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Publications (8)20.34 Total impact

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    ABSTRACT: The reactive molecular ions, OH+, H2O+, and H3O+, key probes of the oxygen chemistry of the interstellar gas, have been observed toward Orion KL with the Heterodyne Instrument for Far Infrared on board the Herschel Space Observatory. All three N = 1 - 0 fine-structure transitions of OH+ at 909, 971, and 1033 GHz and both fine-structure components of the doublet ortho-H2O+ 111 - 000 transition at 1115 and 1139 GHz were detected, and an upper limit was obtained for H3O+. OH+ and H2O+ are observed purely in absorption, showing a narrow component at the source velocity of 9 km s-1, and a broad blue shifted absorption similar to that reported recently for HF and para-H218O, and attributed to the low velocity outflow of Orion KL. We estimate column densities of OH+ and H2O+ for the 9 km s-1 component of 9 ± 3 x 1012 cm-2 and 7 ± 2 x 1012 cm-2, and those in the outflow of 1.9 ± 0.7 x 1013 cm-2 and 1.0 ± 0.3 x 1013 cm-2. Upper limits of 2.4 x 1012 cm-2 and 8.7 ± 1012 cm-2 were derived for the column densities of ortho and para-H3O+ from transitions near 985 and 1657 GHz. 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. A higher gas density, despite the assumption of a large ionization rate, may explain the comparatively low column densities of the ions. A part of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration. Copyright 2010© California Institute of Technology. All rights reserved.
    Astronomy and Astrophysics, v.521 (2010). 01/2011;
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    ABSTRACT: Aims. We aim to study the physical conditions, particularly the excitation state, of the intermediate-temperature gas components in the protoplanetary nebula CRL 618. These components are particularly important for understanding the evolution of the nebula. Methods. We performed Herschel/HIFI observations of several CO lines in the far-infrared/sub-mm in the protoplanetary nebula CRL 618. The high spectral resolution provided by HIFI allows measurement of the line profiles. Since the dynamics and structure of the nebula is well known from mm-wave interferometric maps, it is possible to identify the contributions of the different nebular components (fast bipolar outflows, double shells, compact slow shell) to the line profiles. The observation of these relatively high-energy transitions allows an accurate study of the excitation conditions in these components, particularly in the warm ones, which cannot be properly studied from the low-energy lines. Results. The 12CO J = 16−15, 10−9, and 6−5 lines are easily detected in this source. Both 13CO J = 10−9 and 6−5 are also detected.Wide profiles showing spectacular line wings have been found, particularly in 12CO J = 16−15. Other lines observed simultaneously with CO are also shown. Our analysis of the CO high-J transitions, when compared with the existing models, confirms the very low expansion velocity of the central, dense component, which probably indicates that the shells ejected during the last AGB phases were driven by radiation pressure under a regime of maximum transfer of momentum. No contribution of the diffuse halo found from mm-wave data is identified in our spectra, because of its low temperature. We find that the fast bipolar outflow is quite hot, much hotter than previously estimated; for instance, gas flowing at 100 km s−1 must have a temperature higher than ∼200 K. Probably, this very fast outflow, with a kinematic age <100 yr, has been accelerated by a shock and has not yet cooled down. The double empty shell found from mm-wave mapping must also be relatively hot, in agreement with the previous estimate.
    Astronomy and Astrophysics 10/2010; · 5.08 Impact Factor
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    ABSTRACT: During their asymptotic giant branch evolution, low-mass stars lose a significant fraction of their mass through an intense wind, enriching the interstellar medium with products of nucleosynthesis. We observed the nearby oxygen-rich asymptotic giant branch star IK Tau using the highresolution HIFI spectrometer onboard Herschel. We report on the first detection of H16 2 O and the rarer isotopologues H17 2 O and H18 2 O in both the ortho and para states. We deduce a total water content (relative to molecular hydrogen) of 6.6 × 10−5, and an ortho-to-para ratio of 3:1. These results are consistent with the formation of H2O in thermodynamical chemical equilibrium at photospheric temperatures, and does not require pulsationally induced non-equilibrium chemistry, vaporization of icy bodies or grain surface reactions. High-excitation lines of 12CO, 13CO, 28SiO, 29SiO, 30SiO, HCN, and SO have also been detected. From the observed line widths, the acceleration region in the inner wind zone can be characterized, and we show that the wind acceleration is slower than hitherto anticipated.
