172 ANNTJAL REPORT SMITHSONIAN INSTITUTION, 19 64 



Observations made at the Kitt Peak National Observatory concern- 

 ing magnetic fields in the solar photosphere have been analyzed by 

 Dr. Noyes. These observations yielded a definite correlation between 

 photospheric velocities and magnetic fields, in the sense that the highest 

 magiietic fields (about 50-75 gauss) found in quiet regions tend to 

 occur in regions where material is moving downward (with velocities 

 of about 0.2 km sec"^). This has been interpreted as a result of con- 

 vective sweeping of magnetic fields toward the downward-descending 

 periphery of the large convective cells (supergranulation) which cover 

 the surface of the quiet sun. 



Dr. Giovanni Fazio has reduced gamma-ray detector data from 1,000 

 orbits of Orbiting Solar Observatory I.^^ These reductions have 

 shown no evidence of gamma rays with energy greater than 50 million 

 ev from the sun, even during solar flares, with an upper limit of the 

 order of 10"^ photons/cm^ sec. Likewise, no evidence was fomid for 

 celestial sources of primary gamma rays. The sensitivity of the detec- 

 tor was limited by background radiation. 



The possibility of detecting neutrinos from the sun is a lively topic 

 of discussion in astrophysical circles. Some authors suggest that this 

 can be accomplished by using the reaction in which a solar ve combines 

 with a CP^ nucleus to give Ar^'^ and an electron. The radioactive gas 

 Ar'^ may be detected by comiting techniques. The Observatory has 

 laboratories equipped to do this counting, as Ar^^ is one of the radio- 

 active isotopes analyzed in meteorites. Since the ve reaction cross sec- 

 tion with Ar^^ is extremely low, vast quantities of CP'^ must be used. 

 Since Ar^^ can also be generated by cosmic-ray-induced rections, the 

 experiment must be performed under conditions of extreme radiation 

 shielding — say deep in the earth. Dr. Lundquist has suggested that 

 commercially pumped brine wells might meet these requirements, if 

 the Ar^^ from the chlorine-rich brine could be measured. Dr. Mitler 

 has made a study of the relative amounts of Ar^^ generated by the solar 

 neutrino reaction and by other undesired reactions. The practical 

 implementation of the experiment is being studied. 



Stellar ohservations. — A feature of current astrophysics is the rapid 

 expansion of observational possibilities into previously inaccessible 

 parts of the electromagnetic spectrum and to radiation other than 

 electromagnetic. This has been accomplished in part by carrying 

 instruments above the absorption of the atmosphere. New teclinology 

 has also contributed to the enlarged observational capabilities. Com- 

 parison and correlation of data from widely spaced frequencies have 

 also proved to be powerful procedures. 



An example of correlated observations at quite different frequencies 

 is the study of flare stars.^ During preagreed time intervals, the 



See footnotes, p. 177. 



