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"
http://adsabs.harvard.edu/abs/2012A%26A...537A.151N
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:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1866214/
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4511053/
http://www.livescience.com/53228-top-retracted-science-papers-2015.html
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 ?
NO
Fig. 9 in Stift (2016) shews that differences in profiles are huge.
http://arxiv.org/abs/1604.06960
2)
Using
the published abundance maps and incorporating the magnetic field as assumed
by the authors, is it possible to carry out a successful zero-field inversion ?
NO
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."
The answer is of course
NO
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 compare apparent abundances?
Again a clear
NO
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 silicon
allegedly becoming as abundant as hydrogen in a spot, oxygen and manganese
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
http://adsabs.harvard.edu/abs/2012MNRAS.421.3004K
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
http://adsabs.harvard.edu/abs/2007A%26A...469.1083K
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 a staggering > 4 dex, of oxygen by > 2 dex and
of manganese by > 5 dex?
The answer must needs be
NO
6)
Have
you ever tried or succeeded in establishing a stellar atmosphere with
such extreme, unstratified abundances?
As the lack of references and of discussion in your paper reveals,
NO
7)
Would it
it at least be possible to construct such an atmosphere with any
of the existing atmospheric codes, Atlas9, Atlas12, (Atlas based) LLmodels,
Atlas12_ada, Tlusty, Sterne .... ?
NO
8)
Has any of the authors ever considered the question of vastly differing
pressure scale heights implied by the abundance maps?
NO
You might say they have not even ignored this issue.
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. Kochukhov, Wade and Shulyak (2012)
might well 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
contrasts."
but as it turns out, your results -- which are almost as extreme as those
of Piskunov et al. (1998) -- constitute a third case, leading right to the
conclusions outlined in
http://www.ada2012.eu/OKTL/index.html#C
Did any of you realise and discuss the fact that in HD3980 the mean
molecular weight reaches locally more than
25 times the solar value,
and that in kappa Psc it would be more than
70 times solar ?
Obviously once more the answer is
NO
10)
Has anyone of you ever discussed horizontal pressure equilibrium in HD3980
or any other CP star?
It's definitely a resounding
NO
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 ?
On account of basic physics it will forever be
NO
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
spots."
Well known to all of you there has been the contribution to the
Proceedings of the CP#AP Workshop (2008) by Alecian & Stift
http://www.ta3.sk/caosp/Eedition/Abstracts/2008/Vol_38/No_2/pp113-122_abstract.html
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 ?
As so often, the answer is
NO
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."
Safely
anchored in basic physics, diffusion theory
cannot explain results of ZDM inversions which are
at variance with well-established physical knowledge.
Writing this open letter years ago, I anticipated
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.
but
Multi-element Doppler imaging of the CP2 star HD 3980
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