Scientific Results in Press

Carbon budget and carbon chemistry in Photon Dominated Regions

Teyssier D.$(^{1,2})$, Fossé D.$(^{2})$, Gerin M.$(^{2})$, Pety J.$(^{2,3})$, Abergel A$(^{4})$.and Roueff E.$(^{5})$
$(^{1})$Space Research Organization Netherlands, PO Box 800, 9700 AV Groningen, The Netherlands $(^{2})$Laboratoire d'Étude du Rayonnement et de la Matière, UMR 8112, CNRS, École Normale Supérieure et Observatoire de Paris, 24 rue Lhomond, 75231 Paris Cedex 05, France, $(^{3})$Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 St Martin d'Hères, France, $(^{4})$Institut d'Astrophysique Spatiale, Université Paris-Sud, Bât. 121, 91405 Orsay Cedex, France, $(^{5})$LUTH, UMR8102 du CNRS, Observatoire de Paris, Place J. Janssen, 92195 Meudon Cedex, France

Abstract:
We present a study of small carbon chains and rings in Photon Dominated Regions (PDRs) performed at millimetre wavelengths. Our sample consists of the Horsehead nebula (B33), the $\rho$ Oph L1688 cloud interface, and the cometary-shaped cloud IC 63. Using the IRAM 30-m telescope, the SEST and the Effelsberg 100-m telescope, we mapped the emission of C$_2$H, c-C$_3$H$_2$ and C$_4$H, and searched for heavy hydrocarbons such as c-C$_3$H, l-C$_3$H, l-C$_3$H$_2$, l-C$_4$H$_2$ and C$_6$H. The large scale maps show that small hydrocarbons are present until the edge of all PDRs, which is surprising as they are expected to be easily destroyed by UV radiation. Their spatial distribution reasonably agrees with the aromatic emission mapped in mid-IR wavelength bands. C$_2$H and c-C$_3$H$_2$ correlate remarkably well, a trend already reported in the diffuse ISM (Lucas & Liszt 2000). Their abundances relative to H$_2$ are relatively high and comparable to the ones derived in dark clouds such as L134N or TMC-1, known as efficient carbon factories. The heavier species are however only detected in the Horsehead nebula at a position coincident with the aromatic emission peak around 7 $\mu$m. In particular, we report the first detection of C$_6$H in a PDR. We have run steady-state PDR models using several gas-phase chemical networks (UMIST95 and the New Standard Model) and conclude that both networks fail in reproducing the high abundances of some of these hydrocarbons by an order of magnitude. The high abundance of hydrocarbons in the PDR may suggest that the photo-erosion of UV-irradiated large carbonaceous compounds could efficiently feed the ISM with small carbon clusters or molecules. This new production mechanism of carbon chains and rings could overcome their destruction by the UV radiation field. Dedicated theoretical and laboratory measurements are required to understand and implement these additional chemical routes.


Appeared in: A&A 417, 135

High-spatial-resolution CN and CS observation of two regions of massive star formation

H. Beuther$(^{1})$, P. Schilke$(^{2})$ and F. Wyrowski$(^{2})$
$(^{1})$Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, $(^{2})$Max-Planck-Institute for Radioastronomy, Auf dem Hügel 69, 53121 Bonn, Germany

Abstract:
Molecular line CN, CS and mm continuum observations of two intermediate- to high-mass star-forming regions - IRAS20293+3952 and IRAS19410+2336 - obtained with the Plateau de Bure Interferometer at high spatial resolution reveal interesting characteristics of the gas and dust emission. In spite of the expectation that the CN and CS morphology might closely follow the dense gas traced by the dust continuum, both molecules avoid the most central cores. Comparing the relative line strengths of various CN hyperfine components, this appears not to be an opacity effect but to be due to chemical and physical effects. The CN data also indicate enhanced emission toward the different molecular outflows in the region. Regarding CS, avoiding the central cores can be due to high optical depth, but the data also show that the CS emission is nearly always associated with the outflows of the region.

