Recent publications
Formation of Fullerenes in H-containing Planetary Nebulae
García-Hernández, D. A., Manchado, A., García-Lario, P., Stanghellini, L., Villaver, E., Shaw, R. A., Szczerba, R., Perea-Calderón, J. V.
2010, The Astrophysical Journal Letters, Volume 724, Issue 1, pp. L39-L43 (2010).
Abstract:
Hydrogen depleted environments are considered an essential requirement for the formation of fullerenes. The recent detection of C60 and C70 fullerenes in what was interpreted as the hydrogen-poor inner region of a post-final helium shell flash planetary nebula (PN) seemed to confirm this picture. Here, we present strong evidence that challenges the current paradigm regarding fullerene formation, showing that it can take place in circumstellar environments containing hydrogen. We report the simultaneous detection of polycyclic aromatic hydrocarbons (PAHs) and fullerenes toward C-rich and H-containing PNe belonging to environments with very different chemical histories such as our own Galaxy and the Small Magellanic Cloud. We suggest that PAHs and fullerenes may be formed by the photochemical processing of hydrogenated amorphous carbon. These observations suggest that modifications may be needed to our current understanding of the chemistry of large organic molecules as well as the chemical processing in space.
Detection of OH+ and H2O+ towards Orion KL
Gupta, H., Rimmer, P., Pearson, J. C., Yu, S., Herbst, E., Harada, N., Bergin, E. A., Neufeld, D. A., Melnick, G. J., Bachiller, R., Baechtold, W., Bell, T. A., Blake, G. A., Caux, E., Ceccarelli, C., Cernicharo, J., Chattopadhyay, G., Comito, C., Cabrit, S., Crockett, N. R., Daniel, F., Falgarone, E., Diez-Gonzalez, M. C., Dubernet, M.-L., Erickson, N., Emprechtinger, M., Encrenaz, P., Gerin, M., Gill, J. J., Giesen, T. F., Goicoechea, J. R., Goldsmith, P. F., Joblin, C., Johnstone, D., Langer, W. D., Larsson, B., Latter, W. B., Lin, R. H., Lis, D. C., Liseau, R., Lord, S. D., Maiwald, F. W., Maret, S., Martin, P. G., Martin-Pintado, J., Menten, K. M., Morris, P., Müller, H. S. P., Murphy, J. A., Nordh, L. H., Olberg, M., Ossenkopf, V., Pagani, L., Pérault, M., Phillips, T. G., Plume, R., Qin, S.-L., Salez, M., Samoska, L. A., Schilke, P., Schlecht, E., Schlemmer, S., Szczerba, R., Stutzki, J., Trappe, N., van der Tak, F. F. S., Vastel, C., Wang, S., Yorke, H. W., Zmuidzinas, J., Boogert, A., Güsten, R., Hartogh, P., Honingh, N., Karpov, A., Kooi, J., Krieg, J.-M., Schieder, R., Zaal, P.
2010, Astronomy and Astrophysics, Volume 521, id.L47
Abstract:
We report observations of the reactive molecular ions OH+, H2O+, and H3O+ 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-H2O+ 111-000 transition at 1115 and 1139 GHz were detected; 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 blueshifted 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 × 1012 cm-2 and 7 ± 2 × 1012 cm-2, and those in the outflow of 1.9 ± 0.7 × 1013 cm-2 and 1.0 ± 0.3 × 1013 cm-2. Upper limits of 2.4 × 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. The comparatively low column densities may be explained by a higher gas density despite the assumption of a very high ionization rate.
Herschel observations of deuterated water towards Sgr B2(M)
Comito, C., Schilke, P., Rolffs, R., Lis, D. C., Belloche, A., Bergin, E. A., Phillips, T. G., Bell, T. A., Crockett, N. R., Wang, S., Blake, G. A., Caux, E., Ceccarelli, C., Cernicharo, J., Daniel, F., Dubernet, M.-L., Emprechtinger, M., Encrenaz, P., Gerin, M., Giesen, T. F., Goicoechea, J. R., Goldsmith, P. F., Gupta, H., Herbst, E., Joblin, C., Johnstone, D., Langer, W. D., Latter, W. D., Lord, S. D., Maret, S., Martin, P. G., Melnick, G. J., Menten, K. M., Morris, P., Müller, H. S. P., Murphy, J. A., Neufeld, D. A., Ossenkopf, V., Pearson, J. C., Pérault, M., Plume, R., Qin, S.-L., Schlemmer, S., Stutzki, J., Trappe, N., van der Tak, F. F. S., Vastel, C., Yorke, H. W., Yu, S., Olberg, M., Szczerba, R., Larsson, B., Liseau, R., Lin, R. H., Samoska, L. A., Schlecht, E.
2010, Astronomy and Astrophysics, Volume 521, id.L38
Abstract:
Observations of HDO are an important complement for studies of water, because they give strong constraints on the formation processes - grain surfaces versus energetic process in the gas phase, e.g. in shocks. The HIFI observations of multiple transitions of HDO in Sgr B2(M) presented here allow the determination of the HDO abundance throughout the envelope, which has not been possible before with ground-based observations only. The abundance structure has been modeled with the spherical Monte Carlo radiative transfer code RATRAN, which also takes radiative pumping by continuum emission from dust into account. The modeling reveals that the abundance of HDO rises steeply with temperature from a low abundance (2.5 × 10-11) in the outer envelope at temperatures below 100 K through a medium abundance (1.5 × 10-9) in the inner envelope/outer core at temperatures between 100 and 200 K, and finally a high abundance (3.5 × 10-9) at temperatures above 200 K in the hot core. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Water in massive star-forming regions: HIFI observations of W3 IRS5
