next up previous
Next: New Preprints Up: IRAM Newsletter 56 (August 2003) Previous: VLBI: what changes compared


Scientific Results in Press

Dense gas in nearby galaxies -
XV. Hot ammonia in NGC253, Maffei2 and IC342

R.Mauersberger(1), C.Henkel(2), A.Weiß(1,3), A.B.Peck(2,4) and Y. Hagiwara(2,5)
(1)Instituto de Radioastronomía Milimétrica (IRAM), Avda. Divina Pastora 7NC, E-18012 Granada, Spain, (2)Max-Planck-Institut für Radioastronomie, Auf dem Hügel 71, D-53121 Bonn, Germany, (3)Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 69, D-53121 Bonn, Germany (4)Smithsonian Submillimeter Array (SMA), PO Box 824, Hilo, HI 96721, USA, (5)ASTRON, Westerbork Observatory, P.O. Box 2, 7990AA Dwingeloo, The Netherlands

The detection of NH3 inversion lines up to the (J,K)=(6,6) level is reported toward the central regions of the nearby galaxies NGC253, Maffei2, and IC342. The observed lines are up to 406K (for (J,K)=(6,6)) and 848K (for the (9,9) transition) above the ground state and reveal a warm ( $T_{\rm kin}= 100 \ldots 140 $K) molecular component toward all galaxies studied. The tentatively detected (J,K)=(9,9) line is evidence for an even warmer ($>400\,$K) component toward IC342. Toward NGC253, IC342 and Maffei2 the global beam averaged NH3 abundances are $1-2\,10^{-8}$, while the abundance relative to warm H2 is around 10-7. The temperatures and NH3 abundances are similar to values found for the Galactic central region. C-shocks produced in cloud-cloud collisions can explain kinetic temperatures and chemical abundances. In the central region of M82, however, the NH3 emitting gas component is comparatively cool ($\sim 30\,$K). It must be dense (to provide sufficient NH3 excitation) and well shielded from dissociating photons and comprises only a small fraction of the molecular gas mass in M82. An important molecular component, which is warm and tenuous and characterized by a low ammonia abundance, can be seen mainly in CO. Photon dominated regions (PDRs) can explain both the high fraction of warm H2 in M82 and the observed chemical abundances.

Astronomy and Astrophysics, in Press

Design of 129-174 GHz SSB SIS Mixer for Band 2 of New Generation Receiver of IRAM PdB Interferometer

A. Navarrini(1), B. Lazareff(2)
(1)Radio Astronomy Lab (RAL), University of California, Berkeley, CA 94720-3411, USA. (2)Institut de Radio Astronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 St Martin d'Hères, France

We present the design of a backshort tuned Single Side Band (SSB) SIS mixer covering the frequency range 129-174 GHz, for Band 2 of New Generation Receiver of IRAM's Plateau de Bure Interferometer. A stability criterion for an SSB SIS mixer has been derived using the standard quantum theory of mixing and applied to the design. The mixer is based on a wideband single ended probe transition from WR6 full-height waveguide to microstrip line. The RF signal is coupled in a series array of two Nb/Al-AlOx/Nb junctions, each having an area of 1.6 x 1.6 $\mu m^2$, and a critical current density of jc=4 kA/cm2. A parallel inductor tunes out the reactive part of the series combination of the SIS array with a capacitive stub that provides a ground for the RF and a path for the IF output. The intrinsic capacitance and inductance of the chip have been kept to a minimum value to achieve 4 GHz IF band. A receiver noise below 15 K (quasi-SSB, image gain less than -14 dB) is estimated over the 129-174 GHz band. The mixer can be operated in DSB mode with low noise and stable operation.

