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We report SOFIA-upGREAT spectroscopic imaging of the [C II] 158um spectral line, as well as a number of [O I] 63um spectra, across a 67x45 pc field toward the Sgr B region in our Galactic center. The fully-sampled and velocity-resolved [C II] images have 0.55 pc spatial and 1 km/s velocity resolutions. We find that Sgr B extends as a coherent structure spanning some 34 pc along the Galactic plane. Bright [C II] emission encompasses Sgr B1 (G0.5-0.0), the G0.6-0.0 HII region, and passes behind and beyond the luminous star forming cores toward Sgr B2 (G0.7-0.0). Sgr B is a major contributor to the entire Galactic center's [C II] luminosity, with surface brightness comparable to [C II] from the Arches region. [C II], 70um, and 20cm emission share nearly identical spatial distributions. Combined with the lack of [C II] self-absorption, this indicates that these probes trace UV on the near surfaces of more extended clouds visible in CO isotopologues and 160um continuum. Stars from regions of local star formation likely dominate the UV field. Photodissociation regions and HII regions contribute similar amounts of [C II] flux. The extreme star formation cores of Sgr B2 contribute negligible amounts to the total [C II] intensity from the Sgr B region. Velocity fields and association with a narrow dust lane indicate that they may have been produced in a local cloud-cloud collision. The cores are likely local analogs of the intense star formation regions where ideas to explain the "C+ deficit" in ultra-luminous galaxies can be tested., Comment: 22 pages, 13 figures. Accepted for publication in the Astrophysical Journal

Massive stars inject mechanical and radiative energy into the surrounding environment, which stirs it up, heats the gas, produces cloud and intercloud phases in the interstellar medium, and disrupts molecular clouds (the birth sites of new stars). Stellar winds, supernova explosions and ionization by ultraviolet photons control the lifetimes of molecular clouds. Theoretical studies predict that momentum injection by radiation should dominate that by stellar winds, but this has been difficult to assess observationally. Velocity-resolved large-scale images in the fine-structure line of ionized carbon ([C II]) provide an observational diagnostic for the radiative energy input and the dynamics of the interstellar medium around massive stars. Here we report observations of a one-square-degree region (about 7 parsecs in diameter) of Orion molecular core -- the region nearest to Earth that exhibits massive-star formation -- at a resolution of 16 arcseconds (0.03 parsecs) in the [C II] line at 1.9 terahertz (158 micrometres). The results reveal that the stellar wind originating from the massive star ${\theta}^{1}$ Orionis C has swept up the surrounding material to create a bubble roughly four parsecs in diameter with a 2,600-solar-mass shell, which is expanding at 13 kilometres per second. This finding demonstrates that the mechanical energy from the stellar wind is converted very efficiently into kinetic energy of the shell and causes more disruption of the Orion molecular core 1 than do photo-ionization and evaporation or future supernova explosions., Comment: Published in Nature

We present the performance of the upGREAT heterodyne array receivers on the SOFIA telescope after several years of operations. This instrument is a multi-pixel high resolution (R > 10^7) spectrometer for the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA). The receivers use 7-pixel subarrays configured in a hexagonal layout around a central pixel. The low frequency array receiver (LFA) has 2x7 pixels (dual polarization), and presently covers the 1.83-2.06 THz frequency range, which allows to observe the [CII] and [OI] lines at 158 um and 145 um wavelengths. The high frequency array (HFA) covers the [OI] line at 63 um and is equipped with one polarization at the moment (7 pixels, which can be upgraded in the near future with a second polarization array). The 4.7 THz array has successfully flown using two separate quantum-cascade laser local oscillators from two different groups. NASA completed the development, integration and testing of a dual-channel closed-cycle cryocooler system, with two independently operable He compressors, aboard SOFIA in early 2017 and since then, both arrays can be operated in parallel using a frequency separating dichroic mirror. This configuration is now the prime GREAT configuration and has been added to SOFIA's instrument suite since observing cycle 6., Comment: Accepted to the Journal of Astronomical Instrumentation (SOFIA Special Edition) on 12th November 2018

Determining the properties of the warm ionized medium (WIM) at the leading edge of spiral arms is important for understanding its dynamics and cloud formation. The inner edge of the Scutum arm tangency is a unique location in which to disentangle the WIM from other components. We use high spectral resolution [C II] 158 micron and [N II] 205 micron fine structure line observations taken with the upGREAT and GREAT instruments on SOFIA, along with auxiliary HI and 13CO observations. The observations were in and out of the Galactic plane along 18 lines of sight between longitude 30deg and 32deg. We detect strong [N II] emission throughout the Scutum tangency. At VLSR = 110 to 125 km/s, where there is little, if any, 13CO, we could disentangle the [N II] and [C II] emission that arises from the WIM at the inner edge. We find an average electron density, about 0.9 cm{-3} in the plane, and about 0.4 cm{-3} above the plane. For VLSR < 110 km/s there is [N II] emission tracing highly ionized gas throughout the arm's molecular layer. This ionized gas has a high density, n(e) ~ 30 cm{-3}, and a few percent filling factor. Thus, [N II] and [C II] at the Scutum arm tangency reveal a highly ionized gas with about 10 to 20 times those of the interarm WIM, which is best explained by a model in which the interarm WIM is compressed as it falls into the potential well of the arm. The widespread distribution of [N II] in the molecular layers shows that high density ionized gas is distributed throughout the Scutum arm. The n(e) derived from [N II] for these molecular cloud regions are about 30 cm{-3}, and probably arise in the ionized boundary layers of clouds. This [N II] emission from the ionized boundary layers is probably the result of the shock compression of the WIM as it impacts the arm's neutral gas, but some could arise from extended HII regions., Comment: 12 pages, 9 figures

