Atmospheric opacity severely attenuates millimeter and submillimeter signals. Fluctuations in refractive index limit the angular resolution of interferometers. Conventional phase calibration does not remove atmospheric phase fluctuations, but new techniques may.

Over the past several years, there has been substantial progress both in algorithms for mosaicing and in our understanding of the effects of errors on mosaiced image. I describe the current state of knowledge in both these areas and also indicate where future improvements are likely to lie.

In the paper we describe the results of active holography RATAN-600 surface testing including the measurements of a single element profile and topography. The RATAN-600 beam pattern at 3.2 mm after an antenna correction and its dynamics during daytime are presented.

SIS receivers have higher sensitivity than Schottky diode receivers. The SIS mixer, however, must be cooled at 4 K level, and either a GM (Gifford-McMahon) + JT (Joule- Thomson) refrigerator or liquid helium is used. Therefore, SIS receivers are usually much larger and heavier than Schottky diode receivers which are usually cooled by a GM refrigerator only.

Kuriyama et al. developed a GM refrigerator using Er3Ni as a regenerator material which achieved to cool at 4 K level.

In this work, the SIS receiver was constructed and investigated, which was cooled below 4 K by the GM refrigerator with Er3Ni. It resulted in the SIS receiver which was about the same size and weight as a usual Schottky diode receiver.

The design and performance details for a link, and a tracking delay system operating in the 0.5 to 4 GHz band are presented. This is a composite fiber optical and microwave system, with delay bits ranging from 512 to ns in binary steps.

This paper describes the delay lines designed and built for the JCMT-CSO submillimeter interferometer located on the summit of Mauna Kea, Hawaii and described in the paper by Carlstrom et al. in these proceedings.

One of the major features of the project is the use of fiber optics instead of coaxial cable to bring the IF signals (l-2GHz) from the receivers to the spectral line correlator via a set of fiber optic delay lines. Optical fiber now has many advantages over coax including very large bandwidth, low loss, economical cost and size and immunity to electrical interference.

Soares et al. (these proceedings) describe a delay line system that can be used with a broadband continuum correlator requiring very fine delay steps The JCMT-CSO interferometer was intended to be used primarily with a digital correlating spectrometer that has a range of built-in delays, greatly easing the demand on delay line resolution.

Large-field radio interferometer at 10.65GHz have been developed to search for transient radio objects such as radio supernovae and radio bursts in stellar systems (Daishido et al. 1984). This is a spatial fast-fourier transform (FFT) type radio interferometer, being an equally-spaced, maximum redundant, two-dimensional (2D) array in an 8 × 8 configuration. Sixty-four identically-designed frontend elements are comprised of 2.4 m diameter cassegrain antennas and 200K HEMT receivers. These are steerable in elevetion and are fixed in azimuth. Although it is only partially operating, the completed system having 64 beams in the northern hemisphere is expected to provide maps having 0.1° angular resolution and a sensitivity of 50 mJy. The beams are formed by a newly-developed “Digital Lens” (complex amplitude equalizer + 2D FFT pipelined processor), with the array’s overall size being 20 × 20m.

The phase structure function can be estimated from water vapor radiometer data. We present typical phase structure functions and indicate how residual calibration errors are related to the phase structure function and the calibration parameters. From this, we can estimate the amount of time the array can be used and compare different calibration methods.

The resolving powers of existing telescope arrays are quite different. For example the extended new MERLIN at 5 GHz readily yields maps of ~ 50 mas resolution compared with the VLA ~ 350 mas, WSRT ~ 4000 mas, EVN ~ 5 mas, global VLBI ~ 1 mas, etc. This means that images obtained with these instruments yield information on different scales that sometimes appear unrelated. However, the need to have structural information on intermediate scales demands that data from different arrays be combined to make a single image. This is particularly important in extra-galactic radio sources where the relationship between core-jet features on different scales (parsec and kiloparsec) and the connection between small-scale and extended features need to be established.

By combining uvdata from two or more arrays we can routinely make images that represent a balance between the capabilities of the combined arrays, (e.g. VLA + MERLIN, MERLIN+VLBI, VLA+WSRT etc) at cm wavelengths. In order to do this, one has to overcome a number of calibration and mapping difficulties (see Zhang et al. 1991; Akujor et al. 1992, in prep.).

Assume that a set of visibility data

{(uj, vj, zj)| j = 1, 2,...,N}

is given where visibility zj observed at time j can be expressed in terms of “true visibility” defined by the brightness distribution T(x,y) and observation noise εj:

where{(uj, vj)} is a given set of points in the u-v plane. It is assumed that u-v plane is gridded with the interval Δ. The dirty map obtained by

is a crude estimate of the true brightness distribution. CLEAN and MEM are two typical methods to get better estimates.

