arXiv subjects

M. Olberg

Publications and source records attributed to M. Olberg.

At least 19 recordsLinked to original sources

arXiv2023

SKA Science Data Challenge 2: analysis and results

The Square Kilometre Array Observatory (SKAO) will explore the radio sky to new depths in order to conduct transformational science. SKAO data products made available to astronomers will be correspondingly large and complex, requiring the application of advanced analysis techniques to extract key science findings. To this end, SKAO is conducting a series of Science Data Challenges, each designed to familiarise the scientific community with SKAO data and to drive the development of new analysis techniques. We present the results from Science Data Challenge 2 (SDC2), which invited participants to find and characterise 233245 neutral hydrogen (Hi) sources in a simulated data product representing a 2000~h SKA MID spectral line observation from redshifts 0.25 to 0.5. Through the generous support of eight international supercomputing facilities, participants were able to undertake the Challenge using dedicated computational resources. Alongside the main challenge, `reproducibility awards' were made in recognition of those pipelines which demonstrated Open Science best practice. The Challenge saw over 100 participants develop a range of new and existing techniques, with results that highlight the strengths of multidisciplinary and collaborative effort. The winning strategy -- which combined predictions from two independent machine learning techniques to yield a 20 percent improvement in overall performance -- underscores one of the main Challenge outcomes: that of method complementarity. It is likely that the combination of methods in a so-called ensemble approach will be key to exploiting very large astronomical datasets.

astro-ph.IM↗

arXiv2020

18-year long monitoring of the evolution of H2O vapor in the stratosphere of Jupiter with the Odin space telescope

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.

astro-ph.EP↗

arXiv2017

SEPIA - a new single pixel receiver at the APEX Telescope

Context: We describe the new SEPIA (Swedish-ESO PI Instrument for APEX) receiver, which was designed and built by the Group for Advanced Receiver Development (GARD), at Onsala Space Observatory (OSO) in collaboration with ESO. It was installed and commissioned at the APEX telescope during 2015 with an ALMA Band 5 receiver channel and updated with a new frequency channel (ALMA Band 9) in February 2016. Aims: This manuscript aims to provide, for observers who use the SEPIA receiver, a reference in terms of the hardware description, optics and performance as well as the commissioning results. Methods: Out of three available receiver cartridge positions in SEPIA, the two current frequency channels, corresponding to ALMA Band 5, the RF band 158--211 GHz, and Band 9, the RF band 600--722 GHz, provide state-of-the-art dual polarization receivers. The Band 5 frequency channel uses 2SB SIS mixers with an average SSB noise temperature around 45K with IF (intermediate frequency) band 4--8 GHz for each sideband providing total 4x4 GHz IF band. The Band 9 frequency channel uses DSB SIS mixers with a noise temperature of 75--125K with IF band 4--12 GHz for each polarization. Results: Both current SEPIA receiver channels are available to all APEX observers.

astro-ph.IM↗

arXiv2017

Vibrationally excited water emission at 658 GHz from evolved stars

Several rotational transitions of water have been identified toward evolved stars in the ground vibrational state as well as in the first excited state of the bending mode. In the latter vibrational state of water, the 658 GHz J = 1_1,0-1_0,1 rotational transition is often strong and seems to be widespread in late-type stars. Our main goals are to better characterize the nature of the 658 GHz emission, compare the velocity extent of the 658 GHz emission with SiO maser emission to help locate the water layers and, more generally, investigate the physical conditions prevailing in the excited water layers of evolved stars. Another goal is to identify new 658 GHz emission sources and contribute in showing that this emission is widespread in evolved stars. Eleven evolved stars were extracted from our mini-catalog of existing and potential 658 GHz sources for observations with the APEX telescope equipped with the SEPIA receiver. The 13CO J=6-5 line was placed in the same receiver sideband for simultaneous observation with the 658 GHz line of water. We have compared the 658 GHz line properties with our H2O radiative transfer models in stars and we have compared the velocity ranges of the 658 GHz and SiO J=2-1, v=1 maser lines. All stars show 658 GHz emission with a peak flux density in the range 50-70 Jy to 2000-3000 Jy. We have shown that the 658 GHz line is masing and we found that the 658 GHz velocity extent tends to be correlated with that of the SiO maser suggesting that both emission lines are excited in circumstellar layers close to the central star. Broad and stable line profiles are observed at 658 GHz. This could indicate maser saturation although we have tentatively provided first information on time variability at 658 GHz.

