R. Gusten

Max Planck Institute for Radio Astronomy, Bonn, North Rhine-Westphalia, Germany

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Publications (23)

  • A. Gusdorf · R. Gusten · K. M. Menten · [...] · al
    [Show abstract] [Hide abstract] ABSTRACT: Context. OH is a key molecule in H2O chemistry, a valuable tool for probing physical conditions, and an important contributor to the cooling of shock regions around high-mass protostars. OH participates in the re-distribution of energy from the protostar towards the surrounding Interstellar Medium. Aims. Our aim is to assess the origin of the OH emission from the Cepheus A massive star-forming region and to constrain the physical conditions prevailing in the emitting gas. We thus want to probe the processes at work during the formation of massive stars. Methods. We present spectrally resolved observations of OH towards the protostellar outflows region of Cepheus A with the GREAT spectrometer onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) telescope. Three triplets were observed at 1834.7 GHz, 1837.8 GHz, and 2514.3 GHz (163.4 μm, 163.1 μm between the 2Π1/2 J = 1/2 states, and 119.2 μm, a ground transition between the 2Π3/2 J = 3/2 states), at angular resolutions of 16″3, 16″3, and 11″9, respectively. We also present the CO (16-15) spectrum at the same position. We compared the integrated intensities in the redshifted wings to the results of shock models. Results. The two OH triplets near 163 μm are detected in emission, but with blending hyperfine structure unresolved. Their profiles and that of CO (16-15) can be fitted by a combination of two or three Gaussians. The observed 119.2 μm triplet is seen in absorption, since its blending hyperfine structure is unresolved, but with three line-of-sight components and a blueshifted emission wing consistent with that of the other lines. The OH line wings are similar to those of CO, suggesting that they emanate from the same shocked structure. Conclusions. Under this common origin assumption, the observations fall within the model predictions and within the range of use of our model only if we consider that four shock structures are caught in our beam. Overall, our comparisons suggest that all the observations might be consistently fitted by a J-type shock model with a high pre-shock density (nH> 105 cm-3), a high shock velocity (νs ≃ 25 km s-1), and with a filling factor of the order of unity. Such a high pre-shock density is generally found in shocks associated to high-mass protostars, contrary to low-mass ones.
    Article · Sep 2015 · Astronomy and Astrophysics
  • [Show abstract] [Hide abstract] ABSTRACT: We present the first superconducting hot electron bolometer (HEB) waveguide mixer operating at 4.7 THz. The 5.5-nm-thick, 300-nm-long, and 3600-nm-wide NbN HEB microbridge is integrated into a normal metal (Au) planar circuit on a 2 m thick silicon substrate. This circuit is integrated in a 24 m 48 m 21 m waveguide cavity and a 14 m 7 m 200 m substrate channel, which is directly machined into a CuTe alloy block. The power spectrum of the HEB mixer, measured with a Fourier transform spectrometer, is in good agreement with the results of 3-D EM circuit simulation. Measured mixer performance shows a state-of-the-art double sideband noise temperature of 1100 K, averaged over the IF bandwidth of 0.2–3.5 GHz. The 3-dB noise roll-off is 3.5 GHz. This mixer is used in the German REceiver for Astronomy at Terahertz frequencies (GREAT) at the airborne Stratospheric Observatory for Far Infrared Astronomy (SOFIA).
