=1. Unlikely other species detected in Orion KL (IRc2), the emission peak of SiS appears at a velocity of ~15.5 km s-1; a study of the 5-4 SiO line around IRc2 shows this feature as an extended component that probably arises from the interaction of the outflow with the ambient cloud. We derive a SiO/SiS column density ratio of ~13 in the plateau component. Besides, we provide upper limits to the column density of several non-detected Silicon-bearing species. The results of our chemical models show that while it is possible to reproduce SiO in the gas phase (as well as on the grains), SiS is a product of surface reactions, most likely involving direct reactions of S with Si. Comment: Astronomy and Astrophysics, in press
12/2010;
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L. Decin,
J. Cernicharo,
M. J. Barlow,
P. Royer,
B. Vandenbussche,
R. Wesson,
E. T. Polehampton,
E. De Beck,
M. Agúndez,
J. A. D. L. Blommaert, [......],
G. Olofsson,
T. Posch,
S. Regibo,
G. Savini,
B. Sibthorpe,
B. M. Swinyard, B. Tercero,
C. Waelkens,
D. K. Witherick,
J. A. Yates
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ABSTRACT: The interstellar medium is enriched primarily by matter ejected from evolved low and intermediate mass stars. The outflows from these stars create a circumstellar envelope in which a rich gas-phase and dust-nucleation chemistry takes place. We observed the nearest carbon-rich evolved star, IRC+10216, using the PACS (55-210 {\mu}m) and SPIRE (194-672 {\mu}m) spectrometers on board Herschel. We find several tens of lines from SiS and SiO, including lines from the v=1 vibrational level. For SiS these transitions range up to J=124-123, corresponding to energies around 6700K, while the highest detectable transition is J=90-89 for SiO, which corresponds to an energy around 8400K. Both species trace the dust formation zone of IRC+10216, and the broad energy ranges involved in their detected transitions permit us to derive the physical properties of the gas and the particular zone in which each species has been formed. This allows us to check the accuracy of chemical thermodynamical equilibrium models and the suggested depletion of SiS and SiO due to accretion onto dust grains. Comment: 5 pages, 3 figures, 7 pages in online appendix, Astronomy & Astrophysics in press
05/2010;
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ABSTRACT: We perform a sensitive (line confusion limited), single-side band spectral survey towards Orion KL with the IRAM 30m telescope, covering the following frequency ranges: 80-115.5 GHz, 130-178 GHz, and 197-281 GHz. We detect more than 14 400 spectral features of which 10 040 have been identified up to date and attributed to 43 different molecules, including 148 isotopologues and lines from vibrationally excited states. In this paper, we focus on the study of OCS, HCS+, H2CS, CS, CCS, C3S, and their isotopologues. In addition, we map the OCS J=18-17 line and complete complementary observations of several OCS lines at selected positions around Orion IRc2 (the position selected for the survey). We report the first detection of OCS v2 = 1 and v3 = 1 vibrationally excited states in space and the first detection of C3S in warm clouds. Most of CCS, and almost all C3S, line emission arises from the hot core indicating an enhancement of their abundances in warm and dense gas. Column densities and isotopic ratios have been calculated using a large velocity gradient (LVG) excitation and radiative transfer code (for the low density gas components) and a local thermal equilibrium (LTE) code (appropriate for the warm and dense hot core component), which takes into account the different cloud components known to exist towards Orion KL, the extended ridge, compact ridge, plateau, and hot core. The vibrational temperature derived from OCS v2 = 1 and v3 = 1 levels is about 210 K, similar to the gas kinetic temperature in the hot core. These OCS high energy levels are probably pumped by absorption of IR dust photons. We derive an upper limit to the OC3S, H2CCS, HNCS, HOCS+, and NCS column densities. Finally, we discuss the D/H abundance ratio and infer the following isotopic abundances: 12C/13C=45+-20, 32S/34S=20+-6, 32S/33S=75+-29, and 16O/18O=250+-135. Comment: Accepted for publication in A&A
04/2010;
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M. Carvajal,
L. Margulès, B. Tercero,
K. Demyk,
I. Kleiner,
Guillemin,
J.~C,
V. Lattanzi,
A. Walters,
J. Demaison,
G. Wlodarczak,
Huet,
T.~R,
H. Møllendal,
Ilyushin,
V.~V,
J. Cernicharo
åp. 06/2009; 500:1109-1118.
