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Title: EFFECT OF COULOMB COLLISIONS ON THE GRAVITATIONAL SETTLING OF LOW AND HIGH FIRST IONIZATION POTENTIAL ELEMENTS

Abstract

We model the effect of gravitational settling in the upper chromosphere on O, Fe, Si, and Ne, studying whether Coulomb collisions between ionized low First Ionization Potential (FIP) elements and protons is sufficient to cause abundance enhancements relative to oxygen. We find that low-FIP abundance enhancements comparable to observed values can be obtained provided the hydrogen ionization degree lies in the approximate range 10%-30%, which agrees with chromospheric models. Lower or higher hydrogen ionization causes the FIP-effect to become smaller or absent (depletion of all heavy elements). Iron must be almost fully ionized in order to become enriched relative to high-FIP elements, and this requires a high iron photoionization rate. The time scale necessary to produce the enrichment increases rapidly with increasing H ionization. For iron in a background from a semiempirical chromospheric model, with an H ion fraction of the order of 30%-40% in the upper chromosphere, 1-2 hr of settling is required to produce enhancements comparable to observations. The absolute abundance (relative to H), which monotonically decreases with time during settling, has by that time decreased by less than 50% in the same altitude region. With the same background conditions, the silicon abundance is more strongly enhanced bymore » the settling than the iron abundance. The high-FIP element neon is depleted, relative to O and low-FIP elements, in the same background and altitude region where iron is enhanced, typically by 50% or more relative to O after 1-2 hr of settling.« less

Authors:
 [1];  [2];  [3]
  1. Piazza Europa 16, I-52026 Pian di Sco (Italy)
  2. Institute of Science and Technology, University of Tromso, NO-9037 Tromso (Norway)
  3. Norwegian Defence Research Establishment (FFI), P.O. Box 25, NO-2027 Kjeller (Norway)
Publication Date:
OSTI Identifier:
22126596
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 769; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; APPROXIMATIONS; CHROMOSPHERE; COLLISIONS; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; COULOMB FIELD; ENRICHMENT; HYDROGEN IONS; IONIZATION POTENTIAL; IRON; NEON; OXYGEN; PHOTOIONIZATION; PROTONS; SILICON; SUN

Citation Formats

Bo, Iselin M. Th., Esser, Ruth, and Lie-Svendsen, Oystein. EFFECT OF COULOMB COLLISIONS ON THE GRAVITATIONAL SETTLING OF LOW AND HIGH FIRST IONIZATION POTENTIAL ELEMENTS. United States: N. p., 2013. Web. doi:10.1088/0004-637X/769/1/60.
Bo, Iselin M. Th., Esser, Ruth, & Lie-Svendsen, Oystein. EFFECT OF COULOMB COLLISIONS ON THE GRAVITATIONAL SETTLING OF LOW AND HIGH FIRST IONIZATION POTENTIAL ELEMENTS. United States. https://doi.org/10.1088/0004-637X/769/1/60
Bo, Iselin M. Th., Esser, Ruth, and Lie-Svendsen, Oystein. 2013. "EFFECT OF COULOMB COLLISIONS ON THE GRAVITATIONAL SETTLING OF LOW AND HIGH FIRST IONIZATION POTENTIAL ELEMENTS". United States. https://doi.org/10.1088/0004-637X/769/1/60.
@article{osti_22126596,
title = {EFFECT OF COULOMB COLLISIONS ON THE GRAVITATIONAL SETTLING OF LOW AND HIGH FIRST IONIZATION POTENTIAL ELEMENTS},
author = {Bo, Iselin M. Th. and Esser, Ruth and Lie-Svendsen, Oystein},
abstractNote = {We model the effect of gravitational settling in the upper chromosphere on O, Fe, Si, and Ne, studying whether Coulomb collisions between ionized low First Ionization Potential (FIP) elements and protons is sufficient to cause abundance enhancements relative to oxygen. We find that low-FIP abundance enhancements comparable to observed values can be obtained provided the hydrogen ionization degree lies in the approximate range 10%-30%, which agrees with chromospheric models. Lower or higher hydrogen ionization causes the FIP-effect to become smaller or absent (depletion of all heavy elements). Iron must be almost fully ionized in order to become enriched relative to high-FIP elements, and this requires a high iron photoionization rate. The time scale necessary to produce the enrichment increases rapidly with increasing H ionization. For iron in a background from a semiempirical chromospheric model, with an H ion fraction of the order of 30%-40% in the upper chromosphere, 1-2 hr of settling is required to produce enhancements comparable to observations. The absolute abundance (relative to H), which monotonically decreases with time during settling, has by that time decreased by less than 50% in the same altitude region. With the same background conditions, the silicon abundance is more strongly enhanced by the settling than the iron abundance. The high-FIP element neon is depleted, relative to O and low-FIP elements, in the same background and altitude region where iron is enhanced, typically by 50% or more relative to O after 1-2 hr of settling.},
doi = {10.1088/0004-637X/769/1/60},
url = {https://www.osti.gov/biblio/22126596}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 769,
place = {United States},
year = {Mon May 20 00:00:00 EDT 2013},
month = {Mon May 20 00:00:00 EDT 2013}
}