Asteroseismic Analysis of a Red Giant KIC 9145955 by Including the Small-scale Magnetic Fields in the Atmosphere

Abstract

Recent convincing evidence is found within asteroseismology that suggests the magnetic fields exist in three red giants. Research on small-scale magnetic fields in the Sun and HD 49385 has shown that they have a certain corrective effect on the systematic discrepancies between observed and theoretical frequencies. Here we apply a similar method applied for the Sun to a red giant, KIC 9145955, to explore the impact of small-scale magnetic fields in the photosphere on its frequencies. We find that the calculated frequencies of our best-fit model, which simulates the effect of the magnetic fields by artificially modifying the Eddington $T-\tau$ relation, perfectly match those of the observed l = 0, 1, and 2 modes, indicating the existence of small-scale magnetic fields with an upper strength limit of 65 G and concentrating at a height 13,100 km in the photosphere. Based on the best-fit model, we revise the stellar parameters of KIC 9145955 as: $M=1.23\pm 0.04M_{\odot }$, $R=5.57\pm 0.06R_{\odot }$, $L=19.85\pm 0.5L_{\odot }$, $Age=3.83\pm 0.5$\,Gyr, $M_{\mathrm{He}}=0.2108\pm 0.0005M_{\odot }$, and $R_{\mathrm{He}}=0.0306\pm 0.0001R_{\odot }$.

has been published in ApJ

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