The EC 14026 stars -- X. A multi-site campaign on the sdBV star PG 1605+072

Results are reported from a multi-site photometric campaign on PG 1605+072, a member of the recently discovered class of pulsating hot subdwarfs, or EC 14026 stars. The main part of the campaign covered two weeks and produced ∼ 180 h of photoelectric photometry from the five sites involved. Periodogram analysis shows that the light curve is dominated by five frequencies in the range 1.89–2.74 mHz (periods 529–365 s) with the main frequency at 2.075 76 mHz (481.75 s), though there appear to be more than 50 frequencies identifiable down to a semi-amplitude of 0.0007 (in fractional intensity) in the range 1.74–4.84 mHz (573–206 s). Compared with other pulsating sdB stars, the low gravity (log g= 5.25) and long periods indicate that the star has evolved away from the core helium-burning horizontal branch. A preliminary model of a post-horizontal-branch star with appropriate parameters yields many pulsation periods in the range 300–600 s, but detailed mode identification is not possible at present.