Stellar coronal abundances. 2: The first ionization potential effect and its absence in the corona of procyon

Details Stellar coronal abundances. 2: The first ionization potential effect and its absence in the corona of procyon Stellar coronal abundances. 2: The first ionization potential effect and its absence in the corona of procyon

Apr 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...443..393d&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 443, no. 1, p. 393-415

Astronomy and Astrophysics

Astrophysics

108

Abundance, Emission Spectra, Ionization Potentials, Stellar Atmospheres, Stellar Coronas, Cosmic Rays, Extreme Ultraviolet Explorer Satellite, Spectrum Analysis, Ultraviolet Spectra

Scientific paper

We present a detailed study of element abundances in the corona of Procyon based on spectroscopic observations obtained with the Extreme Ultraviolet Explorer Satellite (EUVE). Emission measures (EMs) have been derived from observed line fluxes for the elements O, Ne, Mg, Si, S, Ar, Fe, and Ni, using the most recent atomic data. The slope of the resulting EM distribution is very similar to the well known result of 1.5 (EM is proportional to T3/2 found for the solar corona for log T = 5.3-6.0. The abundances in the corona of Procyon are found to be consistent with their photospheric values. No enhancement of species with low first ionization potentials (FIPs) is observed, such as is the case for the solar corona: the 'FIP effect' appears to be absent in Procyon. We speculate that the dominant emission from the corona and transition region in Procyon could originate in low-altitude structures analogous to the solar supergranulation network, which does not appear to exhibit an FIP effect. A considerable body of observational evidence suggests both that Procyon is a 'basal' star in terms of its chromospheric activity and that it is on the spectral type boundary which separates stars which exhibit activity levels correlated with rotation and those which do not. Such stars are though by some workers to sustain coronae which are heated predominantly by acoustic means. We also note that an acoustically heated outer atmosphere might not possess sufficiently small structures to support a fractionation of elements with respect to FIP. Our results demonstrate that the FIP effect is not an ubiquitous feature of late-type stellar coronae. Consequently, speculations in the literature that the FIP effect observed in cosmic rays is a result of their originating from seed particles injected by late-type stellar coronae must await observational confirmation that the FIP effect does indeed operate on M dwarfs, which are likely to be the dominant particle injection source.

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