Light Variability from UV to Near-Infrared in the Ap Star CU Vir Induced by Chemical Spots

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Light variability from UV to near-infrared in AP star CU Vir induced by chemical spots
by Pakhomov et al.

As the authors state, rotationally modulated spectroscopic and light variability is one of the key characteristics of chemically peculiar magnetic Ap/Bp stars. Albeit the manuscript under review studies only one target, it does it using long wavelength range. Thus the findings are relevant and worth publishing.

In general, the manuscript is in a very good shape, all relevant information has been given and analysis is easy to follow. The observations show that theoretical interpretation still needs some improvement. Further, possible  reasons for discrepancies have been discussed. The only slightly annoying thing is that one can not yet look at the DI maps since that paper seems to be still under preparation. Thus Section 2.1, and similarly Section 4.1, is only partially informative to a reader at this point.

Minor revision of the manuscript is needed before it can be published.

One issue is repeated throughout the manuscript and that is related to the references.
Sometimes only the number(s), i.e. [1], are given and sometimes also the
author(s) are given, i.e. Deutsch [12]. Personally, I would prefer using latter format everywhere.

Further minor issues:

Abstract, line 2:
MThe -> The

Sect. 1, line 31
model Krivoseina -> model by Krivoseina

Sect. 1, lines 33-35
The sentence starting Krticka et al. is missing something.
Please, reformulate.

Sect. 1, lines 38-39
except near-UV -> except in near-UV

Sect. 1, line 44
NARVAL, add reference

Sect. 1, line 52
TESS, add reference
Further, TESS is explained later but it should be done already here since this is the first appearance.

Sect. 2.1, lines 60-61
elements: He, Mg, Si, Fe, Cr were
-> elements - He, Mg, Si, Fe, Cr - were
or
-> elements (He, Mg, Si, Fe, Cr) were

Sect. 2.1, line 64
2009/11
it is not clear if this means November 2009 or 2009-2011

Sect. 2.1, line 69.
Repeating reference is not bad, then it is totally clear which paper is meant.

Sect. 2.2, line 79
LWR and SWP - do they mean something?

Sect. 2.2, line 89
analized -> analysed

Sect. 2.2, lines 95-96
The dataset covers 50 rotational cycles of CU Vir, with complete phase coverage for 37 cycles.

-> The TESS dataset of CU Vir covers 50 rotational cycles of which 37 have complete phase coverage.

Sect. 3, line 110
Adelman et al. [26], Hoeg et al. [27]
-> Adelman et al. [26] as well as Hoeg et al. [27]

Fig. 1
-X-axis label, should it not be Year instead of Date?
-The error bars are rather difficult to see, could you use stronger color?

Sect. 3, line 142
RMS -> of course the meaning is obvious, but since BIC is explained, for
consistency also RMS should be explained

Sect. 3, line 145
a smaller RMS
-but this is true only for times with more data points, not for time interval 1955-1983

Sect. 4.3, line 193
the Sun Strom -> the Sun by Strom

Sect. 4.3, line 209
range at CU Vir, -> range at CU Vir

Sect. 4.3, line 213
MAST is explained already on line 92, so no need to repeat it here

Sect. 4.3, line 214
Fig. 3 -> Figure 3
Åin -> Å in

Sect. 4.3, line 218
stars.Consequently -> stars. Consequently

Sect. 5.1, line 232
Fig.4 -> Fig. 4

Sect. 5.1, line 237
is also exists -> also exists

Sect. 5.1, line
Longward 3500 Å the theoretical curve precisely follows the observations.
-> From 3500 Å onward, the theoretical curve precisely follows the observations.

Sect. 6, lines 285-286
several possible reasons.
-You could very briefly mention some examples here so that the reader does not need to look at the original paper.

Sect. 6, line 313
line blending, do not allow -> line blending do not allow

Sect. 6, lines 316-317
star MX TrA, which is ∼ 1000 K cooler than CU Vir [9] using
->star MX TrA [9], which is ∼1000 K cooler than CU Vir using

(the reference was in totally wrong place)

Sect. 6, line 318
from Fig. 5 in [9]
-> from fig. 5 in [9]
(I'm not 100% sure of the guidelines of this journal, but usually when referring to a figure in other paper, it is not written with capital letter)

Appendix A, line 380
, where
-> the comma should be in equation A1, not at the beginning of the line

Author Response

Comment: One issue is repeated throughout the manuscript and that is related to the references.

