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convert_flux_to_rayleigh

Response-corrected counts of a slit spectrograph to rayleigh per nm.
Category Flux calibration
Backend numpy - implemented here on top of numpy primitives
Version 1.0.0
Reads ctx.spectrum (a Spectrum1D)
Writes spectrum, metrics.applied, metrics.solid_angle_sr, metrics.response_abs, metrics.exptime_s

Per sample: I_λ [R/nm] = (norm / (EXPTIME · dispersion · scale · Ω)) · (λ[cm] / hc) · 4π · 1e-6 · 10, where norm is meta['normalization_factor'] (1 when the spectrum was not normalised ; a normalize_to_region step is undone), dispersion is the median wavelength step times samples_per_pixel (Å per native pixel), scale is the absolute response read from the header of ctx.extras[response_key] under response_scale_keyword (ADU s⁻¹ Å⁻¹ per erg s⁻¹ cm⁻² Å⁻¹, a convention of whoever built the response, hence no default keyword) and EXPTIME is read from the spectrum header, else from the image header. A missing reference, scale or exposure time goes to on_missing: 'fail' or 'skip' (applied = 0, spectrum untouched). The uncertainty is scaled like the flux ; flux_unit becomes 'R/nm' ; meta drops normalized_to_region and normalization_factor, sets flux_calibrated = True, relative_window (window_lo / window_hi, else the normalisation window) and absolute_flux = {unit, solid_angle_sr, response_abs}. Metrics: applied, solid_angle_sr, response_abs, exptime_s. Companions: response_from_standard and flux_calibrate_easyspec give erg s⁻¹ cm⁻² Å⁻¹ for point sources ; this brick is for an extended source filling the slit, through a solid angle.

Parameters

Parameter Default Required Description
slit_width_um None yes Width of the slit (µm). Required, > 0.
focal_mm None yes Focal length of the objective imaging the sky on the slit (mm). Required.
aperture_rows None yes Number of detector rows summed by the extraction. Required, > 0.
pixel_um None yes Detector pixel size (µm). Required, > 0.
magnification 1.0 - Slit-to-detector magnification along the slit.
samples_per_pixel 1.0 - Output samples per native detector pixel (the oversampling of the wavelength grid) ; 1 when the spectrum is on its native sampling.
response_key 'reference_spectrum' - ctx.extras key of the response spectrum whose header holds the scale.
response_scale_keyword None yes Header keyword of the response spectrum holding its absolute scale (ADU s⁻¹ Å⁻¹ per erg s⁻¹ cm⁻² Å⁻¹). Required.
exptime_keyword 'EXPTIME' - Header keyword of the exposure time (s).
window_lo None - Reference window of a relative view (Å), recorded in meta.
window_hi None - Upper bound of that window (Å).
on_missing 'fail' - 'fail' (default) or 'skip' when the scale or the exposure time is missing.

Use it

from spectro_kernel import run_algorithm

output = run_algorithm("convert_flux_to_rayleigh", ctx, {
    "slit_width_um": "<value>",
    "focal_mm": "<value>",
    "aperture_rows": "<value>",
    "pixel_um": "<value>",
    "magnification": 1.0,
    "samples_per_pixel": 1.0,
    "response_key": "reference_spectrum",
    "response_scale_keyword": "<value>",
    "exptime_keyword": "EXPTIME",
    "window_lo": None,
    "window_hi": None,
    "on_missing": "fail"
})

spectro run convert_flux_to_rayleigh --input spectrum.fits \
  --param slit_width_um=<value> \
  --param focal_mm=<value> \
  --param aperture_rows=<value> \
  --param pixel_um=<value> \
  --param magnification=1.0 \
  --param samples_per_pixel=1.0 \
  --param response_key=reference_spectrum \
  --param response_scale_keyword=<value> \
  --param exptime_keyword=EXPTIME \
  --param window_lo=none \
  --param window_hi=none \
  --param on_missing=fail

{
  "tool": "convert_flux_to_rayleigh",
  "arguments": {
    "session_id": "<session_id>",
    "params": {
      "slit_width_um": "<value>",
      "focal_mm": "<value>",
      "aperture_rows": "<value>",
      "pixel_um": "<value>",
      "magnification": 1.0,
      "samples_per_pixel": 1.0,
      "response_key": "reference_spectrum",
      "response_scale_keyword": "<value>",
      "exptime_keyword": "EXPTIME",
      "window_lo": null,
      "window_hi": null,
      "on_missing": "fail"
    }
  }
}

Every algorithm is an MCP tool of the same name; describe_algorithm returns this page's metadata as JSON.

References

  • Hunten, Roach & Chamberlain 1956, J. Atmos. Terr. Phys. 8, 345–346, DOI 10.1016/0021-9169(56)90111-8 — the rayleigh, a photometric unit for the airglow and aurora.
  • Baker 1974, Appl. Opt. 13(9), 2160–2163, DOI 10.1364/AO.13.002160 — Rayleigh, the unit for light radiance.
  • Baker & Romick 1976, Appl. Opt. 15(8), 1966, DOI 10.1364/AO.15.001966 — the rayleigh: interpretation of the unit in terms of column emission rate.