Which type of star can sustain life

As stated, it is known for sure that Sirius has two stars, with a possibility for a third, but let's focus on the two Science knows about for sure right now. Sirius A is a spectral type A star - also known as a white star. These stars have a high mass and burn brighter and hotter than our sun, which is a class G (yellow) star, because of this they tend to consume the supply of hydrogen faster and thus are shorter lived. They tend to give off a lot of ultraviolet light and, due to all of this, biological evolution is severely restricted in Sirius. (2) (3)

Sirius B is a white dwarf on a 49.9 year orbit of Sirius A and during that orbit is between 8 and 31 AU distance from Sirius A. This star would give off similar brightness and radiation to Sirius A and, when it is closest to Sirius A would be a very strong 'second sun' for any planet near the outer rim of the goldilocks zone for Sirius A. The existence of a second white dwarf star in the Sirius system would seem to suggest that the possibility of life is extremely remote indeed.

But wait, there is a supposed third star in the Sirius system. According to Robert Temple's Dogon information, this should be a red dwarf star. He was so certain of it that he made the following quote:

"If a Sirius-C is ever discovered and found to be a red dwarf, I will conclude that the Dogon information has been fully validated."

So, what about that third star? Well, funny you should ask that. According to gravitational studies done in 1995 showed a possible Brown Dwarf star orbiting Sirius A every 6 years. Could this be the elusive Sirius C spoken about by the Dogon?( 4)

A brown dwarf star is a sub-stellar object whose mass is too low to sustain a hydrogen fusion reaction in its core. So it never becomes a full blown star and resembles a large Jupiter like gas giant.

However, before we lose ourselves too much in determining the effects this third star would have on any planets in the goldilocks zone it should be noted that a more recent study published in 2008 and using advanced infrared imaging technology came to the conclusion that Sirius PROBABLY did not have a third star. I say probably as the survey of the entire system was not fully complete having a region roughly 5 AU from Sirius A being unexplored during this study. (5)