Accepted for Publication in: Proceedings of the 14th International Symposium on Space Terahertz Technology, 22-24 April 2003, Tucson, AZ, USA

Design of a Dual Polarization SIS Sideband Separating Receiver based on waveguide OMT for the 275-370 GHz frequency band

A. Navarrini(1), M. Carter(2)
(1)Radio Astronomy Lab (RAL), University of California, Berkeley, CA 94720-3411, USA. (2)Institut de Radio Astronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 St Martin d'Hères, France

We report on the design of a wideband Orthomode Transducer (OMT) integrated with two 90$^\circ $ waveguide hybrid couplers and four 16 dB branch-guide LO directional couplers for the 275-370 GHz frequency band. The device allows the sideband separation for each of two mutually orthogonal polarizations to be achieved by employing four fixed-tuned SIS DSB mixer-units. The central part of the system is based on a Boifot type junction OMT as realized by Wollack, and is similar to the design discussed by Narayanan. The proposed device takes advantage of the -3 dB splitting operated over one polarization of the RF input power that is delivered in the two side arms of the Boifot orthomode junction by a thick septum parallel to the E-field of the considered polarization; the RF signals of the split polarization are added through two 16 dB branch-guide couplers to the signals of a Local Oscillator (LO) that enter the Boifot orthomode junction side arms with phase difference of 90$^\circ $. The RF and LO are applied in two fixed-tuned DSB SIS mixers whose IF outputs are recombined in a 4-8 GHz IF 90$^\circ $ quadrature hybrid, so that the resulting downconverted upper (USB) and lower (LSB) sideband of the considered polarization are separated. The LO quadrature hybrid, the 16 dB waveguide couplers, and the idea of assembling these elements to get a single polarization sideband separating receiver (2SB) are adopted from the work of Claude. The RF signal of the orthogonal polarization passing the septum is divided using an in-phase power divider and delivered through side arms perpendicular to the previous. The sideband separation for this second polarization is realized using the same scheme as for the first polarization. The advantage of the device is to exploit the -3 dB splitting operated over each of two mutually orthogonal polarizations by the waveguide OMT junction and power divider, as required for sideband separation, and to avoid the problem of signals recombination of classical waveguide OMTs. The proposed dual polarization sideband separating receiver design results directly from the intrinsic properties of a classical Boifot orthomode junction. Both the OMT junction and the in-phase power splitter have been optimised using a 3D electromagnetic simulator. Return loss better than 16 dB, and trasmitted power to the four side arms within 0.1 dB of the reference value at -3 dB of the single polarization input excitation are expected over the RF band of design. Because of symmetry properties, the structure has not cross-polarization. Although the 3D structure looks complex, the proposed device can easily be constructed using conventional split-block techniques with reliability and cost-effectiveness.

Accepted for Publication in: Proceedings of the 14th. International Symposium on Space Terahertz Technology, 22-24 April 2003, Tucson, AZ, USA.


(1)Institut de Radio Astronomie Millimétrique, 300 rue de la Piscine, Domaine Universitaire de Grenoble, 38406 St Martin d'Heres, France

The design of a 210-320 GHz multi-hole directional coupler is described. The coupler performance is measured with a millimeter vector network analyser across the band 205-350 GHz and compared with simulations. The coupler consists of two waveguides whose broad walls are separated by a thin metal sheet with an array of circular holes according to a Chebyshev distribution of couplings. The coupling is 11 dB with a typical variation of $\pm 2$ dB across the WR3 band and the isolation is more than 25 dB.

International Journal of Infrared and Millimeter Waves, Vol. 24, Number 7, July 2003

The young cluster in the CB34 globule - II. The clumps and the outflows

C. Codella(1) and F. Scappini(2)
(1)Istituto di Radioastronomia, CNR, Sezione di Firenze, Largo E. Fermi 5, 50125 Firenze, Italy, (2)Istituto per lo Studio dei Materiali Nanostrutturati, CNR, Sezione di Bologna, Via P. Gobetti 101, 40129 Bologna, Italy

The molecular environment of the young cluster of Class 0 YSOs located in the globule CB34 has been investigated through a multiline millimetre survey. The CO, 13CO, C18O, and CS emissions show that the present star forming process is concentrated into three molecular clumps with size of $\sim$ 0.25 pc which are embedded in a cool more extended gas. The spatial distribution of the high-velocity emission reveals the occurrence of multiple outflows which are associated with the brightest YSOs.

The interaction of the outflows with the molecular clumps has been studied by using the abundances of products of shocked chemistry such as SiO and SO. The abundances of these molecules at the high velocities of the outflows can be used to further specify, with respect to the continuum results, the characteristics of the Class 0 YSOs. In particular, one of the YSOs which does not show the presence of SiO and SO at high velocities is thought to be in a more evolved phase where most of the molecules produced at high velocities in the shocked regions have been already destroyed.

