The Spiral Structure of Our Galaxy

The idea of the organization of a Symposium on Spiral Structure came at a special meeting of Commission 33 on Spiral Structure during the 12th General Assembly of the IAU in Prague, 1967. So much interest was shown during this meeting that one of us proposed a special Symposium on the 'Spiral Structure of Our Galaxy' for 1969. The response was immediate and it was finally agreed upon holding the Symposium in Basel, a center of galactic research in the center of Europe. During the next months a special 'List of Problems', related to this Symposium, was sent to many prospective participants by the president of Commission 33. This stimulated an increase of interest in problems of galactic spiral structure and a con­ centrated effort on some problems. The organizing Committee of the Symposium was composed of Drs. L. Woltjer (president), W. Becker, A. Blaauw, B. J. Bok, G. Contopoulos, F. J. Kerr, C. C. Lin, S. W. McCuskey and S. B. Pikel'ner. Most of the work for the organization of the Symposium was carried by Dr. L. W oltjer. The Local Committee, composed of Drs. W. Becker, U. W. Steinlin, R. P. Fenkart, and G. A. Tammann, made every effort to secure the success of the Symposium. Most of the credit goes to Dr. Steinlin. The Symposium was supported financially by the IAU and by the Swiss National Science Foundation. The meetings took place at the University of Basel, which provided also secretarial help and many other facilities.

1. Survey of spiral structure problems.- I / Spiral Structure in Galaxies.- 2. Spiral structure in external galaxies.- 3. Spiral structure of our Galaxy and of other galaxies.- 4. Statistics of spiral patterns and comparison of our Galaxy with other galaxies.- 5. The distribution of dark nebulae in late-type spirals.- 6. Angular momenta of late-type spiral galaxies.- 7. Applying the model of a normal logarithmic spiral to galaxies.- 8. Density distribution and the radial velocity field in the spiral arms of M31.- 9. The rotation curve, mass, light, and velocity distribution of M31.- 10. A comparison of dynamical models of the Andromeda Nebula and the Galaxy.- 11. OB stars on the outermost borders of M31.- 12. Observations of radio continuum emission from M31.- 13. Kinematics of M33, M51 and the L.M.C..- 14. The stellar velocity field in M51.- 15. Hii Regions in NGC 628, NGC 4254 and NGC 5194.- 16. Spiral structure and distribution of stellar associations in NGC 6946.- II / Observations of Spiral Structure in Our Galaxy.- A. Radio Observations.- 17. Spiral structure of neutral hydrogen in our Galaxy.- 18. The distribution of Hii regions.- 19. A motion picture film of galactic 21-cm line emission.- 20. Spiral structure of the Galaxy derived from the Hat Creek survey of neutral hydrogen.- 21. Galactic continuum source counts.- 22. Matter far from the galactic plane associated with spiral arms.- 23. On a possible corrugation of the galactic plane.- 24. A study of spiral structure for 270°?lII?310°.- 25. A peculiar neutral hydrogen concentration at lII=280° bII=18°.- 26. Contribution to the study of the distribution of neutral hydrogen in the region 230°?lII?280°.- 27. Radial velocities of neutral hydrogen in the anticenter region of the Galaxy.- 28. Radio observations of some details in the Hi local spiral arm.- 29. Hydrogen in the regions of four stellar clusters.- 30. The distribution in galactic longitude of observable pulsars.- 31. Pulsar distances, spiral structure and the interstellar medium.- 32. On the physical conditions in interstellar Hi gas.- B. Optical Observations.- 33. Local stellar distribution and galactic spiral structure.- 34. Remarks on local structure and kinematics.- 35. Galactic clusters and Hii regions.- 36. A new interpretation of the galactic structure from Hii regions.- 37. The distribution of Hii regions in the local spiral arm in the direction of Cygnus.- 38. Reflection nebulae and spiral structure.- 39. The galactic structure and the appearance of the Milky Way.- 40. The study of the Milky Way integrated spectrum and the spiral structure of the Galaxy.- 41. Space distribution of interstellar dust in connection with the galactic spiral structure.- 42. A comparison of the density gradients of main sequence stars obtained by two different methods in different galactic latitudes.- 43. The galactic distribution of young Cepheids.- 44. A progress report on the Carina spiral feature.- 45. The space distribution of the OB-type stars in Carina.- 46. Photometric investigation of the association Car OB 2.- 47. Photometric and spectroscopic data for some distant O and B stars.- 48. Progress report on the Cleveland-Chile survey for southern OB stars.- 49. A study of O and B stars in Vela, along the galactic equator.- 50. Progress report of the current research on the galactic structure in Vela.- 51. Calibration of 4-color and H? photometry for B- and A-type stars.- 52. Wolf-Rayet stars, ring-type Hii regions, and spiral structure.- 53. Stellar rings and galactic structure.- 54. Radial velocities of early-type stars.- 55. The velocity dispersions of O- and B-stars within a few kpc.- 56. On the distribution of space velocities of OB-stars.- 57. Questions concerning the usefulness and feasibility of large-scale stellar statistics.- III / Theory of Spiral Structure.- A. Normal Spirals.- 58. Gravitational theories of spiral structure.- 59. The theory of spiral structure of galaxies.- 60. Small amplitude density waves on a flat galaxy.- 61. The propagation and absorption of spiral density waves.- 62. Large scale oscillations of galaxies.- 63. Generating mechanisms for spiral waves.- 64. Spiral waves caused by a passage of the LMC?.- 65. Non-linear density waves in pressureless disks.- 66. Density waves in galaxies of finite thickness.- 67. Particle resonance in a spiral field.- B. Barred Spirals.- 68. Barred spiral galaxies.- 69. Structure and dynamics of barred spiral galaxies with an asymmetric mass distribu­tion.- C. Numerical Experiments.- 70. Numerical experiments in spiral structure.- 71. Computer models of spiral structure.- IV / Comparison of Theory and Observations.- A. Gravitational Effects.- 72. Interpretation of large-scale spiral structure.- 73. Theoretical 21-cm line profiles: Comparison with observations.- 74. Neutral hydrogen in the Sagittarius and Scutum spiral arms.- 75. Large-scale galactic shock phenomena and the implications on star formation.- 76. Deviation of the vertex of the velocity ellipse of young stars and its connection with spiral structure.- 77. Possible influence of the galactic spiral structure on the local distributions of stellar residual velocities.- 78. Additional evidence for the cataclysmic origin of spiral structure in galaxies.- B. Magnetic Effects.- 79. Magnetic fields and spiral structure.- 80. On the circulation of gas near the galactic center.- 81. Magnetohydrodynamical models of helical magnetic fields in spiral arms.- 82. Local magnetic field and its relation to the local spiral arm structure.- 83. Polarization of southern OB-stars.- 84. On a corollary to the magnetic dipole theory of the origin of spiral structure.- V.- 85. Summary and outlook.- 86. Desiderata for future work.