    Article · Mar 2015 · IEEE Transactions on Terahertz Science and Technology
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    [Show abstract] [Hide abstract] ABSTRACT: We probe the column densities and masses traced by the ionized and neutral atomic carbon with spectrally resolved maps, and compare them to the diffuse and dense molecular gas traced by [C I] and low-$J$ CO lines toward the star-forming region M17SW. We mapped a 4.1pc x 4.7pc region in the [C I] 609 m$\mu$ line using the APEX telescope, as well as the CO isotopologues with the IRAM 30m telescope. We analyze the data based on velocity channel maps that are 1 km/s wide. We correlate their spatial distribution with that of the [C II] map obtained with SOFIA/GREAT. Optically thin approximations were used to estimate the column densities of [C I] and [C II] in each velocity channel. The spatial distribution of the [C I] and all CO isotopologues emission was found to be associated with that of [C II] in about 20%-80% of the mapped region, with the high correlation found in the central (15-23 km/s ) velocity channels. The excitation temperature of [C I] ranges between 40 K and 100 K in the inner molecular region of M17 SW. Column densities in 1 km/s channels between ~10$^{15}$ and ~10$^{17}$ cm$^{-2}$ were found for [C I]. Just ~20% of the velocity range (~40 km/s) that the [C II] line spans is associated with the star-forming material traced by [C I] and CO. The total gas mass estimated from the [C II] emission gives a lower limit of ~4.4x10$^3$ $M_{\odot}$. At least 64% of this mass is not associated with the star-forming material in M17SW. We also found that about 36%, 17%, and 47% of the [C II] emission is associated with the HII, HI, and H_2 regimes, respectively. Comparisons with the H41$\alpha$ line shows an ionization region mixed with the neutral and part of the molecular gas, in agreement with the clumped structure and dynamical processes at play in M17SW. These results are also relevant to extra-galactic studies in which [C II] is often used as a tracer of star-forming material.
    Full-text Article · Jan 2015 · Astronomy and Astrophysics
  • Christophe Risacher · Rolf Gusten · Jurgen Stutzki · [...] · Achim Wunsch
    [Show abstract] [Hide abstract] ABSTRACT: Far Infrared Astronomy is one of the last explored fields in astronomy. Several bolometer cameras have already been developed with several hundred or more pixels and there is rapid progress in this area, however high resolution spectroscopy using heterodyne receivers have still not reached that level of maturity. Indeed, until now, only single pixel or small size arrays have been achieved in a handful of observatories. We present here upGREAT - two medium-size array receivers, operating cooled using closed-cycle pulse tube coolers. The Low Frequency Array (LFA) covers the 1.9-2.5 THz range using dual polarization 7-pixel HEB arrays. The second receiver, the High Frequency Array (HFA), will observe the O[I] line at ∼4.7 THz using a 7-pixel HEB array.
    Article · Nov 2014
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    Thomas Klein · Miroslaw Ciechanowicz · Christian Leinz · [...] · Yutaro Sekimoto
    [Show abstract] [Hide abstract] ABSTRACT: We report on the design and on-site performance of the recently upgraded FLASH$^{+}$ instrument operated at the APEX telescope in the Chilean Atacama desert in 5100 m altitude. The dual-channel receiver allows parallel observations in the atmospheric submillimeter windows between 268 and 516 GHz. A signal of in total 16 GHz is processed simultaneously. Equipped with state-of-the-art sideband separating mixers (spin-off developments from the ALMA bands 7 and 8), its outstanding on-sky performance makes FLASH$^{+}$ a most efficient spectral line mapping machine. Operation is fully automated and allows flexible remote observations from the APEX base in San Pedro de Atacama.
    Full-text Article · Sep 2014 · IEEE Transactions on Terahertz Science and Technology
  • [Show abstract] [Hide abstract] ABSTRACT: The realization of large format fully sampled sensitive focal plane arrays of direct detectors is a long standing development goal for advanced astrophysical instrumentation for submillimeter wavelengths. Recently a superconducting microwave kinetic inductors detector (MKID) technology has been developed which offers high sensitivity and unprecedented multiplexing ratio. We report on development of MKID antenna coupled MKID arrays for 350μm and 850μm atmospheric transmission windows each containing of order of 5000 and 1000 detectors per superconducting chip respectively. We present design and measurement results on first detector chips including pixel responsivity, noise distribution and detector yields.
