Orion KL Region Research Articles

The Apparent Sizes of the 62–61E‐Type Methanol Masers in OMC‐1

The 62-61 E transition of CH3OH has been observed toward the Orion KL region with an angular resolution of 007 and frequency resolution of 12 kHz (0.15 km s-1) at two epochs, 1 year apart. The observations have a sensitivity of 1 Jy beam-1 (corresponding to a main beam brightness temperature of 4 × 105 K). Only the brightest masers previously measured with 3'' resolution are detected; these are resolved into several bright features. The brightness temperatures of the detected masers range from 2 × 106 to 3 × 107 K, with apparent sizes in the range 22-56 AU.

A line survey of Orion KL from 325 to 360 GHz.

We present a high-sensitivity spectral line survey of the high-mass star-forming region Orion KL in the 325-360 GHz frequency band. The survey was conducted at the Caltech Submillimeter Observatory on Mauna Kea, Hawaii. The sensitivity achieved is typically 0.1-0.5 K and is limited mostly by the sideband separation method utilized. We find 717 resolvable features consisting of 1004 lines, among which 60 are unidentified. The identified lines are due to 34 species and various isotopomers. Most of the unidentified lines are weak, and many of them most likely due to isotopomers or vibrationally or torsionally excited states of known species with unknown line frequencies, but a few reach the 2-5 K level. No new species have been identified, but we were able to strengthen evidence for the identification of ethanol in Orion and found the first nitrogen sulfide line in this source. The molecule dominating the integrated line emission is S02, which emits twice the intensity of CO, followed by SO, which is only slightly stronger than CO. In contrast, the largest number of lines is emitted from heavy organic rotors like HCOOCH3, CH3CH2CN, and CH3OCH3, but their contribution to the total flux is unimportant. CH3OH is also very prominent, both in the number of lines and in integrated flux. An interesting detail of this survey is the first detection of vibrationally excited HCN in the v2 = 2 state, 2000 K above ground. Clearly this is a glimpse into the very inner part of the Orion hot core.

What is powering the Orion Kleinmann-low infrared nebula

view Abstract Citations (193) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS What is Powering the Orion Kleinmann-Low Infrared Nebula? Menten, Karl M. ; Reid, Mark J. Abstract We used the Very Large Array (VLA) to observe the Orion BN/KL region simultaneously at frequencies of 8.4 and 43.1 GHz with 0.25 sec resolution. At 8.4 GHz we detect a rich cluster of compact radio continuum sources, some of which are coincident with infrared sources while others do not have known infrared counterparts. At 43.1 GHz we observed continuum emission together with the v = 1, J = 1-0 SiO maser line, allowing precise registration of radio continuum relative to SiO emission. We find that the radio continuum emission from one of the radio sources, I, coincides with the centroid of the SiO maser distribution. Our SiO maser maps show intricate velocity structure indicative of ordered motions that must have a rotating and expanding (or contracting) component. Since source I powers an SiO maser, it must have a high luminosity, most likely exceeding 104 solar luminosity. Precise astrometry shows that it does not coincide with the mid-infrared source IRc2. Given that the radio emission from source I is not affected by dust extinction, it locates the central (proto)star powering the IRc2 complex. This suggests that the location and morphology of the infrared emission from 'IRc2' is determined by inhomogeneities of the dust envelope surrounding the central star. Furthermore, this brings into question all previous luminosity estimates of IRc2 and opens the possibility that other sources contribute significantly to the energetics of the Orion KL region. In particular, we suggest that another infrared source, n, which is coincident with a peculiar double radio source, may be responsible for at least some of the energetic phenomena observed in the region. Publication: The Astrophysical Journal Pub Date: June 1995 DOI: 10.1086/187913 Bibcode: 1995ApJ...445L.157M Keywords: Continuous Spectra; Emission Spectra; Interstellar Masers; Interstellar Matter; Line Spectra; Orion Nebula; Radio Astronomy; Radio Spectra; Silicon Oxides; Star Formation; Centimeter Waves; Extremely High Frequencies; Infrared Radiation; Millimeter Waves; Stellar Luminosity; Superhigh Frequencies; Very Large Array (Vla); Astronomy; STARS: FORMATION; ISM: INDIVIDUAL NAME: BECKLIN-NEUGEBAUER; ISM: INDIVIDUAL NAME: ORION KLEINMANN-LOW; ISM: INDIVIDUAL ALPHANUMERIC: IRC2; MASERS full text sources ADS | data products SIMBAD (19)

