Professor Icko Iben, Jr. (Emeritus Distinguished Professor, University of Illinois, Member of United State National Academy of Science) visited Hokkaido University for four months from July 1st through October 31st, 2003. He was engaged in educational activities and cooperative researches mostly in the Department of Physics, Graduate School of Science, and in addition, made academic exchanges with researchers of space and planetary scientists of other departments, faculty and institute of Hokkaido University. Prof. Iben also visited National Astronomical Observatory of Japan for four days in September, and had talks with the director and other staffs and attended a conference with central researchers in the field of stellar physics in Japan.
The main purpose of the invitation program is to promote the education and research activities of Hokkaido University in his major field of stellar evolution and to train younger astrophysicists in collaboration with him and to make contributions to the progress of the research program in the field of stellar physics in Japan. At the same time it is expected Hokkaido University to take a part in the reformation of education and research organizations of Hokkaido University in space and planetary science.
Since this was the first year of the two-year invitation program, he was asked to establish a basis for the collaborative researches and for the education programs and to apprehend the present circumstances and the issues of the education and research systems of space and planetary science of Hokkaido University. It was also expected for him to be acquainted with the current activities in the relevant fields of astronomy and astrophysics in Japan. In this sense, the activities of this year resulted satisfactory and laid the foundation to produce fruits next year.
The outlines of educative activities, cooperative researches, and academic exchanges are as follows.
(1) Educative activities and collaborative researches
A distinguished contribution to the education of graduate students and of post-doctoral fellows was made mainly through the guidance and discussions in the regular seminars during the semester and in the small conferences occasionally organized on the stellar physics and nuclear astrophysics. A joint research was organized on one of the currently central topics in the astrophysics, i.e., on the formation and evolution of extremely metal-poor stars with three postdoctoral fellows as collaborators, graduated from our department, for the purpose of their training. In addition, the construction of new numerical simulation code for stellar evolution was planed in collaboration between Prof. Iben and the stellar evolution group of Hokkaido University.
The Extremely metal-poor stars with the iron abundance less than about 1/300 of the solar value are thought to be born in the very beginning of our Universe, and have been attracting wide interest as tool for investigating the evolution of early Universe. Recently lots of information have been provided by their detailed observations with use of large-scaled telescope such as Subaru telescope. The purpose of our paper is to expand the former theory, developed by Prof. Iben and Fujimoto and to elucidate the peculiarity and general pictures of the evolution of the evolution of extremely metal-poor stars, distinguished from the stars of younger generations with larger metal abundances, with taking into account their properties revealed by the recent observations. On the basis of the results, we further explore the origin of a star HE0170-5240 with the iron abundance of 1/200,000 of the solar value, discovered in 2002, the most iron-deficient one among the stars known to date. We show that this star is possible a survivor of the first generation stars of our Universe and propose a observation to verify it. In this paper, we can formulate a new process of nucleosynthesis with neutron captures, peculiar to the extremely metal-poor stars. This work will give a basis to the future research in this field (T. Suda, M. Aikawa, M. Machida, M.Y. Fujimoto, and I. Iben, Jr. 'Is HE0170-5240 A Primordial Star? -- The Characteristics of Extremely Metal-Poor, Carbon-Rich Star', accepted for publication in Astrophysical Journal).
From recently observations with large telescopes, new aspects of stellar properties have been accumulated, which cannot be accommodated within the current standard theory of stellar evolution. One of main purpose of collaborative research is to construct a new code of stellar evolution necessary to solve the new problems of stellar evolution at this stage. For that purpose, it has to be equipped with a powerful nuclear network, applicable to different situations, which may vary largely with the stellar parameters, mass and metallicity, and with the evolutionary stages. In addition, it is also indispensable to incorporate the prescription, which at least makes it possible to simulate the extra element mixing, other than thermal convection, due to turbulence, such as generated as a result of hydrodynamic instabilities in different rotating stars. A layout of the new code was discussed and the first step of construction has been successfully performed. It is now on test run and under the process of debugging. We plan to investigate the newly revealed aspects of stellar properties theoretically with this newly constructed code, which may hopefully serve as an instrument for our group to promote the researches and to contribute to the development in the theory of stellar evolution.