    Conference Paper · Sep 2014
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    [Show abstract] [Hide abstract] ABSTRACT: NGC 1333 IRAS 4A and IRAS 4B sources are among the best studied Stage 0 low-mass protostars which are driving prominent bipolar outflows. Most studies have so far concentrated on the colder parts (T<30K) of these regions. The aim is to characterize the warmer parts of the protostellar envelope in order to quantify the feedback of the protostars on their surroundings in terms of shocks, UV heating, photodissociation and outflow dispersal. Fully sampled large scale maps of the region were obtained; APEX-CHAMP+ was used for 12CO 6-5, 13CO 6-5 and [CI] 2-1, and JCMT-HARP-B for 12CO 3-2 emissions. Complementary Herschel-HIFI and ground-based lines of CO and its isotopologs, from 1-0 upto 10-9 (Eu/k 300K), are collected at the source positions. Radiative-transfer models of the dust and lines are used to determine temperatures and masses of the outflowing and UV-heated gas and infer the CO abundance structure. Broad CO emission line profiles trace entrained shocked gas along the outflow walls, with typical temperatures of ~100K. At other positions surrounding the outflow and the protostar, the 6-5 line profiles are narrow indicating UV excitation. The narrow 13CO 6-5 data directly reveal the UV heated gas distribution for the first time. The amount of UV-heated and outflowing gas are found to be comparable from the 12CO and 13CO 6-5 maps, implying that UV photons can affect the gas as much as the outflows. Weak [CI] emission throughout the region indicates a lack of CO dissociating photons. Modeling of the C18O lines indicates the necessity of a "drop" abundance profile throughout the envelope where the CO freezes out and is reloaded back into the gas phase, thus providing quantitative evidence for the CO ice evaporation zone around the protostars. The inner abundances are less than the canonical value of CO/H_2=2.7x10^-4, indicating some processing of CO into other species on the grains.
    Full-text Article · Mar 2012 · Astronomy and Astrophysics
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    [Show abstract] [Hide abstract] ABSTRACT: We report ground-based follow-up observations of the exceptional source, ID141, one the brightest sources detected so far in the H-ATLAS cosmological survey. ID141 was observed using the IRAM 30-meter telescope and Plateau de Bure interferometer (PdBI), the Submillimeter Array (SMA) and the Atacama Pathfinder Experiment (APEX) submillimeter telescope to measure the dust continuum and emission lines of the main isotope of carbon monoxide and carbon ([C I] and [C II]). The detection of strong CO emission lines with the PdBI confirms that ID141 is at high redshift (z=4.243 +/- 0.001). The strength of the continuum and emission lines suggests that ID141 is gravitationally lensed. The width (Delta V (FWHM) ~ 800 km/s}) and asymmetric profiles of the CO and carbon lines indicate orbital motion in a disc or a merger. The properties derived for ID141 are compatible with a ultraluminous (L_FIR ~ 8.5 +/- 0.3 x 10^13/mu_L Lsun, where mu_L is the amplification factor, dense (n ~ 10^4 cm^-3) and warm (T_kin ~ 40K) starburst galaxy, with an estimated star-formation rate of (0.7 to 1.7) x 10^4/mu_L Msun/yr. The carbon emission lines indicate a dense (n ~ 10^4 cm^-3) Photo-Dominated Region, illuminated by a far-UV radiation field a few thousand times more intense than that in our Galaxy. In conclusion, the physical properties of the high-z galaxy, ID141, are remarkably similar to those of local ultraluminous infrared galaxies.
    Full-text Article · Jul 2011 · The Astrophysical Journal
  • [Show abstract] [Hide abstract] ABSTRACT: A 3D hydrodynamical model of an AGN torus (Wada, Papadopoulos & Spaans, 2009), which follows the formation of H2 out of the neutral hydrogen phase according to the evolving ambient ISM conditions (at a resolution of 0.25 pc), is used to estimate the abundance of different atomic and molecular species from a chemical model driven by X-rays. The abundance of several species is estimated based on the local hydrogen density and impinging X-ray flux at each grid element in the computational box. A 3D radiative transfer model is used to produce maps of different atomic and molecular lines to be used as diagnostic for high resolution observations of near by (< 20 Mpc) galaxy nuclei. Galactic observations of atomic and molecular gas ([C I] and mid-J CO lines) in M17 SW, obtained with CHAMP+ and FLASH on APEX, are presented as template for future extragalactic observations with ALMA.
