Abundance Analysis of the Spectroscopic Binary α Equulei
Giovanni Catanzaro
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis manuscript presents a detailed spectroscopic study of the binary system α Equulei, combining high-resolution observations with spectral disentangling and atmospheric modeling. The authors derive fundamental parameters and chemical abundances for both components of the system, identifying the primary as a G-type star with nearly solar abundances, and the secondary as a chemically peculiar star with an abundance pattern consistent with Am-type stars.
The scientific goal is well motivated, and the authors apply advanced analysis techniques, including non-LTE corrections for selected elements. The paper provides valuable results, particularly in characterizing the abundance pattern of the secondary component for the first time with this level of detail.
Overall, the manuscript represents a substantial contribution to the field of stellar astrophysics and chemically peculiar stars. However, the presentation, especially the language and organization, needs some minor improvement before the manuscript can be accepted for publication.
Below some suggestion to improve the paper
- Table 3 is dense and difficult to navigate. It could be split into two separate tables for each component, or include highlights (e.g., color or bold font) to draw attention to the most relevant abundance anomalies.
- Placeholder text such as “Table ??”, especially in Section 2, must be corrected.
- The authors provide internal errors, but a more critical assessment of systematic uncertainties—arising from model assumptions, line lists, or continuum normalization—would improve transparency.
- For elements represented by a single spectral line, the limitations of those measurements should be discussed more explicitly.
- The authors apply non-LTE corrections to many elements, which is commendable. However, the description of the model atoms used is somewhat vague, and more specific references or model descriptions would strengthen this section.
Comments on the Quality of English Language
The manuscript contains grammatical and syntactical errors that affect readability. For example:
- “Am stars characterised by absent of large scaled magnetic field...” should be “Am stars are characterized by the absence of large-scale magnetic fields...”
- “this means these difference is generated...” should be “this means these differences are generated...”
Suggestion: The entire manuscript must undergo professional English language editing before publication.
Author Response
We thank the reviewer for the detailed review and valuable comments on the manuscript. Our responses to the points raised are provided below. All corresponding changes have been incorporated into the manuscript and are highlighted in bold.
1) Table 3 is dense and difficult to navigate. It could be split into two separate tables for each component, or include highlights (e.g., color or bold font) to draw attention to the most relevant abundance anomalies.
Answer: We rephrased the Note after table 3 to: “Note. L and N symbols indicate LTE and non-LTE mean abundances. [X/H] indicates the abundance relative to solar ones. nl is the number of spectral lines used for abundance determination. The standard deviation is given in parentheses, and was assumed to be 0.2 dex when the abundance was obtained from a single line. ’Mean’ in the lower index indicates an average abundance for both ionisation stages. The last column contains present-day solar system abundances taken from [22].” We hope that this will make the table clearer and easier to read.
2) Placeholder text such as “Table ??”, especially in Section 2, must be corrected.
Answer: Agree. Corrected.
3) The authors provide internal errors, but a more critical assessment of systematic uncertainties—arising from model assumptions, line lists, or continuum normalization—would improve transparency.
Answer: Agree. In the paper, we use two independent methods to estimate the uncertainties of the free parameters, but we did not write it clearly. We rephrase sentences after 147 line to:
“We use two independent methods to estimate the uncertainties of the free parameters. The first is the classical approach based on the covariance matrix of the least-squares fit, which yields small internal errors that do not exceed 5 K for Teff and 0.01 dex for the other parameters. Note that these uncertainties are not summarized in Table 2. The second method is based on the analysis of cumulative probability distributions (see eg. [14]), which accounts for observational noise, continuum normalization, atomic data uncertainties, and other potential sources of systematic error. While the exact magnitude of these systematics is difficult to quantify, the true uncertainties likely lie between the estimates obtained from the two methods."
4) For elements represented by a single spectral line, the limitations of those measurements should be discussed more explicitly.