astro-ph.SR↗

arXiv2017

Data processing pipeline for Herschel HIFI

{Context}. The HIFI instrument on the Herschel Space Observatory performed over 9100 astronomical observations, almost 900 of which were calibration observations in the course of the nearly four-year Herschel mission. The data from each observation had to be converted from raw telemetry into calibrated products and were included in the Herschel Science Archive. {Aims}. The HIFI pipeline was designed to provide robust conversion from raw telemetry into calibrated data throughout all phases of the HIFI missions. Pre-launch laboratory testing was supported as were routine mission operations. {Methods}. A modular software design allowed components to be easily added, removed, amended and/or extended as the understanding of the HIFI data developed during and after mission operations. {Results}. The HIFI pipeline processed data from all HIFI observing modes within the Herschel automated processing environment as well as within an interactive environment. The same software can be used by the general astronomical community to reprocess any standard HIFI observation. The pipeline also recorded the consistency of processing results and provided automated quality reports. Many pipeline modules were in use since the HIFI pre-launch instrument level testing. {Conclusions}. Processing in steps facilitated data analysis to discover and address instrument artefacts and uncertainties. The availability of the same pipeline components from pre-launch throughout the mission made for well-understood, tested, and stable processing. A smooth transition from one phase to the next significantly enhanced processing reliability and robustness.

astro-ph.IM↗

arXiv2017

Simultaneous 183 GHz H2O Maser and SiO Observations Towards Evolved Stars Using APEX SEPIA Band 5

We investigate the use of 183 GHz H2O masers for characterization of the physical conditions and mass loss process in the circumstellar envelopes of evolved stars. We used APEX SEPIA Band 5 to observe the 183 GHz H2O line towards 2 Red Supergiant and 3 Asymptotic Giant Branch stars. Simultaneously, we observed lines in 28SiO v0, 1, 2 and 3, and for 29SiO v0 and 1. We detected the 183 GHz H2O line towards all the stars with peak flux densities greater than 100 Jy, including a new detection from VY CMa. Towards all 5 targets, the water line had indications of being due to maser emission and had higher peak flux densities than for the SiO lines. The SiO lines appear to originate from both thermal and maser processes. Comparison with simulations and models indicate that 183 GHz maser emission is likely to extend to greater radii in the circumstellar envelopes than SiO maser emission and to similar or greater radii than water masers at 22, 321 and 325 GHz. We speculate that a prominent blue-shifted feature in the W Hya 183 GHz spectrum is amplifying the stellar continuum, and is located at a similar distance from the star as mainline OH maser emission. From a comparison of the individual polarizations, we find that the SiO maser linear polarization fraction of several features exceeds the maximum fraction allowed under standard maser assumptions and requires strong anisotropic pumping of the maser transition and strongly saturated maser emission. The low polarization fraction of the H2O maser however, fits with the expectation for a non-saturated maser. 183 GHz H2O masers can provide strong probes of the mass loss process of evolved stars. Higher angular resolution observations of this line using ALMA Band 5 will enable detailed investigation of the emission location in circumstellar envelopes and can also provide information on magnetic field strength and structure.

astro-ph.SR↗

arXiv2017

Odin observations of ammonia in the Sgr A +50 km/s Cloud and Circumnuclear Disk

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.

astro-ph.GA↗

arXiv2015

Ortho-to-para ratio of NH2. Herschel-HIFI observations of ortho- and para-NH2 rotational transitions towards W31C, W49N, W51 and G34.3+0.1

