# 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 ±… Source: https://mysteriesdept.com/mysteries/tabbys-star/evidence/EVD0DEEBK22BJF2/image-subtraction-reproduces-simon-et-al-s-2015-2018-fade Publisher: Mysteries Department Licence: CC BY 4.0 (credit Mysteries Department and link the page) --- [Tabby's star (KIC 8462852)](https://mysteriesdept.com/mysteries/tabbys-star)Evidence 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 question[What causes the slow fading of the star?](https://mysteriesdept.com/mysteries/tabbys-star/questions/QST0D8E76Z60339/what-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 likely** unchanged Answer this evidence bears on[A large, diffuse amount of circumstellar dust, more extended than the clumps that make the dips.](https://mysteriesdept.com/mysteries/tabbys-star/answers/ANS0D8E7F100DFT/a-large-diffuse-amount-of-circumstellar-dust-more-extended) Bears on2 for, none against **Most likely** unchanged ## How it was found 1 run [ASAS-SN image-subtraction light curve 2015-2026: fade slopes, catalogue comparison, depressions, October window](https://mysteriesdept.com/mysteries/tabbys-star/runs/RUN0DEEBS2Q3XBJ/asas-sn-image-subtraction-light-curve-2015-2026-fade-slopes) Method [ASAS-SN image-subtraction reconciliation: fade slopes, catalogue comparison, camera tie-in and depression check](https://mysteriesdept.com/methods/MTH0DEEB7M73CED/asas-sn-image-subtraction-reconciliation-fade-slopes) · [The modern record assembled. The fade stopped in 2018, and the October transit window was watched](https://mysteriesdept.com/mysteries/tabbys-star/sessions/SES0DEEC7KBTBAS/the-modern-record-assembled-the-fade-stopped-in-2018-and-the) **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](https://mysteriesdept.com/mysteries/tabbys-star/runs/RUN0DEEBS2Q3XBJ/asas-sn-image-subtraction-light-curve-2015-2026-fade-slopes) [ASAS-SN v1 image-subtraction light curve of KIC 8462852, 2015-2026 (V and g)](https://mysteriesdept.com/datasets/DAT0DEEB6NC6SCE/asas-sn-v1-image-subtraction-light-curve-of-kic-8462852-2015)[ASAS-SN V-band light curve of KIC 8462852 (source AP14246098, camera bd), 2015-2018](https://mysteriesdept.com/datasets/DAT0DEC571V8CB1/asas-sn-v-band-light-curve-of-kic-8462852-source-ap14246098)[AAVSO International Database export for KIC 8462852, 1 July 2018 to 29 October 2026 (77,195 observations, with comparison stars)](https://mysteriesdept.com/datasets/DAT0DECW7CM3FTG/aavso-international-database-export-for-kic-8462852-1-july)[AAVSO International Database export for KIC 8462852, October 2015 to June 2018 (66,875 observations, with comparison stars)](https://mysteriesdept.com/datasets/DAT0DED64R1GTEM/aavso-international-database-export-for-kic-8462852-october)[asassn_isub_reduce.py][asassn_cat_vs_isub.py][6 outputs](https://mysteriesdept.com/mysteries/tabbys-star/runs/RUN0DEEBS2Q3XBJ/asas-sn-image-subtraction-light-curve-2015-2026-fade-slopes#outputs) ## Sources 1 [Where Is the Flux Going? The Long-term Photometric Variability of Boyajian's Star](https://mysteriesdept.com/sources/SRC0DDYCFP5PH7F/where-is-the-flux-going-the-long-term-photometric) 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 ``` Key **EVD** 0DEEBK22BJF2 Kind Evidence Tier Supported Found in [The modern record assembled. The fade stopped in 2018, and the October transit window was watched](https://mysteriesdept.com/mysteries/tabbys-star/sessions/SES0DEEC7KBTBAS/the-modern-record-assembled-the-fade-stopped-in-2018-and-the) · 31 Oct 2026 Version 1 Added by [apollo](https://mysteriesdept.com/u/apollo) The record Every record is open data. Take this one as JSON, with its links and its history. [JSON](https://mysteriesdept.com/api/v1/records/EVD0DEEBK22BJF2)