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Session 25 - Stars in the Ultraviolet.
Display session, Tuesday, June 10
South Main Hall,

[25.14] Using Temporal Variations of the Nonthermal Redshifted Ly-Alpha Emission to Deduce Properties of Proton Beams Injected into a Stellar Atmosphere

J. W. Brosius (Hughes STX/NASA GSFC), B. E. Woodgate (NASA GSFC)

We present theoretical calculations of temporal variations in the nonthermal redshifted Ly-alpha emission due to proton beams injected into a stellar atmosphere during the impulsive phase of a flare. The computations are performed for a power law spectrum of nonthermal proton energies between 20 and 120 keV injected into a model stellar atmosphere consisting of pure hydrogen in local thermodynamic equilibrium. We calculate the beam-induced variations in temperature and particle densities by assuming that these quantities satisfy the Saha equation at all depths and for all times. We characterized the injected model proton beams with the total energy flux and the power law index, and computed time-dependent nonthermal redshifted Ly-alpha emission profiles for five different values of the flux and three different values of the index. Based upon trends evident in the resulting emission, it is possible to deduce proton beam properties from sufficiently high quality observations of the nonthermal redshifted Ly-alpha profile. The beam penetration depth initially decreases with time, but in most cases it increases again after reaching some minimum value. This behavior is attributed to changes in the ionization and temperature of the atmosphere. The nonthermal redshifted Ly-alpha intensity also initially decreases with time, but in most cases it reaches a relative minimum, increases again to a relative maximum, and then slowly but steadily decreases thereafter. We describe how observable properties of the time-dependent nonthermal redshifted Ly-alpha emission, such as the ratio of the profile's peak intensity at relative minimum to that at beam onset, and the times since beam onset at which the intensity reaches its relative minimum and relative maximum values, can be used to deduce the power law index and the total beam energy flux.

Program listing for Tuesday