We have used the Herschel-HIFI instrument to observe both nuclear spin symmetries of amidogen (NH2) towards the high-mass star-forming regions W31C (G10.6-0.4), W49N (G43.2-0.1), W51 (G49.5-0.4) and G34.3+0.1. The aim is to investigate the ratio of nuclear spin types, the ortho-to-para ratio (OPR), of NH2. The excited NH2 transitions are used to construct radiative transfer models of the hot cores and surrounding envelopes in order to investigate the excitation and possible emission of the ground state rotational transitions of ortho-NH2 N_(K_a,K_c} J=1_(1,1) 3/2 - 0_(0,0) 1/2 and para-NH2 2_(1,2) 5/2 - 1_(0,1) 3/2$ used in the OPR calculations. Our best estimate of the average OPR in the envelopes lie above the high temperature limit of three for W49N, specifically 3.5 with formal errors of \pm0.1, but for W31C, W51, and G34.3+0.1 we find lower values of 2.5\pm0.1, 2.7\pm0.1, and 2.3\pm0.1, respectively. Such low values are strictly forbidden in thermodynamical equilibrium since the OPR is expected to increase above three at low temperatures. In the translucent interstellar gas towards W31C, where the excitation effects are low, we find similar values between 2.2\pm0.2 and 2.9\pm0.2. In contrast, we find an OPR of 3.4\pm0.1 in the dense and cold filament connected to W51, and also two lower limits of >4.2 and >5.0 in two other translucent gas components towards W31C and W49N. At low temperatures (T \lesssim 50 K) the OPR of H2 is <10^-1, far lower than the terrestrial laboratory normal value of three. In such a "para-enriched H2" gas, our astrochemical models can reproduce the variations of the observed OPR, both below and above the thermodynamical equilibrium value, by considering nuclear-spin gas-phase chemistry. The models suggest that values below three arise in regions with temperatures >20-25 K, depending on time, and values above three at lower temperatures.

astro-ph.GA↗

arXiv2015

On the accretion process in a high-mass star forming region - A multitransitional THz Herschel-HIFI study of ammonia toward G34.26+0.15

[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.

astro-ph.SR↗

arXiv2015

Gas and dust in the star-forming region rho Oph A: The dust opacity exponent beta and the gas-to-dust mass ratio g2d

We aim at determining the spatial distribution of the gas and dust in star-forming regions and address their relative abundances in quantitative terms. We also examine the dust opacity exponent beta for spatial and/or temporal variations. Using mapping observations of the very dense rho Oph A core, we examined standard 1D and non-standard 3D methods to analyse data of far-infrared and submillimeter (submm) continuum radiation. The resulting dust surface density distribution can be compared to that of the gas. The latter was derived from the analysis of accompanying molecular line emission, observed with Herschel from space and with APEX from the ground. As a gas tracer we used N2H+, which is believed to be much less sensitive to freeze-out than CO and its isotopologues. Radiative transfer modelling of the N2H+(J=3-2) and (J=6-5) lines with their hyperfine structure explicitly taken into account provides solutions for the spatial distribution of the column density N(H2), hence the surface density distribution of the gas. The gas-to-dust mass ratio is varying across the map, with very low values in the central regions around the core SM 1. The global average, =88, is not far from the canonical value of 100, however. In rho Oph A, the exponent beta of the power-law description for the dust opacity exhibits a clear dependence on time, with high values of 2 for the envelope-dominated emission in starless Class -1 sources to low values close to 0 for the disk-dominated emission in Class III objects. beta assumes intermediate values for evolutionary classes in between. Since beta is primarily controlled by grain size, grain growth mostly occurs in circumstellar disks. The spatial segregation of gas and dust, seen in projection toward the core centre, probably implies that, like C18O, also N2H+ is frozen onto the grains.

astro-ph.GA↗

arXiv2014

Upper limits to interstellar NH+ and para-NH2- abundances. Herschel-HIFI observations towards Sgr B2 (M) and G10.6-0.4 (W31C)

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.

astro-ph.GA↗

arXiv2014

First detection of [N II] 205 micrometer absorption in interstellar gas

We present high resolution [NII] 205 micrometer ^3P_1-^3P_0 spectra obtained with Herschel-HIFI towards a small sample of far-infrared bright star forming regions in the Galactic plane: W31C (G10.6-0.4), W49N (G43.2-0.1), W51 (G49.5-0.4), and G34.3+0.1. All sources display an emission line profile associated directly with the HII regions themselves. For the first time we also detect absorption of the [NII] 205 micrometer line by extended low-density foreground material towards W31C and W49N over a wide range of velocities. We attribute this absorption to the warm ionised medium (WIM) and find N(N^+)\approx 1.5x10^17 cm^-2 towards both sources. This is in agreement with recent Herschel-HIFI observations of [CII] 158 micrometer, also observed in absorption in the same sight-lines, if \approx7-10 % of all C^+ ions exist in the WIM on average. Using an abundance ratio of [N]/[H] = 6.76x10^-5 in the gas phase we find that the mean electron and proton volume densities are ~0.1-0.3 cm^-3 assuming a WIM volume filling fraction of 0.1-0.4 with a corresponding line-of-sight filling fraction of 0.46-0.74. A low density and a high WIM filling fraction are also supported by RADEX modelling of the [NII] 205 micrometer absorption and emission together with visible emission lines attributed mainly to the WIM. The detection of the 205 micrometer line in absorption emphasises the importance of a high spectral resolution, and also offers a new tool for investigation of the WIM.

