Asteroseismological studies of three Beta Cephei stars: IL Vel, V433 Car and KZ Mus

We have acquired between 127 and 150 h of time-resolved multicolour photometry for each of the three Beta Cephei stars IL Vel, V433 Car and KZ Mus over a time span of four months from two observatories. All three objects are multiperiodic with at least three modes of pulsation. Mode identification from the relative colour amplitudes is performed. We obtain unambiguous results for the two highest-amplitude modes of IL Vel (both are l=1) and the three strongest modes of KZ Mus (l=2,0 and 1), but none for V433 Car. Spectroscopy shows the latter star to be a fast rotator (v sin i = 240 km/s), whereas the other two have moderate v sin i (65 and 47 km/s, respectively). We performed model calculations with the Warsaw-New Jersey stellar evolution and pulsation code. We find that IL Vel is an object of about 12 Msun in the second half of its main sequence evolutionary track. Its two dipole modes are most likely rotationally split components of the mode originating as p1 on the ZAMS; one of these modes is m=0. V433 Car is suggested to be an unevolved 13 Msun star just entering the Beta Cephei instability strip. KZ Mus seems less massive (about 12.7 Msun) and somewhat more evolved, and its radial mode is probably the fundamental one. In this case its quadrupole mode would be the one originating as g1, and its dipole mode would be p1. It is suggested that mode identification of slowly rotating Beta Cephei stars based on photometric colour amplitudes is reliable; we estimate that a relative accuracy of 3% in the amplitudes is sufficient for unambiguous identifications. Due to the good agreement of our theoretical and observational results we conclude that the prospects for asteroseismology of multiperiodic slowly rotating Beta Cephei star are good.Comment: 16 pages, 16 figures, MNRAS, in pres

A multisite photometric study of two unusual Beta Cep stars: the magnetic V2052 Oph and the massive rapid rotator V986 Oph

We report a multisite photometric campaign for the Beta Cep stars V2052 Oph and V986 Oph. 670 hours of high-quality differential photoelectric Stromgren, Johnson and Geneva time-series photometry were obtained with eight telescopes on five continents during 182 nights. Frequency analyses of the V2052 Oph data enabled the detection of three pulsation frequencies, the first harmonic of the strongest signal, and the rotation frequency with its first harmonic. Pulsational mode identification from analysing the colour amplitude ratios confirms the dominant mode as being radial, whereas the other two oscillations are most likely l=4. Combining seismic constraints on the inclination of the rotation axis with published magnetic field analyses we conclude that the radial mode must be the fundamental. The rotational light modulation is in phase with published spectroscopic variability, and consistent with an oblique rotator for which both magnetic poles pass through the line of sight. The inclination of the rotation axis is 54o <i< 58o and the magnetic obliquity 58o <beta< 66o. The possibility that V2052 Oph has a magnetically confined wind is discussed. The photometric amplitudes of the single oscillation of V986 Oph are most consistent with an l=3 mode, but this identification is uncertain. Additional intrinsic, apparently temporally incoherent, light variations of V986 Oph are reported. Different interpretations thereof cannot be distinguished at this point, but this kind of variability appears to be present in many OB stars. The prospects of obtaining asteroseismic information for more rapidly rotating Beta Cep stars, which appear to prefer modes of higher l, are briefly discussed.Comment: 12 pages, 8 figures, MNRAS, in pres

Asteroseismology of the Beta Cephei star Nu Eridani: photometric observations and pulsational frequency analysis

We undertook a multisite photometric campaign for the Beta Cephei star Nu Eridani. More than 600 hours of differential photoelectric uvyV photometry were obtained with 11 telescopes during 148 clear nights. The frequency analysis of our measurements shows that the variability of Nu Eri can be decomposed into 23 sinusoidal components, eight of which correspond to independent pulsation frequencies between 5 - 8 c/d. Some of these are arranged in multiplets, which suggests rotational m-mode splitting of nonradial pulsation modes as the cause. If so, the rotation period of the star must be between 30 - 60 d. One of the signals in the light curves of Nu Eri has a very low frequency of 0.432 c/d. It can be a high-order combination frequency or, more likely, an independent pulsation mode. In the latter case Nu Eri would be both a Beta Cephei star and a slowly pulsating B (SPB) star. The photometric amplitudes of the individual pulsation modes of Nu Eri appear to have increased by about 20 per cent over the last 40 years. So do the amplitudes of the dominant combination frequencies of the star. Among the latter, we only could identify sum frequencies with certainty, not difference frequencies, which suggests that neither light-curve distortion in its simplest form nor resonant mode coupling are their single cause. One of our comparison stars, Mu Eridani, turned out to be variable with a dominant time scale of 1.62 d. We believe that it is either an SPB star just leaving its instability strip or that its variations are of rotational origin.Comment: 10 pages, 5 figure

The d Scuti star FG Vir. V. The 2002 photometric multisite campaign

Astronomy and Astrophysics, v. 419, n. 2, p. 695-701, 2004. http://dx.doi.org/10.1051/0004-6361:20035830International audienc