Kosuke Namekata's HP

Superflares, starspots, and mass ejections on Sun-like stars
The sun is actually constantly undergoing explosive and mass ejection phenomena on the solar surface. In particular, sudden explosive phenomena are called solar flares. Solar flares have a severe impact on the Earth's environment in the form of magnetic storms and radiation, and therefore understanding them is essential for our human civilization. Currently, we have not succeeded in predicting the occurrence of solar flares, so "When will it happen? How large a solar flare will occur?" are very important issues.

In 2012, it was discovered that stars very similar to our Sun (solar-type stars) actually experienced a "superflare," a flare 10-10,000 times larger than the largest solar flare in the history of solar observations. This discovery was a surprise to the world, as it had been believed in astronomy that such a superflare would not occur on the Sun. I have been asking myself questions such as, "Do superflares actually occur on the sun?" If so, "what will happen to the Earth?". I am conducting research to compare the Sun with such active Sun-like stars that cause these superflares.

So far, I have found observationally that the superflares of solar-type stars and the giant sunspots (huge magnetic energy blobs) that are essential to trigger them are produced by the same mechanism as the small-scale flares and spots of the Sun (Namekata et al. 2017b&c, 2019, 2020a). Recently, we have also promoted research using the Kyoto University Seimei Telescope to obtain hints about the heating mechanism in M-type stellar superflares (Namekata et al. 2020b), and succeeded in the first detection of giant filament ejections associated with stellar superflares on young Sun-like stars (Namekata et al. 2021, Nature Astronomy). 2021, Nature Astronomy). However, the study of superflares in solar-type stars has just begun and we need to continue our research in order to solve our ultimate questions.

Figure 1. Press release on the detection of a superflare on the M-type star AD Leo (Copyright:NAOJ). This study (Namekata et al. 2020b) was ranked second on the "MOST DISCUSSED" list of "High Impact Articles From PASJ" in 2020.

Figure 2: Imaginary picture of giant filament eruption associated with a superflare on the young Sun-like star EK Dra (Copyright:NAOJ). This study was published in Nature Astronomy, a Nature-based British astronomy journal (Namekata et al. 2022).

2021.04-: JSPS fellow (PD) at National Astronomical Observatory of Japan/ALMA Project

[Download publication list pdf]

Refereed papers as first author

1. Namekata, K., Ichimoto, K., Ishii, T. T., Shibata, K. 2022, ApJ, accepted (3 June, 2022),
   "Sun-as-a-star Analysis of Hα Spectra of a Solar Flare Observed by SMART/SDDI: Time Evolution of Red Asymmetry and Line Broadening"
   [Publication Link] [ADS]


2. Namekata, K., Maehara, H., Honda, S. et al. 2022, ApJ Letters, 926, 5
   "Discovery of a Long-Duration Superflare on a Young Solar-Type Star EK Draconis with Nearly Similar Time Evolution for Hα and White-Light Emissions"
   [Publication Link] [ADS]


3. Namekata, K., Maehara, H., Honda, S. et al. 2021, Nature Astronomy, 6, 241 (Open Access),
   "Probable detection of an eruptive filament from a superflare on a solar-type star"
   [Publication Link] [ADS]


4. Namekata, K., Maehara, H., Sasaki, R. et al. 2020, PASJ, 72, 68,
   "Optical and X-ray observations of stellar flares on an active M dwarf AD Leonis with Seimei Telescope, SCAT, NICER and OISTER"
   [Publication Link] [ADS]


5. Namekata, K., Davenport, J., Morris, B., et al. 2020, ApJ, 891, 103,
   "Temporal Evolution of Spatially-Resolved Individual Star Spots on a Planet-Hosting Solar-type Star: Kepler 17"
   [Publication Link] [ADS]


6. Namekata, K., Maehara, H., Notsu, Y., et al. 2019, ApJ, 871, 187,
   "Lifetimes and Emergence/Decay Rates of Star Spots on Solar-type Stars Estimated by Kepler Data in Comparison with Those of Sunspots"
   [Publication Link] [ADS]