Observations towards L1630 in the Orion B molecular cloud, comprising the iconic Horsehead Nebula, allow us to study the interplay between stellar radiation and a molecular cloud under relatively benign conditions, that is, intermediate densities and an intermediate UV radiation field. Contrary to the well-studied Orion Molecular Cloud 1 (OMC1), which hosts much harsher conditions, L1630 has little star formation. We aim to relate the [CII] fine-structure line emission to the physical conditions predominant in L1630 and compare it to studies of OMC1. The [CII] $158\,\mu\mathrm{m}$ emission from an area of $12' \times 17'$ in L1630 was observed using the upGREAT instrument onboard SOFIA. Of the [CII] emission from the mapped area 95%, $13\,L_{\odot}$, originates from the molecular cloud; the adjacent HII region contributes only 5%, that is, $1\,L_{\odot}$. From comparison with other data (CO (1-0)-line emission, far-infrared (FIR) continuum studies, emission from polycyclic aromatic hydrocarbons (PAHs)), we infer a gas density of the molecular cloud of $n_{\mathrm{H}}\sim 3\cdot 10^3\,\mathrm{cm^{-3}}$, with surface layers, including the Horsehead Nebula, having a density of up to $n_{\mathrm{H}}\sim 4\cdot 10^4\,\mathrm{cm^{-3}}$. The temperature of the surface gas is $T\sim 100\,\mathrm{K}$. The average [CII] cooling efficiency within the molecular cloud is $1.3\cdot 10^{-2}$. The fraction of the mass of the molecular cloud within the studied area that is traced by [CII] is only $8\%$. Our PDR models are able to reproduce the FIR-[CII] correlations and also the CO (1-0)-[CII] correlations. Finally, we compare our results on the heating efficiency of the gas with theoretical studies of photoelectric heating by PAHs, clusters of PAHs, and very small grains, and find the heating efficiency to be lower than theoretically predicted, a continuation of the trend set by other observations., Comment: 23 pages, 30 figures, accepted for publication in Astronomy & Astrophysics

We present a new multi-pixel high resolution (R >10^7) spectrometer for the Stratospheric Observatory for Far-Infrared Astronomy (SOFIA). The receiver uses 2 x 7-pixel subarrays in orthogonal polarization, each in an hexagonal array around a central pixel. We present the first results for this new instrument after commissioning campaigns in May and December 2015 and after science observations performed in May 2016 . The receiver is designed to ultimately cover the full 1.8-2.5 THz frequency range but in its first implementation, the observing range was limited to observations of the [CII] line at 1.9 THz in 2015 and extended to 1.83-2.07 THz in 2016. The instrument sensitivities are state-of-the-art and the first scientific observations performed shortly after the commissioning confirm that the time efficiency for large scale imaging is improved by more than an order of magnitude as compared to single pixel receivers. An example of large scale mapping around the Horsehead Nebula is presented here illustrating this improvement. The array has been added to SOFIA's instrument suite already for ongoing observing cycle 4., Comment: 7 pages, 11 figures. Accepted for publication in Astronomy & Astrophysics

This paper presents [CII], [CI] and CO emission line maps of the star-forming regions N66, N25+N26, and N88 in the metal-poor Local Group dwarf galaxy SMC. The spatial and velocity structure of the large HII region N66 reveals an expanding ring of shocked molecular gas centered on the exciting star cluster NGC346, whereas a more distant dense molecular cloud is being eroded by UV radiation from the same cluster. In the N25+N26 and N88 maps, diffuse [CII] emission at a relatively low surface brightness extends well beyond the compact boundaries of the bright emission associated with the [CII] regions. In all regions, the distribution of this bright [CII] emission and the less prominent [CI] emission closely follows the outline of the CO complexes, but the intensity of the [CII] and [CI] emission is generally anticorrelated, which can be understood by the action of photodissociation and photoionization processes. Notwithstanding the overall similarity of CO and [CII] maps, the intensity ratio of these lines varies significantly, mostly due to changes in CO brightness. [CII] emission line profiles are up to 50% wider in velocity than corresponding CO profiles. A radiative transfer analysis shows that the [CII] line is the dominant tracer of (CO-dark) molecular hydrogen in the SMC. CO emission traces only a minor fraction of the total amount of gas. The similarity of the spatial distribution and line profile shape, and the dominance of molecular gas associated with [[CII] rather than CO emission imply that in the low-metallicity environment of the SMC the small amount of dense molecular gas traced by CO is embedded in the much more extended molecular gas traced only by [CII] emission. The contribution from neutral atomic and ionized hydrogen zones is negligible in the star-forming regions observed., Comment: 17 pages, 16 figures, Accepted in A&A

