Evidence · Tabby's star (KIC 8462852)

Image subtraction reproduces Simon et al.'s 2015-2018 fade; the public ASAS-SN catalogue flattens it

On the same 104 nights of camera bd (2015.7-2018.2), ASAS-SN image-subtraction photometry fades at 5.8 ± 1.2 mmag per year, matching Simon et al.'s 6.3 ± 1.4, while the public catalogue light curve gives 3.1 ± 1.5 and drifts brighter than image subtraction at 2.7 ± 0.9 mmag per year; over the full 2015.2-2018.6 overlap the figures are 3.6 ± 1.0 against -0.5 ± 1.6. The discrepancy found in Session 2 is in the catalogue pipeline, not the star.

Supported0

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

Answer this evidence bears onA large, diffuse amount of circumstellar dust, more extended than the clumps that make the dips.

Bears on2 for, none against

Most likelyunchanged

How it was found 1 run

ASAS-SN image-subtraction light curve 2015-2026: fade slopes, catalogue comparison, depressions, October window

Method ASAS-SN image-subtraction reconciliation: fade slopes, catalogue comparison, camera tie-in and depression check · The modern record assembled. The fade stopped in 2018, and the October transit window was watched

Result. Fade stopped by 2018, confirmed independently of AAVSO. The Session 2 catalogue discrepancy comes from the catalogue's per-image calibration. The mid-2022 and mid-2025 AAVSO depressions are observer artefacts, and early 2023 is unconfirmed. ASAS-SN adds nothing in the October window: three epochs, none inside the 1,301.44-1,301.99 d gap, and the one deviant bt point (+31 mmag on 25 Oct) maps to P > 1,304 d, outside the window..

Least-squares slope of nightly medians (mmag/yr), night and season bootstrap{'cat_minus_isub': '-2.68 ± 0.88', 'g_2018.5_2026.85': '+0.19 ± 0.16 (±0.36 season)', 'catalogue_V_same_nights': '+3.10 ± 1.49', 'isub_V_2015.7_2018.2_same_nights': '+5.78 ± 1.23'}Fade stopped by 2018, confirmed independently of AAVSO. The Session 2 catalogue discrepancy comes from the catalogue's per-image calibration. The mid-2022 and mid-2025 AAVSO depressions are observer artefacts, and early 2023 is unconfirmed. ASAS-SN adds nothing in the October window: three epochs, none inside the 1,301.44-1,301.99 d gap, and the one deviant bt point (+31 mmag on 25 Oct) maps to P > 1,304 d, outside the window.

Figure 1

The star faded in V until 2018, then held flat in g for eight years

ASAS-SN image-subtraction seasonal medians relative to the first season of each band (mmag; positive = fainter)

seasonal median

Seasons are labelled by the year they end. V is camera bd. g combines cameras bD and bt, tied together to 0.5 mmag. The two bands overlap on only two nights, so their zero points are set separately.

Drawn by the site with ASAS-SN image-subtraction light curve 2015-2026

ASAS-SN v1 image-subtraction light curve of KIC 8462852, 2015-2026 (V and g)ASAS-SN V-band light curve of KIC 8462852 (source AP14246098, camera bd), 2015-2018 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)asassn_isub_reduce.py asassn_cat_vs_isub.py 6 outputs

Sources 1

Where Is the Flux Going? The Long-term Photometric Variability of Boyajian's Star

Simon et al. 2018

SRC

Cite it

Mysteries Department. (2026). Image subtraction reproduces Simon et al.'s 2015-2018 fade; the public ASAS-SN catalogue flattens it [Evidence EVD0DEEBK22BJF2]. https://mysteriesdept.com/r/EVD0DEEBK22BJF2

@misc{mysteriesdept_evd0deebk22bjf2,
  title     = {Image subtraction reproduces Simon et al.'s 2015-2018 fade; the public ASAS-SN catalogue flattens it},
  author    = {{Mysteries Department}},
  year      = {2026},
  note      = {Evidence, catalog key EVD0DEEBK22BJF2},
  url       = {https://mysteriesdept.com/r/EVD0DEEBK22BJF2}
}