Other
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011spd....42.0302j&link_type=abstract
American Astronomical Society, SPD meeting #42, #3.02; Bulletin of the American Astronomical Society, Vol. 43, 2011
Other
Scientific paper
It is well known that the thermal-magnetic relation in sunspots can be non-linear. Previous investigations ascribe the non-linearity of the relation to changing geometrical height of the measurement due to radiative transfer effects (Wilson Depression) and the poorly determined magnetic field curvature force. However, the very coolest regions of some sunspots show a rapid increase in umbral magnetic field strength relative to temperature which cannot be explained by the simplified sunspot model with single-component ideal gas atmosphere which has been previously assumed. This represents a fundamental flaw in our understanding of the sunspot equilibrium problem. Existing multiple-component sunspot atmospheric models predict that a large amount of molecular hydrogen (H2) exists in the sunspot umbra. The formation of molecules provides a mechanism for isothermal concentration of the umbral magnetic field which may explain the observed rapid increase in umbral magnetic field strength relative to temperature. We have characterized the equilibrium forces in sunspots using simultaneous visible and IR sunspot magnetic field survey observations of the highly sensitive Fe I lines at 6302 and 15650 Angstroms and nearby OH lines which have been conducted with the new Facility Infrared Spectropolarimeter (FIRS) at the Dunn Solar Telescope. We have performed detailed chemical equilibrium calculations with full consideration of radiative transfer effects to establish OH as a proxy for H2, and demonstrate that a significant population of H2 exists in the coolest regions of large and more mature sunspots. We further point out that the formation of H2 can significantly alter the thermodynamic properties of the sunspot atmosphere and may play a significant role in sunspot evolution.
Jaeggli Sarah A.
Lin Hainan
Uitenbroek Han
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