Sometimes only the number(s), i.e. [1], are given and sometimes also the

author(s) are given, i.e. Deutsch [12]. Personally, I would prefer using latter format everywhere.

 

Response: We use default settings of MDPI latex class to generate pdf document. Command \citep will be presented as [12], while \citet as Deutsch [12]. This corresponds to (Deutsch, 1952) and Deutsch (1952) for other journals, for example, MNRAS.

 

Comment: Abstract, line 2:

MThe -> The

 

Response: Corrected

 

Comment: Sect. 1, line 31

model Krivoseina -> model by Krivoseina

 

Response: Corrected

 

Comment: Sect. 1, lines 33-35

The sentence starting Krticka et al. is missing something.

Please, reformulate.

 

Response: Done

 

Comment: Sect. 1, lines 38-39

except near-UV -> except in near-UV

 

Response: Corrected

 

Comment: Sect. 1, line 44

NARVAL, add reference

 

Response: Added

 

Comment: Sect. 1, line 52

TESS, add reference

Further, TESS is explained later but it should be done already here since this is the first appearance.

 

Response: Fixed

 

Comment: Sect. 2.1, lines 60-61

elements: He, Mg, Si, Fe, Cr were

-> elements - He, Mg, Si, Fe, Cr - were

or

-> elements (He, Mg, Si, Fe, Cr) were

 

Response: Corrected

 

Comment: Sect. 2.1, line 64

2009/11

it is not clear if this means November 2009 or 2009-2011

 

Response: It means 2009-2011. Corrected

 

Comment: Sect. 2.1, line 69.

Repeating reference is not bad, then it is totally clear which paper is meant.

 

Response: We rephrased this text.

 

Comment: Sect. 2.2, line 79

LWR and SWP - do they mean something?

 

Response: It’s abbreviations for IUE Long Wavelength Redudant and Short Wavelength Prime cameras. It’s introduced now in the text.

 

Comment: Sect. 2.2, line 89

analized -> analysed

 

Response: Corrected

 

Comment: Sect. 2.2, lines 95-96

The dataset covers 50 rotational cycles of CU Vir, with complete phase coverage for 37 cycles.

-> The TESS dataset of CU Vir covers 50 rotational cycles of which 37 have complete phase coverage.

 

Response: Corrected

 

Comment: Sect. 3, line 110

Adelman et al. [26], Hoeg et al. [27]

-> Adelman et al. [26] as well as Hoeg et al. [27]

 

Response: Corrected

 

Comment: Fig. 1

-X-axis label, should it not be Year instead of Date?

-The error bars are rather difficult to see, could you use stronger color?

 

Response: Fixed

 

Comment: Sect. 3, line 142

RMS -> of course the meaning is obvious, but since BIC is explained, for

consistency also RMS should be explained

 

Response: Corrected

 

Comment: Sect. 3, line 145

a smaller RMS

-but this is true only for times with more data points, not for time interval 1955-1983

 

Response: Yes. Now we have noted this in the text

 

Comment: Sect. 4.3, line 193

the Sun Strom -> the Sun by Strom

 

Response: Corrected

 

Comment: Sect. 4.3, line 209

range at CU Vir, -> range at CU Vir

 

Response: Corrected

Comment: Sect. 4.3, line 213

MAST is explained already on line 92, so no need to repeat it here

 

Response: Removed

 

Comment: Sect. 4.3, line 214

Fig. 3 -> Figure 3

Åin -> Å in

 

Response: Corrected

 

Comment: Sect. 4.3, line 218

stars.Consequently -> stars. Consequently

 

Response: Corrected

 

Comment: Sect. 5.1, line 232

Fig.4 -> Fig. 4

 

Response: Corrected

 

Comment: Sect. 5.1, line 237

is also exists -> also exists

 

Response: Corrected

 

Comment: Sect. 5.1, line

Longward 3500 Å the theoretical curve precisely follows the observations.

-> From 3500 Å onward, the theoretical curve precisely follows the observations.

 

Response: Corrected

 

Comment: Sect. 6, lines 285-286

several possible reasons.

-You could very briefly mention some examples here so that the reader does not need to look at the original paper.