MNRAS, in press

Mass-loss from dusty, low outflow-velocity AGB stars
I. Wind structure and mass-loss rates

J.M. Winters(1,2), T. Le Bertre(2), K.S. Jeong(2), L.-Å. Nyman(3,4), and N. Epchtein(5)
(1)IRAM, 300 rue de la Piscine, 38406 St. Martin d'Hères, France, (2)LERMA, UMR 8112, Observatoire de Paris, 61 av. de l'Observatoire, F-75014 Paris, France, (3)Swedish-ESO Submillimetre Telescope, European Southern Observatory, Casilla 19001, Santiago 19, Chile, (4)Onsala Space Observatory, SE-439 92 Onsala, Sweden, (5)Observatoire de la Côte d'Azur, BP 4229, 06304, Nice cedex 4, France

We present the first results of a CO(2-1), (1-0), and 86GHz SiO maser survey of AGB stars, selected by their weak near-infrared excess. Among the 65 sources of the present sample we find 10 objects with low CO outflow velocities, $v_{\rm exp} \leq 5\,$kms-1. Typically, these sources show (much) wider SiO maser features. Additionally, we get 5 sources with composite CO line profiles, i.e. a narrow feature is superimposed on a broader one, where both components are centered at the same stellar velocity. The gas mass-loss rates, outflow velocities and velocity structures suggested by these line profiles are compared with the results of hydrodynamical model calculations for dust forming molecular winds of pulsating AGB stars. The observations presented here give support to our recent low outflow-velocity models, in which only small amounts of dust are formed. Therefore, the wind generation in these models is dominated by stellar pulsation. We interpret the composite line profiles in terms of successive winds with different characteristics. Our hydrodynamical models, which show that the wind properties may be extremely sensitive to the stellar parameters, support such a scenario.

accepted by Astronomy & Astrophysics

Self-consistent modeling of the outflow from the O-rich Mira IRC -20197

K.S. Jeong (1,2,3), J.M. Winters(4,1), T. Le Bertre(1)and E. Sedlmayr(2)
(1)LERMA, UMR 8112, Observatoire de Paris, 61 av. de l'Observatoire, F-75014 Paris, France, (2)Technische Universität Berlin, Zentrum für Astronomie und Astrophysik, Sekr. PN 8-1, Hardenbergstr. 36, D-10623 Berlin, Germany, (3)Deutsches Zentrum für Luft- und Raumfahrt, Institute of Space Sensor Technology and Planetary Exploration, Rutherfordstr. 2, D-12489 Berlin, Germany (4)IRAM, 300 rue de la Piscine, 38406 St. Martin d'Hères, France

We present a self-consistent time-dependent model for the oxygen-rich Mira variable IRC -20197. This model includes a consistent treatment of the interactions among hydrodynamics, thermodynamics, radiative transfer, equilibrium chemistry, and heterogeneous dust formation with TiO2 nuclei. The model is determined by the stellar parameters, stellar mass ${\rm M_{*} = 1.3\, M_{\odot}}$, stellar luminosity ${\rm L_{*} = 1.4\,10^{4}\, L_{\odot}}$, stellar temperature ${\rm T_{*} = 2400\, K}$, and solar abundances of the elements. The pulsation of the star is simulated by a piston at the inner boundary where the velocity varies sinusoidally with a period of ${\rm P = 636\, d}$ and an amplitude of $\Delta v_{p} = 8\, {\rm
km\,s^{-1}}$. Based on the atmospheric structure resulting from this hydrodynamic calculation at different phases, we have performed angle- and frequency-dependent continuum radiation transfer calculations, which result in the spectral energy distributions at different phases of the pulsation cycle and in synthetic light curves at different wavelengths. These are in good agreement with the infrared observations of IRC -20197. The model yields a time averaged outflow velocity of ${\rm 11.9\, km\,s^{-1}}$ and an average mass loss rate of $7.3\,10^{-6}\, {\rm M_{\odot}yr^{-1}}$ which are in good agreement with the values derived from radio observations. Furthermore, the chemical composition of the resulting grains is discussed.

Appeared in: A&A 407, 191-206 (2003)

next up previous
Next: New Preprints Up: IRAM Newsletter 56 (August 2003) Previous: VLBI: what changes compared