    Article · May 2011 · Proceedings of the International Astronomical Union
  • M. A. Requena Torres · R. Gusten · J. Martin-Pintado · [...] · S. Heyminck
    [Show abstract] [Hide abstract] ABSTRACT: Spectral surveys provide the only way to determine the full molecular inventory of an object and hence build a comprehensive view of the state of the molecular gas and its role in star formation and the structure and evolution of the ISM. Of course spectral surveys also provide the most efficient method of identifying new and unexpected species that have to be include in the chemical networks. The most extensive and complete survey of an extragalactic system has been the continuous spectral survey from 129 GHz to 175 GHz carried out by Martín et al. (2006) toward NGC253. This first spectral line surveys at 2 mm towards the prototypical starbursts galaxies NGC253 have shown an unexpected chemical richness. Due to the limitations of observing at a single atmospheric window, missing maybe part of the material that will affect the chemistry, our next step has been to extend the extragalactic spectral line survey of NGC253. Using the APEX telescope we have extend the survey to higher frequencies and carried out the first spectral line survey of an AGN nucleus like NGC4945, and a close ULIRG, ARP220. Those Surveys allow as to get better estimates on the physical and chemical characteristics of the three galaxies, as well to search for better tracers to study the star-formation in those distant objects, with different physical characteristics. We present here the three spectral surveys together with some new observations of several anions and dense tracers observed in a larger sample of galaxies, covering more types of galaxies, i.e. seyfert.
    Article · May 2011 · Proceedings of the International Astronomical Union
  • A. Gusdorf · R. Gusten · Y. Yuan · D. Neufeld
    [Show abstract] [Hide abstract] ABSTRACT: Supernovae are an important source of energy input to the interstellar medium. They send shock waves that propagate through and interact with the Interstellar Medium. These shock waves originally create large cavities filled with hot ionized material. At some point, supernova-driven shock waves become radiative, emitting strong line emissions, initially at optical and ultraviolet wavelengths, that are widely observed from supernova remnants. In the interaction region of these remnants with the ambient molecular cloud, slower shock waves heat, accelerate, and compress the surrounding medium. The physical processes at work in such shocked regions (density, temperature and associated timescales) in turn generate a specific chemistry, both in the gas-phase and through grains interactions, that can significantly alter the abundance of certain species. The resulting infra-red, but also sub-mm molecular emission can be used as a diagnostic tool to study the physical and chemical characteristics of the shocked region, yielding constraints on shock parameters such as the pre-shock density, magnetic field, or shock type, velocity or type. IC443 is a typical example of such galactic SuperNova Remnants, at an estimated distance of 1.5 kpc, with a diameter of about 50 arcminutes. In this talk, I will present new extensive maps of CO gas of the whole remnant, at the highest frequencies accessible from the ground. I will also explain how the use of such observations on selected positions, in combination with pure rotational H_2 transitions acquired with the Spitzer telescope (IRS) can allow us to place constraints on shock model parameters through comparisons with a grid of shock models. Based on this preliminary study, I will also show how the additional comparison of water observations (as provided by the HIFI receiver onboard the Herschel telescope) with our shock simulations is a good way to refine these constraints and test our understanding of the water formation processes in shocked regions.
    Article · Jan 2011 · Proceedings of the International Astronomical Union
  • F. Wyrowski · K. Menten · R. Gusten · [...] · C. Leinz
    [Show abstract] [Hide abstract] ABSTRACT: Hydrides are key ingredients of interstellar chemistry since they are the initial products of chemical networks that lead to the formation of more complex molecules. The fundamental rotational transitions of light hydrides fall into the submillimeter wavelength range. Using the APEX telescope, we observed the long sought hydrides SH+ and OH+ in absorption against the strong continuum source Sagittarius B2(M). Both, absorption from Galactic center gas as well as absorption from diffuse clouds in intervening spiral arms in a large velocity range are observed. The detected absorption of a continuous velocity range on the line-of-sight shows these hydrides to be an abundant component of diffuse clouds. In addition, we used the strongest submillimeter dust continuum sources in the inner Galaxy to serve as background candles for a systematic census of these hydrides in diffuse clouds and massive star forming regions of our Galaxy and initial results of this survey are presented. For this survey, the CHAMP+ array receiver as well as the MPIfR THz receiver was used. We will discuss the scientific potential of the first THz atmospheric window from 1.0 to 1.1 THz for observations from the Chajnantor high site.
