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DQ Herculis

DQ Herculis (Nova Herculis 1934) was an exceptional nova in outburst, and remains an important object in astrophysics.  The light curve shows the first 5000 days of the DQ Her lightcurve. Most notably, it shows the precipitous drop in light starting 100 days after outburst, and dropping nearly ten magnitudes in the space of a month.  The star recovered somewhat within a few hundred days, and began an uninterrupted return to quiescence that lasted several more years.  The sharp drop was speculated at the time to be due to the formation of dust, but it took several more decades until infrared observations of the similar Nova Serpentis 1970 (FH Ser) confirmed dust formation in novae.  DQ Her also has two other noteworthy properties: it is an eclipsing binary, and it is also an intermediate polar.  Polars are cataclysmic variables where the accreting white dwarf has a strong magnetic field that strongly confines the accretion stream from the surface of the secondary all the way down to the magnetic poles of the white dwarf.  Intermediate polars have moderately strong magnetic fields; they form accretion disks like other CVs, but the inner accretion disk is disrupted and matter flows onto the white dwarf's magnetic poles just like in the true polars.  DQ Her shows variability with a period of 71 seconds caused by rotation of the white dwarf and the radiation emitted by the two magnetic poles.  We see that light reprocessed through the accretion disk because we see the disk edge-on, and the white dwarf itself is obscured.

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