Chavarría, L., Herpin, F., Jacq, T., Braine, J., Bontemps, S., Baudry, A., Marseille, M., van der Tak, F., Pietropaoli, B., Wyrowski, F., Shipman, R., Frieswijk, W., van Dishoeck, E. F., Cernicharo, J., Bachiller, R., Benedettini, M., Benz, A. O., Bergin, E., Bjerkeli, P., Blake, G. A., Bruderer, S., Caselli, P., Codella, C., Daniel, F., di Giorgio, A. M., Dominik, C., Doty, S. D., Encrenaz, P., Fich, M., Fuente, A., Giannini, T., Goicoechea, J. R., de Graauw, T., Hartogh, P., Helmich, F., Herczeg, G. J., Hogerheijde, M. R., Johnstone, D., Jørgensen, J. K., Kristensen, L. E., Larsson, B., Lis, D., Liseau, R., McCoey, C., Melnick, G., Nisini, B., Olberg, M., Parise, B., Pearson, J. C., Plume, R., Risacher, C., Santiago-García, J., Saraceno, P., Stutzki, J., Szczerba, R., Tafalla, M., Tielens, A., van Kempen, T. A., Visser, R., Wampfler, S. F., Willem, J., Yıldız, U. A.
2010, Astronomy and Astrophysics, Volume 521, id.L37
Abstract:
We present Herschel observations of the water molecule in the massive star-forming region W3 IRS5. The o-H_217O 110-101, p-H_218O 111-000, p-H2O 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-H_217O 110-101 and p-H_218O 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. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Sensitive limits on the abundance of cold water vapor in the DM Tauri protoplanetary disk
Bergin, E. A., Hogerheijde, M. R., Brinch, C., Fogel, J., Yıldız, U. A., Kristensen, L. E., van Dishoeck, E. F., Bell, T. A., Blake, G. A., Cernicharo, J., Dominik, C., Lis, D., Melnick, G., Neufeld, D., Panić, O., Pearson, J. C., Bachiller, R., Baudry, A., Benedettini, M., Benz, A. O., Bjerkeli, P., Bontemps, S., Braine, J., Bruderer, S., Caselli, P., Codella, C., Daniel, F., di Giorgio, A. M., Doty, S. D., Encrenaz, P., Fich, M., Fuente, A., Giannini, T., Goicoechea, J. R., de Graauw, T., Helmich, F., Herczeg, G. J., Herpin, F., Jacq, T., Johnstone, D., Jørgensen, J. K., Larsson, B., Liseau, R., Marseille, M., McCoey, C., Nisini, B., Olberg, M., Parise, B., Plume, R., Risacher, C., Santiago-García, J., Saraceno, P., Shipman, R., Tafalla, M., van Kempen, T. A., Visser, R., Wampfler, S. F., Wyrowski, F., van der Tak, F., Jellema, W., Tielens, A. G. G. M., Hartogh, P., Stützki, J., Szczerba, R.
2010, Astronomy and Astrophysics, Volume 521, id.L33
Abstract:
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 3σ levels in 0.5 km s-1 channels of 4.2 mK for the 110-101 line and 12.6 mK for the 111-000 line. We report a very tentative detection, however, of the 110-101 line in the wide band spectrometer, with a strength of Tmb = 2.7 mK, a width of 5.6 km s-1 and an integrated intensity of 16.0 mK km s-1. The latter constitutes a 6σ 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. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with participation important from NASA.
Herschel/HIFI observations of high-J CO transitions in the protoplanetary nebula CRL 618
Bujarrabal, V., Alcolea, J., Soria-Ruiz, R., Planesas, P., Teyssier, D., Marston, A. P., Cernicharo, J., Decin, L., Dominik, C., Justtanont, K., de Koter, A., Melnick, G., Menten, K. M., Neufeld, D. A., Olofsson, H., Schmidt, M., Schöier, F. L., Szczerba, R., Waters, L. B. F. M., Quintana-Lacaci, G., Güsten, R., Gallego, J. D., Díez-González, M. C., Barcia, A., López-Fernández, I., Wildeman, K., Tielens, A. G. G. M., Jacobs, K.
2010, Astronomy and Astrophysics, Volume 521, id.L3
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. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
A HIFI preview of warm molecular gas around χ Cygni: first detection of H2O emission toward an S-type AGB star
Justtanont, K., Decin, L., Schöier, F. L., Maercker, M., Olofsson, H., Bujarrabal, V., Marston, A. P., Teyssier, D., Alcolea, J., Cernicharo, J., Dominik, C., de Koter, A., Melnick, G., Menten, K., Neufeld, D., Planesas, P., Schmidt, M., Szczerba, R., Waters, R., de Graauw, T., Whyborn, N., Finn, T., Helmich, F., Siebertz, O., Schmülling, F., Ossenkopf, V., Lai, R.
2010, Astronomy and Astrophysics, Volume 521, id.L6
Abstract:


