radio astronomy and very large telescopes

3
RADIO ASTRONOMY AND VERY LARGE TELESCOPES* NORIO KAIFU Nobeyama Radio Observatory, National Astronomical Observatory, Nobeyama, Minamimaki, Japan (Received 30 March, 1989) Abstract. The current achievements of the observational abilities of radio astronomy is briefly reviewed putting emphasis on the imaging capability. The new projects in radio astronomy are discussed in connection with the new generation of optical/IR telescope projects. The imaging with higher resolution and higher quality has been a central target of the developments of the astronomical instruments for htmdreds of years. The recent remarkable situation is that the radio, IR, and X-ray images are attaining the comparable (sometimes exceeding) qualities to those of the images with the optical telescopes, and such improvements in various wavelength regions provided us the multi-dimensional aspects of the distant objects which lead us to the direct understanding of the substantial of the phenomena in the Universe. 1. Imaging with Single Dish Radiotelescopes The single dish radio observations have achieved 10" spatial resolutions in the mm and sub-mm wavelength regions. The homologous deformation technique, as well as the various developments on the telescope design, measurements and adjustment, provided a jump &the surface accuracy of large paraboloid dishes. Very recently the JCMT (JAC, Hawaii) 15-m telescope has achieved 8 arc sec resolution at 350 ~tm wavelength. The discovery of small protostellar disks, structure of the bipolar molecular flows, and numbers of new results in interstellar clouds, star forming regions, late-type stars, the galactic center and external galaxies were produced by recent high-resolution observa- tions with these large mm and sub-ram wave telescopes. The main high-resolution single dish telescopes in the mm and sub-mm wave regions are: Nobeyama Pico Velta Hawaii (JCMT) 45-m telescope 30-m telescope 15-m telescope 15" resolution at 115 GHz, 10" resolution at 230 GHz, 8" resolution at 860 GHz. However, the further improvements seem not to be rosy. One of the difficulties is the pointing accuracy problem of large dishes. Instead, the higher capability of the imaging * Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29-December 1988. Astrophysics and Space Science 160: 27-29, 1989. 1989 Kluwer Academic Publishers. Printed in Belgium.

Upload: norio-kaifu

Post on 10-Jul-2016

217 views

Category:

Documents


1 download

TRANSCRIPT

RADIO A S T R O N O M Y AND VERY LARGE T E L E S C O P E S *

N O R I O K A I F U

Nobeyama Radio Observatory, National Astronomical Observatory, Nobeyama, Minamimaki, Japan

(Received 30 March, 1989)

Abstract. The current achievements of the observational abilities of radio astronomy is briefly reviewed putting emphasis on the imaging capability. The new projects in radio astronomy are discussed in connection with the new generation of optical/IR telescope projects.

The imaging with higher resolution and higher quality has been a central target of the developments of the astronomical instruments for htmdreds of years. The recent remarkable situation is that the radio, IR, and X-ray images are attaining the comparable (sometimes exceeding) qualities to those of the images with the optical telescopes, and such improvements in various wavelength regions provided us the multi-dimensional aspects of the distant objects which lead us to the direct understanding of the substantial of the phenomena in the Universe.

1. Imaging with Single Dish Radiotelescopes

The single dish radio observations have achieved 10" spatial resolutions in the mm and sub-mm wavelength regions. The homologous deformation technique, as well as the various developments on the telescope design, measurements and adjustment, provided a jump &the surface accuracy of large paraboloid dishes. Very recently the JCMT (JAC, Hawaii) 15-m telescope has achieved 8 arc sec resolution at 350 ~tm wavelength. The discovery of small protostellar disks, structure of the bipolar molecular flows, and numbers of new results in interstellar clouds, star forming regions, late-type stars, the galactic center and external galaxies were produced by recent high-resolution observa- tions with these large mm and sub-ram wave telescopes.

The main high-resolution single dish telescopes in the mm and sub-mm wave regions are :

Nobeyama

Pico Velta

Hawaii (JCMT)

45-m telescope

30-m telescope

15-m telescope

15" resolution at 115 GHz ,

10" resolution at 230 GHz ,

8" resolution at 860 GHz .

However, the further improvements seem not to be rosy. One of the difficulties is the pointing accuracy problem of large dishes. Instead, the higher capability of the imaging

* Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29-December 1988.

