Open Letter to
  N. Nesvacil, T. Lüftinger, D. Shulyak, M. Obbrugger, W. Weiss,
  N.A. Drake, S. Hubrig, T. Ryabchikova, O. Kochukhov, N. Piskunov
13 reasons why you should retract your HD3980 paper


The paper on "Multi-element Doppler imaging of the CP2 star HD 3980"


is an article that not only does not advance astrophysical knowledge in
any way but does prove a serious obstacle to the understanding of CP
stars, since it consistently disregards basic astrophysical principles. I
see at least 13 compelling reasons why you should retract this paper.

A few links on the subject of retraction:

     https://www.elsevier.com/about/company-information/policies/article-withdrawal#Article Retraction

The 13 reasons :

1) The whole Doppler mapping analysis has been made without taking into
account the magnetic field as stated by the authors:

 "In the present Doppler imaging analysis we used a nonmagnetic spectrum
  synthesis for computating the line profiles of respective elements

Using the published abundance maps, are the spectra synthesised with
the 7 kG polar field and without this field in good or at least in
approximate agreement ?


Fig. 9 in Stift (2016) shews that differences in profiles are huge.


2) Using the published abundance maps and incorporating the magnetic
field as postulated by the authors, is it possible to carry out a successful
zero-field inversion ?


Even when the starting map is identical to the published map, it proves
impossible to get the inversion converge.

3) The authors clearly (and correctly) state

 "The INVERS12 code was used to invert the rotational variability in line
  profiles to elemental surface distributions."
 "These spots are observed through rotational line profile variations of
  respective elements."

This means that ZDM is all about velocities and Doppler space.
Equivalent widths do not enter anywhere. As Fig. 7 in Stift (2016)
demonstrates, a 7 kG field greatly modifies the shape of the Mn II
doublet but hardly the equivalent width. Can the following statements
be considered to bear any relation to the ZDM algorithm?

 "We found that including the Zeeman splitting in the presence of a magnetic
  field leads to an abundance decrease of 0.10−0.15 dex for Fe and Cr."
  except for Eu and Gd, the upper abundance limits of the maps computed
  with INVERS12 are not very affected by neglecting the magnetic field."


4) Nothing could have been easier than to take the maps as published
in the incriminated paper and to carry out a spectrum synthesis with
these maps and the magnetic field. Why has this obvious approach not
been taken, although it would be the only means to unequivocally
shew the validity of a zero-field inversion for HD3980 ?

The INVERS12 code was there, the maps were there, there was an
estimate of the magnetic field, so does it make sense to use SYNTH3
and SYNTHMAG in conjunction with an assumed 5 kG field modulus to
carry out a comparison of apparent abundances?


5) In Fig. 2 you have plotted elemental abundances of HD3980
relative to the sun. A number of elements exhibit a large spread in
abundances, with Si allegedly becoming as abundant as hydrogen
in a spot, O and Mn as abundant as helium. In other places, O, Si,
Ca, Mn and Fe are claimed to be under-abundant.

Kochukhov, Wade and Shulyak (2012) have dismissed the necessity
of considering local atmospheric structure due to high elemental
abundances in


sticking solely to α2CVn. Still, their Fig. 9 leaves no doubt as
to the effects of local abundances on the atmospheric structure
and on the resulting maps for Fe (differences range from -0.8 dex
to +0.7 dex).

These findings are not entirely new, having been explored by
Chandrasekhar as early as 1935. Coming to your group of authors,
I want to cite


which established the importance of the Si abundance for up
to a +3 dex over-abundance (Fig. 1 and subsection 3.1.5.
Large ( > 3%) changes: Si, Cr, Fe and [M/H]).

Is there any consistency in the choice to consider it a necessity
to use LL models based on mean abundances

 "For further analysis LLmodels model atmospheres (Shulyak et al.
  2004) were considered a more appropriate choice for a star with
  a rather complex abundance pattern such as for HD 3980. The
  LLmodels code was used to construct a final model atmosphere
  with the individual abundances presented in Fig. 2. If elements
  were found to be inhomogeneously distributed across the stellar
  surface, average homogeneous abundance values were implemented
  in the model atmosphere calculations."

but to implicitly label as "luxury" the establishment of a local
atmosphere with silicon over-abundant by > 4 dex, of oxygen by
> 2 dex and of manganese by > 5 dex?


6) Have you ever tried or succeeded in establishing a stellar
atmosphere with these extreme, unstratified abundances?

As the lack of references and of discussion in your paper
reveals, the answer is


7) Is it at least possible to construct such an atmosphere with
any of the existing atmospheric codes, Atlas9, Atlas12, the
Atlas based LLmodels, Tlusty, Sterne .... ?


8) Has any of the authors ever considered the question of vastly
differing pressure scale heights implied by the abundance maps?


9) Kochukhov, Wade and Shulyak (2012) state on page 2 of their paper

 "In regions of high enrichment, some metals are sometimes inferred
  to be only a factor of ∼30 less abundant compared to hydrogen (e.g.
  Kuschnig et al. 1998), which is challenging to explain theoretically."

but the findings of Piskunov et al. (1988) would constitute an even
more challenging task for theoreticians. One has however to be aware
that Kochukhov, Wade and Shulyak (2012) on page 14 of their same
paper voice the following caveat

 "The choice by S12 of the abundance DI studies yielding “unrealistic”
  elemental overabundances is highly selective, confined to two extreme
  results, both published in conference proceedings (Kuschnig et al. 1998;
  Piskunov et al. 1998). This ignores the majority of DI studies published
  in the refereed literature which reported much more modest abundance

Your results are almost as extreme as those of Piskunov et al. (1998)
and lead right to the conclusions outlined in


Did any of you realise and discuss the fact that in HD3980 the
mean molecular weight reaches locally more than 25 times the solar
, and that in kappa Psc it would be more than 70 times solar ?


10) Has anyone of you ever discussed horizontal pressure equilibrium
in HD3980 or in another CP star?


11) Pressure extrema in the atmosphere of our earth (taken from the
Guinness Book of Records) differ by less than 20%. Still, we experience
winds, even hurricanes.

Can astrophysics explain why the most extreme CP star spots are so
incredibly stable that despite horizontal pressure differences of several
orders of magnitude there is no exchange of material, no mixing over
time-scales of at least several years ?


12) You wrote

 " .... particle diffusion rules the spatial distribution of atoms of
  different species, depending on the balance between gravitational
  and radiative forces (Michaud 1970). As a result, elements become
  inhomogeneously distributed both vertically and horizontally, which
  results in vertical abundance stratification and surface abundance

Well known to all of you there has been the contribution to the
Proceedings of the CP#AP Workshop (2008) by Alecian & Stift


where Fig. 4 shews the influence of vertical and of horizontal
magnetic fields on the stratification of Si in a 8500K atmosphere.

Has this field-dependent stratification of Si been taken into account
or at least mentioned and discussed in your paper ?


13) Is there thus any scientific basis for the following claim ?

 "No obvious correlation between theoretical predictions of
  diffusion in CP stars and the abundance patterns could be found.
  This is likely attributed to a lack of up-to-date theoretical models."

                      NOT AT ALL

I am absolutely convinced that your innate sense of honour and of scientific
probity so characteristic of genuine scientists will lead you along the right
path, viz. towards retraction of the HD3980 paper.

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