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Contours of equal radio brightness at 21 cm, as measured with the Westerbork Synthesis Radio Telescope (operated by the Netherlands Foundation for Radio Astronomy) of Galaxy M51 compared with the optical image made by the Hale 200-inch telescope. The radio-image provides evidence of the continuity of M51.

6. SETI RELATED SCIENTIFIC AND TECHNOLOGICAL ADVANCES

The material in this section contains specific examples of scientific or technological advances that could arise either as a direct result of a SETI program, or as a result of the science of SETI (see Section II-6).

1. Observational studies of high brightness contrast systems: Direct detection of other planetary systems either at visible or infrared wavelengths, will require the development of telescopes capable of studying systems with very high brightness contrast ratios. Particularly valuable contributions could arise from the use of such telescopes to study faint nebulosities associated with quasars and galactic nuclei, for example. One could also examine details hitherto unobservable in short period, mass-transfer binary systems.

2. Observational studies of small-scale structure in astronomical systems: The high spatial resolution required of an optical or infrared interferometer used to detect other planetary systems could provide major advances in observational studies of small-scale structure, such as mapping of spiral structure in external galaxies. A high resolution infrared interferometer would prove invaluable for mapping dark interstellar clouds and regions of active star formation.

3. Improved knowledge of galactic dynamics and distance scales: The development of an astrometric telescope for the detection of other planetary systems will improve the precision of parallax measurements by two or more orders of magnitude, thereby increasing to several hundred parsecs the range for which parallax studies can provide high precision measures of distance. Use of high sensitivity astrometric telescopes can also provide refined proper motion observations that will allow for more detailed modeling of the dynamics of the Galaxy.

4. Studies relating to binary frequency: There are at present few comprehensive studies of the binary frequency of main sequence stars. It would be very useful to carry out such studies over a wide range of spectral types; they could be accomplished with high precision radical velocity machines of the type under development for the task of detecting other planetary systems (see Section II-3). An important aspect of binary studies is the birth function of the secondary bodies. Is it a van Rhijn function, or is it different?

5. Studies of M-dwarfs: M-dwarfs constitute the most abundant class of stars, but we know very little concerning their detailed behavior. A coherent program aimed at determining the nature of violent flare events in M-dwarfs would be valuable, not only to a SETI effort, but to stellar astrophysics. At present it is unclear whether flaring is confined to a particular range of spectral type, or whether it is an evolutionary phase through which all M-dwarfs must pass. A flare patrol of M-dwarfs near the galactic pole would be helpful, as those stars are known to be old. Studies of the flare events themselves are important in determining the mechanism, energy spectrum and frequency of these intriguing phenomena.

6. Studies of the Sun: The long-term stability of stellar properties, such as luminosity and size, is an important astrophysical topic, and it also relates to a SETI program. The long-term

stability of the Sun's luminosity is currently under debate. The time scale over which luminosity variations might manifest themselves is too long to admit valid conclusions on the question as a consequence of studying one star (e.g., the Sun). However, a proper statistical analysis of a large sample of stars of similar spectral type could answer the question. The classification (spectral and luminosity class) techniques necessary for a stellar census (see Section III-4) will permit high luminosity resolution over a narrow spectral range. High precision radial velocity machines (Section II-3) would make it possible to carry out long-term (months, years) studies of the stability of the Sun's radial velocity (and hence size). This is best accomplished by means of a highly polished sphere in orbit, or mirrors on the ground, which could be used to produce a stellar image of the Sun.

7. Studies of the luminosity function: The taking of a stellar census in the solar neighborhood would provide many orders of magnitude more data upon which to model a luminosity function. In conjunction, the high precision astrometric telescopes developed for detection of other planetary systems will both increase the precision with which one can determine the distance to binary star systems, and determine the masses of the stars in a binary system. This will provide a quantum jump in data that can be used to define a mass-luminosity relation over a wide range of spectral type (or mass).

8. Studies of star and planetary system formation: It is extremely important to pursue both theoretical and observational studies of star formation. The ability to study fine-structure in dark interstellar clouds (see paragraph 2 above) will provide valuable observational data on the early stages of star formation. It is just as important to carry out theoretical modeling of the star formation process. At present, theory lags observation in this area by a significant amount. Particularly important are studies of angular momentum transport during the dynamic phases of protostellar evolution, studies of the factors controlling the mass spectrum of stars and studies of conditions in circumstellar material. The latter studies provide the much needed link, if such a link exists, between the star formation process and the formation of planetary systems. Theoretical studies of the growth of planets in circumstellar nebulae, and the evolution of such nebulae are also very valuable.

9. Studies of planetary evolution: An important aspect of planetary evolution concerns the formation and evolution of planetary atmospheres. Theoretical modeling of this stage of a planet's evolution is fairly rudimentary, and can be improved with additional effort and data. Continued examination of the evolution of the Earth's atmosphere and the atmospheres of other planets in the solar system will provide needed data. Increased studies of the relationship between the Sun and the atmosphere of the Earth in particular, and planets in general, would be very valuable. One would like to be able to estimate how such interactions varied as a function of the spectral type of the parent star in a planetary system.

10. Studies of chemical evolution and the origin of life: Great advances have been made in this subject in recent years. However, the transition from chemical evolution to biological evolution (see Section II-1) is not understood at present. Additional laboratory studies in this area, as well as continued attempts to find evidence relating to this transition on the Earth, are very important.