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Structural disorder causes materials surface electronic properties, e.g. work function ($\phi$) to vary spatially, yet it is challenging to prove exact causal relationships to underlying ensemble disorder, e.g. roughness or granularity. For polycrystalline Pt, nanoscale resolution photoemission threshold mapping reveals a spatially varying $\phi= 5.70\pm 0.03$~eV over a distribution of (111) textured vicinal grain surfaces prepared by sputter deposition and annealing. With regard to field emission and related phenomena, e.g. vacuum arc initiation, a salient feature of the $\phi$ distribution is that it is skewed with a long tail to values down to 5.4 eV, i.e. far below the mean, which is exponentially impactful to field emission via the Fowler-Nordheim relation. We show that the $\phi$ spatial variation and distribution can be explained by ensemble variations of granular tilts and surface slopes via a Smoluchowski smoothing model wherein local $\phi$ variations result from spatially varying densities of electric dipole moments, intrinsic to atomic steps, that locally modify $\phi$. Atomic step-terrace structure is confirmed with scanning tunneling microscopy (STM) at several locations on our surfaces, and prior works showed STM evidence for atomic step dipoles at various metal surfaces. From our model, we find an atomic step edge dipole $\mu=0.12$ D/edge atom, which is comparable to values reported in studies that utilized other methods and materials. Our results elucidate a connection between macroscopic $\phi$ and nanostructure that may contribute to the spread of reported $\phi$ for Pt and other surfaces, and may be useful toward more complete descriptions of polycrystalline metals in models of field emission and other related vacuum electronics phenomena, e.g. arc initiation.

The Odin satellite is now into its twentieth year of operation, much surpassing its design life of two years. One of its major pursuits was the search for and study of H2O in the Solar System and the Milky Way galaxy. Herschel has observed the central region of NGC 1365 in two positions, and both its SPIRE and PACS observations are available in the Herschel Science Archive. Herschel PACS images have been produced of the 70 and 160 micron infrared emission from the whole galaxy, and also of the cold dust distribution as obtained from the ratio of the 160 to 70 micron images. The Herschel SPIRE observations have been used to produce maps of the 557 GHz o-H2O, 752 GHz p-H2O, 691 GHz CO(6-5), 1037 GHz CO(9-8), 537 GHz CH, 835 GHz CH+, and the 1461 GHz NII lines; however, these observations have no effective velocity resolution. Odin has recently observed the 557 GHz o-H2O ground state line in the central region with high (5 km/s) spectral resolution. The emission and absorption of H2O at 557 GHz, with a velocity resolution of 5 km/s, has been marginally detected in NGC 1365 with Odin. The H2O is predominantly located in a shocked 15" (1.3 kpc) region near some central compact radio sources and hot-spot HII regions, close to the northeast component of the molecular torus surrounding the nucleus. An analysis of the H2O line intensities and velocities indicates that a shock-region is located here. This is corroborated by a statistical image deconvolution of our SEST CO(3-2) observations, yielding 5" resolution, and a study of our VLA HI absorption observations. Additionally, an enticing 20" HI ridge is found to extend south-southeast from the nucleus, coinciding in position with the southern edge of an OIII outflow cone, emanating from the nucleus. The molecular chemistry of the shocked central region is analyzed with special emphasis on the CO, H2O and CH, CH+ results., Comment: 25 pages, 11 figures

Comet Shoemaker-Levy 9 impacted Jupiter in July 1994, leaving its stratosphere with several new species, among them water vapor (H2O). With the aid of a photochemical model H2O can be used as a dynamical tracer in the jovian stratosphere. In this paper, we aim at constraining vertical eddy diffusion (Kzz) at the levels where H2O resides. We monitored the H2O disk-averaged emission at 556.936 GHz with the Odin space telescope between 2002 and 2019, covering nearly two decades. We analyzed the data with a combination of 1D photochemical and radiative transfer models to constrain vertical eddy diffusion in the stratosphere of Jupiter. The Odin observations show us that the emission of H2O has an almost linear decrease of about 40% between 2002 and 2019.We can only reproduce our time series if we increase the magnitude of Kzz in the pressure range where H2O diffuses downward from 2002 to 2019, i.e. from ~0.2 mbar to ~5 mbar. However, this modified Kzz is incompatible with hydrocarbon observations. We find that, even if allowance is made for the initially large abundances of H2O and CO at the impact latitudes, the photochemical conversion of H2O to CO2 is not sufficient to explain the progressive decline of the H2O line emission, suggestive of additional loss mechanisms. The Kzz we derived from the Odin observations of H2O can only be viewed as an upper limit in the ~0.2 mbar to ~5 mbar pressure range. The incompatibility between the interpretations made from H2O and hydrocarbon observations probably results from 1D modeling limitations. Meridional variability of H2O, most probably at auroral latitudes, would need to be assessed and compared with that of hydrocarbons to quantify the role of auroral chemistry in the temporal evolution of the H2O abundance since the SL9 impacts. Modeling the temporal evolution of SL9 species with a 2D model would be the next natural step., Comment: 9 pages, 8 figures, accepted in Astronomy and Astrophysics

