Using Temporal Variations of the Nonthermal Redshifted LYalpha Emission to Deduce Properties of Proton Beams Injected into a Stellar Atmosphere

Details Using Temporal Variations of the Nonthermal Redshifted LYalpha Emission to Deduce Properties of Proton Beams Injected into a Stellar Atmosphere Using Temporal Variations of the Nonthermal Redshifted LYalpha Emission to Deduce Properties of Proton Beams Injected into a Stellar Atmosphere

Mar 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...514..430b&link_type=abstract

The Astrophysical Journal, Volume 514, Issue 1, pp. 430-440.

Astronomy and Astrophysics

Astronomy

3

Radiation Mechanisms: Nonthermal, Stars: Flare, Sun: Flares, Sun: Uv Radiation, Ultraviolet: Stars

Scientific paper

We present theoretical calculations of temporal variations in the nonthermal redshifted Lyalpha emission due to time-invariant 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 injected into a model stellar atmosphere consisting of pure hydrogen in local thermodynamic equilibrium; beam-induced variations in temperature and particle densities at all depths and for all times are calculated with the Saha equation. We characterized the injected model proton beams with the total energy flux F and the power-law index delta and computed time-dependent nonthermal redshifted Lyalpha emission profiles for five different values of F and three different values of delta. Based upon trends evident in the resulting emission, proton beam properties can be deduced from sufficiently high-quality observations of the nonthermal redshifted Lyalpha profile. The beam penetration depth initially decreases with time, but in most cases it increases again after reaching some minimum value. This behavior is due to changes in the ionization and temperature of the atmosphere. The Lyalpha intensity also initially decreases with time, but in most cases it reaches a relative minimum, increases again to a secondary relative maximum, and then slowly but steadily decreases thereafter. Observable properties of this time-dependent emission, such as the ratio of the profile's peak spectral intensity at relative minimum to that at beam onset (I_relmin/I_0), the difference between the profile's width at beam onset and that at the secondary relative maximum (FWHM_0-FWHM_relmax), and the difference between the profile's centroid wavelength shift at beam onset and that at relative minimum (Deltalambda_0-Deltalambda_relmin) can be used to deduce delta. Once delta is known, F can be deduced from other observable properties such as I_0 and the times since beam onset at which the Lyalpha intensity reaches its relative minimum and secondary relative maximum values (t_relmin and t_relmax).

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