A Spectroscopic and Photometric Study of MWC 342 and Its B[e] Phenomenon over the Last 40 Years

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors discuss spectroscopic and photometric data for the unusual star MWC 342 aquired during the last 40 years. The work is important because it provides a preliminary analysis of a decades-long observations of MWC 342. However, the article lacks factual material showing i)fragments of spectra that would specify some of the unillustrated conclusions, ii) links to Internet resources where interested readers could get the factual material they need. Figure 2 shows spectroscopic lines profies. However, these are not all lines discussed in the paper (see, e.g., page 7, rows 211-226). The statements "We found a nearly 20 year-long quasi-period in the optical brightness of the object","There is an anti-correlation between the optical brightness and the EW of the Hα line that suggests that the latter is due to the variations of the underlying continuum", "Using higher-resolution and higher S/N spectra than those published previously, we did not confirm the presence of He II emission lines in the spectrum of MWC 342 that wereearlier suspected in [9]" (page 7, rows 235-240) are not substantiated. There is no answer to the question of how unique all the observed properties are.

Abstract. Literature suggestions on the nature of MWC 342 are briefly summarised. It would be more useful here to summarize the main results of the work done by the authors. Especially since the history of the study of the star is described in detail in the introduction.

Author Response

The authors discuss spectroscopic and photometric data for the unusual star MWC 342 aquired during the last 40 years. The work is important because it provides a preliminary analysis of a decades-long observations of MWC 342.

However, the article lacks factual material showing i) fragments of spectra that would specify some of the unillustrated conclusions, ii) links to Internet resources where interested readers could get the factual material they need.

Answer: We added a Figure that shows spectral parts with possible locations of the He II lines mentioned in the paper and an explanation of our lines identification. As far as the Internet resources are concerned, only a few spectra from our collection are accessible from the existing archives (e.g., the CFHT archive). Other spectra can be sent to interested researchers on request to some of the co-authors of this paper indicated in the text.

Figure 2 shows spectroscopic lines profiles. However, these are not all lines discussed in the paper (see, e.g., page 7, rows 211-226).

Answer:  The spectral line profiles shown in Fig. 2 are just examples of the spectroscopic variations of the object. We added a discussion of these variations in the corrected version.

The statements "We found a nearly 20 year-long quasi-period in the optical brightness of the object"," There is an anti-correlation between the optical brightness and the EW of the Hα line that suggests that the latter is due to the variations of the underlying continuum", "Using higher-resolution and higher S/N spectra than those published previously, we did not confirm the presence of He II emission lines in the spectrum of MWC 342 that were earlier suspected in [9]" (page 7, rows 235-240) are not substantiated. There is no answer to the question of how unique all the observed properties are.

Answer: The 20-year-long cycle can be traces in the upper panel of Fig. 1. We added a line to guide the eye to this cycle. However, a description of these long-term variations was already given in the original version of the paper.

The He II identification issue is addressed above. The anti-correlation of the Hα line EW and the V-band brightness is elaborated in the updated text.

Abstract. Literature suggestions on the nature of MWC 342 are briefly summarised. It would be more useful here to summarize the main results of the work done by the authors. Especially since the history of the study of the star is described in detail in the introduction.

Answer: corrected accordingly

Reviewer 2 Report

Comments and Suggestions for Authors

The paper deals with an interesting, and even enigmatic, object MWC 342 (V1972 Cyg). It is an early-type star with spectral emissions, maybe possessing a late-type companion. Its evolution stage remains unclear. The authors performed, as well as collected, a large amount of spectroscopic and photometric observations, found considerable photometric variations and variations of spectral-line shapes, detected an optical quasi-period of about 20 years but no exact periodicity, suggested directions for further research. The object being sufficiently interesting, the publication of the paper seems quite justified.

I have a number of suggestions, mostly technical, towards the improvement of the manuscript.

First of all, I think that the Abstract, in its current form, is not sufficiently informative. I would recommend to include more detail about the findings from the study into the Abstract (for example, to mention the 20-year quasi-period, to give some more information about spectroscopic results). In the present form, the Abstract is mainly describing older publications about the star.

I recommend to refer to Gaia DR3 rather than to Gaia EDR3. The third release is already not very new. I expect that the change of this reference will not alter any data in the paper.