Context. The Odin satellite is now into its sixteenth year of operation, much surpassing its design life of two years. One of the sources which Odin has observed in great detail is the Sgr A Complex in the centre of the Milky Way. Aims. To study the presence of NH3 in the Galactic Centre and spiral arms. Methods. Recently, Odin has made complementary observations of the 572 GHz NH3 line towards the Sgr A +50 km/s Cloud and Circumnuclear Disk (CND). Results. Significant NH3 emission has been observed in both the +50 km/s Cloud and the CND. Clear NH3 absorption has also been detected in many of the spiral arm features along the line of sight from the Sun to the core of our Galaxy. Conclusions. The very large velocity width (80 km/s) of the NH3 emission associated with the shock region in the southwestern part of the CND may suggest a formation/desorption scenario similar to that of gas-phase H2O in shocks/outflows., Comment: 5 pages, 3 figures, 3 tables

The apparition of bright comets C/2012 F6 (Lemmon) and C/2014 Q2 (Lovejoy) in March-April 2013 and January 2015, combined with the improved observational capabilities of submillimeter facilities, offered an opportunity to carry out sensitive compositional and isotopic studies of the volatiles in their coma. We observed comet Lovejoy with the IRAM 30m telescope between 13 and 26 January 2015, and with the Odin submillimeter space observatory on 29 January - 3 February 2015. We detected 22 molecules and several isotopologues. The H$_2^{16}$O and H$_2^{18}$O production rates measured with Odin follow a periodic pattern with a period of 0.94 days and an amplitude of ~25%. The inferred isotope ratios in comet Lovejoy are $^{16}$O/$^{18}$O = 499 $\pm$ 24 and D/H = 1.4 $\pm$ 0.4 $\times 10^{-4}$ in water, $^{32}$S/$^{34}$S = 24.7 $\pm$ 3.5 in CS, all compatible with terrestrial values. The ratio $^{12}$C/$^{13}$C = 109 $\pm$ 14 in HCN is marginally higher than terrestrial and $^{14}$N/$^{15}$N = 145 $\pm$ 12 in HCN is half the Earth ratio. Several upper limits for D/H or 12C/13C in other molecules are reported. From our observation of HDO in comet C/2014 Q2 (Lovejoy), we report the first D/H ratio in an Oort Cloud comet that is not larger than the terrestrial value. On the other hand, the observation of the same HDO line in the other Oort-cloud comet, C/2012 F6 (Lemmon), suggests a D/H value four times higher. Given the previous measurements of D/H in cometary water, this illustrates that a diversity in the D/H ratio and in the chemical composition, is present even within the same dynamical group of comets, suggesting that current dynamical groups contain comets formed at very different places or times in the early solar system., Comment: Accepted for publication in Astronomy and Astrophysics

To date O2 has definitely been detected in only two sources, namely rho Oph A and Orion, reflecting the extremely low abundance of O2 in the interstellar medium. One of the sources in the HOP program is the +50 km/s Cloud in the Sgr A Complex in the centre of the Milky Way. The Herschel HIFI is used to search for the 487 and 774 GHz emission lines of O2. No O2 emission is detected towards the Sgr A +50 km/s Cloud, but a number of strong emission lines of methanol (CH3OH) and absorption lines of chloronium (H2Cl+) are observed. A 3 sigma upper limit for the fractional abundance ratio of (O2)/(H2) in the Sgr A +50 km/s Cloud is found to be X(O2) less than 5 x 10(-8). However, since we can find no other realistic molecular candidate than O2 itself, we very tentatively suggest that two weak absorption lines at 487.261 and 487.302 GHz may be caused by the 487 GHz line of O2 in two foreground spiral arm clouds. By considering that the absorption may only be apparent, the estimated upper limit to the O2 abundance of less than (10-20) x 10(-6) in these foreground clouds is very high. This abundance limit was determined also using Odin non-detection limits. If the absorption is due to a differential Herschel OFF-ON emission, the O2 fractional abundance may be of the order of (5-10) x 10(-6). With the assumption of pure absorption by foreground clouds, the unreasonably high abundance of (1.4-2.8) x 10(-4) was obtained. The rotation temperatures for CH3OH-A and CH3OH-E lines in the +50 km/s Cloud are found to be 64 and 79 K, respectively, and the fractional abundance of CH3OH is approximately 5 x 10(-7)., Comment: Accepted by Astronomy & Astrophysics, 11 pages, 12 figures

