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activity_index_caii_hk

Mount Wilson S index from the Ca II H & K cores, plus R'_HK when B−V is given.
Category Stellar activity
Backend numpy - implemented here on top of numpy primitives
Version 2.0.0
Reads ctx.spectrum (a Spectrum1D)
Writes metrics.s_index, metrics.s_index_error, metrics.s_index_alpha, metrics.s_index_calibrated, metrics.log_rhk, metrics.caii_h_flux, metrics.caii_k_flux, metrics.caii_r_flux, metrics.caii_v_flux

S = alpha · 8 · (H + K) / (R + V) where H, K, R, V are fluxes integrated (flux × Å) through the HKP-2 passbands : K 3933.664 Å and H 3968.470 Å triangular with 1.09 Å FWHM (2.18 Å base), V 3891.07–3911.07 Å and R 3991.07–4011.07 Å rectangular. Each sample is weighted by its transmission and its pixel width, so the value is sampling-independent ; band edges fall on the nearest pixel centre. The spectrum must cover 3891–4011 Å (air wavelengths), be at rest wavelength (correct the radial velocity first) and have at least 3 samples inside the 1.09 Å FWHM of each H / K triangle (pixels ≲ 0.36 Å). s_index is an INSTRUMENTAL S : bring it onto the Mount Wilson scale with a linear fit against standard stars, then pass the (a, b) of S_MW = a·S + b as s_index_calibration. s_index_error propagates the spectrum's uncertainty array (None without one). log_rhk is written only when b_v is given ; it applies Noyes et al. 1984 to the calibrated S (log C_cf = 1.13(B−V)³ − 3.91(B−V)² + 2.84(B−V) − 0.47 + blue-end term, R_HK = 1.34e-4·C_cf·S, log R_phot = −4.898 + 1.918(B−V)² − 2.893(B−V)³). The photospheric correction is calibrated on 0.44 < B−V < 0.82 : outside that range log_rhk is still written but flagged in the message. Rejects (no log_rhk) when R_HK ≤ R_phot. Metrics are prefixed for provenance: s_index_alpha and s_index_calibrated echo the inputs. v2.0.0: masked samples (Spectrum1D.mask) are ignored — dropped from the passband integrals (and their transmission from the weight sum) like non-finite ones.

Parameters

Parameter Default Required Description
alpha 2.3 - Mount Wilson calibration constant α in S = α·8·(H+K)/(R+V). 2.3 (Lovis et al. 2011) by default ; Duncan et al. 1991 use 2.4.
b_v None - Johnson B−V colour of the star. When given, log R'_HK (Noyes et al. 1984) is computed ; valid for 0.44 < B−V < 0.82.
s_index_calibration None - Optional [a, b] such that S_MW = a·S_inst + b, applied before the R'_HK conversion and reported as s_index_calibrated.

Use it

from spectro_kernel import run_algorithm

output = run_algorithm("activity_index_caii_hk", ctx, {
    "alpha": 2.3,
    "b_v": None,
    "s_index_calibration": None
})

spectro run activity_index_caii_hk --input spectrum.fits \
  --param alpha=2.3 \
  --param b_v=none \
  --param s_index_calibration=none

{
  "tool": "activity_index_caii_hk",
  "arguments": {
    "session_id": "<session_id>",
    "params": {
      "alpha": 2.3,
      "b_v": null,
      "s_index_calibration": null
    }
  }
}

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

References

  • Vaughan, Preston & Wilson 1978, PASP 90, 267 — HKP-2 : triangular 1.09 Å FWHM H and K passbands, 20 Å R and V bands, S = α(H+K)/(R+V).
  • Duncan et al. 1991, ApJS 76, 383 — Mount Wilson survey ; α = 2.4 and the 8× H/K exposure ratio of HKP-2.
  • Noyes et al. 1984, ApJ 279, 763 — R'_HK = R_HK − R_phot with R_HK = 1.34e-4·C_cf·S and the C_cf / R_phot polynomials in B−V.
  • Middelkoop 1982, A&A 107, 31 — log C_cf polynomial adopted by Noyes.
  • Lovis et al. 2011, arXiv:1107.5325 — S from échelle spectra (α = 2.3) and S_MW = 1.111·S_HARPS + 0.0153 calibration.
  • activity_index_halpha - Hα activity index : mean core flux over the sum of two reference-band fluxes.
  • ccf_bisector - Bisector of a CCF (or one line) and the Queloz et al. 2001 Bisector Inverse Slope.