How did Sirius A and B evolve ?

[dougettinger]

Sirius A star is an A type star twice as large as our Sun. It companion star, Sirius B, is a white dwarf. Obviously, Sirius A is a long-lived star like our Sun - although it may have a shorter life because it is more massive. Sirius B being a white dwarf was a star the size of our Sun or Sirius A. Some good questions arise about their evolution.

1) Since they are companion stars they had to be birthed at the same time. Sirius B is now a white dwarf because it had to be much more massive but not more then what would create a supernova, and hence shorter-lived than its companion at twice the size of our Sun. When Sirius B lost most of its mass by shedding it during the Red Giant phase did the star move farther away from its companion. Their distance apart is from 8 to 32 AU.

2) For Sirius B to be shorter-lived than Sirius A, it is estimated to have been a B-type star with 5 solar masses; but according to theory any star greater than 2 to 2.5 solar masses should eventually become a supernova. An since this star system is only 300 million years old, then Sirius B had to be a supernova that did not have a Red Giant phase. Yet theory states that a white dwarf comes from a long-lived star and goes through a Red Giant phase. Wikipedia claims that this is the case for Sirius B. Why does this dichotomy exist ?

3) In the event that Sirius B did have a Red Giant phase would not its companion strip away the outer layers of this Red Giant phase and grow in size ? It metallicity apparently indicates that this did occur.

4) In the event that Sirius B became a supernova during the fusion of carbon did it have a previous Red Giant stage ? In general, do certain massive stars that eventually become supernovas have a Red Giant phase ? I was led to believe that stars about the size of our Sun went through a Red Giant phase, then became a nova, and settled to being a white dwarf inside a planetary nebula. Stars greater than about 2 solar masses evoled into WR type stars, then a supernova , and finally a neuton star inside a SN remnant. Why does my thinking now seem a little foggy afer reviewing the Sirius system ??