[Abridged] Our aim is to explore the gas dynamics and the accretion process in the early phase of high-mass star formation. The inward motion of molecular gas in the massive star forming region G34.26+0.15 is investigated by using high-resolution profiles of seven transitions of ammonia at THz frequencies observed with Herschel-HIFI. The shapes and intensities of these lines are interpreted in terms of radiative transfer models of a spherical, collapsing molecular envelope. An accelerated Lambda Iteration (ALI) method is used to compute the models. The seven ammonia lines show mixed absorption and emission with inverse P-Cygni-type profiles that suggest infall onto the central source. A trend toward absorption at increasingly higher velocities for higher excitation transitions is clearly seen in the line profiles. The $J = 3\leftarrow2$ lines show only very weak emission, so these absorption profiles can be used directly to analyze the inward motion of the gas. This is the first time a multitransitional study of spectrally resolved rotational ammonia lines has been used for this purpose. Broad emission is, in addition, mixed with the absorption in the $1_0-0_0$ ortho-NH$_3$ line, possibly tracing a molecular outflow from the star forming region. The best-fitting ALI model reproduces the continuum fluxes and line profiles, but slightly underpredicts the emission and absorption depth in the ground-state ortho line $1_0-0_0$. The derived ortho-to-para ratio is approximately 0.5 throughout the infalling cloud core similar to recent findings for translucent clouds in sight lines toward W31C and W49N. We find evidence of two gas components moving inwards toward the central region with constant velocities: 2.7 and 5.3 km$\,$s$^{-1}$, relative to the source systemic velocity. The inferred mass accretion rates derived are sufficient to overcome the expected radiation pressure from G34.26+0.15., Comment: 20 pages, 18 figures, accepted by A&A 3 October 2015

We report observations of molecular oxygen (O$_2$) rotational transitions at 487 GHz, 774 GHz, and 1121 GHz toward Orion Peak A. The O2 lines at 487 GHz and 774 GHz are detected at velocities of 10-12 km/s with line widths 3 km/s; however, the transition at 1121 GHz is not detected. The observed line characteristics, combined with the results of earlier observations, suggest that the region responsible for the O$_2$ emission is 9" (6e16 cm) in size, and is located close to the H2 Peak 1position (where vibrationally-excited H$_2$ emission peaks), and not at Peak A, 23" away. The peak O2 column density is 1.1e18/cm2. The line velocity is close to that of 621 GHz water maser emission found in this portion of the Orion Molecular Cloud, and having a shock with velocity vector lying nearly in the plane of the sky is consistent with producing maximum maser gain along the line-of-sight. The enhanced O$_2$ abundance compared to that generally found in dense interstellar clouds can be explained by passage of a low-velocity C-shock through a clump with preshock density 2e4/cm3, if a reasonable flux of UV radiation is present. The postshock O$_2$ can explain the emission from the source if its line of sight dimension is ~10 times larger than its size on the plane of the sky. The special geometry and conditions required may explain why O$_2$ emission has not been detected in the cores of other massive star-forming molecular clouds., Comment: 28 pages, 13 figures

