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.
A fade that ran about three years and then held level for eight is an episode, not a steady trend: whatever dims the star switched off around 2018.For: Did the slow fade continue, stop or reverse after 2018?
That suits a diffuse dust cloud that stopped thickening on our line of sight better than a star relaxing after swallowing a planet, which predicts a smooth, continuing fade.For the key question: What causes the slow fading of the star?
The AAVSO B slope after 2018 (+1.79 ± 0.45 mmag/yr in B) differs from V (-0.04 ± 0.32) by 3.0σ. Re-reduce B against each observer's own comparison star and fit the comparison stars themselves; a drift there is the B band's systematic floor, not the star.
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.
Ranked by how likely each is to move the key question, for the time it takes
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.
Test · estimate [95% interval]Against the null and the answersVerdict
V fade rate, late 2015 to early 2018mmag per year · null: no fade (0)
+8.51 [+3.45, +13.57]
Excludes no fadep = 0.001
V fade rate, mid-2018 to late 2026mmag per year · against the two answers
−0.04 [−0.67, +0.59]
Excludes “fade continued”consistent with “fade stopped”
B fade rate, mid-2018 to late 2026B 1.79 ± 0.45, as V (× 0.77) · against the two answers
+1.38 [+0.69, +2.07]
Excludes “fade continued”but differs from AAVSO V by 3.0σ
One change point after 2018ΔBIC against a constant level
ΔBIC −3.2
Model comparison: a change point does not beat a constant level (ΔBIC −3.2; 10 would be strong).
No change pointa constant level is preferred
Estimate, 68% interval (thick) and 95% (thin). Rule declared with the run: rule out “fade continued” if the 95% interval lies below +3.
Across the evidence every measurement of the same quantity
Fade rate, late 2015 to early 20185 measurements · 4 with intervals
Pooled, all four+5.5 [+4.0, +7.0]
Disagreement (I²)31%
The measurements agree (I² 31%), so the pooled value stands.
Fade rate, mid-2018 to late 20263 measurements
Pooled+0.3 [+0.1, +0.6]
Disagreement (I²)82%
Against the answers“fade continued” excluded
Every measurement excludes “fade continued”, so it is ruled out whichever is right. They disagree with each other. Next step added Reconcile AAVSO B with the other measurements.
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}
}