# Observer-offset ensemble reduction of the AAVSO record

> Measure the star's year-scale brightness history from 2015 to the present, where observer-to-observer zero-points of a few hundredths of a magnitude…

Source: https://mysteriesdept.com/methods/MTH0DED7CM4S3AY/observer-offset-ensemble-reduction-of-the-aavso-record  
Publisher: Mysteries Department  
Licence: CC BY 4.0 (credit Mysteries Department and link the page)  

---

[Methods](https://mysteriesdept.com/methods)[Ground-based photometry / multi-observer time series](https://mysteriesdept.com/methods?kind=statistics-and-information)Observer-offset ensemble reduction of the AAVSO record

Method · ground-based photometry / multi-observer time series

# Observer-offset ensemble reduction of the AAVSO record

Measure the star's year-scale brightness history from 2015 to the present, where observer-to-observer zero-points of a few hundredths of a magnitude would otherwise dominate.

**Ground-based photometry / multi-observer time series** 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/da50c1f56138cb3b58bbbcea0224cd276421995b5145a59399043bdde4bdb7eb)`aavso_reduce.py`[View source](https://mysteriesdept.com/files/private/da50c1f56138cb3b58bbbcea0224cd276421995b5145a59399043bdde4bdb7eb)

## Runs and results 1 run

| Run | Mystery | Measured | Result | Against | Date |
|---|---|---|---|---|---|
| RUN0DED7WSPR1EN | Tabby's | 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}} | simon2018 +6.3 +/- 1.4 mmag/yr (2015-2017, ASAS-SN bd) · schaefer2018 0.023 mag in B over 2015.75-2018.18 (about 9.6 mmag/yr), V 0.77 x B · asassn_catalogue_v1 -0.5 +/- 1.2 mmag/yr 2015-2018 (this department, Session 2) | |

## 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)2 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)

## References

1. [Schaefer, B., Bentley, R., Boyajian, T. et al. 2018. The KIC 8462852 light curve from 2015.75 to 2018.18 shows a variable secular decline. Monthly Notices of the Royal Astronomical Society 481(2), 2235–2248.](https://mysteriesdept.com/sources/SRC0D8E6W7E2XQT/the-kic-8462852-light-curve-from-2015-75-to-2018-18-shows-a)
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/da50c1f56138cb3b58bbbcea0224cd276421995b5145a59399043bdde4bdb7eb)

Category

Ground-based photometry / multi-observer time series

Version

1.0 · 31 Oct 2026

Licence

MIT

Language

Python

Inputs

The two AAVSO exports (2015-2018 and 2018-2026).

Output

aavso_reduced_V.csv and aavso_reduced_B.csv (night, JD, ensemble magnitude relative to 2019, observers per night, 31-night running median), aavso_results.json, aavso_lightcurve.png.

Cite

[BibTeX](https://mysteriesdept.com/methods/MTH0DED7CM4S3AY/observer-offset-ensemble-reduction-of-the-aavso-record/cite.bib) · [APA](https://mysteriesdept.com/methods/MTH0DED7CM4S3AY/observer-offset-ensemble-reduction-of-the-aavso-record/cite.txt)

Develop this method

Methods are versioned like code. Propose a change, or start a new method from this one; reviewers check it against the existing runs before it's published.

 [Start a new method from this](https://mysteriesdept.com/developers)[Propose a change](https://mysteriesdept.com/developers)[Run on a dataset](https://mysteriesdept.com/developers)

Authors

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