 

Response: added details to the text

 

Comment: Sect. 6, line 313

line blending, do not allow -> line blending do not allow

 

Response: Corrected

 

Comment: Sect. 6, lines 316-317

star MX TrA, which is ∼ 1000 K cooler than CU Vir [9] using

->star MX TrA [9], which is ∼1000 K cooler than CU Vir using

(the reference was in totally wrong place)

 

Response: Corrected

 

Comment: Sect. 6, line 318

from Fig. 5 in [9]

-> from fig. 5 in [9]

(I'm not 100% sure of the guidelines of this journal, but usually when referring to a figure in other paper, it is not written with capital letter)

 

Response: left unchanged

 

Comment: Appendix A, line 380

, where

-> the comma should be in equation A1, not at the beginning of the line

 

Response: Corrected

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

I read the paper by Pakhomov et al. with great interest. The authors
used new abundance maps of Ap star CU Vir to predict light curves of
this star from UV to near-IR and successfully compare the derived light
curves with observational data. The paper contains new interesting
results and should be published. However, before I can recommend the
paper for acceptance, I think that the authors should correct several
issues:

-line 2: "MThe modelling is based" > "The modelling is based"

-line 28: "The star possesses fastest axial rotation among the known
Ap/Bp stars...": It is not clear if the authors mean "fastest" in terms
of rotational speed or period, but HD 60431 has a shorter period
(Astronomy & Astrophysics, 668, A159).

-line 66: "The abundance gradients...": I would rather suggest
differences.

-line 68: "...relative to the Sun": Please, include reference to the
adopted solar abundance values.

-line 91: "TESS space mission": Please, include a reference to the TESS
mission.

-line 110: "were not splitted" > "were not split"

-line 117: The estimate of the period uncertainty is strange. It does
not contain the amplitude of the variability and number of measurements.
Why is the maximum duration of the observations 365 days?

-table 2: RMS was not introduced.

-table 2: Adopted values of M0 and P should be included somewhere. Why
the period 1983-1992 is missing?

-line 145: "M19 having a smaller RMS but a larger number of free
parameters": I do not understand this statement. M19 seems to use 6 free
parameters, while the model with constant periods apparently uses 4 sets
of M0 and P parameters.

-line 156: LLMODELS assume LTE? This should be specified.

-line 159: Please, add also a reference to bound-free transitions used
in LLMODELS.

-table 3: How were the ranges selected? Does the adopted range of
abundances cover range of abundances observed on the surface of CU Vir?

-line 177: The term "intensity" is confusing to me. Is this the specific
intensity or the flux?

-line 178+4: What is "flattened intensity map"?

-equations between line 178 and 179: Apparently, the products "x" and
"." are different. It seems to me that "x" refers to the usual matrix
product, while "." is the product of matrix elements. This should be
explained.

-line 198: Reference to a index should be included.

-line 202: "by 1 dex": This means increasing the abundances or
decreasing? Higher abundance of He would explain why Khan and Shulyak
claim weak effect of He, while fig. 2 shows a strong effect of this
element.

-fig 3: The line profiles look strange between 1334-1335 A. Was an
interstellar line omitted from the profile? If this is the case,
then this should be mentioned.

-line 207: "carbon distribution can affects" > "carbon distribution can
affect"

-line 223: "To summarise, we expect that apart from Fe and Cr, only the
joint effect of iron peak and lighter elements may have a slight impact
on the light curve." What about Si?

-line 237: "is also exists" > "also exists"

-figure 4: Blue points corresponding to IUE extend also into an optical
region.

-figure 5: The description of black points are missing in the caption.

-figure 6: Which line corresponds to observations?

-figure 7: The caption should include information on wavelengths, which
are likely provided in the plots.

-line 288: "Our maps are in general agreement with those by Kuschnig et
al.": What about the maps of Kochukhov et al. (2014)?

-line 330: "The model with discrete period changes is formally preferred
as being simpler": Please, see my comment above.

-line 378: Please, include a citation to Bayesian information criterion.

-A4: The second term should include ln.

Author Response

Comment:

-line 2: "MThe modelling is based" > "The modelling is based"

 

Response: Corrected

 

Comment:

-line 28: "The star possesses fastest axial rotation among the known

Ap/Bp stars...": It is not clear if the authors mean "fastest" in terms

of rotational speed or period, but HD 60431 has a shorter period

(Astronomy & Astrophysics, 668, A159).

 

Response: We rephrased this text

 

Comment:

-line 66: "The abundance gradients...": I would rather suggest

differences.

 

Response: Done

 

Comment:

-line 68: "...relative to the Sun": Please, include reference to the

adopted solar abundance values.