The gas-solid budget of carbon in protoplanetary disks is related to the composition of the cores and atmospheres of the planets forming in them. The key gas-phase carbon carriers CO, C$^{0}$ and C$^{+}$ can now be observed in disks. The gas-phase carbon abundance in disks has not yet been well characterized, we aim to obtain new constraints on the [C]/[H] ratio in a sample of disks, and to get an overview of the strength of [CI] and warm CO emission. We carried out a survey of the CO$\,6$--$5$ and [CI]$\,1$--$0$ and $2$--$1$ lines towards $37$ disks with APEX, and supplemented it with [CII] data from the literature. The data are interpreted using a grid of models produced with the DALI code. We also investigate how well the gas-phase carbon abundance can be determined in light of parameter uncertainties. The CO$\,6$--$5$ line is detected in $13$ out of $33$ sources, the [CI]$\,1$--$0$ in $6$ out of $12$, and the [CI]$\,2$--$1$ in $1$ out of $33$. With deep integrations, the first unambiguous detections of [CI]~$1$--$0$ in disks are obtained, in TW~Hya and HD~100546. Gas-phase carbon abundance reductions of a factor $5$--$10$ or more can be identified robustly based on CO and [CI] detections. The atomic carbon detection in TW~Hya confirms a factor $100$ reduction of [C]/[H]$_{\rm gas}$ in that disk, while the data are consistent with an ISM-like carbon abundance for HD~100546. In addition, BP~Tau, T~Cha, HD~139614, HD~141569, and HD~100453 are either carbon-depleted or gas-poor disks. The low [CI]~$2$--$1$ detection rates in the survey mostly reflect insufficient sensitivity to detect T~Tauri disks. The Herbig~Ae/Be disks with CO and [CII] upper limits below the models are debris disk like systems. A roughly order of magnitude increase in sensitivity compared to our survey is required to obtain useful constraints on the gas-phase [C]/[H] ratio in most of the targeted systems., Comment: 8 figures, accepted for publication in A\&A

Intermediate mass protostarsprovide a bridge between theories of low- and high-mass star formation. Emerging molecular outflows can be used to determine the influence of fragmentation and multiplicity on protostellar evolution through the correlation of outflow forces of intermediate mass protostars with the luminosity. The aim of this paper is to derive outflow forces from outflows of six intermediate mass protostellar regions and validate the apparent correlation between total luminosity and outflow force seen in earlier work, as well as remove uncertainties caused by different methodology. By comparing CO 6--5 observations obtained with APEX with non-LTE radiative transfer model predictions, optical depths, temperatures, densities of the gas of the molecular outflows are derived. Outflow forces, dynamical timescales and kinetic luminosities are subsequently calculated. Outflow parameters, including the forces, were derived for all sources. Temperatures in excess of 50 K were found for all flows, in line with recent low-mass results. However, comparison with other studies could not corroborate conclusions from earlier work on intermediate mass protostars which hypothesized that fragmentation enhances outflow forces in clustered intermediate mass star formation. Any enhancement in comparison with the classical relation between outflow force and luminosity can be attributed the use of a higher excitation line and improvement in methods; They are in line with results from low-mass protostars using similar techniques. The role of fragmentation on outflows is an important ingredient to understand clustered star formation and the link between low and high-mass star formation. However, detailed information on spatial scales of a few 100 AU, covering all individual members is needed to make the necessary progress., Comment: 14 pages, accepted for publication in A&A; changed a few boldface text left in

The temperature and density structure of molecular cloud cores are the most important physical quantities that determine the course of the protostellar collapse and the properties of the stars they form. Nevertheless, density profiles often rely either on the simplifying assumption of isothermality or on observationally poorly constrained model temperature profiles. With the aim of better constraining the initial physical conditions in molecular cloud cores at the onset of protostellar collapse, we initiated the Guaranteed Time Key Project (GTKP) "The Earliest Phases of Star Formation" (EPoS) with the Herschel satellite. This paper gives an overview of the low-mass sources in the EPoS project, including all observations, the analysis method, and the initial results of the survey. We study the thermal dust emission of 12 previously well-characterized, isolated, nearby globules using FIR and submm continuum maps at up to eight wavelengths between 100 micron and 1.2 mm. Our sample contains both globules with starless cores and embedded protostars at different early evolutionary stages. The dust emission maps are used to extract spatially resolved SEDs, which are then fit independently with modified blackbody curves to obtain line-of-sight-averaged dust temperature and column density maps. We find that the thermal structure of all globules is dominated by external heating from the interstellar radiation field and moderate shielding by thin extended halos. All globules have warm outer envelopes (14-20 K) and colder dense interiors (8-12 K). The protostars embedded in some of the globules raise the local temperature of the dense cores only within radii out to about 5000 AU, but do not significantly affect the overall thermal balance of the globules., Comment: 35 pages, 47 figures, Accepted for publication in Astronomy and Astrophysics

(Abriged) In the framework of the Herschel GTKP "The earliest phases of star formation", we have imaged B68 between 100 and 500 um. Ancillary (sub)mm data, spectral line maps of the 12/13CO(2-1) transitions as well as a NIR extinction map were added to the analysis. We employed a ray-tracing algorithm to derive the 2D mid-plane dust temperature and volume density distribution without suffering from LoS averaging effects of simple SED fitting procedures. Additional 3D radiative transfer calculations were employed to investigate the connection between the external irradiation and the peculiar crescent shaped morphology found in the FIR maps. For the first time, we spatially resolve the dust temperature and density distribution of B68. We find T_dust dropping from 16.7 K at the edge to 8.2 K in the centre, which is about 4 K lower than the result of the simple SED fitting approach. N_H peaks at 4.3x10^22 cm^-2 and n_H at 3.4x10^5 cm^-3 in the centre. B68 has a mass of 3.1 M_sun of material with A_K > 0.2 mag for an assumed distance of 150 pc. We detect a compact source in the southeastern trunk, which is also seen in extinction and CO. We find the radial density distribution from the edge of the inner plateau outward to be n_H ~ r^-3.5. Such a steep profile can arise from either or both of the following: external irradiation with a significant UV contribution or the fragmentation of filamentary structures. Our 3D radiative transfer model of an externally irradiated core by an anisotropic ISRF reproduces the crescent morphology. Our CO observations show that B68 is part of a chain of globules in both space and velocity, which may indicate that it was once part of a filament which dispersed. We also resolve a new compact source in the SE trunk and find that it is slightly shifted in centroid velocity from B68, lending qualitative support to core collision scenarios., Comment: Accepted for publication by A&A, 21 pages (+ appendix), 21 figures

