Interesting articles about "micronovas"

American Association of Variable Star Observers (AAVSO)
Thu, 05/05/2022 - 00:08

A couple of recent articles describe what is called "micronovas" by some astronomers. These are small, rapid outbursts of 2-3 magnitudes that have been observed in several CVs. The outburst is very rapid: it takes just a few minutes to reach peak brightness and then the star slowly returns to normal over an hour or two. Objects that exhibit this include the well-placed bright targets EI UMa and TV Col (see Scaringi,  See Shaefer, Pagnotta, Zoppelt for another object, V2487 Oph (one of a handful of recurrent novae), that exhibits similar outbursts.

In another recent article, Scarigini, ( propose that these small outbursts are "localized thermonuclear runaway" (LTNR) events - basically a nova explosion but only on a portion of the white dwarf's surface. In a regular nova, hydrogen builds up in a more or less uniform shell on the star's surface until the gas becomes dense and hot enough to sustain fusion. The entire shell then erupts in a massive thermonuclear explosion. Scaringi proposes that the hydrogen accreted from the white dwarf's companion piles up on certain regions of the dwarf, most likely due to strong magnetic fields present in some white dwarfs. These smaller regions erupt when the critical density and temperature are reached locally.

Interesting stuff, and another reason to monitor cataclysmic variables

Shawn (DKS)