Cool Stars 14 - Submitted Abstract # 156
This version created on 05 October 2006

The life and death of stellar prominences


Nicholas Dunstone, University of St. Andrews
Andrew Cameron, University of St. Andrews
Moira Jardine,  University of St. Andrews
John Barnes, University of Hertfordshire

Observations of stellar prominences on young rapidly rotating stars
provide unique probes of their magnetic fields out to many stellar
radii.  We present high resolution time-series spectra of the K dwarfs
AB Dor and Speedy Mic (BO Mic).  From high signal-to-noise
observations of Speedy Mic we show that prominences can be observed as
both absorption features as they transit the stellar disc and as loops
of emission when seen off the stellar disc.  Combining both methods of
observation allows us to develop an improved understanding of the
physical properties of the prominence system.  We find that the
majority of the emission comes from lower heights than those estimated
from tracking the prominence absorption signatures.  This can be
explain by the relatively high optical thickness of the clouds which
we obtain from observations of prominences in the first eight lines of
the hydrogen Balmer series.  We also investigate the evolution of
stellar prominences by monitoring a single AB Dor prominence every
night for a week.  On the last night we observe what appears to be an
erupting stellar prominence.  We find that the prominence, which is
located near the stellar co-rotation radius, undergoes a disruptive
event whilst transiting the stellar disc.  A period of acceleration is
observed resulting in absorption blue-shifted (outflow) velocities in
excess of 300  km/s.  Also observed is a red-shifted (in-fall)
velocity of approximately 100  km/s.  We discuss possible mechanisms
for the eruption event.

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