Publications (54)36.51 Total impact
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Article: Excited OH+, H2O+, and H3O+ in NGC 4418 and Arp 220
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ABSTRACT: We report on Herschel/PACS observations of absorption lines of OH+, H2O+ and H3O+ in NGC 4418 and Arp 220. Excited lines of OH+ and H2O+ with E_lower of at least 285 and \sim200 K, respectively, are detected in both sources, indicating radiative pumping and location in the high radiation density environment of the nuclear regions. Abundance ratios OH+/H2O+ of 1-2.5 are estimated in the nuclei of both sources. The inferred OH+ column and abundance relative to H nuclei are (0.5-1)x10^{16} cm-2 and \sim2x10^{-8}, respectively. Additionally, in Arp 220, an extended low excitation component around the nuclear region is found to have OH+/H2O+\sim5-10. H3O+ is detected in both sources with N(H3O+)\sim(0.5-2)x10^{16} cm-2, and in Arp 220 the pure inversion, metastable lines indicate a high rotational temperature of ~500 K, indicative of formation pumping and/or hot gas. Simple chemical models favor an ionization sequence dominated by H+ - O+ - OH+ - H2O+ - H3O+, and we also argue that the H+ production is most likely dominated by X-ray/cosmic ray ionization. The full set of observations and models leads us to propose that the molecular ions arise in a relatively low density (\gtrsim10^4 cm-3) interclump medium, in which case the ionization rate per H nucleus (including secondary ionizations) is zeta>10^{-13} s-1, a lower limit that is severalx10^2 times the highest rate estimates for Galactic regions. In Arp 220, our lower limit for zeta is compatible with estimates for the cosmic ray energy density inferred previously from the supernova rate and synchrotron radio emission, and also with the expected ionization rate produced by X-rays. In NGC 4418, we argue that X-ray ionization due to an AGN is responsible for the molecular ion production.11/2012; -
Article: Terahertz and far-infrared synchrotron spectroscopy and global modeling of methyl mercaptan, CH(3) (32)SH.
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ABSTRACT: In this work, terahertz and Fourier transform far-infrared (FTFIR) synchrotron spectra of methyl mercaptan, CH(3)SH, have been investigated in order to provide new laboratory information for enhanced observations of this species in interstellar molecular clouds and star-forming regions. Like its methanol cousin, methyl mercaptan has particularly rich spectra associated with its large-amplitude internal rotation that extend throughout the THz and FIR regions. We have recorded new spectra for CH(3)SH from 1.1-1.5 and 1.790-1.808 THz at the University of Cologne as well as high-resolution FTFIR synchrotron spectra from 50-550 cm(-1) at 0.001 cm(-1) resolution on the far-IR beam-line at the Canadian Light Source. Assignments are reported for rotational quantum numbers up to J ≈ 40 and K ≈ 15, and torsional states up to v(t) = 2 for the THz measurements and v(t) = 3 for the FTFIR observations. The THz and FTFIR measurements together with literature results have been combined in a global analysis of a dataset comprising a total of 1725 microwave and THz frequencies together with ∼18000 FTFIR transitions, ranging up to v(t) = 2 and J(max) = 30 for MW∕THz and 40 for FTFIR. The global fit employs 78 torsion-rotation parameters and has achieved a weighted standard deviation of ∼1.1. A prediction list (v(t) ≤ 2, J ≤ 45 and K ≤ 20) has been generated from the model giving essentially complete coverage of observable CH(3) (32)SH transitions within the bandwidths of major new astronomical facilities such as HIFI (Heterodyne Instrument for the Far Infrared) on the Herschel Space Observatory, ALMA (Atacama Large Millimeter Array), SOFIA (Stratospheric Observatory For Infrared Astronomy) and APEX (Atacama Pathfinder Experiment) to close to spectroscopic accuracy.The Journal of chemical physics 09/2012; 137(10):104313. · 3.09 Impact Factor -
Article: Herschel/HIFI observation of highly excited rotational lines of HNC toward IRC +10 216
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ABSTRACT: We report the detection in emission of various highly excited rotational transitions of HNC (J = 6-5 through J =12-11) toward the carbon-star envelope IRC +10 216 using the HIFI instrument on-board the Herschel Space Observatory. Observations of the J = 1-0 and J = 3-2 lines of HNC with the IRAM 30-m telescope are also presented. The lines observed with HIFI have upper level energies corresponding to temperatures between 90 and 340 degrees Kelvin, and trace a warm and smaller circumstellar region than that seen in the interferometric maps of the J = 1-0 transition, whose emission extends up to a radius of 20". After a detailed chemical and radiative transfer modeling, we find that the presence of HNC in the circumstellar envelope of IRC +10 216 is consistent with formation from the precursor ion HCNH+, which in turn is produced through several proton transfer reactions which are triggered by the cosmic-ray ionization. We also find that the radiative pumping through 21 um photons to the first excited state of the bending mode v2 plays a crucial role to populate the high-J HNC levels involved in the transitions observed with HIFI. Emission in these high-J rotational transitions of HNC is expected to be strong in regions which are warm and dense and/or have an intense infrared flux at wavelengths around 21 um.04/2012; -
