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Register a new userModelling the molecular Zeeman effect in M-dwarfs: methods and first results
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D. Shulyak
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We present first quantitative results of the surface magnetic field measurements in selected M-dwarfs based on detailed spectra synthesis conducted simultaneously in atomic and molecular lines of the FeH Wing-Ford $F^4,Delta-X^4,Delta$ transitions. A modified version of the Molecular Zeeman Library (MZL) was used to compute Lande g-factors for FeH lines in different Hunds cases. Magnetic spectra synthesis was performed with the Synmast code. We show that the implementation of different Hunds case for FeH states depending on their quantum numbers allows us to achieve a good fit to the majority of lines in a sunspot spectrum in an automatic regime. Strong magnetic fields are confirmed via the modelling of atomic and FeH lines for three M-dwarfs YZ~CMi, EV~Lac, and AD~Leo, but their mean intensities are found to be systematically lower than previously reported. A much weaker field ($1.7-2$~kG against $2.7$~kG) is required to fit FeH lines in the spectra of GJ~1224. Our method allows us to measure average magnetic fields in very low-mass stars from polarized radiative transfer. The obtained results indicate that the fields reported in earlier works were probably overestimated by about $15-30$%. Higher quality observations are needed for more definite results.
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We present the methods and first results of a survey of nearby high proper motion main sequence stars to probe for cool companions with the Gemini camera at Lick Observatory. This survey uses a sample of old (age > 2 Gyr) stars as targets to probe for companions down to temperatures of 500 K. Multi-epoch observations allow us to discriminate comoving companions from background objects. So far, our survey successfully re-discovers the wide T8.5 companion to GJ 1263 and discovers a companion to the nearby M0V star GJ 660.1. The companion to GJ 660.1 (GJ 660.1B) is ~4 magnitudes fainter than its host star in the J-band and is located at a projected separation of ~120AU. Known trigonometric parallax and 2MASS magnitudes for the GJ 660.1 system indicate a spectral type for the companion of M9 +/- 2.
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