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Infrared Zeeman analysis of epsilon Eridani
Valenti, Jeff A.; Marcy, Geoffrey W.; Basri, Gibor
AA(University of California, Berkeley, CA, US), AB(University of California, Berkeley, CA, US), AC(University of California, Berkeley, CA, US)
The Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 439, no. 2, p. 939-956 (ApJ Homepage)
Publication Date:
NASA/STI Keywords:
Data Reduction, Infrared Spectra, Late Stars, Stellar Atmospheres, Stellar Magnetic Fields, Stellar Models, Zeeman Effect, High Resolution, Spectrographs, Spectrometers, Spectroscopy, Spectrum Analysis, Stellar Composition, Telluric Lines
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We analyze high-resolution infrared FTS spectra near 1.6 micrometers to obtain the most accurate measurement to date of the magnetic field on a typical active star. A total of 16 infrared Fe I lines are analyzed, including the geff = 3 line at 1.56485 micrometers. We find the 8.8% of the deep photosphere of the active star epsilon Eridiani (K2 V) is covered with a 1.44 kG magnetic field. This corresponds to an absolute magnetic flux of absolute value of B f = 0.13 kG, which is about half the value found in all recent optical studies but agrees with one existing infrared upper limit. We discuss possible explanations for this discrepancy in terms of models with different atmospheres for the quiet and magnetic components. We carefully assess the impact of random noise on our derived mmagnetic parameters and find that the quantity absolute value of B f0.8 is most accurately known, witha formal uncertainty of 0.1%. The 1 sigma confidence interval along this curve ranges between (absolute value of B, f) = (1.31 kG, 10.0%) and (1.60 kG, 7.8%). We also study various sources of systematic errors, and find a 35% uncertainty in f, primarily because the structure of stellar flux tubes is poorly known, but also because of uncertainty in log g. Systematic errors in absolute value of B are smaller (less than 15%) because the sigma components of the 1.56485 micrometer line are resolved. We place low upper limits on the surface magnetic flux on two inactive stars, 40 Eri (Ki V) and sigma Dra (KO V), reinforcing the significance of our magnetic field detection for epsilon Eri. As a byproduct of the Zeeman analysis, we have derived accurate effective temperatures, iron abundances, and macroturbulences for all three stars. In addition, we have determined oscillator strengths (most previously unmeasured) for 21 Fe I transitions near 1.6 micrometers by matching models to the observed solar sprectrum.

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