NICER / ISS Science Nugget
for July 30, 2020

AM Her: The X-ray-Optical Connection

NICER executed a target-of-opportunity request to observe the cataclysmic variable system called AM Her. Cataclysmic variables (CVs) are binary star systems consisting of a white dwarf and a secondary star that feeds mass onto the WD through accretion. NICER observed simultaneously with the Mt. Palomar 200-in. Hale telescope, which provided high-speed optical photometry. The orbital period of AM Her is 3.1 hours, and NICER and Palomar together observed more than two full orbits (see figure). CVs such as AM Her are known, when active, to exhibit flaring behavior in visible light, and they are also X-ray emitters. The relationship between the X-ray and fast flaring optical emissions has never been established. The joint NICER-Palomar data will enable cross-correlation of AM Her's brightness in the two bands, enabling a unique probe of the direct-accretion process (inflowing matter impacts the white dwarf directly, rather than forming a accretion disk) that powers these systems.

Figure: The NICER X-ray lightcurve of the CV AM Her over more than two full orbits of the binary system.

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