203 research outputs found
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
A cautionary tale of interpreting O-C diagrams: period instability in a classical RR Lyr Star Z CVn mimicking as a distant companion
We present a comprehensive study of Z CVn, an RR Lyrae star that shows
long-term cyclic variations of its pulsation period. A possible explanation
suggested from the shape of the O-C diagram is the light travel-time effect,
which we thoroughly examine. We used original photometric and spectroscopic
measurements and investigated the period evolution using available maximum
times spanning more than one century. If the binary hypothesis is valid, Z CVn
orbits around a black hole with minimal mass of
on a very wide ( years) and eccentric orbit (). We
discuss the probability of a formation of a black hole-RR Lyrae pair and,
although we found it possible, there is no observational evidence of the black
hole in the direction to Z CVn. However, the main objection against the binary
hypothesis is the comparison of the systemic radial velocity curve model and
spectroscopic observations that clearly show that Z CVn cannot be bound in such
a binary. Therefore, the variations of pulsation period are likely intrinsic to
the star. This finding represents a discovery/confirmation of a new type of
cyclic period changes in RR Lyrae stars. By the analysis of our photometric
data, we found that the Blazhko modulation with period of 22.931 d is strongly
dominant in amplitude. The strength of the phase modulation varies and is
currently almost undetectable. We also estimated photometric physical
parameters of Z CVn and investigated their variations during the Blazhko cycle
using the Inverse Baade-Wesselink method.Comment: 15 pages, 8 tables, 9 figures, accepted for publication in MNRA
New inclination changing eclipsing binaries in the Magellanic Clouds
Context: Multiple stellar systems are unique laboratories for astrophysics.
Analysis of their orbital dynamics may reveal invaluable information about the
physical properties of the participating stars. Unfortunately, there are only a
few known and well described multiple systems, this is even more so for systems
located outside the Milky Way galaxy. A particularly interesting situation
occurs when the inner binary in a compact triple system is eclipsing. This is
because the stellar interaction, typically resulting in precession of orbital
planes, may be observable as a variation of depth of the eclipses on a long
timescale. Aims: We aim to present a novel method to determine compact triples
using publicly available photometric data from large surveys. Here we apply it
to eclipsing binaries (EBs) in Magellanic Clouds from OGLE III database.
Methods: We analyzed light curves (LCs) of 26121 LMC and 6138 SMC EBs with the
goal to identify those for which the orbital inclination varies in time.
Archival LCs of the selected systems, when complemented by our own observations
with Danish 1.54m telescope, were thoroughly analyzed using the PHOEBE program.
Time dependence of the EB's inclination was described using the theory of
orbital-plane precession. By observing the parameter-dependence of the
precession rate, we were able to constrain the third companion mass and its
orbital period around EB. Results: We identified 58 candidates of new compact
triples in Magellanic Clouds. This is the largest published sample of such
systems so far. Eight of them were analyzed thoroughly and physical parameters
of inner binary were determined together with an estimation of basic
characteristics of the third star. These data may provide important clues about
stellar formation mechanisms for objects with different metalicity than found
in our galactic neighborhood.Comment: Accepted for publication in Astronomy and Astrophysic
Surprising variations in the rotation of the chemically peculiar stars CU Virginis and V901 Orionis
CU Vir and V901 Ori belong among these few magnetic chemically peculiar stars
whose rotation periods vary on timescales of decades. We aim to study the
stability of the periods in CU Vir and V901 Ori using all accessible
observational data containing phase information. We collected all available
relevant archived observations supplemented with our new measurements of these
stars and analysed the period variations of the stars using a novel method that
allows for the combination of data of diverse sorts. We found that the shapes
of their phase curves were constant, while the periods were changing. Both
stars exhibit alternating intervals of rotational braking and acceleration. The
rotation period of CU Vir was gradually shortening until the year 1968, when it
reached its local minimum of 0.52067198 d. The period then started increasing,
reaching its local maximum of 0.5207163 d in the year 2005. Since that time the
rotation has begun to accelerate again. We also found much smaller period
changes in CU Vir on a timescale of several years. The rotation period of V901
Ori was increasing for the past quarter-century, reaching a maximum of 1.538771
d in the year 2003, when the rotation period began to decrease. A theoretically
unexpected alternating variability of rotation periods in these stars would
remove the spin-down time paradox and brings a new insight into structure and
evolution of magnetic upper-main-sequence stars.Comment: 5 pages, 3 figure
Targeting of the Plzf gene in the rat by transcription activator-like effector nuclease results in caudal regression syndrome in spontaneously hypertensive rats
Recently, it has been found that spontaneous mutation Lx (polydactyly-luxate syndrome) in the rat is determined by deletion of a conserved intronic sequence of the Plzf (Promyelocytic leukemia zinc finger protein) gene. In addition, Plzf is a prominent candidate gene for quantitative trait loci (QTLs) associated with cardiac hypertrophy and fibrosis in the spontaneously hypertensive rat (SHR). In the current study, we tested the effects of Plzf gene targeting in the SHR using TALENs (transcription activator-like effector nucleases). SHR ova were microinjected with constructs pTAL438/439 coding for a sequence-specific endonuclease that binds to target sequence in the first coding exon of the Plzf gene. Out of 43 animals born after microinjection, we detected a single male founder. Sequence analysis revealed a deletion of G that resulted in frame shift mutation starting in codon 31 and causing a premature stop codon at position of amino acid 58. The Plzftm1Ipcv allele is semi-lethal since approximately 95% of newborn homozygous animals died perinatally. All homozygous animals exhibited manifestations of a caudal regression syndrome including tail anomalies and serious size reduction and deformities of long bones, and oligo- or polydactyly on the hindlimbs. The heterozygous animals only exhibited the tail anomalies. Impaired development of the urinary tract was also revealed: one homozygous and one heterozygous rat exhibited a vesico-ureteric reflux with enormous dilatation of ureters and renal pelvis. In the homozygote, this was combined with a hypoplastic kidney. These results provide evidence for the important role of Plzf gene during development of the caudal part of a body-column vertebrae, hindlimbs and urinary system in the rat
The SERMON project: 48 new field Blazhko stars and an investigation of modulation-period distribution
Aims: We investigated 1234 fundamental mode RR Lyrae stars observed by the All Sky Automated Survey (ASAS) to identify the Blazhko (BL) effect. A sample of 1547 BL stars from the literature was collected to compare the modulation-period distribution with stars newly identified in our sample.
Methods: A classical frequency spectra analysis was performed using Period04 software. Data points from each star from the ASAS database were analysed individually to avoid confusion with artificial peaks and aliases. Statistical methods were used in the investigation of the modulation-period distribution.
Results: Altogether we identified 87 BL stars (48 new detections), 7 candidate stars, and 22 stars showing long-term period variations. The distribution of modulation periods of newly identified BL stars corresponds well to the distribution of modulation periods of stars located in the Galactic field, Galactic bulge, Large Magellanic Cloud, and globular cluster M5 collected from the literature. As a very important by-product of this comparison, we found that pulsation periods of BL stars follow Gaussian distribution with the mean period of 0.54 ± 0.07 d, while the modulation periods show log-normal distribution with centre at log (Pm [d]) = 1.78 ± 0.30 dex. This means that 99.7% of all known modulated stars have BL periods between 7.6 and 478 days. We discuss the identification of long modulation periods and show, that a significant percentage of stars showing long-term period variations could be classified as BL stars
Comparison of the electron work function, hole concentration and exciton diffusion length for P3HT and PT prepared by thermal or acid cleavage
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