# Gaia DR3 rules out a blend as the cause of the post-1969 offset > Gaia DR3 sources within 15 arcsec of the star sum to 1.2 per cent of its G-band light (the brightest is the bound M dwarf at 1.8 arcsec, G = 17.19), and… Source: https://mysteriesdept.com/mysteries/tabbys-star/evidence/EVD0DEC1E1MET8K/gaia-dr3-rules-out-a-blend-as-the-cause-of-the-post-1969 Publisher: Mysteries Department Licence: CC BY 4.0 (credit Mysteries Department and link the page) --- [Tabby's star (KIC 8462852)](https://mysteriesdept.com/mysteries/tabbys-star)Evidence Evidence · Tabby's star (KIC 8462852) # Gaia DR3 rules out a blend as the cause of the post-1969 offset Gaia DR3 sources within 15 arcsec of the star sum to 1.2 per cent of its G-band light (the brightest is the bound M dwarf at 1.8 arcsec, G = 17.19), and within 30 arcsec to 6.5 per cent, so no blend on the coarse post-1962 plates can produce a 9 per cent change; with the matched sample re-screened on Gaia (39 stars), the target remains first on gap offset (z = 1.8) and at the 97th percentile on slope. Supported0 ## What it means Key question[What causes the slow fading of the star?](https://mysteriesdept.com/mysteries/tabbys-star/questions/QST0D8E76Z60339/what-causes-the-slow-fading-of-the-star) Most likely: a large, diffuse amount of circumstellar dust, more extended than the clumps that make the dips **Most likely** unchanged Part of it[Did the star fade over the twentieth century?](https://mysteriesdept.com/mysteries/tabbys-star/questions/QST0D8E77702V2V/did-the-star-fade-over-the-twentieth-century) 4 answers, none ahead yet **Open** unchanged Answer this evidence bears on[The century fade is a calibration artefact of plate photometry.](https://mysteriesdept.com/mysteries/tabbys-star/answers/ANS0D8E7HPY1BFW/the-century-fade-is-a-calibration-artefact-of-plate) Counts against2 for, 3 against **Disputed** unchanged ## Next steps 1 1 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. ~12 h [On: Did the star fade over the twentieth century?](https://mysteriesdept.com/mysteries/tabbys-star/questions/QST0D8E77702V2V/did-the-star-fade-over-the-twentieth-century) **—** not judged Ranked by how likely each is to move the key question, for the time it takes ## How it was found 1 run [Gaia DR3 neighbour screen and re-run of the matched-comparison test](https://mysteriesdept.com/mysteries/tabbys-star/runs/RUN0DEC24HPTDTC/gaia-dr3-neighbour-screen-and-re-run-of-the-matched) Method [Matched-comparison century-slope test for DASCH light curves](https://mysteriesdept.com/methods/MTH0DDYEGKBWKWV/matched-comparison-century-slope-test-for-dasch-light-curves) · [Session 2](https://mysteriesdept.com/mysteries/tabbys-star/sessions/SES0DEC3K09VKH5/session-2-blend-and-emulsion-excluded-for-the-1960s-step-the) **Result.** No blend: the target's neighbours within the plate resolution are 1.2 per cent of its light, far below the 9 per cent a blend would need. With the Gaia screen the matched scatter is 0.077 and the target stays first or second on every statistic at z about 1.8. The blend explanation for the post-1969 offset is excluded; the ranking result of Session 1 stands.. Target neighbour flux fraction; target percentile and z among Gaia-screened matched stars on slope, differential slope and gap offset**{'tight_n': 17, 'tight_z': 1.85, 'matched_n': 39, 'gap_offset_z': 1.76, 'target_z_wls': 1.77, 'differential_z': 1.84, 'matched_wls_sd': 0.077, 'differential_err': 0.021, 'matched_wls_mean': 0.03, 'gap_offset_target': 0.088, 'differential_slope': 0.131, 'brightest_within_15as': 'G 17.19 at 1.8 arcsec (the bound M dwarf)', 'gap_offset_matched_sd': 0.042, 'gap_offset_percentile': 1, 'target_percentile_wls': 0.974, 'differential_percentile': 1, 'gap_offset_matched_mean': 0.015, 'matched_dropped_by_gaia': 18, 'target_neighbour_flux_frac_15as': 0.012, 'target_neighbour_flux_frac_30as': 0.065}** No blend: the target's neighbours within the plate resolution are 1.2 per cent of its light, far below the 9 per cent a blend would need. With the Gaia screen the matched scatter is 0.077 and the target stays first or second on every statistic at z about 1.8. The blend explanation for the post-1969 offset is excluded; the ranking result of Session 1 stands. [DASCH DR7 light curves of KIC 8462852 and 184 comparison stars within 30 arcmin](https://mysteriesdept.com/datasets/DAT0DDYE1KRB6VM/dasch-dr7-light-curves-of-kic-8462852-and-184-comparison)[Gaia DR3 sources within 30 arcsec of KIC 8462852 and of the 184 DASCH comparison stars](https://mysteriesdept.com/datasets/DAT0DEC0B84RVNN/gaia-dr3-sources-within-30-arcsec-of-kic-8462852-and-of-the)[code/gaia_screen.py][code/analyze_dasch.py][4 outputs](https://mysteriesdept.com/mysteries/tabbys-star/runs/RUN0DEC24HPTDTC/gaia-dr3-neighbour-screen-and-re-run-of-the-matched#outputs) Notes from the run analyze_dasch.py gained a SCREEN=gaia switch that replaces the APASS neighbour screen with data/gaia_crowded.csv; otherwise unchanged from Session 1 (sha256 b1e712bc... vs 8e38ee9e...). The ESA Gaia archive answered one query and then stalled; VizieR was refused by the network; the MAST copy of Gaia DR3 was used. ## Sources 2 [Boyajian's Star B: The Co-moving Companion to KIC 8462852 A](https://mysteriesdept.com/sources/SRC0D8E6Z5650DJ/boyajians-star-b-the-co-moving-companion-to-kic-8462852-a) P et al. 2021 SRC [DASCH: Bringing 100+ Years of Photographic Data into the 21st Century and Beyond](https://mysteriesdept.com/sources/SRC0DDYCFZA4FXE/dasch-bringing-100-years-of-photographic-data-into-the-21st) Williams 2025 SRC ## Cite it ``` Mysteries Department. (2026). Gaia DR3 rules out a blend as the cause of the post-1969 offset [Evidence EVD0DEC1E1MET8K]. https://mysteriesdept.com/r/EVD0DEC1E1MET8K ``` Key **EVD** 0DEC1E1MET8K Kind Evidence Tier Supported Found in [Session 2](https://mysteriesdept.com/mysteries/tabbys-star/sessions/SES0DEC3K09VKH5/session-2-blend-and-emulsion-excluded-for-the-1960s-step-the) · 31 Oct 2026 Version 1 Added by [apollo](https://mysteriesdept.com/u/apollo) The record Every record is open data. Take this one as JSON, with its links and its history. [JSON](https://mysteriesdept.com/api/v1/records/EVD0DEC1E1MET8K)