Stellar Flares, Superflares, and Coronal Mass Ejections—Entering the Big Data Era

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Review report

This review paper attempt to collect some new observational results of flaring stars, including the flares, superflares, and CMEs on sun-like stars, cool dwarfs, red giants, and binary stars. They listed many observational facts, which are meaningful for our understanding the star activity and space weather. However, this review still has the following shortcomings,

1.     As a review paper, it is important to list a wide range of observational facts. At the same time, it is even more important to summarize and generalize these observational facts, and draw some new conclusions. It is obvious that this article only lists a large number of observational facts, but lacks necessary induction and summary, and does not draw the author's own conclusion. I hope to strengthen the refinement in this aspect during the author's revision process.

2.     The author repeatedly mentions super flares in this review paper, but does not provide a clear definition of super flares, which is not rigorous. 

3.     The authors mentioned “Moving type IV bursts are produced by electrons that are trapped in CME loops” in page 3. However, to my knowledge, the radio moving type IV burst is related to a certain closed magnetic structure (such as flaring loops, active region coronal loops, etc.) and the emission of the trapped non-thermal electrons. Currently, there is no clear evidence to suggest a physical correlation between the radio moving IV bursts and CME.

4.     In page 12, the authors mentioned the closely interaction between the star and substellar objects, such as hot Jupiter. Here, I suggest the authors consider to the work of Tan and Cheng (2013, Astrophys. Space Sci., 343: 511-521), where they studied the correlation between the mid-term to long-term solar quasi-periodic cycles and planetary motions, and found that solar activity has multiple quasi periodic components, some of which have strong correlation with planetary motion. It is inferred that the tidal force of planets plays an important role in the formation of the multiple solar cycles, and Jupiter plays a key role in most periodic modes.

5. There are some spelling issues in the article, such as “flare star” should be “flaring star”, and so on. I won't list them all here, I hope the authors will carefully check them. 

Comments on the Quality of English Language

Minor editing of English language required

Author Response

We took into account all the suggestions of the referee, and changed the manuscript accordingly.

Answers are marked with ">" symbol below.

---

 

This review paper attempt to collect some new observational results of flaring stars, including the flares, superflares, and CMEs on sun-like stars, cool dwarfs, red giants, and binary stars. They listed many observational facts, which are meaningful for our understanding the star activity and space weather. However, this review still has the following shortcomings,

1.     As a review paper, it is important to list a wide range of observational facts. At the same time, it is even more important to summarize and generalize these observational facts, and draw some new conclusions. It is obvious that this article only lists a large number of observational facts, but lacks necessary induction and summary, and does not draw the author's own conclusion. I hope to strengthen the refinement in this aspect during the author's revision process.

> Section 8 has been expanded in accordance with the reviewer's request to point out the results achieved so far, as well as highlight the main conclusions and the critical points that can determine future research directions.

2.     The author repeatedly mentions super flares in this review paper, but does not provide a clear definition of super flares, which is not rigorous. 

> We give a definition on p2, l41, E>1033 erg:

“In general, flares with radiative energy of $\sim$10$^{33}$\,erg, or more are labeled with the prefix "super", so in our paper, we follow this custom in nomenclature as well.”

3.     The authors mentioned “Moving type IV bursts are produced by electrons that are trapped in CME loops” in page 3. However, to my knowledge, the radio moving type IV burst is related to a certain closed magnetic structure (such as flaring loops, active region coronal loops, etc.) and the emission of the trapped non-thermal electrons. Currently, there is no clear evidence to suggest a physical correlation between the radio moving IV bursts and CME.

> We added more details to this part with a reference to the recent review paper of Carley et al on radio observation of solar CMEs to make this section a bit more clear.

4.     In page 12, the authors mentioned the closely interaction between the star and substellar objects, such as hot Jupiter. Here, I suggest the authors consider to the work of Tan and Cheng (2013, Astrophys. Space Sci., 343: 511-521), where they studied the correlation between the mid-term to long-term solar quasi-periodic cycles and planetary motions, and found that solar activity has multiple quasi periodic components, some of which have strong correlation with planetary motion. It is inferred that the tidal force of planets plays an important role in the formation of the multiple solar cycles, and Jupiter plays a key role in most periodic modes.

> Thank you for the suggestion, we included a reference to the connection between planetary motions and stellar activity. (we added a more recent paper, Stefani et al. 2024 as well)

5. There are some spelling issues in the article, such as “flare star” should be “flaring star”, and so on. I won't list them all here, I hope the authors will carefully check them. 

