5 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
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 56.5 M_{⊙} on a very wide (Porbit = 78.3 yr) and eccentric orbit (e = 0.63). We discuss the probability of the 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
Apsidal motion in eccentric eclipsing binary WW Camelopardalis
WW Camelopardalis is a relatively bright eclipsing binary system with a slightly eccentric orbit. A dozen of its new eclipse times were measured as part of our long-term observational project of eccentric eclipsing binaries. Based on a new solution of the current O – C diagram, we found for the first time an apsidal motion in good agreement with theory. Its period is about 370 ± 50 years. The determined internal structure constant is close to the theoretically expected value. The relativistic effect is significant, being about 13% of the total apsidal motion rate