We report SOFIA/GREAT, Herschel/HIFI, and ground-based velocity-resolved spectroscopy of carbon monoxide (CO) rotational transitions from J=2-1 to J=16-15 toward two positions in the circum-nuclear disk (CND) in our Galactic center. Radiative transfer models were used to derive information on the physical state of the gas traced by CO. The excitation of the CO gas cannot be explained by a single physical component, but is clearly the superposition of various warm gas phases. In a two-component approach, our large velocity gradient (LVG) analysis suggests high temperatures of ~200 K with moderate gas densities of only ~10^4.5 cm^-3 for the bulk of the material. A higher excited phase, carrying ~20-30% of the column densities, is warmer (~300-500 K) but only slightly denser ~10^5.3 cm^-3. These densities are too low to self-stabilize the clumps against their high internal turbulence and fall below the Roche density (>10^7 cm^-3) at 1.5 pc galactocentric distance. We conclude that the bulk of the material in the CND is not organized by self-gravity nor stable against tidal disruption, and must be transient., Comment: Accepted in A&A special issue for SOFIA/GREAT

We present and analyze two spectrally resolved high-J CO lines towards the molecular outflow Cep E, driven by an intermediate-mass class 0 protostar. Using the GREAT receiver on board SOFIA, we observed the CO (12--11) and (13--12) transitions (E_u ~ 430 and 500 K, respectively) towards one position in the blue lobe of this outflow, that had been known to display high-velocity molecular emission. We detect the outflow emission in both transitions, up to extremely high velocities (~ 100 km/s with respect to the systemic velocity). We divide the line profiles into three velocity ranges that each have interesting spectral features: standard, intermediate, and extremely high-velocity. One distinct bullet is detected in each of the last two. A large velocity gradient analysis for these three velocity ranges provides constraints on the kinetic temperature and volume density of the emitting gas, >~ 100 K and > ~ 10^4 cm^-3, respectively. These results are in agreement with previous ISO observations and are comparable with results obtained by Herschel for similar objects. We conclude that high-J CO lines are a good tracer of molecular bullets in protostellar outflows. Our analysis suggests that different physical conditions are at work in the intermediate velocity range compared with the standard and extremely high-velocity gas at the observed position., Comment: Accepted for publication in A&A (SOFIA/GREAT special issue)

HERSCHEL-HIFI observations of water from the intermediate mass protostar NGC7129 FIRS 2 provide a powerful diagnostic of the physical conditions in this star formation environment. Six spectral settings, covering four H216O and two H218O lines, were observed and all but one H218O line were detected. The four H2 16 O lines discussed here share a similar morphology: a narrower, \approx 6 km/s, component centered slightly redward of the systemic velocity of NGC7129 FIRS 2 and a much broader, \approx 25 km/s component centered blueward and likely associated with powerful outflows. The narrower components are consistent with emission from water arising in the envelope around the intermediate mass protostar, and the abundance of H2O is constrained to \approx 10-7 for the outer envelope. Additionally, the presence of a narrow self-absorption component for the lowest energy lines is likely due to self-absorption from colder water in the outer envelope. The broader component, where the H2O/CO relative abundance is found to be \approx 0.2, appears to be tracing the same energetic region that produces strong CO emission at high J., Comment: 6 pages, 4 figures, accepted by A&A

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., Comment: 8 pages, 9 figures

Early results from the Herschel Space Observatory revealed the water cation H2O+ to be an abundant ingredient of the interstellar medium. Here we present new observations of the H2O and H2O+ lines at 1113.3 and 1115.2 GHz using the Herschel Space Observatory toward a sample of high-mass star-forming regions to observationally study the relation between H2O and H2O+ . Nine out of ten sources show absorption from H2O+ in a range of environments: the molecular clumps surrounding the forming and newly formed massive stars, bright high-velocity outflows associated with the massive protostars, and unrelated low-density clouds along the line of sight. Column densities per velocity component of H2 O+ are found in the range of 10^12 to a few 10^13 cm-2 . The highest N(H2O+) column densities are found in the outflows of the sources. The ratios of H2O+/H2O are determined in a range from 0.01 to a few and are found to differ strongly between the observed environments with much lower ratios in the massive (proto)cluster envelopes (0.01-0.1) than in outflows and diffuse clouds. Remarkably, even for source components detected in H2O in emission, H2O+ is still seen in absorption., Comment: 5 pages, 4 figures, accepted for publication as a letter in the A&A Herschel-HIFI special issue

