arXiv subjects

Alexios Liakos

Publications and source records attributed to Alexios Liakos.

At least 37 records · Page 2Linked to original sources

arXiv2016

Poetry in Motion: Asteroseismology of Delta Scuti Stars in Binaries using Kepler Data

The results of our six year systematic observational survey on candidate eclipsing binaries with a delta Sct component are briefly presented. A new catalogue for this kind of systems as well as the properties of their delta Sct members are also presented. The comparison between the components-pulsators and the single delta Sct stars shows that both the evolution and the pulsating properties differ significantly. Finally, we introduce the new era of studying stellar pulsations using high accuracy data from Kepler mission and emphasizing the great opportunities that are now opened for a deep knowledge of the properties of stellar pulsations.

astro-ph.SR↗

arXiv2015

WASP-135b: a highly irradiated, inflated hot Jupiter orbiting a G5V star

We report the discovery of a new transiting planet from the WASP survey. WASP-135b is a hot Jupiter with a radius of 1.30 pm 0.09 Rjup, a mass of 1.90 pm 0.08 Mjup and an orbital period of 1.401 days. Its host is a Sun-like star, with a G5 spectral type and a mass and radius of 0.98 pm 0.06 Msun and 0.96 pm 0.05 Rsun respectively. The proximity of the planet to its host means that WASP-135b receives high levels of insolation, which may be the cause of its inflated radius. Additionally, we find weak evidence of a transfer of angular momentum from the planet to its star.

astro-ph.EP↗

arXiv2015

The Absolute Parameters of The Detached Eclipsing Binary V482 Per

We present the results of the spectroscopic, photometric and orbital period variation analyses of the detached eclipsing binary \astrobj{V482~Per}. We derived the absolute parameters of the system (M$_{1}$ = 1.51 M$_{\odot}$, M$_{2}$ = 1.29 M$_{\odot}$, R$_{1}$ = 2.39 R$_{\odot}$, R$_{2}$ = 1.45 R$_{\odot}$, L$_{1}$ = 10.15 L$_{\odot}$, L$_{2}$ = 3.01 L$_{\odot}$) for the first time in literature, based on an analysis of our own photometric and spectroscopic observations. We confirm the nature of the variations observed in the system's orbital period, suggested to be periodic by earlier works. A light time effect due to a physically bound, star-sized companion (M$_{3}$ = 2.14 M$_{\odot}$) on a highly eccentric (e = 0.83) orbit, seems to be the most likely cause. We argue that the companion can not be a single star but another binary instead. We calculated the evolutionary states of the system's components, and we found that the primary is slightly evolving after the Main Sequence, while the less massive secondary lies well inside it.

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arXiv2015

Binaries with a $δ$ Scuti component: Results from a long term observational survey, updated catalogue and future prospects

Results from a six year systematic observational survey on candidate eclipsing binaries with a $δ$ delta Sct component are presented. More than a hundred systems with component(s) of A-F spectral types were observed in the frame of this survey in order to be checked for possible pulsational behaviour. The 14% (13 cases) of the currently known such systems were discovered during this survey. Using all the available information from the literature, an updated list with all the currently known systems of this type is presented, while possible correlations between their pulsational and binarity properties are discussed.

astro-ph.SR↗

arXiv2014

First frequency analysis for three new members of the group of eclipsing binaries with a pulsating component

We present the first light curves and pulsation analysis results for V729 Aql and two newly discovered eclipsing binaries, namely USNO-A2.0 0975-17281677 and USNO-A2.0 1200-03937339. Frequency search was applied on the residuals of their light curves and the results showed that their primary components pulsate in multiperiodic modes and lie well inside the frequency and temperature range of ? delta Scuti stars. Moreover, for USNO-A2.0 1200-03937339 two frequencies inside the gamma Dor frequency range were also detected, but their origin is discussed. The photometric models of USNO-A2.0 1200-03937339 and V729 Aql are also presented, while their absolute parameters as well as the evolutionary status of their components were roughly estimated.

astro-ph.SR↗

arXiv2014

The \b{eta} Lyrae-Type Eclipsing Binary EG Cep: New BVRI Photometry and Modelling