Answer: For elements represented by a single spectral line in spectra of normal A and Am stars, we adopt an uncertainty of 0.2 dex, consistent with our previous studies (e.g. Table 3 in Romanovskaya et al. 2023). For elements with multiple lines, the typical uncertainty can reach up to 0.2 dex; for instance, in the case of the Alf Equ system components, the abundance uncertainties ranged between 0.14 and 0.18 dex.
5) The authors apply non-LTE corrections to many elements, which is commendable. However, the description of the model atoms used is somewhat vague, and more specific references or model descriptions would strengthen this section.
Answer: Agree. We have added a table of model atoms and corresponding references to Section 5, and rephrased the sentence after line 192 as follows: “For C, O, Na, Mg, Si, K, Ca, Sc, Ti, Fe, Zn, Sr, Y, Zr, and Ba, we determine LTE and non-LTE abundances using model atoms. The model atoms and references to their detailed descriptions are summarized in Table 3.”.
6) “Am stars characterised by absent of large scaled magnetic field...” should be “Am stars are characterized by the absence of large-scale magnetic fields…”
Answer: Agree. Corrected.
7) “this means these difference is generated...” should be “this means these differences are generated...”
Answer: Agree. Corrected.
Reviewer 2 Report
Comments and Suggestions for AuthorsI read your manuscript with great interest. The paper presents results of a detailed spectroscopic analysis of the bright double-lined spectroscopic binary alpha Equ. Your analysis confirms the G + Am nature of the binary and produces detailed elemental abundances for each of the components separately, indicating a different abundance pattern for the two stars likely due to evolutionary differences. I have no specific comments related to scientific methods, reasoning, or rigor. However, some English language editing will make the text easier to read.
Comments on the Quality of English LanguageLine 13: change “and abundance pattern is close to those in Am star” to “and the abundance pattern is close to that in Am stars.”
Lines 18-20: this is a long sentence which is difficult to understand I suggest splitting into two sentences, maybe something like “Am stars are characterized by the absence of a large-scaled magnetic field and show an overabundance of metals. The question of the formation of chemical anomalies in the atmospheres of Am stars remains unclear.”
Line 33: “…, a decrease of atmospheric abundances in the star’s atmosphere is places.” I am not sure what you are trying to say here; please rephrase.
Line 56: the word “understating” is probably meant to be “understanding,” and “leading to anomaly creations” is better replaced by “leading to the creation of anomalies in …”
Line 87: change the first sentence of section 3 to” We used a new technique of spectral disentangling introduced in our previous paper [12].”
Line 96: Change “For the SB2 system in particular,” to “For SB2 systems in particular,”
Line 103: change “performed” to “applied.”
Throughout the paper, there is an unusual large distance between element symbols and their ionization level. Please check the Latex manual for how to handle chemical elements and ionization levels.
Author Response
We thank the reviewer for the detailed review and valuable comments on the manuscript. Our responses to the points raised are provided below. All corresponding changes have been incorporated into the manuscript and are highlighted in bold.
1) Line 13: change “and abundance pattern is close to those in Am star” to “and the abundance pattern is close to that in Am stars.”
Answer: Agree. We have changed the comparison star from υ Aql to HD 145788 and revised the Discussion section accordingly. Consequently, we have updated the abstract from line 11 as follows: "The primary giant component (G7-type) exhibits a typical abundance pattern for normal stars, with elements from He to Fe matching solar values and neutron-capture elements showing overabundances up to 0.5 dex. In contrast, the secondary dwarf component displays characteristics of an early stage Am star. The observed abundance differences imply distinct diffusion processes in their atmospheres. Our results supports the scenario in which chemical peculiarities in Am stars develop during the main sequence and may decrease as the stars evolve toward the subgiant branch."
2) Lines 18-20: this is a long sentence which is difficult to understand I suggest splitting into two sentences, maybe something like “Am stars are characterized by the absence of a large-scaled magnetic field and show an overabundance of metals. The question of the formation of chemical anomalies in the atmospheres of Am stars remains unclear.”
Answer: Agree. Corrected.
3) Line 33: “…, a decrease of atmospheric abundances in the star’s atmosphere is places.” I am not sure what you are trying to say here; please rephrase.