Therefore, neither CS nor CN appear well suited for dense gas and disk studies in these two sources, and we recommend the use of different molecules for future massive disk studies. An analysis of the 1 and 3mm continuum fluxes toward IRAS20293+3952 reveals that the dust opacity index $\beta$ is lower than the canonical value of 2. Tentatively, we identify a decreasing gradient of $\beta$ from the edge of the core to the core center. This could be due to increasing optical depth toward the core center and/or grain growth within the densest cores and potential central disks. We detect 3mm continuum emission toward the collimated outflow emanating from IRAS20293+3952. The spectral index of $\alpha \sim 0.8$ in this region is consistent with standard models for collimated ionized winds.

Accepted for publication in ApJ

The disrupted molecular envelope of Frosty Leo

A. Castro-Carrizo$(^{1})$, V. Bujarrabal$(^{2})$, C. Sanchez Contreras$(^{3})$, R. Sahai$(^{4})$, J. Alcolea$(^{2})$
$(^{1})$Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, 38406 St. Martin d'Hères, France, $(^{2})$Observatorio Astronómico Nacional, c/Alfonso XII 3, 28014 Madrid, Spain, $(^{3})$California Institute of Technology, Astronomy Department, MS 105-24, 1200 East California Boulevard, Pasadena, CA 91125, USA, $(^{4})$Jet Propulsion Laboratory, California Institute of Technology, MS 183-900, 4800 Oak Grove Drive, Pasadena, CA 91109,USA

Abstract:
We present maps of CO emission in the protoplanetary nebula Frosty Leo. Observations of the rotational transitions $^{12}$CO $J$=2-1 and 1-0 have been obtained with the IRAM interferometer and the OVRO array. The molecular envelope of Frosty Leo is found to be complex and compact; most of the gas extends $\mathrel{\rlap{\lower4pt\hbox{\hskip1pt$\sim$}} \raise1pt\hbox{$<$}}$ 6 $^{\prime\prime}$ and shows a structure that is very different to the extended optical nebula. It is composed of a central ring-like structure, whose symmetry axis is inclined $\sim$ $-40$ with respect to the sky plane and expands at speeds of up to $\sim$ 30 kms$^{-1}$, and high-velocity jets distributed along the symmetry axis of the ring, which reach expansion velocities as high as $\sim$ 75 kms$^{-1}$. The symmetry axis of the molecular jets in the plane of the sky coincides with the direction of some jet$-$like features seen in the optical, which are not aligned at all with the main symmetry axis of the optical nebula. The brightness distribution of the ring presents a clumpy structure. We have modeled the spatio-kinematical distribution of, and the excitation conditions in, the molecular envelope. For both transitions, the $^{12}$CO emission is found to be very optically thick in the center of the nebula. From our best-fit model, we find that the nebular particle density varies between $\sim$ 10$^{5}$ cm$^{-3}$ and $\sim$ 10$^{3}$ cm$^{-3}$, and that the rotational temperature is very low, $\sim$ 10 K. The kinematical lifetime of the molecular jets is $\sim$ 1700 yr, long in comparison with the lifetime of the post-AGB winds of most PPNe. It is very remarkable that the bulk of the gas accelerated during the post-AGB phase of Frosty Leo is located within the central ring, reaching expansion velocities of up to $\sim$ 30 kms$^{-1}$. The central ring-like distribution of Frosty Leo is probably not the undisrupted remnant of the previous AGB envelope (as found for most PPNe), but its dynamics likely result from multiple post-AGB interactions.

Accepted for publication in A&A

Deuterated Thioformaldehyde in the Barnard 1 Cloud

N. Marcelino$(^{1})$, J. Cernicharo$(^{2})$, E. Roueff$(^{3})$, M. Gerin$(^{4})$, R. Mauersberger$(^{1})$
$(^{1})$IRAM, Av. Divina Pastora, 7, 18012 Granada, Spain, $(^{2})$DAMIR, IEM-CSIC, 28006 Madrid, Spain, $(^{3})$LUTH (CNRS/UMR8102 and Observatoire de Paris), place J. Janssen, 92195 Meudon cedex France, $(^{4})$LERMA (CNRS/UMR 8112 - Observatoire de Paris and Ecole Normale Superieure), 24 Rue Lhomond, 75231 Paris cedex 05, France

