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CSS_J091600.8+525002 is a red variable star seemingly superimposed on the south-southwestern edge of the nearby galaxy UGC 4879. This galaxy is probably a member of The Local Group.

Variability in this star was first noticed in the Catalina Sky Survey (CSS) images available through the supernova search SNHunt in 2014. FITS images of the field going back to 2010 when the search began were downloaded and a light curve was made. Early in the survey there was no obvious variability and there were no positive or negative fluxes noticed on the subtractions. However, the light curve shows that beginning in early 2013 long-term variations began. The star was then submitted to and accepted by VSX. www.aavso.org/vsx/index.php?view=detail.top&oid=469849.

The current fading is by far the faintest on record. Normally, the star is brighter than a blue star some 15" northeast of it. This blue star is probably a blue supergiant in UGC 4879.

Is this a red dwarf within the Milky Way that the variation is due to the rotation of spots? If so, this would be an extremely long rotation rate. The SDSS DR12 image does show a number of stars of similar color and brightness scattered throughout the area. If it is a red dwarf then the B-V = 1.77 would place it near magnitude 14 on the main sequence. Then, it would only be about 250 light-years away. There is no noticeable proper motion when blinking the images. The initial Gaia release shows proper motions of -2.6 +/- 4.2 mas/yr in right ascension and -5.4 +/- 4.2 mas/yr in declination (The Initial Gaia Source List (IGSL) (Smart, 2013)). With the errors about as much or more than the proper motions, this does not rule out a distant object. Is this a subgiant or giant whose variation is due to pulsations such as a Mira? If so, that would place it in the halo of the Milky Way. If it is becoming a Mira then with an absolute magnitude of 1.0 to -1.0 that would place it anywhere from 98,000 light-years to 250,000 light-years distant. Perhaps it is from a long disrupted dwarf satellite. Lastly, is it a semi-regular supergiant in UGC 4879 and may eventually become supernova? For a maximum of about 18.4 that would correspond to an absolute brightness from -6.8 to -7.3 for the distance modulus range of 25.2 to 25.7 and negligible extinction. That certainly could make it a supergiant in the galaxy. However, there are no other stars in this galaxy of comparative brightness and color. A spectrum could solve the conundrum.

Lastly, due to the evolving nature of this object, even if it is a Milky Way star, someone might post it as a supernova or LBV candidate when it next brightens. The question is will it return to previous brightness or perhaps go brighter?

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