7. Namekata, K., Sakaue, T., Watanabe, K., Asai, A., Maehara, H., Notsu, Y., Notsu, S., Honda, S., Ishii, T. T., Ikuta, K., Nogami, D., Shibata, K., 2017, ApJ, 851, 91,
   "Statistical Studies of Solar White-light Flares and Comparisons with Superflares on Solar-type Stars"
   [Publication Link] [ADS]


8. Namekata, K., Sakaue, T., Watanabe, K., Asai, A., Shibata, K., 2017, PASJ, 69, 7
   "Validation of a Scaling Law for the Coronal Magnetic Field Strengths and Loop Lengths of Solar and Stellar Flares"
   [Publication Link] [ADS]


9. Namekata, K., Isogai, K., Kato, T., and 38 coauthors, 2017, PASJ, 69, 2
   "Superoutburst of WZ Sge-type dwarf nova below the period minimum: ASASSN-15po"
   [Publication Link] [ADS]

Refereed papers as co-author

1. Maehara, H., Notsu, Y., Namekata, K., et al. 2020, PASJ, in press,
   "Time-resolved spectroscopy and photometry of an M dwarf flare star YZ Canis Minoris with OISTER and TESS: Blue asymmetry in Hα line during the non-white light flare"


2. Ikuta, K., Maehara, H., Notsu, Y., Namekata, K., et al. 2020, ApJ, in press,
   "Starspot mapping with adaptive parallel tempering I: Implementation of computational code"


3. Yamashiki, Y., Maehara, H., Airapetian, V., Notsu, Y. Sato, T., Notsu, S., Kuroki, R., Murashima, K., Sato, H., Namekata, K., et al. 2019, ApJ, 881, 114,
   "Impact of Stellar Superflares on Planetary Habitability"


4. Notsu, Y., Maehara, H., Honda, S., Hawley, S., Davenport, J., Namekata, K., et al. 2019, ApJ, 876, 58,
   "Do Kepler superflare stars really include slowly-rotating Sun-like stars ? - Results using APO 3.5m telescope spectroscopic observations and Gaia-DR2 data -"


5. Hayakawa, H., Ebihara, Y., Cliver, Edward W., Hattori, K., Toriumi, S., Love, J. J., Umemura, N., Namekata, K., et al. 2018, MNRAS, 484, 4083,
   "The Extreme Space Weather Event in September 1909"


6. Honda, S., Notsu, Y., Namekata, K., et al. 2018, PASJ, 70, 62
   "Time-resolved spectroscopic observations of an M-dwarf flare star EV Lacertae during a flare"


7. Maehara, H., Notsu, Y., Notsu, S., Namekata, K., Honda, S., Ishii, T. T., Nogami, D., Shibata, K., 2017, PASJ, 69, 41
   "Starspot activity and superflares on solar-type stars"


8. Notsu, Y., Honda, S., Maehara, H., Notsu, S., Namekata, K., Nogami, D., Shibata, K., 2017, PASJ, 69, 12
   "Spectroscopic observations of active solar-analog stars with high X-ray luminosity, as a proxy of superflare stars"

Features

1. HMI Science Nugget, "Statistical Study of Solar White-light Flares and Comparison with Superflares on Solar-type Stars" http://hmi.stanford.edu/hminuggets/?p=2066


2. AAS NOVA-Research highlights from the journals of the Americal Astronomical Society-, "What Are Starspots Like on Sun-like Stars?" https://aasnova.org/2018/12/12/what-are-starspots-like-on-sun-like-stars/


3. Press release in 2020/7/10 https://kosukenamekata.github.io/SEIMEI-Telescope/Press_release/


4. Press release in 2021/12/10 - Nature Astronomy Article metrics https://www.nature.com/articles/s41550-021-01532-8/metrics


5. Nature RESEARCH HIGHLIGHT, "Young star’s streamer of scorching-hot gas gives astronomers a fiery first" https://www.nature.com/articles/d41586-021-03683-0

