Subaru Telescope observes superflare stars with large starspots

Source: Subaru Telescope

A team of astronomers has used the High Dispersion Spectrograph on the Subaru Telescope to conduct spectroscopic observations of Sun-like “superflare” stars first observed and cataloged by the Kepler Space Telescope. The investigations focused on the detailed properties of these stars and confirmed that Sun-like stars with large starspots can experience super flares.

The team targeted a set of solar-type stars emitting very large flares that release total energies 10-10000 times greater than the biggest solar flares, and carried out spectroscopic observations on 50 solar-type superflare stars selected from the Kepler Space Telescope’s data. From the investigation of the detailed properties of spectral lines, the team obtained the following results:

1. More than half the observed 50 stars show no evidence of binarity (that is, they are not binary stars). The team confirmed the characteristics of the target stars as similar to those of the Sun.
2. On the basis of the Kepler data, superflare stars show somewhat regular, periodic changes in their brightnesses. The typical periods range from one day to a few tens of days. Such variations are explained by the rotation of the star and its starspots. As shown in figure, the stars seem to become dimmer when their starspots are on their visible sides. Moreover, the timescales of the brightness variations should correspond to the stars’ rotation speeds.

The artificial image of a superflare star seen with visible light shows a large superflare (shown in white) occurring in the large starspot area.