We present observations of twelve rotational transitions of H2O-16, H2O-18, and H2O-17 toward the massive star-forming region NGC 6334 I, carried out with Herschel/HIFI as part of the guaranteed time key program Chemical HErschel Surveys of Star forming regions (CHESS). We analyze these observations to obtain insights into physical processes in this region. We identify three main gas components (hot core, cold foreground, and outflow) in NGC 6334 I and derive the physical conditions in these components. The hot core, identified by the emission in highly excited lines, shows a high excitation temperature of 200 K, whereas water in the foreground component is predominantly in the ortho- and para- ground states. The abundance of water varies between 4 10^-5 (outflow) and 10^-8 (cold foreground gas). This variation is most likely due to the freeze-out of water molecules onto dust grains. The H2O-18/H2O-17 abundance ratio is 3.2, which is consistent with the O-18/O-17 ratio determined from CO isotopologues. The ortho/para ratio in water appears to be relatively low 1.6(1) in the cold, quiescent gas, but close to the equilibrium value of three in the warmer outflow material (2.5(0.8))., Comment: 7 pages, 3 figures, accepted by A&A

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., Comment: Accepted for publication in the A&A HIFI special issue

The Heterodyne Instrument for the Far Infrared (HIFI) onboard the Herschel Space Observatory allows the first observations of light diatomic molecules at high spectral resolution and in multiple transitions. Here, we report deep integrations using HIFI in different lines of hydrides towards the high-mass star forming region AFGL 2591. Detected are CH, CH+, NH, OH+, H2O+, while NH+ and SH+ have not been detected. All molecules except for CH and CH+ are seen in absorption with low excitation temperatures and at velocities different from the systemic velocity of the protostellar envelope. Surprisingly, the CH(JF,P = 3/2_2,- - 1/2_1,+) and CH+(J = 1 - 0, J = 2 - 1) lines are detected in emission at the systemic velocity. We can assign the absorption features to a foreground cloud and an outflow lobe, while the CH and CH+ emission stems from the envelope. The observed abundance and excitation of CH and CH+ can be explained in the scenario of FUV irradiated outflow walls, where a cavity etched out by the outflow allows protostellar FUV photons to irradiate and heat the envelope at larger distances driving the chemical reactions that produce these molecules., Comment: Accepted for publication in Astronomy and Astrophysics (HIFI first results issue)

'Water In Star-forming regions with Herschel' (WISH) is a key programme dedicated to studying the role of water and related species during the star-formation process and constraining the physical and chemical properties of young stellar objects. The Heterodyne Instrument for the Far-Infrared (HIFI) on the Herschel Space Observatory observed three deeply embedded protostars in the low-mass star-forming region NGC1333 in several H2-16O, H2-18O, and CO transitions. Line profiles are resolved for five H16O transitions in each source, revealing them to be surprisingly complex. The line profiles are decomposed into broad (>20 km/s), medium-broad (~5-10 km/s), and narrow (<5 km/s) components. The H2-18O emission is only detected in broad 1_10-1_01 lines (>20 km/s), indicating that its physical origin is the same as for the broad H2-16O component. In one of the sources, IRAS4A, an inverse P Cygni profile is observed, a clear sign of infall in the envelope. From the line profiles alone, it is clear that the bulk of emission arises from shocks, both on small (<1000 AU) and large scales along the outflow cavity walls (~10 000 AU). The H2O line profiles are compared to CO line profiles to constrain the H2O abundance as a function of velocity within these shocked regions. The H2O/CO abundance ratios are measured to be in the range of ~0.1-1, corresponding to H2O abundances of ~10-5-10-4 with respect to H2. Approximately 5-10% of the gas is hot enough for all oxygen to be driven into water in warm post-shock gas, mostly at high velocities., Comment: Accepted for publication in the A&A HIFI special issue

Water in Star-forming regions with Herschel (WISH) is a Herschel Key Program investigating the water chemistry in young stellar objects (YSOs) during protostellar evolution. Hydroxyl (OH) is one of the reactants in the chemical network most closely linked to the formation and destruction of H2O. High-temperature chemistry connects OH and H2O through the OH + H2 <-> H2O + H reactions. Formation of H2O from OH is efficient in the high-temperature regime found in shocks and the innermost part of protostellar envelopes. Moreover, in the presence of UV photons, OH can be produced from the photo-dissociation of H2O. High-resolution spectroscopy of the OH 163.12 micron triplet towards HH 46 and NGC 1333 IRAS 2A was carried out with the Heterodyne Instrument for the Far Infrared (HIFI) on board Herschel. The low- and intermediate-mass YSOs HH 46, TMR 1, IRAS 15398-3359, DK Cha, NGC 7129 FIRS 2, and NGC 1333 IRAS 2A were observed with the Photodetector Array Camera and Spectrometer (PACS) in four transitions of OH and two [OI] lines. The OH transitions at 79, 84, 119, and 163 micron and [OI] emission at 63 and 145 micron were detected with PACS towards the class I low-mass YSOs as well as the intermediate-mass and class I Herbig Ae sources. No OH emission was detected from the class 0 YSO NGC 1333 IRAS 2A, though the 119 micron was detected in absorption. With HIFI, the 163.12 micron was not detected from HH 46 and only tentatively detected from NGC 1333 IRAS 2A. The combination of the PACS and HIFI results for HH 46 constrains the line width (FWHM > 11 km/s) and indicates that the OH emission likely originates from shocked gas. This scenario is supported by trends of the OH flux increasing with the [OI] flux and the bolometric luminosity. Similar OH line ratios for most sources suggest that OH has comparable excitation temperatures despite the different physical properties of the sources., Comment: Accepted for publication in Astronomy and Astrophysics (Herschel special issue)