Resolved images of molecular emission lines from the envelopes of cool evolved stars reveal much about the physical processes by which such stars lose mass, about the chemical processes which occur in the outflowing gas, and about the evolution of the star to the planetary nebula stage. This paper reviews observational work on molecular line imaging at mm-wavelengths of carbon stars, Miras, proto-planetary nebulae, and planetary nebulae. The impact of these observations on our understanding of the late stages of stellar evolution as it affects the circumstellar environment is emphasized.

We summarize the main results obtained with the IRAM Interferometer on Plateau de Bure during its first years of operation, in the field of circumstellar envelopes.

In order to examine the structure and kinematics of the molecular gas around planetary nebulae, we have made aperture synthesis observations of I2CO(J=1-0) emission in three planetary nebulae, IRAS 21282+5050, CRL 618 and M 1-7, using Nobeyama Millimeter Array.

We have determined the inclination of the axis of the HCO+torus in NGC 7027 to the line of sight, based on interferometrie observations and model calculations. We found that the deduced inclination of the HCO+ torus is misaligned with the inclination of the major axis of the ionized core. The result may imply the precession of the axis of the axisymmetric mass loss.

The distribution of HC5N was observed in the envelope of the carbon star IRC+10216 with the Nobeyama Millimeter Array. A shell like distribution with its diameter of about 29″ was found. The diameter is larger than that of HC3N.

As stars evolve up the asymptotic giant branch (AGB), they begin to lose mass at a high rate, and in the process they create extended circumstellar molecular envelopes. Since the transition from AGB to planetary nebula stages is of the order of 1000 yr, the remnant of such molecular envelopes should still be observable in pro to-planetary nebulae (PPN) and planetary nebulae (PN). Recent ground-based survey of cool IRAS sources have discovered ~30 candidates of PPN (Kwok 1992). These sources show the characteristic “double-peak” energy distribution. The cool component is due to the remnant of the AGB dust envelope, and the hot component represents the reddened photosphere. The fact that the two components are clearly separated suggests that the dust envelope is well detached from the photosphere. Radiative transfer model fits to the spectral energy distributions of PPN suggest a typical separation of ~1 arc sec between the dust envelope and the photosphere, and such “hole-in-the-middle” structure can be mapped by millimeter interferometry in CO.

VLBI observations show that the SiO maser emitting regions in oxygen-rich stars are very clumpy and that these clumps extend over a few stellar radii (Mclntosh et al. 1987; Colomer et al. 1992). These observations indicate that the ideal instrument for the study of the SiO masers is an interferometer with baselines covering between a few and several hundreds/thousands km. Such an instrument is so far unavailable.

A classical way to get high angular resolution and a full beam synthesis with a single telescope of moderate size is through lunar occultations. This observing technique provides the angular resolution of a single linear antenna several kilometers long. However, at millimeter wavelengths the Fresnel fringes produced by the Moon limb as the source under study is occulted have never been observed. We present here the observation with the 30-m IRAM radio telescope of the v=1 J=2-1 line of SiO during an occultation (and reappearance) of R Leo by the Moon.

Observations of the 12.8 μm [NeII] line emission, the OH absorption against Sgr A and the HCN emission were compared to determine the relationship between the ionized and neutral gas in the central 10 pc of the Galaxy. The distribution of the neutral gas is too asymmetric to be a ring or disk. Along the western arc, the ionized gas velocity is very different from that of the neutral gas, suggesting it may not be the ionized inner edge of the circum-nuclear neutral gas.

The previous two talks in this session have shown the importance of the nucleus of the Milky Way as the host to a possible massive black hole. SgrA* is apparently surrounded by a circumnuclear ring first seen in the HCN J = l-0 emission (Gusten et al. 1987). Infall from the circumnuclear ring could explain the ionized streamers which appear to orbit SgrA* (Lo and Claussen 1983; Serabyn and Lacy 1985). Recent studies in the NH3 emission using the Nobeyama Millimeter Array (Okumura et al. 1989; 1991) and the Very Large Array (Ho et al. 1991) have suggested that a streamer may feed the Galactic center from the southern cloud M-0.13-0.08. Here we show a second streamer originating from the eastern cloud M-0.02-0.07 as well. In both cases, interactions between the molecular clouds and supernovae seem to be important, and can be seen in position-velocity diagrams. This may be the mechanism by which gas is pushed toward the central gravitational field.

The origin of the straight magnetic filaments in the Radio Arc near the Galactic Center is still controversial: either if they are permanent structure of constant configuration for a galactic-time scale, or they are temporary structure of short life time such as due to a sudden injection of cosmic rays or to sudden shock compression. Measurement of life time of the radio emitting cosmic ray electrons consisting the filaments is one of the crucial methods besides a time variation measurement of the fine structure of the filaments.

In order to investigate possible spatial variation of spectral index at higher frequencies in the filaments, which might give information about the life time of cosmic ray electrons, we have performed high-resolution radio continuum observations at 43 GHz of the GO.18-0.04 region of the radio Arc near the galactic center using the Nobeyama Millimeter-wave Array. A detailed description of this work is given in Sofue et al. (1992).