8,738 research outputs found
Time-resolved multicolour photometry of bright B-type variable stars in Scorpius
The first two of a total of six nano-satellites that will constitute the
BRITE-Constellation space photometry mission have recently been launched
successfully. In preparation for this project, we carried out time-resolved
colour photometry in a field that is an excellent candidate for BRITE
measurements from space. We acquired 117 h of Stromgren uvy data during 19
nights. Our targets comprised the Beta Cephei stars Kappa and Lambda Sco, the
eclipsing binary Mu 1 Sco, and the variable super/hypergiant Zeta 1 Sco. For
Kappa Sco, a photometric mode identification in combination with results from
the spectroscopic literature suggests a dominant (l, m) = (1, -1) Beta
Cephei-type pulsation mode of the primary star. The longer period of the star
may be a rotational variation or a g-mode pulsation. For Lambda Sco, we recover
the known dominant Beta Cephei pulsation, a longer-period variation, and
observed part of an eclipse. Lack of ultraviolet data precludes mode
identification for this star. We noticed that the spectroscopic orbital
ephemeris of the closer pair in this triple system is inconsistent with eclipse
timings and propose a refined value for the orbital period of the closer pair
of 5.95189 +/- 0.00003 d. We also argue that the components of the Lambda Sco
system are some 30% more massive than previously thought. The binary light
curve solution of Mu 1 Sco requires inclusion of the irradiation effect to
explain the u light curve, and the system could show additional low amplitude
variations on top of the orbital light changes. Zeta 1 Sco shows long-term
variability on a time scale of at least two weeks that we prefer to interpret
in terms of a variable wind or strange mode pulsations.Comment: 7 pages, 7 figures, 3 Tables, accepted by A&
Asteroseismology and evolution of EHB stars
The properties of the Extreme Horizontal Branch stars are quite well
understood, but much uncertainty surrounds the many paths that bring a star to
this peculiar configuration. Asteroseismology of pulsating EHB stars has been
performed on a number of objects, bringing us to the stage where comparisons of
the inferred properties with evolutionary models becomes feasible. In this
review I outline our current understanding of the formation and evolution of
these stars, with emphasis on recent progress. The aim is to show how the
physical parameters derived by asteroseismology can enable the discrimination
between different evolutionary models.Comment: 13 pages, 6 figures, invited review to appear in Communications in
Asteroseismology vol.159, "Proceedings of the JENAM 2008 Symposium No 4:
Asteroseismology and Stellar Evolution
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