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ABSTRACT: We report on the first detection in space of fulminic acid, HCNO. This isomer of HNCO has been observed in three starless cores, B1, L1544 and L183, and in the low mass star forming region L1527 with a measured abundance ratio of HNCO/HCNO between 40-70. However, HCNO was not detected towards the direction of the cyanopolyyne peak of TMC-1 or towards the Orion Hot Core region. The derived HNCO/HCNO abundance ratio in these cases is greater than 350 and 1000 in TMC-1 and Orion, respectively. We find that CH_2 + NO \to HCNO + H is a key reaction for the formation of fulminic acid. A value of 5.5 10^{-12} cm^3 s^{-1} of the corresponding reaction rate coefficient, as given by Miller et al. (2003), allows to reproduce the observed abundances of fulminic acid in both the observed dark clouds and low mass star forming core, where the determined abundance of HNCO in these regions with respect to molecular hydrogen is 1-5 10^{-10}.
The Astrophysical Journal 12/2008; · 6.02 Impact Factor
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ABSTRACT: We report on the first detection of maser emission in the J=11-10, J=14-13 and J=15-14 transitions of the v=0 vibrational state of SiS toward the C-rich star IRC+10216. These masers seem to be produced in the very inhomogeneous region between the star and the inner dust formation zone, placed at 5-7 R*, with expansion velocities below 10 km/s. We interpret the pumping mechanism as due to overlaps between v=1-0 ro-vibrational lines of SiS and mid-IR lines of C2H2, HCN and their 13C isotopologues. The large number of overlaps found suggests the existence of strong masers for high-J v=0 and v=1 SiS transitions, located in the submillimeter range. In addition, it could be possible to find several rotational lines of the SiS isotopologues displaying maser emission. Comment: 4 pages, 1 figure, published in the ApJ Letters
10/2007;
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åp. 04/2007; 466:255-259.
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L. Decin,
J. Cernicharo,
MJ Barlow,
P. Royer,
B. Vandenbussche,
R. Wesson,
ET Polehampton,
E. De Beck,
M. Agundez,
JADL Blommaert, [......],
G. Olofsson,
T. Posch,
S. Regibo,
G. Savini,
B. Sibthorpe,
BM Swinyard, B. Tercero,
C. Waelkens,
DK Witherick,
JA Yates
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M. Carvajal,
L. Margulès, B. Tercero,
K. Demyk,
I. Kleiner,
J. C. Guillemin,
V. Lattanzi,
A. Walters,
J. Demaison,
G. Wlodarczak,
T R Huet,
H. Møllendal,
V. V. Ilyushin,
J. Cernicharo
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ABSTRACT: Context. Laboratory measurements and analysis of the microwave and millimeter-wave spectra of potential interstellar molecules are a prerequisite for their subsequent identification by radioastronomical techniques. The spectral analysis provides spectroscopic parameters that are used in the assignment procedure of the laboratory spectra, and that also predict the frequencies of transitions not measured in the laboratory with a high degree of precision.