New BVRI CCD observations of the semi-detached eclipsing binary EG Cep are presented. The observed light curves are analyzed with the Wilson-Devinney program and new geometrical and photometric elements are derived. These elements are used to compute the physical parameters of the system in order to study its evolutionary status.

astro-ph.SR↗

arXiv2014

The contact system DF Hya revisited

New BVRI CCD photometric observations of the contact system DF Hya have been obtained. The light curves were analyzed with the Wilson-Devinney code and new geometric and photometric elements were derived. Moreover, the light curve solution, with the assumption of a third light in the system, revealed the existence of a tertiary component around the eclipsing pair. The present results are compared with those of other recent studies.

astro-ph.SR↗

arXiv2014

Updated analysis for the system V1464 Aql

New BVRI light curves of the system V1464 Aql (ellipsoidal variable with a delta Scuti component) were obtained. Using these observations and taking into account previous studies of the system, its light curve model was reproduced and the pulsation frequencies of the delta Scuti component were recalculated. Moreover, the derived parameters were used to estimate the evolutionary status of both components.

astro-ph.SR↗

arXiv2014

Photometry and spectroscopy of the newly discovered eclipsing binary GSC 4589-2999

New CCD light curves of the recently detected eclipsing variable GSC 4589-2999 were obtained and analysed using the Wilson-Deninney code. Spectroscopic observations of the system allowed the spectral classification of the components and the determination of their radial velocities. The physical properties and absolute parameters of the components and an updated ephemeris of the system are given.

astro-ph.SR↗

arXiv2014

The Light-Time Effect in the Eclipsing Binaries GK Cep and VY Cet

New times of minima of the eclipsing binaries GK Cep and VY Cet, obtained at the Observatory of the University of Athens, have been used together with all reliable timings found in the literature in order to study the period variation and search for the presence of third body in the systems.

astro-ph.SR↗

arXiv2014

A comprehensive study of six Algol type binaries

CCD light curves of the Algol type eclipsing binaries DP Cep, AL Gem, FG Gem, UU Leo, CF Tau and AW Vul were analysed using the Wilson-Deninney code and new geometric and absolute parameters were derived. Due to cyclic apparent orbital period changes of the systems, probably caused by the Light-Time Effect, the contribution of a third light was taken into account in the light curve solution. All the reliable timings of minima found in the literature were used to study the period variations and search for the presence of a tertiary component in the systems. A comparison between the parameters of the third body derived from the light curve and orbital period analyses is also discussed. Moreover, the absolute parameters of the eclipsing binary components were also used to determine their current evolutionary state.

astro-ph.SR↗

arXiv2014

A photometric study of the neglected eclipsing binaries: V405 Cep, V948 Her, KR Mon and UZ Sge

CCD multi-band light curves of the neglected eclipsing binaries V405 Cep, V948 Her, KR Mon and UZ Sge were obtained and analysed using the Wilson-Devinney code. New geometric and absolute parameters were derived and used to determine their current evolutionary state. V405 Cep, V948 Her and KR Mon are detached systems with their components in almost the same evolutionary stage. UZ Sge is a classical Algol system with a tertiary companion around it. Moreover, since the systems V405 Cep, V948 Her and UZ Sge contain an early type component, their light curves were examined for possible pulsation behaviour.

astro-ph.SR↗

arXiv2014

A fresh insight into the evolutionary status and third body hypothesis of the eclipsing binaries AD Andromedae, AL Camelopardalis, and V338 Herculis

Aims: We aim to derive the absolute parameters of the components of AD And, AL Cam, and V338 Her, interpret their orbital period changes and discuss their evolutionary status. Methods: New and complete multi-filter light curves of the eclipsing binaries AD And, AL Cam, and V338 Her were obtained and analysed with modern methods. Using all reliably observed times of minimum light, we examined orbital period irregularities using the least squares method. In addition, we acquired new spectroscopic observations during the secondary eclipses for AL Cam and V338 Her. Results: For AL Cam and V338 Her, we derive reliable spectral types for their primary stars. Statistical checks of orbital period analysis for all systems are very reassuring in the cases of V338 Her and AD And, although less so for AL Cam. The LIght-Time Effect (LITE) results are checked by inclusion of a third light option in the photometric analyses. Light curve solutions provide the means to calculate the absolute parameters of the components of the systems and reliably estimate their present evolutionary status. Conclusions: AL Cam and V338 Her are confirmed as classical Algols of relatively low mass in similar configurations. Unlike AL Cam, however, V338 Her is still transferring matter between its components, raising interest in the determinability of the evolutionary histories of Algols. AD And is found to be a detached system in which both close stars are of age ~109 yr and is probably a "non-classical" young triple, at an interesting stage of its dynamical evolution.

