May 2016No.2016-016-e

Journal of Integrated Creative Studies

A Report on the Workshop “Superflares on Solar-type Stars
and Solar Flares, and Their Impacts on Exoplanets and theEarth.” held in 2016 March 1st (Tue)– March 4th (Fri)
Kazunari Shibata１ and Daisaku Nogami 2
1
Kwasan and Hida Observtories, Kyoto University
E-mail: shibata@kwasan.kyoto-u.ac.jp
2
Department of Astronomy, Kyoto University
E-mail: nogami@kwasan.kyoto-u.ac.jp

Abstract. A workshop on superflares on solar-type stars and related subjects was held inMarch, 2016 at Kyoto University. Here, a report on the workshop is given, including thepurpose of the workshop, SOC, LOC, invited speakers, the program, and a brief summary oftalks and discussions.
Keywords: Stars: flare, Stars: activity, Sun: flare, Sun: activity, Astrobiology

1. Purpose of the Workshop
We held the workshop“Superflares on Solar-type Stars and Solar Flares, and Their Impacts on
Exoplanets and the Earth” at Faculty of Science of Kyoto University on March 1st (Tue)– March 4th(Fri), 2016, supported by the International Research Unit of Advanced Future Studies, Kyoto
University.
The main reason why we held the workshop at Kyoto was that the study of superflares on solartype stars has been significantly developed by the Kyoto group in recent years (Maehara et al. 2012,Shibata et al. 2013, Shibayama et al. 2013, Notsu, Y. et al. 2013, Notsu, S. et al. 2014, Nogami et al.
2014, Maehara et al. 2015, Notsu, Y. et al. 2015a,b, Honda et al. 2015).
Using Kepler data, Maehara et al. (2012) discovered many superflares (with energy of 1034-1036erg) on solar type stars (G-type main sequence stars). In the case of the Sun-like stars (with surfacetemperature 5600–6000 K and slowly rotating with a period longer than 10 days), the occurrence rateof superflares with an energy of 1034-1035 erg is once in 800–5000 yr. There is evidence that thesesuperflare stars have extremely large starspots with a size about 10 times larger than that of the largest
sunspot (Shibayama et al. 2013, Notsu, Y. et al. 2013). There was no signature of hot Jupiter on thesestars against previous prediction (Schaefer et al. 2000, Rubenstein and Schaefer 2000), suggesting thepossibility of superflares on the Sun. Such a possibility of solar superflares (with energy 1034 erg) wastheoretically supported using order-of-magnitude estimate of total magnetic flux that can be generated
by the differential rotation of the present Sun on the basis of a current solar dynamo model (Shibata et1

al. 2013). The spectroscopic observations of these superflare stars have started (Notsu, S. et al. 2014),
and two Sun-like superflare stars rotating as slow as the Sun were discovered (Nogami et al. 2014).
More recently, using spectroscopic data of 34 superflare stars taken by Subaru telescope, it wasconfirmed that the rotational velocity, v sini, and spot coverage are consistent with those estimatedfrom the brightness variation observed by Kepler (Notsu, Y. et al., 2015a,b). The Lithium abundanceof these superflare stars was also measured from Subaru data (Honda et al. 2015).
Since the subject is so important for both solar and stellar physics as well as for astrobiology, theidea to hold this workshop has emerged on the basis of the recent active research on superflares by theKyoto group as discussed above.
Main purpose of this workshop was to review and discuss superflares on solar-type stars andrelated stars, solar white-light flares, modelling of optical spectra of solar white-light flares and stellarflares, long-term variations of the stellar activity and starspots, the dynamo theory of big spots leading
to superflares on solar-type stars, and to discuss the possibility of superflares on the Sun, impacts ofstellar superflares on exoplanets, and future possible impacts of solar superflares on the Earth.
Collaboration on these subjects among participants has also been encouraged during the workshop andfuture.
2. SOC and LOC
SOC members are as follows:
Kazunari Shibata (Kyoto University, Chair)
Suzanne Hawley (University of Washington)
Hiroyuki Maehara (NAOJ)
Satoshi Honda (University of Hyogo)
Kiyoshi Ichimoto (Kyoto University)
Hiroaki Isobe (Kyoto University)
LOC members are as follows:
Daisaku Nogami (Kyoto University, Chair)
Ayumi Asai (Kyoto University)
Takako T. Ishii (Kyoto University)
Yuta Notsu (Kyoto University)
Shota Notsu (Kyoto University)
Kosuke Namekata (Kyoto University)
Invited speakers are:Suzanne L. Hawley (University of Washington, USA)
Adam F. Kowalski (NASA, GSFC, USA)
Steven Saar (Harvard-Smithsonian Center for Astrophysics, USA)
Luis A. Balona (South African Astronomical Observatory, South Africa)
Valery M. Nakariakov (University of Warwick, UK)Kyoko Watanabe (National Defense Academy of Japan, Japan)
Masashi Omiya (NAOJ, Japan)
Yoichi Takeda (NAOJ, Japan)
Hideyuki Hotta (Chiba University, Japan)

