Stellar activity with LAMOST - I. Spot configuration in Pleiades
Abstract
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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- December 2016
- DOI:
- 10.1093/mnras/stw1923
- arXiv:
- arXiv:1608.05452
- Bibcode:
- 2016MNRAS.463.2494F
- Keywords:
-
- stars: activity;
- stars: late-type;
- stars: rotation;
- starspots;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 20 pages, 20 figures