42 research outputs found
Discovery of Delta Scuti variables in eclipsing binary systems II.Southern TESS field search
The presence of pulsating stars in eclipsing binary systems (EBs) makes these
objects significant since they allow us to investigate the stellar interior
structure and evolution. Different types of pulsating stars could be found in
EBs such as Delta Scuti variables. Delta Scuti stars in EBs have been known for
decades and the increasing number of such systems is important for
understanding pulsational structure. Hence, in this study, a research was
carried out on the southern TESS field to discover new Delta Scuti stars in
EBs. We produced an algorithm to search for detached and semi-detached EBs
considering three steps; the orbital period (P)'s harmonics in the
Fourier spectrum, skewness of the light curves, and classification of
\textsc{UPSILON} program. If two of these steps classify a system as an EB, the
algorithm also identifies it as an EB. The TESS pixel files of targets were
also analyzed to see whether the fluxes are contaminated by other systems. No
contamination was found. We researched the existence of pulsation through EBs
with a visual inspection. To confirm Delta Scuti-type oscillations, the binary
variation was removed from the light curve, and residuals were analyzed.
Consequently, we identified 42 Delta Scuti candidates in EBs. The P,
, and M of systems were calculated. Their positions on the H-R diagram
and the known orbital-pulsation period relationship were analyzed. We also
examined our targets to find if any of them show frequency modulation with the
orbital period and discovered one candidate of tidally tilted pulsators.Comment: Published in MNRA
Kepler Binary Stars in NGC 6819 Open Cluster: KIC 5113146 and KIC 5111815
In this study, investigation of two double-lined binary stars KIC 5113146 and
KIC 5111815 in NGC 6819 is presented based on both photometric and
spectroscopic data. Simultaneous analysis of light and radial velocity curves
was made and the absolute parameters of the systems' components were determined
for the first time. We find that both systems have F-type main-sequence
components. The masses and radii were found to be ,
and ,
for the primary and secondary components of KIC
5113146; , and
, for components of
KIC 5111815, respectively. Evolutionary status of the components was evaluated
based on the MESA evolutionary tracks and isochrones. The ages of the KIC
5111815 and KIC 5113146 were derived to be about Gyr and
Gyr, respectively. Photometric distances were calculated to be
pc for KIC 5113146 and pc for KIC 5111815. The
results obtained in this study, astrometric data and researches in the
literature reveal that both KIC 5113146 and KIC 5111815 systems are the most
likely member of NGC 6819.Comment: 26 pages, including 7 figures and 4 tables, accepted for publication
in Astronomical Journa
Comprehensive spectroscopic and photometric study of pulsating eclipsing binary star AI Hya
The pulsating eclipsing binaries are remarkable systems that provide an
opportunity to probe the stellar interior and to determine the fundamental
stellar parameters precisely. Especially the detached eclipsing binary systems
with (a) pulsating component(s) are significant objects to understand the
nature of the oscillations since the binary effects in these systems are
negligible. Recent studies based on space data have shown that the pulsation
mechanisms of some oscillating stars are not completely understood. Hence,
comprehensive studies of a number of pulsating stars within detached eclipsing
binaries are important. In this study, we present a detailed analysis of the
pulsating detached eclipsing binary system AI Hya which was studied by two
independent groups with different methods. We carried out a spectroscopic
survey to estimate the orbital parameters via radial velocity measurements and
the atmospheric parameters of each binary component using the composite and/or
disentangled spectra. We found that the more luminous component of the system
is a massive, cool and chemically normal star while the hotter binary component
is a slightly metal-rich object. The fundamental parameters of AI Hya were
determined by the analysis of binary variations and subsequently used in the
evolutionary modelling. Consequently, we obtained the age of the system as 850
20 Myr and found that both binary components are situated in the Delta
Scuti instability strip. The frequency analysis revealed pulsation frequencies
between the 5.5 - 13.0 d and we tried to estimate which binary component
is the pulsating one. However, it turned out that those frequencies could
originate from both binary components.Comment: Accepted for publication in MNRA
Spectroscopic Survey of {\gamma} Doradus Stars I. Comprehensive atmospheric parameters and abundance analysis of {\gamma} Doradus stars
We present a spectroscopic survey of known and candidate \,Doradus
stars. The high-resolution, high signal-to-noise spectra of 52 objects were
collected by five different spectrographs. The spectral classification,
atmospheric parameters (\teff, , ), and chemical
composition of the stars were derived. The stellar spectral and luminosity
classes were found between G0-A7 and IV-V, respectively. The initial values for
\teff\ and \logg\ were determined from the photometric indices and spectral
energy distribution. Those parameters were improved by the analysis of hydrogen
lines. The final values of \teff, \logg\ and were derived from the iron
lines analysis. The \teff\ values were found between 6000\,K and 7900\,K, while
\logg\,values range from 3.8 to 4.5\,dex. Chemical abundances and
values were derived by the spectrum synthesis method. The values were
found between 5 and 240\,km\,s. The chemical abundance pattern of
\,Doradus stars were compared with the pattern of non-pulsating stars.
It turned out that there is no significant difference in abundance patterns
between these two groups. Additionally, the relations between the atmospheric
parameters and the pulsation quantities were checked. A strong correlation
between the and the pulsation periods of \,Doradus variables
was obtained. The accurate positions of the analysed stars in the H-R diagram
have been shown. Most of our objects are located inside or close to the blue
edge of the theoretical instability strip of \,Doradus.Comment: 18 pages, 13 figure
Radio and optical intra-day variability observations of five blazars
We carried out a pilot campaign of radio and optical band intra-day
variability (IDV) observations of five blazars (3C66A, S5 0716+714, OJ287,
B0925+504, and BL Lacertae) on December 18--21, 2015 by using the radio
telescope in Effelsberg (Germany) and several optical telescopes in Asia,
Europe, and America. After calibration, the light curves from both 5 GHz radio
band and the optical R band were obtained, although the data were not smoothly
sampled over the sampling period of about four days. We tentatively analyse the
amplitudes and time scales of the variabilities, and any possible periodicity.
The blazars vary significantly in the radio (except 3C66A and BL Lacertae with
only marginal variations) and optical bands on intra- and inter-day time
scales, and the source B0925+504 exhibits a strong quasi-periodic radio
variability. No significant correlation between the radio- and optical-band
variability appears in the five sources, which we attribute to the radio IDV
being dominated by interstellar scintillation whereas the optical variability
comes from the source itself. However, the radio- and optical-band variations
appear to be weakly correlated in some sources and should be investigated based
on well-sampled data from future observations.Comment: 6 pages, 6 figures, accepted by MNRA