In this study, vibrational properties and stability of delta-Scuti like pulsating pre-main sequence stars have been investigated. Studies were held in the mass range 2-4 Mo and limited to radial linear adiabatic pulsations. Numerical computations were performed by the oscillation program written by Kýrbýyýk & Al-Murad (1993). The models were selected to be at the latest phases of the pre-main sequence evolution where the luminosity starts to increase. We have limited our calculations upto the end of the radiative inner regions, since at the surface of the star, our adiabatic perturbation computation does not perfectly fit to the relatively thin non-adiabatic convective envelope of the star. The results of the stability analysis showed that the PMS models undergo an instability whose time period is a function of mass. Instability Strip of pulsating PMS stars was re-drawn with comparison to M. Marconi & F. Palla (1998). The effect of gravitational contraction on stability was also investigated.

This volume contains the fifteenth tri-annual reports of the Presidents of the forty Commissions of the International Astronomical Union; it refers to the progress in our discipline during the three years 1970, 1971 and 1972. As compared to earlier volumes a gradual change in character is unmistakable. The ever increasing flow of publications, combined with the obvious necessity to keep the Reports at a reasonable size and price level has gradually forced the Commission Presidents to be more selective than before in drafting their Reports. I have certainly stimulated them into that direction - in order that Reports like these be valuable and lasting, it seems imperative that the individual contributions have the character of a critical overall review, where a fairly complete summary is given of the major develop ments and discoveries of the past three years, and in which the broad developments and new trends be clearly outlined, while at the same time essential problems for future research are identified. With respect to the latter item I have suggested the Commission Presidents to add to their reports a brief section on scientific priorities for future research in the field of their Commissions. In order to save space I have suggested to Commission Presidents that references to published papers are given on the basis of their number in the published issues of Astronomy and Astrophysics Abstracts. For instance, the indication (06. 078. 019) or (AAA 06. 078.

"This is a remarkable book: a symposium proceedings volume that will also function as a graduate-level text. Dedicated to the great theorist S. Chandrasekhar, the book consists of ten well-written chapters that cover the essential tools of theoretical astrophysics. The first half of the volume is concerned with the theory of how stars work (structure, stability, rotation, magnetism, dynamics) and the latter half is mainly a survey of relativistic astrophysics. . . . Read it for a broad-brush view of what theorists are up to now and how they solve problems."—Journal of the British Astronomical Association "The book as a whole should be a gift from every research supervisor to every new graduate student in theoretical astronomy."—D. W. Sciama, Science

A complete and comprehensive treatment of the physics of the stellar interior and the underlying fundamental processes and parameters. The text presents an overview of the models developed to explain the stability, dynamics and evolution of the stars, and great care is taken to detail the various stages in a star's life. The authors have succeeded in producing a unique text based on their own pioneering work in stellar modeling. Since its publication, this textbook has come to be considered a classic by both readers and teachers in astrophysics. This study edition is intended for students in astronomy and physics alike.

"This thesis came about against the backdrop of the query of massive star formation, with a special focus on young intermediate- to high-mass stars in their natal environment: massive star forming regions (mSFRs). The outcome of the (massive) star-formation process is studied by characterizing young (high-mass) stars that reveal their photosphere as well as signs remnant of formation in optical to near-infrared spectra. A sample of these relatively massive pre-main-sequence (PMS) stars in the giant H II region M17 is extensively studied in multiple wavelength regimes with the aim to characterize their circumstellar disks. The observational and theoretical results presented touch upon a broad range of topics ranging from the formation of high-mass close binaries to disk formation and evolution in the harsh and dense environments of giant H II regions. Following the introduction in Chapter 1, Chapter 2 presents a census of the young stellar content of the three giant H II regions M8, G333.6−0.2, and NGC6357, including the classification of H- and K-band spectra of about 200 stars in these regions. Chapter 3 presents an analysis of the CO ro-vibrational first and second overtone bandhead emission from the circumstellar disks of five intermediate- to high-mass PMS stars in the mSFR M17. Chapter 4 is a further study of four of those objects, using high resolution ALMA (sub-)mm continuum and CO rotational line observations, that provide constraints on disk size, and total gas and dust mass. Chapter 5 presents a theoretical exploration of the CO fundamental ro-vibrational transitions as a probe of the intermediate disk regions (1-10 au) between the innermost and extended disk areas investigated in the previous two chapters."--