552 research outputs found
A spectroscopic survey of Orion KL between 41.5 and 50 GHz
Orion KL is one of the most frequently observed sources in the Galaxy, and
the site where many molecular species have been discovered for the first time.
With the availability of powerful wideband backends, it is nowadays possible to
complete spectral surveys in the entire mm-range to obtain a spectroscopically
unbiased chemical picture of the region. In this paper we present a sensitive
spectral survey of Orion KL, made with one of the 34m antennas of the Madrid
Deep Space Communications Complex in Robledo de Chavela, Spain. The spectral
range surveyed is from 41.5 to 50 GHz, with a frequency spacing of 180 kHz
(equivalent to about 1.2 km/s, depending on the exact frequency). The rms
achieved ranges from 8 to 12 mK. The spectrum is dominated by the J=1-0 SiO
maser lines and by radio recombination lines (RRLs), which were detected up to
Delta_n=11. Above a 3-sigma level, we identified 66 RRLs and 161 molecular
lines corresponding to 39 isotopologues from 20 molecules; a total of 18 lines
remain unidentified, two of them above a 5-sigma level. Results of radiative
modelling of the detected molecular lines (excluding masers) are presented. At
this frequency range, this is the most sensitive survey and also the one with
the widest band. Although some complex molecules like CH_3CH_2CN and CH_2CHCN
arise from the hot core, most of the detected molecules originate from the low
temperature components in Orion KL.Comment: Accepted for Astronomy and Astrophysics. 29 pages, 5 tables, 6
figure
Complex organic molecules in strongly UV-irradiated gas
We investigate the presence of COMs in strongly UV-irradiated interstellar
molecular gas. We have carried out a complete millimetre line survey using the
IRAM30m telescope towards the edge of the Orion Bar photodissociation region
(PDR), close to the H2 dissociation front, a position irradiated by a very
intense far-UV (FUV) radiation field. These observations have been complemented
with 8.5 arcsec resolution maps of the H2CO 5(1,5)-4(1,4) and C18O 3-2 emission
at 0.9 mm. Despite being a harsh environment, we detect more than 250 lines
from COMs and related precursors: H2CO, CH3OH, HCO, H2CCO, CH3CHO, H2CS, HCOOH,
CH3CN, CH2NH, HNCO, H13-2CO, and HC3N (in decreasing order of abundance). For
each species, the large number of detected lines allowed us to accurately
constrain their rotational temperatures (Trot) and column densities (N). Owing
to subthermal excitation and intricate spectroscopy of some COMs (symmetric-
and asymmetric-top molecules such as CH3CN and H2CO, respectively), a correct
determination of N and Trot requires building rotational population diagrams of
their rotational ladders separately. We also provide accurate upper limit
abundances for chemically related molecules that might have been expected, but
are not conclusively detected at the edge of the PDR (HDCO, CH3O, CH3NC,
CH3CCH, CH3OCH3, HCOOCH3, CH3CH2OH, CH3CH2CN, and CH2CHCN). A non-LTE LVG
excitation analysis for molecules with known collisional rate coefficients,
suggests that some COMs arise from different PDR layers but we cannot resolve
them spatially. In particular, H2CO and CH3CN survive in the extended gas
directly exposed to the strong FUV flux (Tk = 150-250 K and Td > 60 K), whereas
CH3OH only arises from denser and cooler gas clumps in the more shielded PDR
interior (Tk = 40-50 K). We find a HCO/H2CO/CH3OH = 1/5/3 abundance ratio.
These ratios are different from those inferred in hot cores and shocks.Comment: 29 pages, 22 figures, 17 tables. Accepted for publication in A&A
(abstract abridged
Improved determination of the 1(0)-0(0) rotational frequency of NH3D+ from the high resolution spectrum of the v4 infrared band
The high resolution spectrum of the v4 band of NH3D+ has been measured by
difference frequency IR laser spectroscopy in a multipass hollow cathode
discharge cell. From the set of molecular constants obtained from the analysis
of the spectrum, a value of 262817(6) MHz (3sigma) has been derived for the
frequency of the 1(0)-0(0) rotational transition. This value supports the
assignment to NH3D+ of lines at 262816.7 MHz recorded in radio astronomy
observations in Orion-IRc2 and the cold prestellar core B1-bS.Comment: Accepted for publication in the Astrophysical Journal Letters 04 June
201
A line confusion-limited millimeter survey of Orion KL. III. Sulfur oxide species
We present a study of the sulfur-bearing species detected in a line
confusion-limited survey towards Orion KL performed with the IRAM 30m telescope
in the range 80-281 GHz. The study is part of an analysis of the line survey
divided into families of molecules. Our aim is to derive accurate physical
conditions and molecular abundances in the different components of Orion KL
from observed SO and SO2 lines. First we assumed LTE conditions obtain
rotational temperatures. We then used a radiative transfer model, assuming
either LVG or LTE excitation to derive column densities of these molecules in
the different components of Orion KL. We have detected 68 lines of SO, 34SO,
33SO, and S18O and 653 lines of SO2, 34SO2, 33SO2, SO18O and SO2 v2=1. We
provide column densities for all of them and also upper limits for the column
densities of S17O, 36SO, 34S18O, SO17O and 34SO2 v2=1 and for several
undetected sulfur-bearing species. In addition, we present 2'x2' maps around
Orion IRc2 of SO2 transitions with energies from 19 to 131 K and also maps with
