Mon. Not. R. Astron. Soc., 463, 2494-2512 (2016/December-2)
Stellar activity with LAMOST - I. Spot configuration in Pleiades.
FANG X.-S., ZHAO G., ZHAO J.-K., CHEN Y.-Q. and BHARAT KUMAR Y.
Abstract (from CDS):
We use the spectra of Pleiades and field stars from the LAMOST DR2 archive to study how spottedness and activity vary as a function of mass at young ages. We obtained the standard TiO band strength by measuring TiO bands near 7050 Å from LAMOST spectra (R ≃ 1800) for a large sample of field GKM dwarfs with solar metallicity. Analysis shows that active dwarfs, including those of late G and early K types, have extra TiO absorption compared to their inactive counterparts, indicating the presence of cool spots on their surface. Active late K and M dwarfs show deeper TiO2 and shallower TiO4 compared to inactive stars at a given TiO5, which could be partly explained through cool spots. We estimated the cool-spot fractional coverage for 304 Pleiades candidates by modelling their TiO2 (and TiO5) band strength with respect to the standard value. The results show that the surfaces of a large fraction of K- and M-type members have very large spot coverage (∼50 per cent). We analysed the correlation between spot coverage, rotation and the amplitude of light variation, and found spot coverage on slow rotators (Ro > 0.1) increases with decreasing Rossby number Ro. Interestingly, we detected a saturation-like feature for spot coverage in fast rotators with a saturation level of 40-50 per cent. In addition, the spot distribution in hotter fast rotators is more symmetrical compared to slow rotators. More interestingly, we detected a large spot coverage in many M-type members with no or little light variation. In the bigger picture, these results provide important constraints for the stellar dynamos of these cool active stars.
© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
stars: activity - stars: late-type - stars: rotation - starspots - starspots
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