In addition, it is a great experience for students and fellows to have contact with the distinguished astrophysicist daily and to have daily conversations on the topics of their investigations and the related topics in astrophysics. These young people seem to be fascinated with Prof. Iben's profound knowledge and stimulated by his professional attitude to the research. He also kindly reviewed the papers written by the students and to correct their English. One of the papers, reviewed, is to appear in Astrophysical Journal (M. Aikawa et al, 'An Insight onto the Reaction Rates of the NeNA and MgAl Chain from the Abundance Anomalies in Globular Cluster Red Giants', 2004, June 20 issue).
(2) Academic exchanges within the University
In Hokkaido University, researchers in Astrophysics and related fields are distributed separately in various faculty and institute, other than Graduate School of Science since there has been no department of Astronomy to date. In addition to the daily communications with peoples in laboratories of Astrophysics and Nuclear Astrophysics, Department of Physics, Prof. Iben had made contact with people in solar-physics group of Department of Earth and Planet Science. He also visited Institute of Low Temperature Science to look over the experimental facilities and discuss on the researches with people of Ice & Planetary Science Laboratory. The exchanges with the research groups made it possible to gain insight into the current circumstances and activities in the fields of Astrophysics and Planetary Science.
Among these people in Space and Planetary Science and Technology, an endeavor has been raised to unite the researches in the university and reform the system of education and research after the construction of radio telescope and the foundation of radio astronomy group two years ago. Since then, there has been discussion on the plan of reorganization, and with this visit as an opportunity, the members in the group of Space Planetary Science and Engineering arranged the meeting with Prof. Iben to present a state of affairs on the ways of education and research and to consult about the way to improve them. In the course of discussion in the meeting and afterwards, Prof. Iben made useful advices on the basis of his long and broad experience in the various universities, as a faculty member and a department head, and as member of United States National Academy of Science. In particular, one of his proposal on the system was that he experienced in Massachusetts Institute of Technology was very interesting, which is quite different from current systems in Japan, but has proved to keep the activities of group at high level. His advises are very helpful and worth further considerations. It is planed next year to formulate a concrete proposal on the basis of these activities.
(3) Academic exchanges with other Universities and Institute
In order to inspect the status of researches in Astrophysics of Japan, Prof. Iben visited National Astronomical Observatory of Japan for days, and exchanged views with Dr. Norio Kaifu, Director general, and other principal members on the recent outcomes and future developments of astronomy and astrophysics in Japan. In particular, as for the activities in the optical and infrared observations with Subaru telescope, which is closely related to his major field, a detailed lecture was provided, and seemed very helpful for Prof. Iben to comprehend the current status and new directions in development. The activities in the fields of stellar astrophysics have been increased recently with aid of Subaru telescope. But serious problem is a scarcity of young talents, which has resulted historically.
In collaborations with the researches in the Observatory, the University of Tokyo, and Tokai University, who are working actively in the stellar astrophysics, a workshop was organized on September 11 at the National Astronomical Observatory of Japan. The topics discussed in the workshop are the theories of formation and evolution and the observational characteristics of extremely metal-poor stars in Galactic halo. In this workshop, more than a half of attendants are young talents. The purpose of this workshop is to reveal the potentials of the researches in Japan and to encourage young talents to work in the fields of stellar physics, in addition to formulate the tasks in near future. Prof. Iben played a positive role to lead the discussion and stimulate the young talent though sincere comments and arguments. The knowledge and understanding gained during his visit to the observatory may form a sound basis for advise and proposal on the promotion of activities in the relevant fields of Hokkaido University and on the development of researches of the stellar evolution in Japan.