Yushchenko V. Heavy element in the atmospheres of peculiar stars

This research is devoted to the investigations of neutrons capture elements with atomic numbers Z>30 in the atmospheres of different type stars. These are four stars of the upper main sequence with effective temperatures from 6500 to 13000 K – Przybylski’s star (HD101065), HR465, HD25354, and HD91375, three F-type stars - ? Puppis and two components of eclipsing binary system ZZ Bootis, two galactic halo giants – HD221170 and HD47536 and two red supergiants of Magellanic Clouds – PMMR 144 and RM_1-667. The absorption lines of short-lived actinides were investigated in the spectra of the 22 atmospheres of Przybylski’s star and HR465. The possible detections for lines of plutonium (Z=94) and other actinides were found in the spectra. These lines and also the detection of promethium and technetium need the existence of unknown physical process to explain the observations. For HR465 we confirmed the variability of spectrum and abundance pattern with possible time near 23 years. The strength of absorption lines of chromium and heavier elements are very distinct in the observed spectra obtained in 1994 and 2004, the abundance variations can reach more than one dex for lanthanides. The abundance pattern of HD25354 was found for the first time, the effective temperature of the star appeared to be close to 13000 K. This value is near three thousands degrees higher than most of previous determinations. The lines of chemical elements in the second and third ionization stages are found in the spectrum. The lanthanides in the atmosphere of this peculiar star are overabundant by 4 to 6 dex. HD91375 found to be metallic line star. It belongs to the Sirius moving group, but its chemical composition shows the significant difference with respect to the primary component of Sirius binary system. The abundance patterns of ? Puppis, components of eclipsing binary ZZ Bootis as well as the chemical composition of other stars published by different researches exhibit the clear signs of accretion of hydrogen and helium from interstellar medium or from circumstellar envelopes. This type of accretion changes the relative abundances of chemical elements in the atmospheres of normal stars and should be taken into account in the evolutionary calculations. As a result of this scenario the dependence of relative abundances of chemical elements vs second ionization potentials of these elements is observed. HD221170 and HD47536 are galaxy halo giants with overabundances of heavy elements. The distribution of abundances of chemical elements in the atmosphere of HD47536 shows the clear signs of accretion of hydrogen atoms from the circumstellar envelope of this star – the host of two planets. It proves the possibility of accretion effects in halo giant stars and confirms the necessity of taking this effect into account in cosmochronology. The red supergiants of Large Magellanic Cloud (RM_1-667) and Small one (PMMR 144) exhibit the absorption lines of heavy elements, including thorium (Z=90) in the spectra. Heavy elements in the atmospheres of these stars are overabundant with respect to iron group elements. The relative abundances of chemical elements in these stars show the dependence vs the second ionization potentials of these elements. It can be explained as the consequence of accretion of interstellar hydrogen.