170 research outputs found
Peculiar double-periodic pulsation in RR Lyrae stars of the OGLE collection. I. Long-period stars with dominant radial fundamental mode
We present the discovery of a new, peculiar form of double-periodic pulsation
in RR Lyrae stars. In four, long-period ( d) stars observed by the
Optical Gravitational Lensing Experiment, and classified as fundamental mode
pulsators (RRab), we detect additional, low-amplitude variability, with period
shorter than fundamental mode period. The period ratios fall in a range similar
to double-mode fundamental and first overtone RR Lyrae stars (RRd), with the
exception of one star, in which the period ratio is significantly lower and
nearly exactly equals 0.7. Although period ratios are fairly different for the
four stars, the light curve shapes corresponding to the dominant, fundamental
mode are very similar. The peak-to-peak amplitudes and amplitude ratios
(Fourier parameters and ) are among the highest observed in
RRab stars of similar period, while Fourier phases ( and
) are among the lowest observed in RRab stars.
If the additional variability is interpreted as due to radial first overtone,
then, the four stars are the most extreme RRd variables of the longest
pulsation periods known. Indeed, the observed period ratios can be well
modelled with high metallicity pulsation models. However, at such long
pulsation periods, first overtone is typically damped.
Five other candidates, with weak signature of additional variability, sharing
the same characteristics, were also detected and are briefly discussed.Comment: Accepted for publication in MNRA
Apsidal motion and light a curve solution for eighteen SMC eccentric eclipsing binaries
Aims: The Danish 1.54-meter telescope at the La Silla observatory was used
for photometric monitoring of selected eccentric eclipsing binaries located in
the Small Magellanic Cloud. The new times of minima were derived for these
systems, which are needed for accurate determination of the apsidal motion.
Moreover, many new times of minima were derived from the photometric databases
OGLE and MACHO. Eighteen early-type eccentric-orbit eclipsing binaries were
studied.
Methods: Their (O-C) diagrams of minima timings were analysed and the
parameters of the apsidal motion were obtained. The light curves of these
eighteen binaries were analysed using the program PHOEBE, giving the light
curve parameters. For several systems the additional third light also was
detected.
Results: We derived for the first time and significantly improved the
relatively short periods of apsidal motion from 19 to 142 years for these
systems. The relativistic effects are weak, up to 10% of the total apsidal
motion rate. For one system (OGLE-SMC-ECL-0888), the third-body hypothesis was
also presented, which agrees with high value of the third light for this system
detected during the light curve solution.Comment: 8 pages, 5 figures, 4 tables, plus the appendix data tables with
times of minima. Published in 2014A&A...572A..71
On the interpretation of the long-term cyclic period variations in RR Lyrae stars
Many RR Lyrae stars show long-term variations of their pulsation period, some
of them in a cyclic way. Such behaviour can be attributed to the light-travel
time effect (LTTE) caused by an unseen companion. Solutions of the LTTE often
suggest very eccentric orbits and minimal mass of the companion on the order of
several solar masses, thus, in the black hole range. We discuss the possibility
of the occurrence of the RR Lyr-black hole pairs and on the case of Z CVn
demonstrate that the LTTE hypothesis can be false in some of the binary
candidates.Comment: 5 pages, 2 figures, published in the proceedings of "The RR Lyrae
2017 Conference", Niepolomice, Poland, 17-21 September 201
Petersen Diagram Revolution
Over the recent years, the Petersen diagram for classical pulsators, Cepheids
and RR Lyr stars, populated with a few hundreds of new multiperiodic variables.
We review our analyses of the OGLE data, which resulted in the significant
extension of the known, and in the discovery of a few new and distinct forms of
multiperiodic pulsation. The showcase includes not only radial mode pulsators,
but also radial-non-radial pulsators and stars with significant modulation
observed on top of the beat pulsation. First theoretical models explaining the
new forms of stellar variability are briefly discussed.Comment: 5 pages; to be published in the proceedings of the 22nd Los Alamos
Stellar Pulsation Conference "Wide-field variability surveys: a 21st-century
perspective", San Pedro de Atacama, Chile, Nov. 28 - Dec. 2, 201
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