astro-ph.GA↗

arXiv2013

Herschel celestial calibration sources: Four large main-belt asteroids as prime flux calibrators for the far-IR/sub-mm range

Celestial standards play a major role in observational astrophysics. They are needed to characterise the performance of instruments and are paramount for photometric calibration. During the Herschel Calibration Asteroid Preparatory Programme approximately 50 asteroids have been established as far-IR/sub-mm/mm calibrators for Herschel. The selected asteroids fill the flux gap between the sub-mm/mm calibrators Mars, Uranus and Neptune, and the mid-IR bright calibration stars. All three Herschel instruments observed asteroids for various calibration purposes, including pointing tests, absolute flux calibration, relative spectral response function, observing mode validation, and cross-calibration aspects. Here we present newly established models for the four large and well characterized main-belt asteroids (1) Ceres, (2) Pallas, (4) Vesta, and (21) Lutetia which can be considered as new prime flux calibrators. The relevant object-specific properties (size, shape, spin-properties, albedo, thermal properties) are well established. The seasonal (distance to Sun, distance to observer, phase angle, aspect angle) and daily variations (rotation) are included in a new thermophysical model setup for these targets. The thermophysical model predictions agree within 5% with the available (and independently calibrated) Herschel measurements. The four objects cover the flux regime from just below 1,000 Jy (Ceres at mid-IR N-/Q-band) down to fluxes below 0.1 Jy (Lutetia at the longest wavelengths). Based on the comparison with PACS, SPIRE and HIFI measurements and pre-Herschel experience, the validity of these new prime calibrators ranges from mid-infrared to about 700 micron, connecting nicely the absolute stellar reference system in the mid-IR with the planet-based calibration at sub-mm/mm wavelengths.

astro-ph.EP↗

arXiv2011

Herschel observations of the Herbig-Haro objects HH52-54

We are aiming at the observational estimation of the relative contribution to the cooling by CO and H2O, as this provides decisive information for the understanding of the oxygen chemistry behind interstellar shock waves. Methods. The high sensitivity of HIFI, in combination with its high spectral resolution capability, allows us to trace the H2O outflow wings at unprecedented signal-to-noise. From the observation of spectrally resolved H2O and CO lines in the HH52-54 system, both from space and from ground, we arrive at the spatial and velocity distribution of the molecular outflow gas. Solving the statistical equilibrium and non-LTE radiative transfer equations provides us with estimates of the physical parameters of this gas, including the cooling rate ratios of the species. The radiative transfer is based on an ALI code, where we use the fact that variable shock strengths, distributed along the front, are naturally implied by a curved surface. Based on observations of CO and H2O spectral lines, we conclude that the emission is confined to the HH54 region. The quantitative analysis of our observations favours a ratio of the CO-to-H2O-cooling-rate >> 1. From the best-fit model to the CO emission, we arrive at an H2O abundance close to 1e-5. The line profiles exhibit two components, one of which is triangular and another, which is a superposed, additional feature. This additional feature likely originates from a region smaller than the beam where the ortho-water abundance is smaller than in the quiescent gas. Comparison with recent shock models indicate that a planar shock can not easily explain the observed line strengths and triangular line profiles.We conclude that the geometry can play an important role. Although abundances support a scenario where J-type shocks are present, higher cooling rate ratios than predicted by these type of shocks are derived.

