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activity_index_halpha

Hα activity index : mean core flux over the sum of two reference-band fluxes.
Category Stellar activity
Backend numpy - implemented here on top of numpy primitives
Version 2.0.0
Reads ctx.spectrum (a Spectrum1D)
Writes metrics.halpha_index, metrics.halpha_index_error, metrics.halpha_core_flux, metrics.halpha_ref1_flux, metrics.halpha_ref2_flux

I_Hα = F_Hα / (F_1 + F_2) with F the pixel-width-weighted MEAN flux in each rectangular band (6562.008–6563.608 Å core ; 6545.495–6556.245 Å and 6575.935–6584.685 Å references). Band edges fall on the nearest pixel centre. The spectrum must cover 6545.5–6584.7 Å in the star's rest frame with at least 3 samples in the core band. The index is instrument-dependent : use it to follow one star's chromospheric variability, not to compare instruments. halpha_index_error propagates the uncertainty array (absent without one). For a Ca II H & K equivalent see activity_index_caii_hk. v2.0.0: masked samples (Spectrum1D.mask) are ignored — dropped from the passband means (and their pixel width from the weight sum) like non-finite ones.

Parameters

This algorithm takes no parameters.

Use it

from spectro_kernel import run_algorithm

output = run_algorithm("activity_index_halpha", ctx, {})

spectro run activity_index_halpha --input spectrum.fits

{
  "tool": "activity_index_halpha",
  "arguments": {
    "session_id": "<session_id>",
    "params": {}
  }
}

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

References

  • Gomes da Silva et al. 2011, A&A 534, A30 — Hα index : 1.6 Å core on 6562.808 Å, reference bands 6550.87 ± 5.375 Å and 6580.31 ± 4.375 Å.
  • Boisse et al. 2009, A&A 495, 959 — Hα index definition for HD 189733.
  • activity_index_caii_hk - Mount Wilson S index from the Ca II H & K cores, plus R'_HK when B−V is given.
  • ccf_bisector - Bisector of a CCF (or one line) and the Queloz et al. 2001 Bisector Inverse Slope.