Volume 635, March 2020
|Number of page(s)||14|
|Published online||31 March 2020|
Hydrogen ionization equilibrium in magnetic fields
Instituto de Ciencias Astronómicas, de la Tierra y del Espacio (CONICET),
Av. España 1512 (sur), 5400 San Juan, Argentina
Accepted: 10 February 2020
We assess the partition function and ionization degree of magnetized hydrogen atoms at thermodynamic equilibrium for a wide range of field intensities, B ≈ 105–1012 G. Evaluations include fitting formulae for an arbitrary number of binding energies, the coupling between the internal atomic structure and the center-of-mass motion across the magnetic field, and the formation of the so-called decentered states (bound states with the electron shifted from the Coulomb well). Non-ideal gas effects are treated within the occupational probability method. We also present general mathematical expressions for the bound state correspondence between the limits of zero-field and high-field. This let us evaluate the atomic partition function in a continuous way from the Zeeman perturbative regime to very strong fields. Results are shown for conditions found in atmospheres of magnetic white dwarf (MWD) stars, with temperatures T ≈ 5000–80 000 K and densities ρ ≈ 10−12–10−3 g cm3. Our evaluations show a marked reduction of the gas ionization due to the magnetic field in the atmospheres of strong MWDs. We also found that decentered states could be present in the atmospheres of currently known hot MWDs, giving a significant contribution to the partition function in the strongest magnetized atmospheres.
Key words: atomic processes / magnetic fields / stars: atmospheres
© ESO 2020
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.