astro-ph.GA↗

arXiv2010

Water in massive star-forming regions: HIFI observations of W3 IRS5

We present Herschel observations of the water molecule in the massive star-forming region W3 IRS5. The o-H17O 110-101, p-H18O 111-000, p-H2O 22 202-111, p-H2O 111-000, o-H2O 221-212, and o-H2O 212-101 lines, covering a frequency range from 552 up to 1669 GHz, have been detected at high spectral resolution with HIFI. The water lines in W3 IRS5 show well-defined high-velocity wings that indicate a clear contribution by outflows. Moreover, the systematically blue-shifted absorption in the H2O lines suggests expansion, presumably driven by the outflow. No infall signatures are detected. The p-H2O 111-000 and o-H2O 212-101 lines show absorption from the cold material (T ~ 10 K) in which the high-mass protostellar envelope is embedded. One-dimensional radiative transfer models are used to estimate water abundances and to further study the kinematics of the region. We show that the emission in the rare isotopologues comes directly from the inner parts of the envelope (T > 100 K) where water ices in the dust mantles evaporate and the gas-phase abundance increases. The resulting jump in the water abundance (with a constant inner abundance of 10^{-4}) is needed to reproduce the o-H17O 110-101 and p-H18O 111-000 spectra in our models. We estimate water abundances of 10^{-8} to 10^{-9} in the outer parts of the envelope (T < 100 K). The possibility of two protostellar objects contributing to the emission is discussed.

astro-ph.SR↗

arXiv2010

Ground-state ammonia and water in absorption towards Sgr B2

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.

astro-ph.GA↗

arXiv2010

Detection of OH$^+$ and H$_2$O$^+$ towards Orion~KL

We report observations of the reactive molecular ions OH$^+$, H$_2$O$^+$, and H$_3$O$^+$ towards Orion KL with Herschel/HIFI. All three $N=1-0$ fine-structure transitions of OH$^+$ at 909, 971, and 1033GHz and both fine-structure components of the doublet {\it ortho}-H$_2$O$^+$ $1_{11}-0_{00}$ transition at 1115 and 1139GHz were detected; an upper limit was obtained for H$_3$O$^+$. OH$^+$ and H$_2$O$^+$ are observed purely in absorption, showing a narrow component at the source velocity of 9 kms$^{-1}$, and a broad blueshifted absorption similar to that reported recently for HF and {\it para}-H$_{2}^{18}$O, and attributed to the low velocity outflow of Orion KL. We estimate column densities of OH$^+$ and H$_2$O$^+$ for the 9 km s$^{-1}$ component of $9 \pm 3 \times 10^{12}$cm$^{-2}$ and $7 \pm 2 \times 10^{12}$cm$^{-2}$, and those in the outflow of $1.9 \pm 0.7 \times 10^{13}$cm$^{-2}$ and $1.0 \pm 0.3 \times 10^{13}$cm$^{-2}$. Upper limits of $2.4\times 10^{12}$cm$^{-2}$ and $8.7\times 10^{12}$cm$^{-2}$ were derived for the column densities of {\it ortho} and {\it para}-H$_3$O$^+$ from transitions near 985 and 1657GHz. The column densities of the three ions are up to an order of magnitude lower than those obtained from recent observations of W31C and W49N. The comparatively low column densities may be explained by a higher gas density despite the assumption of a very high ionization rate.

astro-ph.GA↗

arXiv2010

Herschel-HIFI observations of high-J CO lines in the NGC 1333 low-mass star-forming region

Herschel-HIFI observations of high-J lines (up to J_u=10) of 12CO, 13CO and C18O are presented toward three deeply embedded low-mass protostars, NGC 1333 IRAS 2A, IRAS 4A, and IRAS 4B, obtained as part of the Water In Star-forming regions with Herschel (WISH) key program. The spectrally-resolved HIFI data are complemented by ground-based observations of lower-J CO and isotopologue lines. The 12CO 10-9 profiles are dominated by broad (FWHM 25-30 km s^-1) emission. Radiative transfer models are used to constrain the temperature of this shocked gas to 100-200 K. Several CO and 13CO line profiles also reveal a medium-broad component (FWHM 5-10 km s^-1), seen prominently in H2O lines. Column densities for both components are presented, providing a reference for determining abundances of other molecules in the same gas. The narrow C18O 9-8 lines probe the warmer part of the quiescent envelope. Their intensities require a jump in the CO abundance at an evaporation temperature around 25 K, thus providing new direct evidence for a CO ice evaporation zone around low-mass protostars.

astro-ph.SR↗