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Asteroseismological studies of three β Cephei stars: IL Vel, V433 Car and KZ Mus
We have acquired between 127 and 150 h of time-resolved multicolourphotometry for each of the three β Cephei stars IL Vel, V433 Carand KZ Mus over a time-span of 4 months from two observatories. Allthree objects are multiperiodic with at least three modes of pulsation.Mode identification from the relative colour amplitudes is performed. Weobtain 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 fastrotator (v sin i= 240 km s-1), whereas the other two havemoderate v sin i (65 and 47 km s-1, respectively).We performed model calculations using the Warsaw-New Jersey stellarevolution and pulsation code. We find that IL Vel is an object of about12 Msolar in the second half of its main-sequenceevolutionary track. Its two dipole modes are most probably rotationallysplit components of the mode originating as p1 on thezero-age main sequence; one of these modes is m= 0. V433 Car issuggested to be an unevolved 13-Msolar star just entering theβ Cephei instability strip. KZ Mus seems less massive (~12.7Msolar) and somewhat more evolved, and its radial mode isprobably the fundamental one. In this case its quadrupole mode would bethe one originating as g1, and its dipole mode would bep1.Two of our photometric comparison stars also turned out to be variable.HD 90434 is probably a new slowly pulsating B-type star, the dominantmode of which is a dipole, whereas the variability of HD 89768 seems tobe a result of binarity.It is suggested that mode identification of slowly rotating βCephei stars based on photometric colour amplitudes is reliable; weestimate that a relative accuracy of 3 per cent in the amplitudes issufficient for unambiguous identifications. Owing to the good agreementof our theoretical and observational results we conclude that theprospects for asteroseismology of multiperiodic slowly rotating βCephei stars are good.
| Five-colour photometry of early-type stars in the direction of galactic X-ray sources
The results of five-color (Walraven system) photometry of 551 O- andB-type stars located in 17 fields of a few square degrees aroundgalactic X-ray sources are presented. From a comparison ofreddening-free combinations of color indices with theoretical values,calculated for model atmospheres of Kurucz (1979), effective temperatureand surface gravity for these stars are derived. In addition theirabsolute magnitude are determined by combining these parameters with theresults of evolutionary calculations of massive stars. These effectivetemperatures are in good agreement with the temperature scale ofBohm-Vitense (1981) for stars of luminosity classes II to V. For thesupergiants the effective temperatures are about 40 percent higher. Forstars of luminosity classes III to V the absolute magnitudes agree wellwith the results of independent luminosity calibrations of spectraltypes, but for brighter stars they deviate systematically. Thephotometric data are also used to study the interstellar reddening inthe direction of the X-ray sources.
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