On the acceleration of shock waves in the atmosphere of cool Mira variable giants

Details On the acceleration of shock waves in the atmosphere of cool Mira variable giants On the acceleration of shock waves in the atmosphere of cool Mira variable giants

Dec 1976

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1976apj...210..750s&link_type=abstract

Astrophysical Journal, vol. 210, Dec. 15, 1976, pt. 1, p. 750-756.

Physics

8

Giant Stars, Mira Variables, Photosphere, Propagation Velocity, Shock Wave Propagation, Stellar Mass Ejection, Variable Stars, Acceleration (Physics), Astronomical Spectroscopy, Cool Stars, Emission Spectra, Escape Velocity, Hydrogen Clouds, M Stars, Stellar Atmospheres, Stellar Spectra

Scientific paper

The velocity of shock waves in the photosphere of Mira variables can be observed through emission lines. These velocities are typically 5 to 10 km/s, which are less than their escape velocities (20 to 40 km/s). This paper considers the propagation of these shocks outward from the photosphere, in particular the question of whether these shocks accelerate to a velocity that is sufficient to eject matter. It is found that shocks do accelerate, but not indefinitely. They reach a terminal velocity which is a function of the initial conditions of the gas (the fraction of hydrogen in its molecular state). For cool stars, nearly all hydrogen is in its molecular form, and the terminal velocity is approximately 25 km/s. The velocity jump across the shock is approximately three-fourths of the propagation velocity, or about 20 km/s. For stars with escape velocities less than 20 km/s, the shocks should eject a shell of matter once each stellar pulsation period. For hotter stars, the terminal velocity will be correspondingly less. This mechanism should only be important for very cool stars with low escape velocities, the type of stars that are known to have high mass-loss rates.

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