Article: The quest for complex molecules in space: Laboratory spectroscopy of n-butyl cyanide, n-C4H9CN, in the millimeter wave region and its astronomical search in Sagittarius B2(N)
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ABSTRACT: The saturated n-propyl cyanide was recently detected in Sagittarius B2(N). The next larger unbranched alkyl cyanide is n-butyl cyanide. We provide accurate rest frequency predictions beyond the millimeter wave range to search for this molecule in the Galactic center source Sagittarius B2(N) and facilitate its detection in space. We investigated the laboratory rotational spectrum of $n$-butyl cyanide between 75 GHz and 348 GHz. We searched for emission lines produced by the molecule in our sensitive IRAM 30 m molecular line survey of Sagittarius B2(N). We identified more than one thousand rotational transitions in the laboratory for each of the three conformers for which limited data had been obtained previously in a molecular beam microwave study. The quantum number range was greatly extended to J ~ 120 or more and Ka > 35, resulting in accurate spectroscopic parameters and accurate rest frequency calculations up to about 500 GHz for strong to moderately weak transitions of the two lower energy conformers. Upper limits to the column densities of N <= 3 x 10E15 cm-2 and 8 x 10E15 cm-2 were derived towards Sagittarius B2(N) for the two lower energy conformers, anti-anti and gauche-anti, respectively. Our present data will be helpful for identifying n-butyl cyanide at millimeter or longer wavelengths with radio telescope arrays such as ALMA, NOEMA, or EVLA. In particular, its detection in Sagittarius B2(N) with ALMA seems feasible.04/2012; -
Article: On the physical structure of IRC+10216. Ground-based and Herschel observations of CO and CCH
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ABSTRACT: The C-rich AGB star IRC+10216 undergoes strong mass loss, and quasi-periodic density enhancements in the circumstellar matter have been reported. CO is ubiquitous in the CSE, while CCH emission comes from a spatially confined shell. With the IRAM 30m telescope and Herschel/HIFI, we recently detected unexpectedly strong emission from the CCH N=4-3, 6-5, 7-6, 8-7, and 9-8 transitions, challenging the available chemical and physical models. We aim to constrain the physical properties of IRC+10216's CSE, including the effect of episodic mass loss on the observed emission. In particular, we aim to determine the excitation region and conditions of CCH and to reconcile these with interferometric maps of the N=1-0 transition. Via radiative-transfer modelling, we provide a physical description of the CSE, constrained by the SED and a sample of 20 high-resolution and 29 low-resolution CO lines. We further present detailed radiative-transfer analysis of CCH. Assuming a distance of 150pc, the SED is modelled with a stellar luminosity of 11300Lsun and a dust-mass-loss rate of 4.0\times10^{-8}Msun/yr. Based on the analysis of 20 high resolution CO observations, an average gas-mass-loss rate for the last 1000yrs of 1.5\times10^{-5}Msun/yr is derived. This gives a gas-to-dust-mass ratio of 375, typical for an AGB star. The gas kinetic temperature throughout the CSE is described by 3 powerlaws: it goes as r^{-0.58} for r<9R*, as r^{-0.40} for 9<=r<=65R*, and as r^{-1.20} for r>65R*. This model successfully describes all 49 CO lines. We show the effect of wind-density enhancements on the CCH-abundance profile, and the good agreement of the model with the CCH N=1-0 transition and with the lines observed with the 30m telescope and HIFI. We report on the importance of radiative pumping to the vibrationally excited levels of CCH and the significant effect this has on the excitation of all levels of the CCH-molecule.01/2012; -
Article: Analysis of Herschel /HIFI observations towards W49N and G10.6−0.4 (W31C)
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ABSTRACT: As a part of the Herschel key programme PRISMAS, we have used the Herschel/HIFI instrument to observe interstellar nitrogen hydrides along the sight-lines towards eight high-mass star-forming regions in order to elucidate the production pathways leading to nitrogen-bearing species in diffuse gas. Here, we report observations towards W49N of the NH N = 1–0, J = 2–1, and J = 1–0, ortho-NH 2 N Ka,Kc J = 1 1,1 3/2–0 0,0 1/2, ortho-NH 3 J K = 1 0 –0 0 and 2 0 –1 0 , para-NH 3 J K = 2 1 –1 1 transitions, and unsuccessful searches for NH + . All detections show absorption by foreground material over a wide range of velocities, as well as absorption associated directly with the hot-core source itself. As in the previously published observations towards G10.6−0.4, the NH, NH 2 and NH 3 spectra towards W49N show