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After a successful photometry run, Node v1 can write a science-ready copy of the FITS file enriched with observatory, detector, and processing metadata. The export preserves the original Seestar file untouched — a byte-for-byte copy is made first with shutil.copy2, and all additional keywords are written only into the copy. This gives downstream users and archives a self-describing file that carries its own provenance without any risk of corrupting the source data.

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Configuration

FITS export is controlled by two keys nested under photometry.fits_export in config.yaml:
config.yaml
photometry:
  fits_export:
    enabled: true
    export_dir: "fits_export"   # directory to write enriched copies into
When enabled: true, export_enhanced_fits() is called automatically after every successful pipeline run. The export_dir path is relative to the working directory. An optional export_dir argument to the function itself overrides the config value (useful for tests or scripted batch processing). Exported files are written to <export_dir>/YYYY-MM-DD/<original_basename>, where the date is derived from the result’s bjd field (converted to UTC via astropy.time.Time) or from DATE-OBS in the source FITS header, falling back to today’s date if neither is available.

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Headers Added

The following FITS header keywords are set on the exported copy. All keywords pass through _set_if_absent(), which means they are only written if the keyword does not already exist in the source file. Existing Seestar headers are never overwritten.
_set_if_absent() is defined as a single conditional check: if keyword not in hdr: hdr[keyword] = value. Original Seestar metadata — including its own TELESCOP, INSTRUME, or AIRMASS — is always preserved exactly as the camera wrote it.

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Observatory Block

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TELESCOP
string
Telescope name, from observatory.telescope in config. Default: ZWO Seestar S50.
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INSTRUME
string
Instrument/detector name, from observatory.instrument in config. Default: ZWO Seestar S50 IMX462.
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OBSERVER
string
Observer name or code, from observatory.observer in config. Falls back to aavso.observer_code if observatory.observer is not set. Omitted if neither is configured.
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SITENAME
string
Human-readable site name, from observatory.name in config. Omitted if not configured.
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SITELAT / OBSLAT
float
Observer latitude in decimal degrees (north positive), from observatory.latitude or safety.observer.latitude. Both keywords are set to the same value for maximum compatibility with analysis tools.
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SITELONG / OBSLONG
float
Observer longitude in decimal degrees (east positive, negative for west), from observatory.longitude or safety.observer.longitude. Both keywords are set to the same value.
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SITEELEV
float
Observer altitude above sea level in metres, from observatory.elevation in config. Default: 0.0.

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Detector Block

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GAIN
float
Detector gain in e⁻/ADU, from photometry.gain in config. Default: 1.0.
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RDNOISE
float
Read noise in ADU, from photometry.read_noise in config. Default: 5.0.
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IMAGETYP
string
Always set to LIGHT. The pipeline only processes light frames; calibration frames are rejected in Step 1.
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RADESYS
string
Always set to ICRS. The coordinate reference system used by the WCS solution and all sky coordinates in the file.
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EQUINOX
float
Always set to 2000.0.

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Science Block

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AIRMASS
float
Airmass at time of observation, copied from the photometry result dict. Only set if the result contains a non-null airmass value.
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BJD-OBS
float
Barycentric Julian Date (TCB) of the observation midpoint, copied from the photometry result dict. Only set if the result contains a non-null bjd value. Comment: Barycentric Julian Date (TCB).
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BARY-SYS
string
Always set to TCB when BJD-OBS is written, identifying the time scale of the barycentric correction.

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Processing Block

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SWCREATE
string
Software identification string: Boundless Skies Node <node_id>. The node_id is taken from photometry.node_id in config.
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DATE-BLD
string
UTC timestamp of when the header enrichment was applied, in ISO 8601 format (YYYY-MM-DDTHH:MM:SSZ). Comment: UTC timestamp of header enrichment.
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HISTORY
string (multiple)
Multiple HISTORY lines are always appended (never overwritten, since HISTORY is an additive FITS keyword):
  • Processed by Boundless Skies Node v1 (<node_id>)
  • Differential photometry: mag=<mag>+/-<err> snr=<snr> quality=<flag> (if photometry succeeded)
  • BJD-OBS computed via astropy barycentric correction (TCB) (if BJD is present)
  • Comparison stars used: <n> (if comparison star count is present)
  • Zero point: <zp>+/-<zp_scatter> mag (if zero point is present)
  • Astrometric solution: WCS present (Seestar or ASTAP) (if CD1_1 or CDELT1 is in the header)

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Public API

fits_export.py
from fits_export import export_enhanced_fits

path = export_enhanced_fits(source_fits, result, config)
if path:
    print(f"Exported: {path}")
export_enhanced_fits() returns the full path to the enriched copy on success, or None if the copy could not be written or the header enrichment raised an exception. All failures are logged at ERROR level.

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Function Signature

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source_fits
str
required
Absolute or relative path to the source FITS file to be copied and enriched. The file must be readable by astropy.io.fits. The source file is never modified.
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result
dict
required
The measurement dict returned by run_pipeline(). Science keywords (AIRMASS, BJD-OBS) and all HISTORY lines are derived from this dict. Pass an empty dict to export with observatory/detector headers only.
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config
dict
required
The full application config dict (loaded from config.yaml). Observatory, detector, and processing keyword values are all drawn from config["observatory"] and config["photometry"].
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export_dir
str
Optional override for the export root directory. When provided, this value takes precedence over config["photometry"]["fits_export"]["export_dir"]. The date sub-directory (YYYY-MM-DD) is still appended automatically.

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