    Article · Jan 2011 · Proceedings of the International Astronomical Union
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    [Show abstract] [Hide abstract] ABSTRACT: We discuss the detection of absorption by interstellar hydrogen fluoride (HF) along the sight line to the submillimeter continuum sources W49N and W51. We have used Herschel's HIFI instrument in dual beam switch mode to observe the 1232.4762 GHz J = 1 - 0 HF transition in the upper sideband of the band 5a receiver. We detected foreground absorption by HF toward both sources over a wide range of velocities. Optically thin absorption components were detected on both sight lines, allowing us to measure - as opposed to obtain a lower limit on - the column density of HF for the first time. As in previous observations of HF toward the source G10.6-0.4, the derived HF column density is typically comparable to that of water vapor, even though the elemental abundance of oxygen is greater than that of fluorine by four orders of magnitude. We used the rather uncertain N(CH)-N(H2) relationship derived previously toward diffuse molecular clouds to infer the molecular hydrogen column density in the clouds exhibiting HF absorption. Within the uncertainties, we find that the abundance of HF with respect to H2 is consistent with the theoretical prediction that HF is the main reservoir of gas-phase fluorine for these clouds. Thus, hydrogen fluoride has the potential to become an excellent tracer of molecular hydrogen, and provides a sensitive probe of clouds of small H2 column density. Indeed, the observations of hydrogen fluoride reported here reveal the presence of a low column density diffuse molecular cloud along the W51 sight line, at an LSR velocity of ~ 24kms-1, that had not been identified in molecular absorption line studies prior to the launch of Herschel. Comment: 4 pages, 3 figures, A&A Letter special issue, accepted on 07/13/2010
    Full-text Article · Jul 2010 · Astronomy and Astrophysics
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    [Show abstract] [Hide abstract] ABSTRACT: Mon R2, at a distance of 830 pc, is the only ultracompact HII region (UC HII) where the photon-dominated region (PDR) between the ionized gas and the molecular cloud can be resolved with Herschel. HIFI observations of the abundant compounds 13CO, C18O, o-H2-18O, HCO+, CS, CH, and NH have been used to derive the physical and chemical conditions in the PDR, in particular the water abundance. The 13CO, C18O, o-H2-18O, HCO+ and CS observations are well described assuming that the emission is coming from a dense (n=5E6 cm-3, N(H2)>1E22 cm-2) layer of molecular gas around the UC HII. Based on our o-H2-18O observations, we estimate an o-H2O abundance of ~2E-8. This is the average ortho-water abundance in the PDR. Additional H2-18O and/or water lines are required to derive the water abundance profile. A lower density envelope (n~1E5 cm-3, N(H2)=2-5E22 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, v_e =0.5 x (r/Rout)^{-1} km/s, although the expansion velocity is poorly constrained by the observations presented here. Comment: 4 pages, 5 figures
    Full-text Article · Jul 2010 · Astronomy and Astrophysics
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    J. Mehl · P. A. R. Ade · K. Basu · [...] · M. White
    [Show abstract] [Hide abstract] ABSTRACT: We will report on the APEX-SZ bolometer camera which houses a 320 element Transition-Edge Sensor (TES) bolometer array designed to survey for galaxy clusters using the 12-meter diameter APEX telescope sited in Chile. Design and fabrication of the TES bolometer array will be discussed, as well as its integration with a frequency-domain SQUID multiplexed readout system. The full configuration of the APEX-SZ camera was deployed in April 2007. A preliminary galaxy cluster map from this deployment will be presented.
    Full-text Article · May 2008 · Journal of Low Temperature Physics
  • G. Wieching · U. U. Graf · R. Gusten · [...] · F. Schmillling
    [Show abstract] [Hide abstract] ABSTRACT: The CO N+ Deuterium Observations Receiver (CONDOR) is an astronomical heterodyne receiver that successfully operates between 1.25-1.53 THz. The instrument follows the standard heterodyne design, using a solid state local oscillator and a superconducting NbTiN hot electron bolometer (HEB) as a mixer. For easy maintenance at the telescope CONDOR is the first receiver that cools the HEB with a closed-cycle system using a pulse tube cooler. The system has receiver noise temperatures around 1500 K and spectral Allan variance times of about 30 s. In November 2005, CONDOR was successfully commissioned on the 12-m Atacama Pathfinder Experiment.