 

Response: Here we indicate the approximate value. The detailed discussion is given in the paper of Potravnov et al (2025, accepted in Galaxies).

 

Comment:

-line 91: "TESS space mission": Please, include a reference to the TESS

mission.

 

Response: Done

 

Comment:

-line 110: "were not splitted" > "were not split"

 

Response: Corrected

 

Comment:

-line 117: The estimate of the period uncertainty is strange. It does

not contain the amplitude of the variability and number of measurements.

Why is the maximum duration of the observations 365 days?

 

Response: This is mistake in the manuscript. sqrt(N) should be in the denominator of the fraction. Corrected. We present in the text approximate formula to show the main parameters on which accuracy depends. Also we used the gradient of the light curve (up to ~0.2) which reflects the amplitude. We selected one year to show the change of the CU Vir period. This value is quite suitable for demonstrating changes. However, if the number of measurements is insufficient, we combined them over three years, as indicated in the text. For one source we used one values. For example, for all measurements of Pyper (2013) we selected one year, although there were few measurements during five years.

 

Comment:

-table 2: RMS was not introduced.

 

Response: Corrected

 

Comment:

-table 2: Adopted values of M0 and P should be included somewhere. Why

the period 1983-1992 is missing?

 

Response: Adopted values of Mikulasek (2019) model were indicated in the text (lines 127-129). The period 1983-1992 contains only two measurements, not suitable for statistics. However, we included in the Table with corresponding footnote.

 

Comment:

-line 145: "M19 having a smaller RMS but a larger number of free

parameters": I do not understand this statement. M19 seems to use 6 free

parameters, while the model with constant periods apparently uses 4 sets

of M0 and P parameters.

 

Response: According to the formula A1, the number of parameters increases BIC, i.e. worsens the accuracy. We recalculated BIC values.

 

Comment:

-line 156: LLMODELS assume LTE? This should be specified.

 

Response: Yex. Fixed

 

Comment:

-line 159: Please, add also a reference to bound-free transitions used

in LLMODELS.

 

Response: The references for Kurucz’ ATLAS9/12 codes are added

 

Comment:

-table 3: How were the ranges selected? Does the adopted range of

abundances cover range of abundances observed on the surface of CU Vir?

 

Response: Yes. The adopted ranges cover completely the abundances from recovered maps.

 

Comment:

-line 177: The term "intensity" is confusing to me. Is this the specific

intensity or the flux?

 

Response: This is the specific intensity. We corrected in the text.

Comment:

-line 178+4: What is "flattened intensity map"?

Response: This is 1D vector created from 2D map as a sequence of values. Explained

 

Comment:

-equations between line 178 and 179: Apparently, the products "x" and

"." are different. It seems to me that "x" refers to the usual matrix

product, while "." is the product of matrix elements. This should be

explained.

 

Response: We used in this sense, exactly. Added in the text.

 

Comment:

-line 198: Reference to a index should be included.

 

Response: peculiarity index a designed to measure the strength of the 5200A depression with respect to normal stars. The last reference to Khan and Shulyak (2007) is presented in text above.

 

Comment:

-line 202: "by 1 dex": This means increasing the abundances or

decreasing? Higher abundance of He would explain why Khan and Shulyak

claim weak effect of He, while fig. 2 shows a strong effect of this

element.

 

Response: Increasing the abundances. Corrected in text.

 

Comment:

-fig 3: The line profiles look strange between 1334-1335 A. Was an

interstellar line omitted from the profile? If this is the case,

then this should be mentioned.

 

Response: Yes, ISM lines of CII were removed from spectra. Corrected in the caption.

 

Comment:

-line 207: "carbon distribution can affects" > "carbon distribution can

affect"

 

Response: Corrected

 

Comment:

-line 223: "To summarise, we expect that apart from Fe and Cr, only the

joint effect of iron peak and lighter elements may have a slight impact

on the light curve." What about Si?

 

Response: This is mistake. Should be “apart from Si, Fe, He, and Cr”. Corrected.

 

Comment:

-line 237: "is also exists" > "also exists"

 

Response: Corrected

 

Comment:

-figure 4: Blue points corresponding to IUE extend also into an optical

region.

 

Response: Corrected in the legend.

 

Comment:

-figure 5: The description of black points are missing in the caption.

 

Response: Corrected in the caption.

 

Comment:

-figure 6: Which line corresponds to observations?

