Rotating Stars and the Formation of Bipolar Planetary Nebulae II: Tidal Spin-up

TL;DR

This study uses binary stellar evolution models including tidal forces, rotation, and magnetic torques to investigate if tidal spin-up can lead to bipolar planetary nebulae formation, concluding it is unlikely in non-contact binaries.

Contribution

It introduces detailed binary evolution models with tidal effects to assess their role in shaping bipolar planetary nebulae, providing new insights into the limitations of tidal spin-up.

Findings

Detached binaries avoid RLOF and do not spin up the AGB star sufficiently.

AGB stars in these systems lose angular momentum via winds, preventing bipolar PNe formation.

Tidal spin-up in non-contact binaries is not a sufficient condition for bipolar PNe.

Abstract

We present new binary stellar evolution models that include the effects of tidal forces, rotation, and magnetic torques with the goal of testing Planetary Nebulae (PNe) shaping via binary interaction. We explore whether tidal interaction with a companion can spin up the AGB envelope. To do so we have selected binary systems with main sequence masses of 2.5 \Mo and of 0.8 \Mo and evolve them allowing initial separations of 5, 6, 7, and 8 AU. The binary stellar evolution models have been computed all the way to the PNe formation phase or until Roche lobe overflow (RLOF) is reached, whatever happens first. We show that with initial separations of 7 and 8 AU, the binary avoids entering into RLOF, and the AGB star reaches moderate rotational velocities at the surface ($\sim 3.5 $ and $\sim 2 $ \kms respectively) during the inter-pulse phases, but after the thermal pulses it drops to a final rotational velocity of only $\sim 0.03 $ \kms. For the closest binary separations explored, 5 and 6 AU, the AGB star reaches rotational velocities of $\sim 6 $ and $\sim 4 $ \kms respectively when the RLOF is initiated. We conclude that the detached binary models that avoid entering the RLOF phase during the AGB will not shape bipolar PNe, since the acquired angular momentum is lost via the wind during the last two thermal pulses. This study rules out tidal spin-up in non-contact binaries as a sufficient condition to form bipolar PNe.