ON HIGHLY CLUMPED MAGNETIC WIND MODELS FOR COOL EVOLVED STARS
- School of Physics, Trinity College, Dublin 2 (Ireland)
Recently, it has been proposed that the winds of non-pulsating and non-dusty K and M giants and supergiants may be driven by some form of magnetic pressure acting on highly clumped wind material. While many researchers believe that magnetic processes are responsible for cool evolved stellar winds, existing MHD and Alfven wave-driven wind models have magnetic fields that are essentially radial and tied to the photosphere. The clumped magnetic wind scenario is quite different in that the magnetic flux is also being carried away from the star with the wind. We test this clumped wind hypothesis by computing continuum radio fluxes from the {zeta} Aur semiempirical model of Baade et al., which is based on wind-scattered line profiles. The radio continuum opacity is proportional to the electron density squared, while the line scattering opacity is proportional to the gas density. This difference in proportionality provides a test for the presence of large clumping factors. We derive the radial distribution of clump factors (CFs) for {zeta} Aur by comparing the nonthermal pressures required to produce the semiempirical velocity distribution with the expected thermal pressures. The CFs are {approx}5 throughout the sub-sonic inner wind region and then decline outward. These implied clumping factors lead to excess radio emission at 2.0 cm, while at 6.2 cm it improves agreement with the smooth unclumped model. Smaller clumping factors of {approx}2 lead to better overall agreement but also increase the discrepancy at 2 cm. These results do not support the magnetic clumped wind hypothesis and instead suggest that inherent uncertainties in the underlying semiempirical model probably dominate uncertainties in predicted radio fluxes. However, new ultraviolet line and radio continuum observations are needed to test the new generations of inhomogeneous magnetohydrodynamic wind models.
- OSTI ID:
- 21460025
- Journal Information:
- Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 720; ISSN ASJOAB; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
Similar Records
MALT90 Kinematic Distances to Dense Molecular Clumps
X-RAY EMISSION LINE PROFILES FROM WIND CLUMP BOW SHOCKS IN MASSIVE STARS
Related Subjects
ALFVEN WAVES
ATMOSPHERES
DISTRIBUTION
ELECTROMAGNETIC RADIATION
ELECTRON DENSITY
FLUID MECHANICS
HYDRODYNAMICS
HYDROMAGNETIC WAVES
MAGNETIC FIELDS
MAGNETIC FLUX
MAGNETOHYDRODYNAMICS
MECHANICS
PHOTOSPHERE
RADIATIONS
SOLAR ATMOSPHERE
SPATIAL DISTRIBUTION
STARS
STELLAR ACTIVITY
STELLAR ATMOSPHERES
STELLAR WINDS
ULTRAVIOLET RADIATION