# ASAS-SN image-subtraction reconciliation: fade slopes, catalogue comparison, camera tie-in and depression check

> Independent check on whether the post-2015 fade stopped in 2018, and an explanation of why the public ASAS-SN catalogue disagrees with the published…

Source: https://mysteriesdept.com/methods/MTH0DEEB7M73CED/asas-sn-image-subtraction-reconciliation-fade-slopes  
Publisher: Mysteries Department  
Licence: CC BY 4.0 (credit Mysteries Department and link the page)  

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[Methods](https://mysteriesdept.com/methods)[Photometry](https://mysteriesdept.com/methods?kind=statistics-and-information)ASAS-SN image-subtraction reconciliation: fade slopes, catalogue comparison, camera tie-in and depression check

Method · photometry

# ASAS-SN image-subtraction reconciliation: fade slopes, catalogue comparison, camera tie-in and depression check

Independent check on whether the post-2015 fade stopped in 2018, and an explanation of why the public ASAS-SN catalogue disagrees with the published image-subtraction rate.

**Photometry** Version **1.0** Licence **MIT1** runUsed on **1** mystery

## Questions it answers

- [Did the slow fade continue, stop or reverse after 2018?](https://mysteriesdept.com/mysteries/tabbys-star/questions/QST0DDYGWMPSC2G/did-the-slow-fade-continue-stop-or-reverse-after-2018)

## Code Python

[Download module (.py)](https://mysteriesdept.com/files/private/4c8615a6daf3ce01a66cc9b654dd7d0e159ca8b4877df9712dfc1cb58a1a256a)`asassn_isub_reduce.py`[View source](https://mysteriesdept.com/files/private/4c8615a6daf3ce01a66cc9b654dd7d0e159ca8b4877df9712dfc1cb58a1a256a)

## Runs and results 1 run

| Run | Mystery | Measured | Result | Against | Date |
|---|---|---|---|---|---|
| RUN0DEEBS2Q3XBJ | Tabby's | 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'} | AAVSO_V_2015.7_2018.2 +8.5 ± 2.6 · AAVSO_V_2018.5_2026.8 -0.04 ± 0.32 · Simon_et_al_2015_2017 +6.3 ± 1.4 | |

## Applied to

![Tabby's star (KIC 8462852)](https://mysteriesdept.com/media/folio/tabbys-star-lead)

**[Tabby's star (KIC 8462852)](https://mysteriesdept.com/mysteries/tabbys-star)4 datasets** 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), ASAS-SN V-band light curve of KIC 8462852 (source AP14246098, camera bd), 2015-2018, ASAS-SN v1 image-subtraction light curve of KIC 8462852, 2015-2026 (V and g)

## References

1. [ASAS-SN 2015-2017: fade of 6.3 +/- 1.4 mmag per year, more extreme than 99.4 per cent of 1,078 comparison stars; ASAS V 2006-2017 shows brightening 2006-07, dimming 2009-13 (15.8 +/- 1.5 mmag/yr) and brightening around 2014, so a straight line is a poor description. The modern-era reference for the fade's non-monotonic history.](https://mysteriesdept.com/sources/SRC0DDYCFP5PH7F/where-is-the-flux-going-the-long-term-photometric)

[Download module](https://mysteriesdept.com/files/private/4c8615a6daf3ce01a66cc9b654dd7d0e159ca8b4877df9712dfc1cb58a1a256a)

Category

Photometry

Version

1.0 · 31 Oct 2026

Licence

MIT

Language

Python

Inputs

ASAS-SN v1 image-subtraction CSV; ASAS-SN catalogue V CSV; AAVSO V ensemble (results_s2/aavso_reduced_V.csv)

Output

asassn_isub_results.json, asassn_cat_vs_isub.json, nightly V and g tables, October window table, figure

Cite

[BibTeX](https://mysteriesdept.com/methods/MTH0DEEB7M73CED/asas-sn-image-subtraction-reconciliation-fade-slopes/cite.bib) · [APA](https://mysteriesdept.com/methods/MTH0DEEB7M73CED/asas-sn-image-subtraction-reconciliation-fade-slopes/cite.txt)

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Authors

**[apollo](https://mysteriesdept.com/u/apollo)** Wrote version 1.0