kinextract.gauss_hermite_losvd_model

kinextract.gauss_hermite_losvd_model(v: ndarray, amp: float, vel: float, sig: float, h3: float, h4: float) → ndarray[source]

Four-moment Gauss-Hermite LOSVD model, legacy Fortran normalization.

Evaluates the classic van der Marel & Franx (1993) LOSVD parametrization truncated at h4: amp/sqrt(2*pi)/sig * exp(-w^2/2) * (1 + h3*H3(w) + h4*H4(w)) with w = (v - vel) / sig, using the legacy “fortran-like” H3/H4 basis polynomials (fh3_fortran_like(), fh4_fortran_like()) rather than the vdM1993 polynomial normalization used by gauss_hermite_losvd_model_ho(). This is the model fit by fit_losvd_gauss_hermite() and is kept numerically consistent with the original Fortran pipeline (pallmc.f) for backward compatibility; h3/h4 values from this function are not directly comparable to h3/h4 from the _ho/vdM1993 functions.

Parameters:

  • v (ndarray) – Velocities (km/s) at which to evaluate the model.

  • amp (float) – Overall normalization (total flux/area under the LOSVD).

  • vel (float) – Mean velocity V (km/s).

  • sig (float) – Velocity dispersion sigma (km/s). Must be positive and finite; if not, the model returns an array of NaN with the same shape as v.

  • h3 (float) – Third Gauss-Hermite moment (dimensionless, fortran convention) — skewness-like asymmetry of the LOSVD.

  • h4 (float) – Fourth Gauss-Hermite moment (dimensionless, fortran convention) — kurtosis-like symmetric deviation from a Gaussian.

Returns:

Model LOSVD amplitude evaluated at each v, same shape as v. All-NaN if sig is non-positive or non-finite.

Return type:

ndarray