This is a general description of the BIMA millimeter wavelength array, including some recent scientific results, the status of the expansion to a larger number of antennas, and preliminary results of attempts to correct for atmospheric “seeing”. The examples of scientific results show CO images of the galaxy IC 342, emission in other spectral lines from the two regions of massive star formation SGR B2 and Orion South, and continuum emission from solar flares and the planet Mercury. There follows a brief description of the new antennas, new correlator, new receivers, and new refrigerators of the expanded array. Finally, there is a discussion of the first results from attempts to use measured fluctuations in the brightness of the atmosphere at the observing wavelength to infer the visibility phase fluctuatons due to the atmosphere. Removal of the phase fluctuations using the brightness fluctuations provides a better image of a test observation of M87.

The present status and projected two year developments for the Owens Valley Millimeter Array are described and a brief summary of the astronomical research is presented.

The present status and the upgrading projects for the Nobeyama Millimeter Array are described. The array is currently being upgraded to produce higher sensitivity and new spectral windows. The major items have been a new 10-m antenna, new receivers, and a new correlator. There follows a brief summary of the astronomical research is presented.

In November 1992, the IRAM interferometer on Plateau de Bure has reach two years of operation. After a review of its current technical status, with emphasis on its specificities, this paper presents an overview of its capabilities, illustrated by examples taken from the scientific program carried on during these two years. On-going upgrades and future plans are presented.

A linked submillimeter-wave interferometer using the CSO 10.4 m and the JCMT 15 m telescopes located on Mauna Kea at an elevation of 4200 m, has been built and tested successfully. The capabilities of the instrument and an outline of the type of observations that can be made with a single, fixed-baseline interferometer are given. In particular, an experiment to detect gas infalling onto low-mass protostellar sources is proposed. The design of the instrument is described briefly and the successful results of the first tests are summarized.

Although the Very Large Array (VLA) and the Very Large Baseline Array (VLBA) were originally intended as centimeter wavelength instruments, the exciting results from high resolution millimeter radio astronomy over the last ten years have generated interest in pushing these arrays into the millimeter region. This report will describe two aspects of recent development at NRAO: the new capability of the VLA at 7mm wavelength which will be operational in 1994, and the completion of the VLBA with its anticipated use at 7mm and 3.6mm.

VLBI has now made its breakthrough into the mm-wavelength region and is becoming a viable and important new instrument. In this talk I aim to convince you that VLBI will be an important user of your instruments in the future.

In the present paper we report a sharp rise in the flux density of the quasar 3C273 observed with the Itapetinga radiotelescope in 1991. The intensity increased by factor 2, reaching a maximum value in May and July 1991 at 43 and 22 GHz, respectively.

With the exception of some pioneering mm-VLBI observations, the present-day VLBI cannot resolve the most compact components in active galaxies, nor measure their brightness temperatures. In addition, the observing frequencies are too low: the innermost components are still self-absorbed and often completely undetectable at standard VLBI frequencies. However, studies of continuum spectra and variations of AGN can give us estimates of what will eventually be seen when VLBI techniques reach sufficient resolutions and frequencies. These estimates are also useful in considering what capabilities will be required from future interferometry for studying AGN.

We have used multifrequency continuum monitoring data together with standard shock-in-jet models to derive flux, size and brightness temperature distributions for the innermost core components in a complete 2 Jy sample of AGN. The millimeter spectra and its variations can be satisfactorily explained by just two types of high-frequency components, a relativistic inhomogeneous jet and evolving shocks in this jet (Valtaoja et al. 1988). Moreover, with extended multifrequency flux monitoring the contributions from these two components can be separated, which makes possible the extraction of limited amounts of structural data (average sizes, brightness distributions, etc.) just from continuum data.

We have used two main methods. Cm-to-mm spectra can reveal the existence of persistent high frequency components and give estimates of their fluxes and turnover frequencies. Continuum monitoring gives fluxes and variability timescales of transient components, and further their sizes and brightness temperatures.

The preliminary results of an mm-VLBI survey of spectral index on active galactic nuclei (AGN) are presented which suggest that their activities are only in the central regions. The difference in central activities may correspond to their different stages of evolution. We found a strong concentration to α = 0 for quasar and a spread distribution for HPQ.

We report the observations of compact steep-spectrum radio sources (CSSs) by VLBI at 22 and 43 GHz and single dich at 22, 43, and 92 GHz. Our results show that CSS also has an active core as well as other AGNs.

A molecular outflow is one of the most conspicuous active phenomena associated with protostars, and the kinetic energy of its outflowing mass is as large as that of random motions of ambient molecular cloud, which suggests that outflow has dynamically influence on ambient molecular gas. Possible observational evidence which suggests the existence of dynamical interaction between molecular outflow and ambient molecular cloud has been detected in several star forming regions (Fukui et al. 1986; Iwata et al. 1988). Recent detections of H2O maser emission associated with low-mass protostars (e.g. Comoretto et al. 1990) also suggest that there still exist active phenomena in the low-mass star forming regions.

