One of the great challenges of modern astrophysics is the proper understanding of the interstellar processes that lead to new generations of stars, or, if you wish, of how older stars like our Sun once formed. The problems involved are of relevance to both our own galaxy, the Milky Way, and to external galaxies.
According to current understanding the formation of stars involves a complex feed-back, and presumably self-regulating, energy-transforming scheme of non-linear, non-equilibrium physics and chemistry. The building blocks are ensembles of elementary particles, atoms, molecules and solid state particles being subject to gravitational, electromagnetic and radiative interactions. These forces bring eventually order into chaos, `creating' out of close to nothingness a stellar body that is dense and hot enough to ignite and maintain thermonuclear fusion reactions as in our Sun. Together with this new sun, there will also have formed planets, one of which might eventually become inhabited by beings who are able to contemplate their life giving star's formation and evolution.
Our research in the field of stellar formation is oriented along four major lines: (i) The study of the media forming stars, with particular emphasis on the understanding of the initial physical and chemical conditions as functions of space and time. (ii) The study of ensembles of very young stellar objects, in order to empirically determine the mass distribution spectrum at stellar birth. The functional form of this spectrum appears universal, i.e., it is the same in our Galaxy and in external galaxies, and our primary objective is to understand to what degree the memory of the initial cloud condition is `frozen in' into this function. (iii) The study of the dynamics of forming stars, especially during the earliest, protostellar, phases. The physics of the apparently co-existent mass building infall and angular momentum shedding mass outflows are not well understood, but this understanding is clearly important as these processes limit the final stellar mass and incorporate the formation of planets. (iv) The study of young stars and in particular the evolution of their accretion disks.
The analyses of the ISOCAM survey of nearby star formation regions continued. A.A. Kaas defended her PhD thesis mainly based on this work. A theoretical interpretation of the ISOCAM colours for field stars was initiated. The reduction and analyses of LWS data continued. The work has been concentrated on two regions, L1551 (a well known outflow region) and the Serpens star formation region.
Brown dwarf candidates discovered in the ISOCAM survey were observed spectroscopically at ESO. For some of them the analysis confirms their brown dwarf status. Based on high resolution spectroscopy (NOT/SOFIN), the T Tauri star RW Aur A was found to have a close low-mass companion, possibly a brown dwarf. An extended survey of dark globules, mainly carried out using the SEST, has been completed. This catalogue will be useful as a reference in different contexts an in particular serve as a database for the Odin mission. Research on interstellar filaments in regions with no star formation continued in 1999. An extensive study of the patterns of linear polarization of stars in such regions were completed during the year. New observations were collected at Onsala and NOT.
Laboratory tests and some software and hardware modifications of the infrared camera 'SIRCA' were carried out in preparation for the first telescope tests on the NOT (scheduled for Feb. 2000). Regarding ODIN satellite, the international coordination of scientific preparations has continued and the scheduling program was further developed. The participation in the ESA satellite FIRST (to be launched around 2007) concerns the heterodyne receiver and the bolometer camera/spectrometer and continued during 1999. The ESA study called 'Darwin' concerns a space infrared interferometer capable of identifying earth-like planets. We participated in this study and organized an international conference 'Darwin and Astronomy' in Stockholm.