LSD and ZDM, an unhappy combination


If one carries out a ZDM inversion according to the procedure of Kochukhov et al. (2014) as applied to CU Virginis
"This new magnetic inversion approach relies on the spectrum synthesis calculations over the full wavelength range  covered by observations and does not assume that the LSD profiles behave as a single spectral line with mean parameters."
and if you are reluctant to overlook details, you may well find a perfect fit between the observed phase-dependent mean profiles and the mean profiles synthesised from the recovered abundance map; virtually all the individual lines can however exhibit bad to very bad fits.

In the example shown below I plot the differences (normalised to the continuum) observed minus predicted for 10 lines at 10 different phases. These differences for individual lines can get as large as 6% -- positive and negative -- whereas they are about 10 times lower for the mean line (in red) for which the rms scatter is better than 10^-3. It is clear that a kind of compensation is at work to the detriment of the ZDM afficionado.


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