Aims. A set of new, sensitive, and spectrally resolved, sub-millimeter line observations are used to probe the warm circumstellar gas around the S-type AGB star χ Cyg. The observed lines involve high rotational quantum numbers, which, combined with previously obtained lower-frequency data, make it possible to study in detail the chemical and physical properties of, essentially, the entire circumstellar envelope of χ Cyg.

Methods. The data were obtained using the HIFI instrument aboard Herschel, whose high spectral resolution provides valuable information about the line profiles. Detailed, non-LTE, radiative transfer modelling, including dust radiative transfer coupled with a dynamical model, has been performed to derive the temperature, density, and velocity structure of the circumstellar envelope.

Results. We report the first detection of circumstellar H2O rotational emission lines in an S-star. Using the high-J CO lines to derive the parameters for the circumstellar envelope, we modelled both the ortho- and para-H2O lines. Our modelling results are consistent with the velocity structure expected for a dust-driven wind. The derived total H2O abundance (relative to H2) is (1.1±0.2) × 10-5, much lower than that in O-rich stars. The derived ortho-to-para ratio of 2.1±0.6 is close to the high-temperature equilibrium limit, consistent with H2O being formed in the photosphere. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Herschel observations in the ultracompact HII region Mon R2. Water in dense photon-dominated regions (PDRs)
Fuente, A., Berné, O., Cernicharo, J., Rizzo, J. R., González-García, M., Goicoechea, J. R., Pilleri, P., Ossenkopf, V., Gerin, M., Güsten, R., Akyilmaz, M., Benz, A. O., Boulanger, F., Bruderer, S., Dedes, C., France, K., García-Burillo, S., Harris, A., Joblin, C., Klein, T., Kramer, C., Le Petit, F., Lord, S. D., Martin, P. G., Martín-Pintado, J., Mookerjea, B., Neufeld, D. A., Okada, Y., Pety, J., Phillips, T. G., Röllig, M., Simon, R., Stutzki, J., van der Tak, F., Teyssier, D., Usero, A., Yorke, H., Schuster, K., Melchior, M., Lorenzani, A., Szczerba, R., Fich, M., McCoey, C., Pearson, J., Dieleman, P.
2010, Astronomy and Astrophysics, Volume 521, id.L23
Abstract:

Context. Monoceros R2, at a distance of 830 pc, is the only ultracompact H ii region (UC H ii) where the photon-dominated region (PDR) between the ionized gas and the molecular cloud can be resolved with Herschel. Therefore, it is an excellent laboratory to study the chemistry in extreme PDRs (G0 > 105 in units of Habing field, n > 106 cm-3).

Aims. Our ultimate goal is to probe the physical and chemical conditions in the PDR around the UC H ii Mon R2.

Methods. HIFI observations of the abundant compounds 13CO, C18O, o-H218O, HCO+, CS, CH, and NH have been used to derive the physical and chemical conditions in the PDR, in particular the water abundance. The modeling of the lines has been done with the Meudon PDR code and the non-local radiative transfer model described by Cernicharo et al.

