Hi Rodney
Without knowing too much about your equipment, field of view, set up for this image etc., at face value, the smaller star looks far too bright to be a candidate for the Pup, Sirius B? With the 150mm F5 at F15 (using an x3 Barlow?) you’ll be shooting at 2250mm?
Just for comparison, here are a couple of images I took. The 1st one shows Sirius A & B at an effective focal length of 8640mm and the 2nd one is a prime focus exposure through my Vixen 4” at F6.3 showing some brighter field stars.
If you can establish your field of view and measure the separation between Sirius A and the brighter star in your image, it might give some insight into what you have managed to capture? The current separation is approximately 9 arcsecs.
Not trying to rain on your parade, especially given that you’re a Queenslander, but the secondary in your image looks awfully bright!
Cheers
Dennis