A Cataclysmic Delight

This week’s OOTW features Jean Tate’s OOTD posted on the 6th of October

CV star

This is SDSS J120231.00+450349.1; a Cataclysmic Variable star in the constellation Ursa Major.

Cataclysmic Variables are stars in a binary system, with one white dwarf and another star of varying type. The white dwarf steals matter from its companion as it orbits closely, often completing an orbit within hours! As the white dwarf pulls the matter off its companion it surrounds itself with an accretion disk mostly made of hydrogen. If this CV was observed in the X-ray or UV you’d see it as strong sources in both wavelengths, as both X-rays and UV are being strongly emitted from the accretion disk!

As the name suggests this CV varies in brightness, getting brighter for a period as the accretion disk falls onto the white dwarf, setting off nuclear fusion at the stars surface.

Jean Tate found this CV to be of ZZ Ceti type, which are stars that pulsate, swelling from one size to another. Jean Tate writes:

In the H-R diagram, there is a thing called the instability strip; stars which fall in this strip pulsate (move in and out, usually radially) … and that pulsation is used, in Cepheids, as a key ‘standard candle’ in the cosmic distance ladder. Some white dwarfs pulsate; some which pulsate are called ZZ Ceti stars, after the variable ZZ Ceti: they are hydrogen WDs (classified as DA), and because they are variable, DAV stars (helium WDs (DB) can be variable too; they are DBVs. I don’t know if carbon (DQ) or metal (DZ) white dwarfs can pulsate).

I highly recommend reading her OOTD for a lot more information; and for details on the spectra!


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