Astrophysics and Space Science 160: 27-29, 1989. �9 1989 Kluwer Academic Publishers. Printed in Belgium.

28 N. KAIFU

by applying the sensitive multi-receiver system or multi-elements heterodyne detector receiver (10-20 elements so far) are being developed intensively in some radio observa- tories and it will add considerable power to the mm and sub mm single dish telescopes by combining with the larger spectrometers and improved imaging software systems.

2. Imaging with Super Synthesis Telescopes

The cm and mm wave supersynthesis arrays obtain the 'radio pictures' with 5"-0.1" resolution, comparable to those of optical/near IR images (e.g., VLA, 0.1" at 15 GHz, MERLIN, 0.35" at 1.6 GHz). The mm wave arrays can provide velocity resolved high spatial resolution images of coldjwarm molecular gas. Although the objects are more or less limited because of relatively poor sensitivity, the mm-wave supersynthesis arrays (listed below) are producing numbers of exciting results especially on the external galaxies.

Hat Creek 6-m x 3 (planned to be 6-m x 6),

Owens Valley 10-m x 3,

Nobeyama 10-m x 5,

Plateau de Buel 15-m x 4 (under adjustments).

The new powerful mm-wave imaging instruments which aim to the 1" or higher resolution, very quick and high-quality images with various molecular lines and con- tinuum emission are proposed in Japan (Nobeyama) and U.S.A. (NRAO).

Nobeyama plan 10-m x 30, 40-230 G H z , baseline - 600 m ;

NRAO plan 7.5-m x 40, 100-300 G H z , baseline ~ 500 m .

These instruments can be called as 'mm-wave VLA', but with very high abilities of spectroscopic imaging and will produce enormous amount of velocity resolved pictures. The Nobeyama plan puts emphasis on the high quality imaging of cold and general medium in the galaxies and in our Galaxy, and the NRAO plan aims at rather warm and compact sub-mm objects.

3. Imaging with VLBI

The extremely high-resolution images (milli-arc sec or higher) can be obtained by the VLBI observations for limited objects with very high brightness like quasars and maser spots. Recent successful experiments of the ram-wave VLBI (Japan- Sweden-U. S.A.) resulted the first mm-wave maps of 3C84 and 3C273 with the resolution of 50 g arc sec. The high quality VLBI maps will become to be available soon by new large instruments in U.S.A. (VLBA, 25-m x 10) and in Australia (AT, 25-m x 6).

RADIO ASTRONOMY AND VERY LARGE TELESCOPES 29

A considerable progress of the VLBI imaging quality as well as the resolution will be achieved by the space VLBI. The baseline between the orbit antenna and the ground- based antenna rotates rapidly and the rich Fourier components can be used for the image construction. The undergoing first space VLBI projects are:

RADIOASTRON USSR, 1994-95? 20-m orbit antenna, 0.37, 1.6, 5, 22 GHz ,

VSOP JAPAN, 1994-95? 10-m orbit antenna, 1.6, 5, 22 GHz .

High-quality VLBI images from above-mentioned newly coming instruments should be compared with the Space Telescope images or with the optical/IR interferometers which are also expected to be available in the near future.

4. Spectroscopy, sub-mm and IR Regions

It should be emphasized that the high spectral resolution mm wave observations combined with the high spatial resolution images have provided extremely rich informa- tion on the structure and dynamics of the molecular clouds and related various phenomena. The obvious next targets are the sub-mm wave and IR regions, and the developments of the techniques and instruments for the velocity-resolved imaging in these regions are essentially important.

The JNLT could be one of the most powerful instruments for the near IR and intermediate IR (1-30 ~tm) with its design suitable for high resolution (0.2"-0.3") and IR-oriented optics. The developments of new and excellent IR detector (and spectrometer) systems for JNLT should be exciting job.

The sub-mm wave capability of JNLT is also high. The sensitivity of JNLT for compact sources at 350 lain (860 GHz) is comparable to that of JCMT 15-m sub-mm telescope, and the beam will be very well shaped with HPFW of 11.5".

Finally I wish to stress again the importance of the efforts to develop novel instru- ments which make it possible or much easier to observe the new world.