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 ) |
| 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) |
| 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) |
| 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) |
| 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 |