I am in the middle of getting a presentation together for Cataclysmic Variables (CV) and thought you might like a crash course in it as well. Cataclysmic variables are binary systems that consist of an normal star and a white dwarf. They are typically small. The typical binary system is roughly the size of the Earth-Moon system - with an orbital period in the range 1-10 hrs. The companion star, a more or less normal star like our Sun, loses material onto the white dwarf by accretion. This part is kind of interesting so I will give you some background on the setup. The white dwarf was at one time a regular schlep of a star. For few billion years or so it cooked hydrogen into helium by fusion. Sadly the star eventually ran out of hydrogen so what do you do? you start fusing helium together until you wind up with a mostly carbon rich star that has ceased fusion and is just hanging out cooling down for the next billion years. While all of this was happening the star went through the red giant phase etc. So there it sits a sun like mass squished down into the size of the earth.This makes for a very dense and more to the point, a huge gravity well. Ah but what if there was a close by companion star? A regular star in most ways except for the fact that it is in an orbit with the earlier mentioned white dwarf? This scenario has the makings for a CV
There are several types of CVs out there and all of them have different ways of doing their business. Let's break CVs down into some bite sized chunks. For starters there are two major types of CVs. One has a fusion dominated phase. The second has an accretion disk dominated phase.
Fusion Dominated includes
1.Classical Novae
2.Super Soft Sources (SSS)
Classical Novae
A classical nova occurs when material (drawn from the companion star) accretes onto the surface of a white dwarf star's surface and thus begins an unstable thermonuclear fusion reaction. Material transfer will gradually occur between novae explosions The mass will be accreted onto the white dwarf's surface at a low rate, generating only weak X-ray emission. The nova outburst will increase the apparent brightness of the binary star system by ten thousand to a million times (an increase in stellar magnitude of 10 to 15). Can I get a Wow! there? The reason is fairly simple in that the slow build up of material causes the bottom layer to compress and finally is set off on the fusion path. At this point all of the material is fused at the same moment releasing a massive explosion of light /energy They are thought to recur, though with recurrence time scales of 10,000 years, We will just have to wait and see if it happens again. No known classical novae recurrence have been observed.
Super Soft Sources
Super Soft Sources (or SSSs) are the new kids on the block in the family of cataclysmic variables. This CV was first categorized by ROSAT observations. SSSs are objects with temperatures of between 200,000 and 800,000 K and luminosities around 1038 ergs/s. More than 90% of their observed X-ray emission is below 0.5 keV. The leading theory is SSSs are white dwarfs with classic hydrogen fusion occurring from material accreting onto their surfaces. This could make SSSs the progenitor for Type Ia supernovae.
Accretion dominated CVs can be chopped up into three main categories. all of which are fascinating in their workings. They are:
1.Dwarf Novae
2.Polars
3.Intermediate Polars
Dwarf Novae

Polars

X-ray emission from polar systems is entirely due to the accretion column and its impact, so in quiescent times when matter is not accreting onto the system, the entire system is much dimmer.
Intermediate Polars
When a Polar has a wide separation between companions or does not have an outstanding magnetic field but still a very good one an accretion disk can and will form. When this action is found The moniker of Intermediate Polar is bestowed on the pair As material migrates inwards in the disk, it may eventually encounter a magnetic field strong enough to control the flow of material, at which point matter would instead stream from the inner edge of the disk along magnetic field lines onto the pole of the white dwarf. Such a system would therefore be expected to be a source of hard X-rays from the shock at the magnetic poles. Intermediate polars, either due to weaker magnetic fields or wider star separations, will not necessarily have orbital and spin rates locked. Observed systems have longer orbital periods than polars, which given that the systems have comparable masses verifies their wider separation.
Now if that wet your whistle for the wild world of variable stars then hop on over to the American Association of Variable Star Observers here and get a handle on variable stars You could even discover one! They happen all the time
Until next time
Keep looking up!
Steve T
Now if that wet your whistle for the wild world of variable stars then hop on over to the American Association of Variable Star Observers here and get a handle on variable stars You could even discover one! They happen all the time
Until next time
Keep looking up!
Steve T
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