Velocity field of the Orion-KL region in molecular hydrogen emission

Velocity field of the Orion-KL region in molecular hydrogen emission

A near-infrared fabry-perot imager at CRL 1.5m telescope and the structure and velocity field of shocked H2 emission in orion KL region

We have developed a near-infrared Fabry-Perot imager at the Nasmyth focus of the Communications Research Laboratory (CRL) 1.5 m telescope at Tokyo. Using this wide field Fabry-Perot imager, we obtained continuum-subtracted images of the H2 v=1−0 S(1) line for the Orion KL region.

Fabry-Perot imaging of molecular hydrogen emission on Orion-KL region

view Abstract Citations (21) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Fabry-Perot Imaging of Molecular Hydrogen Emission in Orion-KL Region Sugai, Hajime ; Usuda, Tomonori ; Kataza, Hirokazu ; Tanaka, Masuo ; Inoue, Motoko Y. ; Takami, Hideki ; Aoki, Tetsuo ; Hiromoto, Norishisa ; Kawavata, Hironobu Abstract A continuum-subtracted image of the H2 nu = 1 goes to 0 S(1) line covering the central 4 min square portion of the Orion-KL region, has been obtained using a wide-field Fabry-Perot imager at the Communication Research Laboratoy 1.5 m telescope. Nine H2 peaks (including four newly identified) are found in te core, as well as a curved, bridgelike structure that enroaches on the inner edge of the disk structure observed in CS (J = 1 goes to 0) emission. This existence of the bridge indicates that the outflow from IRc2 occurs not only toward the bipolar axis but also toward the disk, and suggests channeling by the disk of a more or less isotropics flow from IRc2 into a bipolar flow. Outside the core, where finger-like features of H2 emission are seen, we identify 43 hot H2 clumps. These are located along filamentary structures seen in CS (J = 1 goes to 0) maps and avoid peaks of CS intensity. The geometrical thickness of the hot H2 in these features is much smaller than their typical dimension. We conclude that the H2 emission from the clumps is radiated at the surface of the CS filaments, implying that outflow form IRc2 shocks the H2 at the surfaces. From comparison of polarization measurements of Burton et al. (1991) with the present meausrements, as well as from discussion of the energetics, we rule out the possibility that the H2 clumps are due to reflection. Publication: The Astrophysical Journal Pub Date: January 1994 DOI: 10.1086/173599 Bibcode: 1994ApJ...420..746S Keywords: Hydrogen Clouds; Interstellar Matter; Orion Nebula; Data Reduction; Emission Spectra; Fabry-Perot Spectrometers; Herbig-Haro Objects; Isotropic Media; Shock Waves; Astrophysics; ISM: INDIVIDUAL NAME: ORION NEBULA; ISM: JETS AND OUTFLOWS; ISM: MOLECULES; SHOCK WAVES full text sources ADS | data products SIMBAD (58)