Results. The 13CO, C18O, o-H_218O, HCO+ and CS observations are well described assuming that the emission is coming from a dense (n = 5 × 106 cm-3, N(H2)> 1022 cm-2) layer of molecular gas around the H ii region. Based on our o-H_218O observations, we estimate an o-H2O abundance of ≈2 × 10-8. This is the average ortho-water abundance in the PDR. Additional H_218O and/or water lines are required to derive the water abundance profile. A lower density envelope (n ~ 105 cm-3, N(H2) = 2-5 × 1022 cm-2) is responsible for the absorption in the NH 1_1→ 0_2 line. The emission of the CH ground state triplet is coming from both regions with a complex and self-absorbed profile in the main component. The radiative transfer modeling shows that the 13CO and HCO+ line profiles are consistent with an expansion of the molecular gas with a velocity law, ve = 0.5 × (r/Rout)-1 km s-1, although the expansion velocity is poorly constrained by the observations presented here.

Conclusions. We determine an ortho-water abundance of ≈2 × 10-8 in Mon R2. Because shocks are unimportant in this region and our estimate is based on H_218O observations that avoids opacity problems, this is probably the most accurate estimate of the water abundance in PDRs thus far. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Figures 1 and 4 (page 5) are only available in electronic form at http://www.aanda.org
Herschel/HIFI deepens the circumstellar NH3 enigma
Menten, K. M., Wyrowski, F., Alcolea, J., de Beck, E., Decin, L., Marston, A. P., Bujarrabal, V., Cernicharo, J., Dominik, C., Justtanont, K., de Koter, A., Melnick, G., Neufeld, D. A., Olofsson, H., Planesas, P., Schmidt, M., Schöier, F. L., Szczerba, R., Teyssier, D., Waters, L. B. F. M., Edwards, K., Olberg, M., Phillips, T. G., Morris, P., Salez, M., Caux, E.
2010, Astronomy and Astrophysics, Volume 521, id.L7
Abstract:

Context. Circumstellar envelopes (CSEs) of a variety of evolved stars have been found to contain ammonia (NH3) in amounts that exceed predictions from conventional chemical models by many orders of magnitude.

Aims. The observations reported here were performed in order to better constrain the NH3 abundance in the CSEs of four, quite diverse, oxygen-rich stars using the NH3 ortho JK = 10-00 ground-state line.

Methods. We used the Heterodyne Instrument for the Far Infrared aboard Herschel to observe the NH3 JK = 10-00 transition near 572.5 GHz, simultaneously with the ortho-H2O JKa , Kc = 11,0 - 10,1 transition, toward VY CMa, OH 26.5+0.6, IRC+10420, and IK Tau. We conducted non-LTE radiative transfer modeling with the goal to derive the NH3 abundance in these objects' CSEs. For the last two stars, Very Large Array imaging of NH3 radio-wavelength inversion lines were used to provide further constraints, particularly on the spatial extent of the NH3-emitting regions.

Results. We find remarkably strong NH3 emission in all of our objects with the NH3 line intensities rivaling those of the ground state H2O line. The NH3 abundances relative to H2 are very high and range from 2×10-7 to 3×10-6 for the objects we have studied.

