Did the star fade over the twentieth century?

Answers 4

What would settle it

1. Gaia DR3 neighbour screen: replace the APASS 30-arcsec screen with Gaia DR3 sources within 30 arcsec and 4 mag of each comparison star and of the target (the dnb plates resolve about 10 arcsec), then rerun analyze_dasch.py. If the target itself has a faint neighbour inside the dnb seeing disk, the post-1969 offset could be a blend.
2. Colour-term stratification: pull the exposures table (sess.exposures(), median_colorterm_apass) for every plate in the differential series, keep only "good blue" plates (-0.164 to 0.212), and test whether the 0.09 mag post-1969 offset survives; also regress the offset on colour term across series. This is the direct test of the emulsion-colour explanation that DR7 makes possible for the first time.
3. Full per-plate differential with the Starglass platephot endpoint (needs a free API key): for each of the ~900 plates, pull every source within 10 arcmin and fit a plate zero-point from colour-matched stars within 5 arcmin of the target rather than 30 arcmin, then a hierarchical model with one zero-point per plate and one slope per star. Removes the position-dependent part of the plate systematics that the current 30-arcmin differential cannot.

History

1. 2016Schaefer puts forward: the star faded by about 0.16 magnitudes per century from 1890 to 1989.
2. 2016Hippke et al. puts forward: the century fade is a calibration artefact of plate photometry.
3. 2016Hippke et al.: the pre-1953 record is flat; the slope comes from the post-1969 offsetAgainst: The star faded by about 0.16 magnitudes per century from 1890 to 1989.
4. 2016Michael B. Lund et al.: the pre-1953 record is flat; the slope comes from the post-1969 offsetAgainst: The star faded by about 0.16 magnitudes per century from 1890 to 1989.
5. 2016Schaefer: 1,338 B-band magnitudes show a fade of 0.193 ± 0.030 mag while nearby check stars are flat.For: The star faded by about 0.16 magnitudes per century from 1890 to 1989.
6. 2016Hippke et al.: dASCH photometry has systematics of up to about 0.2 mag per century for most constant stars, so the trend is…For: The century fade is a calibration artefact of plate photometry.
7. 2017Michael Hippke et al.: sonneberg plates covering 1934-1995 show no step and no fadeAgainst: A single drop of about 0.1 mag across the 1953-1969 plate gap, not a steady century fade
8. 2018Michael Castelaz: maria Mitchell Observatory plates give an independent +0.12 mag/centuryFor: The star faded by about 0.16 magnitudes per century from 1890 to 1989.
9. 2018Michael Castelaz: sonneberg plates covering 1934-1995 show no step and no fadeAgainst: A single drop of about 0.1 mag across the 1953-1969 plate gap, not a steady century fade
10. 2025Peter K. G. Williams: dR7 reproduces the 0.17 mag/century slope and the target is the steepest of 49 matched starsFor: The star faded by about 0.16 magnitudes per century from 1890 to 1989.
11. 2025Peter K. G. Williams: matched stars do not share the target's post-1969 offsetAgainst: The century fade is a calibration artefact of plate photometry.
12. 2025Peter K. G. Williams: both halves of the Harvard record are flat and the offset between them is not shared by matched starsFor: A single drop of about 0.1 mag across the 1953-1969 plate gap, not a steady century fade
13. Oct 2026Session 1: took the question up again, proposed one answer, ran one test, found eight results bearing on its answers and worked on one of its sub-questions

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