The distribution of the 6(2)-6(1) and 5(2)-5(1) E-type methanol masers in OMC-1

view Abstract Citations (58) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Distribution of the 6 2--6 1 and 5 2--5 1 E-Type Methanol Masers in OMC-1 Johnston, K. J. ; Gaume, R. ; Stolovy, S. ; Wilson, T. L. ; Walmsley, C. M. ; Menten, K. M. Abstract Results are presented of mapping of the 6(2)-6(1) and 5(2)-5(1) E transition of CH3OH toward the Orion-KL region with an angular resolution of 3 arcsec and a frequency resolution of 12 kHz (0.15 km/s). They are shown to lie over an area of approximately 40 arcsec, as previously shown by Matsakis et al. (1980). A detailed comparison exhibits a qualitative agreement of the intensities and sizes with the previous map. In 11 of 14 cases, the positions, flux densities, and radial velocities of the 6(2)-6(1) E and 5(2)-5(1) E maser components agree. Although individual maser emission regions are unresolved in the present 3-arcsec beam, the variation of position with velocity within what is thought to be a single feature implies clustering of masers on scales of less than 3 arcsec. The most intense feature has a brightness temperature in excess of 100,000 K. The best agreement is within the map of the 8(0)-7(1) A transition of methanol. Publication: The Astrophysical Journal Pub Date: January 1992 DOI: 10.1086/170930 Bibcode: 1992ApJ...385..232J Keywords: Interstellar Masers; Maser Outputs; Methyl Alcohol; Molecular Clouds; Orion Nebula; Angular Resolution; Brightness Temperature; Very Large Array (Vla); Astrophysics; ISM: KINEMATICS AND DYNAMICS; ISM: MOLECULES; ISM: STRUCTURE; MASERS full text sources ADS | data products SIMBAD (17)

Aperture synthesis observations of NH3 in OMC-1 - Filamentary structures around Orion-KL

Aperture synthesis observations of the Orion molecular cloud 1 (OMC-1) have been made in NH3 (1, 1) and (2, 2) emission at 23.7 GHz, using the Nobeyama Millimeter Array (NMA), and obtained 16 arcsec resolution maps for OMC-1 and 8 arcsec resolution maps for the Orion-KL region. Filamentary structures extending over 0.5 pc from the Orion-KL region to the north and northwest directions were found. These structures are associated with the H2 finger structures and Herbig-Haro objects which are located at the blue-shifted side of the bipolar molecular outflow. The results suggest that these filaments are ambient molecular cloudlets with shocked surfaces caused by the strong stellar wind from the Orion-KL region. The 8 arcsec resolution NH3 (2, 2) maps show the extended features around the hot core of Orion-KL. These extended features correspond to the rotating disk and shocked shell associated with the bipolar molecular outflow.

Further observations of rotationally excited far-infrared O-16H and O-18H emission in Orion-KL - Tighter constraints on the nature of the emitting region

The Orion-KL region, within 1 arc minute, is observed. The rotational cross ladder (53.351 microns) and rotational ground state (120.1719 microns) transitions are studied. It is shown that these lines exhibit a P-Cygni profile and unambiguously show that the OH gas is expanding out from the central BN-KL infrared cluster. The OH-16 rotational ground state transition (119.234 microns) is velocity resolved and it is found that its intrinsic full width at half maximum is 75 km/s. The line fluxes and line profiles are modeled and it is shown that no single temperature and density component can reproduce the data. Rather, the best fit to the data requires emission from three main components of the gas: post shocked gas with the profiles of temperature, density, and OH abundance; a high density component to the cool post shocked region; and the plateau region.

Fast molecular shocks. II - Emission from fast dissociative shocks

The line radiations emitted in the cooling gas behind a fast dissociative shock are studied. The intensities emitted in high rotational transitions of the neutral molecules CO, SiO, HCN, CN, NO, and SO are estimated, as well as in rovibrational transitions of the molecular ions HeH(+) and OH(+) in radio recombination lines of atomic hydrogen and in fine-structure transitions of C, C(+), O, and Si(+). The predictions are compared with the observed intensities of line emission from the Orion-KL region. For Orion-KL the observations do not exclude, but probably do not require, the presence of a fast dissociative shock. Emission from SiO in high-J rotational states and from vibrationally excited OH(+), HeH(+), HeH(+), and SO(+) may be detectable from dissociative shocks under suitable conditions of preshock density and shock velocity; such emission may prove to be a useful diagnostic probe of fast shock activity.