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3. Program
The program of this workshop was as follows:
3/1 (Tue) Observation of Stellar Superflares and Solar White Light FlaresTime
Name
Rough contents of the talk
Chair: Kazunari Shibata
10:00-10:10
Kazunari Shibata Opening remarks
10:10-11:00
Hiroyuki Maehara Superflares and starspot activity on solar-type stars
11:00-12:00
Suzanne Hawley Observation of stellar flares
12:00-13:30
Lunch
Chair: Ayumi Asai
13:30-14:30
Adam Kowalski Modeling of optical spectrum of stellar flares
14:30-15:30
Kyoko Watanabe Solar white-light flares
15:30-16:00
Break
Chair: Kiyoshi Ichimoto
16:00-16:30
Takako T. Ishii
White light flares observed at Hida Observatory
16:30-16:45
Kosuke Namekata Statistical properties of solar white-light flares
16:45-17:00
Han Yuan Chang A LAMOST-Kepler spectrophotometric study of hyper flares ofM dwarfs
17:00-17:15
Li-Ching Huang Physical Properties of G-type Kepler Eclipsing Binaries
3/2 (Wed) Observation of Stellar Superflares and Spectroscopic Observations
Chair: Hiroaki Isobe
10:00-11:00
Luis A. Balona
Flare stars across the H–R diagram
11:00-12:00
Valery Nakariakov Oscillations of stellar flares
12:00-13:30
Lunch
Chair: Suzanne Hawley
13:30-14:15
Yuta Notsu
Spectroscopic observations of solar-type superflare stars
14:15-14:30
Satoshi Honda
Spectroscopic observations of flare star EV Lac at NHAO
14:30-15:00
BreakChair: Satoshi Honda
15:00-16:00
Yoichi Takeda
Activities and related properties of solar-type stars
16:00-17:00
Steven Saar
Observations of Magnetic Cycles in Late-type Single Dwarfs:
What are They Telling Us?
17:00-17:30
Mark Cheung
Evolving Models of Stellar Photospheric and Coronal MagneticFields
19:00~Banquet at Ganko Nijo
3/3 (Thu) Possibility of Superflares on the Sun
Chair: Hiroyuki Maehara
10:00-10:30
Kazunari Shibata Can superflares occur on the Sun?
10:30-11:30
Hideyuki HottaCurrent understanding of solar global scale magnetic field anddynamo
11:30-11:45
Hisashi Hayakawa World-Wide Records of Solar Flare Candidates in the 10thcentury and the 18th century3

11:45Lunch
PM Tour to Kwasan Observatory (Excursion)
http://www.kwasan.kyoto-u.ac.jp/general/facilities/index_kwasan_en.html
3/4 (Fri) Planets (AM) & Future Plans (PM)
Chair: Takanori Sasaki
10:00-11:00
Masashi Omiya Observations of exoplanets and stellar activity
11:00-11:15
Takuya Takahashi CMEs of solar superflares
11:15-11:45
Daisaku Nogami Kyoto 3.8m telescope and future plans of our superflare studies
11:45-13:30
Lunch
Chair: Daisaku Nogami
13:30-17:00
Discussion ~Future plans of superflare studies~(Moderators: Daisaku Nogami and Kazunari Shibata)
Short comments & Topics-Daisaku Nogami: Future plans of our superflare studies-Fumihide Iwamuro: Short comment on spectrograph of Kyoto 3.8m telescope-Suzanne L. Hawley: Some thoughts on observing flares and starspots with new Japanese 3.8m
telescope-Bun’ei Sato: Comment on spectroscopic observations with Kyoto 3.8m telescope (Introduction ofTESS)-Hiroyuki Ishikawa: Comment on the habitability of M-type stars-Possibility of International Collaboration
4. Talks and Discussions
Though the total number of participants was limited by the size of the room for the purpose ofeffective discussion, the workshop was attended by total number of 39 participants including 8 foreign
researchers from 4 countries. Figure 1 shows a group photograph of this workshop.
As shown in the program, the workshop mainly consisted of invited review talks:
On the 1st day, Maehara gave a review of the study of superflares and related starspots based on
Kepler data. Hawley presented an excellent review on optical observations of stellar flares. Kowalski
introduced a detailed review on modeling of optical spectrum of stellar flares. Stellar flares
spectroscopically observed in the optical light are physically the same as white light flares on the Sun.
Hence, Watanabe presented a nice review on solar white light flares based on recent spaceobservations, whereas Ishii discussed recent ground-based observations of solar white light flares
taken at Hida Observatory of Kyoto University.
On the 2nd day, Balona reviewed flare stars across the H–R diagram, including the amazing
discovery of superflares on A stars. Nakariakov discussed interesting study of oscillations ofsuperflares on stars. Notsu (Y.) gave a review of spectroscopic observations of solar-type superflarestars taken with the Subaru 8.2m telescope, and Takeda gave a comprehensive review of activities andrelated properties of solar-type stars. Saar presented an interesting review on observations of magnetic
cycles in late-type single dwarfs. Cheung commented a future plan of the study of the stellar flareactivity as an extention of the solar flare study.
On the 3rd day, Shibata discussed “Can superflares occur on the Sun?” from the theoretical point ofview. Hotta gave an excellent review on the current understanding of the solar dynamo theory.
On the 4th day, Omiya discussed an interesting plan of observations of exoplanets and related stellar
activity. Since one of the important targets of the Okayama Kyoto 3.8m telescope is superflares andtheir host stars, Nogami discussed future plans of the superflare studies using the Kyoto Okayama
3.8m telescope. Especially in the afternoon of the 4th day, future plans of spectroscopic observations of4

