Efficiency of O-C diagrams as diagnostic tools for long-term period variations. I. Wind-driven mass loss and magnetic braking

Details Efficiency of O-C diagrams as diagnostic tools for long-term period variations. I. Wind-driven mass loss and magnetic braking Efficiency of O-C diagrams as diagnostic tools for long-term period variations. I. Wind-driven mass loss and magnetic braking

Nov 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011a%26a...535a.126n&link_type=abstract

Astronomy & Astrophysics, Volume 535, id.A126

Astronomy and Astrophysics

Astrophysics

Binaries: Close, Stars: Late-Type, Stars: Mass-Loss, Methods: Miscellaneous

Scientific paper

Context. The credibility of an O-C diagram analysis is investigated when long-term processes are examined in binary systems. The morphology of period and O-C diagrams is thoroughly explored when mass loss and magnetic braking, induced by stellar winds, drive the orbital evolution of late-type detached binaries. Conditions are specified that determine which process dominates. Aims: Our objective is to determine the minimum time intervals that observations are expected to span for a physical mechanism to be detectable by means of an O-C diagram analysis. Computations for various values that account for the noise level and the orbital period are performed to find out to which degree these affect the inferred intervals. Methods: Generalized dot{J-dot{P}} relations that govern the orbital evolution of a binary system are set and solved analytically to determine in a closed form the period and the function expected to represent the respective O-C variations. Semi-empirical relations adapting mass loss and magnetic braking processes for single cool stars are adopted and properly modified to be consistent with the latest observational constraints. A standard Newton-Raphson numerical procedure is then employed to estimate the minimum temporal range over which a specific mechanism is rendered measurable. Results: Mass loss rates comparable to or greater than -10-9 M&sun; yr-1 are measurable for typical noise levels of the O-C diagrams when the data span more than a century. Magnetic braking was proved to be very sensitive on the orbital period and on the braking law adopted for inference. It is expected to be detectable in current O-C diagrams of very short-period binaries only, for others it needs at least two centuries of observations to confirm its effects safely. Conclusions: Both wind driven mass loss and magnetic braking processes are able to drive the orbital evolution of short-period detached binaries (Porb1d) in amounts traced on human timescales. There are also special conditions under which their strength is equalized, locking the orbital period invariable in time. Several short-period RS CVn-type binaries are fine candidates where this regime is expected to prevail.

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