four transitions of SO, 34SO and 34SO2. We observe an elongation of the gas
along the NE-SW direction. An unexpected emission peak appears at 20.5 km/s in
most lines of SO and SO2. A study of the spatial distribution of this emission
feature shows that it is a new component ~5" in diameter, which lies ~4" west
of IRc2. We suggest the emission from this feature is related to shocks
associated to the BN object. The highest column densities for SO and SO2 are
found in the high-velocity plateau (a region dominated by shocks) and in the
hot core. These values are up to three orders of magnitude higher than the
results for the ridge components. We also find high column densities for their
isotopologues in both components. Therefore, we conclude that SO and SO2 are
good tracers, not only of regions affected by shocks, but also of regions with
warm dense gas.Comment: Paper (ref AA/2013/21285) accepted for publication by A&A. 52 Pages,
26 figures, 13 table
Spectroscopic characterization and detection of Ethyl Mercaptan in Orion
New laboratory data of ethyl mercaptan, CHCHSH, in the millimeter
and submillimeter-wave domains (up to 880 GHz) provided very precise values of
the spectroscopic constants that allowed the detection of
-CHCHSH towards Orion KL. 77 unblended or slightly blended
lines plus no missing transitions in the range 80-280 GHz support this
identification. A detection of methyl mercaptan, CHSH, in the spectral
survey of Orion KL is reported as well. Our column density results indicate
that methyl mercaptan is 5 times more abundant than ethyl mercaptan in
the hot core of Orion KL.Comment: Accepted for publication in ApJL (30 January 2014)/ submitted (8
January 2014
CH2D+, the Search for the Holy Grail
CH2D+, the singly deuterated counterpart of CH3+, offers an alternative way
to mediate formation of deuterated species at temperatures of several tens of
K, as compared to the release of deuterated species from grains. We report a
longstanding observational search for this molecular ion, whose rotational
spectroscopy is not yet completely secure. We summarize the main spectroscopic
properties of this molecule and discuss the chemical network leading to the
formation of CH2D+, with explicit account of the ortho/para forms of H2, H3+
and CH3+. Astrochemical models support the presence of this molecular ion in
moderately warm environments at a marginal level.Comment: 25 pages, 6 Figures Accepted in Journal of Physical Chemistry A. "Oka
Festschrift: Celebrating 45 years of Astrochemistry
Extended warm gas in Orion KL as probed by methyl cyanide
In order to study the temperature distribution of the extended gas within the
Orion Kleinmann-Low nebula, we have mapped the emission by methyl cyanide
(CH3CN) in its J=6_K-5_K, J=12_K-11_K, J=13_K-12_K, and J=14_K-13_K transitions
at an average angular resolution of ~10 arcsec (22 arcsec for the 6_K-5_K
lines), as part of a new 2D line survey of this region using the IRAM 30m
telescope. These fully sampled maps show extended emission from warm gas to the
northeast of IRc2 and the distinct kinematic signatures of the hot core and
compact ridge source components. We have constructed population diagrams for
the four sets of K-ladder emission lines at each position in the maps and have
derived rotational excitation temperatures and total beam-averaged column
densities from the fitted slopes. In addition, we have fitted LVG model spectra
to the observations to determine best-fit physical parameters at each map
position, yielding the distribution of kinetic temperatures across the region.
The resulting temperature maps reveal a region of hot (T > 350 K) material
surrounding the northeastern edge of the hot core, whereas the column density
distribution is more uniform and peaks near the position of IRc2. We attribute
this region of hot gas to shock heating caused by the impact of outflowing
material from active star formation in the region, as indicated by the presence
of broad CH3CN lines. This scenario is consistent with predictions from C-shock
chemical models that suggest that gas-phase methyl cyanide survives in the
post-shock gas and can be somewhat enhanced due to sputtering of grain mantles
in the passing shock front.Comment: 24 pages, 20 figures, accepted for publication in A&
Searching for Trans Ethyl Methyl Ether in Orion KL
We report on the tentative detection of Ethyl Methyl Ether (tEME),
, through the identification of a large number of rotational
lines from each one of the spin states of the molecule towards Orion KL. We
also search for --n-propanol, , an isomer
of tEME in the same source. We have identified lines of both species in the
IRAM 30m line survey and in the ALMA Science Verification data. We have
obtained ALMA maps to establish the spatial distribution of these species.
Whereas tEME mainly arises from the compact ridge component of Orion,
Gt-n-propanol appears at the emission peak of ethanol (south hot core). The
derived column densities of these species at the location of their emission
peaks are and
for tEME and Gt-n-propanol,
respectively. The rotational temperature is for both molecules. We
also provide maps of , , , , and
to compare the distribution of these organic saturated O-bearing
species containing methyl and ethyl groups in this region. Abundance ratios of
related species and upper limits to the abundances of non-detected ethers are
provided. We derive an abundance ratio in the
compact ridge of Orion.Comment: Accepted in A&A Letter
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