What Sets the Initial Rotation Rates of Massive Stars?

Abstract

The physical mechanisms that set the initial rotation rates in massive stars are a crucial unknown in current star formation theory. Observations of young, massive stars provide evidence that they form in a similar fashion to their low-mass counterparts. The magnetic coupling between a star and its accretion disk may be sufficient to spin down low-mass pre-main sequence (PMS) stars to well below breakup at the end stage of their formation when the accretion rate is low. However, we show that these magnetic torques are insufficient to spin down massive PMS stars due to their short formation times and high accretion rates. We develop a model for the angular momentum evolution of stars over a wide range in mass, considering both magnetic and gravitational torques. We find that magnetic torques are unable to spin down either low or high mass stars during the main accretion phase, and that massive stars cannot be spun down significantly by magnetic torques during the end stage of their formation either. Spin-down occurs only if massive stars' disk lifetimes are substantially longer or their magnetic fields are much stronger than current observations suggest.

12 pages, 10 figures, Accepted for publication in ApJ

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• Unifying low and high mass star formation through density amplified hubs of filaments
• The VLT-FLAMES Tarantula Survey XXI. Stellar spin rates of O-type spectroscopic binaries
• Zooming in on Individual Star Formation: Low- and High-mass Stars
• Stellar and nebular diagnostics in the UV for star-forming galaxies
• The IACOB project. VII. The rotational properties of Galactic massive O-type stars revisited
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• A Novel Approach to Constrain Rotational Mixing & Convective-Core Overshoot in Stars Using the Initial-Final Mass Relation
• The magnetic field and spectral variability of the He-weak star HR 2949
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• Very Massive Stars (VMS) in the Local Universe
• On the magnetic fields of Be/X-ray pulsars in the Small Magellanic Cloud
• Helium and Nitrogen Enrichment in Massive Main Sequence Stars: Mechanisms and Implications for the Origin of WNL Stars
• Radio Loud vs. Radio Quiet Gamma-ray Bursts: the Role of Binary Progenitors
• On the Role of the $\Omega \Gamma$ Limit in the Formation of Population III Massive Stars
• Tracing the evolution of short-period binaries with super-synchronous fast rotators
• Non-synchronous rotations in massive binary systems. HD93343 revisited
• Extreme mass ratios and fast rotation in three massive binaries
• Strong nebular HeII emission induced by He${}^{+}$ ionizing photons escaping through the clumpy winds of massive stars
• Understanding the angular momentum evolution of T Tauri and Herbig Ae/Be stars
• Progenitors of Long-Duration Gamma-ray Bursts
• WISE Discovery of Mid-infrared Variability in Massive Young Stellar Objects
• Spindown of massive main sequence stars in the Milky Way
• Exploring the Stellar Rotation of Early-type Stars in the LAMOST Medium-resolution Survey. III. Evolution
• Large Scale Dynamo in a Primordial Accretion Flow -- An Interpretation from Hydrodynamic Simulation
• BD+30${}^{\circ }$549: young helium-weak silicon star in NGC 1333 star-forming region
• The High-resolution Accretion Disks of Embedded protoStars (HADES) simulations. I. Impact of Protostellar Magnetic Fields on the Accretion Modes