Conclusions. Our observations confirm and even deepen the circumstellar NH3 enigma. While our radiative transfer modeling does not yield satisfactory fits to the observed line profiles, it does lead to abundance estimates that confirm the very high values found in earlier studies. New ways to tackle this mystery will include further Herschel observations of more NH3 lines and imaging with the Expanded Very Large Array. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendix A (page 5) is only available in electronic form at http://www.aanda.org
Discovery of water vapour in the carbon star V Cygni from observations with Herschel/HIFI
Neufeld, D. A., González-Alfonso, E., Melnick, G., Pułecka, M., Schmidt, M., Szczerba, R., Bujarrabal, V., Alcolea, J., Cernicharo, J., Decin, L., Dominik, C., Justtanont, K., de Koter, A., Marston, A. P., Menten, K., Olofsson, H., Planesas, P., Schöier, F. L., Teyssier, D., Waters, L. B. F. M., Edwards, K., McCoey, C., Shipman, R., Jellema, W., de Graauw, T., Ossenkopf, V., Schieder, R., Philipp, S.
2010, Astronomy and Astrophysics, Volume 521, id.L5
Abstract:
We report the discovery of water vapour toward the carbon star V Cygni. We have used Herschel's HIFI instrument, in dual beam switch mode, to observe the 111-000 para-water transition at 1113.3430 GHz in the upper sideband of the Band 4b receiver. The observed spectral line profile is nearly parabolic, but with a slight asymmetry associated with blueshifted absorption, and the integrated antenna temperature is 1.69 ± 0.17 K km s-1. This detection of thermal water vapour emission, carried out as part of a small survey of water in carbon-rich stars, is only the second such detection toward a carbon-rich AGB star, the first having been obtained by the Submillimeter Wave Astronomy Satellite toward IRC+10216. For an assumed ortho-to-para ratio of 3 for water, the observed line intensity implies a water outflow rate ~3-6 × 10-5 Earth masses per year and a water abundance relative to H2 of ~2-5 × 10-6. This value is a factor of at least 104 larger than the expected photospheric abundance in a carbon-rich environment, and - as in IRC+10216 - raises the intriguing possibility that the observed water is produced by the vapourisation of orbiting comets or dwarf planets. However, observations of the single line observed to date do not permit us to place strong constraints upon the spatial distribution or origin of the observed water, but future observations of additional transitions will allow us to determine the inner radius of the H2O-emitting zone, and the H2O ortho-to-para ratio, and thereby to place important constraints upon the origin of the observed water emission. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
HIFI spectroscopy of low-level water transitions in M 82
Weiß, A., Requena-Torres, M. A., Güsten, R., García-Burillo, S., Harris, A. I., Israel, F. P., Klein, T., Kramer, C., Lord, S., Martin-Pintado, J., Röllig, M., Stutzki, J., Szczerba, R., van der Werf, P. P., Philipp-May, S., Yorke, H., Akyilmaz, M., Gal, C., Higgins, R., Marston, A., Roberts, J., Schlöder, F., Schultz, M., Teyssier, D., Whyborn, N., Wunsch, H. J.
2010, Astronomy and Astrophysics, Volume 521, id.L1
Abstract:
We present observations of the rotational ortho-water ground transition, the two lowest para-water transitions, and the ground transition of ionised ortho-water in the archetypal starburst galaxy M 82, performed with the HIFI instrument on the Herschel Space Observatory. These observations are the first detections of the para-H2O(111-000) (1113 GHz) and ortho-H2O+(111-000) (1115 GHz) lines in an extragalactic source. All three water lines show different spectral line profiles, underlining the need for high spectral resolution in interpreting line formation processes. Using the line shape of the para-H2O(111-000) and ortho-H2O+(111-000) absorption profile in conjunction with high spatial resolution CO observations, we show that the (ionised) water absorption arises from a ~2000 pc2 region within the HIFI beam located about ~50 pc east of the dynamical centre of the galaxy. This region does not coincide with any of the known line emission peaks that have been identified in other molecular tracers, with the exception of HCO. Our data suggest that water and ionised water within this region have high (up to 75%) area-covering factors of the underlying continuum. This indicates that water is not associated with small, dense cores within the ISM of M 82 but arises from a more widespread diffuse gas component. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with participation from NASA.