Journal of Integrated Creative Studies

superflares and their host stars with Kyoto 3.8m telescope have been extensively discussed (see Fig 2).
Finally, possibility of international collaboration has been discussed.
5. Acknowledgement
We would like to thank all invited and contributed speakers to present interesting and informative
talks, and thank all participants to attend this workshop and to have active discussion.
We also would like to thank the International Research Unit of Advanced Future Studies, Kyoto
University for the support of this workshop. Especially, we thank Professor Muraki for his varioushelp. Finally, we thank Kwasan and Hida Observatories as well as Department of Astronomy,
Graduate School of Science, Kyoto University, and the Unit of Synergetic Studies for Space, Kyoto
University.
6. References
Honda, S., Notsu, Y., Maehara, H., Notsu, S., Shibayama, T., Nogami, D. and Shibata, K., Highdispersion spectroscopy of solar-type superflare stars. III. Lithium abundances. Publications ofthe Astronomical Society of Japan, 67, 85, 2015
Maehara, H., Shibayama, T., Notsu, S., Notsu, Y., Nagao, T., Kusaba, S., Honda, S., Nogami, D. andShibata, K., Superflares on solar-type stars. Nature, 485, 478, 2012
Maehara, H., Shibayama, T., Notsu, Y., Notsu, S., Honda, S., Nogami, D. and Shibata, K., Statisticalproperties of superflares on solar-type stars based on 1-min cadence data. Earth, Planets andSpace, 67, 59, 2015
Nogami, D., Notsu, Y., Honda, S., Maehara, H., Notsu, S., Shibayama, T. and Shibata, K., Two sunlike superflare stars rotating as slow as the Sun. Publications of the Astronomical Society ofJapan, 66, L4, 2014
Notsu, Y., Honda, S., Maehara, H., Notsu, S., Shibayama, T., Nogami, D. and Shibata, K., Highdispersion spectroscopy of solar-type superflare stars. I. Temperature, surface gravity, metallicity,and vsin i. Publications of the Astronomical Society of Japan, 67, 32, 2015a
Notsu, Y., Honda, S., Maehara, H., Notsu, S., Shibayama, T., Nogami, D. and Shibata, K., Highdispersion spectroscopy of solar-type superflare stars. II. Stellar rotation, starspots, andchromospheric activities. Publications of the Astronomical Society of Japan, 67, 33, 2015bNotsu, Y., Shibayama, T., Maehara, H., Notsu, S., Nagao, T., Honda, S., Ishii, T. T., Nogami, D. andShibata, K., Superflares on Solar-type Stars Observed with Kepler II. Photometric Variability ofSuperflare-generating Stars: A Signature of Stellar Rotation and Starspots. Astrophysical Journal,771, 127, 2013
Notsu, S., Honda, S., Notsu, Y., Nagao, T., Shibayama, T., Maehara, H., Nogami, D. and Shibata, K.,
High-Dispersion Spectroscopy of the Superflare Star KIC 6934317. Pubilcations of theAstronomical Socity of Japan, 65, 112, 2014
Rubenstein, E. P. and Schaefer, B. E., Are Superflares on Solar Analogues Caused by ExtrasolarPlanets?. Astrophysical Journal, 529, 1031, 2000
Schaefer, B. E., King, J. R. and Deliyannis, C. P., Superflares on Ordinary Solar-Type Stars.
Astrophysical Journal, 529, 1026, 2000
Shibata, K., Isobe, H., Hillier, A., Choudhuri, A. R., Maehara, H., Ishii, T. T., Shibayama, T., Notsu,S., Notsu, Y., Nagao, T., Can Superflares Occur on Our Sun?. Publications of the Astronomical
Sciety of Japan, 65, 49, 2013
Shibayama, T., Maehara, H., Notsu, S., Notsu, Y., Nagao, T., Honda, S., Ishii, T. T., Nogami, D. andShibata, K., Superflares on Solar-type Stars Observed with Kepler. I. Statistical Properties ofSuperflares. Astrophysical Journal Supplement Series, 209, 5, 2013

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Fig 1 Group photo of participants of the superflare workshop, on March 1, 2016, in front of theentrance of the building 4 (Dept of Astronomy) of graduate school of science, Kyoto University.

Fig 2 One scene of discussion on future plans of the superflare research using the Kyoto
Okayama 3.8m telescope.

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