GJ 9827 d

What the corrected fit shows

The timing-adjusted transit is strongly preferred by ΔBIC = 28.2. Its fitted midpoint is +0.032 hours from the historical prediction; the model's mid-transit depth is 491.5 ± 78.7 ppm. The support decision uses ΔBIC ≥ 10; timing-search p-values are not presented as blind-detection probabilities.

Explicit model comparison

The null fits a local intercept and slope. The transit adds bounded midpoint, radius-ratio, and impact-parameter freedom while retaining the same baseline terms. Fixed limb darkening and circular geometry make this a diagnostic fit rather than a full system retrieval.

Multi-sector robustness and noise

The archive prediction was timing-adjusted independently in Sectors 42, 70, and 92; all three meet ΔBIC ≥ 10. Formal errors were inflated by sqrt(max(reduced χ², 1)) and the residual time-averaging beta factor. The inverse-variance depth is 536.5 ± 69.4 ppm. Cochran's Q does not detect excess depth dispersion after that inflation (Q = 1.92 for 2 dof; p = 0.384), but three sectors provide limited power and Sector 70's beta = 3.16 flags substantial correlated residual noise. This is a robustness diagnostic, not a global physical transit retrieval.

The system

Values are from the exact saved NASA Exoplanet Archive pscomppars row in data/system_parameters.csv.

Data and reproducibility

The observed photometry comprises three public MAST SPOC 2-minute files from TESS Sectors 42, 70, and 92, collection DOI 10.17909/t9-nmc8-f686. They are stored unmodified. Exact archive URI, URL, retrieval date, and checksum are in data/SOURCE.md.

Run python scripts/analyze_transit.py and python scripts/analyze_multisector.py to regenerate the figures and CSVs, then pytest tests/ -v to check the documented values against the real file.

Limitations

• The orbit is circular and the quadratic limb-darkening coefficients are fixed representative values.
• This is a lower-margin supported result within this portfolio. Its support is more sensitive than the very large-ΔBIC cases to the fixed outlier rule, fitting window, and limb-darkening coefficients.
• The scaled semi-major axis comes from saved composite values whose uncertainties are not propagated.
• The midpoint is searched within a bounded window; ΔBIC is used as the support gate.
• PDCSAP processing, dilution, stellar variability, timing variations, and covariance can bias the geometry.
• Published global fits with physical priors, instrument-specific detrending, and simultaneous sectors remain authoritative.

References

1. Niraula et al. 2017 — discovery reference listed by the NASA Exoplanet Archive.
2. Ricker et al. (2015), Transiting Exoplanet Survey Satellite (TESS), doi:10.1117/1.JATIS.1.1.014003.
3. TESS Team, TESS Light Curves — All Sectors, MAST, doi:10.17909/t9-nmc8-f686; Sectors 42, 70, and 92 used here.
4. NASA Exoplanet Archive, saved TAP row retrieved 2026-08-15.