def metalicity_nemec(period, phi31_v):
    """
    Returns the Nemec formula metalicity of the given RRab RR Lyrae.

    The version of the formula used is from Skowron et al. (2016), where I band
    phi31 is used, as opposed to the original usage of Kp-passband phi31.

    (Nemec et al., 2013) (2)
    (Skowron et al., 2016) (5)

    Parameters
    ----------
    period : float64
        The period of the star.
    phi31_v : float64
        The V band phi31 of the star.

    Returns
    -------
    metalicity_neme : float64
        The Nemec formula metalicity of the star.
    """
    return -7.63 - 39.03 * period + 5.71 * phi31_v + 6.27 * phi31_v * period \
            - 0.72 * phi31_v ** 2