 

Response: Black points merged into a line. Corrected in the caption.

 

Comment:

-figure 7: The caption should include information on wavelengths, which

are likely provided in the plots.

 

Response: Corrected in the caption.

 

Comment:

-line 288: "Our maps are in general agreement with those by Kuschnig et

al.": What about the maps of Kochukhov et al. (2014)?

 

Response: Maps of CU Vir constructed by Kuschnig or Kochukhov, or by us, are qualitatively identical. However, Kuschnig presented rectangular maps ready to digitize it. While maps of Kochukhov et al. (2014) have orthographic projection only. We converted them to Mercator projection and tried to use them to model light curves. Some differences between them are in amplitude and shape of the light curves. But our maps fit the light curves better.

 

Comment:

-line 330: "The model with discrete period changes is formally preferred

as being simpler": Please, see my comment above.

 

Response: We deleted this test

 

Comment:

-line 378: Please, include a citation to Bayesian information criterion.

 

Response: Included

 

Comment:

-A4: The second term should include ln.

 

Response: Corrected. This is mistake only in paper, the l values were calculated correctly

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The star studied in this paper, CU Vir, has one of the most intriguing behaviours observed among Ap stars, a variable rotation period. The origin of this variability remains an enigma. In order to understand it, it is essential to identify in the greatest detail the origin of the photometric variations from which the period is inferred. This is the main objective of the analysis reported in this manuscript, which was carried out using better observational material, better atomic data, and improved methodology, compared to previous similar attempts. This modelling effort yields the most satisfactory representation of the observations achieved until now. 

  The paper is well organised and clearly describes the approach followed to carry out a very careful analysis using the best available data. The outcome is very interesting, convincing and valuable, so that this work fully deserves to be published. However, there are some mostly minor deficiencies that need to be addressed before final acceptance. In particular, there are language issues that may hamper the understanding or introduce ambiguities. They are identified in the list below, but the rest of the text could still benefit from review by a language editor, to straighten out lesser-impact language details.    The issues to be addressed are listed below.   1. Title: “in Ap star CU Vir” –> “in the Ap star CU Vir”.   2. Abstract, l. 1: “in chemical peculiar star CU Vir” –> “in the chemically peculiar star CU Vir”.   3. Abstract, l. 2: “MThe” –> “The” (typo).   4. Abstract, l. 7: “in photometric period of CU Vir” –> “in the photometric period of CU Vir”.   5. Abstract, l. 8: “of CU Vir period” –> “of the CU Vir period”.   6. Line 22: “such as variations in low-amplitude variability” –> “such as low-amplitude variability”.   7. Introduction, par. 2: since this is the first time that CU Vir is named in the text, a second identifier should be given (e.g., HD 124224).   8. Lines 28-29: “The star possesses fastest axial rotation” –> “The star possesses one of the fastest axial rotation rates”. There is at least one Ap star known to rotate faster: HD 60431, P = 0.4755 d (North et al. 1988, IBVS, 3155, 1).    9. Line 32: “satisfactory” –> “satisfactorily”.   10. Line 37: “those” –> “that”.   11. Lines 38-39: “except near-UV region” –> “except in the near-UV region”.   12. Lines 44-45: “The results derived the topology” –> “These authors derived the topology”.   13. Lines 46-47: “The chemical spots pattern possessed general agreement” –> “The chemical spot pattern was in general agreement”.   14. Line 62: the number of epochs in the time series could usefully be indicated in the text.    15. Line 66: “differences” should probably be a better wording than “gradients” in this specific case.   16. Line 69: “in the paper cited above” is rather ambiguous. The exact reference should be repeated here. Incidentally, if this reference is Potravnov et al. [22], this referee could not consult it since this paper is not published yet.    17. Line 70: “that resulted surface maps” –> “that the resulting surface maps”.   18. Line 99: “which are necessary to account” –> “that must be taken into account”.    19. Line 104: “another glitches” –> “other glitches”.   20. Line 128: “constant period and smoothly changing ones” –> “several constant periods and a smoothly changing one”.   21. Line 129: “to marginally favour for M19 model” –> “to favour marginally the M19 model”.   22. Line 147: “abrupt change, that in better agreement” –> “abrupt change, in better agreement”.   23. Table 3, caption: “grid” –> “grid of models”.   24. After line 182: “Limb darkening coefficients for quadratic law” –> “The limb darkening coefficients for a quadratic law”.   25. Line 193: add parentheses around “Strom an Strom [40]”.   26. Line 196: “produces” –> "is produced”.   27. Line 197: “Authors” is ambiguous. If it refers to Khan and Shulyak, use “These authors” for the sake of clarity. Otherwise, give the authors’ names.    28. Line 199: “for stellar parameters” –> “for the stellar parameters”.   29. Figure 2, caption: "for Strömgren photometric system” –> “for the Strömgren photometric system”.   30. Line 213: the MAST acronym has already been defined earlier; it should not be spelled out a second time.   31. Figure 3, caption and line 214: “in HST/STIS spectra” –> “in the HST/STIS spectra”.   32. Line 215: “following to” –> “using”.   33. Line 221: “It is appeared” –> “It is found”.   34. Line 236: “the latter displays” –> “the latter display”.   35. Line 237: “but predicted by model” –> “but is predicted by the model”.   36. Figure 4: there must be an error in some of the symbols used in the figure: blue dots (IUE) cannot appear at wavelengths longer than 3000 Å.    37. Line 254: “cased” –> “caused” (presumably).   38. Line 268: “The reason for these could be due to contribution” –> “The reason for this could be the contribution”.   39. Line 269: “in narrow band” –> “in narrow bands” (presumably).    40. Line 294: “became an important step” –> “represents an important step”.    41. Line 303: “missed opacity” –> “missing opacity”.    42. Lines 305-306: “the elements discussed above” is vague and ambiguous. It would be clearer to list these elements.   43. Line 315: the intended meaning of “Meanwhile” is unclear. It may not be the appropriate wording.   44. Line 316: “a more slowly rotating star MX TrA,” –> “a more slowly rotating star, MX TrA,” (or “the more slowly rotating star MX TrA,”).   45. Lines 317-318: “of slowly rotating Ap star BD+00 1659” –> “of the slowly rotating star BD+0 1659”.   46. Line 333: “The subsequent 5-10 yrs” –> “The next 5-10 years”.   47. Line 342: “We have made a further attempt” –> “We have made a new attempt”.   48. Lines 343-344: “a inhomogeneous surface distribution of elements” –> “the inhomogeneous surface distribution of chemical elements”.    49. Lines 380-381: “k - is a number of model parameters, n - is size of the sample, l - logarithmic likehood function” –> “k is the number of model parameters, n is the size of sample, and l, the logarithmic likelihood function”.   50. Line 381: “For calculation of the l” –> “For calculation of the value of l”.  Comments on the Quality of English Language

