def indicator_bollinger(df_t, lookback=20):
    """Creates columns for bollinger channel.  Requires columns "high" and "low" in intraday_df

    Args:
        df (pd.DataFrame): OHLCV intraday dataframe, only needs close
        lookback (:obj:int, optional): rolling window.  Default is 20

    Returns:
        pd.DataFrame: columns are:
            - bollinger_high
            - bollinger_low
    """
    df = df_t[["close"]].copy()
    df["bb_ma"] = df.close.rolling(window=lookback).mean()
    df["bb_std"] = df.close.rolling(window=lookback).std()
    df["bollinger_high"] = df.bb_ma + df.bb_std
    df["bollinger_low"] = df.bb_ma - df.bb_std
    df = df.drop(["close", "bb_ma", "bb_std"], axis=1)
    return df