arXiv subjects

Ekrem M. Esmer

Publications and source records attributed to Ekrem M. Esmer.

5 recordsLinked to original sources

arXiv2026

A Detailed Study of the Physical and Orbital Characteristics, and Eclipse Timing Variations of the Post Common Envelope Binary DD CrB

We present an in-depth analysis of the eclipsing binary DD CrB, composed of a B-type subdwarf primary and an M-type main-sequence secondary, with the main goal of investigating its eclipse timing variations (ETVs). Our new multi-color photometric observations, radial velocity measurements, and precise eclipse timings from TESS allow us to constrain the system parameters. The Romer delay between primary and secondary minima yields a mass ratio of $q = 0.299 \pm 0.009$, enabling robust simultaneous modeling of the light and radial velocity curves with {\sc phoebe} 2.17. By fixing the albedo of the secondary to its maximum physically plausible value (A$_2 = 1.0$), despite the degeneracy between albedo, surface temperature, and radius, we obtained a satisfactory fit, resulting in a significantly lower temperature ($T_2 \sim 2360$ K) and a radius ($R_2 \sim 0.16$ R$_\odot$) in agreement with literature values. Using the total mass of the components and the orbital size derived from this modeling, we interpret the ETVs and find them best explained by a Jupiter-mass tertiary companion on a $\sim13$-year orbit in all competing models, while the eccentric (e $\sim0.46$) models perform better in terms of fit statistics.

astro-ph.SR↗

arXiv2021

Investigation of an orbital decay and global modeling of the planet WASP-43 b

WASP-43 b is one of the most important candidates for detecting an orbital decay. We investigate pieces of evidence for this expectation as variations in its transit timings, based on the ground and space observations. The data set includes the transit observations at the TUBITAK National Observatory of Turkey and Transiting Exoplanet Survey Satellite (TESS). We present a global model of the system, based on the most precise photometry from space, ground, and archival radial velocity data. Using the homogenized data set and modeled light curves, we measure the mid-transit times for WASP-43 b. Our analysis agrees with a linear ephemeris for which we refine the light elements for future observations of the system. However, there is a negative difference between the transit timings derived from TESS data in two sectors (9 and 35) and a hint of an orbital period decrease in the entire data set. Both findings are statistically insignificant due to the short baseline of observations, which prevents us from drawing firm conclusions about the orbital decay of this ultra-short-period planet. However, assuming the effect of this decrease of the period in the planet's orbit, we derive a lower limit for the reduced tidal quality factor as Q'_* > (4.01 +_ 1.15). 10^5 from the best-fitting quadratic function. Finally, we calculate a probable rotational period for this system as 7.52 days from the out-of-transit flux variation in the TESS light curves due to spot modulation.

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arXiv2021

Revisiting the analysis of HW Vir eclipse timing data I. A frequentist data modeling approach and a dynamical stability analysis

HW Vir is a short-period binary that presents eclipse timing variations. Circumbinary planets have been proposed as a possible explanation, although the properties of the planets differ in each new study. Our aim is to perform robust model selection methods for eclipse timing variations (ETV) and error calculation techniques based on a frequentist approach for the case of the HW Vir system. We initially performed simultaneous light and radial velocity curve analysis to derive the masses of the binary. We then analyzed the eclipse timing variation of the system by fitting multiple models. To select the best model, we searched the confidence levels for the best model by creating an $χ^2$ surface grid and bootstrap methods for each pair of parameters. We searched for stable orbital configurations for our adopted ETV model. The masses of the binary are found as 0.413 $\pm$ 0.008 $M_\odot$ and 0.128 $\pm$ 0.004 $M_\odot$. Under the assumption of two light time effects superimposed on a secular change, the minimum masses of the circumbinary objects are calculated as $25.0_{-2.2}^{+3.5} \ M_{Jup}$ and $13.9_{-0.45}^{+0.60}\ M_{Jup}$. The projected semi-major axes are found to be $7.8_{-1.0}^{+1.4}\ au$ and $4.56_{-0.22}^{+0.27}\ au$ in respective order. We find that this configuration is unstable within a 3$σ$ range on the semi-major axis and eccentricity of the outer circumbinary object.

astro-ph.SR↗

arXiv2019

Transit Timing Variations of Five Transiting Planets

Transiting planets provide a unique opportunity to search for unseen additional bodies gravitationally bound to a system. It is possible to detect the motion of the center-of-mass of the observed transiting planet-host star duo due to the gravitational tugs of the unseen bodies from the Roemer delay. In order to achieve the goal, determination of the mid-times of the transits of the planets in high precision and accuracy and correct them for the orbital motion of the Earth is a primary condition. We present transit timing variations and update the ephemeris information of 5 transiting planets; HAT-P-23b, WASP-103b, GJ-1214b, WASP-69b, and KELT-3b within this contribution, based on all the quality transit light curves from amateur and professional observers, converted to Dynamic Barycentric Julian Days (BJD-TDB).

astro-ph.EP↗

arXiv2019

A Holistic and Probabilistic Approach to the Ground-based Data of HAT-P-19 System

We update the fundamental physical and orbital properties of the transiting hot-Saturn type exoplanet HAT-P-19b and its host star HAT-P-19 as a result of the global modeling of our high-precision transit light curves, an archive spectrum, radial velocity observations, brightness values from broadband photometry in different passbands, and the precise distance of the system derived from its Gaia parallax. We collected all the light curves obtained with ground-based photometry by amateur and professional observers, measured mid-transit times, analyzed their differences from calculated transit timings based on reference ephemeris information, which we update as a result. We haven't found any periodicity in the residuals of a linear trend, which we attribute to the accumulation of uncertainties in the reference mid-transit time and the orbital period. We discuss the potential origins of the variation in transit timings briefly and find stellar activity as the most likely cause. Finally, we comment on the scenarios describing the formation and migration of this hot-Saturn type exoplanet with a bloated atmosphere yet a small core, although it is orbiting a metal-rich ([Fe / H] = 0.24 dex) host star based on the planetary, orbital, and stellar parameters of the system that we derived from our global model, the age and the evolutionary history of the star.

astro-ph.EP↗