2 The new sdBV stars

Short period oscillations in the sdB stars HS0039+4302, HS0444+0408, HS1824+5745 and HS2151+0857 have been discovered by time-series photometry at the NOT. We have searced the SIMBAD catalouge for any previous observations and classifications of these stars, and for HS0444+0408 and HS1824+5745 the search comes out empty. For the two other stars, the results are as follows.

2.1 HS0039+4302

The SIMBAD catalogue lists a few registrations that match the coordinates of HS0039+4302. Both the Balloon far-ultraviolet survey (Bixler et al. 1991) and the first Byurakan spectral sky survey (Abrahamian et al. 1990) list this object as a UV-excess object, with catalogue numbers of Balloon84041013 and FBS0039+430 = FBSB210, respectively. No further references have been found in the literature.

2.2 HS2151+0857

A search in the SIMBAD catalogue around the coordinates of HS2151+0857 reveals that the sdB star PG2151+089 should be less than two arcminutes away. Our images reveal no other blue stars in this region, so we conclude that the coordinates of PG2151+089 are wrong and that this is actually the same star. The PG catalogue B-band magnitude of 16.31 (Green et al. 1986) is also in accordance with the value B=16.5, estimated from the Schmidt plates. According to SIMBAD, PG2151+089 is listed in the Catalogue of spectroscopically identified hot subdwarf stars (Kilkenny et al. 1988).

Figure 2: Comparison of the four newly discovered sdBVs to previously known ones in the ( $T_{\rm eff}$, log g) plane. The position of the Zero Age Extreme Horizontal Branch (ZAEHB), the Terminal Age Extreme Horizontal Branch (TAEHB), the Helium Main Sequence (HeMS) and evolutionary tracks for EHB stars (Dorman et al. 1993) are also shown.