kinextract.build_emission_line_mask

kinextract.build_emission_line_mask(x: ndarray, g: ndarray, gerr: ndarray, cfg: FitConfig) → ndarray[source]

Build a boolean mask of emission-line pixels to exclude from the fit.

Called from ~kinextract.spectrum.make_fit_state to set gerr = BIG at detected emission-line pixels before any LOSVD/template fitting begins. Stellar templates contain no emission lines, so an unmasked emission feature (e.g. [N I], [Cl II], or other nebular/AGN lines superposed on the stellar spectrum) would otherwise bias the recovered LOSVD; pre-masking ensures this even for lines too weak to later be caught by the kinematic sigma-clipping in _update_clean_mask.

Detection is based on the excess flux above the local continuum within the line window, not on the raw continuum signal-to-noise of the region (which would produce false positives near strong, high-S/N absorption features like Ca II even when no emission is present). For each candidate line (drawn from the “em”-tagged, and optionally “paschen”-tagged, entries of ~kinextract.continuum._STELLAR_ABSORPTION_LINE_TABLES):

  1. Estimate the local continuum and noise from the flanking regions just outside the line window (within ±snr_context_A but excluding ±half_width_A), after excluding the Ca II triplet windows from the flanks so their absorption troughs cannot bias the continuum estimate downward.

  2. Compute excess_snr = (peak_flux_in_line - cont_est) / noise_est.

  3. Mask the line window only if excess_snr >= snr_threshold.

Parameters:

  • x (ndarray) – Wavelength array (Å), same frame as the fit state’s st.x.

  • g (ndarray) – Flux array corresponding to x.

  • gerr (ndarray) – Flux uncertainty array corresponding to x; used to estimate the local noise level and to identify already-bad pixels (gerr >= BIG).

  • cfg (FitConfig) – Fit configuration; supplies mask_emission_lines_in_fit, mask_emission_line_half_width_A, mask_emission_line_snr_threshold, mask_emission_line_snr_context_A, mask_paschen_lines_in_fit, and wavefitmin/wavefitmax. The fixed Ca II triplet window used to protect the flanking-continuum estimate is not configurable (see _CAII_CENTERS_A/_CAII_HALF_WIDTHS_A).

Returns:

Mask of length len(x); True marks pixels to exclude from the fit (by setting gerr = BIG). All-False if cfg.mask_emission_lines_in_fit is False.

Return type:

ndarray of bool