The understanding of interstellar nitrogen chemistry has improved significantly with recent results from the Herschel Space Observatory. To set even better constraints, we report here on deep searches for the NH+ ground state rotational transition J=1.5-0.5 of the ^2Pi_1/2 lower spin ladder, with fine-structure transitions at 1013 and 1019 GHz, and the para-NH2- 1_1,1-0_0,0 rotational transition at 934 GHz towards Sgr B2(M) and G10.6-0.4 using Herschel-HIFI. No clear detections of NH+ are made and the derived upper limits are <2*10^-12 and <7*10^-13 in Sgr B2(M) and G10.6-0.4, respectively. The searches are complicated by the fact that the 1013 GHz transition lies only -2.5 km/s from a CH2NH line, seen in absorption in Sgr B2(M), and that the hyperfine structure components in the 1019 GHz transition are spread over 134 km/s. Searches for the so far undetected NH2- anion turned out to be unfruitful towards G10.6-0.4, while the para-NH2- 1_1,1-0_0,0 transition was tentatively detected towards Sgr B2(M) at a velocity of 19 km/s. Assuming that the absorption occurs at the nominal source velocity of +64 km/s, the rest frequency would be 933.996 GHz, offset by 141 MHz from our estimated value. Using this feature as an upper limit, we found N(p-NH2-)<4*10^11 cm^-2. The upper limits for both species in the diffuse line-of-sight gas are less than 0.1 to 2 % of the values found for NH, NH2, and NH3 towards both sources. Chemical modelling predicts an NH+ abundance a few times lower than our present upper limits in diffuse gas and under typical Sgr B2(M) envelope conditions. The NH2- abundance is predicted to be several orders of magnitudes lower than our observed limits, hence not supporting our tentative detection. Thus, while NH2- may be very difficult to detect in interstellar space, it could, be possible to detect NH+ in regions where the ionisation rates of H2 and N are greatly enhanced., Comment: 14 pages, 19 figures, accepted for publication in Astronomy & Astrophysics 21 May, 2014

We observed OH, H$_2$O, HN$_3$, C$^{18}$O, and C$_I$ towards the +50 km/s cloud (M-0.02-0.07), the CND and the +20 km/s (M-0.13-0.08) cloud in the Sgr A complex with the VLA, Odin and SEST. Strong OH absorption, H$_2$O emission and absorption lines were seen at all three positions. Strong C$^{18}$O emissions were seen towards the +50 and +20 km/s clouds. The CND is rich in H$_2$O and OH, and these abundances are considerably higher than in the surrounding clouds, indicating that shocks, star formation and clump collisions prevail in those objects. A comparison with the literature reveals that it is likely that PDR chemistry including grain surface reactions, and perhaps also the influences of shocks has led to the observed abundances of the observed molecular species studied here. In the redward high-velocity line wings of both the +50 and +20 km/s clouds and the CND, the very high H$_2$O abundances are suggested to be caused by the combined action of shock desorption from icy grain mantles and high-temperature, gas-phase shock chemistry. Only three of the molecules are briefly discussed here. For OH and H$_2$O three of the nine observed positions are shown, while a map of the C$^{18}$O emission is provided. An extensive paper was recently published with Open Access (Karlsson et al. 2013; http://www.aanda.org/articles/aa/pdf/2013/06/aa20471-12.pdf )., Comment: Proc. of a Conf. on IAU Symposium No.303: The Galactic Center: Feeding and Feedback in a Normal Galactic Nucleus 2013, Santa Fe, NM (USA)

We report the results of a search for molecular oxygen (O2) toward the Orion Bar, a prominent photodissociation region at the southern edge of the HII region created by the luminous Trapezium stars. We observed the spectral region around the frequency of the O2 N_J = 3_3 - 1_2 transition at 487 GHz and the 5_4 - 3_4 transition at 774 GHz using the Heterodyne Instrument for the Far Infrared on the Herschel Space Observatory. Neither line was detected, but the 3sigma upper limits established here translate to a total line-of-sight O2 column density < 1.5 10^16 cm^-2 for an emitting region whose temperature is between 30K and 250 K, or < 1 10^16 cm^-2 if the O2 emitting region is primarily at a temperature of ~< 100 K. Because the Orion Bar is oriented nearly edge-on relative to our line of sight, the observed column density is enhanced by a factor estimated to be between 4 and 20 relative to the face-on value. Our upper limits imply that the face-on O2 column density is less than 4 10^15 cm^-2, a value that is below, and possibly well below, model predictions for gas with a density of 10^4 - 10^5 cm^-3 exposed to a far ultraviolet flux 10^4 times the local value, conditions inferred from previous observations of the Orion Bar. The discrepancy might be resolved if: (1) the adsorption energy of O atoms to ice is greater than 800 K; (2) the total face-on Av of the Bar is less than required for O2 to reach peak abundance; (3) the O2 emission arises within dense clumps with a small beam filling factor; or, (4) the face-on depth into the Bar where O2 reaches its peak abundance, which is density dependent, corresponds to a sky position different from that sampled by our Herschel beams., Comment: 30 pages, 7 figures, 1 table. Accepted for publication in ApJ