Abstract:
We present observations of the singly and doubly deuterated species of thioformaldehyde, HDCS and D$_2$CS, towards the dark cloud Barnard 1. This is the first detection of D$_2$CS in Space and in dense and cold prestellar regions. Column densities obtained using rotational diagrams and a Large Velocity Gradient model show an extremely high D-enhancement in thioformaldehyde in Barnard 1. Although the column density of H$_2$CS is smaller than that of H$_2$CO, both species show similar D-enhancements in their singly and doubly deuterated species. A chemical model -including multiply deuterated species- has been used in order to interpret the observations.

Predicted rotational frequencies from laboratory data for HDCS and D$_2$CS are significantly in error when compared to the observed frequencies in Space. Consequently, we have derived new rotational constants for these two species and for H$_2$CS and H$_2$C$^{34}$S using the observed frequencies in Barnard 1. The new rotational constants allow to predict the rotational transitions of these species with the accuracy needed for the narrow line emerging from dark clouds. Rotational constants for HDCS and D$_2$CS have been obtained from the observed transitions in the laboratory and in Space.

Based on observations carried out with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

Accepted for publication in ApJ

22 GHz tunable Bandpass Filters based on Niobium MEMS

M. Schicke$(^{1})$, A. Navarrini$(^{2})$, K. F. Schuster$(^{1})$
$(^{1})$Institute for Radio Astronomy in the Millimeter range (IRAM), 300 rue de la Piscine, 38406 St. Martin d Hères, France, $(^{2})$Radio Astronomy Lab, University of California, 601 Campbell Hall, Berkeley CA 94720-3411, USA

Abstract:
We present the design of two 22 GHz tunable bandpass filters based on variable capacitors (in Niobium MEMS technology) realized as short sections of superconductive lines with properties similar to microstrips. The air gap between the top electrode (the microbridge) and the bottom electrode of the thin film Niobium (Nb) microstrips can be varied by $\propto 30$% through the electrostatic force generated by a DC bias voltage (Fig. 9). Electromagnetic simulation of the two filters predicts a tuning range of $\propto 11$% and $\propto 14$% of the central filter frequency. One goal of this development is to demonstrate the application of Nb microbridges for variable filters at 22 GHz in view of a transfer to several hundreds of GHz. All steps of the low temperature ($< 150^\circ$C) fabrication procedure are compatible with the fabrication of Nb- Al/AlOx-Nb SIS tunnel diodes, used in heterodyne high frequency mixers operated at 4 K. This fabrication procedure sets limits to the dimensions of the microbridges.

Figure 9: Nb air bridges, $5 \mu$m high, $100 \mu$m long and $100 \mu$m wide. The Nb film is 700 nm thick (240 nm in the inset). The inset shows the bending of the bridge layer and the reduced height due to stress in the Nb film.

Appeared in Proc. SPIE Astronomical Instr., Glasgow, Scotland, 2004

Sulfur chemistry and isotopic ratios in the starburst galaxy NGC253

S. Martín$(^{1})$, J. Martín-Pintado$(^{2})$ , R. Mauersberger$(^{1})$ , C. Henkel$(^{3})$, S. García-Burillo$(^{4})$
$(^{1})$Instituto de Radioastronomía Milimétrica (IRAM), Avda. Divina Pastora 7 NC, 18012 Granada, Spain, $(^{2})$Departamento de Astrofisíca Molecular e Infrarroja, Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006 Madrid, Spain, $(^{3})$Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany, $(^{4})$Observatorio Astronómico Nacional (OAN), Apartado 1143, 28800 Alcalá de Henares, Madrid, Spain

Abstract:
Based on observations of the most abundant sulfur-bearing molecules (H$_2$S, CS, NS, SO, H$_2$CS, OCS, and SO$_2$) carried out with the IRAM 30m telescope and SEST, we present the first analysis of the sulfur chemistry of an extragalactic source, the nuclear region of the starburst galaxy NGC253. This is the first time that H$_2$S and, tentatively, H$_2$CS are detected towards the nucleus of a starburst galaxy.