Answer: Agree. We corrected to “Furthermore, when the star reaches the subgiant branch, there is a decrease in atmospheric abundances in the star's atmosphere.”.
4) Line 56: the word “understating” is probably meant to be “understanding,” and “leading to anomaly creations” is better replaced by “leading to the creation of anomalies in …”
Answer: Agree. Corrected.
5) Line 87: change the first sentence of section 3 to” We used a new technique of spectral disentangling introduced in our previous paper [12].”
Answer: Agree. Corrected.
6) Line 96: Change “For the SB2 system in particular,” to “For SB2 systems in particular,”
Answer: Agree. Corrected.
7) Line 103: change “performed” to “applied.”
Answer: Agree. Corrected.
8) Throughout the paper, there is an unusual large distance between element symbols and their ionization level. Please check the Latex manual for how to handle chemical elements and ionization levels.
Answer: Agree. An extra space has been removed.
Reviewer 3 Report
Comments and Suggestions for AuthorsDear Authors,
The manuscript provides a thorough spectroscopic and abundance analysis of the binary α Equulei. Your use of spectral disentangling and rigorous LTE and non-LTE determinations shows a strong command of stellar spectroscopy. The modeling of both components, especially the secondary Am star, and broad element abundance analysis, is valuable for the field. With clearer presentation, method clarification, and a deeper discussion of implications, this paper could be a major contribution. Please revise to improve clarity, precision, and communication. My detailed comments are -
(1) Please clearly define what is novel in your abundance analysis compared to earlier studies (e.g., Griffin & Griffin 2002). For instance, emphasize that detailed abundances of the secondary are derived here for the first time using modern non-LTE tools.
(2) Briefly expand on the chemical differences' significance, focusing on diffusion theory, binary evolution, and Am star formation for broader impact.
(3) In Section 3, the SLD technique is central. Explain more simply how the flux ratio and line masks are refined per iteration. State convergence criteria clearly.
(4) Table 2 shows low uncertainties (e.g., ±65 K in Teff), while later text cites only 5 K from SME. Carefully check and present realistic total uncertainties, including potential systematic sources like continuum normalization or atomic data.
(5) SED-fitting is appropriate, but clarify the reddening correction application. Note if the extinction law variation or distance uncertainty affects results.
(6) In abundance analysis, group elements by nucleosynthetic origin (e.g., light, iron-peak, neutron-capture) to clarify trends.
(7) For non-LTE calculations, clearly tabulate or summarize which elements are used in non-LTE. Provide references for atomic models in a single, clear section.
(8) In Section 6, ensure consistency in star comparisons (e.g., α Equulei B, υAql, o Peg, Fig. 6 stars). Offer more quantitative comparisons (e.g., RMS of [X/H]) to strengthen interpretation.
(9) Improve legends and captions in figures (especially 5, 6). Clearly define symbols, explain uncertainties, and indicate if the values shown are non-LTE or LTE.
(10) Revise language throughout to improve fluency and professionalism. For example:
“absence of large-scale magnetic field” → “absence of large-scale magnetic fields”
“abundance pattern is close to those in Am star” → “...close to that of an Am star”
Replace “disentagling” with “disentangling” consistently.
Please revise the manuscript carefully for consistency, clarity, and minor typographical issues, and ensure all references are complete, properly cited, and correctly numbered. Check the reference 23 carefully, which is not correct. Ensure consistency in citation styles (some citations miss author initials or years). Verify that all cited non-LTE model atom references are properly included and clearly linked to the elements analyzed.
Author Response
We thank the reviewer for the detailed review and valuable comments on the manuscript. Our responses to the points raised are provided below. All corresponding changes have been incorporated into the manuscript and are highlighted in bold.
1) Please clearly define what is novel in your abundance analysis compared to earlier studies (e.g., Griffin & Griffin 2002). For instance, emphasize that detailed abundances of the secondary are derived here for the first time using modern non-LTE tools.