Water content and wind acceleration in the envelope around the oxygen-rich AGB star IK Tauri as seen by Herschel/HIFI
Decin, L., Justtanont, K., de Beck, E., Lombaert, R., de Koter, A., Waters, L. B. F. M., Marston, A. P., Teyssier, D., Schöier, F. L., Bujarrabal, V., Alcolea, J., Cernicharo, J., Dominik, C., Melnick, G., Menten, K., Neufeld, D. A., Olofsson, H., Planesas, P., Schmidt, M., Szczerba, R., de Graauw, T., Helmich, F., Roelfsema, P., Dieleman, P., Morris, P., Gallego, J. D., Díez-González, M. C., Caux, E.
2010, Astronomy and Astrophysics, Volume 521, id.L4
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 high-resolution HIFI spectrometer onboard Herschel. We report on the first detection of H_216O and the rarer isotopologues H_217O and H_218O 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. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices (pages 6 and 7) are only available in electronic form at http://www.aanda.org
Herschel/HIFI observations of interstellar OH+ and H2O+ towards W49N: a probe of diffuse clouds with a small molecular fraction
Neufeld, D. A., Goicoechea, J. R., Sonnentrucker, P., Black, J. H., Pearson, J., Yu, S., Phillips, T. G., Lis, D. C., de Luca, M., Herbst, E., Rimmer, P., Gerin, M., Bell, T. A., Boulanger, F., Cernicharo, J., Coutens, A., Dartois, E., Kazmierczak, M., Encrenaz, P., Falgarone, E., Geballe, T. R., Giesen, T., Godard, B., Goldsmith, P. F., Gry, C., Gupta, H., Hennebelle, P., Hily-Blant, P., Joblin, C., Kołos, R., Krełowski, J., Martín-Pintado, J., Menten, K. M., Monje, R., Mookerjea, B., Perault, M., Persson, C., Plume, R., Salez, M., Schlemmer, S., Schmidt, M., Stutzki, J., Teyssier, D., Vastel, C., Cros, A., Klein, K., Lorenzani, A., Philipp, S., Samoska, L. A., Shipman, R., Tielens, A. G. G. M., Szczerba, R., Zmuidzinas, J.
2010, Astronomy and Astrophysics, Volume 521, id.L10
Abstract:
We report the detection of absorption by interstellar hydroxyl cations and water cations, along the sight-line to the bright continuum source W49N. We have used Herschel's HIFI instrument, in dual beam switch mode, to observe the 972 GHz N = 1-0 transition of OH+ and the 1115 GHz 111-000 transition of ortho-H2O+. The resultant spectra show absorption by ortho-H2O+, and strong absorption by OH+, in foreground material at velocities in the range 0 to 70 km s-1 with respect to the local standard of rest. The inferred OH+/H2O+ abundance ratio ranges from ~3 to ~15, implying that the observed OH+ arises in clouds of small molecular fraction, in the 2-8% range. This conclusion is confirmed by the distribution of OH+ and H2O+ in Doppler velocity space, which is similar to that of atomic hydrogen, as observed by means of 21 cm absorption measurements, and dissimilar from that typical of other molecular tracers. The observed OH+/H abundance ratio of a few × 10-8 suggests a cosmic ray ionization rate for atomic hydrogen of 0.6-2.4×10-16 s-1, in good agreement with estimates inferred previously for diffuse clouds in the Galactic disk from observations of interstellar H3+ and other species. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Polarisation observations of VY Canis Majoris H2O 532-441 620.701 GHz maser emission with HIFI
Harwit, M., Houde, M., Sonnentrucker, P., Boogert, A. C. A., Cernicharo, J., de Beck, E., Decin, L., Henkel, C., Higgins, R. D., Jellema, W., Kraus, A., McCoey, C., Melnick, G. J., Menten, K. M., Risacher, C., Teyssier, D., Vaillancourt, J. E., Alcolea, J., Bujarrabal, V., Dominik, C., Justtanont, K., de Koter, A., Marston, A. P., Olofsson, H., Planesas, P., Schmidt, M., Schöier, F. L., Szczerba, R., Waters, L. B. F. M.
2010, Astronomy and Astrophysics, Volume 521, id.L51
Abstract:

