Asteroseismology of the β Cephei star ν Eridani -: IV.: The 2003-2004 multisite photometric campaign and the combined 2002-2004 data

We report on the second multisite photometric campaign devoted to nu Eridani (nu Eri). The campaign, carried out from 2003 September 11 to 2004 February 16, was very nearly a replica of the first campaign, 2002-2003: the five telescopes and photometers we used were the same as those in the first campaign, the comparison stars and observing procedure were identical, and the numbers and time baselines of the data were comparable. For nu Eri, analysis of the new data adds four independent frequencies to the nine derived previously from the 2002-2003 data: three in the range 7.20-7.93 d(-1) and a low one, equal to 0.614 d(-1). Combining the new and the old data results in two further independent frequencies, equal to 6.7322 and 6.2236 d(-1). Altogether, the oscillation spectrum is shown to consist of 12 high and two low frequencies. The latter have u amplitudes about twice as large as the nu and y amplitudes, a signature of high radial-order g modes. Thus, we confirm the suggestion, put forward on the basis of the data of the first campaign, that nu Eri is both a beta Cephei and a slowly pulsating B (SPB) star. Nine of the 12 high frequencies form three triplets, of which two are new. The triplets represent rotationally split l = 1 modes, although in case of the smallest-amplitude one this may be questioned. Mean separations and asymmetries of the triplets are derived with accuracy sufficient for meaningful comparison with models. The first comparison star, mu Eri, is shown to be an SPB variable with an oscillation spectrum consisting of six frequencies, three of which are equidistant in period. The star is also found to be an eclipsing variable. The eclipse is a transit, probably total, the secondary is fainter than the primary by several magnitudes, and the system is widely detached. The second comparison star, xi Eri, is confirmed to be a delta Scuti variable. To the frequency of 10.8742 d(-1) seen already in the data of the first campaign, another, equal to 17.2524 d(-1), is added.