Discovery and asteroseismological analysis of a new pulsating DB white dwarf star, PG 2246+121

We report 36.6h of time-resolved CCD photometry of the DB white dwarf star PG 2246+121 and the discovery that it is a new pulsating variable. Analysis of our compact single-site data set allowed the detection of three mode mu ltiplets, two triplets at 256 and 329 s, respectively, and one doublet at 2 86 s. The frequency splitting within those structures is exactly the same w ithin the length and accuracy of our data set. We argue that these multiplets are the result of non-radial g-mode pulsatio ns, most probably of spherical degree l = 1, which then yields a formal ste llar rotation period of 2.00 +/- 0.12 d. We suggest that the excited modes are three consecutive radial overtones of order 3-7, most likely k = 4, 5, 6. This discovery's impact on the understanding of pulsating DB white dwarf s is discussed.