def _colnames(elements):
    """Generate column names for output text file.

    Args:
        elements (list): List of output element abbreviations (str).

    Returns:
        str: header line that describes columns.
    """
    time = ['{:8}'.format('Time')]
    sfr = ['{:8}'.format('SFR')]
    survivors = ['{:10}'.format('Survivors')]
    feh = ['{:8}'.format('[Fe/H]')]
    abunds = ['{:8}'.format('[{}/Fe]'.format(item)) for item in elements]
    line = time + sfr + survivors + feh + abunds
    return '  '.join(line) + '\n'