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.

Abstract. By pursuing the goal to find new variables in the COROT field-of-view we characterised a sample of stars located in the lower part of the instability strip. Our sample is composed of stars belonging to the disk population in the solar neighbourhood. We found that 23% of the stars display multiperiodic light variability up to a few mmag in amplitude, i.e., easily detectable on a single night of photometry. uvbyβ photometry fixed most of the variables in the middle of the instability strip and high-resolution spectroscopy established that they have v sin i > 100 km s −1 . An analysis of the Rodríguez & Breger (2001) sample (δ Sct stars in the whole Galaxy) shows slightly different features, i.e., most δ Sct stars have a 0.05-mag redder (b − y) 0 index and lower v sin i values. Additional investigation in the open cluster NGC 6633 confirms the same incidence of variability, i.e., around 20%. The wide variety of pulsational behaviours of δ Sct stars (including unusual objects such as a variable beyond the blue edge or a rapidly rotating high-amplitude pulsator) makes them very powerful asteroseismic tools to be used by COROT. Being quite common among bright stars, δ Sct stars are suitable targets for optical observations from space.

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Abstract. We present in this paper new uvbyβ photometry of eight stars suspected to be γ Doradus variables according to Handler & Kaye (2000). The new observational material has been analyzed and previously published data re-analyzed by means of an objective period search technique, based on the least-squares algorithm, called Multifre (Bossi & Nuñez 2002). We found evidence for the inclusion of seven of these stars in the list of recognized γ Doradus variables.

Abstract. We discuss new photometric data collected on the γ Dor variables HD 224945 and HD 224638. Multiperiodicity was detected in both stars, thanks to the clear spectral window of a multisite campaign that involved five observatories. HD 224945 shows the shortest period among the γ Dor stars, i.e., 0.3330 d. The pulsation behaviour is very different: HD 224945 displays a set of frequencies spread over an interval much larger than that of HD 224638. We clearly found evidence for amplitude variations in the excited modes by comparing data from different years. HD 224945 and HD 224638 are among the best examples of γ Dor stars that show multimode pulsations, which make them very interesting from an asteroseismological point of view.