    Astronomy and Astrophysics 10/2010; · 5.08 Impact Factor
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    ABSTRACT: 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. Comment: 5 pages, 1 figure. Accepted to and to be published in the Herschel HIFI special issue of A\&A Letters
    09/2010;
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    ABSTRACT: To investigate the accretion and feedback processes in massive star formation, we analyze the shapes of emission lines from hot molecular cores, whose asymmetries trace infall and expansion motions. The high-mass star forming region SgrB2(M) was observed with Herschel/HIFI (HEXOS key project) in various lines of HCN and its isotopologues, complemented by APEX data. The observations are compared to spherically symmetric, centrally heated models with density power-law gradient and different velocity fields (infall or infall+expansion), using the radiative transfer code RATRAN. The HCN line profiles are asymmetric, with the emission peak shifting from blue to red with increasing J and decreasing line opacity (HCN to H$^{13}$CN). This is most evident in the HCN 12--11 line at 1062 GHz. These line shapes are reproduced by a model whose velocity field changes from infall in the outer part to expansion in the inner part. The qualitative reproduction of the HCN lines suggests that infall dominates in the colder, outer regions, but expansion dominates in the warmer, inner regions. We are thus witnessing the onset of feedback in massive star formation, starting to reverse the infall and finally disrupting the whole molecular cloud. To obtain our result, the THz lines uniquely covered by HIFI were critically important. Comment: A&A, HIFI special issue, accepted
    Astronomy and Astrophysics 07/2010; · 5.08 Impact Factor
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    ABSTRACT: We have observed CH absorption lines ($J=3/2, N=1 \leftarrow J=1/2, N=1$) against the continuum source Sgr~B2(M) using the \textit{Herschel}/HIFI instrument. With the high spectral resolution and wide velocity coverage provided by HIFI, 31 CH absorption features with different radial velocities and line widths are detected and identified. The narrower line width and lower column density clouds show `spiral arm' cloud characteristics, while the absorption component with the broadest line width and highest column density corresponds to the gas from the Sgr~B2 envelope. The observations show that each `spiral arm' harbors multiple velocity components, indicating that the clouds are not uniform and that they have internal structure. This line-of-sight through almost the entire Galaxy offers unique possibilities to study the basic chemistry of simple molecules in diffuse clouds, as a variety of different cloud classes are sampled simultaneously. We find that the linear relationship between CH and H$_2$ column densities found at lower $A_V$ by UV observations does not continue into the range of higher visual extinction. There, the curve flattens, which probably means that CH is depleted in the denser cores of these clouds. Comment: Accepted for publication in A&A, HIFI Special Issue
    07/2010;
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    ABSTRACT: The molecular gas in the DR21 massive star formation region is known to be affected by the strong UV field from the central star cluster and by a fast outflow creating a bright shock. The relative contribution of both heating mechanisms is the matter of a long debate. By better sampling the excitation ladder of various tracers we provide a quantitative distinction between the different heating mechanisms. HIFI observations of mid-J transitions of CO and HCO+ isotopes allow us to bridge the gap in excitation energies between observations from the ground, characterizing the cooler gas, and existing ISO LWS spectra, constraining the properties of the hot gas. Comparing the detailed line profiles allows to identify the physical structure of the different components. In spite of the known shock-excitation of H2 and the clearly visible strong outflow, we find that the emission of all lines up to > 2 THz can be explained by purely radiative heating of the material. However, the new Herschel/HIFI observations reveal two types of excitation conditions. We find hot and dense clumps close to the central cluster, probably dynamically affected by the outflow, and a more widespread distribution of cooler, but nevertheless dense, molecular clumps. Comment: Accepted for publication by A&A
    05/2010;
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    ABSTRACT: 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 1033 GHz and both fine-structure components of the doublet ortho-H 2 O + 1 11 −0 00 transition at 1115 and 1139 GHz 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 km s −1 , and a broad blueshifted absorption similar to that reported recently for HF and para-H 18 2 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±3×10 12 cm −2 and 7± 2× 10 12 cm −2 , and those in the outflow of 1.9± 0.7× 10 13 cm −2 and 1.0± 0.3× 10 13 cm −2 . Upper limits of 2.4× 10 12 cm −2 and 8.7× 10 12 cm −2 were derived for the column densities of ortho and para-H 3 O + from transitions near 985 and 1657 GHz. 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.
    Astronomy and Astrophysics 01/2010; 2526(14). · 5.08 Impact Factor