| |
 |
| Paper: |
Constraints on the Surface Magnetic Field Structure of
Aldebaran (α Tauri, K5 III) |
| Volume: |
448, 16th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun |
| Page: |
1145 |
| Authors: |
Harper, G. M.; Brown, A.; Redfield, S. |
| Abstract: |
The presence of both a stellar wind and the coronal proxy
O VI 1032 & 1038 Å emission (Ayres et al. 2003; Dupree et al. 2005) shows that the outer atmosphere
of the red giant Aldebaran (α Tauri) is influenced by magnetic fields.
Exactly how these magnetic structures are organized is unknown but future
thermal continuum observations with the Expanded Very Large Array (EVLA) and
the Atacama Large Millimeter Array (ALMA) would provide
powerful new insights into this thorny problem. Observations using these
facilities would sample over three orders of magnitude in continuum optical
depth and
provide an area-averaged sweep through the wind and chromospheric layers.
Here we examine how current 1-D time-independent models compare to existing
centimeter and millimeter data.
The 1-D chromospheric model of (McMurry 1999) embedded in the wind model of
Robinson et al. (1998) predicts an excess of sub-mm emission. This excess may reflect that
these
wavelengths arise in pervasive and cold ∼ 2000 K structures, known from
ultraviolet fluorescent CO studies.
If this cold material lies beneath a magnetic canopy then the implied
photospheric
filling factor is < 0.04. The filling factor of the wind launch sites
is difficult
to constrain because the wind temperature is currently uncertain
(≤ 20,000 K) and at
chromosphere-like temperatures. The evolution of spectrally-resolved
Ca II circumstellar absorption observed with the
Harlan J. Smith 107″
at McDonald Observatory suggests the turbulence and
wind acceleration in
published models require revision. The filling factor parameter space
can be constricted by future EVLA and ALMA data. |
|
|
|
|
|
