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International audience; We report observations of three rotational transitions of molecular oxygen (O2) in emission from the H2 Peak 1 position of vibrationally excited molecular hydrogen in Orion. We observed the 487 GHz, 774 GHz, and 1121 GHz lines using the Heterodyne Instrument for the Far Infrared on the Herschel Space Observatory, having velocities of 11 km s-1 to 12 km s-1 and widths of 3 km s-1. The beam-averaged column density is N(O2) = 6.5 × 1016 cm-2, and assuming that the source has an equal beam-filling factor for all transitions (beam widths 44, 28, and 19''), the relative line intensities imply a kinetic temperature between 65 K and 120 K. The fractional abundance of O2 relative to H2 is (0.3-7.3) × 10-6. The unusual velocity suggests an association with a ~5'' diameter source, denoted Peak A, the Western Clump, or MF4. The mass of this source is ~10 M sun and the dust temperature is >=150 K. Our preferred explanation of the enhanced O2 abundance is that dust grains in this region are sufficiently warm (T >= 100 K) to desorb water ice and thus keep a significant fraction of elemental oxygen in the gas phase, with a significant fraction as O2. For this small source, the line ratios require a temperature >=180 K. The inferred O2 column density sime5 × 1018 cm-2 can be produced in Peak A, having N(H2) ~= 4 × 1024 cm-2. An alternative mechanism is a low-velocity (10-15 km s-1) C-shock, which can produce N(O2) up to 1017 cm-2. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

This paper reviews a number of ways in which the results of far-infrared and submillimeter (FIR/SMM) observations (50 μm ≤ λ ≤ 1 mm) have been used to address some of the important questions in astrochemistry. On scales of kiloparsecs these might include questions of abundance gradients; on scales of parsecs these might include questions about the chemical structure of molecular clouds; and on scales of tenths of parsecs or less, these might include questions about chemical processing in shocks.

Comparisons of Saturn observations at far-IR and submillimeter wavelengths, obtained during the earth's March 1980 passage through the plane of Saturn's rings, with spectroscopic observations obtained at an earlier time when the ring plane tilt angle was 21.8 deg, allow a separation of disk and ring contributions to the flux observed in this wavelength range. It is noted that the observed disk emission at 60-180 microns corresponds to a brightness temperature of 104 + or 2 K, and that the brightness temperature of the rings drops 20 K in the 60-80 micron range. An improved estimate of total Saturnian surface brightness is derived which corresponds to an effective temperature of 96.1 + or - 1.6 K.

The article discusses the geodesic motion of photons, considering particularly whether oppositely polarized photons fall at the same rate. It is assumed that orthogonally polarized photons would be equally deflected by the gravitational field of a nonrotating mass. Upon the introduction of rotation, the angular momentum of the deflecting source couples to the photon spin through gravitational field action. Thus there arise separate trajectories for orthogonal polarizations. Searching for changes in polarization in a deflected beam is accomplished by a relative phase delay technique. If the beam is split into orthogonal linear polarization, final polarization is elliptical. Experiments have been performed on searching for ellipticity developments in the linearly polarized carrier waves from Helios 1 and 2, and the results are presented.

The 51.8-micron forbidden O III line has been detected in four H II regions: M42, M17, W51, and NGC 6357A. The respective line strengths are 7 x 10 to the -15th, 1.0 x 10 to the -14th, 2.1 x 10 to the -15th, and 2.6 x 10 to the -15th W/sq cm. The observations are consistent with a previously reported line position and place the line at 51.80 + or - 0.05-micron. When combined with the 88.35-micron forbidden O III observations reported earlier, clumpiness is found to be an important factor in NGC 6357A and M42 and nonnegligible in W51 and M17. The combined data also suggest an O III abundance of about 0.0003 times the electron density, which is a factor of 2 greater than a number of investigators have reported.