Dust and the Gas Phase Composition of Dense Clouds

A review is given of our current knowledge of the gas phase abundance of interstellar molecules. A comparison is made between cold dust clouds, where presumably gas phase processes dominate the chemistry, and regions of high mass star formation such as Orion where both shocks and evaporation of dust grain mantles may play a role. In dust clouds, carbon rich molecules often show enhanced abundances, whereas in hot turbulent star formation regions, saturated species such as methanol and ammonia are often favored. In both types of source, there is evidence for abundance gradients and inhomogeneities. A probable cause is that the chemistry is far from a steady state situation. A useful diagnostic in such cases is the relative abundance of deuterated species and our current knowledge concerning deuterium fractionation is discussed. Recent results show that the observed degree of deuterium enhancement in species such as water, methanol, and ammonia in the Orion-KL region is much too great to be explained on the basis of normal gas phase chemistry. It is argued that a plausible explanation of the observations is that one is observing material which has recently been evaporated from dust grain mantles. One important consequence of this hypothesis is that molecular line observations may yield important information on the composition of the solid phase.

Polarimetry at 1.3 MM using MILLIPOL - Methods and preliminary results for Orion

This paper describes a polarimeter for use at wavelengths near 1 mm, designed to be self-contained and portable. Only minor modifications should be required to adapt this instrument for use on any of several millimeter and submillimeter telescopes. The polarimeter system and data-taking techniques are described, and a preliminary measurement is reported of the polarized dust emission from the Orion KL region at 1.3 mm using the NRAO 12 m telescope. The results are similar to previous polarization measurements of Orion at far-infrared and submillimeter wavelengths. The magnetic field direction implied by the polarization position angle is parallel to that found in the surrounding Orion region using optical and near- to midinfrared polarimetric techniques. 17 references.

Evidence for strong magnetic fields in the inner envelopes of late-type stars

Strong SiO masers occur in the inner regions of the stellar envelopes (within a few stellar radii) of variable late-type stars (Miras, semi-regular variables and supergiants), and in the vicinity of IRc2 in Orion, a site of recent star formation. Although linear polarization is a common feature of these masers1–3, previous attempts to detect circular polarization have been inconclusive. Johnson and Clark4 claimed detection of 10–20% polarization in Stokes V (left-hand circular minus right-hand circular) spectra of the Orion masers at 86.2 GHz. Troland et al.1 failed to confirm this result, while reporting small signals in Stokes V spectra for several sources which they attributed to instrumental effects. Here we report sensitive measurements of circular polarization in SiO masers associated with late-type stars, which reveal significantly polarized features at the several per cent level in five of six stars observed. Under the Zeeman splitting hypothesis, these measurements imply magnetic fields in the masing gas in the range 10–100 G. The masers associated with IRc2 in the Orion-KL region were not detected in circular polarization.

The Rotational Excitation of OH in Orion

The Orion–KL region has been studied extensively by observations of lines originating from highly–excited rotational levels of CO (see Watson et al. 1985). The lines arise in the shocked gas that lies at the interface of the hypersonic mass outflow of a newly–formed star and the quiescent material in Orion. The CO line intensities are sensitive to the physical conditions in the shocked region, and have been interpreted with a kinetic temperature T ≃ 600 K and density n(H2)≃ 2 × 106 cm−3. Recently, pure rotational lines of OH have been detected as well in the far-infrared spectrum of Orion. Since the OH and CO molecules differ substantially in their energy level structure and in other properties, it is of interest to investigate whether the OH excitation probes the same physical conditions as the CO excitation or whether the two molecules reside in different parts of the shock.

