In the first part of this paper, a review is given of the situation of the Big Bang nucleosynthesis of the nuclides D, 3He, 4He and 7Li, taking into account the latest experimental data (number of neutrino species, lifetime of the neutron) and theoretical developments (quark-hadron phase transition). In the second part. I review the process of Galactic Cosmic Ray formation of lithium, beryllium and boron throughout the life of the galaxy, taking advantage of recent measurements of Be and Li in iron deficient stars.

Recent spectroscopic studies of the elemental abundance patterns associated with extremely metal deficient field halo stars and globular cluster stars are briefly reviewed. These metal deficient stellar populations have been found to be characterized by abundance patterns which differ quite distinctly from those of solar system abundances, but are consistent with the view that they reflect primarily the nucleosynthesis products of the evolution of massive stars and associated Type II supernovae. Guided by our current knowledge of nucleosynthesis as a function of stellar mass occurring in stars and supernovae, we identify some interesting constraints upon theories of the formation and early history of our Galaxy.

Theoretical models of supernova explosions of various types are reviewed to obtain heavy element yields from supernovae. We focus on new models for SN 1987A, and Type Ia, Ib, and Ic supernovae. Maximum brightness and decline rate of their light curves suggest that 12–18 M⊙ stars produce larger amount of 56Ni than more massive stars. We discuss relative roles of various types of supernovae in the chemical evolution of galaxies.

The information content of (photospheric) stellar spectra and the accuracy of abundance determinations are discussed. Besides the physical properties of the line spectra, the spectral resolution, the signal-to-noise ratio, but also the incompleteness of the knowledge of the contributing blends limit the abundance information. For a perfect model atmosphere the main factors determining the accuracy of the abundances are S/N, the line saturation, and the location of the continuum (or, in a synthetic spectrum, the background of numerous lines). In addition systematic errors introduced by missing atomic data and an imperfect model atmosphere (non-LTE, line blanketing, hydrodynamics) are important. The typical accuracy of abundance determinations is discussed for main sequence stars for which the most reliable data are available, and for a few selected other stellar types.

The limitations imposed on the accuracy of the abundance determination by the current status of the stellar atmosphere models are discussed. It is shown that the very high S/N ratio and resolution in spectroscopic observations require the new additional steps in stellar atmosphere modeling and in the line formation theory.

We summarize the recent critical compilation and analysis of the solar and meteoritic abundances by Anders and Grevesse (1989). We also update a few solar photospheric results and present a detailed discussion of the problem of the solar abundance of iron.

The physical mechanisms that control the rotational history of stars like the Sun are reviewed, and the likely role of the associated rotational mixing is described. Results of stellar evolution calculations that include the effects of rotation are also described. The same theory, based on a single calibration for stars of different masses and metallicities, can successfully explain the observed Li and Be depletion in young open clusters and Li in field dwarf stars of the halo population, and the striking difference between metal-rich and metal- poor abundance patterns. There is evidence, both observational and theoretical, that angular momentum remains hidden in stellar interiors into advanced phases of evolution. Internal rotation also offers a natural explanation for the CNO isotopic anomalies observed among red giants. Finally, some of the questions raised by recent progress are considered.

Li and Be abundances in Main Sequence stars later than F0 are reviewed. Observations of Li in open cluster stars and metal-poor dwarf halo stars has promoted the development of a great variety of models invoking transport processes in the outermost layers of these stars. Although measurements in their present state do not allow to establish definitive conclusions on which process is the most important for each range of masses, they do manifest that metallicity and stellar rotation play an important role in controlling the processes which trigger disappearance of these elements from stellar atmospheres.

The classical anomalies of Am-Fm stars are reviewed. Progresses already made, or expected to come, due to improvements in observations thanks to the new generation of telescopes and high S/N detectors as well as from theoretical advances are described. Current unsolved problems are identified.

Photospheric abundances are used to determine the importance of atomic diffusion, meridional circulation, mass loss and turbulence in main sequence and horizontal branch stars. Atomic diffusion leads to the appearance of the Li gap and the AmFm and HgMn phenomena at approximately the Teff at which they are observed. It leads to a 12 to 25% reduction in the age of halo stars. The Li abundance in Halo stars is probably 50% of the original abundance. Atomic diffusion competes with meridional circulation. The V sin i at which the HgMn and AmFm phenomena disappear give an argument in favour of the meridional circulation model of Tassoul and Tassoul. Mass loss is probably present in AmFm stars and cooler F stars but only at the rate of 10-15 M⊙ yr-1. In many objects, the turbulent particle diffusion coefficient is at most 10 times larger than the atomic diffusion coefficient.

