def _band_detection(observations, min_freq, max_freq):
    """
    Obtain a subset of the provided pandas.DataFrame that contains observations in the range of minimum frequency
    (min_freq) to maximum frequency (max_freq) in GHz. This is used to define the frequency range of various ALMA bands.

    """
    band_obs = observations[(observations['central_freq_GHz'] >= min_freq)
                            & (observations['central_freq_GHz'] <= max_freq)]
    return band_obs