Multi-line detection of O_2 toward ρ Ophiuchi A

Context. Models of pure gas-phase chemistry in well-shielded regions of molecular clouds predict relatively high levels of molecular oxygen, O_2, and water, H_(2)O. These high abundances imply high cooling rates, leading to relatively short timescales for the evolution of gravitationally unstable dense cores, forming stars and planets. Contrary to expectations, the dedicated space missions SWAS and Odin typically found only very small amounts of water vapour and essentially no O_2 in the dense star-forming interstellar medium. Aims. Only toward ρOph   A did Odin detect a very weak line of O_2 at 119 GHz in a beam of size 10 arcmin. The line emission of related molecules changes on angular scales of the order of some tens of arcseconds, requiring a larger telescope aperture such as that of the Herschel Space Observatory to resolve the O2 emission and pinpoint its origin. Methods. We use the Heterodyne Instrument for the Far Infrared (HIFI) aboard Herschel to obtain high resolution O_2 spectra toward selected positions in the ρOph A   core. These data are analysed using standard techniques for O_2 excitation and compared to recent PDR-like chemical cloud models. Results. The N_J = 3_(3) − 1_(2) line at 487.2 GHz is clearly detected toward all three observed positions in the ρOph A  core. In addition, an oversampled map of the 5_(4)−3_(4) transition at 773.8 GHz reveals the detection of the line in only half of the observed area. On the basis of their ratios, the temperature of the O_2 emitting gas appears to vary quite substantially, with warm gas (≳ 50K) being adjacent to a much colder region, of temperatures lower than 30 K. Conclusions. The exploited models predict that the O_2 column densities are sensitive to the prevailing dust temperatures, but rather insensitive to the temperatures of the gas. In agreement with these models, the observationally determined O_2 column densities do not seem to depend strongly on the derived gas temperatures, but fall into the range N(O_2) = 3 to ≳ 6 × 10^(15) cm^(-2). Beam-averaged O2 abundances are about 5 × 10^(-8) relative to H_2. Combining the HIFI data with earlier Odin observations yields a source size at 119 GHz in the range of 4 to 5 arcmin, encompassing the entire ρOph A core. We speculate that one of the reasons for the generally very low detection rate of O2 is the short period of time during which O_2 molecules are reasonably abundant in molecular clouds

Submillimeter Imaging of NGC 891 with SHARC

The advent of submillimeter wavelength array cameras operating on large ground-based telescopes is revolutionizing imaging at these wavelengths, enabling high-resolution submillimeter surveys of dust emission in star-forming regions and galaxies. Here we present a recent 350 micron image of the edge-on galaxy NGC 891, which was obtained with the Submillimeter High Angular Resolution Camera (SHARC) at the Caltech Submillimeter Observatory (CSO). We find that high resolution submillimeter data is a vital complement to shorter wavelength satellite data, which enables a reliable separation of the cold dust component seen at millimeter wavelengths from the warmer component which dominates the far-infrared (FIR) luminosity.Comment: 4 pages LaTeX, 2 EPS figures, with PASPconf.sty; to appear in "Astrophysics with Infrared Surveys: A Prelude to SIRTF

First results on Martian carbon monoxide from Herschel/HIFI observations

We report on the initial analysis of Herschel/HIFI carbon monoxide (CO) observations of the Martian atmosphere performed between 11 and 16 April 2010. We selected the (7–6) rotational transitions of the isotopes ^(13)CO at 771 GHz and C^(18)O and 768 GHz in order to retrieve the mean vertical profile of temperature and the mean volume mixing ratio of carbon monoxide. The derived temperature profile agrees within less than 5 K with general circulation model (GCM) predictions up to an altitude of 45 km, however, show about 12–15 K lower values at 60 km. The CO mixing ratio was determined as 980 ± 150 ppm, in agreement with the 900 ppm derived from Herschel/SPIRE observations in November 2009

HIFI observations of water in the atmosphere of comet C/2008 Q3 (Garradd)

