Photospheric acne at the bottom of the main-sequence: Doppler images of M4.5 - M9V stars

Barnes, John; Haswell, Carole; Jeffers, Sandra; Jones, Hugh; Pavlenko, Yakiv; Lohr, Marcus and Jenkins, James (2016). Photospheric acne at the bottom of the main-sequence: Doppler images of M4.5 - M9V stars. In: The 19th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun (Feiden, Gregory ed.).

DOI: https://doi.org/10.5281/zenodo.59198

Abstract

Starspots are an important manifestation of stellar activity and yet their distribution patterns on the lowest mass stars is not well known. Time series spectra of fully convective M dwarfs taken in the red-optical with UVES reveal numerous line profile distortions which are interpreted as starspots. New Doppler images of HU Del (GJ 791.2A; M4.5V), BL Ceti (GJ 65A; M5.5V) and UV Ceti (GJ 65B; M6V) at two epochs separated by three nights are presented. We find that contrast ratios corresponding to photosphere-spot temperature differences of only 100-400 K are sufficient to model the time series spectra of M4.5V - M9V stars. Starspots are reconstructed at a range of phases and latitudes with mean spot filling factors of only a few per cent. The distribution and low-contrast of the spots/spot-groups that we recover are likely to be responsible for the low amplitude photometric variability seen in late-M dwarfs. The stability of the spot patterns in the two sets of timeseries observations enables us to measure the latitude dependent differential rotation, which we find to be consistent with zero