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Description
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star over a wide wavelength range from the UV to the mid- infrared from 2015 October through 2016 December, using Swift, Spitzer and AstroLAB IRIS. The star faded in a manner similar to the long-term fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period reported is 22.1+/-9.7mmag/yr in the Swift wavebands, with amounts of 21.0+/-4.5mmag in the ground-based B measurements, 14.0+/-4.5mmag in V, and 13.0+/-4.5 in R, and a rate of 5.0+/-1.2mmag/yr averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at >~3{sigma} by three different observatories operating from the UV to the IR. The presence of long-term secular dimming means that previous spectral energy distribution models of the star based on photometric measurements taken years apart may not be accurate. We find that stellar models with Teff=7000-7100K and A_V_~0.73 best fit the Swift data from UV to optical. These models also show no excess in the near-simultaneous Spitzer photometry at 3.6 and 4.5{mu}m, although a longer wavelength excess from a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of the fading favors a relatively neutral color (i.e., R_V_>~5, but not flat across all the bands) compared with the extinction law for the general interstellar medium (R_V_=3.1), suggesting that the dimming arises from circumstellar material.
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