Models of pure gas-phase chemistry in well-shielded regions of molecular clouds predict relatively high levels of molecular oxygen, O2, and water, H2O. Contrary to expectation, the space missions SWAS and Odin found only very small amounts of water vapour and essentially no O2 in the dense star-forming interstellar medium. Only toward rho Oph A did Odin detect a weak line of O2 at 119 GHz in a beam size of 10 arcmin. A larger telescope aperture such as that of the Herschel Space Observatory is required to resolve the O2 emission and to pinpoint its origin. We use the Heterodyne Instrument for the Far Infrared aboard Herschel to obtain high resolution O2 spectra toward selected positions in rho Oph A. These data are analysed using standard techniques for O2 excitation and compared to recent PDR-like chemical cloud models. The 487.2GHz line was clearly detected toward all three observed positions in rho Oph A. In addition, an oversampled map of the 773.8GHz transition revealed the detection of the line in only half of the observed area. Based on their ratios, the temperature of the O2 emitting gas appears to vary quite substantially, with warm gas (> 50 K) adjacent to a much colder region, where temperatures are below 30 K. The exploited models predict O2 column densities to be sensitive to the prevailing dust temperatures, but rather insensitive to the temperatures of the gas. In agreement with these model, the observationally determined O2 column densities seem not to depend strongly on the derived gas temperatures, but fall into the range N(O2) = (3 to >6)e15/cm^2. Beam averaged O2 abundances are about 5e-8 relative to H2. Combining the HIFI data with earlier Odin observations yields a source size at 119 GHz of about 4 - 5 arcmin, encompassing the entire rho Oph A core., Comment: 10 pages, 8 figures intended for publication in A&A

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 HIFI 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\times1016 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\times10-6. 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\odot and the dust temperature is \geq 150 K. Our preferred explanation of the enhanced O2 abundance is that dust grains in this region are sufficiently warm (T \geq 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 \geq 180 K. The inferred O2 column density \simeq 5\times1018 cm-2 can be produced in Peak A, having N(H2) \simeq 4\times1024 cm-2. An alternative mechanism is a low-velocity (10 to 15 km s-1) C-shock, which can produce N(O2) up to 1017 cm-2.

We have used the Odin submillimetre-wave satellite telescope to observe the ground state transitions of ortho-ammonia and ortho-water, including their 15N, 18O, and 17O isotopologues, towards Sgr B2. The extensive simultaneous velocity coverage of the observations, >500 km/s, ensures that we can probe the conditions of both the warm, dense gas of the molecular cloud Sgr B2 near the Galactic centre, and the more diffuse gas in the Galactic disk clouds along the line-of-sight. We present ground-state NH3 absorption in seven distinct velocity features along the line-of-sight towards Sgr B2. We find a nearly linear correlation between the column densities of NH3 and CS, and a square-root relation to N2H+. The ammonia abundance in these diffuse Galactic disk clouds is estimated to be about (0.5-1)e-8, similar to that observed for diffuse clouds in the outer Galaxy. On the basis of the detection of H218O absorption in the 3 kpc arm, and the absence of such a feature in the H217O spectrum, we conclude that the water abundance is around 1e-7, compared to ~1e-8 for NH3. The Sgr B2 molecular cloud itself is seen in absorption in NH3, 15NH3, H2O, H218O, and H217O, with emission superimposed on the absorption in the main isotopologues. The non-LTE excitation of NH3 in the environment of Sgr B2 can be explained without invoking an unusually hot (500 K) molecular layer. A hot layer is similarly not required to explain the line profiles of the 1_{1,0}-1_{0,1} transition from H2O and its isotopologues. The relatively weak 15NH3 absorption in the Sgr B2 molecular cloud indicates a high [14N/15N] isotopic ratio >600. The abundance ratio of H218O and H217O is found to be relatively low, 2.5--3. These results together indicate that the dominant nucleosynthesis process in the Galactic centre is CNO hydrogen burning., Comment: 10 pages, 5 figures

