The aim of this project was to examine binary stars containing at least one unusual and hydrogen-deficient hot subdwarf, allowing us to explore possible outcomes of common-envelope ejection in a close binary. The first object studied was PG 1544+488, an exceptional short-period spectroscopic binary containing two helium-rich subdwarfs. I obtained and improved orbital and atmospheric parameters for each component. The orbital period P = 0.496 ± 0.002 d, dynamical mass ratio M(B)/M(A) = 0.911 ± 0.015, and spectroscopic radius ratio R(B)/R(A) = 0.939±0.004 indicate a binary containing nearly identical twins. The surfaces of both stars are slightly metal-poor (1/3 solar) and carbon-rich (0.3% by number). The best model for the origin of PG 1544+488 requires the ejection of a common envelope from a binary in which both stars are red giants with helium cores of nearly equal mass. The second object was 81Lyn and the first goal was to determine whether the relative motion of the two components could be resolved, and subsequently to obtain the dynamical mass ratio. Radial velocities of both components were measured but it was not possible to determine a period. An emission feature at Ha is also observed, which varies within a single night's observation. I discuss the origin of this feature. Additionally, 17 subdwarf stars, are classified according to their helium abundances. For two of these; I obtained and improved orbital and atmospheric parameters for [CW83] 1419-09 and recognised a variability of radial velocity for CD-314800. Exotic' binaries like PG 1544+488 and 81 Lyn place strong constraints on models for binary-star evolution. Further observations are required for BI Lyn, and to discover other exotic post-common-envelope binaries
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:677285 |
| Date | January 2015 |
| Creators | Sener Satir, H. Tugça |
| Publisher | Queen's University Belfast |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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