Deriving density, temperature and abundances

Deriving these parameters requires interpreting the measured line intensities with atomic data. It is essential that you realise that atomic data is not perfect! Here we'll discuss how you can go about deriving the above quantities from the line intensities.


For this you need to use density diagnostics. A list of some of the more important NIS diagnostics is given in Table II of Mason et al. (Sol. Phys. 170, 143, 1997). A routine that will allow you to convert your observed line ratio into a density is dens_plotter. For instance

IDL> dens_plotter,26,14 ; for Fe XIV (Fe -> 26, XIV -> 14)

For more information about this routine, look at CDS Software Note #52. Routines for use with the CHIANTI database (PostScript 336 Kb)
The routine takes atomic data from the CHIANTI database. Note that before running dens_plotter for the first time in the CDS software, you should run the routine use_dere_chianti (with no arguments) first, otherwise an error will be generated.

Temperature (emission measure)

A direct measurement of the temperature can be made from a temperature diagnostic (analogous to the density diagnostics mentioned above), although there are none in the NIS wavebands that have significant variability.

Another method is to take lines emitted from ions that are formed over similar, though different temperature ranges. For example, you can take the ratio of MgIX 368.1 to MgX 624.9. The atomic data for doing this is contained in CHIANTI, and can be extracted using the g_of_t routine - see CDS Software Note #52 Routines for use with the CHIANTI database (PostScript 336 Kb)
on how to use this routine.

Through any line of sight, there will be plasma with a distribution of temperatures. The amount of plasma at any particular temperature is determined through an emission measure analysis. Further information and routines are contained in CDS Software Notes #50 and #52.


Element abundances can be derived by comparing emission measure curves for different elements (e.g., the neon ions Ne IV-VII and the magnesium ions Mg V-VIII). Alternatively one can choose two ions that are formed over the same temperature range and use the observed line ratio to yield the abundance ratio (e.g., Mg VI and Ne VI). See Young & Mason (Sol. Phys. 175, 523, 1997), and Young & Mason (Proc. of the ISSI workshop `Solar composition and its evolution - from core to corona', in press).

For further advice on these topics will be willingly and freely given by Helen Mason.