We report the first detection of chloronium, H$_2$Cl$^+$, in the interstellar medium, using the HIFI instrument aboard the \emph{Herschel} Space Observatory. The $2_{12}-1_{01}$ lines of ortho-H$_2^{35}$Cl$^+$ and ortho-H$_2^{37}$Cl$^+$ are detected in absorption towards NGC~6334I, and the $1_{11}-0_{00}$ transition of para-H$_2^{35}$Cl$^+$ is detected in absorption towards NGC~6334I and Sgr~B2(S). The H$_2$Cl$^+$ column densities are compared to those of the chemically-related species HCl. The derived HCl/H$_2$Cl$^+$ column density ratios, $\sim$1--10, are within the range predicted by models of diffuse and dense Photon Dominated Regions (PDRs). However, the observed H$_2$Cl$^+$ column densities, in excess of $10^{13}$~cm$^{-2}$, are significantly higher than the model predictions. Our observations demonstrate the outstanding spectroscopic capabilities of HIFI for detecting new interstellar molecules and providing key constraints for astrochemical models., Comment: Accepted for publication in A&A, HIFI Special Issue; 4 pages, 2 figures, 1 table

Our aim is to observationally investigate the cosmic Dark Ages in order to constrain star and structure formation models, as well as the chemical evolution in the early Universe. Spectral lines from atoms and molecules in primordial perturbations at high redshifts can give information about the conditions in the early universe before and during the formation of the first stars in addition to the epoch of reionisation. The lines may arise from moving primordial perturbations before the formation of the first stars (resonant scattering lines), or could be thermal absorption or emission lines at lower redshifts. The difficulties in these searches are that the source redshift and evolutionary state, as well as molecular species and transition are unknown, which implies that an observed line can fall within a wide range of frequencies. The lines are also expected to be very weak. Observations from space have the advantages of stability and the lack of atmospheric features which is important in such observations. We have therefore, as a first step in our searches, used the Odin satellite to perform two sets of spectral line surveys towards several positions. The first survey covered the band 547-578 GHz towards two positions, and the second one covered the bands 542.0-547.5 GHz and 486.5-492.0 GHz towards six positions selected to test different sizes of the primordial clouds. Two deep searches centred at 543.250 and 543.100 GHz with 1 GHz bandwidth were also performed towards one position. The two lowest rotational transitions of H2 will be redshifted to these frequencies from z~20-30, which is the predicted epoch of the first star formation. No lines are detected at an rms level of 14-90 and 5-35 mK for the two surveys, respectively, and 2-7 mK in the deep searches with a channel spacing of 1-16 MHz. The broad bandwidth covered allows a wide range of redshifts to be explored for a number of atomic and molecular species and transitions. From the theoretical side, our sensitivity analysis show that the largest possible amplitudes of the resonant lines are about 1 mK at frequencies <200 GHz, and a few micro K around 500-600 GHz, assuming optically thick lines and no beam-dilution. However, if existing, thermal absorption lines have the potential to be orders of magnitude stronger than the resonant lines. We make a simple estimation of the sizes and masses of the primordial perturbations at their turn-around epochs, which previously has been identified as the most favourable epoch for a detection. This work may be considered as an important pilot study for our forthcoming observations with the Herschel Space Observatory., Comment: 15 pages, 9 figures, 3 on-line pages. Accepted for publication in Astronomy & Astrophysics 8 March 2010.

Observations of the (N_J=1_1-1_0) ground state transition of O_2 with the Odin satellite resulted in a about 5 sigma detection toward the dense core rho Oph A. At the frequency of the line, 119 GHz, the Odin telescope has a beam width of 10', larger than the size of the dense core, so that the precise nature of the emitting source and its exact location and extent are unknown. The current investigation is intended to remedy this. Telluric absorption makes ground based O_2 observations essentially impossible and observations had to be done from space. mm-wave telescopes on space platforms were necessarily small, which resulted in large, several arcminutes wide, beam patterns. Although the Earth's atmosphere is entirely opaque to low-lying O_2 transitions, it allows ground based observations of the much rarer O18O in favourable conditions and at much higher angular resolution with larger telescopes. In addition, rho Oph A exhibits both multiple radial velocity systems and considerable velocity gradients. Extensive mapping of the region in the proxy C18O (J=3-2) line can be expected to help identify the O_2 source on the basis of its line shape and Doppler velocity. Line opacities were determined from observations of optically thin 13C18O (J=3-2) at selected positions. During several observing periods, two C18O intensity maxima in rho Oph A were searched for in the 16O18O (2_1-0_1) line at 234 GHz with the 12m APEX telescope. Our observations resulted in an upper limit on the integrated O18O intensity of < 0.01 K km/s (3 sigma) into the 26.5" beam. We conclude that the source of observed O_2 emission is most likely confined to the central regions of the rho Oph A cloud. In this limited area, implied O_2 abundances could thus be higher than previously reported, by up to two orders of magnitude., Comment: 7 pages, 6 figures (5 colour), Astronomy & Astrophysics

