Mysteries Department
Sign inRequest access
Tabby's star (KIC 8462852)Evidence
Evidence · Tabby's star (KIC 8462852)

Over 20 years, the star faded only while it was dipping: 2011-2013 and 2015-2018

On one V scale from 2006 to 2026 (ASAS, ASAS-SN and AAVSO tied on their overlaps), the star's two fading episodes coincide with its two known dip episodes. It faded 47 ± 5 mmag from the 2010 to the 2013 season (the D800 dip in March 2011 and the D1500 cluster in early 2013) and recovered 34 ± 7 mmag by 2015. It faded again by about 10 mmag over 2015-2018 (the 2017 dips), and has been flat to within about 5 mmag through 2019-2026, when no dip episode was seen.

Suggestive0

What it means

Key questionWhat causes the slow fading of the star?
Most likely: a large, diffuse amount of circumstellar dust, more extended than the clumps that make the dips
Most likelyunchanged
Most likelyunchanged
What it implies
  1. The fade and the dips look like one phenomenon on two scales, a diffuse screen that thickens while clumps are being made, so a renewed fade should accompany the next dip episode and a slow fade can serve as an early warning.For the key question: What causes the slow fading of the star?
  2. Whatever supplies the dip clumps works in episodes of a few years separated by quiet periods, with 2019-2026 the longest quiet period on record.For: What blocks the light during the deep, irregular dips?

Next steps 2

1
Quantify the dip-fade link in Kepler; set an early-warning rule
Could shiftGood odds~4 h
On: What causes the slow fading of the star?
40score
Details

Test the dip-fade link quantitatively. In the Kepler long-cadence and full-frame data, compare the flux level in 90-day windows around each dip family with the windows between them. Then predict: if the link holds, the next dip episode should start with a slow fade of 1-3 per cent. Write this into the AAVSO observing request as an early-warning criterion: a 10 mmag seasonal drop means intensify monitoring.

2
Measure the colour of the 2015-2018 fade
Could shiftFair odds~10 h
On: What causes the slow fading of the star?
17score
Details

From the department's AAVSO export, fit the 2015-2018 fade separately in B and V, each observer against their own comparison star, after the B band's systematic floor is checked (see the step on the B band under the post-2018 question). Compare the ratio of the B and V fade rates with three predictions: circumstellar dust shallower than interstellar extinction (as Meng et al. found for 2015-16), an interstellar extinction law, and a temperature drop of the star. A dust-like ratio supports the diffuse circumstellar screen; an interstellar-law ratio supports intervening material; a temperature-like ratio revives the planet-engulfment relaxation.

Ranked by how likely each is to move the key question, for the time it takes

How it was found 1 run

Result. Two fading episodes (2011-2013 and 2015-2018) coincide with the two dip episodes (Kepler Q8 and Q16-17; 2017). Recovery followed each. The star has held flat through the dip-free years 2019-2026. Suggestive of one dust supply behind both the dips and the slow changes. The recovery is against a monotonic relaxation..
Seasonal median V on the ASAS-SN V scale (mmag relative to the 2007 season){'flat_2019_2026': 'within about 5 mmag', 'fade_2010_to_2013': '+47 ± 5', 'fade_2015_to_2018': 'about +10', 'recovery_2013_to_2015': '-34 ± 7', 'tie_rms_g_vs_aavso_mmag': 4}Two fading episodes (2011-2013 and 2015-2018) coincide with the two dip episodes (Kepler Q8 and Q16-17; 2017). Recovery followed each. The star has held flat through the dip-free years 2019-2026. Suggestive of one dust supply behind both the dips and the slow changes. The recovery is against a monotonic relaxation.
Figure 1

The star faded twice in 20 years, each time while it was dipping, and has been flat since 2019

Seasonal median V relative to the 2007 season (mmag; positive = fainter): ASAS to 2015, ASAS-SN V 2015-2018, AAVSO V from 2019

-200204060mmag fainter than 200720072008200920102011201220132014201520162017201820192020202120222023202420252026D800 dipD1500 dips2017 dips2017 dips
-200204060mmag fainter than 200720072008200920102011201220132014201520162017201820192020202120222023202420252026
seasonal median
Seasons run July-June and are labelled by the year they end. ASAS seasonal errors are 3-9 mmag; ASAS-SN and AAVSO are 1-3 mmag. The three series are tied on their overlaps to within about 5 mmag.
Drawn by the site with The 2006-2026 V light curve on one scale
ASAS V photometry of KIC 8462852, 2006-2017 (Simon et al. 2018, full table)ASAS-SN v1 image-subtraction light curve of KIC 8462852, 2015-2026 (V and g)AAVSO International Database export for KIC 8462852, 1 July 2018 to 29 October 2026 (77,195 observations, with comparison stars)AAVSO International Database export for KIC 8462852, October 2015 to June 2018 (66,875 observations, with comparison stars)code/stitch_modern.py3 outputs

Sources 2

SRC
SRC

Cite it

Mysteries Department. (2026). Over 20 years, the star faded only while it was dipping: 2011-2013 and 2015-2018 [Evidence EVD0DFQ24NXSGHG]. https://mysteriesdept.com/r/EVD0DFQ24NXSGHG
Private beta Downloads are for beta members

We're in a private beta while we get things right. Everything here is free to read; downloading datasets, sources and code is open to members for now.

Apply to the betaSign in
It takes a couple of minutes. We'll reply by email.