A Century of Studies of the Object with the B[e] Phenomenon HD 50138

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

I have included my comments in a file.

Comments for author File: Comments.pdf

Author Response

Comment: The paper presents long-term observations of the peculiar star HD 50138. This object has been studied for more than 100 years. Still, it is not clear if it is a Herbig Ae/Be star or mass-transferring binary system, for example. This study does not add any significant information to the characteristics. It cannot be accepted in its present form. 

 

Answer: We respectfully disagree with this opinion. Although the object’s nature remains unclear, but many observational features have been revealed for the first time, such as long-term light curve, line profile variations, correlations between the line strength and brightness. Nevertheless, we thank you for a careful reading and pointing out to weak points and data, that we were not aware of. It has to be taken into account that this paper was intended as a progress report on this large project and presented at a conference of Hot Stars with Circumstellar Matter. 

 

Table 1: For which wavelength are the resolutions given? Please clearly mark which observations have already been published. 

Answer: Nearly all the spectra in our collection were taken with èchelle spectrographs. Their spectral resolving power does not change significantly over the detected spectral range. The already published observations are clearly mentioned in the text (Ondrejov data and a 8 HERMES spectra from Borges Fernandes et al. (2012, A&A, 548, A13). All the spectra reported in Table 1 (again, except for the 8 HERMES spectra) were not published. 

Photometry: There are significant data from the KWS (Kamogata/Kiso/Kyoto Wide-field Survey) data (2400 points) and Optical Monitoring Camera (OMC)/INTEGRAL (600 points) missing. They cover the time from 2 453 000 to 2 461 000. These data must be included. 

Answer: Thank you for bringing our attention to this database. We were unaware of its existence. It was unavailable for some time due maintenance, but we finally got the data and included them in Figure 1 as well as in the new Figure 4. 

Significant contributions to the circumstellar disk and its environment are missing and must be included, for example, Varga et al. (2019, MNRAS, 485, 3112) and Koutoulaki et al. (2018, A&A, 614, A90). There are also studies for the accretion rate, for example, Wichittanakom et al. (2020, MNRAS, 493, 234), and a multicolour study of polarisation variability by Lee et al. (2018, AJ, 156, 115), which are missing. Overall, many theoretical and observational studies are not mentioned or compared with the drawn conclusions. 

Answer: Our paper focuses on the object’s spectroscopic variability. This is not a review of all studies of the object. We are aware of these papers, but only those relevant to our goals are mentioned in the Introduction. As for the accretion rate, it is unclear whether this technique is applicable to this object.  

What is the source of the luminosity listed on page 7? The Gaia catalogue? If so, the value must bere calculated, taking the peculiar nature of the star into account. 

Answer: We added a calculation of the luminosity and refined our previous value. 

Binarity: Why do the authors not show any plots of the radial velocity? They have a huge spectroscopic database. In the “Abbreviations” one finds “RV – radial velocity”, but it was never use in the text … 

Answer: It is tricky to interpret the radial velocity because of a constant line width changes. We added a brief discussion of this topic. The abbreviation RV is removed, and a list of abbreviations is updated. 

Several features are just listed, but not tried to explain, for example: “However, 18 spectra continuously taken during 5 hours on 2013/01/20 showed a sudden jump of both parameters in the last two spectra. In particular, EW changed from 0.46+-0.03 to 0.52+-0.01 A and FWCL changed from 5.87+-0.15 to 7.8+-0.3 A (see right panel of Fig. 4).” What are the possible reasons? 

Answer: It can be pulsations but still unclear. We mention some explanations in the text, but refrain from elaborating on this topic and leave it for the future work. 

What is the location of this object in the Hertzsprung-Russell diagram? Where are the Herbig Ae/Be and FS CMa type objects located? 

Answer: The location in the HR diagram was shown in the paper by Borges Fernandes et al. (2009, A&A, 508, 309, Fig 16) along with the evolutionary tracks of single pre-main-sequence stars and those evolving away from the zero-age main-sequence. Our luminosity estimate is within the uncertainty from that of Borges Fernandes et al. We added a paragraph showing how the luminosity was calculated and referred to the mentioned Figure in the paper by Borges Fernandes et al. 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper is very interesting. This is a review with a lot of new observations. Rapid variations of absorption and emission line profiles have been detected. The authors report quasi-periodic variations of H(alpha) equivalent widths. They are not sure if the star is a binary. The authors also present a large amount of photometric data; optical fadings were detected. Observations cover a record time interval. The star is bright and thus is of interest also for amateur astronomers.

 

Though the authors are either native English speakers of have spent many years in English-speaking countries, the paper contains minor language mistakes (starting with "an large IR-excess" in p. 2 - and further on), but they are not numerous and are not an obstacle for understanding.

Author Response

The paper is very interesting. This is a review with a lot of new observations. Rapid variations of absorption and emission line profiles have been detected. The authors report quasi-periodic variations of H(alpha) equivalent widths. They are not sure if the star is a binary. The authors also present a large amount of photometric data; optical fadings were detected. Observations cover a record time interval. The star is bright and thus is of interest also for amateur astronomers. 

Though the authors are either native English speakers of have spent many years in English-speaking countries, the paper contains minor language mistakes (starting with "an large IR-excess" in p. 2 - and further on), but they are not numerous and are not an obstacle for understanding. 

Answer: Thank you for the comment. We carefully checked the text for grammatical errors and typos. All of them seem to be corrected now. 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript reviews the century long history of studies of HD50138, the star with apparent B[e] phenomenon, and presents some results of the authors' own study based on assembled spectroscopic data covering last 20 years. The material presented is interesting and important, and the analysis is in general detailed and solid.

