HD 47366 (HIP 31674, BD−12 1566, HR 2437, TYC 5373-2001-1) is listed in the Hipparcos Catalogue (ESA 1997) as a K1 III star, with a visual magnitude of V = 6.11 and a color index of B − V = 0.994. The Hipparcos parallax π = 12.5 ± 0.42 mas (van Leeuwen 2007) corresponds to a distance of 80.0 ± 2.7 pc. The reddening E(B − V) = 0.028 was obtained from the Galactic dust map of Schlegel et al. (1998), with the correction given by Bonifacio et al. (2000) and a scaling factor of 





, where d is the distance, b is the Galactic latitude, and h = 125 pc is the scale height of the reddening layer. The absolute magnitude MV = 1.51 was derived from the distance and the interstellar extinction AV = 3.1E(B − V). By adopting the broadband photometric color B − V and the estimated metallicity with the empirical calibration relation of Alonso et al. (1999, 2001), we derived the bolometric correction B.C. = −0.309 and the effective temperature Teff = 4866 ± 100 K. We used a high signal-to-noise ratio (S/N ∼ 200), iodine-free spectrum taken with HRS to measure the equivalent widths (EWs) of ∼30 Fe i lines, to derive the iron abundance [Fe/H]. The line lists as well as their oscillation strengths (





) were mainly taken from Hekker & Meléndez (2007), in which iron lines were carefully selected to avoid any blend by atomic or CN lines. The model atmosphere used in this work was interpolated from the line-blanketed, local thermodynamic equilibrium (LTE) ATLAS9-ODFNEW grid (Castelli & Kurucz 2004). The microturbulent velocity vt was obtained by minimizing the trend between the abundances of different Fe i lines and their reduced equivalent widths (





). The macroturbulent velocity was estimated with the empirical relations of vmacro versus Teff given by Hekker & Meléndez (2007), and the projected rotational velocity (





) was determined with the method of Fekel (1997). The stellar mass, surface gravity (





), radius, and age were derived using a Bayesian approach with the Geneva database (Lejeune & Schaerer 2001), which includes the post-helium flash phases for stars with M ≥ 1.7 M⊙. First, we interpolated an extensive grid of evolutionary tracks, with ΔM = 0.05 within 1.2 ≤ M/M⊙ ≤ 3.6, Δ[Fe/H] = 0.02 within −0.4 ≤ [Fe/H] ≤ +0.3, and 500 points in each track. Then, for each data point, we calculated the likelihood functions of 





, Teff and [Fe/H] to match the observed values by assuming Gaussian errors. We adopted uniform prior probabilities of mass and [Fe/H]. It is noted that stars evolving more slowly have a higher probability of being observed. Without correcting this evolution effect, the resulting parameters would bias toward the rapid evolution phases. We therefore weighted the probability of each point along its evolutionary track by the normalized time-step (ai+1,j − ai,j)/(an,j − aa,j), where ai,j is the age of the ith interpolated point in the jth track, and n = 500 is the number of interpolated points in each track. Eventually, the probability distribution functions (PDFs) of the parameters yield M = 1.81 ± 0.13 M⊙, R = 7.30 ± 0.33 R⊙, 





, and age = 1.61 ± 0.53 Gyr. The stellar mass is particularly important to derive the minimum masses of the orbiting planets detected with the Doppler technique. However, previous spectroscopic analyses gave discrepant results (1.87 M⊙ by Liu et al. 2010; 1.2 M⊙ by Mishenina et al. 2006) for HD 47366, which may be due to the different methods on finding Teff and 





. Our determinations were based on a similar method to that of Liu et al. (2010), but used the Geneva evolutionary tracks, instead of the Y2 model (Yi et al. 2003), which does not account for the evolutionary phases after the helium-core flash. We found that the probability that the star has passed through the RGB tip and in-core helium burning phase is ∼88%. The stellar parameters of HD 47366 are listed in Table 1. In Figure 2, we plotted HD 47366 on the H-R diagram, together with the evolutionary tracks for stars with different masses and metal contents.
Citation: Castelli & Kurucz 2004
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