A rich photographic star field solves cleanly. Independent fit checks favor the simpler tangent-plane model over the tested polynomial corrections.
The existing northern field identification and TAN preference remain supported. No additional field or repeated-image sequence has been independently recovered in this reassessment. The apparent S Cass / 19 September 1919 inscription is a logbook lead. A lack of detected secondary structure does not prove a single shutter exposure.
Many compact stars survive away from the handwritten margin. Their geometry supplies a strong blind identification and an independent test of extra distortion terms.
The readable, mirrored margin appears to include “R4011”, “S Cass”, “1919 Sept. 19”, “17½ inch” and “Seed 30”. These are tentative visual readings, not independently verified telescope or emulsion metadata.
The revised layer uses local contrast in both polarities, expanded inspected writing regions and contextual recovery of short fragments and round digits. Known photographic targets and sampled spectral apertures are protected. It is not OCR and does not reconstruct hidden sky or invent pen strokes.
The selection covers 2.41% of this scan (503,324 pixels). Faint marks, scratches and contacts between ink and photographic images remain ambiguous. The cyan overlay shows the wider exclusion footprint used by the photographic remainder; the stroke mask is supplied separately.
The writing PNG is a white, contrast-rendered stencil of bright and dark observed marks. The observed-pixel PNG preserves their stretched scan appearance. Both use original scan coordinates. The photographic remainder displays excluded pixels as black holes. It is neither a clean-sky reconstruction nor a new photometric product. Keep the mask alongside any measurements. Native original-intensity TIFF/FITS products, where generated, remain in the analysis workspace and are not duplicated in this handoff.
This revision recovers short letter fragments, round digits and inspected dark marks, with broader writing regions. The stroke selection grows from 221,914 to 503,324 pixels (2.27×). The photographic remainder uses a separate 3-pixel exclusion margin, covering 6.41% of the scan.
The wider selection deliberately favors removing writing. Nearby stars, scratches and ambiguous fragments can also be excluded. Explicit photographic protection regions retain known target images and sampled spectra; this does not establish perfect separation elsewhere.
The blind solution has 72 matches and odds 2.00 × 10⁷⁵ against index 4108. The fitted center is 01h 21m 06.68s, +72° 43′ 10.12″, with a field about 2.668 × 2.063 degrees.
The DSS2 image is resampled into the recovered plate orientation and footprint. Its photographic epochs, bands, resolution and contrast differ. Brightness and morphology need not match. It is context from the recovered WCS, not an additional independent fit check.
The existing northern field identification and TAN preference remain supported. No additional field or repeated-image sequence has been independently recovered in this reassessment. The apparent S Cass / 19 September 1919 inscription is a logbook lead. A lack of detected secondary structure does not prove a single shutter exposure.
Across these scans, repeated photographic images need not imply the same mechanism. Shutter timing, guiding offsets, objective optics and different pointings can leave related patterns. Establish consistent component membership before fitting a smooth warp. No result here isolates glass deformation from telescope optics, emulsion, scanner geometry and centroid bias.
There are 79 reference associations, with 60 training stars and 17 held out from the distortion fit. TAN gives a held-out median of 0.660 original pixels (1.22 arcsec) and a 90th percentile of 1.929 pixels. SIP orders 2 and 3 worsen the median to 0.859 and 0.828 pixels, although their upper tails are smaller.
The saved WCS therefore retains TAN without an additional polynomial distortion correction. This is a model-selection result at the available precision, not evidence that the glass is physically flat. No resampled plate image is claimed for this specimen.
| Model | Held-out median | Held-out p90 | Retained |
|---|---|---|---|
| TAN | 0.660 | 1.929 | Yes |
| TAN-SIP 2 | 0.859 | 1.780 | — |
| TAN-SIP 3 | 0.828 | 1.681 | — |
The reference footprint describes where the model is constrained. A smooth polynomial outside that footprint can look plausible while remaining unmeasured.
Reference catalogs were not propagated to the plate epoch. Proper motion, centering errors, repeated images, optical projection, emulsion, the glass and the scanner may all contribute to residuals. One scan cannot separate these physical causes.
Batch held-out stars were excluded from distortion fitting, but may have participated in the initial field identification. They are not a wholly independent astrometric experiment.
Select a numbered pin or a note. Locations are editorial review pointers, not measured confidence contours; plate-wide limitations also apply.
Stars near the inscription can be lost or blended. The selection mask should be checked before precision measurement.
Astrometric confidence falls outside the reference-star footprint. The coverage figure marks this boundary explicitly.
Seventeen held-out stars constrain global behavior, but do not identify the physical source of individual residuals or a detailed local warp.
Verify the inscription against a plate log, propagate reference positions to the dated epoch, and measure a denser set of clean centroids before reconsidering a higher-order model.
The field identification is strong. Keep the simpler WCS and the evidence for its limits together; a glass-distortion map is not yet supported.
All scientific numbers are snapshots of the saved analysis products. The original 16-bit scans remain the measurement source. JPEG derivatives, contrast stretching and masked previews are inspection tools; do not derive photographic density or absolute response from their appearance.