strikingly similar and non-saturated absorption features. We decompose the absorption of the foreground material towards W49N into different velocity components in order to investigate whether the relative abundances vary among the velocity components, and, in addition, we re-analyse the absorption lines towards G10.6−0.4 in the same manner. Abundances, with respect to molecular hydrogen, in each velocity component are estimated using CH, which is found to correlate with H 2 in the solar neighbourhood diffuse gas. The analysis points to a co-existence of the nitrogen hydrides in diffuse or translucent interstellar gas with a high molecular fraction. Towards both sources, we find that NH is always at least as abundant as both o-NH 2 and o-NH 3 , in sharp contrast to previous results for dark clouds. We find relatively constant N(NH)/N(o-NH 3) and N(o-NH 2)/N(o-NH 3) ratios with mean values of 3.2 and 1.9 towards W49N, and 5.4 and 2.2 towards G10.6−0.4, respectively. The mean abundance of o-NH 3 is ∼2 × 10 −9 towards both sources. The nitrogen hydrides also show linear correlations with CN and HNC towards both sources, and looser correlations with CH. The upper limits on the NH + abundance indicate column densities 2–14% of N(NH), which is in contrast to the behaviour of the abundances of CH + and OH + relative to the values determined for the corresponding neutrals CH and OH. Surprisingly low values of the ammonia ortho-to-para ratio are found in both sources, ≈0.5–0.7 ± 0.1, in the strongest absorption components. This result cannot be explained by current models as we had expected to find a value of unity or higher.Astronomy and Astrophysics 01/2012; 543(145). · 4.59 Impact Factor -
Article: Spectroscopic parameters for silacyclopropynylidene, SiC2, from extensive astronomical observations toward CW Leo (IRC +10216) with the Herschel satellite
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ABSTRACT: A molecular line survey has been carried out toward the carbon-rich asymptotic giant branch star CW Leo employing the HIFI instrument on board of the Herschel satellite. Numerous features from 480 GHz to beyond 1100 GHz could be assigned unambiguously to the fairly floppy SiC2 molecule. However, predictions from laboratory data exhibited large deviations from the observed frequencies even after some lower frequency data from this survey were incorporated into a fit. Therefore, we present a combined fit of all available laboratory data together with data from radio-astronomical observations.12/2011; -
Article: Millimeter-wave spectroscopy of titanium dioxide, TiO $_ 2 $
Journal of Molecular Spectroscopy 07/2011; 268:173-176. · 1.51 Impact Factor -
Conference Proceeding: Analysis of the Rotational Spectrum of HDO in its v_2 = 0 and 1 Vibrational States up to 2.8 THz
66th International Symposium On Molecular Spectroscopy; 06/2011 -
Conference Proceeding: Analysis of New Data Sets Pertaining to the Water Molecule
66th International Symposium On Molecular Spectroscopy; 06/2011 -
Article: Detection of OH$^+$ and H$_2$O$^+$ towards Orion~KL
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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 Letters09/2010; -
Article: Herschel observations of extra-ordinary sources: Detecting spiral arm clouds by CH absorption lines
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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 Issue07/2010; -
Article: Herschel/HIFI measurements of the ortho/para ratio in water towards Sagittarius B2(M) and W31C
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ABSTRACT: We present Herschel/HIFI observations of the fundamental rotational transitions of ortho- and para-H$_2^{16}$O and H$_2^{18}$O in absorption towards Sagittarius~B2(M) and W31C. The ortho/para ratio in water in the foreground clouds on the line of sight towards these bright continuum sources is generally consistent with the statistical high-temperature ratio of 3, within the observational uncertainties. However, somewhat unexpectedly, we derive a low ortho/para ratio of $2.35 \pm 0.35$, corresponding to a spin temperature of $\sim$27~K, towards Sagittarius~B2(M) at velocities of the expanding molecular ring. Water molecules in this region appear to have formed with, or relaxed to, an ortho/para ratio close to the value corresponding to the local temperature of the gas and dust. Comment: Accepted for publication in A&A, HIFI Special Issue; 5 pages, 3 figures07/2010; -
Article: Herschel/HIFI discovery of interstellar chloronium (H$_2$Cl$^+$)
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ABSTRACT: We report the first detection of chloronium, H$_2$Cl$^+$, in the interstellar medium, using the HIFI instrument aboard the \emph{Herschel} Space Observatory. The $2_{12}-1_{01}$ lines of ortho-H$_2^{35}$Cl$^+$ and ortho-H$_2^{37}$Cl$^+$ are detected in absorption towards NGC~6334I, and the $1_{11}-0_{00}$ transition of para-H$_2^{35}$Cl$^+$ is detected in absorption towards NGC~6334I and Sgr~B2(S). The H$_2$Cl$^+$ column densities are compared to those of the chemically-related species HCl. The derived HCl/H$_2$Cl$^+$ column density ratios, $\sim$1--10, are within the range predicted by models of diffuse and dense Photon Dominated Regions (PDRs). However, the observed H$_2$Cl$^+$ column densities, in excess of $10^{13}$~cm$^{-2}$, are significantly higher than the model predictions. Our observations demonstrate the outstanding spectroscopic capabilities of HIFI for detecting new interstellar molecules and providing key constraints for astrochemical models. Comment: Accepted for publication in A&A, HIFI Special Issue; 4 pages, 2 figures, 1 table07/2010; -