Molecular outflow ρ Oph-East, discovered toward a low-mass protostar IRAS 16293-2422 (Fukui et al. 1986), has been known as a site of dynamical interaction between molecular outflowing gas and ambient molecular cloud by CO and NH3 observation (Mizuno et al. 1990). Existence of several strong H2O maser spots (Wilking & Claussen 1987; Wotten 1989; Terebey et al. 1992) also suggests that active phenomena are occurring in this region. In this paper, we report our result of H2O maser observation for molecular outflow ρ Oph-East with milli-arcsecond resolution by VLBI.

The results of a VLBI observation between Kashima 34 m and Nobeyama 45 m are presented. Water maser at 22.235 GHz and SiO masers at 43 GHz in some late type stars are mapped almost simultaneously. Data reduction is still on the way, then we report mainly for the blocking model of H2O maser.

VLBI observations of millimeter wavelengths can probe the broad line emission and jet forming regions of quasars, and the scale of an accretion disk around massive black holes in nearby active galaxies, which are self-absorbed at longer wavelengths. Therefore, the extension of the mm-VLBI network is timely and urgent problem. We are now planning to move Nobeyama 6 m mm VLBI telescope to Kagoshima. The telescope will be placed at Kinkohwan park in Kagoshima City in late 1992 and will be operated in 1993. The frequencies for VLBI observations will range from 22 GHz to 100 GHz.

To date, there are two mm-VLBI facilities in Japan: Nobeyama 45 m and Kashima 34 m, However, the longest baseline is only about 200km EW which provides a fringe separation of 17 mas. This is not sufficient for high resolution mapping. A 10 m telescope which is under construction at Mizusawa, 400 km north from Kashima which will be usable up to 43 GHz and will add a north-south baseline, which is very important for astrometrie measurement.

The Max-Planck-Institut für Radioastronomie, Bonn and the Steward Observatory of the University of Arizona, Tucson are collaborating on the construction and operation of a dedicated submillimeter facility. The Submillimeter Telescope (SMT) is a 10 m diameter reflector surrounded by a corotating enclosure. The instrument is an alt-azimuth mounted f/13.8 Cassegrain homology telescope with two Nasmyth and bent Cassegrain foci. The SMT will have diffraction limited performance at a wavelength of 300 μm. and an operating overall figure accuracy of 15 μm rms. The primary and secondary reflector surfaces are constructed out of aluminum-core, carbon-fiber-reinforced-plastic (CFRP) face sheet sandwich panels. The primary reflector backup structure and secondary support are fabricated from CFRP structural members. This modern technology provides both the means for reaching the required precision of the SMT for both night and day operation (basically because of the low coefficient of thermal expansion and high strength-to-weight ratio of CFRP) and a potential route for the realization of lightweight telescopes of even greater accuracy in the future. The SMT will be the highest accuracy radio telescope ever built.

The SMT is located at an altitude of 3180 m on Emerald Peak (Mt. Graham) 120 km northeast of Tucson in southern Arizona. Measurements indicate that atmospheric conditions allow submillimeter observations during about 40% of the time in winter months. The telescope is placed in a co-rotating enclosure of novel design. The enclosure fits tightly around the telescope, with the focus flanges extending from the elevation bearings into the receiver rooms of the enclosure. A flat tertiary mirror is used to direct the beam through either of the two elevation bearings. Thus, we are able to mount receivers directly on the telescope while maintaining laboratory type conditions in the access area surrounding the receivers. On the “facility instrument” side, several receivers can be operated simultaneously.

Various types of receivers can be used for millimeter and submillimeterwave astronomy. The choices are amplifiers or mixer detectors. For the millimeter band, in the past, maser and paramp devices have been successfully used, but in the last few years HEMT amplifiers have proved to be the best option up to about 40 GHz, because they are inexpensive, quite low noise (about 1-2 K/GHz), stable and wideband. However, currently, above ~40 GHz the best performance is obtained from mixer receivers and this review will address that topic only. When used in either interferometers or in single dish spectroscopy, the receivers measure simultaneously the amplitude and phase of the astronomical signal and are therefore fundamentally limited by the quantum noise inherent in the measurement process, which increases linearly with frequency. A receiver which achieves a noise temperature within a factor of 10 of this limit is considered to be well optimized, so that the usual criterion for the noise temperature characterizing a single side-band receiver is that it should be ≲ 10hv/k or equivalently ≲ 0.5 K/GHz.

The performance of the new SIS receiver systems at the Nobeyama Millimeter Array are described. These receivers operate at 100 GHz and 150 GHz bands and tunerless mixer mounts have been adopted. These receivers show very low noise temperature (< 50 K) over a very wide frequency range because of the large embedding impedance range.

An optical fiber IF transmission and tracking delay system and a wideband continuum correlator have been developed for the Owens Valley (OVRO) Millimeter Array. The IF system processes two 1-2 GHz bands which are frequency multiplexed through an optical fiber link. This allows simultaneous dual wavelength observations in the 2.7 and 1.3-mm bands or dual polarization observations in either band.