We performed a sensitive search for the ground-state emission lines of ortho- and para-water vapor in the DM Tau protoplanetary disk using the Herschel/HIFI instrument. No strong lines are detected down to 3sigma levels in 0.5 km/s channels of 4.2 mK for the 1_{10}--1_{01} line and 12.6 mK for the 1_{11}--0_{00} line. We report a very tentative detection, however, of the 1_{10}--1_{01} line in the Wide Band Spectrometer, with a strength of T_{mb}=2.7 mK, a width of 5.6 km/s and an integrated intensity of 16.0 mK km/s. The latter constitutes a 6sigma detection. Regardless of the reality of this tentative detection, model calculations indicate that our sensitive limits on the line strengths preclude efficient desorption of water in the UV illuminated regions of the disk. We hypothesize that more than 95-99% of the water ice is locked up in coagulated grains that have settled to the midplane., Comment: 5 pages, 3 figures. Accepted for publication in the Herschel HIFI special issue of A&A

We report the first detection of the ground-state rotational transition of the methylidyne cation CH+ towards the massive star-forming region DR21 with the HIFI instrument onboard the Herschel satellite. The line profile exhibits a broad emission line, in addition to two deep and broad absorption features associated with the DR21 molecular ridge and foreground gas. These observations allow us to determine a CH+ J=1-0 line frequency of 835137 +/- 3 MHz, in good agreement with a recent experimental determination. We estimate the CH+ column density to be a few 1e13 cm^-2 in the gas seen in emission, and > 1e14 cm^-2 in the components responsible for the absorption, which is indicative of a high line of sight average abundance [CH+]/[H] > 1.2x10^-8. We show that the CH+ column densities agree well with the predictions of state-of-the-art C-shock models in dense UV-illuminated gas for the emission line, and with those of turbulent dissipation models in diffuse gas for the absorption lines., Comment: Accepted for publication in A&A

SWAS and Odin provided stringent upper limits on the gas phase water abundance of dark clouds (x(H2O) < 7x10^-9). We investigate the chemistry of water vapor in starless cores beyond the previous upper limits using the highly improved angular resolution and sensitivity of Herschel and measure the abundance of water vapor during evolutionary stages just preceding star formation. High spectral resolution observations of the fundamental ortho water (o-H2O) transition (557 GHz) were carried out with Herschel HIFI toward two starless cores: B68, a Bok globule, and L1544, a prestellar core embedded in the Taurus molecular cloud complex. The rms in the brightness temperature measured for the B68 and L1544 spectra is 2.0 and 2.2 mK, respectively, in a velocity bin of 0.59 km s^-1. The continuum level is 3.5+/-0.2 mK in B68 and 11.4+/-0.4 mK in L1544. No significant feature is detected in B68 and the 3 sigma upper limit is consistent with a column density of o-H2O N(o-H2O) < 2.5x10^13 cm^-2, or a fractional abundance x(o-H2O) < 1.3x10^-9, more than an order of magnitude lower than the SWAS upper limit on this source. The L1544 spectrum shows an absorption feature at a 5 sigma level from which we obtain the first value of the o-H2O column density ever measured in dark clouds: N(o-H2O) = (8+/-4)x10^12 cm^-2. The corresponding fractional abundance is x(o-H2O) ~ 5x10^-9 at radii > 7000 AU and ~2x10^-10 toward the center. The radiative transfer analysis shows that this is consistent with a x(o-H2O) profile peaking at ~10^-8, 0.1 pc away from the core center, where both freeze-out and photodissociation are negligible. Herschel has provided the first measurement of water vapor in dark regions. Prestellar cores such as L1544 (with their high central densities, strong continuum, and large envelopes) are very promising tools to finally shed light on the solid/vapor balance of water in molecular clouds., Comment: Accepted for publication in Astronomy and Astrophysics (HIFI first results issue)

CONTEXT: Water vapour maser emission from evolved oxygen-rich stars remains poorly understood. Additional observations, including polarisation studies and simultaneous observation of different maser transitions may ultimately lead to greater insight. AIMS: We have aimed to elucidate the nature and structure of the VY CMa water vapour masers in part by observationally testing a theoretical prediction of the relative strengths of the 620.701 GHz and the 22.235 GHz maser components of ortho water vapour. METHODS: In its high-resolution mode (HRS) the Herschel Heterodyne Instrument for the Infrared (HIFI) offers a frequency resolution of 0.125 MHz, corresponding to a line-of-sight velocity of 0.06 km/s, which we employed to obtain the strength and linear polarisation of maser spikes in the spectrum of VY CMa at 620.701 GHz. Simultaneous ground based observations of the 22.235 GHz maser with the Max-Planck-Institut f\"ur Radioastronomie 100-meter telescope at Effelsberg, provided a ratio of 620.701 GHz to 22.235 GHz emission. RESULTS:We report the first astronomical detection to date of water vapour maser emission at 620.701 GHz. In VY CMa both the 620.701 and the 22.235 GHz polarisation are weak. At 620.701 GHz the maser peaks are superposed on what appears to be a broad emission component, jointly ejected asymmetrically from the star. We observed the 620.701 GHz emission at two epochs 21 days apart, both to measure the potential direction of linearly polarised maser components and to obtain a measure of the longevity of these components. Although we do not detect significant polarisation levels in the core of the line, they rise up to approximately 6% in its wings.

