Constraints on decreases in η Carinae's mass-loss from 3D hydrodynamic simulations of its binary colliding winds
Abstract
Recent work suggests that the mass-loss rate of the primary star ηA in the massive colliding wind binary η Carinae dropped by a factor of 2-3 between 1999 and 2010. We present results from large- (±1545 au) and small- (±155 au) domain, 3D smoothed particle hydrodynamics (SPH) simulations of η Car's colliding winds for three ηA mass-loss rates (dot{M}_{η A}= 2.4, 4.8 and 8.5 × 10-4 M⊙ yr-1), investigating the effects on the dynamics of the binary wind-wind collision (WWC). These simulations include orbital motion, optically thin radiative cooling and radiative forces. We find that dot{M}_{η A} greatly affects the time-dependent hydrodynamics at all spatial scales investigated. The simulations also show that the post-shock wind of the companion star ηB switches from the adiabatic to the radiative-cooling regime during periastron passage (φ ≈ 0.985-1.02). This switchover starts later and ends earlier the lower the value of dot{M}_{η A} and is caused by the encroachment of the wind of ηA into the acceleration zone of ηB's wind, plus radiative inhibition of ηB's wind by ηA. The SPH simulations together with 1D radiative transfer models of ηA's spectra reveal that a factor of 2 or more drop in dot{M}_{η A} should lead to substantial changes in numerous multiwavelength observables. Recent observations are not fully consistent with the model predictions, indicating that any drop in dot{M}_{η A} was likely by a factor of ≲2 and occurred after 2004. We speculate that most of the recent observed changes in η Car are due to a small increase in the WWC opening angle that produces significant effects because our line of sight to the system lies close to the dense walls of the WWC zone. A modest decrease in dot{M}_{η A} may be responsible, but changes in the wind/stellar parameters of ηB, while less likely, cannot yet be fully ruled out. We suggest observations during η Car's next periastron in 2014 to further test for decreases in dot{M}_{η A}. If dot{M}_{η A} is declining and continues to do so, the 2014 X-ray minimum should be even shorter than that of 2009.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- December 2013
- DOI:
- 10.1093/mnras/stt1871
- arXiv:
- arXiv:1310.0487
- Bibcode:
- 2013MNRAS.436.3820M
- Keywords:
-
- hydrodynamics;
- binaries: close;
- stars: mass-loss;
- stars: individual: Eta Carinae;
- stars: winds;
- outflows;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 38 pages, 25 figures, 1 table. Accepted for publication in MNRAS