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.