6 research outputs found
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
Preparing the COROT space mission: incidence and characterisation of pulsation in the Lower Instability Strip
By pursuing the goal to find new variables in the COROT field-of-view we
characterised a sample of stars located in the lower part of the instability
strip. Our sample is composed of stars belonging to the disk population in the
solar neighbourhood. We found that 23% of the stars display multiperiodic light
variability up to few mmag of amplitude. uvbyBeta photometry fixed most of the
variables in the middle of the instability strip and high-resolution
spectroscopy established that they have vsin i>100 km/s. The comparison with
delta Sct stars in the whole Galaxy shows slightly different features, i.e.,
most delta Sct stars have a 0.05-mag redder (b-y)_0 index and lower vsin i
values. Additional investigation in the open cluster NGC 6633 confirms the same
incidence of variability, i.e., around 20%. The wide variety of pulsational
behaviours of delta Sct stars (including unusual objects such as a variable
beyond the blue edge or a rapidly rotating high-amplitude pulsator) makes them
very powerful asteroseismic tools to be used by COROT. Being quite common among
bright stars, delta Sct stars are suitable targets for optical observations
from space.Comment: 9 pages, 9 figures Accepted for publication in Astronomy &
Astrophysics, Main Journa
On the Period-Luminosity-Colour-Metallicity relation and the pulsational characteristics of lambda Bootis type stars
The group of lambda Bootis type stars comprises late B- to early F-type,
Population I objects which are basically metal weak, in particular the Fe group
elements, but with the clear exception of C, N, O and S. The present work is a
continuation of the studies by Paunzen et al. (1998, A&A, 335, 533), who
presented first results on the pulsational characteristics of the lambda Bootis
stars. Since then, we have observed 22 additional objects; we found eight new
pulsators and confirmed another one. Furthermore, new spectroscopic data
(Paunzen, 2001, A&A, 373, 633) allowed us to sort out misidentified candidates
and to add true members to the group. From 67 members of this group, only two
are not photometrically investigated yet which makes our analysis highly
representative. We have compared our results on the pulsational behaviour of
the lambda Bootis stars with those of a sample of delta Scuti type objects. We
find that at least 70% of all lambda Bootis type stars inside the classical
instability strip pulsate, and they do so with high overtone modes (Q <
0.020d). Only a few stars, if any, pulsate in the fundamental mode. Compared to
the delta Scuti stars, the cool and hot borders of the instability strip of the
lambda Bootis stars are shifted by about 25mmag, towards smaller (b-y)0. Using
published abundances and the metallicity sensitive indices of the Geneva
7-colour and Stroemgren uvbybeta systems, we have derived [Z] values which
describe the surface abundance of the heavier elements for the group members.
We find that the Period-Luminosity-Colour relation for the group of lambda
Bootis stars is within the errors identical with that of the normal delta Scuti
stars. No clear evidence for a statistically significant metallicity term was
detected.Comment: 14 pages, 8 figures, accepted by A&
Irregular amplitude variations and another abrupt period change in the δ Scuti star V 1162 Ori
We report that the intermediate amplitude δ Scuti
star V 1162 Ori has changed its main pulsational period in the course of the year
2000. This new period change falls in a
sequence of period changes observed during the last 5 years. While the
average amplitude value of all our new data, 63 mmag, fits a cyclic amplitude
variation suggested by Arentoft et al. (2001), splitting the data up in
smaller subsets discloses
significant deviations from regularity, with stretches of constant amplitude
during short intervals of time.
The new data show that the amplitude of one of the secondary frequencies,
f2, has in 3 years dropped from more than 3 mmag to now about 1 mmag,
and that the previously obtained f5
probably is a 1 d-1 alias of the real frequency. We present the newly
acquired times of minimum and maximum light as support for subsequent
observing campaigns