Observations of far-infrared line profiles in the Orion-KL region

Measurements of several far-infrared emission line profiles in the Orion-KL region are reported. The emission from the CO, OH, and forbidden O I emission lines toward the BN-KL and H2 peak 1 positions probably comes from dense, hot molecular gas in the Orion-KL shock. The CO and forbidden O I lines have similar profiles, suggesting that the high-velocity forbidden O I emission also arises in magnetohydrodynamic 'cloud' shocks. The velocity centroids of the lines are somewhat blueshifted. The far-infrared data thus support the interpretation that the blue asymmetry of the H2 2 micron lines is not mainly due to differential dust extinction, but rather to the kinematics and geometry of the shocked gas in the Orion-KL outflow. The forbidden O I and CO lines, however, have significantly less extreme blueshifted emission than the H2 lines. Both the forbidden O I 63 micron and forbidden C II 158 micron lines have features strongly supporting a common origin near the surface of the Orion molecular cloud.

Detection of (Si II) (34.8 micron) emission in Orion-KL - A measurement of the silicon abundance in dense interstellar gas

view Abstract Citations (52) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of SI II (34.8 Micron) Emission in Orion-KL: A Measurement of the Silicon Abundance in Dense Interstellar Gas Haas, M. R. ; Hollenbach, D. J. ; Erickson, E. F. Abstract The first detection of the ground state fine structure transition of Si+ at a rest wavelength determined to be 34.815 + or - 0.004 micron are reported. These observations were obtained with the facility spectrometer on NASA's Kuiper Airborne Observatory. A 6' NW-SE strip scan across the Orion-KL region shows Si II emission from both the extended photodissociation region surrounding theta 1 Ori C and from the shocked gas NW of BN-KL. The inferred gas-phase silicon elemental abundance relative to hydrogen in the dense 10 to the 5/cc primarily neutral photodissociation region is approximately 2.6 x 10 the -6, a factor of 0.075 times the solar value and 3.4 times greater than the abundance in the moderate density aprox. 10 to the 3/cc cloud toward Zeta Oph The silicon abundance in the shocked gas is approximately solar, indicating that any pre-existing grains have been destroyed in the shock wave or that the preshock gas carries a near solar abundance of gas phase silicon. The shock-excited Si II (34.8 micron) emission may arise from shocked wind material in the outflow around IRc2, with wind velocities approx. 100 km/s. Publication: The Astrophysical Journal Pub Date: February 1986 DOI: 10.1086/184623 Bibcode: 1986ApJ...301L..57H Keywords: Abundance; Electron Transitions; Fine Structure; Orion Nebula; Silicon; Airborne Equipment; Emission; Photodissociation; Shock Waves; Spectrometers; Spectroscopy; Astrophysics; INFRARED: SPECTRA; INTERSTELLAR: ABUNDANCES; NEBULAE: ORION NEBULA full text sources ADS | data products SIMBAD (4)

The Kleinmann-Low nebula - an infrared cavity

view Abstract Citations (144) References (57) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Kleinmann-Low nebula : an infrared cavity. Wynn-Williams, C. G. ; Genzel, R. ; Becklin, E. E. ; Downes, D. Abstract High-resolution observations of the 2 - 30 μm infrared continuum emission in the Orion-KL region are presented. The authors derive the distributions of dust, color temperature, and opacity at different wavelengths, and the dependence of apparent silicate depth toward IRc2 and IRc4 on diaphragm size. These data, combined with recent 3.8 μm polarization results and high-resolution molecular line observations, give a self-consistent model of the central 30arcsec of the nebula. In this model, the geometry of the KL nebula is that of a clumpy cavity (diameter 1017 cm), rather than that of a number of isolated objects. The cavity is centred on IRc2 which is confirmed to be the source of essentially all the luminosity of the region (L ≡ 105 L_sun;). The intrinsic spectrum of IRc2 is approximately that of a blackbody of temperature 700±200K. Publication: The Astrophysical Journal Pub Date: June 1984 DOI: 10.1086/162086 Bibcode: 1984ApJ...281..172W Keywords: Astronomical Photometry; Infrared Astronomy; Molecular Clouds; Orion Nebula; Astronomical Maps; Continuous Spectra; Emission Spectra; Far Infrared Radiation; Infrared Spectra; Infrared Stars; Interstellar Matter; Opacity; Polarimetry; Astrophysics full text sources ADS | data products SIMBAD (1)

