title: Extract confidence interval values from ACF correlogram
body: <p>In R, we can run an ACF correlogram of time series and the confidence interval bands will be plotted in light blue. But when I pull the structure of ACF object, I cannot find these values.  Does anyone know how to extract the values of the confidence interval bands?</p>
  
  <p>e.g.</p>
  
  <pre><code>List of 6
   $ acf   : num [1:27, 1, 1] 1 0.06453 -0.06354 0.00213 -0.01324 ...
   $ type  : chr "correlation"
   $ n.used: int 501
   $ lag   : num [1:27, 1, 1] 0 1 2 3 4 5 6 7 8 9 ...
   $ series: chr "tser[i:(i + 500)]"
   $ snames: NULL
   - attr(*, "class")= chr "acf"
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/rMzaa.jpg" alt="enter image description here"></p>