Probing and Simulating Rotation Induced Asymmetry in Stellar Wind Bow Shocks

Overview

A common assumption in the literature when studying stellar wind bow shocks is a spherically symmetric stellar wind, despite $\sim25\%$ of O-type stars being rapid rotators, inducing severe stellar wind anisotropy. To investigate this anisotropy and what can be discerned observationally, I ran 3D hydrodynamic simulations and radiative transfer on the results to generate synthetic observations. Using a novel asymmetric parabolic fitting algorithm, I found that asymmetry is consistently detectable for stellar inclinations $\ge 30^\circ$, observational inclinations between $50^\circ$ and $140^\circ$, and stellar rotational velocity greater than $60\%$ of its critical breakup velocity. Applying this framework to 11 observed bow shocks, I found that all binary star systems exhibited extreme asymmetry, and that asymmetry may be degenerate with binarity. The most notable case was the unary rapid rotator HD 203064, with an extreme asymmetry of $A=0.3309$ $(15.37\sigma)$. Using the asymmetry, along with its projected rotational velocity, I constrained its true rotational velocity to $548.5_{-13.3}^{+11.6}$km/s, or $\sim 89.3\pm2.2\%$ of its critical velocity. Similarly, HD 41997’s rotational velocity was constrained to $339.8_{-48.5}^{+57.3}$. This study defines the exact observational regimes where rotation is detectable, and provides a way to use bow shocks to constrain rotational velocity and inclination, parameters that are nearly inaccessible without detailed asteroseismology, spectroscopy, or interferometry for massive O-type stars.

Competition history

• CSEF 2026 Physics & Astronomy (Senior Division) · Entry S-17-05

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