First polarimetric observations and modeling of the FeH F^4 Delta-X^4 Delta system - AstrophysicsReport as inadecuate

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Abstract: Lines of diatomic molecules are more temperature and pressure sensitive thanatomic lines, which makes them ideal tools for studying cool stellaratmospheres an internal structure of sunspots and starspots. The FeH F^4Delta-X^4 Delta system represents such an example that exhibits in addition alarge magnetic field sensitivity. The current theoretical descriptions of thesetransitions including the molecular constants involved are only based onintensity measurements because polarimetric observations have not beenavailable so far, which limits their diagnostic value. We present for the firsttime spectropolarimetric observations of the FeH F^4 Delta-X^4 Delta systemmeasured in sunspots to investigate their diagnostic capabilities for probingsolar and stellar magnetic fields. We investigate whether the currenttheoretical model of FeH can reproduce the observed Stokes profiles includingtheir magnetic properties. The polarimetric observations are compared withsynthetic Stokes profiles modeled with radiative transfer calculations. Thisallows us to infer the temperature and the magnetic field strength of theobserved sunspots. We find that the current theory successfully reproduces themagnetic properties of a large number of lines in the FeH F^4 Delta-X^4 Deltasystem. In a few cases the observations indicate a larger Zeeman splitting thanpredicted by the theory. There, our observations have provided additionalconstraints, which allowed us to determine empirical molecular constants. TheFeH F^4 Delta-X^4 Delta system is found to be a very sensitive magneticdiagnostic tool. Polarimetric data of these lines provide us with more directinformation to study the coolest parts of astrophysical objects.

Author: N. Afram, S.V. Berdyugina, D.M. Fluri, M. Semel, M. Bianda, R. Ramelli


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