163 research outputs found
New ammonia masers towards NGC6334I
We report the detection of new ammonia masers in the non-metastable (8,6) and
(11,9) transitions towards the massive star forming region NGC6334I.
Observations were made with the ATCA interferometer and the emitting region
appears unresolved in the 2.7" x 0.8" beam, with deconvolved sizes less than an
arcsecond. We estimate peak brightness temperatures of 7.8 x 10^5 and 1.2 x
10^5 K for the (8,6) and (11,9) transitions, respectively. The masers appear
coincident both spatially and in velocity with a previously detected ammonia
(6,6) maser. We also suggest that emission in the (10,9), (9,9) and (7,6)
transitions may also be masers, based on their narrow line widths and
overlapping velocity ranges with the above masers, as observed with the
single-dish Mopra radiotelescope
Physical conditions in the Protoplanetary Nebula CRL 618 derived from observations of vibrationally excited HCCCN
We used the Effelsberg 100m and IRAM 30m telescopes to observe vibrationally
excited cyanoacetylene (HCCCN) in several rotational transitions toward the
proto-planetary nebula CRL618. Lines from 9 different vibrationally excited
states with energies ranging up to 1600 K above ground were detected. The lines
show P Cygni profiles indicating that the HCCCN emission originates from an
expanding and accelerating molecular envelope. The HCCCN rotational temperature
varies with velocity, peaks at 520 K, 3 km/s blue-shifted from the systemic
velocity and decreases with higher blueshift of the gas. The column density of
the absorbing HCCCN is 3-6 x 1E17 cm^2. We modeled spectra based on spherical
models of the expanding envelope which provide an excellent fit to the
observations, and discuss the implications of the models. Additionally, lines
from 13C substituted cyanoacetylene were observed. They can be used to
constrain the 12C/13C ratio in this source to 10+-2.Comment: 27 pages, 9 figures, to appear in Ap
Rotational Spectroscopy of PAHs: Acenaphthene, Acenaphthylene and Fluorene
Pure rotational spectra of three polycyclic aromatic hydrocarbons -
acenaphthene, acenaphthylene and fluorene - have been obtained by Fourier
transform microwave spectroscopy of a molecular beam and subsequently by
millimeter wave absorption spectroscopy for acenaphthene and fluorene. The data
presented here will be useful for deep radio astronomical searches for PAHs
employing large radio telecopes.Comment: 2 pages, 1 figure (uses iaus.sty), to appear in IAU Symposium No.
231, Astrochemistry - Recent Successes and Current Challenges, eds. D. C.
Lis, G. A. Blake & E. Herbst (Cambridge Univ. Press
Hot HCN around young massive stars at 0.1" resolution
Massive stars form deeply embedded in dense molecular gas, which they stir
and heat up and ionize. During an early phase, the ionization is confined to
hypercompact HII regions, and the stellar radiation is entirely absorbed by
dust, giving rise to a hot molecular core. To investigate the innermost
structure of such high-mass star-forming regions, we observed vibrationally
excited HCN (via the direct -type transition of v2=1, =0, J=13,
which lies 1400 K above ground) toward the massive hot molecular cores
G10.47+0.03, SgrB2-N, and SgrB2-M with the Very Large Array (VLA) at 7 mm,
reaching a resolution of about 1000 AU (0.1"). We detect the line both in
emission and in absorption against HII regions. The latter allows to derive
lower limits on the column densities of hot HCN, which are several times
cm. We see indication of expansion motions in G10.47+0.03 and
detect velocity components in SgrB2-M at 50, 60, and 70 km/s relative to the
Local Standard of Rest. The emission originates in regions of less than 0.1 pc
diameter around the hypercompact HII regions G10.47+0.03 B1 and SgrB2-N K2, and
reaches brightness temperatures of more than 200 K. Using the three-dimensional
radiative transfer code RADMC-3D, we model the sources as dense dust cores
heated by stars in the HII regions, and derive masses of hot (>300 K) molecular
gas of more than 100 solar masses (for an HCN fractional abundance of
10), challenging current simulations of massive star formation. Heating
only by the stars in the HII regions is sufficient to produce such large
quantities of hot molecular gas, provided that dust is optically thick to its
own radiation, leading to high temperatures through diffusion of radiation.Comment: 12 pages, 14 figures, accepted for publication in A&
A 1.3 cm line survey toward IRC +10216
IRC +10216 is the prototypical carbon star exhibiting an extended molecular
circumstellar envelope. Its spectral properties are therefore the template for
an entire class of objects. The main goal is to systematically study the
1.3 cm spectral line characteristics of IRC +10216. We carried
out a spectral line survey with the Effelsberg-100 m telescope toward IRC
+10216. It covers the frequency range between 17.8 GHz and 26.3 GHz (K-band).
