arXiv subjects

F. Soydugan

Publications and source records attributed to F. Soydugan.

At least 19 recordsLinked to original sources

arXiv2024

Kinematics of Cataclysmic Variables in the Solar Neighborhood in the Gaia Era

Using high-precision astrometric data from Gaia DR3 and updated systemic velocities from the literature, kinematical properties of cataclysmic variables (CVs) were investigated. By constraining the data according to the total space velocity error and Galactic population class, a reliable sample of data was obtained. Non-magnetic CVs located in the thin disk have been found to have a total space velocity dispersion of $σ_ν = 46.33\pm4.23$ km s$^{-1}$, indicating that the thin disk CVs with a mean kinematical age of $τ= 3.95\pm0.75$ Gyr are much younger than the local thin disk of the Galaxy with $τ\sim$6-9 Gyr. Total space velocity dispersions of non-magnetic CVs belonging to the thin disk component of the Galaxy were found to be $σ_ν=47.67\pm3.94$ and $σ_ν=44.43\pm4.33$ km s$^{-1}$ for the systems below and above the orbital period gap, respectively, corresponding to kinematical ages of $τ=4.19\pm0.71$ and $τ=3.61\pm0.74$ Gyr. $γ$ velocity dispersions of the thin disk CVs below and above the gap were obtained $σ_γ = 27.52\pm2.28$ and $σ_γ = 25.65\pm2.44$ km s$^{-1}$, respectively. This study also shows that the orbital period is decreasing with increasing age, as expected from the standard theory. The age-orbital period relation for non-magnetic thin disk CVs was obtained as $dP/dt=-2.09\pm0.22\times10^{-5}$ sec yr$^{-1}$. However, a significant difference could not be found between the $γ$ velocity dispersions of the systems below and above the gap, which were calculated to be $σ_γ = 27.52\pm2.28$ and $σ_γ = 25.65\pm2.44$ km s$^{-1}$, respectively.

astro-ph.GA↗

arXiv2024

Fundamentals of Stars: Critical Looks at Mass-Luminosity Relations and Beyond

Developments on various relations among stellar variables such as the main sequence empirical mass-luminosity (MLR), mass-radius (MRR) and mass-effective temperature (MTR) relations were reviewed. Conceptual changes in their understanding and usages were discussed. After its discovery, MLR was treated as one of the fundamental secrets of the cosmos. Differences between fundamental laws and statistical relations were used to understand long-term developments of MLR, MRR and MTR. Developments show a break point, initiated by Andersen et al. (1991), in the line of progress. Before the break when reliable data were limited, MLR and MRR were calibrated using M, L, and R of binary components of all kinds visual, spectroscopic, and eclipsing for two purposes: i) obtaining mean mass, mean luminosity, and mean radius, ii) to estimate M and R of single stars. By the time of the break, the number of solutions from detached double-lined eclipsing binaries (DDEB) giving accurate M and R within a few percent levels are increased. Parameters from very close, semi-detached, and contact binaries were excluded for refinement, however, MLR and MRR diagrams were found insufficient to derive MLR and MRR functions because the dispersions are not only due to random observational errors but also due to chemical composition and age differences. Then, a new trend was adopted by replacing classical MLR and MRR with empirical M and R predicting relations. Thus, the purpose one was suppressed also because the new trend found a fruitful application in determining M and R of exoplanet hosting single stars. Corrections on misnames and devising new classical MLR, MRR, and MTR, giving mean values are encouraged since they are still useful and needed by astrophysical models requiring such mean values, not only beneficial to astrophysics, but also beneficial to Galactic, extragalactic search, even cosmological models.

astro-ph.SR↗

arXiv2022

A Silent Revolution in Fundamental Astrophysics

Arbitrariness in the zero point of bolometric corrections is a nearly century-old paradigm leading to two more paradigms. "Bolometric corrections must always be negative," and "bolometric magnitude of a star ought to be brighter than its $V$ magnitude". Both were considered valid before IAU 2015 General Assembly Resolution B2, a revolutionary document that supersedes all three aforementioned paradigms. The purpose of this article is to initiate a new insight and a new understanding of the fundamental astrophysics and present new capabilities to obtain standard and more accurate stellar luminosities and gain more from accurate observations in the era after Gaia. The accuracy gained will aid in advancing stellar structure and evolution theories, and also Galactic and extragalactic research, observational cosmology and dark matter and dark energy searches.

