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ABSTRACT: We have observed the 158 μm2P3/2←2P1/2 fine-structure line of C II, the J = 9 → 8, 12 → 11, and 17 → 16 lines of 12CO, and the J = 9 → 8 rotational transition of 13CO in the molecular cloud and photodissociation region (PDR) associated with NGC 3576. The line profiles were fully resolved using a heterodyne spectrometer with better than 1 km s-1 resolution. The high-J CO emission arises from a spatially compact region near the infrared peak that is characterized by a kinetic temperature near 150 K and a density nH2 5 × 105 cm-3. The 12CO J = 9 → 8 line is found to be optically thick and arises from a more extended, cooler region with Tkin ~ 60 K. The increase in excitation temperature with the rotational level of CO suggests that the ionizing source is located behind much of the molecular cloud. Less than 1% of the molecular cloud material is found in the warm PDR and cloud interface region. The C II fine-structure line emission is intense over more than 4' × 4' and shows a central "self-absorption" feature at many locations. This absorption may represent a cooler or less dense component of ionized gas associated with the foreground molecular cloud.
The Astrophysical Journal Supplement Series 01/2009; 111(2):409. · 13.46 Impact Factor
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ABSTRACT: We have locked the frequency of a 3 THz quantum cascade laser (QCL) to that of a far-infrared gas laser with a tunable microwave offset frequency. The locked QCL line shape is essentially Gaussian, with linewidths of 65 and 141 kHz at the -3 and -10 dB levels, respectively. The lock condition can be maintained indefinitely, without requiring temperature or bias current regulation of the QCL other than that provided by the lock error signal. The result demonstrates that a terahertz QCL can be frequency controlled with 1-part-in-10(8) accuracy, which is a factor of 100 better than that needed for a local oscillator in a heterodyne receiver for atmospheric and astronomic spectroscopy.
Optics Letters 08/2005; 30(14):1837-9. · 3.40 Impact Factor
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ABSTRACT: By optically pumping the deuterated isotopomers of 14NH3 and 15NH3 using 12C16O2, 13C16O2, 12C18O2, and 13C18O2 lasers, several new far-infrared (FIR) emission lines between 65μm and 125μm have been detected. The existing spectroscopy
of 14N-ammonia isotopomers has been used to identify many of these lines, as well as some previously observed but unidentified.
The spectroscopic data have been analyzed to predict over 20 additional FIR laser lines that could be pumped by a more capable
CO2 laser. This effort was motivated by a need for strong laser lines in frequency coincidence with molecular transitions of
astrophysical interest. Of particularnote is the measurement of the 2680-GHz line of 14NHD2, whose frequency is 4.9GHz higher than that of the important J=1-0 line of interstellar HD.
Applied Physics B 01/2002; 75(8):823-826. · 2.19 Impact Factor
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ABSTRACT: We are developing a heterodyne focal plane array with up to eight elements to study lines of the interstellar medium and planetary atmospheres with frequencies of 2 THz and above. Our fabrication process utilizes selective ion milling techniques to produce Nb Diffusion-Cooled Hot Electron Bolometric (DHEB) mixers from a bilayer thin film of Au/Nb deposited on a silicon substrate. A micro-bridge of 10 nm thick Nb forms the HEB device. The first generation of devices with lateral dimensions of 100 nm by 80 nm were fabricated at the feed of a broadband spiral antenna with a frequency response designed for up to 16 THz. Harmonic multiplier sources becoming available within the next few years should have sufficient power to provide a local-oscillator source for small-format, quasi-optically coupled arrays of these mixers. First generation devices measured at our laboratory have demonstrated a critical temperature (Tc) of 4.8 K with a 0.5 K transition width. These DHEB mixers are expected to have an optimum operational temperature of 1.8-2.0 K. The current four element array mixer block will ultimately be replaced by a dual polarization slot-ring array configuration with up to eight elements.