We present high resolution HIFI spectroscopy of the nucleus of the archetypical starburst galaxy M82. Six 12CO lines, 2 13CO lines and 4 fine-structure lines are detected. Besides showing the effects of the overall velocity structure of the nuclear region, the line profiles also indicate the presence of multiple components with different optical depths, temperatures and densities in the observing beam. The data have been interpreted using a grid of PDR models. It is found that the majority of the molecular gas is in low density (n=10^3.5 cm^-3) clouds, with column densities of N_H=10^21.5 cm^-2 and a relatively low UV radiation field (GO = 10^2). The remaining gas is predominantly found in clouds with higher densities (n=10^5 cm^-3) and radiation fields (GO = 10^2.75), but somewhat lower column densities (N_H=10^21.2 cm^-2). The highest J CO lines are dominated by a small (1% relative surface filling) component, with an even higher density (n=10^6 cm^-3) and UV field (GO = 10^3.25). These results show the strength of multi-component modeling for the interpretation of the integrated properties of galaxies., Comment: Accepted for publication in A&A Letters

Aims: We present preliminary results of the first Herschel spectroscopic observations of NGC7129 FIRS2, an intermediate mass star-forming region. We attempt to interpret the observations in the framework of an in-falling spherical envelope. Methods: The PACS instrument was used in line spectroscopy mode (R=1000-5000) with 15 spectral bands between 63 and 185 microns. This provided good detections of 26 spectral lines seen in emission, including lines of H2O, CO, OH, O I, and C II. Results: Most of the detected lines, particularly those of H2O and CO, are substantially stronger than predicted by the spherical envelope models, typically by several orders of magnitude. In this paper we focus on what can be learned from the detected CO emission lines. Conclusions: It is unlikely that the much stronger than expected line emission arises in the (spherical) envelope of the YSO. The region hot enough to produce such high excitation lines within such an envelope is too small to produce the amount of emission observed. Virtually all of this high excitation emission must arise in structures such as as along the walls of the outflow cavity with the emission produced by a combination of UV photon heating and/or non-dissociative shocks., Comment: A&A Special Issue on Herschel

In the framework of the Water in Star-forming regions with Herschel (WISH) key program, maps in water lines of several outflows from young stars are being obtained, to study the water production in shocks and its role in the outflow cooling. This paper reports the first results of this program, presenting a PACS map of the o-H2O 179 um transition obtained toward the young outflow L1157. The 179 um map is compared with those of other important shock tracers, and with previous single-pointing ISO, SWAS, and Odin water observations of the same source that allow us to constrain the water abundance and total cooling. Strong H2O peaks are localized on both shocked emission knots and the central source position. The H2O 179 um emission is spatially correlated with emission from H2 rotational lines, excited in shocks leading to a significant enhancement of the water abundance. Water emission peaks along the outflow also correlate with peaks of other shock-produced molecular species, such as SiO and NH3. A strong H2O peak is also observed at the location of the proto-star, where none of the other molecules have significant emission. The absolute 179 um intensity and its intensity ratio to the H2O 557 GHz line previously observed with Odin/SWAS indicate that the water emission originates in warm compact clumps, spatially unresolved by PACS, having a H2O abundance of the order of 10^-4. This testifies that the clumps have been heated for a time long enough to allow the conversion of almost all the available gas-phase oxygen into water. The total water cooling is ~10^-1 Lo, about 40% of the cooling due to H2 and 23% of the total energy released in shocks along the L1157 outflow., Comment: Accepted for publication in Astronomy and Astrophysics (Herschel special issue)

In order to detect and characterise cold extended circumstellar dust originating from collisions of planetesimal bodies in disks, belts, or rings at Kuiper-Belt distances (30-50 AU or beyond) sensitive submillimetre observations are essential. Measurements of the flux densities at these wavelengths will extend existing IR photometry and permit more detailed modelling of the Rayleigh-Jeans tail of the disks spectral energy distribution (SED), effectively constraining dust properties and disk extensions. By observing stars spanning from a few up to several hundred Myr, the evolution of debris disks during crucial phases of planet formation can be studied. We have performed 870-micron observations of 22 exo-Kuiper-Belt candidates, as part of a Large Programme with the LABOCA bolometer at the APEX telescope. Dust masses (or upper limits) were calculated from integrated 870-micron fluxes, and fits to the SED of detected sources revealed the fractional dust luminosities f_dust, dust temperatures T_dust, and power-law exponents beta of the opacity law. A total of 10 detections with at least 3-sigma significance were made, out of which five (HD 95086, HD 131835, HD 161868, HD 170773, and HD 207129) have previously never been detected at submillimetre wavelengths. Three additional sources are marginally detected with >2.5-sigma significance. The best-fit beta parameters all lie between 0.1 and 0.8, in agreement with previous results indicating the presence of grains that are significantly larger than those in the ISM. From our relatively small sample we estimate f_dust proportional to t^(-alpha), with alpha~0.8-2.0, and identify an evolution of the characteristic radial dust distance R_dust that is consistent with the t^(1/3) increase predicted from models of self-stirred collisions in debris disks., Comment: 15 pages, 4 figures, accepted for publication in Astronomy & Astrophysics

'Water in Star-forming regions with Herschel' (WISH) is a Herschel Key Programme aimed at understanding the physical and chemical structure of young stellar objects (YSOs) with a focus on water and related species. The low-mass protostar HH 46 was observed with the Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory to measure emission in H2O, CO, OH, [OI], and [CII] lines located between 63 and 186 um. The excitation and spatial distribution of emission can disentangle the different heating mechanisms of YSOs, with better spatial resolution and sensitivity than previously possible. Far-IR line emission is detected at the position of the protostar and along the outflow axis. The OH emission is concentrated at the central position, CO emission is bright at the central position and along the outflow, and H2O emission is concentrated in the outflow. In addition, [OI] emission is seen in low-velocity gas, assumed to be related to the envelope, and is also seen shifted up to 170 km/s in both the red- and blue-shifted jets. Envelope models are constructed based on previous observational constraints. They indicate that passive heating of a spherical envelope by the protostellar luminosity cannot explain the high-excitation molecular gas detected with PACS, including CO lines with upper levels at >2500 K above the ground state. Instead, warm CO and H2O emission is probably produced in the walls of an outflow-carved cavity in the envelope, which are heated by UV photons and non-dissociative C-type shocks. The bright OH and [OI] emission is attributed to J-type shocks in dense gas close to the protostar. In the scenario described here, the combined cooling by far-IR lines within the central spatial pixel is estimated to be 2 \times 10-2 L_sun, with 60-80% attributed to J- and C-type shocks produced by interactions between the jet and the envelope., Comment: Accepted for publication in Astronomy and Astrophysics (Herschel special issue)

