DETECTION OF P-MODE PULSATIONS IN THE HOT SUBDWARF B-STAR KPD-2109+4401

We report the discovery of multiperiodic luminosity variations in the hot B subdwarf KPD 2109+4401. At least five periodicities are seen in the light curve, from 182.5 to 198.4 s. The largest oscillation has an amplitude similar or equal to 8.6 mmag in white light and a period 19 6.3 s. Our model atmosphere analysis of the time-averaged optical spec trum of KPD 2109+4401 indicates that this star has T-eff similar or eq ual to 31,200 K and log g similar or equal to 5.84. A comparison with pulsation periods computed from stellar models having similar atmosphe ric parameters implies that the observed brightness variations must be identified with low-order radial and nonradial (p and f) pulsation mo des. The overall similarity of periods and derived stellar parameters shows that KPD 2109+4401 is a genuine member of the EC 14026 class, th e most recent family of pulsators uncovered in the field of asteroseis mology. We note, however, that KPD 2109+4401 is slightly but significa ntly cooler than the previously known members of this class, thus wide ning significantly the empirical instability strip. Interestingly, the ory predicts that a cooler EC 14026 pulsator (of a given surface gravi ty) should show larger excited periods, and this is indeed what KPD 21 09+4401 shows, with periods reaching values as large as 198 a, not see n previously in other pulsators of the class. We also report on the cu rrent status of our ongoing survey to search for additional EC 14026 p ulsators.