01/2002;
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ABSTRACT: We have developed a model for the dust and gas envelope of the C star IRC+10 216. Spherical symmetry is assumed, and the model consistently solves the full radiative transfer problem for the rotationally excited far-infrared and submillimetre wavelength CO lines and for the dust continuum. New observations of the CO J=9--8 and 12--11 lines, made with the Kuiper Airborne Observatory, are presented. The model accounts for the first 32 rotational states in the lowest two vibrational levels of CO, and is shown to yield satisfactory fits to both line profiles and spatial maps of the CO J=1--0, 2--1, 3--2, 4--3, 6--5, 7--6, 9--8 and 12--11 lines. The dust model yields a good fit to the spectral energy distribution from the near-IR to millimetre wavelengths, assuming a distance to the star of 170 pc. From the CO model we are able to confirm previous findings that the gas in the outer envelope is heated by the photoelectric effect, and we also find that the mass-loss rate must be of order 5 × 10-5 Mo˙ yr-1, with a gas-to-dust ratio of approximately 220, in order to fit all the CO observations and the spectral energy distribution simultaneously, and to predict accurately the observed wind terminal velocity via radiative acceleration of the dust grains which are momentum-coupled to the gas. The gas temperature distribution is found to be lower than predicted by a simple three-level molecule approach which has been found to work for the envelopes of O-rich asymptotic giant branch stars, but is in good agreement with some previously published models for this source. In contrast with some previously published models, we find no evidence for a recent change in mass-loss rate.
Monthly Notices of the Royal Astronomical Society 01/1999; 302(2):293 - 304. · 4.90 Impact Factor
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ABSTRACT: We have used a laser heterodyne spectrometer to resolve the emission line profile of the 63 ¯m 3 P 1 - 3 P 2 fine-structure transition of O I at two locations in M42. Comparison of the peak antenna temperature with that of the 158 ¯m C II fine-structure line shows that the gas kinetic temperature in the photodissociation region near ` 1 C is 175 - 220 K, the density is greater than 2 Theta 10 5 cm Gamma3 , and the hydrogen column density is about 1:5 Theta 10 22 cm Gamma2 . A somewhat lower temperature and column density are found in the IRc2 region, most likely reflecting the smaller UV flux. The observed width of the O I line is 6.8 km s Gamma1 (FWHM) at ` 1 C, which is slightly broadened over the intrinsic linewidth by optical depth effects. No significant other differences between the O I and C II line profiles are seen, which shows that the narrow emission from both neutral atomic oxygen and ionized carbon comes from the PDR. The O I data do not ru...
06/1998;
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ABSTRACT: We present new data on the photodissociation regions associated with the reflection nebula NGC7023. 13CO(3-2) emission, delineates a molecular cloud containing a cavity largely devoid of molecular gas around this star. Neutral carbon is closely associated with the 13CO emission while ionized carbon is found inside and at the edges of the cavity. The ionized carbon appears to be, at least in part, associated with HI. We have mapped the northern and southern rims in 12CO(6-5) emission and found a good association with the H2 rovibrational emission, though the warm CO gas permeates a larger fraction of the molecular cloud than the vibrationally excited H2. The results are compared with PDR models. We suggest that a second PDR has been created at the surface of the molecular cloud by the scattered radiation from HD 200775. This second PDR produces a layer of atomic carbon at the surface of the sheet, which increases the predicted [C]/[CO] abundance ratio to 10%, close to the observed value. Comment: 34 pages, 8 figures
02/1998;
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ABSTRACT: We present new data on the photodissociation regions associated with the reflection nebula NGC 7023, particularly the three bright rims to the north, south and east of the illuminating star HD 200775. CO-13(3-2) emission, mapped at 20 in resolution at the Caltech Submillimeter Observatory (CSO), delineates a molecular cloud containing a cavity largely devoid of molecular gas around this star. Neutral carbon is closely associated with the CO-13 emission while ionized carbon is found inside and at the edges of the cavity. The ionized carbon appears to be, at least in part, associated with H I. We have mapped the northern and southern rims in CO-12(6-5) emission and found a good association with the H2 rovibrational emission, though the warm CO gas permeates a larger fraction of the molecular cloud than the vibrationally excited H2. The column density contrast between the bright rims and the diffuse region inside and in front of the cavity is about 10. Despite the fact that the edges of the cavity are viewed edge-on, the carbon emission extends much further into the molecular gas than does the photodissociation region, as defined by the H2 emission region. Geometrically, NGC 7023 consists of a sheet of dense molecular gas in which the star was born, subsequently blowing away much of the surrounding gas. The three bright rims are located at the edges of the remaining molecular cloud, and are viewed approximately edge-on. The results are compared with PDR models, invoking direct illumination from the star, which are largely successful, except in explaining the presence of neutral carbon deep in the molecular cloud. We suggest that, in the particular case of NGC 7023, a second PDR has been created at the surface of the molecular cloud by the scattered radiation from HD 200775. This second PDR produces a layer of atomic carbon at the surface of the sheet, which increases the predicted absolute value of C/absolute value of CO abundance ratio 10%, close to observed value. Further tests for the applicability of PDR models in sach regions are suggested.
