Title CNO nucleosynthesis products in mass-transfer binary stars Title (croatian) Produkti CNO nukleosinteze u dvojnim zvijezdama s prijenosom tvari Author Vladimir Kolbas Mentor Krešimir Pavlovski (mentor)Committee member Matko Milin (predsjednik povjerenstva)Committee member Vernesa Smolčić (član povjerenstva)Committee member Pierre Maxted (član povjerenstva) Granter University of Zagreb Defense date and country 2014-11-24, Croatia Scientific / art field, NATURAL SCIENCES Universal decimal classificationUDC ) 53 - Physics Abstract Close binary stars of Algol type consist of a main sequence star accompanied with a cool subgiant or giant, where former is now a more massive component. Apparently, this violates principles of the stellar evolution, and episodic mass transfer between the components has been postulated to explain this evolutionary paradox. In this short-lived process the initially more massive component has been converted into a low-mass giant, and layers which were originally deep within the star and have been altered by thermonuclear fusion during the stars’s main sequence evolution are now exposed. The surface chemical composition of both stars are precious diagnostic of the nucleosynthesis processes that occur deep within stars. Theoretical evolutionary models predict changes in abundances of the elements involved in CNO nucleosynthesis. Principal goal of present observational study was the determination of the abundance pattern in mass transferring binary stars. The two representative systems, archetype of a whole class, Algol itself, and its more massive counterpart, u Her, have been selected for detailed examination. High-resolution and high S/N time-series of spectra were secured with fibre-fed échelle spectrographs at the NOT, La Palma, Spain, BOAO, South Korea, and CAHA, Spain. These spectra were disentangled into individual component spectra of the components which eventually make possible detail atmospheric diagnostics including determination of the elemental composition. A number of auxiliary codes have been developed to facilitate analysis and estimate uncertainties of measured quantities. Algol is a hierarchical triple system in which the inner pair is partially eclipsing. This makes study of this binary quite challenging. For the first time the individual spectra of its components have been separated which eventually yield their complete characterisation. Their orbits and masses are revised which making possible determination of appropriate evolutionary models. The ratio of carbon and nitrogen is a very sensitive indicator of hydrogen-core CNO nucleosynthesis and a different mixing processes occurring before and after episode of masstransfer. In present work constraints on C/N have been found for the case of low and high mass Algol-type binary system.
Abstract (croatian) Bliski dvojni zvjezdani sustavi Algolova tipa sastoje se od zvijezde na glavnom nizu sa pratiocem u evolucijskoj fazi poddivova ili divova, pri čemu je prva masivnija. Ovakva situacija je paradoskalna uzevši u obzir evoluciju zvijezda te je postuliran period u kojem je došlo do procesa prijenosa tvari kako bi se objasnila paradoksalna situacija. Taj je kratkotrajan proces inicijalno masivniju zvijezdu pretvorio u diva manje mase, a slojevi koji su bili duboko u zvjezdanoj unutrašnjosti gdje su bili pod utjecajem nuklearnih reakcija su sada izloženi. Kemijska zastupljenost na površini obje zvjezde je dragocjen dijagnostički alat za procese nukleosinteze koji se odvijaju u dubokim slojevima zvijezda. Teorijski modeli evolucije predviđaju promjenu zastupljenosti elemenata koji sudjeluju u CNO nukleosintezi. Glavni je cilj proučavanja određivanje zastupljenosti kemijskih elemenata u dvojnim zvijezdanim sustavim sa prijenosom tvari. Dva reprezentativna sustava izabrana za proučavanje su Algol, po kojem je nazvana cijela klasa sustava te njegova verzija veće ukupne mase u Her. Spektri visoke rezolucije i odnosa signal-šum su osigurani na échelle spektrografima NOT, La Palma, BOES, J. Koreja te CAHA, Španjolska. Ti su spektri raspetljani u individualne spektre komponenata što omoguc´ava detaljnu analizu uvjeta u zvjezdanoj atmosferi kao i određivanje kemijske zastupljenosti. Velik broj pomoćnih kompjuterskih kodova je razvijen za ostvarivanje tog cilja. Algol je hijerarhijski trostruki sustav u kojem unutrašnji par zvijezda pokazuje djelomične pomrčine. To, us postojanje treće komponente, znatno otežava analizu. Prvi su put raspetljani spektri sve tri komponente iz kojih je izvršena karakterizacija zvijezda. Orbite i mase su revidirane omogučivši određivanje evolucijskog modela. Omjer zastupljenosti dušika i ugljika je vrlo osjetljiv indikator CNO nukleosinteze u sredici te različitih procesa miješanja koji se događaju prije i nakon faze prijenosa tvari. U trenutnom radu, omjer C/N je određen za dvojne sustave Algolovog tipa male i velike mase.
Keywords
stars
fundamental parameters
binaries
eclipsing
spectroscopic
elemental abundances
CNO
Algol
u Her
codes
genetic algorithms
spectra
reduction
echelle
disentangling
evolutionary models
mass transfer
stellar atmospheres
Keywords (croatian)
zvijezde
fundamentalni parametri
zvjezdane atmosfere
dvojne zvijezde
pomrčinske zvijezde
zastupljenost elemenata
CNO
Algol
u Her
kod
genetski algoritam
spektar
redukcija
echelle
raspetljavanje
evolucijski modeli
prijenos tvari
Language english URN:NBN urn:nbn:hr:217:489862 Study programme Title: Physics Type of resource Text Extent 154 str. File origin Born digital Access conditions Open access Terms of use Created on 2017-08-22 11:01:39