Aims. An experimental laboratory study and its theoretical analysis is presented for $^{13}$C$_2$-methyl formate (HCOO$^{13}$CH$_3$) allowing a search for this isotopologue in the Orion molecular cloud. The $^{13}$C$_1$-methyl formate (H$^{13}$COOCH$_3$) molecule was also searched for in this interstellar cloud, using previously published spectroscopic data.Methods. The experimental spectra of $^{13}$C$_2$-methyl formate were recorded in the microwave and sub-mm energy ranges (4–20 GHz, 8–80 GHz, 150–700 GHz). The spectra were analyzed using the Rho-Axis Method (RAM), which takes the CH$_3$ internal rotation and the coupling between internal rotation and global rotation into account.Results. Twenty-seven spectroscopic constants of $^{13}$C$_2$-methyl formate have been obtained from a fit of 936 transitions of the ground torsional state with a standard (unitless) deviation of 1.08. A prediction of line positions and intensities is also produced. This prediction allowed us to identify 230 $^{13}$C$_2$-methyl formate lines in the Orion interstellar molecular cloud. We refitted all previously published ground state transitions of the $^{13}$C$_1$-methyl formate molecule in order to provide a prediction of its ground state spectrum. 234 lines of $^{13}$C$_1$-methyl formate were detected in the Orion interstellar cloud using that prediction.
http://dx.doi.org/10.1051/0004-6361/200811456.
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L. Decin,
J. Cernicharo,
M. J. Barlow,
P. Royer,
B. Vandenbussche,
R. Wesson,
E. T. Polehampton,
E. De Beck,
M. Agúndez,
J. A. D. L. Blommaert, [......],
G. Olofsson,
T. Posch,
S. Regibo,
G. Savini,
B. Sibthorpe,
B. M. Swinyard, B. Tercero,
C. Waelkens,
D. K. Witherick,
J. A. Yates
http://dx.doi.org/10.1051/0004-6361/201014562.
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ABSTRACT: We have carried out a sensitive, fully single side band reduded and line
confusion limited survey toward Orion KL with the IRAM 30 m telescope.
We have covered all the frequencies allowed by the 30 m (more than 168
GHz): 80-115.5 GHz, 130-179 GHz and 197-281 GHz. We present the data and
the strategy for the data reduction and line identification. In
addition, we present the first results like the detection of
Si18O and Si17O for the first time in space. 1.
Introduction The Orion KL cloud is the prototype of high mass star
forming region and one of the best studied regions of our galaxy. The
chemistry in this cloud is particularly rich resulting from the
interaction of the newly formed stars and their environment. The
evaporation of dust mantles in some regions of the KL cloud produces
complex molecules in the gas phase which are responsible of a
spectacularly prolific line spectrum. Many line surveys have been
performed in this region in the last 20 years (Johansson et al., 1984;
Jewell et al., 1989, Turner 1989; Blake et al., 1986, 1996; Ziurys &
McGonagle 1993; Schilke et al., 1997, 2001; Comito et al., 2005) but no
systematic surveys, and highly sensitive, of this exciting source had
been done, so far with the IRAM instruments. Complete frequency coverage
in line surveys is the best way to understand the chemical complexity of
molecular sources. 2. Observations, data reduction and line
identification We carried out the observations during September 2004,
March 2005 and April 2005. We covered all the ranges of frequency
allowed by the telescope down to the proposed S/N (line confusion
limit). The observing time per setting to reach this limit was about 10
minutes in all the frequencies. Due to the high line density in Orion,
and in spite of the good band rejection of the 30 m receivers, each
frquency setting was repeated at a slightly shifted frequency (20 MHz,
no new tunnig needed) in order to allow the separation of all lines
arising from the image side band. However, this scheme does not
guarantee that all lines blended with ISB features could be fully
characterized. The main source for line identification is the millimeter
and submillimeter line catalog created and maintained by one of us (J.
C.) with 1250 molecular species. The catalog is accompained by a set of
routines that allow the computation of LTE spectra for all molecular
species and LVG code providing calculations for more than 500 species
(main and rare isotopologues of most known ISM molecular species). Many
U lines will probably correspond to isotopologues and vibrational
excited states of well known molecules like
CH3OCH3, CH3OH, CH(O)COH... As an
example we show in the next figures detections of rare isotopologues:
Proceedings of the International Astronomical Union 235:203P.