02/1997;
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ABSTRACT: We have observed the 158 micron 2P3/2-2P1/2 fine-structure line of 12C II simultaneously with the F=2-1 and F=1-0 hyperfine components of this transition in 13C II in the Orion photodissociation region near theta1C . The line profiles were fully resolved using a heterodyne spectrometer with 0.5 km/s resolution. The relative intensities of these lines give a 12C/13C isotopic ratio of R=58 (+6,-5) for the most probable 12C II peak optical depth tau=1.3 . The constrained range of tau(12C II) between 1.0 and 1.4 corresponds to a range of 12C/13C between 52 and 61. The most probable value of 58 agrees very well with that obtained from a relationship between the isotopic ratio and galactocentric distance derived from CO measurements, but is lower than the specific value of 67(+-3) obtained for Orion from CO data. An isotopic ratio as low as 43, as previously suggested based on optical absorption measurements of the local interstellar medium, is excluded by the C II data at about the 2 sigma level. Comment: 11 pages, 2 postscript figures, uses aaspp4 macros
06/1996;
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ABSTRACT: Observations of the 609μm line of atomic carbon, the 158μm line of
ionized carbon, and multiple high-J transitions of the CO molecule and
its isotopes are presented for the reflection/emission nebula IC 63. All
important gas-phase forms of carbon have therefore been measured,
enabling an accurate determination of the carbon abundance in the
gas-phase in this well defined cloud. We find that the gas-phase
fraction of carbon in IC 63 is only 13^+6^_-4_% of the solar abundance,
significantly lower than found in diffuse clouds and in some dense
clouds.
Astronomy and Astrophysics 04/1996; 309:899-906. · 4.59 Impact Factor
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ABSTRACT: We have used a laser heterodyne spectrometer to resolve the emission line profile of the 63 micron 3P1 - 3P2 fine-structure transition of O I at two locations in M42. Comparison of the peak antenna temperature with that of the 158 micron C II fine-structure line shows that the gas kinetic temperature in the photodissociation region near theta1C is 175 - 220 K, the density is greater than 2x10 ^5 cm-3, and the hydrogen column density is about 1.5x10 ^22 cm-2. A somewhat lower temperature and column density are found in the IRc2 region, most likely reflecting the smaller UV flux. The observed width of the O I line is 6.8 km/s (FWHM) at theta1C, which is slightly broadened over the intrinsic linewidth by optical depth effects. No significant other differences between the O I and C II line profiles are seen, which shows that the narrow emission from both neutral atomic oxygen and ionized carbon comes from the PDR. The O I data do not rule out the possibility of weak broad-velocity emission from shock-excited gas at IRc2, but the C II data show no such effect, as expected from non-ionizing shock models. Comment: 11 pages including 2 postscript figures, uses aaspp4.sty
03/1996;
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ABSTRACT: We present KAO observations of the CO J=9-8 and 12-11 lines in the C-star IRC+10216; these are the highest rotational transitions so far observed in any AGB star. A model is developed for the CO emission by IRC+10216 in all the observed CO rotational transitions.
02/1995;
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ABSTRACT: We have searched for rovibrational emission and absorption transitions arising from the 63 cm(exp -1) nu(sub 2) (pi(sub u)) bending vibration of the C3 carbon cluster in the interstellar medium using the Betz/Boreiko heterodyne receiver on board the Kuiper Airborne Observatory. The Q(4) line at 1896.707 GHz was searched for in the IRc2 Orion/M42 and the W3 sources, and the R(2) transition at 1968.594 GHz was searched for in Sgr B2. No emission lines were observed in any source. However, a weak absorption was detected in Sgr B2 with a LSR velocity of 63.7+/-0.6 km s(exp -1) and a FWHM linewidth of 7.9+/-0.8 km s(exp -1). This absorption is tentatively identified as the R(2) transition of the C(sub 3) bending mode.