Conference Proceeding: Terahertz Spectroscopy of Excited Water
65th International Symposium On Molecular Spectroscopy; 06/2010 -
Article: Terahertz spectroscopy of oxygen, O2, in its 3$Sigma$-g and 1$Delta$ electronic statesTHz Spectroscopy of O2
jqsrt. 06/2010; 111:1167-1173. -
Article: Detection of interstellar oxidaniumyl: abundant H2O+ towards the star-forming regions DR21, Sgr B2, and NGC6334
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ABSTRACT: We identify a prominent absorption feature at 1115 GHz, detected in first HIFI spectra towards high-mass star-forming regions, and interpret its astrophysical origin. The characteristic hyperfine pattern of the H2O+ ground-state rotational transition, and the lack of other known low-energy transitions in this frequency range, identifies the feature as H2O+ absorption against the dust continuum background and allows us to derive the velocity profile of the absorbing gas. By comparing this velocity profile with velocity profiles of other tracers in the DR21 star-forming region, we constrain the frequency of the transition and the conditions for its formation. In DR21, the velocity distribution of H2O+ matches that of the [CII] line at 158\mu\m and of OH cm-wave absorption, both stemming from the hot and dense clump surfaces facing the HII-region and dynamically affected by the blister outflow. Diffuse foreground gas dominates the absorption towards Sgr B2. The integrated intensity of the absorption line allows us to derive lower limits to the H2O+ column density of 7.2e12 cm^-2 in NGC 6334, 2.3e13 cm^-2 in DR21, and 1.1e15 cm^-2 in Sgr B2. Comment: Accepted for publication in A&A05/2010; -
Article: Detection of OH + and H 2 O + towards Orion KL
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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). · 4.59 Impact Factor -
Article: Accurate laboratory rest frequencies of vibrationally excited CO up to $varv = 3$ and up to 2 THz
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ABSTRACT: Astronomical observations of (sub)millimeter wavelength pure rotational emission lines of the second most abundant molecule in the Universe, CO, hold the promise of probing regions of high temperature and density in the innermost parts of circumstellar envelopes. The rotational spectrum of vibrationally excited CO up to $\varv = 3$ has been measured in the laboratory between 220 and 1940 GHz with relative accuracies up to $5.2 \times 10^{-9}$, corresponding to $\sim 5$ kHz near 1 THz. The rotational constant $B$ and the quartic distortion parameter $D$ have been determined with high accuracy and even the sextic distortion term $H$ was determined quite well for $\varv = 1$ while reasonable estimates of $H$ were obtained for $\varv = 2$ and 3. The present data set allows for the prediction of accurate rest frequencies of vibrationally excited CO well beyond 2 THz.02/2009; -
Article: The Rotational Spectrum of TiO2
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ABSTRACT: The rotational spectrum of titanium dioxide (TiO2) has been detected by laser-ablation molecular beam Fourier transform microwave spectroscopy. Thirteen b-type rotational transitions up to J = 9 and Ka = 4 were measured for the most abundant isotopic species 48TiO2 in the frequency range 7-42 GHz with accuracies of 1-10 kHz, allowing for the precise determination of rotational and centrifugal distortion parameters. In addition, eight and six rotational transitions of the rare isotopic species 46TiO2 and 50TiO2, respectively, have been recorded in the same frequency range. From the derived spectroscopic parameters, rest frequencies of TiO2 can now be calculated to better than 1 km s−1 in equivalent radial velocity up to fairly high J and Ka at millimeter wavelengths, enabling radioastronomical searches for this stable, highly polar transition metal dioxide in space. Preliminary results of two searches for TiO2 in space are presented.The Astrophysical Journal 12/2008; 676(2):1367. · 6.02 Impact Factor
Top co-authors
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Institutions
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2000–2011
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Universität Köln
- • I. Physikalisches Institut
- • II. Physikalisches Institut
Köln, North Rhine-Westphalia, Germany
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2006
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Harvard University
- Harvard-Smithsonian Center for Astrophysics
Boston, MA, USA
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