Location of the known DBV stars on the T_eff–log g diagram (black star symbols) according to the compilation by Córsico et al. (2019). The DB white dwarf evolutionary tracks are depicted with different colors according to the stellar mass. Stellar masses are in solar units. The location of TIC 257459955 as given by spectroscopy according to Voss et al. (2007) and Rolland et al. (2018) are highlighted with black and blue circles and error bars. The stellar mass derived from linear interpolation results using the data from Voss et al. (2007), and employing the data from Rolland et al. (2018).