In the circumstellar shell of IRC +10216, we find 78 spectral lines, among
which 12 remain unidentified. The identified lines are assigned to 18 different
molecules and radicals. A total of 23 lines from species known to exist in this
envelope are detected for the first time outside the Solar System and there are
additional 20 lines first detected in IRC +10216. The potential orgin of "U"
lines is also discussed. Assuming local thermodynamic equilibrium (LTE), we
then determine rotational temperatures and column densities of 17 detected
molecules. Molecular abundances relative to H are also estimated. A
non-LTE analysis of NH shows that the bulk of its emission arises from
the inner envelope with a kinetic temperature of 7020 K. Evidence for
NH emitting gas with higher kinetic temperature is also obtained, and
potential abundance differences between various C-bearing isotopologues
of HCN are evaluated. Overall, the isotopic C/C ratio is
estimated to be 499. Finally, a comparison of detected molecules in the
1.3 cm range with the dark cloud TMC-1 indicates that
silicate-bearing molecules are more predominant in IRC +10216.Comment: 32 pages, 9 figures, Accepted by A&
A 1.3 cm Line Survey toward Orion KL
Orion KL has served as a benchmark for spectral line searches throughout the
(sub)millimeter regime. The main goal is to systematically study spectral
characteristics of Orion KL in the 1.3 cm band. We carried out a spectral line
survey (17.9 GHz to 26.2 GHz) with the Effelsberg-100 m telescope towards Orion
KL. We find 261 spectral lines, yielding an average line density of about 32
spectral features per GHz above 3. The identified lines include 164
radio recombination lines (RRLs) and 97 molecular lines. A total of 23
molecular transitions from species known to exist in Orion KL are detected for
the first time in the interstellar medium. Non-metastable 15NH3 transitions are
detected in Orion KL for the first time. Based on the velocity information of
detected lines and the ALMA images, the spatial origins of molecular emission
are constrained and discussed. A narrow feature is found in SO2
(), possibly suggesting the presence of a maser line. Column
densities and fractional abundances relative to H2 are estimated for 12
molecules with LTE methods. Rotational diagrams of non-metastable 14NH3
transitions with J=K+1 to J=K+4 yield different results; metastable 15NH3 is
found to have a higher excitation temperature than non-metastable 15NH3,
indicating that they may trace different regions. Elemental and isotopic
abundance ratios are estimated: 12C/13C=63+-17, 14N/15N=100+-51,
D/H=0.0083+-0.0045. The dispersion of the He/H ratios derived from
H/He pairs to H/He pairs is very small, which
is consistent with theoretical predictions that the departure coefficients bn
factors for hydrogen and helium are nearly identical. Based on a non-LTE code
neglecting excitation by the infrared radiation field and a likelihood
analysis, we find that the denser regions have lower kinetic temperature, which
favors an external heating of the Hot Core.Comment: 70 pages, 26 figures, 12 tables, accepted for publication in A&A.
Figs. 1, 2, 8, 9 have been downsize
Submillimeter spectroscopy of southern hot cores: NGC6334(I) and G327.3-0.6
High-mass star-forming regions are known to have a rich molecular spectrum
from many species. Some of the very highly excited lines are emitted from very
hot and dense gas close to the central object(s). The physics and chemistry of
the inner cores of two high mass star forming regions, NGC6334(I) and
G327.3-0.6, shall be characterized. Submillimeter line surveys with the APEX
telescope provide spectra which sample many molecular lines at high excitation
stages. Partial spectral surveys were obtained, the lines were identified,
physical parameters were determined through fitting of the spectra. Both
sources show similar spectra that are comparable to that of the only other high
mass star forming region ever surveyed in this frequency range}, Orion-KL, but
with an even higher line density. Evidence for very compact, very hot sources
is found.Comment: APEX A&A special issue, accepte
Deuterium chemistry in the Orion Bar PDR - "warm" chemistry starring CH2D+
High levels of deuterium fractionation in gas-phase molecules are usually
associated with cold regions, such as prestellar cores. Significant
fractionation ratios are also observed in hot environments such as hot cores or
hot corinos, where they are believed to be produced by the evaporation of the
icy mantles surrounding dust grains, and thus are remnants of a previous cold
(either gas-phase or grain surface) chemistry. The recent detection of DCN
towards the Orion Bar, in a clump at a characteristic temperature of 70K, has
shown that high deuterium fractionation can also be detected in PDRs. The Orion
Bar clumps thus appear as a good environment for the observational study of
deuterium fractionation in luke-warm gas, allowing to validate chemistry models
in a different temperature range, where dominating fractionation processes are
predicted to be different than in cold gas (< 20K). We aimed at studying
observationally in detail the chemistry at work in the Orion Bar PDR, to
understand if DCN is produced by ice mantle evaporation, or is the result of
warm gas-phase chemistry, involving the CH2D+ precursor ion (which survives
higher temperatures than the usual H2D+ precursor). Using the APEX and the IRAM
30m telescopes, we targetted selected deuterated species towards two clumps in
the Orion Bar. We confirmed the detection of DCN and detected two new
deuterated molecules (DCO+ and HDCO) towards one clump in the Orion Bar PDR.
Significant deuterium fractionations are found for HCN and H2CO, but a low
fractionation in HCO+. We also give upper limits for other molecules relevant
for the deuterium chemistry. (...)
We show evidence that warm deuterium chemistry driven by CH2D+ is at work in
the clumps.Comment: 14 pages, accepted for publication in A&
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