In the description under Table 1, the authors mention a column named Spectra, while the actual name of the column is #sp

In line 295 (reference No. 3), the name of the journal is not given.

The paper should be published after minor corrections.

Comments on the Quality of English Language

Not being a native English speaker, I nevertheless dare to suggest to change some terms. In the title, and elsewhere in the text, the authors mention “last years”; in my opinion, the term “recent years” would be better. Also, I recommend to change the term “contemporaneously”, “contemporaneous” (lines 132 and 251 of the manuscript) into “simultaneously”, “simultaneous”.

In line 50, there is a typo (should be “nebulosity”).

In line 125, we read: “this may effect may be due”;  should be “this effect may be due”.

The footnote in p.3 should begin with a capital “R”.

The term “high Balmer line series” (line 170) is clumsy, I recommend something like “high members of the Balmer line series”.

In line 207, we read: “in their low-resolution (R ~ 5,000) taken…”. I think the word “spectrum” should be added.

In line 222, instead of “P-Cyg type”, I recommend “P Cyg-type”. And slightly below, in line 223, we read: “…profiles of seen in pure emission…”. My understanding is “…profiles or are seen in pure emission”, but maybe I am wrong and some other correction is needed,

Author Response

We thank the reviewer for a careful reading and suggestions on improvements and corrections.

The paper deals with an interesting, and even enigmatic, object MWC 342 (V1972 Cyg). It is an early-type star with spectral emissions, maybe possessing a late-type companion. Its evolution stage remains unclear. The authors performed, as well as collected, a large amount of spectroscopic and photometric observations, found considerable photometric variations and variations of spectral-line shapes, detected an optical quasi-period of about 20 years but no exact periodicity, suggested directions for further research. The object being sufficiently interesting, the publication of the paper seems quite justified.

I have a number of suggestions, mostly technical, towards the improvement of the manuscript.

First of all, I think that the Abstract, in its current form, is not sufficiently informative. I would recommend to include more detail about the findings from the study into the Abstract (for example, to mention the 20-year quasi-period, to give some more information about spectroscopic results). In the present form, the Abstract is mainly describing older publications about the star.

Answer: The Abstract was changed to include a more extended description of the reported results.

I recommend to refer to Gaia DR3 rather than to Gaia EDR3. The third release is already not very new. I expect that the change of this reference will not alter any data in the paper.

Answer: Corrected.

In the description under Table 1, the authors mention a column named Spectra, while the actual name of the column is #sp

Answer: Corrected.

In line 295 (reference No. 3), the name of the journal is not given.

Answer: Corrected.

The paper should be published after minor corrections.

 

Comments on the Quality of English Language

Not being a native English speaker, I nevertheless dare to suggest to change some terms. In the title, and elsewhere in the text, the authors mention “last years”; in my opinion, the term “recent years” would be better. Also, I recommend to change the term “contemporaneously”, “contemporaneous” (lines 132 and 251 of the manuscript) into “simultaneously”, “simultaneous”.

Answer: The term “last years” is typically applied to a longer period of time and seems to be better to use with “40 years” or “20 years”.  In any case, these terms are considered interchangeable.

The term “simultaneous” is used to describe events that occur exactly at the same time, while “contemporaneous” means close in time but not exactly at the same time. In both cases, we mean the latter.

In line 50, there is a typo (should be “nebulosity”).

Answer: corrected

In line 125, we read: “this may effect may be due”;  should be “this effect may be due”.

Answer: corrected

The footnote in p.3 should begin with a capital “R”.

Answer: corrected

The term “high Balmer line series” (line 170) is clumsy, I recommend something like “high members of the Balmer line series”.

Answer: changed to “high members of the Balmer series”. The word “line” here is not needed.

In line 207, we read: “in their low-resolution (R ~ 5,000) taken…”. I think the word “spectrum” should be added.

Answer: corrected

In line 222, instead of “P-Cyg type”, I recommend “P Cyg-type”. And slightly below, in line 223, we read: “…profiles of seen in pure emission…”. My understanding is “…profiles or are seen in pure emission”, but maybe I am wrong and some other correction is needed,

Answer: this text is changed to “… either P~Cyg--type or purely emission profiles …”