# Matched-comparison century-slope test for DASCH light curves

> Settle whether a claimed century-long fade (Schaefer 2016) exceeds the plate-photometry systematic floor (Hippke et al. 2016, Lund et al. 2016) using the…

Source: https://mysteriesdept.com/methods/MTH0DDYEGKBWKWV/matched-comparison-century-slope-test-for-dasch-light-curves  
Publisher: Mysteries Department  
Licence: CC BY 4.0 (credit Mysteries Department and link the page)  

---

[Methods](https://mysteriesdept.com/methods)[Archival photometry / time-series statistics](https://mysteriesdept.com/methods?kind=statistics-and-information)Matched-comparison century-slope test for DASCH light curves

Method · archival photometry / time-series statistics

# Matched-comparison century-slope test for DASCH light curves

Settle whether a claimed century-long fade (Schaefer 2016) exceeds the plate-photometry systematic floor (Hippke et al. 2016, Lund et al. 2016) using the same, current data release for target and comparisons.

**Archival photometry / time-series statistics** Version **1.0** Licence **MIT1** runUsed on **1** mystery

## Questions it answers

- [Did the star fade over the twentieth century?](https://mysteriesdept.com/mysteries/tabbys-star/questions/QST0D8E77702V2V/did-the-star-fade-over-the-twentieth-century)

## Code Python

[Download module (.py)](https://mysteriesdept.com/files/private/8e38ee9e5bbc7e533bf56571dab87125bccd2377ee759489f23a979a60a29575)`analyze_dasch.py`[View source](https://mysteriesdept.com/files/private/8e38ee9e5bbc7e533bf56571dab87125bccd2377ee759489f23a979a60a29575)

## Runs and results 1 run

| Run | Mystery | Measured | Result | Against | Date |
|---|---|---|---|---|---|
| RUN0DDYGPP634AA | Tabby's | Target slope (mag per century) and its percentile and z among 49 matched comparison stars; plate-differential slope and its matched null; post-1969 minus 1930-1953 offset | {'tight_z': 2.38, 'target_n': 895, 'target_z': 1.96, 'matched_n': 49, 'matched_sd': 0.068, 'pre1953_err': 0.046, 'gap_offset_z': 2.02, 'matched_mean': 0.034, 'target_theil': 0.19, 'pre1953_slope': 0.019, 'differential_z': 2.04, 'target_wls_err': 0.02, 'tight_matched_n': 18, 'differential_err': 0.021, 'target_bin_slope': 0.208, 'target_wls_slope': 0.166, 'gap_offset_target': 0.088, 'target_percentile': 0.98, 'bootstrap_raw_ci95': [0.131, 0.201], 'differential_slope': 0.133, 'differential_null_sd': 0.069, 'gap_offset_matched_sd': 0.034, 'differential_null_mean': -0.008, 'gap_offset_matched_mean': 0.02, 'bic_linear_minus_step_target': -6.9} | hippke2016 0.12-0.14 +/- 0.02 with systematics floor 0.15-0.2; break at 1962 · schaefer2016 0.164 +/- 0.013 (check-star rms 0.043, 4 sigma) · matched_null_this_run mean 0.034, sd 0.068 | |

## 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)1 dataset** DASCH DR7 light curves of KIC 8462852 and 184 comparison stars within 30 arcmin

## References

1. [Schaefer, B. 2016. KIC 8462852 Faded at an Average Rate of 0.164 ± 0.013 Magnitudes per Century from 1890 to 1989. The Astrophysical Journal Letters 822(2), L34.](https://mysteriesdept.com/sources/SRC0D8E6V0C3X81/kic-8462852-faded-at-an-average-rate-of-0-164-0-013)
1. [Hippke, M., Angerhausen, D., Lund, M. et al. 2016. A Statistical Analysis of the Accuracy of the Digitized Magnitudes of Photometric Plates on the Time Scale of Decades with an Application to the Century-long Light Curve of KIC 8462852. The Astrophysical Journal 825(1), 73.](https://mysteriesdept.com/sources/SRC0D8E6V860VNG/a-statistical-analysis-of-the-accuracy-of-the-digitized)
1. [arXiv:1605.02760 (preprint, May 2016). DASCH light curves of 644 F stars (337 Tycho-2 F3 IV/V in APASS B, 307 KIC analogues in g). The population's slope statistics are over-dispersed until a break at 1970 (the Menzel gap) is modelled; the target's full-series B slope of 0.129 +/- 0.026 mag per century splits into two flat segments and a jump; 11 of 644 stars still exceed 5 sigma after the split. Concludes that several apparent F-star fades are artefacts of the gap and that KIC 8462852 is consistent with constant flux.](https://mysteriesdept.com/sources/SRC0DDYCEJ03QA3/the-stability-of-f-star-brightness-on-century-timescales)
1. [Describes Data Release 7 (finalised 29 December 2024), which supersedes DR1-DR6: 429,274 plate mosaics, 23.6 billion B magnitudes for 252 million sources calibrated to APASS DR8; typical light-curve rms about 0.15 mag. The release Schaefer and Hippke used in 2016 is no longer served, so DR7 is the only reproducible basis for the century-fade question. See also https://dasch.cfa.harvard.edu/dr7/ for the known-issues list, colour terms and the daschlab API.](https://mysteriesdept.com/sources/SRC0DDYCFZA4FXE/dasch-bringing-100-years-of-photographic-data-into-the-21st)
1. [Schaefer's public rebuttal (with a follow-up post of 24 May 2016): Hippke's comparison stars mixed red and yellow plates and included flagged data, and crowded stars are merged by SExtractor on the coarse dnb plates; his own uncrowded, colour-matched check stars have a mean slope of -0.007 with rms 0.044 mag per century, making the fade 4 sigma. There is no separate journal rebuttal; v2 of arXiv:1601.03256 carries the same critique.](https://mysteriesdept.com/sources/SRC0DDYDRHV579S/bradley-schaefer-a-response-to-michael-hippke-centauri)

[Download module](https://mysteriesdept.com/files/private/8e38ee9e5bbc7e533bf56571dab87125bccd2377ee759489f23a979a60a29575)

Category

Archival photometry / time-series statistics

Version

1.0 · 30 Oct 2026

Licence

MIT

Language

Python

Inputs

The dataset of raw DR7 light curves (target + matched + control), refcat.csv and sample.csv.

Output

dasch_results.json (all statistics), slopes.csv (one row per star), target_binned.csv, diff_binned.csv, dasch_matched.png.

Cite

[BibTeX](https://mysteriesdept.com/methods/MTH0DDYEGKBWKWV/matched-comparison-century-slope-test-for-dasch-light-curves/cite.bib) · [APA](https://mysteriesdept.com/methods/MTH0DDYEGKBWKWV/matched-comparison-century-slope-test-for-dasch-light-curves/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