May 20, 2016

Long term dimming of KIC8462852 within the large statistical uncertainty error level

Last fall Yale astronomer Tabetha (Tabby) Boyajian and colleagues posted a paper on an astronomy preprint server reporting a star (KIC 8462852) 1,480 light-years away in the constellation Cygnus had found fluctuations in the light coming from the otherwise ordinary F-type star (slightly larger and hotter than the sun).

The most remarkable of these fluctuations consisted of dozens of uneven, unnatural-looking dips that appeared over a 100-day period indicating that a large number of irregularly shaped objects had passed across the face of the star and temporarily blocked some of the light coming from it.

Then a study released in January by a Louisiana State University astronomer threw even more fuel on the fire of alien speculation by announcing that the brightness of Tabby’s star had dimmed by 20 percent over the last century: a finding particularly difficult to explain by natural means but consistent with the idea that aliens were gradually converting the material in the star’s planetary system into giant megastructures that have been absorbing increasing amounts of energy from the star for more than a century. That study has been accepted for publication in the peer reviewed Astrophysical Journal.

A new study indicates that no dimming of star KIC 8462852 can be found within the uncertainties of 0.2mag per century.

The short term fluctuations in the Kepler data has bee found to be rock-solid. The historic Harvard plates have an uncertainty (over 100 years) of order 0.1 to 0.2mag, and this was also visually evident.

Arxiv - A statistical analysis of the accuracy of the digitized magnitudes of photometric plates on the time scale of decades with an application to the century-long light curve of KIC 8462852

Researchers present a statistical analysis of the accuracy of the digitized magnitudes of photometric plates on the time scale of decades. In their examination of archival Johnson B photometry from the Harvard DASCH archive, they find a median RMS scatter of lightcurves of order 0.15mag over the range B~9-17 for all calibrations. Slight underlying systematics (trends or flux discontinuities) are on a level of less than 0.2mag per century (1889-1990) for the majority of constant stars. These historic data can be unambiguously used for processes that happen on scales of magnitudes, and need to be carefully examined in cases approaching the noise floor. The characterization of these limits in photometric stability may guide future studies in their use of plate archives. They explain these limitations for the example case of KIC8462852, which has been claimed to dim by 0.16mag per century, and show that this trend cannot be considered as significant.

SOURCES -Arxiv, Vanderbilt University

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