Silvotti, R × Solheim, JE Perez, JMG Heber, U Dreizler, S Edelmann, H Ostensen, Roy Kotak, R #
Astronomy and astrophysics vol:359 issue:3 pages:1068-1074
The results of two runs of time-series photometry made at the Nordic Optical Telescope clearly show that the sdB scar PG 1618+563B is a new member of the EC 14026 class of sdB pulsators. Its power spectrum shows a doublet of frequencies at about 6.95 and 7.18 mHz (P similar to 144 and 139 s respectively), which produce a modulation effect in the light curve with a beat period of about 1.2 hours. The amplitudes of the two signals are very low, not more than 2 mma. Thanks to its brightness (B=13.4), which makes PG 1618+563B one of the brightest objects of its class, we were able to observe the star also in different colours and measure its UBV pulsation amplitudes and phases. The comparison of these "nonadiabatic observables" with models may help the identification of the oscillation modes. The spectral analysis of the sdB star and the spectral classification of PG 1618+563A suggest that both stars form a wide visual binary (similar to 2500 A.U. separation), at a distance of about 680 pc from the sun.