TOI-836 b

What the corrected fit shows

The timing-adjusted transit is strongly preferred by ΔBIC = 189.2. Its fitted midpoint is -0.035 hours from the historical prediction; the model's mid-transit depth is 605.9 ± 57.8 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 2 fitted sector(s) (S11, S38), of which 2 meet Delta BIC >= 10. Formal depth errors were inflated by sqrt(max(reduced chi-square, 1)) times the residual time-averaging beta factor (observed range 3.21-4.53). The robust inverse-variance model depth across supported sectors is 604.1 +/- 155.4 ppm; Cochran Q = 0.00 for 1 dof (p = 0.9857). These scaled errors address underestimated scatter and short-timescale correlation, but they are not a full Gaussian-process or physical limb-darkened transit fit.

Published planetary spectrum

Across 106 bins, a weighted-flat spectrum gives chi-square/dof = 128.4/105 (p = 0.0599). At a 5% threshold this simple test does not reject flatness. Four published metallicity-grid spectra are also compared with one fitted vertical offset; these goodness-of-fit checks do not constitute a metallicity retrieval.

Atmospheric evidence: detection, limit, or unknown?

This is a high-value null result. The public spectrum is statistically consistent with a flat line, so it does not identify H2O, CO2, CO, CH4, or O2. Under the paper's 0.1-bar opaque-pressure assumption, it excludes clear atmospheres below 250 times solar metallicity and mean molecular weight below about 6 g/mol.

Primary source: Alderson et al. 2024, JWST COMPASS. Oxygen-bearing molecules are not detections of molecular oxygen (O2) and are not, by themselves, biosignatures.

The system

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

Data and reproducibility

The observed photometry is the public MAST file tess2019112060037-s0011-0000000440887364-0143-s_lc.fits, TESS Sector 11, collection DOI 10.17909/t9-nmc8-f686. It is 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 and python scripts/analyze_atmospheric_evidence.py plus python scripts/analyze_spectrum.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.
• 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. Hawthorn et al. 2023 — 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; Sector 11 used here.
4. NASA Exoplanet Archive, saved TAP row retrieved 2026-08-15.