def is_ab_band(band):
    """
    Check if the default system for the provided
    band is AB.

    Parameters
    ----------
    band : str
        Name of a photometric filter

    Returns
    -------
    bool
        True if the default system for this band is AB
    """
    ab_bands = ['u', 'g', 'r', 'i', 'z', 'y']

    if band in ab_bands:
        return True

    else:
        return False