The gamma Dor variable HD 164615: results from a multisite photometric campaign

We present in this paper the results from a multisite photometric campaign devoted to the gamma Dor variable HD 164615. During the campaign data were collected in the Johnson and Stromgren photometric systems. A first search for sinusoidal periodicities yielded a three-term solution with frequencies f(1) = 1.2328, f(2) = 1.0899 and f(3) = 2.3501 d(-1), and a long-term trend f(4) = 0.1301 d(-1). The star may therefore be multiperiodic with each frequency related to a pulsation mode. However, a further examination of the curve provided evidence that the amplitude at the instant of maximum brightness is modulated. Alternatively, HD 164615 may be a monoperiodic variable with frequency f(1) = 1.2321 d(-1), showing amplitude modulation with frequency f(4) = 0.1301 d(-1). The presence in the power spectra of the coupling terms f(2) = f(1) - f(4) and f(3) = f(1) + f(4) - 1 supports the latter interpretation. In the monoperiodic case the previously given interpretation based on a spot carried through the visible disc by rotation still holds, provided that the spot is bright and evolves on a time-scale of a few days. However, similarities with other gamma Dor stars provide indirect indication in favour of the existence of a non-radial pulsation interpretation.