    Article · Sep 2006
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    D. A. Neufeld · P. Schilke · K. M. Menten · [...] · S. Philipp
    [Show abstract] [Hide abstract] ABSTRACT: We discuss the first astronomical detection of the CF+ (fluoromethylidynium) ion, obtained by observations of the J=1-0 (102.6 GHz), J=2-1 (205.2 GHz) and J=3-2 (307.7 GHz) rotational transitions toward the Orion Bar region. Our search for CF+, carried out using the IRAM 30m and APEX 12m telescopes, was motivated by recent theoretical models that predict CF+ abundances of a few times 1.E-10 in UV-irradiated molecular regions where C+ is present. The CF+ ion is produced by exothermic reactions of C+ with HF. Because fluorine atoms can react exothermically with H2, HF is predicted to be the dominant reservoir of fluorine, not only in well-shielded regions but also in the surface layers of molecular clouds where the C+ abundance is large. The observed CF+ line intensities imply the presence of CF+ column densities of at least 1.E+12 cm-2 over a region of size at least ~ 1 arcmin, in good agreement with theoretical predictions. They provide support for our current theories of interstellar fluorine chemistry, which suggest that hydrogen fluoride should be ubiquitous in interstellar gas clouds and widely detectable in absorption by future satellite and airborne observatories. Comment: 4 pages, including 4 figures. To appear in a special A&A issue on "First Science with APEX"
    Full-text Article · Mar 2006 · Astronomy and Astrophysics
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    D. A. Neufeld · P. Schilke · K. M. Menten · [...] · S. Philipp
    [Show abstract] [Hide abstract] ABSTRACT: We report the first astronomical detection of the CF+ (fluoromethylidynium) ion obtained by recent observations of its J = 1 - 0 (102.6 GHz), J = 2 - 1 (205.2 GHz), and J = 3 - 2 (307.7 GHz) pure rotational emissions toward the Orion Bar. Our search for CF+, carried out using the IRAM 30m and APEX 12m telescopes, was motivated by recent theoretical models that predict CF+ abundances of a few x E-10 in UV-irradiated molecular regions where C+ is present. The measurements confirm the predictions. They provide support for our current theories of interstellar fluorine chemistry, which suggest that hydrogen fluoride should be ubiquitous in interstellar gas clouds. Comment: 2 pages, 1 figure (uses iaus.sty), to appear in IAU Symposium No. 231, Astrochemistry - Recent Successes and Current Challenges, eds. D. C. Lis, G. A. Blake & E. Herbst (Cambridge Univ. Press)
    Full-text Article · Sep 2005 · Proceedings of the International Astronomical Union
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    T. de Graauw · E. Caux · R. Gusten · [...] · K. Wildeman
    [Show abstract] [Hide abstract] ABSTRACT: The Heterodyne Instrument for the Far-Infrared (HIFI) is a single sky-pixel, high-resolution (>300.000), spectrometer for ESA's Herschel Space Observatory. The instrument is designed to provide a wide and continuous frequency coverage with a velocity resolved resolution and a high sensitivity. This allows detailed investigations of a wide variety of astronomical sources, ranging from solar system objects, star formation regions to nuclei of galaxies. The frequency bands cover many emission and absorption lines of molecules, like H<sub>2</sub>O, and atomic and ionic lines, like CII, NII. The instrument comprises of 5 frequency bands covering 480-150 GHz with SIS mixers and a sixth dual band for the 1410-1910 GHz range with Hot Electron Bolometer Mixers. The Local Oscillator (LO) subsystem consists of a Ka-band synthesiser followed by 14 chains of frequency multipliers, 2 for each frequency band. Each frequency band has two mixers operating on orthogonal polarisations. All mixers are designed to have a noise performance close to the quantum noise limit. One frequency band is operated at a time. Modular design of the Focal Plane Unit, with a common optical path for all the mixer bands, and of the Local Oscillator Unit with a common LO Source Unit for all the LO chains, make the instrument very compact. A pair of Auto-Correlators and a pair of Acousto-Optic spectrometers process the two IF signals from the dual-polarisation front-ends and provide instantaneous frequency coverage of 4 GHz, resulting in a set of resolutions (140 KHz to 1 MHz), better than <0.1 Km/s. The instrument development is in an advanced state with mixers and LO chains approaching aimed performance.
    Full-text Conference Paper · Nov 2004
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    Thomas Klein · G.A.Ediss · R.Gusten · [...] · C.Kasemann
    Full-text Conference Paper · Mar 1997