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 H2O.

Methods. In its high-resolution mode (HRS) the Herschel Heterodyne Instrument for the Far Infrared (HIFI) offers a frequency resolution of 0.125 MHz, corresponding to a line-of-sight velocity of 0.06 km s-1, 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 für Radioastronomie 100-m 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 H2O 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 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. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendix (page 5) is only available in electronic form at http://www.aanda.org
Water production in comet 81P/Wild 2 as determined by Herschel/HIFI
de Val-Borro, M., Hartogh, P., Crovisier, J., Bockelée-Morvan, D., Biver, N., Lis, D. C., Moreno, R., Jarchow, C., Rengel, M., Szutowicz, S., Banaszkiewicz, M., Bensch, F., Błęcka, M. I., Emprechtinger, M., Encrenaz, T., Jehin, E., Küppers, M., Lara, L.-M., Lellouch, E., Swinyard, B. M., Vandenbussche, B., Bergin, E. A., Blake, G. A., Blommaert, J. A. D. L., Cernicharo, J., Decin, L., Encrenaz, P., de Graauw, T., Hutsemékers, D., Kidger, M., Manfroid, J., Medvedev, A. S., Naylor, D. A., Schieder, R., Stam, D., Thomas, N., Waelkens, C., Szczerba, R., Saraceno, P., di Giorgio, A. M., Philipp, S., Klein, T., Ossenkopf, V., Zaal, P., Shipman, R.
2010, Astronomy and Astrophysics, Volume 521, id.L50
Abstract:
The high spectral resolution and sensitivity of Herschel/HIFI allows for the detection of multiple rotational water lines and accurate determinations of water production rates in comets. In this Letter we present HIFI observations of the fundamental 110-101 (557 GHz) ortho and 111-00 (1113 GHz) para rotational transitions of water in comet 81P/Wild 2 acquired in February 2010. We mapped the extent of the water line emission with five point scans. Line profiles are computed using excitation models which include excitation by collisions with electrons and neutrals and solar infrared radiation. We derive a mean water production rate of 1.0 × 1028 molecules s-1 at a heliocentric distance of 1.61 AU about 20 days before perihelion, in agreement with production rates measured from the ground using observations of the 18-cm OH lines. Furthermore, we constrain the electron density profile and gas kinetic temperature, and estimate the coma expansion velocity by fitting the water line shapes. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Figure 5 (page 5) is only available in electronic form at http://www.aanda.org
Excitation of the molecular gas in the nuclear region of M 82
Loenen, A. F., van der Werf, P. P., Güsten, R., Meijerink, R., Israel, F. P., Requena-Torres, M. A., García-Burillo, S., Harris, A. I., Klein, T., Kramer, C., Lord, S., Martín-Pintado, J., Röllig, M., Stutzki, J., Szczerba, R., Weiß, A., Philipp-May, S., Yorke, H., Caux, E., Delforge, B., Helmich, F., Lorenzani, A., Morris, P., Philips, T. G., Risacher, C., Tielens, A. G. G. M.
2010, Astronomy and Astrophysics, Volume 521, id.L2
Abstract:
We present high-resolution HIFI spectroscopy of the nucleus of the archetypical starburst galaxy M 82. Six 12CO lines, 2 13CO lines and 4 fine-structure lines have been 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 = 103.5 cm-3) clouds, with column densities of NH = 1021.5 cm-2 and a relatively low UV radiation field (G0 = 102). The remaining gas is predominantly found in clouds with higher densities (n = 105 cm-3) and radiation fields (G0 = 102.75), but somewhat lower column densities (NH = 1021.2 cm-2). The highest J CO lines are dominated by a small (1% relative surface filling) component, with an even higher density (n = 106 cm-3) and UV field (G0 = 103.25). These results show the strength of multi-component modelling for interpretating the integrated properties of galaxies.
The SAGE-Spec Spitzer Legacy Program: The Life Cycle of Dust and Gas in the Large Magellanic Cloud
Kemper, F., Woods, P. M., Antoniou, V., Bernard, J.-P., Blum, R. D., Boyer, M. L., Chan, J., Chen, C.-H. R., Cohen, M., Dijkstra, C., Engelbracht, C., Galametz, M., Galliano, F., Gielen, C., Gordon, K. D., Gorjian, V., Harris, J., Hony, S., Hora, J. L., Indebetouw, R., Jones, O., Kawamura, A., Lagadec, E., Lawton, B., Leisenring, J. M., Madden, S. C., Marengo, M., Matsuura, M., McDonald, I., McGuire, C., Meixner, M., Mulia, A. J., O'Halloran, B., Oliveira, J. M., Paladini, R., Paradis, D., Reach, W. T., Rubin, D., Sandstrom, K., Sargent, B. A., Sewilo, M., Shiao, B., Sloan, G. C., Speck, A. K., Srinivasan, S., Szczerba, R., Tielens, A. G. G. M., van Aarle, E., Van Dyk, S. D., van Loon, J. T., Van Winckel, H., Vijh, U. P., Volk, K., Whitney, B. A., Wilkins, A. N., and Zijlstra, A. A.
2010 , The Publications of the Astronomical Society of the Pacific, Volume 122, Issue 892, pp. 683-700.
Abstract:
The SAGE-Spec Spitzer Legacy program is a spectroscopic follow-up to the SAGE-LMC photometric survey of the Large Magellanic Cloud carried out with the Spitzer Space Telescope. We present an overview of SAGE-Spec and some of its first results. The SAGE-Spec program aims to study the life cycle of gas and dust in the Large Magellanic Cloud and to provide information essential to the classification of the point sources observed in the earlier SAGE-LMC photometric survey. We acquired 224.6 h of observations using the infrared spectrograph and the spectral energy distribution (SED) mode of the Multiband Imaging Photometer for Spitzer. The SAGE-Spec data, along with archival Spitzer spectroscopy of objects in the Large Magellanic Cloud, are reduced and delivered to the community. We discuss the observing strategy, the specific data-reduction pipelines applied, and the dissemination of data products to the scientific community. Initial science results include the first detection of an extragalactic 21 μm feature toward an evolved star and elucidation of the nature of disks around RV Tauri stars in the Large Magellanic Cloud. Toward some young stars, ice features are observed in absorption. We also serendipitously observed a background quasar, at a redshift of z ≈ 0.14, which appears to be hostless.
New groups of planetary nebulae with peculiar dust chemistry towards the Galactic bulge
Górny, S. K., Perea-Calderón, J. V., García-Hernández, D. A., García-Lario, P., and Szczerba, R.
2010 , Astronomy and Astrophysics, Volume 516, id.A39
Abstract:


Aims. We investigate Galactic bulge planetary nebulae without emission-line central stars for which peculiar infrared spectra have been obtained with the Spitzer Space Telescope, including the simultaneous signs of oxygen and carbon based dust. Three separate sub-groups can be defined characterized by the different chemical composition of the dust and the presence of crystalline and amorphous silicates.

Methods. We use literature data to analyze the different nebular properties and deduce both the evolutionary status and the origin of these three groups. In particular, we check whether there are signs of evolutionary links between dual-dust chemistry planetary nebulae without detected emission-line central stars and those with emission-line stars.

