Astronomy humor (calling dr_nebula)

[unixronin]

Astronomy-geek humor that dr_nebula would probably appreciate:

<Alaric>  hmm, new unaided-eye-visible nova in Scorpius

<Alaric>  but James Nicoll appears to be confusing novae with type A supernovae

<chrispypa>  type A are the overachievers?

<tocotox>  what's the fixer-upper type?

<Alaric>  Cepheid variables  :)

Comments

[james-nicoll.livejournal.com]

Am I?

http://en.wikipedia.org/wiki/Nova

(Ritual admission that there are better sources)

[unixronin.livejournal.com]

Hm, that's the first time I've ever seen an accretion mechanism described for a nova. Every other source I've seen (including Wikipedia itself) says that's the mechanism of a type 1a (not type A, my error) supernova (http://en.wikipedia.org/wiki/Supernova#Type_Ia).

If we're lucky, dr_nebula will jump in and clarify this. :)

(hint, hint, Doc. Yeah, YOU. Help us out here.)

[unixronin.livejournal.com]

Ah, actually, I see the difference here ... it depends on the rate and extent of the accretion, which can yield either a deflagration front throughout the star or only a surface explosion.

So this is a nova (as distinct from supernova) mechanism that's new to me. This raises the interesting question, then, of what governs which way it goes ... why do some white dwarfs burn off their accreted gas in a surface explosion, while others go on to become a Type 1a supernova? It appears it's a question of the specific atomic makeup of the accreted matter. Hydrogen accretion burns off easily and produces a nova, heavier elements resist fusion long enough to accumulate enough mass to create a Type 1a supernova.

Doc? Do I have this right?

[dr-nebula.livejournal.com]

Yeah - once their accumlated mass exceeds 1.4 solar, the white dwarf implodes and a supernova is formed.

[dr-nebula.livejournal.com]

This mechanism has been known for some time. This is why nova are often recurring with the same star.

[unixronin.livejournal.com]

I was just saying it was new to me as a nova mechanism. But I'm not a serious astronomy geek.