July 31, 2017 to August 3, 2017
Royal Observatory of Belgium
UTC timezone
<br>2nd LAMOST-Kepler workshop<br><br>LAMOST in the era of large spectroscopic surveys<P><img src="https://events.oma.be/indico/event/26/picture/0.jpg" width="466" height="50">

Active stars in the Kepler field of view

Aug 1, 2017, 4:20 PM
Meridian Room (Royal Observatory of Belgium)

Meridian Room

Royal Observatory of Belgium

Invited talk 3.1 Science with the LAMOST 3.1 Science with the LAMOST


Mr Yuta Notsu (Kyoto University)


Superflares are flares that release total energy $10$-$10^{4}$ times greater than that of the biggest solar flares with energy of $\sim10^{32}$ erg. Recent Kepler observations found more than 1000 superflares on a few hundred solar-type stars (e.g., Maehara+2012 Nature). Such superflare stars show quasi-periodic brightness variations with the periods from one to a few tens of days. Rotation period and starspot coverage can be estimated from these brightness variations (Notsu+2013 ApJ). These values are used for discussing detailed properties such as the relation between spot size and flare frequency (Maehara+2017 PASJ), but spectroscopic observations are needed in order to know to what extent estimated values of rotation period and spot sizes are right. Using LAMOST-Kepler Survey spectra, Karoff et al. (2016, Nature Communications) measured intensity of Ca II H&K lines of 5,648 solar-type stars, including 48 superflare stars. The results suggest that there is a good correlation between starspot coverage (from Kepler) and Ca II intensities, and in particular, superflare stars (including slowly-rotating stars) are generally characterized by larger chromospheric emissions than other stars. We are now comparing activity measurements using Ca II H&K lines with measurements using other chromospheric lines in LAMOST spectra (especially Ca II 8542 line). We have also conducted high-dispersion spectroscopic observations of more than 50 superflare stars by using grand-base telescopes like Subaru 8.2m (Notsu+2015a&b PASJ). Similar correlations between starspot coverage and chromosheric emissions can be seen, and we can say that the results from LAMOST (lower resolution but large number of samples) are consistent with those from high-dispersion spectroscopic observations. In this talk, we first briefly summarize statistical study results of superflares from Kepler data, and then overview our spectroscopic studies mentioned above.

Primary author

Mr Yuta Notsu (Kyoto University)


Dr Christoffer Karoff (Aarhus University) Dr Daisaku Nogami (Kyoto University) Dr Hiroyuki Maehara (National Astronomical Observatory of Japan) Mr Kai Ikuta (Kyoto University) Prof. Kazunari Shibata (Kyoto University) Mr Kosuke Namekata (Kyoto University) Dr Satoshi Honda (University of Hyogo) Mr Shota Notsu (Kyoto University)

Presentation materials