There are language issues that may hamper the understanding or introduce ambiguities. These are identified in the comments to the authors, but the rest of the text could still benefit from review by a language editor, to straighten out lesser-impact language details. 

Author Response

1. Title: “in Ap star CU Vir” –> “in the Ap star CU Vir”.  

Corrected

2. Abstract, l. 1: “in chemical peculiar star CU Vir” –> “in the chemically peculiar star CU Vir”.  

Corrected

3. Abstract, l. 2: “MThe” –> “The” (typo).  

Corrected

4. Abstract, l.7: “in photometric period of CU Vir” –> “in the photometric period of CU Vir”.  

Corrected

5. Abstract, l.8: “of CU Vir period” –> “of the CU Vir period”.  

Corrected

6. Line 22: “such as variations in low-amplitude variability” –> “such as low-amplitude variability”.  

Corrected

7. Introduction, par. 2: since this is the first time that CU Vir is named in the text, a second identifier should be given (e.g., HD 124224).  

Done

8. Lines 28-29: “The star possesses fastest axial rotation” –> “The star possesses one of the fastest axial rotation rates”. There is at least one Ap star known to rotate faster: HD 60431, P = 0.4755 d (North et al. 1988, IBVS, 3155, 1). 

Corrected

9. Line 32: “satisfactory” –> “satisfactorily”.  

Corrected

10. Line 37: “those” –> “that”.

Corrected

 

11. Lines 38-39: “except near-UV region” –> “except in the near-UV region”.  

Corrected

12. Lines 44-45: “The results derived the topology” –> “These authors derived the topology”.  

Corrected

13. Lines 46-47: “The chemical spots pattern possessed general agreement” –> “The chemical spot pattern was in general agreement”.  