We investigate the physical and chemical conditions in a typical star forming region, including an unbiased search for new molecules in a spectral region previously unobserved. Due to its proximity, the Orion KL region offers a unique laboratory of molecular astrophysics in a chemically rich, massive star forming region. Several ground-based spectral line surveys have been made, but due to the absorption by water and oxygen, the terrestrial atmosphere is completely opaque at frequencies around 487 and 557 GHz. To cover these frequencies we used the Odin satellite to perform a spectral line survey in the frequency ranges 486-492 GHz and 541-577 GHz, filling the gaps between previous spectral scans. Odin's high main beam efficiency and observations performed outside the atmosphere make our intensity scale very well determined. We observed 280 spectral lines from 38 molecules including isotopologues, and, in addition, 64 unidentified lines. The beam-averaged emission is dominated by CO, H2O, SO2, SO, 13CO and CH3OH. Species with the largest number of lines are CH3OH, (CH33)2O, SO2, 13CH3OH, CH3CN and NO. Six water lines are detected including the ground state rotational transition o-H2O, its isotopologues o-H218O and o-H217O, the Hot Core tracing p-H2O transition 6(2,4)-7(1,7), and the 2(0, 2)-1(1,1) transition of HDO. Other lines of special interest are the 1_0-0_0 transition of NH3 and its isotopologue 15NH3. Isotopologue abundance ratios of D/H, 12C/13C, 32S/34S, 34S/33S, and 18O/17O are estimated. The temperatures, column densities and abundances in the various subregions are estimated, and we find very high gas-phase abundances of H2O, NH3, SO2, SO, NO, and CH3OH. A comparison with the ice inventory of ISO sheds new light on the origin of the abundant gas-phase molecules., Comment: 51 pages, 47 figures, 35 tables, accepted for publication in Astronomy and Astrophysics 17 September 2007

Spectral line surveys are useful since they allow identification of new molecules and new lines in uniformly calibrated data sets. Nonetheless, large portions of the sub-millimetre spectral regime remain unexplored due to severe absorptions by H2O and O2 in the terrestrial atmosphere. The purpose of the measurements presented here is to cover wavelength regions at and around 0.55 mm -- regions largely unobservable from the ground. Using the Odin astronomy/aeronomy satellite, we performed the first spectral survey of the Orion KL molecular cloud core in the bands 486--492 and 541--576 GHz with rather uniform sensitivity (22--25 mK baseline noise). Odin's 1.1 m size telescope, equipped with four cryo-cooled tuneable mixers connected to broad band spectrometers, was used in a satellite position-switching mode. Two mixers simultaneously observed different 1.1 GHz bands using frequency steps of 0.5 GHz (25 hours each). An on-source integration time of 20 hours was achieved for most bands. The entire campaign consumed ~1100 orbits, each containing one hour of serviceable astro-observation. We identified 280 spectral lines from 38 known interstellar molecules (including isotopologues) having intensities in the range 80 to 0.05 K. An additional 64 weak lines remain unidentified. Apart from the ground state rotational 1(1,0)--1(0,1) transitions of ortho-H2O, H218O and H217O, the high energy 6(2,4)--7(1,7) line of para-H2O and the HDO(2,0,2--1,1,1) line have been observed, as well as the 1,0--0,1 lines from NH3 and its rare isotopologue 15NH3. We suggest assignments for some unidentified features, notably the new interstellar molecules ND and SH-. Severe blends have been detected in the line wings of the H218O, H217O and 13CO lines changing the true linewidths of the outflow emission., Comment: 21 pages, 10 figures, 7 tables, accepeted for publication in Astronomy and Astrophysics 30 August 2007

