No. 133 Lithium abundance of the solar-type superflare stars Satoshi Honda1, Yuta Notsu2, Hiroyuki Maehara3, Shota Notsu2, Takuya Shibayama4, Daisaku Nogami2, Kazunari Shibata2 1. University of Hyogo, 2. Kyoto University, 3. National Astronomical Observatory of Japan , 4. Nagoya University

Abstract: We performed the high dispersion spectroscopy of solar-type superflare stars by Subaru/HDS, and estimate the stellar parameters and lithium abundance of the stars to compare with the Sun. Our spectroscopic analysis of superflare stars show more than half of targets have no evidence of binary system and the stellar parameters are in the range of solar-type stars (Notsu et al. 2015a&b). We also investigate the correlations of Lithium abundance with stellar atmospheric parameters, rotational velocity, and superflare activities to understand the nature of superflare stars and the possibility of the nucleosynthesis of lithium by superflares. The derived lithium abundance in superflare stars do not show the correlation with stellar parameters. As compared with the lithium abundance in Hyades cluster which is younger than the sun, it is suggested that half of observed stars are young. However, there are some objects which show the low lithium and slowly rotate from the estimated v sin(i) and period of brightness variation. These results indicate that the superflare stars are not only young stars but also old stars like our sun. In our observations, we could not find the any evidence of lithium productions by superflare. Superflare stars Observations of solar-type superflare stars • Flares are most energetic explosions on the surface • We observed 50 superflare stars Subaru telescope HDS: High dispersion spectrograph of the Sun, and are thought to occur by release of by using Subaru/HDS. magnetic energy. • Wavelength range 6100 – 8800 Å • The rapid rotation stars tend to cause superflares, • R = 50,000 – 100,000 4 which are10 – 10 times larger than the largest solar Imaginary drawings of a superflare star • From 2011 to 2013 (8 nights) flare. • 5100 < Teff < 6000, logg > 4.0 –T Tauri star, close binary stars, dMe stars, etc. • We derive the Li abundances for 34 single • The Sun is the single and slowly rotating star. superflare stars. • It has been recognized that the superflares will not • Atmospheric parameters determined by occur on the Sun. Notsu et al. (2015a); see Notsu’s poster (118). • However, we discovered many superflares on many Light curve of superflare star • We used the analysis program SPTOOL (~300) solar-type (G-type main sequence) stars from Maehara et al. 2012 (Takeda 1995) based on Kurucz’s Kepler photometric data. ATLAS9/WIDTH (Kurucz 1993). Honda et al. 2015 (Mehara et al. 2012, Shibayama et al. 2013) Also see Y. Notsu’s poster (118,117)

Skumanich 1972 Sun-like superflare stars exist Lithium abundance Effective temperature and Li abundances • Li is easily destroyed in the hotter (2×106K) These stars show an especially high region of stellar atmospheres. a value of Li, to be very young stars. 3 • We can obtain information about the evolution of Hyades cluster is old (700 Myr) open cluster the convection layer. 2 but is younger than the Sun. • Li abundance will be reflect the age of solar-type A(Li) More than 10 stars with superflares stars. (e.g., Herbig 1965) 1 Superflare stars (P < 10d) ◎ Superflare stars (P >― 10d) Superflare stars (upper limit) do not show high value of Li • Young stars have high Li abundance, rapid rotation, Sun Comparison stars and high activity. (e.g., Skumanich 1972) 0 Takeda & Kawanomoto (2005) compared with Hyades cluster. • We can estimate the age of superflare stars using Li 6000 5000 abundance. Teff In general, the stellar rotation has a correlation with the age and activity. • The fresh isotopes of Li in the solar and stellar a atmospheres can be produced by nuclear 3 low inclination Some superflare stars show small interactions of ions accelerated during flares. v sin i and low Li abundance. (e.g., Tatischeff & Thibaud 2007) Mishenina et al. 2012 2 This results may indicate that

A(Li) those stars are not young. Are superflare stars very young stars ? 1 T < 5500K Superflare stars P < 10 Superflare stars P > 10 Superflare stars are not Can such superflares occur on the present Sun ? Sun-like stars Sun 0 Comparison stars necessarily young. 100 101 • What kind of single solar-type stars occur superflare ? Now we are investigating Li abundances of 49 nearby v sin i (km/s) • Very young stars generally rotate fast and occur superflares. solar-analog stars with strong X-ray luminosity. Li abundances and Frequency of superflares • These stars will have large star spots and high activities of chromosphere. (Notsu et al. submitted) • Are superflare stars young stars like WTTS ? Li abundance decrease as the 3 • However, Hα lines of superflare stars do not show emission. number of superflares increases. • We could not see any IR excess in superflare stars. →No evidence of Li production by 2 superflare. • There are slowly-rotating stars. A(Li)

1 • An increase of Li is seen only for just after the end of flare ? • Our observations could not show the 0 6 0 0.02 0.04 0.06 0.08 0.1 small contributions of Li. Frequency of superflares [/day]

SOHO/MDI 2003.10.3 http://www.nasa.gov/multimedia/imagegallery/image_feature_1087.html Notsu et al. 2015a Summary Lithium abundance will reflect the age of superflare stars. Our spectroscopic observations show that slightly young (rapid rotation) solar- type stars tend to produce superflares, but that old superflare stars exist. References There is a possibility that superflares could be generated on our Sun. Maehara et al. 2012 Nature, 485, 478 Skumanich 1972 ApJ, 171, 565 Notsu et al. 2015 PASJ, 67, 32 We could not find any evidence of nucleosynthesis of Li in stellar flares from Shibayama et al. 2013 ApJS, 209, 5 Mishenina et al. 2012 A&A, 547, A106 Notsu et al. 2015 PASJ, 67, 33 Herbig 1965 ApJ, 141, 588 Tatischeff & Thibaud 2007 A&A, 469, 265 Honda et al. 2015 PASJ, 67, 85 our observations.