Answer: We corrected the first paragraph of Conclusion section as follows: “In this study, we performed for the first time a self-consistent chemical abundance analysis of the eclipsing spectroscopic binary α Equulei, covering elements from C to Nd. The fundamental stellar parameters were refined using spectral disentangling and the SME package. Additionally we validated the fundamental parameters by demonstrating that the abundance of individual Fe I–II lines does not depend on the reduced equivalent widths and ionisation potential, spectral energy distributions, or hydrogen line profile fitting. We determined the abundances of 25 chemical elements, applying non-LTE methods to 15 of them. The non-LTE abundances of C, O, Na, Mg, Si, K, Ca, Sc, Ti, Fe, Zn, Sr, Y, Zr, and Ba were obtained using the same non-LTE modelling approach as in [34].”
2) Briefly expand on the chemical differences' significance, focusing on diffusion theory, binary evolution, and Am star formation for broader impact.
Answer: We rephrased the last paragraph of Conclusion section as follows: “Since the atmospheric parameters we obtained match those in GG02 paper, we also confirm the conclusion that these stars formed simultaneously. The observed differences in chemical abundance between the two components of the α Equulei binary system suggest different diffusion processes in their stellar atmospheres. Our results support the idea that chemical anomalies in Am stars emerge during the main sequence and may decrease as the stars evolve toward the subgiant branch due to the deepening of the convective zone.”
3) In Section 3, the SLD technique is central. Explain more simply how the flux ratio and line masks are refined per iteration. State convergence criteria clearly.
Answer: We rephrased paragraph 3 of section 3 as follows: “The disentangling process is characterized by an iterative approach which can be described as follows:
(I) theoretical line masks for both stars were calculated based on an initial set of atmospheric parameters.
(II) Equation 1 was solved for the SLD, functions. Subsequently, we optimized the flux ratios of the two stars using the golden section method to determine the radius ratio and line strength corrections were performed by introducing a scale factor for each spectral line across all utilized spectra during the simultaneous disentangling.
(III) The obtained SLD, functions were convolved with improved line masks to produce disentangled spectra for the two components of the binary system. The convergence criterion in the search for the disentangled spectra was the simultaneous maximization of the fit between the computed composite model spectra and the observed spectra across all phases. The resulting spectra, which were free from masking, were then analyzed to refine the atmospheric parameters of the stars.”
4) Table 2 shows low uncertainties (e.g., ±65 K in Teff), while later text cites only 5 K from SME. Carefully check and present realistic total uncertainties, including potential systematic sources like continuum normalization or atomic data.
Answer: Agree. In the paper, we use two independent methods to estimate the uncertainties of the free parameters, but we did not write it clearly. We rephrase sentences after 141 line to:
“We use two independent methods to estimate the uncertainties of the free parameters. The first is the classical approach based on the covariance matrix of the least-squares fit, which yields small internal errors that do not exceed 5 K for Teff and 0.01 dex for the other parameters. Note that these uncertainties are not summarized in Table 2. The second method is based on the analysis of cumulative probability distributions (see eg. [14]), which accounts for observational noise, continuum normalization, atomic data uncertainties, and other potential sources of systematic error. While the exact magnitude of these systematics is difficult to quantify, the true uncertainties likely lie between the estimates obtained from the two methods.
5) SED-fitting is appropriate, but clarify the reddening correction application. Note if the extinction law variation or distance uncertainty affects results.
Answer: The interstellar reddening correction application is described in the paper (line 167): “The correction for interstellar reddening was applied according to the extinction curve from the paper [16] with the Av = 3.1 ∗ E(B − V). E(B − V) value was taken from the dust map from the EXPLORE website1 and for the distance 58 pc it equals 0.024.”
6) In abundance analysis, group elements by nucleosynthetic origin (e.g., light, iron-peak, neutron-capture) to clarify trends.
Answer: We thank the reviewer for the suggestion to group elements by their nucleosynthetic origin to clarify abundance trends. However, in our study, we present abundances element-by-element for each stellar component individually. This approach allows us to retain a complete and detailed picture for each star. This presentation format is consistent with our previous studies; for example, on page 3 of Romanovskaya et al. (2023), where additional elements with non-LTE determinations are analyzed individually. The methodology used in the present work follows the same approach as in those papers.