Source averaged fractional abundances of these molecules are a few 10$^{-9}$, except for CS and OCS which are more abundant (10$^{-8}$). Sulfur isotopic ratios, $^{32}$S/$^{34}$S$\sim$8$\pm 2$ and $^{34}$S/$^{33}$S$>$9, are measured through observations of $^{13}$CS, C$^{34}$S, and C$^{33}$S. A comparison with the observed relative abundances towards different prototypical Galactic sources suggests that the chemical composition of NGC253 is similar to that found towards the molecular clouds complexes like SgrB2 in the nuclear region of the Milky Way. The large overabundance of OCS compared to the predictions of time-dependent sulfur chemistry models supports the idea that OCS is likely injected into the gas phase from the grain mantles by low velocity shocks.

Accepted for publication in ApJ

The polarization of mm methanol masers

H. Wiesemeyer$(^{1})$, C. Thum$(^{1})$ and C. M. Walmsley$(^{2})$
$(^{1})$Institut de Radio Astronomie Millimétrique, 300 Rue de la Piscine, F 38406 Saint Martin d'Hères, France, $(^{2})$Osservatorio Astrofisico di Arcetri, Large E. Fermi, 5, I-50125 Firenze, Italy

Abstract:
We present a survey of the polarization properties of mm-wavelength methanol masers, comprising both classes, and transitions from 84.5 to 157.0GHz. Linear polarization is found in more than half of the observed objects, and circular polarization is tentatively detected in two sources. Class I and Class II CH$_3$OH masers show similar polarization properties. The largest linear polarization is found in the 133GHz Class I maser towards L379 (39.5%), and in the 157GHz Class II maser towards G9.62+0.19 (36.7%). The spectral profiles of the polarization angle of Class I masers are mostly flat, except for two sources showing a linearslope. Since the mm-line methanol masers are expected to be weakly (or not) saturated, we suggest that the stronger fractional polarizations found by us are enhanced by anisotropic pumping and radiative losses. In NGC7538, we find, for both maser classes, a good agreement between our polarization angles, and those measured for the submillimeter dust continuum. This can be taken as evidence for magnetic alignment of dust grains. It is also possible that an unsaturated maser with equally populated magnetic substates simply amplifies polarized continuum seed radiation. For Class II masers, the polarization properties of the various velocity components towards a given source with detectable polarization are quite homogeneous. A possible explanation is discussed. Since methanol is non-paramagnetic, the circular polarization of the unsaturated maser emission can only be due to variations of the angle between the magnetic field and the line of sight along the maser propagation path.

Accepted for publication in A&A, astro-ph/0408446

Extending the radio spectrum of magnetic chemically peculiar stars to the mm range

Leone F.$(^{1})$, Trigilio C.$(^{2})$, Neri R.$(^{3})$, Umana G.$(^{2})$
$(^{1})$INAF - Osservatorio Astrofisico di Catania, Via S. Sofia n. 78, 95123 Catania, Italy, $(^{2})$Istituto di Radioastronomia del C.N.R., sezione di Noto, PO Box 141, 96017 Noto, Italy, $(^{3})$Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 Saint Martin d'Hères, France

Abstract:
Magnetic chemically peculiar (MCP) stars can present radio emission at centimetre wavelengths. The steep decrement of the dominant dipolar component of the photospheric magnetic field results in each radio frequency being mainly emitted in a well localised shell of the circumstellar region. To explore the most internal regions of the magnetosphere, observations of a sample of eleven MCP stars known to be radio sources in the 1.4-22.5 GHz range were carried out at 87.7 GHz with the IRAM interferometer. Millimeter emission, with a flux density at about $4\times$ the sensitivity limit of our observations, was detected towards two of the stars: HD 35298 and HD 124224. Combining our mm-observations with previous cm-observations, it appears that MCP stars with a relatively weak magnetic field present a radio spectrum that increases with frequency up to 22.5 GHz and then decreases towards the mm range. In presence of strong fields, the radio spectrum is always decreasing with frequency. A comparison of the observed cm-mm spectrum of HD 124224 with results of numerical simulations of the gyrosynchrotron emission suggests that circumstellar regions emitting in the mm-range cannot present magnetic fields larger than 1-2 kG.

