Run · Tabby's star (KIC 8462852)

Colour-term stratification of the post-1969 offset

Colour-term stratification of a DASCH DR7 long-term offset: Target offset by plate colour class; residual-vs-colour-term regression within epochs; target rank among matched stars on good-blue plates.

The offset is not an emulsion-colour effect: it is as large on good-blue plates as on all plates, the target is above every matched star either way, and the sign of the within-epoch colour-term dependence would make the post-1969 points brighter, not fainter.{'offset_all': 0.088, 'offset_blue_any': 0.093, 'slope_good_blue': 0.156, 'offset_good_blue': 0.097, 'matched_offset_all': {'n': 41, 'z': 1.64, 'sd': 0.047, 'mean': 0.012, 'target_percentile': 1}, 'slope_good_blue_err': 0.025, 'resid_vs_ct_1890_1953': {'n': 482, 'p': 1.1e-05, 'se': 0.108, 'slope': 0.48}, 'resid_vs_ct_1969_1990': {'n': 172, 'p': 0.36, 'se': 0.129, 'slope': -0.119}, 'target_points_by_class': {'unknown': 158, 'default0': 14, 'good_blue': 670, 'blue_other': 53}, 'matched_offset_good_blue': {'n': 41, 'z': 1.94, 'sd': 0.045, 'mean': 0.01, 'target_percentile': 1}, 'colour_term_median_pre1953': -0.015, 'colour_term_median_post1969': -0.132}0

Result

Run	Measured	Result	Against	Decision	Date
Run	Target offset by plate colour class; residual-vs-colour-term regression within epochs; target rank among matched stars on good-blue plates	{'offset_all': 0.088, 'offset_blue_any': 0.093, 'slope_good_blue': 0.156, 'offset_good_blue': 0.097, 'matched_offset_all': {'n': 41, 'z': 1.64, 'sd': 0.047, 'mean': 0.012, 'target_percentile': 1}, 'slope_good_blue_err': 0.025, 'resid_vs_ct_1890_1953': {'n': 482, 'p': 1.1e-05, 'se': 0.108, 'slope': 0.48}, 'resid_vs_ct_1969_1990': {'n': 172, 'p': 0.36, 'se': 0.129, 'slope': -0.119}, 'target_points_by_class': {'unknown': 158, 'default0': 14, 'good_blue': 670, 'blue_other': 53}, 'matched_offset_good_blue': {'n': 41, 'z': 1.94, 'sd': 0.045, 'mean': 0.01, 'target_percentile': 1}, 'colour_term_median_pre1953': -0.015, 'colour_term_median_post1969': -0.132}		The offset is not an emulsion-colour effect: it is as large on good-blue plates as on all plates, the target is above every matched star either way, and the sign of the within-epoch colour-term dependence would make the post-1969 points brighter, not fainter.

What it used and found

Colour-term stratification of a DASCH DR7 long-term offset

Method

MTH

DASCH DR7 light curves of KIC 8462852 and 184 comparison stars within 30 arcmin

Dataset

DAT

Gaia DR3 sources within 30 arcsec of KIC 8462852 and of the 184 DASCH comparison stars

Dataset

DAT

The century fade is a calibration artefact of plate photometry.

Answer it tests

ANS

Neither a blend nor emulsion colour can produce the offset

Evidence it produced

EVD

The step survives on good-blue plates and runs against the colour-term trend

Evidence it produced

EVD

Parameters

margin = 1, gaia_screen = True, offset_epochs = ['1930-1953', '1969-1990'], good_blue_band = [-0.164, 0.212]

Cite it

Mysteries Department. (2026). Colour-term stratification of the post-1969 offset [Run RUN0DEC25439S86]. https://mysteriesdept.com/r/RUN0DEC25439S86

@misc{mysteriesdept_run0dec25439s86,
  title     = {Colour-term stratification of the post-1969 offset},
  author    = {{Mysteries Department}},
  year      = {2026},
  note      = {Run, catalog key RUN0DEC25439S86},
  url       = {https://mysteriesdept.com/r/RUN0DEC25439S86}
}