Corrected

14. Line 62: the number of epochs in the time series could usefully be indicated in the text. 

Details of DI are given in Table 1 of preview article (Potravnov, I.; Ryabchikova, T.; Kitchatinov, L.; Pakhomov, Y. Long-term stability of chemical spots and reasons for the period variations in Ap star CU Vir. Galaxies 2025, accepted). We used 13 spectra in 2009-2011. We added this information to the article.

15. Line 66: “differences” should probably be a better wording than “gradients” in this specific case.  

Corrected

16. Line 69: “in the paper cited above” is rather ambiguous. The exact reference should be repeated here. Incidentally, if this reference is Potravnov et al. [22], this referee could not consult it since this paper is not published yet.   

The reference is repeated

17. Line 70: “that resulted surface maps” –> “that the resulting surface maps”.  

Corrected

18. Line 99: “which are necessary to account” –> “that must be taken into account”. 

Corrected

19. Line 104: “another glitches” –> “other glitches”.  

Corrected

20. Line 128: “constant period and smoothly changing ones” –> “several constant periods and a smoothly changing one”.  

Corrected

21. Line 129: “to marginally favour for M19 model” –> “to favour marginally the M19 model”.  

Corrected

22. Line 147: “abrupt change, that in better agreement” –> “abrupt change, in better agreement”.

Corrected

23. Table 3, caption: “grid” –> “grid of models”.  

Corrected

24. After line 182: “Limb darkening coefficients for quadratic law” –> “The limb darkening coefficients for a quadratic law”.  

Corrected

25. Line 193: add parentheses around “Strom an Strom [40]”.  

Corrected

26. Line 196: “produces” –> "is produced”.  

Corrected

27. Line 197: “Authors” is ambiguous. If it refers to Khan and Shulyak, use “These authors” for the sake of clarity. Otherwise, give the authors’ names.

Corrected

28. Line 199: “for stellar parameters” –> “for the stellar parameters”.  

Corrected

29. Figure 2, caption: "for Strömgren photometric system” –> “for the Strömgren photometric system”.  

Corrected

30. Line 213: the MAST acronym has already been defined earlier; it should not be spelled out a second time.

Removed

 

31. Figure 3, caption and line 214: “in HST/STIS spectra” –> “in the HST/STIS spectra”.  

Corrected

32. Line 215: “following to” –> “using”.  

Corrected

33. Line 221: “It is appeared” –> “It is found”.  

Corrected

34. Line 236: “the latter displays” –> “the latter display”.  

Corrected

35. Line 237: “but predicted by model” –> “but is predicted by the model”.  

Corrected

36. Figure 4: there must be an error in some of the symbols used in the figure: blue dots (IUE) cannot appear at wavelengths longer than 3000 Å. 

Change to IUE/Opt

37. Line 254: “cased” –> “caused” (presumably).  

Corrected

38. Line 268: “The reason for these could be due to contribution” –> “The reason for this could be the contribution”.  

Corrected

39. Line 269: “in narrow band” –> “in narrow bands” (presumably).

Corrected

40. Line 294: “became an important step” –> “represents an important step”.

Corrected

41. Line 303: “missed opacity” –> “missing opacity”.

Corrected

42. Lines 305-306: “the elements discussed above” is vague and ambiguous. It would be clearer to list these elements.  

We added elements: In addition to the elements He, Si, Mg, Cr, Fe discussed above

43. Line 315: the intended meaning of “Meanwhile” is unclear. It may not be the appropriate wording.  

We remove the word “Meanwhile”

44. Line 316: “a more slowly rotating star MX TrA,” –> “a more slowly rotating star, MX TrA,” (or “the more slowly rotating star MX TrA,”).  

Corrected

45. Lines 317-318: “of slowly rotating Ap star BD+00 1659” –> “of the slowly rotating star BD+0 1659”.  

Corrected

46. Line 333: “The subsequent 5-10 yrs” –> “The next 5-10 years”.  

Corrected

47. Line 342: “We have made a further attempt” –> “We have made a new attempt”.  

Corrected

48. Lines 343-344: “a inhomogeneous surface distribution of elements” –> “the inhomogeneous surface distribution of chemical elements”. 

Corrected

49. Lines 380-381: “k - is a number of model parameters, n - is size of the sample, l - logarithmic likehood function” –> “k is the number of model parameters, n is the size of sample, and l, the logarithmic likelihood function”.  

Corrected

50. Line 381: “For calculation of the l” –> “For calculation of the value of l”. 

Corrected

Author Response File: Author Response.pdf