astro-ph.SR↗

arXiv2014

Survey for δ Sct components in eclipsing binaries and new correlations between pulsation frequency and fundamental stellar characteristics

CCD observations of 68 eclipsing binary systems, candidates for containing δ Scuti components, were obtained. Their light curves are analysed using the PERIOD04 software for possible pulsational behaviour. For the systems QY Aql, CZ Aqr, TY Cap, WY Cet, UW Cyg, HL Dra, HZ Dra, AU Lac, CL Lyn and IO UMa, complete light curves were observed due to the detection of a pulsating component. All of them, except QY Aql and IO UMa, are analysed with modern astronomical softwares in order to determine their geometrical and pulsational characteristics. Spectroscopic observations of WY Cet and UW Cyg were used to estimate the spectral class of their primary components, while for HZ Dra radial velocities of its primary were measured. O - C diagram analysis was performed for the cases showing peculiar orbital period variations, namely CZ Aqr, TY Cap, WY Cet and UW Cyg, with the aim of obtaining a comprehensive picture of these systems. An updated catalogue of 74 close binaries including a δ Scuti companion is presented. Moreover, a connection between orbital and pulsation periods, as well as a correlation between evolutionary status and dominant pulsation frequency for these systems, is discussed.

astro-ph.SR↗

arXiv2014

A new photometric and spectroscopic study of the eclipsing binaries CC Her and CM Lac: Physical parameters and evolutionary status

New complete light and radial velocities curves were obtained for the eclipsing binaries CC Her and CM Lac. The data are analysed with modern techniques in order to derive the physical parameters of the systems and study their present evolutionary status. We found that CC Her is a classical Algol type binary, while CM Lac is a detached system with two Main Sequence stars in asynchronous orbit.

astro-ph.SR↗

arXiv2014

The oEA stars QY Aql, BW Del, TZ Dra, BO Her and RR Lep: Photometric analysis, frequency search and evolutionary status

New and complete multi-band light curves of the oEA stars QY Aql, BW Del, TZ Dra, BO Her and RR Lep were obtained and analysed with the Wilson-Devinney code. The light curves residuals were further analysed with the Fourier method in order to derive the pulsation characteristics of the oscillating components. All the reliable observed times of minimum light were used to examine orbital period irregularities. The orbital period analyses revealed secular changes for QY Aql and BW Del, while the Light-Time Effect seems to be the best explanation for the cyclic period changes in TZ Dra and BO Her. RR Lep has a rather steady orbital period. Light curve solutions provided the means to calculate the absolute parameters of the components of the systems, which subsequently were used to make an estimate of their present evolutionary status.

astro-ph.SR↗

arXiv2013

Asteroseismic Investigation of two Algol-type systems V1241 Tau and GQ Dra

We present new photometric observations of eclipsing binary systems V1241 Tau and GQ Dra. We use the following methodology: Initially, WD code is applied to the light curves, in order to determine the photometric elements of the systems. Then the residuals are analysed using Fourier Transformation techniques. The results show that one frequency can be barely attributed to the residual light variation of V1241 Tau, while there is no evidence of pulsation on the light curve of GQ Dra.

astro-ph.SR↗

arXiv2011

Light Curve and orbital period analysis of the eclipsing binary AT Peg

CCD photometric observations of the Algol-type eclipsing binary AT Peg have been obtained. The light curves are analyzed with modern techniques and new geometric and photometric elements are derived. A new orbital period analysis of the system, based on the most reliable timings of minima found in the literature, is presented and apparent period modulations are discussed with respect to the Light-Time effect (LITE) and secular changes in the system. The results of these analyses are compared and interpreted in order to obtain a coherent view of the system's behaviour.

astro-ph.SR↗