  Observations of the Vela pulsar region with the Chandra X-ray observatory
have revealed the fine structure of its synchrotron pulsar-wind nebula (PWN),
which showed an overall similarity with the Crab PWN. However, contrary to the
Crab, no firm detection of the Vela PWN in optical has been reported yet. To
search for the optical counterpart of the X-ray PWN, we analyzed deep optical
observations performed with different telescopes. We compared the optical
images with those obtained with the Chandra ACIS to search for extended
emission patterns which could be identified as counterparts of the X-ray nebula
elements. Although some features are seen in the optical images, we find no
correlation with the X-ray structure. Thus, we conclude that the diffuse
optical emission is more likely associated with filaments in the host Vela SNR.
The derived upper limits on the optical flux from the PWN are compatibile,
within the uncertainties, with the values expected on the basis of the
extrapolations of the X-ray data.