Results. Our primary finding is that the classification based on the dust properties is reflected in the more general properties of these planetary nebulae. However, some observed properties are difficult to relate to the common view of planetary nebulae. In particular, it is challenging to interpret the peculiar gas chemical composition of many analyzed objects in the standard picture of the evolution of planetary nebulae progenitors. We confirm that the dual-dust chemistry phenomenon is not limited to planetary nebulae with emission-line central stars.

Conclusions. Our results clearly indicate that there is no unique road to the formation of planetary nebulae even in a homogeneous environment such as the Galactic bulge. The evolution of a single asymptotic giant branch star may lead to the formation of different types of planetary nebulae. In addition, the evolution in a close binary system should sometimes also be considered.
Based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407.
New groups of planetary nebulae with peculiar dust chemistry towards the Galactic bulge
Górny, S. K., Perea-Calderón, J. V., García-Hernández, D. A., García-Lario, P., Szczerba, R.
2010, Astronomy and Astrophysics, Volume 516, id.A39
Abstract:


Aims. We investigate Galactic bulge planetary nebulae without emission-line central stars for which peculiar infrared spectra have been obtained with the Spitzer Space Telescope, including the simultaneous signs of oxygen and carbon based dust. Three separate sub-groups can be defined characterized by the different chemical composition of the dust and the presence of crystalline and amorphous silicates.

Methods. We use literature data to analyze the different nebular properties and deduce both the evolutionary status and the origin of these three groups. In particular, we check whether there are signs of evolutionary links between dual-dust chemistry planetary nebulae without detected emission-line central stars and those with emission-line stars.

Results. Our primary finding is that the classification based on the dust properties is reflected in the more general properties of these planetary nebulae. However, some observed properties are difficult to relate to the common view of planetary nebulae. In particular, it is challenging to interpret the peculiar gas chemical composition of many analyzed objects in the standard picture of the evolution of planetary nebulae progenitors. We confirm that the dual-dust chemistry phenomenon is not limited to planetary nebulae with emission-line central stars.

Conclusions. Our results clearly indicate that there is no unique road to the formation of planetary nebulae even in a homogeneous environment such as the Galactic bulge. The evolution of a single asymptotic giant branch star may lead to the formation of different types of planetary nebulae. In addition, the evolution in a close binary system should sometimes also be considered. Based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407.
HST/WFPC2 observations of the LMC pulsar PSR B0540-69
Mignani, R. P., Sartori, A., de Luca, A., Rudak, B., Słowikowska, A., Kanbach, G., and Caraveo, P. A.
2010 , Astronomy and Astrophysics, Volume 515, id.A110
Abstract:

Context. The study of the younger, and brighter, pulsars is important for understanding the optical emission properties of isolated neutron stars through observations which, even in the 10 m-class telescope era, are much more challenging for older and fainter objects. PSR B0540-69, the second brightest (V~22) optical pulsar, is obviously a primary target for these investigations.

Aims. The aims of this work are several: (i) constraining the pulsar proper motion and its velocity on the plane of the sky and improving the determination of the pulsar coordinates through optical astrometry; (ii) obtaining a more precise characterisation of the pulsar optical spectral energy distribution (SED) through a consistent set of multi-band, high-resolution, imaging photometry observations and studying the relation with the X-ray spectrum, including the presence of a spectral turnover between the two bands. Last, we aim at (iii) measuring the pulsar optical phase-averaged linear polarisation, for which only a preliminary and uncertain measurement has been obtained so far from ground-based observations, and at testing the predictions of different neutron star magnetosphere models.

Methods. We performed high-resolution observations of PSR B0540-69 with the Wide Field and Planetary Camera 2 (WFPC2) aboard the Hubble Space Telescope (HST), in both direct imaging and polarimetry modes.

Results. From multi-epoch astrometry we set a 3 σ upper limit of 1 mas yr-1 on the pulsar proper motion, implying a transverse velocity <250 km s-1 at the 50 kpc LMC distance. Moreover, we determined the pulsar absolute position with an unprecedented accuracy of 70 mas. From multi-band photometry we characterised the pulsar power-law spectrum and derived the most accurate measurement of the spectral index (α_O = 0.70 ± 0.07), which indicates a spectral turnover between the optical and X-ray bands. Finally, from polarimetry we obtained a new measurement of the pulsar phase-averaged polarisation degree (PD = 16% ± 4%), consistent with magnetosphere models, depending on the actual intrinsic polarisation degree and depolarisation factor, and we found that the polarisation vector (22° ± 12° position angle) is possibly aligned with the semi-major axis of the pulsar-wind nebula and with the apparent proper motion direction of its bright emission knot.

Conclusions. Deeper studies with the HST can only be possible with the refurbished Advanced Camera for Surveys (ACS) and with the new Wide Field Camera 3 (WFC3).
Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc. under contract No. NAS 5-26555.
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