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Podio L.,Institute Of Planetologie Et Dastrophysique Of Grenoble | Podio L.,National institute for astrophysics | Lefloch B.,Institute Of Planetologie Et Dastrophysique Of Grenoble | Ceccarelli C.,Institute Of Planetologie Et Dastrophysique Of Grenoble | And 2 more authors.
Astronomy and Astrophysics | Year: 2014

Aims. We perform a complete census of molecular ions with an abundance greater than ~10-10 in the protostellar shock L1157-B1. This allows us to study the ionisation structure and chemistry of the shock. Methods. An unbiased high-sensitivity survey of L1157-B1 performed with the IRAM-30 m and Herschel/HIFI as part of the CHESS and ASAI large programmes allows searching for molecular ions emission. Then, by means of a radiative transfer code in the large velocity gradient approximation, the gas physical conditions and fractional abundances of molecular ions are derived. The latter are compared with estimates of steady-state abundances in the cloud and their evolution in the shock calculated with the chemical model Astrochem. Results. We detect emission from HCO+, H13CO+, N2H +, HCS+, and for the first time in a shock, from HOCO + and SO+. The bulk of the emission peaks at blue-shifted velocity, ~0.5-3 km s -1 with respect to systemic, has a width of ~3-7 km s-1 and is associated with the outflow cavities (T kin ~ 20-70 K, nH2~ 105 cm-3). A high-velocity component up to -40 km s-1, associated with the primary jet, is detected in the HCO+ 1-0 line. Observed HCO+ and N2H+ abundances (XHCO + ~ 0.7-3 × 10-8, XN2H+ ~ 0.4-8 × 10 -9) agree with steady-state abundances in the cloud and with their evolution in the compressed and heated gas in the shock for cosmic rays ionisation rate ζ = 3 × 10-16 s-1. HOCO +, SO+, and HCS+ observed abundances (X HOCO +~ 10-9, XSO + ~ 8 × 10-10, XHCS +~ 3-7 × 10 -10), instead, are 1-2 orders of magnitude larger than predicted in the cloud; on the other hand, they are strongly enhanced on timescales shorter than the shock age (~2000 years) if CO2, S or H2S, and OCS are sputtered off the dust grains in the shock. Conclusions. The performed analysis indicates that HCO+ and N2H+ are a fossil record of pre-shock gas in the outflow cavity, whilst HOCO+, SO+, and HCS+ are effective shock tracers that can be used to infer the amount of CO2 and sulphur-bearing species released from dust mantles in the shock. The observed HCS+ (and CS) abundance indicates that OCS should be one of the main sulphur carrier on grain mantles. However, the OCS abundance required to fit the observations is 1-2 orders of magnitude larger than observed. Laboratory experiments are required to measure the reactions rates involving these species and to fully understand the chemistry of sulphur-bearing species. © ESO 2014.

Codella C.,National institute for astrophysics | Lefloch B.,Joseph Fourier University | Ceccarelli C.,Joseph Fourier University | Cernicharo J.,CSIC - National Institute of Aerospace Technology | And 72 more authors.
Astronomy and Astrophysics | Year: 2010

We present the first results of the unbiased survey of the L1157-B1 bow shock, obtained with HIFI in the framework of the key program Chemical HErschel Survey of Star forming regions (CHESS). The L1157 outflow is driven by a low-mass Class 0 protostar and is considered the prototype of the so-called chemically active outflows. The bright blue-shifted bow shock B1 is the ideal laboratory for studying the link between the hot (∼1000-2000 K) component traced by H2 IR-emission and the cold (∼10-20 K) swept-up material. The main aim is to trace the warm gas chemically enriched by the passage of a shock and to infer the excitation conditions in L1157-B1. A total of 27 lines are identified in the 555-636 GHz region, down to an average 3σ level of 30 mK. The emission is dominated by CO(5-4) and H 2O(110-101) transitions, as discussed by Lefloch et al. in this volume. Here we report on the identification of lines from NH3, H2CO, CH3OH, CS, HCN, and HCO+. The comparison between the profiles produced by molecules released from dust mantles (NH3, H2CO, CH3OH) and that of H2O is consistent with a scenario in which water is also formed in the gas-phase in high-temperature regions where sputtering or grain-grain collisions are not efficient. The high excitation range of the observed tracers allows us to infer, for the first time for these species, the existence of a warm (≥200 K) gas component coexisting in the B1 bow structure with the cold and hot gas detected from ground. © 2010 ESO.

Emprechtinger M.,California Institute of Technology | Emprechtinger M.,University of Cologne | Lis D.C.,California Institute of Technology | Bell T.,California Institute of Technology | And 70 more authors.
Astronomy and Astrophysics | Year: 2010

Aims. We present observations of twelve rotational transitions of H 216O, H218O, and H2 17O 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. Methods. We identify three main gas components (hot core, cold foreground, and outflow) in NGC 6334 I and derive the physical conditions in these components. Results. 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 H218O/H2 17O abundance ratio is 3.2, which is consistent with the 18O/17O 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). © 2010 ESO.

Wyrowski F.,Max Planck Institute for Radio Astronomy | Van Der Tak F.,SRON Netherlands Institute for Space Research | Van Der Tak F.,University of Groningen | Herpin F.,University of Bordeaux 1 | And 72 more authors.
Astronomy and Astrophysics | Year: 2010

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 H 2O+ 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 H 2O+. Nine out of ten sources show absorption from H 2O+ 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 H2O+ are found in the range of 1012 to a few 1013 cm-2. The highest N(H2O+) column densities are found in the outflows of the sources. The ratios of H 2O+/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. © 2010 ESO.

Ceccarelli C.,Joseph Fourier University | Ceccarelli C.,University of Bordeaux 1 | Ceccarelli C.,French National Center for Scientific Research | Bacmann A.,Joseph Fourier University | And 85 more authors.
Astronomy and Astrophysics | Year: 2010

High resolution line spectra of star-forming regions are mines of information: they provide unique clues to reconstruct the chemical, dynamical, and physical structure of the observed source. We present the first results from the Herschel key project "Chemical HErschel Surveys of Star forming regions", CHESS. We report and discuss observations towards five CHESS targets, one outflow shock spot and four protostars with luminosities bewteen 20 and 2 × 105 L⊙: L1157-B1, IRAS 16293-2422, OMC2-FIR4, AFGL 2591, and NGC 6334I. The observations were obtained with the heterodyne spectrometer HIFI on board Herschel, with a spectral resolution of 1 MHz. They cover the frequency range 555-636 GHz, a range largely unexplored before the launch of the Herschel satellite. A comparison of the five spectra highlights spectacular differences in the five sources, for example in the density of methanol lines, or the presence/absence of lines from S-bearing molecules or deuterated species. We discuss how these differences can be attributed to the different star-forming mass or evolutionary status. © 2010 ESO.

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