7) For non-LTE calculations, clearly tabulate or summarize which elements are used in non-LTE. Provide references for atomic models in a single, clear section.
Answer: Agree. We have added a table of model atoms and corresponding references to Section 5, and rephrased the sentence after line 188 as follows: “For C, O, Na, Mg, Si, K, Ca, Sc, Ti, Fe, Zn, Sr, Y, Zr, and Ba, we determine LTE and non-LTE abundances using model atoms. The model atoms and references to their detailed descriptions are summarized in Table 3.”.
8) In Section 6, ensure consistency in star comparisons (e.g., α Equulei B, υAql, o Peg, Fig. 6 stars). Offer more quantitative comparisons (e.g., RMS of [X/H]) to strengthen interpretation.
Answer: We have changed the comparison star from υ Aql to HD 145788, as the higher metallicity is already evident. The corresponding updates were made in the figure, its caption, and the conclusion section. The revised text is provided below.
“Since the secondary component exhibits a higher metallicity than the primary component, we investigated the differences in abundance between low-rotation Am-type stars in different evolutionary stages. To make this comparison, we selected stars with close fundamental parameters: the star HD 145788, which is in the early stages of becoming an Am star, with atmospheric parameters of Teff = 9800 and log g = 3.73 [34] and the Am star o Peg with Teff = 9600 and log g = 3.81 [35]. Both stars have well-determined LTE and non-LTE abundances, as well as reliably established atmospheric parameters.This makes them suitable benchmarks for comparison in Fig. 6. The RMS of overall metallicity is −0.08 ± 0.29 between α Equulei B and HD 145788, and −0.21 ± 0.28 between α Equulei B and oPeg. The abundance pattern in the atmosphere of α Equulei B is close to that of the HD145788 despite the Teff discrepancy of 1540K.
The abundances of the elements Al and S are higher than in Am stars, but note that the abundances of both elements were derived from a single line. The abundances of elements from Sc to Zn are lower than in an Am star; however, the abundances of the heavy elements Sr, Y, Zr and Ba are close to the values observed in HD 145788 within errors.”
And
“We therefore conclude that α Equulei B is in the early stages of becoming an Am.”
9) Improve legends and captions in figures (especially 5, 6). Clearly define symbols, explain uncertainties, and indicate if the values shown are non-LTE or LTE.
Answer: Thank you for the suggestion. The figure captions for Figures 5 and 6 already clearly explain the symbols and distinguish LTE and non-LTE abundances.
In the caption for Figure 5, the following are included and we rephrase from “For those elements where non-LTE and LTE abundances are available, the corresponding LTE values are shown with open symbols.” to “For elements where both LTE and non-LTE abundances are available, the corresponding LTE values are shown using open symbols.”
In the caption for Figure 6: from ‘indicated’ to ‘indicate’ - 'Grey lines indicate the non-LTE abundances.'
Therefore, we prefer to keep the legends on figures unchanged.
10) Revise language throughout to improve fluency and professionalism. For example:
“absence of large-scale magnetic field” → “absence of large-scale magnetic fields”
“abundance pattern is close to those in Am star” → “...close to that of an Am star”
Replace “disentagling” with “disentangling” consistently.
Answer: Agree. Corrected.
11) Check the reference 23 carefully, which is not correct. Ensure consistency in citation styles (some citations miss author initials or years). Verify that all cited non-LTE model atom references are properly included and clearly linked to the elements analyzed.
Answer: We have corrected the reference list and added the missing citations for the non-LTE model atoms. What was previously reference 23 is now reference 34. Additionally, we have included the publication details of the article that were previously missing: Romanovskaya, A.M., Ryabchikova, T.A., Mashonkina, L.I., Sitnova, T.M., and Serebryakova, N.: 2025, Astronomy Letters, 51(1), 342, doi:10.1134/S1063773725700173.
