New Stellar Mass-Loss Rates for Massive Stars in Bowshock Nebulae
Abstract
Second only to the initial stellar mass (or interaction with a close companion), the rate of wind-driven mass loss determines the final mass of a massive star and the nature of its remnant. Measurements of mass-loss rates over the last several decades have proven controversial, with orders-of-magnitude discrepancies between different observational approaches. Motivated by the need to reconcile observational values and theoretical expectations, we use a recently vetted measurement technique to analyze a sample of OB stars that generate stellar bowshock nebulae. We measure the peculiar velocities and spectral types for the stars using new Gaia parallax and proper motion data along with new optical and infrared spectroscopy. For our sample of 70 central stars in morphologically selected candidate bowshock nebulae, 66 turn out to be early type (OB) stars. The median peculiar velocity is 15 km/s, significantly smaller than classical ``runaway star'' velocities. Mass-loss rates for these O and early-B stars agree well with recent theoretical predictions, ranging from 10^-6 solar masses for mid-O dwarfs to several times 10^-8 for late-O dwarfs, with an order of magnitude dispersion at any given spectral type and luminosity class, suggesting real variations exist. Evolved stars show elevated mass-loss rates compared to dwarfs, consistent with model expectations. Our results provide the first observational mass-loss rates for B0--B2 dwarfs --- 10^-9 to 10^-7 solar masses per year --- significantly higher than theoretical expectations. Early type dwarfs exhibit a correlation between mass-loss rate and stellar luminosity with a power law index of 2.0, nearly identical to theoretically predicted value of 2.1.
- Publication:
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American Astronomical Society Meeting Abstracts #233
- Pub Date:
- January 2019
- Bibcode:
- 2019AAS...23331804K