Astron. Astrophys. 336, 518-526 (1998)

6. Open problems

In this work we could get a few interesting results about the pulsational pattern presented by a Scuti star and about its relevance to the study of stellar structure and evolution; nevertheless, we are far from drawing an exhausive picture of the pulsational behaviour of HD 2724 as well as of other Scuti objects.

Our light curves allowed us to detect the presence of at least 10 different periodicities, determining unambiguously no more than 7 frequencies. Apparently, observational bases like our 11 high quality photometric nights at La Silla are inadequate if faced by the complex variability of these stars. The last instructive example of such complexity is provided by Breger et al. (1998), who identify 24 frequencies in the light curve of FG Vir, discovering, moreover, 8 additional promising candidate pulsational components and finding evidence of considerable amplitude variations (maybe due to beats between unresolved frequencies) affecting one of the detected periodicities in a time scale of one year. In the above mentioned paper, Breger and his collaborators show also the way to obtain this kind of results, which are basically the fruits of the largest photometric multi-site campaign devoted to date to a Scuti star.

The inadequacy of our data becomes dramatic on the spectroscopic side. In fact, although the scrutiny of our spectroscopic series led us to discover two additional high -order non-radial pulsation invisible in the light curves, the poor spectral window of these data did not even allow a reliable determination of the corresponding frequencies. Besides, blending close periodicities who could be photometrically resolved, it affected also the subsequent mode identification. Unfortunately, it is more difficult, even if not less important, to obtain satisfactory series of spectroscopic observations than photometric ones: to the delicate organizational problems of a multi-site campaign, we would have to add the hard work of elbowing our way to adequate telescopes.

We realize that an exhaustive pulsational picture of the Scuti stars might become, under these conditions, nothing more than a tantalizing dream. Nevertheless, let us end on an optimistic note: as shown, for example, just in this work, interesting results can be obtained also from incomplete patterns; besides, unexpected theoretical developments might help to simplify our task. Chandrasekhar & Ferrari (1991, 1992), for example, began to explore the exciting possibility of getting selection rules of pulsational modes through the tranfer of methods from the quantum field theory to the general-relativistic treatement of non-radial oscillations.

© European Southern Observatory (ESO) 1998

Online publication: July 20, 1998
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