I have some minor comments, outlined below, that I'd suggest the authors to consider before the manuscript may be published.

- It would improve the Introduction to include there (probably in the beginning) a brief overview of B[e] phenomenon in general

- Figure 1 would benefit from the second horizontal axis on top showing the calendar years. It would ease the comparison with the data in Table 1. Also, probably it would be nice to include the table analogous to Table 1 that would summarize various kinds of optical data used in the study.

- For consistency, I'd suggest adding Halpha label into left panel of Figure 3 the same way as it is done for Hbeta and FeII in the right panel.

- The same would be also nice for right panel of Figure 4

- Right panel of Figure 5 is currently very difficult to comprehend, due to variability time scale being too close to the sampling. Maybe you might try connecting the dots with thin lines to better show the variations?

- It would be nice to correlate this EW data, both from Figure 1 and Figure 5, with photometric information to see whether they are synchronous or not. Do the data overlap with TESS segments presented in Figure 2 enough to construct brightness-EW plot?

- There is a large set of V band photometric data for this object in the Kamogata/Kiso/Kyoto Wide-field Survey database, accessible at http://kws.cetus-net.org/~maehara/VSdata.py?object=V743+Mon&plot=1 and covering the missing interval past ASAS measurements in Figure 1. The brightness of HD50138 also lies within the range of unsaturated measurements for this experiment, so maybe it is worth including this dataset to extend Figure 1. It might also improve the comparison of spectral properties like EWs with the star brightness.

- Would it be possible to use the ratio of HeI and MgII equivalent widths to trace the changes of the star' temperature? It might also complement the right panel of Figure 5

- It would be good to mention whether other forbidden lines are visible in the spectra of the star, along with [OI] 6300 A

Also, a couple of textual corrections:

- Abstract, line 1: “6.6–mag” - the dash is not needed here

- Section 5, second paragraph, line 4: "he" -> "the"

 

Author Response

The manuscript reviews the century long history of studies of HD50138, the star with apparent B[e] phenomenon, and presents some results of the authors' own study based on assembled spectroscopic data covering last 20 years. The material presented is interesting and important, and the analysis is in general detailed and solid. 

I have some minor comments, outlined below, that I'd suggest the authors to consider before the manuscript may be published. 

- It would improve the Introduction to include there (probably in the beginning) a brief overview of B[e] phenomenon in general 

Answer: Actually, the B[e] phenomenon was described in the 2nd paragraph on page 2 but in a hidden way. We re-phrased this sentence to make the phenomenon definition better visible. 

- Figure 1 would benefit from the second horizontal axis on top showing the calendar years. It would ease the comparison with the data in Table 1. Also, probably it would be nice to include the table analogous to Table 1 that would summarize various kinds of optical data used in the study. 

Answer: Calendar years were added to the upper X-axis in Figure 1. We tried adding a Table with references to the photometric data, but it does not look good in this paper.  Here we only use V-band data, while our collection contains multicolor photometry. 

- For consistency, I'd suggest adding Halpha label into left panel of Figure 3 the same way as it is done for Hbeta and FeII in the right panel. 

Answer: Done. 

- The same would be also nice for right panel of Figure 4 

Answer: Done. Currently this is Figure 5. 

- Right panel of Figure 5 is currently very difficult to comprehend, due to variability time scale being too close to the sampling. Maybe you might try connecting the dots with thin lines to better show the variations? 

Answer: We have connected the dots by thin lines and showed only a part of our data for better viewing. 

- It would be nice to correlate this EW data, both from Figure 1 and Figure 5, with photometric information to see whether they are synchronous or not. Do the data overlap with TESS segments presented in Figure 2 enough to construct brightness-EW plot? 

Answer: We added a Figure showing a part of the Kamogata/Kiso/Kyoto data that contains a recorded brightness minimum and correlate it with the Halpha data. Since most of the V-band data show a very weak variability, correlating them with the Halpha data would not be illustrative of the material. 

- There is a large set of V band photometric data for this object in the Kamogata/Kiso/Kyoto Wide-field Survey database, accessible at http://kws.cetus-net.org/~maehara/VSdata.py?object=V743+Mon&plot=1 and covering the missing interval past ASAS measurements in Figure 1. The brightness of HD50138 also lies within the range of unsaturated measurements for this experiment, so maybe it is worth including this dataset to extend Figure 1. It might also improve the comparison of spectral properties like EWs with the star brightness. 

Answer: Thank you for bringing our attention to this database. We were unaware of its existence. It was unavailable for some time due maintenance, but we finally got the data and included them in Figure 1 as well as in the new Figure 4. 

- Would it be possible to use the ratio of HeI and MgII equivalent widths to trace the changes of the star' temperature? It might also complement the right panel of Figure 5 

Answer: It is unclear whether this EW ratio can be used, because the nature of the line width variations is unknown. At first glance, the Mg II is always slightly stronger than the He I line that raises doubts in the existence of noticeable temperature variations. We save a detailed investigation of this issue for the next paper. 

- It would be good to mention whether other forbidden lines are visible in the spectra of the star, along with [OI] 6300 A 

Answer: We added information about forbidden lines of other species in the general description of the phenomenon, but there is no place to add it specifically for HD 50138, as we do not discuss its forbidden lines. 

 
Also, a couple of textual corrections: 

- Abstract, line 1: “6.6–mag” - the dash is not needed here -- corrected 

- Section 5, second paragraph, line 4: "he" -> "the" -- corrected 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The paper can now be accepted. The authors have included new data and so on.