Tabby's star (KIC 8462852)Evidence
Evidence · Tabby's star (KIC 8462852)
AAVSO V: +8.5 mmag/yr fading to 2018, then flat to 0.3 mmag/yr for eight years
An ensemble of 24 AAVSO observers (80,214 V measurements, 3,117 nights) fades at +8.5 ± 2.6 mmag per year over 2015.7-2018.2, in line with Schaefer et al. and Simon et al., and then shows -0.04 ± 0.32 mmag per year over 2018.5-2026.8, with every seasonal median from 2019 to 2026 within 0.007 mag of the 2019 level; the 2017 season sits 0.013 mag fainter than 2019, so the decline ended and partly reversed by 2019.
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
Openunchanged
Answer this evidence bears onThe fade stopped around 2018: the star has held a constant year-scale level since, about 0.01 mag brighter than its…
Supports2 for, none against
Still possibleunchanged
Next steps 3
1
Modern-era stitch 2006-2026. Done: ASAS-SN v1 image-subtraction V (2015-2018) and g (2018-2026) are on the site (DAT0DEEB6NC6SCE), and so are the AAVSO B and V records since 2015. Both show the fade stopping in 2018. Remaining: join to the ASAS 2006-2014 V series of Simon et al. 2018 (ask the authors or digitise their figure), and tie g to V using an independent V-g colour, since the ASAS-SN overlap is only two nights. That gives one 20-year curve with the 2006-07 and 2014 brightenings.
~4 h
—not judged
2
The early-2023 depression is the only one left. Mid-2022 (AAVSO 15.7 mmag, ASAS-SN g 1.5) and mid-2025 (4.2 against -3.5) are AAVSO observer artefacts. Early 2023 is about 10-12 mmag in both records, but ASAS-SN has only ten nights there, at season's end with the star low. Next: reduce each AAVSO observer against their own comparison star (comp1_c/cmag) for January-April 2023, require two observers, and test for an airmass dependence in both records before calling it real.
~3 h
—not judged
3
Early-2023 depression: per-observer comparison-star reduction and an airmass test in AAVSO and ASAS-SN before calling it real.
~3 h
—not judged
Ranked by how likely each is to move the key question, for the time it takes
How it was found 1 run
Result. The 2015-2018 decline is real in the AAVSO ensemble at the published rate, and it did not continue: 2018.5-2026.8 is flat to 0.3 mmag per year. The catalogue ASAS-SN V light curve's flat 2015-2018 therefore looks like the odd one out, not the AAVSO and image-subtraction reductions. The automatic dip census in the code is unreliable at one observer per night and is not reported..
Seasonal median relative to 2019; least-squares slope in mmag per year within 2015.7-2018.2 and 2018.5-2026.9; changepoint BIC gain{'B': {'n_obs': 31245, 'nights': 2680, 'observers': 17, 'slope_2015.7_2018.2': [2.41, 2.56], 'slope_2018.5_2026.9': [1.79, 0.45]}, 'V': {'n_obs': 80214, 'nights': 3117, 'seasonal': {'2015': -0.0037, '2016': 0.0024, '2017': 0.0132, '2018': 0.004, '2019': 0, '2020': 0.0025, '2021': 0.002, '2022': 0.0074, '2023': 0.001, '2024': -0.003, '2025': 0.006, '2026': 0.0009}, 'observers': 24, 'slope_2015.7_2018.2': [8.51, 2.58], 'slope_2018.5_2026.9': [-0.04, 0.32], 'changepoint_bic_gain': -3.2}}The 2015-2018 decline is real in the AAVSO ensemble at the published rate, and it did not continue: 2018.5-2026.8 is flat to 0.3 mmag per year. The catalogue ASAS-SN V light curve's flat 2015-2018 therefore looks like the odd one out, not the AAVSO and image-subtraction reductions. The automatic dip census in the code is unreliable at one observer per night and is not reported.
Sources 2
Cite it
Mysteries Department. (2026). AAVSO V: +8.5 mmag/yr fading to 2018, then flat to 0.3 mmag/yr for eight years [Evidence EVD0DED7MHFY6JM]. https://mysteriesdept.com/r/EVD0DED7MHFY6JM
@misc{mysteriesdept_evd0ded7mhfy6jm,
title = {AAVSO V: +8.5 mmag/yr fading to 2018, then flat to 0.3 mmag/yr for eight years},
author = {{Mysteries Department}},
year = {2026},
note = {Evidence, catalog key EVD0DED7MHFY6JM},
url = {https://mysteriesdept.com/r/EVD0DED7MHFY6JM}
}