3,495 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&
Indications of a Large Fraction of Spectroscopic Binaries Among Nuclei of Planetary Nebulae
Previous work indicates that about 10% of planetary-nebula nuclei (PNNi) are
photometrically variable short-period binaries with periods of hours to a few
days. These systems have most likely descended from common-envelope (CE)
interactions in initially much wider binaries. Population-synthesis studies
suggest that these very close pairs could be the short-period tail of a much
larger post-CE binary population with periods of up to a few months. We have
initiated a radial-velocity (RV) survey of PNNi with the WIYN 3.5-m telescope
and Hydra spectrograph, which is aimed at discovering these intermediate-period
binaries. We present initial results showing that 10 out of 11 well-observed
PNNi have variable RVs, suggesting that a significant binary population may be
present. However, further observations are required because we have as yet been
unable to fit our sparse measurements with definite orbital periods, and
because some of the RV variability might be due to variations in the stellar
winds of some of our PNNi.Comment: 11 pages, 1 table, no figures. Accepted by the Astrophysical Journal
Letter
Search for sdB/WD pulsators in the Kepler FOV
In this article we present the preliminary results of an observational search
for subdwarf B and white dwarf pulsators in the Kepler field of view, performed
using the DOLORES camera attached to the 3.6m Telescopio Nazionale Galileo
(TNG).Comment: Communications in Asteroseismology, in press; 2 pages, 1 figur
The asteroseismological potential of the pulsating DB white dwarf stars CBS 114 and PG 1456+103
We have acquired 65 h of single-site time-resolved CCD photometry of the
pulsating DB white dwarf star CBS 114 and 62 h of two-site high-speed CCD
photometry of another DBV, PG 1456+103. The pulsation spectrum of PG 1456+103
is complicated and variable on time scales of about one week and could only
partly be deciphered with our measurements. The modes of CBS 114 are more
stable in time and we were able to arrive at a frequency solution somewhat
affected by aliasing, but still satisfactory, involving seven independent modes
and two combination frequencies. These frequencies also explain the discovery
data of the star, taken 13 years earlier. We find a mean period spacing of 37.1
+/- 0.7 s significant at the 98% level between the independent modes of CBS 114
and argue that they are due to nonradial g-mode pulsations of spherical degree
l=1. We performed a global search for asteroseismological models of CBS 114
using a genetic algorithm, and we examined the susceptibility of the results to
the uncertainties of the observational frequency determinations and mode
identifications (we could not provide m values). The families of possible
solutions are identified correctly even without knowledge of m. Our optimal
model suggests Teff = 21,000 K and M_* = 0.730 M_sun as well as log(M_He/M_*) =
-6.66, X_O = 0.61. This measurement of the central oxygen mass fraction implies
a rate for the ^12C(alpha,gamma)^16O nuclear reaction near S_300=180 keV b,
consistent with laboratory measurements.Comment: 10 pages, 10 embedded figures, 3 embedded tables. Accepted for
publication in MNRA
The Hvar survey for roAp stars: II. Final results (Research Note)
The 60 known rapidly oscillating Ap (roAp) stars are excellent laboratories
to test pulsation models in the presence of stellar magnetic fields. Our survey
is dedicated to search for new group members in the Northern Hemisphere. We
attempt to increase the number of known chemically peculiar stars that are
known to be pulsationally unstable. About 40 h of new CCD photometric data of
21 roAp candidates, observed at the 1m Austrian-Croatian Telescope (Hvar
Observatory) are presented. We carefully analysed these to search for
pulsations in the frequency range of up to 10mHz. No new roAp star was detected
among the observed targets. The distribution of the upper limits for roAp-like
variations is similar to that of previoius similar efforts using
photomultipliers and comparable telescope sizes. In addition to photometric
observations, we need to consolidate spectroscopic information to select
suitable targets.Comment: 8 pages, 5 figures, accepted by Astronomy & Astrophysic
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