> We believe that both “flaring star” and “flare star” are correct, but an ADS exact search for both gave 23 vs. 400 results respectively, we opted for the latter version. We checked the manuscript for remaining typos.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Editor and authors:

Thank you for sending me this paper by Vida et al 2024 for a review on the Stellar flares, superflares and coronal mass ejections – entering the Big data era. The paper summarizes and reviews recent work conducted using Kepler and TESS data, as well as other multi-wavelength data, analyzing the current state of theoretical and observational research on stellar flares and CMEs. It is well written and will be suitable for publication in Universe with moderate revisions.

 

1.       183-185 rows point out that 'the Sun could have a superflare with an energy of ≈ 7 × 10^33 erg (∼X700 class) once every 3000 years, and ≈ 1 × 10^34 erg (∼X1000 class) once every 6000 years. 185.' Where is this derived from? Is it from the references cited in Figure 2? Or from the references mentioned in line 179, such as references 47, 57, 58? Or is it from other sources?  For example, Karoff et al. 2016 also predicts related content.

2.       187-196 rows mention that the flare frequency of 'earlier-M dwarfs' is higher than that of 'mid-M dwarfs,' and later describes the flare frequency from M7 to 'mid-L.' However, the part for M5-M7 is missing in between. It is recommended to complete this part. You can refer to Yang, Z.L. 2023 A&A. Additionally, there is a minor point. In this section, you used both 'dwarves' and 'dwarfs'; I believe it should be consistent.

3.       213-214 rows mention that the FFD is for flares selected within a certain energy range.  221-222 rows mention that this range is different for different stars. Meanwhile, in Figure 3, we can see that when different energy ranges are selected, the difference in alpha is very large. So, which result should we choose? What is the approximate energy range for different stars? Or, for stars of different spectral types, what should this energy range be?

4.       230-231 rows: ‘and 7.7% of the total sample showed flaring activity with cooler stars having larger flare amplitudes’. This is a vague description. What exactly are the 'larger flare amplitudes'?

5.       272-280 rows state that superflares are more common on cooler stars. I would like to know how this ‘more common’ is evaluated—is it based on the number of flares or a proportion? We know that flare energy is closely related to flare temperature. On F and G-type stars, we should observe a higher proportion of high-energy flares. For example, in Figure 19 of C.-L. Lin 2019 ApJ, it is evident that the proportion of flares above 10^34 erg is not high for M-type stars, and K-type stars have significantly more than M-type stars. The G-type star results from Shibayama et al. 2013, which you cited, show a higher proportion of flares above 10^34 erg. There are many similar examples. For instance, in Yang, H.Q. 2019, almost no flares below 10^34 erg are observed for A-type stars in their results (similar examples include A. K. Althukair 2023 RAA, Yang, Z.L. 2023 A&A, Balona, L.A. 2012 MNRAS, Davenport, Janes R.A. 2016, ApJ, etc.).

6.       550-552 rows mention ‘derived upper limits of masses of possibly associated CMEs’, but what is this upper limit? The mass of CMEs is mentioned several times elsewhere in the text, with results provided, but no numerical value is given here.

7.       686-689: The article first introduces flares and then CMEs. It is recommended to change the order to address the issues about flares first and then CMEs to maintain consistency.

8.       - Some figures in the paper do not provide corresponding legends, even though explanations are given in the respective captions. Adding legends directly to the images would make the information more accessible and easier to understand for the readers.

9.       Thanks to the high-quality and abundant data provided by the Kepler and TESS surveys, we have the opportunity to conduct more detailed studies on stellar flares and other activities. There are also several papers to study stellar magnetic activity (including flare) using LAMOST and Kepler or TESS survey (Zhang et al. 2020, MNRAS, 495, 1252; Zhang et al. 2023,ApJS, 264,17; e.g.,).

 

10.   The unit of the effective temperature in Figure 2 was missed.

 

End

Author Response

We took into account all the suggestions of the referee, and changed the manuscript accordingly.

Answers are marked with ">" symbol below.

----

 

 

Thank you for sending me this paper by Vida et al 2024 for a review on the Stellar flares, superflares and coronal mass ejections – entering the Big data era. The paper summarizes and reviews recent work conducted using Kepler and TESS data, as well as other multi-wavelength data, analyzing the current state of theoretical and observational research on stellar flares and CMEs. It is well written and will be suitable for publication in Universe with moderate revisions.

 

1.       183-185 rows point out that 'the Sun could have a superflare with an energy of ≈ 7 × 10^33 erg (∼X700 class) once every 3000 years, and ≈ 1 × 10^34 erg (∼X1000 class) once every 6000 years. 185.' Where is this derived from? Is it from the references cited in Figure 2? Or from the references mentioned in line 179, such as references 47, 57, 58? Or is it from other sources?  For example, Karoff et al. 2016 also predicts related content. 

> We tried to use a more obvious wording here, and added the mentioned reference as well.

