The γ Dor variable HR 8799: results from a multisite campaign

Abstract

In this paper, we present the results of a multisite photometric campaign devoted to the γ Doradus type variable HR 8799. From Johnson and Strömgren data, we were able to identify three independent frequencies (f1 = 1.9791 cycle d−1, f2 = 1.7268 cycle d−1 and f3 = 1.6498 cycle d−1) as well as another signal, which we are able to identify as the coupling term between two of the frequencies (f4 = f1 − f2 = 0.2479 cycle d−1). These four frequencies are able to account for all of the observed variations down to the 1σ significance level. We discuss another possible interpretation of these frequencies using a model of quasi-stochastic amplitude modulation. In this scenario, we are able to show that HR 8799 might be pulsating with two independent frequencies, one of which undergoes amplitude modulation similar to other γ Dor objects. In addition, we discuss a preliminary mode identification based on the observed colour curves. Finally, 18 simultaneous, high-resolution echelle spectra were collected on two nights and we qualitatively compare the radial velocities from these data with our photometry.