A photometric-spectroscopic analysis and the evolutionary status of the Algol-type binary U Coronae Borealis
Abstract
The prime purposes of this study are to obtain reliable orbital parameters for the Algol-type binary U Coronae Borealis (U CrB) and to explain the evolutionary status of this system. All observations of the primary star's radial velocity are consistent with the value K1= 58.6 +/- 2.0 km s-1. Measurements of the radial velocity of the secondary component give K2=185.2+/- 5.0 km s-1. Using the photometrically determined inclination of 78.7 +/- 0.3, the masses of the two stars are therefore deduced to be 4.74 +/- 0.28 and 1.46 +/- 0.06 Msolar for the primary and secondary components, respectively. Using all available observations, we discuss the origin and evolution of the close binary system U CrB. We derive the restrictions concerning masses and period from a general network of calculations of medium mass close binary evolution. Detailed models are calculated within the derived ranges, giving the most likely initial system parameters as and Pi= 1.4 d. It turns out that the interactive evolution up to the present stage has been non-conservative. During its evolution, U CrB has lost about 14 per cent of its initial total mass (ΔM~ 1 Msolar) and around 18 per cent of its initial total angular momentum. We also examine the possibility of probing dynamo action in the mass-losing component of U CrB. We point out that, in order to maintain the evolution of U CrB in its later stages, which is presumably driven by stellar `magnetic braking', an efficient mechanism for producing large-scale surface magnetic fields in the donor star is required. We suggest that observed X-ray activity in U CrB may be a good indicator of its evolutionary status and the internal structure of the mass-losing component.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- July 2003
- DOI:
- 10.1046/j.1365-8711.2003.06644.x
- Bibcode:
- 2003MNRAS.342.1349Y
- Keywords:
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- stars: abundances;
- binaries: eclipsing;
- binaries: spectroscopic;
- stars: evolution;
- stars: individual: U Coronae Borealis