Uncertainties in the calibrations of star formation rate
  The calibrations of star formation rate (SFR) are prone to be affected by
many factors, such as metallicity, initial mass function (IMF), evolutionary
population synthesis (EPS) models and so on. In this paper we will discuss the
effects of binary interactions, metallicity, EPS models and IMF on several
widely used SFR calibrations based on the EPS models of Yunnan with and without
binary interactions, BC03, SB99, PEGASE and POPSTAR. The inclusion of binary
interactions makes these SFR conversion coefficients smaller (less than
0.2dex), and these differences increase with metallicity. The differences in
the calibration coefficient between SFR and the luminosity of $\rm H\alpha$
recombination line (C$_{\rm H\alpha}$) and that between SFR and the ultraviolet
(UV) fluxes at 1500 and 2800\,$\rm \AA$ (C$_{i, {\rm UV}}$), caused by IMF, are
independent of metallicity (0.03-0.33\,dex) except $\Delta$C$_{\rm H\alpha,
IMF}$ when using the POPSTAR and $\Delta$C$_{i, {\rm UV, IMF}}$ when using the
PEGASE models. Moreover, we find that $L_{\rm 2800}$ is not suitable to the
linear calibration of SFR at low metallicities.
  At last, we compare the effects of these several factors on the SFR
calibrations considered in this paper. The effects of metallicity/IMF and EPS
models on the C$_{\rm H\alpha}$ and C$_{\rm FIR}$ (the conversion coefficient
between SFR and the far-infrared flux) are the largest among these factors,
respectively. For the calibration between SFR and C$_{i, {\rm UV}}$, the
effects of these several factors are comparable.
