def teff(cluster):
    """
    Calculate Teff for main sequence stars ranging from Teff 3500K - 8000K. Use
    [Fe/H] of the cluster, if available.

    Returns a list of Teff values.
    """
    b_vs, _ = cluster.stars()
    teffs = []
    for b_v in b_vs:
        teffs.append(8575 - 5222.27 * b_v + 1380.92 * b_v ** 2 + 701.7 *
            b_v * (cluster.fe_h - 0.15))
    return teffs