2.       187-196 rows mention that the flare frequency of 'earlier-M dwarfs' is higher than that of 'mid-M dwarfs,' and later describes the flare frequency from M7 to 'mid-L.' However, the part for M5-M7 is missing in between. It is recommended to complete this part. You can refer to Yang, Z.L. 2023 A&A. Additionally, there is a minor point. In this section, you used both 'dwarves' and 'dwarfs'; I believe it should be consistent.

> We added the reference, although a bit later – around l240 –, as space photometry is mentioned only in the following paragraph. 

3.       213-214 rows mention that the FFD is for flares selected within a certain energy range.  221-222 rows mention that this range is different for different stars. Meanwhile, in Figure 3, we can see that when different energy ranges are selected, the difference in alpha is very large. So, which result should we choose? What is the approximate energy range for different stars? Or, for stars of different spectral types, what should this energy range be?

> Currently, it is not clear if the break in the FFD is due to a physical reason, as claimed by Mullan&Paudel, or just an observational effect. We tried to make this a bit clearer in the text.

4.       230-231 rows: ‘and 7.7% of the total sample showed flaring activity with cooler stars having larger flare amplitudes’. This is a vague description. What exactly are the 'larger flare amplitudes'? 

> We clarified the text.

5.       272-280 rows state that superflares are more common on cooler stars. I would like to know how this ‘more common’ is evaluated—is it based on the number of flares or a proportion? We know that flare energy is closely related to flare temperature. On F and G-type stars, we should observe a higher proportion of high-energy flares. For example, in Figure 19 of C.-L. Lin 2019 ApJ, it is evident that the proportion of flares above 10^34 erg is not high for M-type stars, and K-type stars have significantly more than M-type stars. The G-type star results from Shibayama et al. 2013, which you cited, show a higher proportion of flares above 10^34 erg. There are many similar examples. For instance, in Yang, H.Q. 2019, almost no flares below 10^34 erg are observed for A-type stars in their results (similar examples include A. K. Althukair 2023 RAA, Yang, Z.L. 2023 A&A, Balona, L.A. 2012 MNRAS, Davenport, Janes R.A. 2016, ApJ, etc.).

> Thank you, this part was indeed not obvious, we tried to clarify the manuscript.

6.       550-552 rows mention ‘derived upper limits of masses of possibly associated CMEs’, but what is this upper limit? The mass of CMEs is mentioned several times elsewhere in the text, with results provided, but no numerical value is given here.

> Thank you for this notion, we added the value.

7.       686-689: The article first introduces flares and then CMEs. It is recommended to change the order to address the issues about flares first and then CMEs to maintain consistency.

> Thank you, we changed the order (note that the outlook has been rewritten significantly as requested by another referee)

8.       - Some figures in the paper do not provide corresponding legends, even though explanations are given in the respective captions. Adding legends directly to the images would make the information more accessible and easier to understand for the readers.

> We added legends to the figures

 

9.       Thanks to the high-quality and abundant data provided by the Kepler and TESS surveys, we have the opportunity to conduct more detailed studies on stellar flares and other activities. There are also several papers to study stellar magnetic activity (including flare) using LAMOST and Kepler or TESS survey (Zhang et al. 2020, MNRAS, 495, 1252; Zhang et al. 2023,ApJS, 264,17; e.g.,).

> Thank you for the suggestion, we added some details on the works on the connection between space photometry and LAMOST data.

 

10.   The unit of the effective temperature in Figure 2 was missed.

> Corrected.

Reviewer 3 Report

Comments and Suggestions for Authors

Universe 3061761 review of

"Stellar flares, superflares and coronal mass ejections – entering the Big data era"

Type of submission: review.

 

Summary: 

 

This is an observational review on stellar flares over a wide range of the electromagnetic spectrum, utilizing recent results from the Big Data era (which is the past 2 decades of intense observations and sharing of data). The goal is to focus on results that challenge the standard flare model based on the solar paradigm

 

*******

General comments: 

 

The abstract adequately summarizes the work, but because it is on observational data, I recommend that line 4 be changed to "In our observational review"

 

There is a broad selection of references (202 in the bibliography), appropriate to a review paper.

(9 of these papers include author Vida; 17 include coauthor Leitzinger;  17 include coauthor Leitzinger; 17 include coauthor Odert; 10 include coauthor Seli;  11 include coauthor Kriskovics;  4 include coauthor Greimel. This does not indicate a problem given the total number of references.) 

 

 

The introduction contains sufficient background and references to existing work.

 

The bulk of the paper describes a number of different aspects of results from observations of stellar flares. The figures support the discussion.

 

The summary (section 8, Outlook) is very brief and does not really summarize the main issues, in particular the "focus on results that challenge the standard flare model" is not apparent.

 

Thus my main recommendation is that the Outlook needs to be rewritten and expanded to include "focus on results that challenge the standard flare model".

