cheb6, vcheb6, bcheb6, bvcheb6: differential emission measure using 6-order Chebyshev polynomial

cheb6 is a multi-temperature collisional-ionization model using a sixth-order Chebyshev polynomial for the differential emission measure. The DEM is not constrained to be positive. The switch parameter determines whether spectrum is calculated by running the mekal code, by interpolating on a pre-calculated mekal table, using the AtomDB data or the SPEX data. The final two options are now preferred. See the cie model for further information and options. The reference for this model is Singh et al. (1996, ApJ, 456, 766).

Velocity broadening can only be used with switch=2 or switch=3.

For cheb6 the parameters are:

par1–6	Chebyshev polynomial coefficients
par7	H density (cm$^{-3}$)
par8	abundance wrt to Solar
par9	Redshift
par10	Switch (0 = calculate using mekal model, 1 = interpolate using mekal model, 2 = use AtomDB data, 3 = use SPEX data).
norm	Normalization

For vcheb6 the parameters are:

par1–6	Chebyshev polynomial coefficients
par7	H density (cm$^{-3}$)
par8–21	Abundances of He, C, N, O, Ne, Na, Mg, Al, Si, S, Ar, Ca, Fe, Ni wrt Solar (defined by the abund command)
par22	Redshift
par23	Switch (0 = calculate using mekal model, 1 = interpolate using mekal model, 2 = use AtomDB data, 3 = use SPEX data).
norm	Normalization

For bcheb6 the parameters are:

par1–6	Chebyshev polynomial coefficients
par7	H density (cm$^{-3}$)
par8	abundance wrt to Solar
par9	Redshift
par10	Gaussian sigma for velocity broadening (km/s) (switch=2 only)
par11	Switch (0 = calculate using mekal model, 1 = interpolate using mekal model, 2 = use AtomDB data, 3 = use SPEX data).
norm	Normalization

For bvcheb6 the parameters are:

par1–6	Chebyshev polynomial coefficients
par7	H density (cm$^{-3}$)
par8–21	Abundances of He, C, N, O, Ne, Na, Mg, Al, Si, S, Ar, Ca, Fe, Ni wrt Solar (defined by the abund command)
par22	Redshift
par23	Gaussian sigma for velocity broadening (km/s) (switch=2 only)
par24	Switch (0 = calculate using mekal model, 1 = interpolate using mekal model, 2 = use AtomDB data, 3 = use SPEX data).
norm	Normalization

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