I have two time series. Both series have same columns. They have some common dates. One of columns of both series is Close representing closing price. I want to inner join these closing prices. I have used following code. But it is generating error in last line.

```
dow=pd.read_csv("dow.csv",index_col="Date")
sensex=pd.read_csv("sensex.csv",index_col="Date")
dow_close=dow["Close"]
sensex_close=sensex["Close"]
dow_close.index=pd.to_datetime(dow_close.index)
sensex_close.index=pd.to_datetime(sensex_close.index)
dow_sensex_close=dow_close.join(sensex_close,how='inner')

```