Appeared in: A&A 423, 1095

Near-Arcsecond Resolution Observations of the Hot Corino of the Solar-Type Protostar IRAS 16293-2422

Bottinelli S.$(^{1,2})$, Ceccarelli C.$(^{1})$, Neri R.$(^{3})$, Williams J. P.$(^{2})$, Caux E.$(^{4})$, Cazaux S.$(^{5})$, Lefloch B.$(^{1})$, Maret S.$(^{1})$, Tielens A.G.G.M.$(^{6})$
$(^{1})$Laboratoire d'Astrophysique de l'Observatoire de Grenoble, BP 53, 38041 Grenoble, Cedex 9, France, $(^{2})$Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, $(^{3})$Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint Martin d'Hères, France, $(^{4})$Centre d'Etude Spatiale des Rayonnements, CNRS-UPS, 9 Avenue du Colonel Roche, BP 4346, 31028 Toulouse, Cedex 4, France, $(^{5})$INAF, Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi, 5 I-50125 Florence, Italy, $(^{6})$Kapteyn Astronomical Institute, P.O. Box 800, 9700 AV Groningen, Netherlands

Abstract:
Complex organic molecules have previously been discovered in solar-type protostars, raising the questions of where and how they form in the envelope. Possible formation mechanisms include grain mantle evaporation, the interaction of the outflow with its surroundings, and/or the impact of UV/X-rays inside the cavities. In this Letter we present the first interferometric observations of two complex molecules, CH$_3$CN and HCOOCH$_3$, toward the solar-type protostar IRAS 16293-2422. The images show that the emission originates from two compact regions centered on the two components of the binary system. We discuss how these results favor the grain mantle evaporation scenario, and we investigate the implications of these observations for the chemical composition and physical and dynamical state of the two components.

Appeared in: ApJ 617, L69

Atomic carbon in PSS 2322+1944, a quasar at redshift 4.12

Pety J.$(^{1,2})$, Beelen A.$(^{3})$, Cox P.$(^{3})$, Downes D.$(^{1})$, Omont A.$(^{4})$, Bertoldi F.$(^{5})$, Carilli C. L.$(^{6})$
$(^{1})$IRAM, 300 rue de la Piscine, 38406 St-Martin-d'Hères, France, $(^{2})$LERMA, Observatoire de Paris, 75014 Paris, France, $(^{3})$Institut d'Astrophysique Spatiale, Université de Paris Sud, 91405 Orsay Cedex, France, $(^{4})$Institut d'Astrophysique de Paris, CNRS and Université de Paris VI, 98bis Bd. Arago, 75014 Paris, France, $(^{5})$Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany, $(^{6})$National Radio Astronomy Observatory, PO Box, Socorro, NM 87801, USA

Abstract:
We report the detection of the ${^3}P_1\rightarrow {^3}P_0$ fine-structure line of neutral carbon in the z=4.12 quasar PSS 2322+1944, obtained at the IRAM Plateau de Bure interferometer. The [C II] ${^3}P_1- {^3}P_0$ line is detected with a signal-to-noise ratio of $\propto 6$ with a peak intensity of $\approx 2.5$ mJy and a velocity-integrated line flux of $0.81\pm 0.12$ Jy km s$^{-1}$. Assuming an excitation temperature of 43 K (equal to the dust temperature), we derive a mass of neutral carbon (corrected for magnification) of $M_{C I} \approx 1.2\times 10^7$M$_\odot$. In PSS 2322+1944, the cooling due to C is about 6 times smaller than for CO, whereas the CO and C cooling represents $\approx 10^{-4}$ of the far-infrared continuum and more than half of the cooling due to C$^+$.

Appeared in A&A 428, L21