International Conference

-2021-

1. AGU Fall meeting, (vertial), U.S., Dec 13 - Dec 17, 2021 (TBD), "TBD"


2. AOGS2021 Virtual 18th annual meeting, vertial, Singapore, Aug 2 - Aug 6, 2021 (Oral), "Observational Studies of Star Spot Emergence/decay on Solar-type Stars with Kepler Data"


3. AOGS2021 Virtual 18th annual meeting, vertial, Singapore, Aug 2 - Aug 6, 2021 (Oral), "Filament Eruption from a Superflare on a Solar-type Star"


4. TESS Science Conference II, MIT (vertial), U.S., Jun 3 - Jun 6, 2021 (TBD), "TBD"


5. JpGU Meeting 2021, Yokohama (vertial), Japan, Jun 3 - Jun 6, 2021 (Oral/Invited), "Spectroscopic and photometric observations of superflares and filament eruption on cool stars"


6. Cool Stars 20.5, (vertial), Mar 2 - Mar 6, 2021 (TBD), "Detection of filament eruption on solar-type star"


7. COSPAR 43rd Scientific Assembly, Sydney (vertial), Australia, Jan 28 - Feb 4, 2021 (Oral), "First detection of stellar mass ejection from a superflare on a solar-type star"

-2020-

8. 235th AAS meeting, Honolulu, USA, Jan 4-8, 2020 (Oral), "Lifetimes and emergence/decay rates of star spots on solar-type stars estimated by Kepler data in comparison with those of sunspots"

-2019-

9. SHINE Conference 2019, Boulder, USA, Aug 5-9, 2019 (Poster/Oral), "Lifetimes and emergence/decay rates of star spots on solar-type stars estimated by Kepler data in comparison with those of sunspots"


10. Flux Emergence Workshop 2019, Hongo, Tokyo, Mar 18-22, 2019 (Oral), "Lifetimes and Emergence/Decay Rates of Star Spots on Solar-type Stars Estimated by Kepler Data in Comparison with Those of Sunspots"


11. Kepler & K2 Science Conference V, Glendale, CA, USA, Mar 4-8, 2019 (Poster) , "Lifetimes and Emergence/Decay Rates of Star Spots on Solar-type Stars Estimated by Kepler Data in Comparison with Those of Sunspots"

-2018-

12. Hinode-12 Meeting, Granada, Spain, Sep 10-13, 2018 (Oral), "Statistical Studies of Solar White-light Flares and Comparisons with Superflares on Solar-type Stars"


13. Cool Stars 20, Boston/Cambridge, USA, July 29-Aug 2, 2018 (Poster), "Lifetime, Emerging and Decay Rates of Starspots on Solar-type Stars Estimated by Kepler Data and Comparisons with Sunspots"


14. COSPAR 2018 42th Assembly, Pasadena, CA, USA, July 14-22, 2018 (Oral), "Statistical Studies of Solar White-light Flares and Comparisons with Superflares on Solar-type Stars"


15. IAU Symposium 340 “Long-term Datasets for the Understanding of Solar and Stellar Magnetic Cycles”, Jaipur, India, February 19-24, 2018 (Oral), "Statistical Study of Solar White-light Flares and Comparison with Superflares on Solar-type Stars"

-2017-

16. The 4th Asia-Pacific Solar Physics Meeting (APSPM 2017), Kyoto, Japan, November 7-10, 2017 (Oral), "Statistical Study of Solar White-Light Flares and Comparisons with Superflares on Solar-type Stars"


17. Symposium on Space Weather and Habitable Zones, Kyoto, Japan, June 27-28, 2017 (Oral), "Solar & Stellar white light flares"


18. JpGU-AGU Joint Meeting 2017, Makuhari, Japan, May 20-25, 2017 (Oral), "Solar and Stellar White-light Flares"

-2016-

19. Hinode-10 Science Meeting (Hinode 10), Nagoya, Japan, September 5-8, 2016 (Poster), "Statistical Research on Solar White-Light Flares and Comparison with Superflares on Solar-type Stars"


20. Symposium “Superflares on Solar-type Stars and Solar Flares, and Their Impacts on Exoplanets and the Earth”, Kyoto, Japan, March 1-4, 2016 (Oral), "Statistical properties of solar white-light flares"