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Subsections
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
Abstract:
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 (
K)
molecular component toward all galaxies studied. The tentatively
detected
(J,K)=(9,9) line is evidence for an even warmer (K)
component toward IC342. Toward NGC253, IC342 and Maffei2 the
global beam averaged NH3 abundances are
,
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 (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
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
Abstract:
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 ,
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
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
Abstract:
We report on the design of a wideband Orthomode Transducer (OMT)
integrated with two 90
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.
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
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.
F.Mattiocco(1)
(1)Institut de Radio Astronomie Millimétrique, 300 rue de la
Piscine, Domaine Universitaire de Grenoble,
38406 St Martin d'Heres, France
Abstract:
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 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
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
Abstract:
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
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
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
Abstract:
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,
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
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
Abstract:
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
,
stellar luminosity
,
stellar
temperature
,
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
and an amplitude of
.
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
and an average mass loss
rate of
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: New Preprints
Up: IRAM Newsletter 56 (August 2003)
Previous: VLBI: what changes compared
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