02/1995;
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ABSTRACT: Measurements of the shapes, velocities, and intensities of FIR lines all help to probe the dynamics, physical associations, and excitation conditions of warm gas in molecular clouds. With this in mind, we have observed the J=9-8, 12-11,14-13, and 16-15 lines of (12)CO and the 158 micron line of C II in a number of positions in 4 selected clouds. The data were obtained with a laser heterodyne spectrometer aboard NASA's Kuiper Airborne Observatory. Line measurements at 0.6 km/s resolution allow us to resolve the profiles completely, and thereby to distinguish between UV-and shock-heating mechanisms for the high-excitation gas. For CO, the high-J linewidths lie in the range of 4-20 km/s (FWHM), similar to those observed for low-J (J less than 4) transitions in these sources. This correspondence suggests that the hotter gas (T = 200-600 K) is dynamically linked to the quiescent gas component, perhaps by association with the UV-heated peripheries of the numerous cloud clumps. Much of the C II emission is thought to emanate from these cloud peripheries, but the line profiles generally do not match those seen in CO. None of the observed sources show any evidence in high-J (12)CO emission for shock-excitation (i.e., linewidths greater than 30 km/s).
02/1995;
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ABSTRACT: A search was made for the 1370 GHz lowest rotational transition of the molecular ion H2D+ in NGC 2264, W3, and the IRc2 region of M42. No emission lines were seen, but an absorption feature was detected toward IRc2. The column density and fractional abundance were calculated using a tentative identification of the line as the transition of para H2D+. The LSR velocity and the measured line width are consistent with the dynamical parameters of the hot core source. Physical parameters deduced from the data differ from those derived from millimeter-wave observations of the hot core condensation. It is suggested that significant amounts of low-density gas are associated with this region and that the material is cold enough for enhanced deuterium fractionation to occur. A search was also made for the 985 GHz transition of ortho H3O+ in W3 and IRc2 with negative results.
04/1993;
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12/1992; 41:349.
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ABSTRACT: The 158 micron 2P3/2-2P1/2 fine-structure transition of C(+) at selected locations in the LMC. The C II emission is most intense toward far-infrared continuum peaks and generally is not seen in positions exhibiting strong CO J = 2-1 radiation. Where both C II and CO emission are detected, the V(LSR) centroids are similar but the C II line is wider. The differences in spatial distribution and spectral shape suggest a more pronounced physical separation between the predominantly neutral atomic and molecular gas regions than is the case in the Galaxy. In the LMC, the intense and extended C II emission near 30 Dor implies a total amount of C(+) several times greater than that of Galactic molecular cloud complexes. An attempt was made to detect the 289 micron J = 9-8 transition of (C-12)O in a few locations. The observed upper intensity limit for N159 implies that moderate density molecular gas fills less than 5 percent of the beam and that most of the low J CO emission comes from lower density gas.
11/1991;
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04/1991;
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ABSTRACT: We have observed the 2P3/2-2P1/2 fine-structure line of C II at 1900 GHz in five sources with ionization fronts nearly perpendicular to the plane of the sky. The LSR velocity of the C II emission is generally in good agreement with that observed for molecular species such as CO. However, the observed line widths of 3-14 km s-1 are typically wider than those of molecular lines and often show rapid spatial variations in the regions observed. In some sources this may indicate that part of the C II emanates from an ionized gas component, while for others it suggests an association between C II emission and an outflow. The C II brightness temperatures are typically equal to or slighty higher than the dust temperature at all locations observed. In the optically thin approximation, C II excitation temperatures are > or = 100 K and column densities are < or = 10(18) cm-2 for all sources except M17, which has a more intense and complicated line profile with a larger spatial extent than any other source observed. The quoted column density estimates derived in the optically thin limit appear to be somewhat lower than those predicted by models of photodissociation regions for sources with a side-illuminated geometry, but uncertainties in the UV flux and geometry of the ionization front preclude a definitive comparison. The estimated column densities would be higher if the C II emission were somewhat optically thick, in which case the ionized carbon would be more in equilibrium with the dust at temperatures lower than predicted by current models.
The Astrophysical Journal 04/1990; 353(1 Pt 1):181-92. · 6.02 Impact Factor
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ABSTRACT: We have observed the J = 22-21 line of 12CO at 2528 GHz (118.8 micrometers) in the IRc2 region of Orion. The spectra at 0.6 km s-1 resolution show both plateau emission with FWHM approximately 35 km s-1 and a narrower component with FWHM approximately 8 km s-1. Comparison with heterodyne data of similar quality on the J = 17-16 line indicates that the broad and narrow components both originate in gas with an excitation temperature Tex approximately 600 K. The emission is consistent with the predictions of shock models in which the wide component arises from the heated outflow gas and postshock molecular material, while the narrow component comes from ambient material near the leading edge of the shock front where temperatures are high but significant acceleration has not yet occurred.
The Astrophysical Journal 12/1989; 346(2):L97-100. · 6.02 Impact Factor