The aim of this short review is to pay attention to some problems connected with the He, C and N abundances in atmospheres of B-type main sequence stars. These elements participate in CNO-cycle which is the principle source of energy in such stars. As known, the He, C and N abundances in stellar interiors are considerably changed owing to CNO-cycle (oxygen abundance alter insignificantly). There are some variations of the He, C and N abundances in stellar atmospheres, too, and our task is to discuss probable causes of such variations. It is necessary to emphasize that only normal B-type stars are considered (not He-rich or He-weak, for example).

Abundance analyses of HgMn stars in these 15 years are compiled to clarify the abundance characteristics. NLTE abundance studies relevant to HgMn stars are also surveyed for the period of these 20 years. Discussions are made on influences of uncertainties in the atmospheric parameters and of NLTE effects upon abundance determinations, and further on establishment of abundances.

Some general properties and evolutionary status of magnetic Ap stars are briefly considered. Chemical abundance anomalies are discussed from the point of view of current theories presumably the radiative diffusion theory in the presence of magnetic field.

Some main sequence A and B stars have strong, ordered magnetic fields. These Ap and Bp stars usually have anomalous chemical abundances, and often rather non-uniform distributions of at least some elements (e.g. He, Ca, Ti, Cr) over their surfaces. Maps of magnetic field structure may provide a means of testing theories of how large coherent fields form, and of probing large-scale hydrodynamic flows (meridional circulation) inside stars. Maps of distributions of various elements can help to elucidate the mechanisms, such as diffusion under competing influences of gravity and radiation, turbulence, meridional circulation, mass loss, and perhaps accretion from the interstellar medium, that lead to the distinctive abundances and surface abundance distributions. This kind of mapping is important as an aid to understanding how the Ap and Bp stars develop. It is even more important because the processes involved in producing Ap and Bp stars probably have significant effects on surface chemical abundances of “normal” upper main sequence stars, and so understanding the relevant physics is essential to correctly relating observed surface chemistry to stellar and galactic evolution. In this paper, efforts to map field and abundance structures in Ap stars are reviewed, and some of the principal results obtained thus far are discussed.

Intermediate helium stars are defined by the number ratio of helium to hydrogen: Whereas at the helium rich end, there is a distinct gap between the intermediates and the extreme helium stars, the borderline between the intermediates and the normal B-stars appears less well defined. 24 stars are listed by Drilling and Hill (1986), with V < 11m. It can be anticipated that a major fraction has as yet escaped detection.

Our concept of normal A stars is severely influenced by the dearth of features in the low resolution spectra of these objects that have been used for classification. The relatively small number of lines visible at survey dispersion has also led us to greatly simplify the complexity of spectroscopic patterns that can occur. The λ Boo stars were noted as a class because of the prominence of the λ4481 line of Mg II. We call attention to lines of V II and Ni II that are strong in superficially normal stars, and surprisingly weak in strong-lined stars with obvious overabundances of chromium, manganese, and iron. It is also useful to note that iron itself can be both underabundant and overabundant in CP stars. We call attention to an important new work by Venn and Lambert that develops the earlier suggestion that λ Boo stars may have formed from gas that has been separated from interstellar grains.

Current knowledge of the chemical nature of WR stars determined from UV, optical and IR spectral analyses, is reviewed. By number, the H/He ratio is low in most WN stars: 10 ≥ H/He ≥ 0.4 for WNL stars; 3.0 ≥ H/He ≥ 0.0 for WNE stars with most having near zero H-abundances. The C/N ratio in WN stars lies in the range 1–6 × 10−2, whilst N/He ∼10−4 − 4 × 10−3. These abundances for WN stars are broadly consistent with equilibrium CNO-burning products. In WC stars H/He=0 whilst C/He ∼ 0.1 − 0.7 with some evidence for increasing values from WC7 → WC4. N is highly deficient in WC stars, with C/N≥ 60, and for HD 165763 O/C ≤ 0.2 is deduced. In γ Velorum (WC8+O9), IR spectra give a value of Ne/He = 1.0×10-3 (about twice solar). Thus WC abundances are broadly consistent with He-burning products, although the Ne abundance appears lower than predicted. WO stars show C/He ∼ 0.2 − 0.7, and O/He ∼ 0.03 − 0.1, revealing both He-burning and α-capture products. Ring nebulae around several WN stars shown enhanced He and N, consistent with mass loss enrichment expectations from their chemically evolved central stars. Enhanced He (and probably N) is also seen in the atmospheres of several LBVs, OBN and Of stars - potential precursors of, at least, some WN subtypes.

Model-independent information on the chemical composition of WR stars is obtained from the lines of different ions arising at transitions between highly excited energy levels.

The chemical composition of WR stars strongly differs from the mean cosmic composition. Nuclear processed CNO products of H-burning are revealed in WN envelopes and He-burning products in WC envelopes. The matter enriched with He and N is also present in some ring nebulae around WN stars.