L. T. Little

A detailed study of G35.2–0.7N: collimated outflows in a cluster of high-mass young stellar objects

We present a series of James Clerk Maxwell Telescope, Berkeley‐Illinois‐Maryland Association (BIMA) and Very Large Array (VLA) observations of the massive star-forming region associated with G35.2‐0.7N. These new observations shed considerable light on the nature of the outflows in this region. The combination of our CO, SiO and radio data suggests that there are perhaps as many as four outflows emanating from the core containing G35.2‐0.7N. CO J = 3 → 2 maps show that the outflow has a curved appearance consistent with precession of a central driving source. However, the geometric centre of the flow is found to be not coincident with the radio jet source G35.2N but is instead closer to a peak in SiO, H 13 CO + and dust continuum found in the BIMA data. An elongated finger of CO emission is detected to the north of centre which points back towards the radio jet centred on G35.2N, further ruling it out as the driving source of the larger-scale CO flow. BIMA observations of the 3.5-mm continuum (which is dominated by dust), H 13 CN and H 13 CO + emission trace a dense, elongated, rotating envelope with properties in good agreement with values derived from previous ammonia observations. The peak of the dust continuum and the H 13 CO + peak a few arcsec to the south of G35.2N. SiO J = 2 → 1 data delineate a well-collimated feature parallel with the axis of the CO outflow, but offset to the north by ∼10 arcsec. H 13 CO + emission is detected at the possible origin of this flow but no radio source is observed. VLA A-configuration observations at 6 and 3.5 cm resolve the radio jet into at least six discrete components, with positions consistent with previous observations. The central driving source, G35.2N, is only detected at 3.5 cm. At least two other sources are detected, one of which lies within the flattened core and may be associated with another flow inferred from recent L � -band observations. No radio source is detected at the geometric centre of the CO

A 210–280 GHz sis heterodyne receiver for the James Clerk Maxwell Telescope part I: Design and performance

We describe the design and performance of a 210–280 GHz SIS heterodyne receiver built for use on the Maxwell Telescope. The mixer utilises a lead alloy SIS tunnel junction, mounted in 4∶1 reduced height rectangular waveguide, and is tuned with a backshort in 2∶1 reduced height guide. The receiver has a receiver noise temperature of <200K (DSB) across the RF band from 210–270 GHz, with a best noise temperature measured in the laboratory of 113K (DSB) at 231 GHz. A prototype version of this receiver was successfully operated on the telescope in May 1989. By direct intercalibration with a Schottky diode receiver we deduced a best receiver noise temperature of 140K (DSB) at 245 GHz. Discrepancies between this figure and that derived from broad band thermal load calibration are discussed in the accompanying paper (Little et al., 1992, this issue).

The effect of mixer mount loss on the performance of sis receivers

Tuckers quantum theory of mixing (in the 3-port approximation) is employed with Eisenhart and Khans equivalent circuit for a junction mounted in waveguide to predict the gain of an SIS mixer as a function of guide impedance, series inductance, junction capacitance, IF load impedance and backshort loos. The improvements which will result from optimisation of these parameters are quantified. It is shown that for optimum performance a backshort VSWR>100 is required, which is hard to realise at high frequencies

The TIRGO project: A compact 800-900 GHz heterodyne receiver for submillimetre astronomical spectroscopy

We describe a new Nb SIS junction heterodyne waveguide receiver working in the frequency range between 800–810 GHz. The receiver is light and compact and is designed to fit most infrared and optical telescopes with the minimum of reconfiguration. We present a description of the receiver and its associated RF performance.

A 210–280 GHz sis heterodyne receiver for the James Clerk Maxwell Telescope part II: Calibration

The comparison of a 240 GHz SIS heterodyne receiver with a Schottky diode receiver at the Maxwell telescope revealed difficulties with its calibration using continuum loads. The difficulties arise from the fact that the local oscillator power is not hugely greater than the total load power incident across the RF and IR band. This broadband power influences the receiver gain, principally by varying the slope of the I–V characteristic, and hence the output matching, as a result of the ac Josephson effect. Suppressing the Josephson effect with a magnetic field permits the standard calibration procedure, using hot/cold continuum loads, to be employed.

An SIS Receiver for the JCMT

A 220–280 GHz prototype SIS receiver system is currently being constructed, which will be tested on the JCMT in January 1989. The prototype receiver will act as a test-bed for developing a dualchannel common-user SIS receiver for the JCMT, tunable from 280–360 GHz, in a collaborative project between UKC, RAL and the Herzberg Institute of Astrophysics, Ottawa.

Simulated performance of SIS and SIN junctions as heterodyne receivers in waveguide and open antenna mixer mounts

Tuckers quantum theory of mixing (in the 3-port approximation) is employed to calculate the gain over a wide range of frequencies of model mixers employing SIS and SIN junctions with both real and idealI–V characteristics. A comparison is made between the performance of junctions in waveguide and open antenna mounts. It is concluded that ideal junctions give gain 1.5 to 2 times higher than real ones, SIS junctions have gain approximately three times greater than otherwise similar SIN junctions, and that junction areas need to be typically three times smaller in open antenna structures to provide comparable gain to those in waveguide mounts.

An SIS based 230 GHz receiver for Astronomy

A 230 GHz mixer receiver has been constructed using (Pb/In/Au) - (Pb/Bi) SIS junctions fabricated using the Dolan bridge method and thermal oxidation. The mixer block is of conventional design with reduced height waveguide and contacting backshort. Preliminary results indicate a receiver noise temperature <1000K (DSB).

A low-noise 810 GHz heterodyne receiver for molecular-line astronomy

A low-noise 810 GHz heterodyne receiver for astronomy is described. The mixer consists of a NbTiN SIS junction, mounted in a half-height rectangular waveguide mixer block. The receiver has been successfully tested on the UK Infrared Telescope, Hawaii, with a DSB system noise temperature of 280 K at 808 GHz. Observations of several astronomical sources have verified the sensitivity of the instrument.

Demonstration of the TIRGO compact 800- to 900-GHz heterodyne receiver on UKIRT

A compact sub-millimetre wavelength Nb superconducting tunnel junction receiver (TIRGO) has been installed on the UKIRT facility, Hawaii. The receiver, used in combination with an acousto-optic spectrometer, exhibited excellent noise performance, achieving a best noise equivalent temperature of 280K (DSB) at 808GHz. Despite unfavourable observing conditions, spectral observations of a variety of astronomical sources were made that effectively verified the sensitivity and usefulness of the instrument for astronomical research. The design, construction and performance of the receiver system are described and some of the astronomical data acquired during the observation period briefly presented.