High-resolution far-infrared and sub-millimetre spectroscopy of water lines is an important tool to understand the physical and chemical properties of cometary atmospheres.We present observations of several rotational ortho- and para-water transitions in comet C/2008 Q3 (Garradd) performed with HIFI on Herschel. These observations have provided the first detection of the 2_(12)−1_(01) (1669 GHz) ortho and 1_(11)−0_(00) (1113 GHz) para transitions of water in a cometary spectrum. In addition, the ground-state transition 1_(10)−1_(01) at 557 GHz is detected and mapped. By detecting several water lines quasi-simultaneously and mapping their emission we can constrain the excitation parameters in the coma. Synthetic line profiles are computed using excitation models which include excitation by collisions, solar infrared radiation, and radiation trapping. We obtain the gas kinetic temperature, constrain the electron density profile, and estimate the coma expansion velocity by analyzing the map and line shapes. We derive water production rates of 1.7−2.8 × 10^(28) s^(−1) over the range r_h = 1.83−1.85 AU

Observations of pre-stellar cores

Our understanding of the physical and chemical structure of pre-stellar cores, the simplest star-forming sites, has significantly improved since the last IAU Symposium on Astrochemistry (South Korea, 1999). Research done over these years has revealed that major molecular species like CO and CS systematically deplete onto dust grains at the interior of pre-stellar cores, while species like N2H+ and NH3 survive in the gas phase and can usually be detected towards the core centers. Such a selective behaviour of molecular species gives rise to a differentiated (onion-like) chemical composition, and manifests itself in molecular maps as a dichotomy between centrally peaked and ring-shaped distributions. From the point of view of star-formation studies, the identification of molecular inhomogeneities in cores helps to resolve past discrepancies between observations made using different tracers, and brings the possibility of self-consistent modelling of the core internal structure. Here I present recent work on determining the physical and chemical structure of two pre-stellar cores, L1498 and L1517B, using observations in a large number of molecules and Monte Carlo radiative transfer analysis. These two cores are typical examples of the pre-stellar core population, and their chemical composition is characterized by the presence of large freeze out holes in most molecular species. In contrast with these chemically processed objects, a new population of chemically young cores has started to emerge. The characteristics of its most extreme representative, L1521E, are briefly reviewed.Comment: 10 pages, 5 figures. To appear in IAU 231 conf. proc. "Astrochemistry: Recent Successes and Current Challenges," eds. D.C. Lis, G.A. Blake, and E. Herbs

Discovery of Water Vapor in the High-redshift Quasar APM 08279+5255 at z = 3.91

We report a detection of the excited 2_(20)-2_(11) rotational transition of para-H_2O in APM 08279+5255 using the IRAM Plateau de Bure Interferometer. At z = 3.91, this is the highest-redshift detection of interstellar water to date. From large velocity gradient modeling, we conclude that this transition is predominantly radiatively pumped and on its own does not provide a good estimate of the water abundance. However, additional water transitions are predicted to be detectable in this source, which would lead to an improved excitation model. We also present a sensitive upper limit for the hydrogen fluoride (HF) J = 1-0 absorption toward APM 08279+5255. While the face-on geometry of this source is not favorable for absorption studies, the lack of HF absorption is still puzzling and may be indicative of a lower fluorine abundance at z = 3.91 compared with the Galactic interstellar medium

Water production in comet 81P/Wild 2 as determined by Herschel/HIFI

The high spectral resolution and sensitivity of Herschel/HIFI allows for the detection of multiple rotational water lines and accurate determinations of water production rates in comets. In this Letter we present HIFI observations of the fundamental 1_(10)–1_(01) (557 GHz) ortho and 1_(11)–0_(00) (1113 GHz) para rotational transitions of water in comet 81P/Wild 2 acquired in February 2010. We mapped the extent of the water line emission with five point scans. Line profiles are computed using excitation models which include excitation by collisions with electrons and neutrals and solar infrared radiation. We derive a mean water production rate of 1.0 × 10^(28) molecules s^(−1) at a heliocentric distance of 1.61 AU about 20 days before perihelion, in agreement with production rates measured from the ground using observations of the 18-cm OH lines. Furthermore, we constrain the electron density profile and gas kinetic temperature, and estimate the coma expansion velocity by fitting the water line shapes