Detection of interstellar NH3 in the far-infrared - Warm and dense gas in Orion-KL

Results of an investigation are presented which show the detection of the (J,K) = a(4,3)-s(3,3) rotation-inversion transition of ammonia at 124.6 microns toward the center of the Orion-KL region. The line is found to be in emission and has a FWHM greater than or equal to 30 km/s, while the far-IR ammonia line emission probably comes mainly from the 'hot core', a compact region of warm, very dense gas previously identified by the radio inversion lines of NH3. The a(4,3)-s(3,3) line is very optically thick and it is determined that radiative excitation of the (4,3) NH3 level by far-IR emission from dust within the source can be ruled out. It is concluded that the (4,3) level is probably collisionally excited and the gas in the hot core region is warmer than the dust. Densities of approximately 10 to the 7th/cu cm are high enough to explain the observations, while shock heating by the mass outflow from IRc2 may account for the high gas temperatures in the hot core region.

VLA observations of warm NH3 associated with mass outflows in W51

view Abstract Citations (74) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS VLA observations of warm NH3 associated with mass outflows in W 51. Ho, P. T. P. ; Genzel, R. ; Das, A. Abstract VLA observations of the (J, K) = (3,3) inversion line of NH3 toward the distant H II region complex in W51 are presented. Three small (about 0.1 pc), warm (about 100 K) NH3 condensations are found coincident with every one of the H20 and OH maser sources in the region. This positional emission arises from dense molecular condensations which are interacting with the mass outflows from young stars in these regions. These observations also represent the first direct detection of such high gas temperatures outside the Orion-KL region. Gas heating could be due to the radiation from the exciting sources of the compact H II regions and masers or from the input of mechanical energy due to the outflows. These warm condensations are embedded in a cooler and more extended envelope which dominates lower angular resolution studies. Publication: The Astrophysical Journal Pub Date: March 1983 DOI: 10.1086/160807 Bibcode: 1983ApJ...266..596H Keywords: Ammonia; Molecular Clouds; Radio Sources (Astronomy); Stellar Mass Ejection; Water Masers; Astronomical Maps; B Stars; Condensates; Early Stars; Gas Heating; H Ii Regions; High Temperature Gases; Molecular Spectra; O Stars; Orion Nebula; Astrophysics full text sources ADS | data products SIMBAD (4) NED (1)

NH3 in Orion-KL - A new interpretation

We interpret the observations of ammonia in Orion-KL in a way which greatly simplifies the understanding of single-dish and VLA data. In this new picture, there are only two velocity components: the ''spike'' component from the quiscent molecular cloud and the ''hot core'' component from both streaming and ''stationary'' gas in the 18 km s/sup -1/ outflow from the compact infrared source IRc2. What has been interpreted previously as the NH/sub 3/ ''plateau'' from high-velocity gas is mainly the blended hyperfine satellite emission from the ''hot core'' component. The ammonia lines are highly optically thick (tau>10), and NH/sub 3/ column densities reach 5 x 10/sup 18/ cm/sup -2/. Kinetic temperatures in the outflow region are about 200 K, and NH/sub 3/ is probably collisionally excited at hydrogen densities of 10/sup 8/--10/sup 9/ cm/sup -3/. Ammonia may be highly overabundant in this dense and warm gas and may tie up a considerable fraction of the available nitrogen. The maps can be interpreted as showing a clumpy, expanding, and turbulent shell advancing into the densest part of the Orion-KL region.