 

*************

Detailed requests for changes:

 

line 13: "surrounding astrospheres" (in stellar astronomy the atmosphere is of limited extent, so recommend to replace by e.g. "surrounding extended astrospheres" or "surrounding AU scale region"

 

line 75: did Balona link higher luminosity class to higher magnetic energy?

 

line 98: "opens up" I think you mean in direction, not in time, suggest use "opens upward"

 

line 112: isn't it rather a result of lack of spatial resolution for stars vs. the sun?

 

line 114 " CMEs on stars CMEs" makes no sense, please rewrite (period missing?)

 

line 195: correct term is "duty cycle" rather than cycle

 

line 299: suggest modify to "Earth's polar regions"

 

line 326: "as in" should be "than for"

 

p.9 Fig.5: need some description giving the number of flares vs. point size (e.g. min and max and whether the scale is linear with radius or with area of the point).

 

p.10 Fig. 6: describe what indicates the flares (e.g. sharp increases on timescale ...)

 

line 362: "spherical position" I think you mean "stellar surface position"

 

Fig.9: in the caption at the Time value at which the flare occurs (to make it clear to the 

reader). "function (gray) is not definite" you mean "function (gray) is not definitive"

 

Fig.10: "fastest event" please point out which one

 

line 565: "CMEsf rom" needs correction

 

Author Response

We took into account all the suggestions of the referee, and changed the manuscript accordingly.

Answers are marked with ">" symbol below.

---

 

Universe 3061761 review of

"Stellar flares, superflares and coronal mass ejections – entering the Big data era"

Type of submission: review.

 

Summary: 

 

This is an observational review on stellar flares over a wide range of the electromagnetic spectrum, utilizing recent results from the Big Data era (which is the past 2 decades of intense observations and sharing of data). The goal is to focus on results that challenge the standard flare model based on the solar paradigm

 

*******

General comments: 

 

The abstract adequately summarizes the work, but because it is on observational data, I recommend that line 4 be changed to "In our observational review"

> Changed. 

There is a broad selection of references (202 in the bibliography), appropriate to a review paper.

(9 of these papers include author Vida; 17 include coauthor Leitzinger;  17 include coauthor Leitzinger; 17 include coauthor Odert; 10 include coauthor Seli;  11 include coauthor Kriskovics;  4 include coauthor Greimel. This does not indicate a problem given the total number of references.) 

 

 

The introduction contains sufficient background and references to existing work.

 

The bulk of the paper describes a number of different aspects of results from observations of stellar flares. The figures support the discussion.

 

The summary (section 8, Outlook) is very brief and does not really summarize the main issues, in particular the "focus on results that challenge the standard flare model" is not apparent.

 

Thus my main recommendation is that the Outlook needs to be rewritten and expanded to include "focus on results that challenge the standard flare model".

> In the addition inserted in Section 8, we addressed, among other things, the main points that question the standard solar-based flare model.

*************

Detailed requests for changes:

 

line 13: "surrounding astrospheres" (in stellar astronomy the atmosphere is of limited extent, so recommend to replace by e.g. "surrounding extended astrospheres" or "surrounding AU scale region"

  > Corrected

 

line 75: did Balona link higher luminosity class to higher magnetic energy?

   > Yes, thank you for this comment, we added some further details to this part.

 

line 98: "opens up" I think you mean in direction, not in time, suggest use "opens upward"

 > Thank you for the notion, we tried to clarify this part to be more obvious

line 112: isn't it rather a result of lack of spatial resolution for stars vs. the sun?

  > We added more details to this part.

line 114 " CMEs on stars CMEs" makes no sense, please rewrite (period missing?)

 >Corrected.

line 195: correct term is "duty cycle" rather than cycle

 >Corrected

line 299: suggest modify to "Earth's polar regions"

 >Corrected

line 326: "as in" should be "than for"

 >Corrected

p.9 Fig.5: need some description giving the number of flares vs. point size (e.g. min and max and whether the scale is linear with radius or with area of the point).

> Symbols corresponding to 10-100-200 flares have been placed on the figure (only the stars showing at least 10 flares have been depicted).

p.10 Fig. 6: describe what indicates the flares (e.g. sharp increases on timescale ...)

 >Corrected

line 362: "spherical position" I think you mean "stellar surface position"

 >Corrected

Fig.9: in the caption at the Time value at which the flare occurs (to make it clear to the 

reader). "function (gray) is not definite" you mean "function (gray) is not definitive"

 >Corrected

Fig.10: "fastest event" please point out which one

 >Corrected

line 565: "CMEsf rom" needs correction

 

>Corrected

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I have no further comments to this manuscript. I think it can be accepted to publish.

Comments on the Quality of English Language

I have no other opinions except for the article being too long.

Reviewer 2 Report

Comments and Suggestions for Authors

The author revised all of them. The manuscript can be accepted now.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have satisfactory addressed all the issues raised in my first reviewer report.