We have used the Odin satellite to obtain strip maps of the ground-state rotational transitions of ortho-water and ortho-ammonia, as well as CO(5-4) and 13CO(5-4) across the PDR, and H218O in the central position. A physi-chemical inhomogeneous PDR model was used to compute the temperature and abundance distributions for water, ammonia and CO. A multi-zone escape probability method then calculated the level populations and intensity distributions. These results are compared to a homogeneous model computed with an enhanced version of the RADEX code. H2O, NH3 and 13CO show emission from an extended PDR with a narrow line width of ~3 kms. Like CO, the water line profile is dominated by outflow emission, however, mainly in the red wing. The PDR model suggests that the water emission mainly arises from the surfaces of optically thick, high density clumps with n(H2)>10^6 cm^-3 and a clump water abundance, with respect to H2, of 5x10^-8. The mean water abundance in the PDR is 5x10^-9, and between ~2x10^-8 -- 2x10^-7 in the outflow derived from a simple two-level approximation. Ammonia is also observed in the extended clumpy PDR, likely from the same high density and warm clumps as water. The average ammonia abundance is about the same as for water: 4x10^-9 and 8x10^-9 given by the PDR model and RADEX, respectively. The similarity of water and ammonia PDR emission is also seen in the almost identical line profiles observed close to the bright rim. Around the central position, ammonia also shows some outflow emission although weaker than water in the red wing. Predictions of the H2O(110-101) and (111-000) antenna temperatures across the PDR are estimated with our PDR model for the forthcoming observations with the Herschel Space Observatory., Comment: 13 pages, 14 figures, 10 tables. Accepted for publication in Astronomy & Astrophysics 14 November 2008

Aims. We investigate the ortho-water abundance in outflows and shocks in order to improve our knowledge of shock chemistry and of the physics behind molecular outflows. Methods. We have used the Odin space observatory to observe the H2O(110-101) line. We obtain strip maps and single pointings of 13 outflows and two supernova remnants where we report detections for eight sources. We have used RADEX to compute the beam averaged abundances of o-H2O relative to H2. In the case of non-detection, we derive upper limits on the abundance. Results. Observations of CO emission from the literature show that the volume density of H2 can vary to a large extent, a parameter that puts severe uncertainties on the derived abundances. Our analysis shows a wide range of abundances reflecting the degree to which shock chemistry is affecting the formation and destruction of water. We also compare our results with recent results from the SWAS team. Conclusions. Elevated abundances of ortho-water are found in several sources. The abundance reaches values as high as what would be expected from a theoretical C-type shock where all oxygen, not in the form of CO, is converted to water. However, the high abundances we derive could also be due to the low densities (derived from CO observations) that we assume. The water emission may in reality stem from high density regions much smaller than the Odin beam. We do not find any relationship between the abundance and the mass loss rate. On the other hand, there is a relation between the derived water abundance and the observed maximum outflow velocity., Comment: 19 pages, 20 figures, 4 tables

Aims: Spectrally resolved circumstellar H2O(1_10 - 1_01) lines have been obtained towards three M-type AGB stars using the Odin satellite. This provides additional strong constrains on the properties of circumstellar H2O and the circumstellar envelope. Methods: ISO and Odin satellite H2O line data are used as constraints for radiative transfer models. Special consideration is taken to the spectrally resolved Odin line profiles, and the effect of excitation to the first excited vibrational states of the stretching modes (nu1=1 and nu3=1) on the derived abundances is estimated. A non-local, radiative transfer code based on the ALI formalism is used. Results: The H2O abundance estimates are in agreement with previous estimates. The inclusion of the Odin data sets stronger constraints on the size of the H2O envelope. The H2O(1_10 - 1_01) line profiles require a significant reduction in expansion velocity compared to the terminal gas expansion velocity determined in models of CO radio line emission, indicating that the H2O emission lines probe a region where the wind is still being accelerated. Including the nu3=1 state significantly lowers the estimated abundances for the low-mass-loss-rate objects. This shows the importance of detailed modelling, in particular the details of the infrared spectrum in the range 3 to 6 micron, to estimate accurate circumstellar H2O abundances. Conclusions: Spectrally resolved circumstellar H2O emission lines are important probes of the physics and chemistry in the inner regions of circumstellar envelopes around asymptotic giant branch stars. Predictions for H2O emission lines in the spectral range of the upcoming Herschel/HIFI mission indicate that these observations will be very important in this context., Comment: accepted in A&A, 10 pages, 8 figures