The Beta Pictoris Moving Group is a nearby stellar association of young (12Myr) co-moving stars including the classical debris disk star beta Pictoris. Due to their proximity and youth they are excellent targets when searching for submillimetre emission from cold, extended, dust components produced by collisions in Kuiper-Belt-like disks. They also allow an age independent study of debris disk properties as a function of other stellar parameters. We observed 7 infrared-excess stars in the Beta Pictoris Moving Group with the LABOCA bolometer array, operating at a central wavelength of 870 micron at the 12-m submillimetre telescope APEX. The main emission at these wavelengths comes from large, cold dust grains, which constitute the main part of the total dust mass, and hence, for an optically thin case, make better estimates on the total dust mass than earlier infrared observations. Fitting the spectral energy distribution with combined optical and infrared photometry gives information on the temperature and radial extent of the disk. From our sample, beta Pic, HD181327, and HD172555 were detected with at least 3-sigma certainty, while all others are below 2-sigma and considered non-detections. The image of beta Pic shows an offset flux density peak located near the south-west extension of the disk, similar to the one previously found by SCUBA at the JCMT. We present SED fits for detected sources and give an upper limit on the dust mass for undetected ones. We find a mean fractional dust luminosity f_dust=11x10^{-4} at t=12Myr, which together with recent data at 100Myr suggests an f_dust propto t^{-alpha} decline of the emitting dust, with alpha > 0.8., Comment: 11 pages, 3 figures, 3 tables; accepted for publication in Astronomy & Astrophysics

(Abridged) Studying continuum emission from interstellar dust is essential to locating and characterizing the highest density regions in the interstellar medium. In particular, the early stages of massive star formation remain poorly understood. Our goal is to produce a large-scale, systematic database of massive pre- and proto-stellar clumps in the Galaxy, to understand how and under what conditions star formation takes place. A well characterized sample of star-forming sites will deliver an evolutionary sequence and a mass function of high-mass, star-forming clumps. This systematic survey at submm wavelengths also represents a preparatory work for Herschel and ALMA. The APEX telescope is ideally located to observe the inner Milky Way. The Large APEX Bolometer Camera (LABOCA) is a 295-element bolometer array observing at 870 microns, with a beam size of 19". Taking advantage of its large field of view (11.4') and excellent sensitivity, we started an unbiased survey of the Galactic Plane, with a noise level of 50-70 mJy/beam: the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL). As a first step, we covered 95 sq. deg. These data reveal 6000 compact sources brighter than 0.25 Jy, as well as extended structures, many of them filamentary. About two thirds of the compact sources have no bright infrared counterpart, and some of them are likely to correspond to the precursors of (high-mass) proto-stars or proto-clusters. Other compact sources harbor hot cores, compact HII regions or young embedded clusters. Assuming a typical distance of 5 kpc, most sources are clumps smaller than 1 pc with masses from a few 10 to a few 100 M_sun. In this introductory paper, we show preliminary results from these ongoing observations, and discuss the perspectives of the survey., Comment: Accepted for publication in A&A, 13 pages, 14 figures. Final version after language editing

Only very few solar-type stars exhibiting an infrared excess and harbouring planets are known to date. Indeed, merely a single case of a star-planet-disk system has previously been detected at submillimeter (submm) wavelengths. Consequently, one of our aims is to understand the reasons for these poor statistics, i.e., whether these results reflected the composition and/or the physics of the planetary disks or were simply due to observational bias and selection effects. Finding more examples would be very significant. The selected target, q1 Eri, is a solar-type star, which was known to possess a planet, q1 Eri b, and to exhibit excess emission at IRAS wavelengths, but had remained undetected in the millimeter regime. Therefore, submm flux densities would be needed to better constrain the physical characteristics of the planetary disk. Consequently, we performed submm imaging observations of q1 Eri. The detected dust toward q1 Eri at 870 micron exhibits the remarkable fact that the entire SED, from the IR to mm-wavelengths, is fit by a single temperature blackbody function (60 K). This would imply that the emitting regions are confined to a narrow region (ring) at radial distances much larger than the orbital distance of q1 Eri b, and that the emitting particles are considerably larger than some hundred micron. However, the 870 micron source is extended, with a full-width-half-maximum of roughly 600 AU. Therefore, a physically more compelling model also invokes a belt of cold dust (17 K), located at 300 AU from the star and about 60 AU wide. The minimum mass of 0.04 Mearth (3 Mmoon) of 1 mm-size icy ring-particles is considerable, given the stellar age of about 1 Gyr. These big grains form an inner edge at about 25 AU, which may suggest the presence of an unseen outer planet (q1 Eri c)., Comment: 4 pages, 2 colour figures, Letter for Astronomy and Astrophysics, in press