Are there any good images of Sirius B at apastron in the Sirius system? Sirius B has a distance to Sirius A of 11 arc seconds at apastron; are there any good images of it at that point in its orbit?
HST took pictures close to periastron in 1997, when the separation of the stars was about 3.7 arcsecs. See Bond et al. (2017). There are no pictures exactly at periastron.

HST took pictures close to apastron in August 2016, when the separation was 10.7 arcsecs (see the same reference). There are no pictures from HST closer to apastron but some may be taken over the next year or so.

Here is a raw HST image from August 2016, taken from the HST archive  (freely available and easy to find).



There are many photographs of the binary taken at around 11 arcseconds separation. Table~3 of the same reference above lists a stack of observations taken between 1970 and 1975 when the separation was around 11 arcseconds. One of these images is shown below; Sirius B is the faint object below and to the right of Sirius A. The other symmetrically spaced blobs are image artefacts.