Observations of the Kleinmann-Low Nebula in Orion detected the J = 17-J = 16 transition of CO at 153 microns and at a flux level of 7 x 10 to the -17th W/sq cm. The total mass of hot (not less than about 750 K) carbon monoxide in the nebula is estimated at 8 x 10 to the 30th g, and the total hydrogen mass at this temperature is assessed to be about 1.5 solar masses. A CO column density of about 4 x 10 to the 17th per sq cm is derived for the region, which agrees with those predictions made by Storey et al. (1981), and an apparent deficit of oxygen in the nebula is discussed.

The first observation of a fine-structure transition in NGC 7027 at wavelengths greater than 30 microns is reported. The flux in the 63.2-micron line is found to be approximately 10 to the -16th W/sq cm. It is noted that if NGC 7027 lies at 1 kpc, this corresponds to a luminosity, in the line, approximately 30 times greater than the solar luminosity. The flux of the 88.35-micron line is less than 10 to the -17th W/sq cm, and the upper limit to the line flux at 51.8 microns is found to be 10 to the -16th W/sq cm. These upper limits imply an electron density that is less than 1.6 x 10 to the 5th/cu cm. It is noted that the continuum measurements obtained support a dust temperature of 90 K with an emissivity approximately equal to the reciprocal of the square of the wavelength. The data exclude grain materials whose wavelength-dependent emissivity (the reciprocal of the wavelength raised to nth power) requires n to be outside the range between 1.6 and 2, unless the temperature varies drastically across the dust cloud

The 63 micron fine structure transition P4 : 3Pl yields 3P2 for neutral atomic oxygen was obtained during a series of flights at an altitude of approximately 13.7 km. In the Orion Nebula (M42), the observed line strength was 8 x 10 to the minus 15 power watt cm/2 which is estimated to be approximately 0.3 o/o of the energy radiated at all wavelengths. For the Omega Nebulae (M17), the line strength was 2.4 x 10 to the minus 15 power watt cm/2, and the fraction of the total radiated power was slightly higher. These figures refer to a 4' x 6' field of view centered on the peak for infrared emission from each source. The uncertainty in the line strength is approximately 50% and is caused by variable water vapor absorption along the flight path of the airplane. The line position estimate is 63.2 micron (+0.1, -0.2) micron. The prime uncertainty is due to the uncertain position of the (0 I) emitting regions in the field of view.

We present the first detection of the (C II) fine-structure emission line at a wavelength of 157 ..mu..m. The (C II) line strengths are 7.1 x 10/sup -16/ and 1.0 x 10/sup -15/W cm/sup -2/, respectively, in NGC 2024 and M42. The line-to-continuum ratio is higher in NGC 2024 where the continuum is 7.0 x 10/sup -16/ W cm/sup -2/ ..mu..m/sup -1/, in contrast to M42 where it assumes a value of 2.6 x 10/sup -15/W cm/sup -2/ ..mu..m/sup -1/. The respective luminosities in the line are approx.50 and 80 L/sub sun/. The observations were obtained with a stressed Ge:Ga photoconductor.

The 51.8 micron fine structure transition P2:3P2 3P1 for doubly ionized oxygen was observed in the Orion nebula. The observed line strength is of 5 plus or minus 3 times 10 to the minus 15th power watt/sq cm is in good agreement with theoretical predictions. Observations are consistent with the newly predicted 51.8 micron line position. The line lies close to an atmospheric water vapor feature at 51.7 micron, but is sufficiently distant so that corrections for this feature are straightforward. Observations of the 51.8 (O III) line are particularly important since the previously discovered 88 micron line from the same ion also is strong. This pair of lines should, therefore, yield new data about densities in observed H II regions; or else, if density data already are available from radio or other observations, the lines can be used to determine the differential dust absorption between 52 and 88 micron in front of heavily obscured regions.

Further data on the polarization of the far-infrared (wavelength greater than 40 microns) emission from the Orion Nebula shows no evidence for polarized emission by aligned grains. Results at wavelength about 71-115 microns are consistent with a small (about 1.5%) absorption-induced polarization with about the same position angle on the sky as the polarization measured at shorter wavelengths.