KIC 8462852 dimming events

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Profile Jon Golding
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Message 1786118 - Posted: 9 May 2016, 12:53:55 UTC

Seems like there was a recent dimming of KIC 8462852 (Tabby's star), as monitored by the American Association of Variable Star Observers. https://www.aavso.org/lcg
Is this star planned to be included in the Breakthrough targeted search when Parkes telescope data becomes available?
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Message 1786153 - Posted: 9 May 2016, 15:13:46 UTC
Last modified: 9 May 2016, 15:19:50 UTC

Thanks for that news, Jon!

It appears that the visual magnitude dipped from a typical 11.85 value to around 12.05. My math quite rusty, but I believe that makes a dimming of about 9 percent. That's far too much to be caused by an eclipsing planet.

This dip apparently occurred briefly on May 4th. Unclear if it lasted long enough to allow detailed inspection, such as high resolution spectroscopy.

In any case, if these observations stand up to scrutiny, we have evidence that the short term dimming incidents on Tabby's Star continue to occur.
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Profile Jon Golding
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Message 1786158 - Posted: 9 May 2016, 15:28:35 UTC - in response to Message 1786153.  

Seems that the series of observations showing a possible transit were all recorded by the same observer, so the results could be explained by a technical problem or local atmospheric effect that day. Going back to the original paper on KIC 8462852, some of those dimming events happened in clusters, so there may be more along anytime soon now. Hopefully someone can get a spectrum of the star during a dimming event and that might yield some clues as to what (or who!) is doing this.
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Message 1786223 - Posted: 9 May 2016, 18:09:54 UTC

As I understand it, AAVSO observers are trained to estimate magnitudes by comparing the target star to nearby stars of known brightness. This would tend to reveal atmospheric and technical effects on stars' magnitudes. Naturally, multi-observer data are preferable.
I'm told that a reduction in magnitude of ~11.85 to ~12.05 means a reduction of brightness of something over 30 percent, not 9 percent, as I estimated. So much for my early morning math skills!
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Message 1786241 - Posted: 9 May 2016, 19:20:36 UTC - in response to Message 1786223.  

Wow! That's a huge reduction in brightness. Even bigger than the largest 20% dip reported (https://arxiv.org/abs/1509.03622)
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Message 1787057 - Posted: 12 May 2016, 15:51:14 UTC - in response to Message 1786241.  

Here's the plot showing the dip in brightness in the context of the (usually) steady brightness of around 11.8 - 11.9 mag.
I've taken the raw data from https://www.aavso.org/apps/webobs/results/?star=KIC+8462852&page=21 and made a plot of the dimming event. The entire dimming event lasts around 2 hr and is made up of a series of rapid dips in brightness. This would appear to fit with a cluster of objects rapidly moving across the face of the star (comets?)


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