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[en] For 25 years the conception has been well established that the overwhelming majority of chemical elements and their isotopes have been synthesized in stars during the course of stellar evolution, in particular during the advanced stages and in supernova explosions. Until now this general idea has not led to major difficulties or inconsistencies. On the contrary, the theoretical models have been very successful in explaining the observed abundances in meteorites, planets (including the earth), stars (including the sun) and galactic cosmic rays. Our present understanding of nucleosynthesis will be reviewed with special attention given to nucleosynthetic processes in primordial stars and supernovae. We will concentrate primarily on predictions which can be made for relative abundances rather than for absolute abundances, because the latter problem requires evolutionary models of the galaxy which are beyond the scope of this article. (orig.)
[en] Advances made by this Commission over the past three years are presented as a series of reviews covering all organizational problems and selected research areas. Topics include archives of unpublished observations, general catalogue of variable stars, cepheids, beta Canis Majoris stars, delta Scuti stars/dwarf cepheids, T Tauri stars and related objects, RR Lyrae variables, variable stars in galactic globular clusters, red variables, theory of stellar pulsations, flare stars, novae at outbursts, magnetic variables and related objects and variable star survey work. (C.F.)
[en] Determination of the age of the universe from the age of the oldest stars yields values exceeding 15 billion years; it is based on the knowledge of the development of star clusters. Age determination based on radioisotope abundance depends on a number of presumptions and is little accurate. It gives values of 8 to 19 billion years. The cosmological method determines age by the expansion of the universe. At first the Hubble constant only allowed 2 billion years for the age of the universe. More recent values of the constant give a range of 10 to 20 billion years for the age of the universe. (M.D.). 3 figs., 3 tabs
[en] The Monoceros ring, a circular optical nebulosity approx. 30.5 in diameter and centred at R.A. = 6sup(h)37sup(m), Dec. = 6030'(lsup(II) = 2050.5, bsup(II) = 00.2) is in good structural agreement with radio observations. A neutral hydrogen shell is also accurately projected on the ring. These observations are consistent with the Monoceros ring being a supernova remnant 90-100 pc in diameter expanding at about 45 km s-1 and having an age of the order of a million years. Bright H II regions containing early-type stars (e.g., galactic cluster NGC 2244 in the Rosette nebula) and extremely young stars of the OB association Mon OB2 lie at the edges of the ring. The positional and temporal coincidence of the Mon OB2 association with a supernova remnant suggests that probably the star formation in this region is induced or speeded up by the passage of a supernova shock wave through the clumpy interstellar medium. (orig.)
[en] A photometric and spectroscopic study of the Type II cepheid AU Pegasi indicates it is a member of a binary with a period < or approx. =50 days. Constraints on the orbit indicate the companion is likely to be more massive than AU Peg and may be a compact object. The light curve, pulsation-velocity curve, and spectrum of AU Peg are consistent with its cepheid nature. However, the colors are peculiar and the large period changes remain to be explained
[en] The age of the universe is the time that has elapsed since the Big Bang. To calculate the age, the expansion rate of the universe and distance to the galaxies must be determined. Unfortunately, it appears that the expansion rate is not constant but is decelerating. In the 1920's and 30's, Edwin Hubble set out to estimate the age of universe based on the expansion rate and distance to the galaxies. His method is described along with its flaw. Since that time several others have estimated the age of the universe. Their methods as well as results vary. These are discussed in the article. The ages determined from the various methods range from 10 to 20 billion years. There are two independent ways to determine the age of the universe. What they actually do is determine the age of our galaxy which would give a lower limit to the age of the universe. The first method calculates age of globular clusters which yields as age range from 8 to 18 billion years. The second method involves observing the speed at which radioactive substances decay. This also yields and age greater than 10 billion years. It is clear that there is still a lot of work to do before the true age of the universe can be determied
[en] We present low-resolution spectra for variable stars in the Cepheid period range from the ROTSE-I Demonstration Project and the All Sky Automated Survey, some of which were previously identified as type II Cepheid candidates. We have derived effective temperatures, gravities, and metallicities from the spectra. Based on this, three types of variables were identified: Cepheid strip stars, cool stars that lie along the red subgiant and giant branch, and cool main-sequence stars. Many fewer type II Cepheids were found than expected and most have amplitudes less than 0.4 mag. The cool variables include many likely binaries as well as intrinsic variables. Variation among the main-sequence stars is likely to be mostly due to binarity or stellar activity.
[en] The author studies the past paths of the run-away star Zeta Oph from the OB association Sco-Cen, and of the run-away stars AE Aur, Mu Col and 53 Ari from the OB association Ori OB1, in connection with the question of the origin of these high velocities. Should the binary-hypothesis be adhered to (supernova explosion of one of the components) or, perhaps, dynamical evolution in young, dense clusters offer a clue to this phenomenon? It is shown that the latter hypothesis is very unlikely to apply to Zeta Oph. For the run-away stars from Orion conclusive evidence may well be obtained in the course of the next decade, from improved accuracy of the proper motions
[en] We present photometric and spectroscopic observations of SN 2013aa and SN 2017cbv, two nearly identical type Ia supernovae (SNe Ia) in the host galaxy NGC 5643. The optical photometry has been obtained using the same telescope and instruments used by the Carnegie Supernova Project. This eliminates most instrumental systematics and provides light curves in a stable and well-understood photometric system. Having the same host galaxy also eliminates systematics due to distance and peculiar velocity, providing an opportunity to directly test the relative precision of SNe Ia as standard candles. The two SNe have nearly identical decline rates, negligible reddenings, and remarkably similar spectra, and, at a distance of ∼20 Mpc, they are ideal potential calibrators for the absolute distance using primary indicators such as Cepheid variables. We discuss to what extent these two SNe can be considered twins and compare them with other supernova “siblings” in the literature and their likely progenitor scenarios. Using 12 galaxies that hosted two or more SNe Ia, we find that when using SNe Ia, and after accounting for all sources of observational error, one gets consistency in distance to 3%.
[en] Three main problems are discussed, they are: (1) That there is no mechanism known which will maintain pulsations in these stars, (2) problems regarding the type of pulsation observed, whether it is radial, non-radial, a fundamental vibration or an overtore, and (3) the determination of exactly which stage of evolution these stars have reached