astro-ph.SR↗

arXiv2021

The Transient Ultra-luminous X-ray Source, ULX-4, in M51

We present the results of a temporal and spectral analysis of the transient source ULX-4 in the galaxy M51. The data used were drawn from Chandra, XMM-Newton and Swift-XRT archives, spanning the years 2000-2019. The X-ray flux of the source is seen to vary by two orders of magnitudes within a month but a short-term variability was not observed over the time intervals of 100-2000 second in the 0.3-10 keV energy band. We find some evidence for the existence of bi-modality feature in the flux distribution of ULX-4. We identified two optical sources as possible counterparts within an error radius of 0."18 at 95% confidence level for ULX-4 based on the archival HST/ACS and HST/WFC3 data. Blackbody fits of the spectral energy distributions (SEDs) indicate the spectral type to be B-type stars. One of these counterparts exhibits a low-amplitude optical periodicity of 264 days in the F606W filter; if we assume this apparent periodicity is associated with the orbital motion of the donor, then it is more likely that the donor is a red supergiant satisfying the long periodicity and accretion via Roche-lobe overflow. Consequently, the SED would then have to be interpreted as a superposition of emissions from a cold donor and a hot flow component, most likely from an accretion disk. If, on the other hand, the periodicity is super orbital in nature i.e., due to possible interactions of the compact object with a circumstellar disk, the donor could then be a Be/X star hosting a neutron star.

astro-ph.GA↗

arXiv2021

Standard stellar luminosities; what are typical and limiting accuracies in the era after Gaia?

Methods of obtaining stellar luminosities (L) have been revised and a new concept, standard stellar luminosity, has been defined. Among the three methods (direct method from radii and effective temperatures, method using a mass-luminosity relation (MLR), and method requiring a bolometric correction), the third method, which uses the unique bolometric correction (BC) of a star extracted from a flux ratio ($f_{\rm V}/f_{\rm Bol}$) obtained from the observed spectrum with sufficient spectral coverage and resolution, is estimated to provide an uncertainty ($ΔL/L$) typically at a low percentage, which could be as accurate as 1% perhaps more. The typical and limiting uncertainties of the predicted L of the three methods were compared. The secondary methods requiring either a pre-determined non-unique BC or MLR were found to provide less accurate luminosities than the direct method, which could provide stellar luminosities with a typical accuracy of 8.2% - 12.2% while its estimated limiting accuracy is 2.5%.

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arXiv2021

On the Zero Point Constant of the Bolometric Correction Scale

Arbitrariness attributed to the zero point constant of the $V$ band bolometric corrections ($BC_V$) and its relation to "bolometric magnitude of a star ought to be brighter than its visual magnitude" and "bolometric corrections must always be negative" was investigated. The falsehood of the second assertion became noticeable to us after IAU 2015 General Assembly Resolution B2, where the zero point constant of bolometric magnitude scale was decided to have a definite value $C_{Bol}(W)= 71.197~425~...$~. Since the zero point constant of the $BC_V$ scale could be written as $C_2=C_{Bol}-C_V$, where $C_V$ is the zero point constant of the visual magnitudes in the basic definition $BC_V=M_{Bol}-M_V=m_{bol}-m_V$, and $C_{Bol}>C_V$, the zero point constant ($C_2$) of the $BC_V$ scale cannot be arbitrary anymore; rather, it must be a definite positive number obtained from the two definite positive numbers. The two conditions $C_2>0$ and $0<BC_V<C_2$ are also sufficient for $L_V<L$, a similar case to negative $BC_V$ numbers, which means that "bolometric corrections are not always negative". In sum it becomes apparent that the first assertion is misleading causing one to understand bolometric corrections must always be negative, which is not necessarily true.

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arXiv2020

Identification of a New Ultraluminous X-ray Source in NGC 1316

In this study, we report identification of a new ultraluminous X-ray source (ULX) named as X-7 in NGC 1316, with an unabsorbed luminosity of 2.1$\times$10$^{39}$ erg s$^{-1}$ using the two recent Chandra archival observations. The X-7 was detected in the Chandra 2001 observation and was included in the source list of the NGC 1316 as CXOUJ032240.8-371224 with a luminosity of 5.7$\times$10$^{38}$ erg s$^{-1}$. Present luminosity implies a luminosity increase of a factor of $\sim$ 4. The best fit spectral model parameters indicate that X-7 has a relatively hot disk and hard spectra. If explained by a diskblackbody model, the mass of compact object is estimated as $\sim$ 8 M$\odot$ which is in the range of a stellar-mass black hole. The X-7 shows a relatively long-term count rate variability while no short-term variability is observed. We also identified a unique optical candidate within 0.22" error circle at 95\% confidence level for X-7 using the archival HST/ACS and HST/WFC3 data. Absolute magnitude (M$_{V}$) of this candidate is -7.8 mag. Its spectral energy distribution is adequately fitted a blackbody model with a temperature of 3100 K indicating an M type supergiant, assuming the donor star dominates the optical emission. In addition, we identified a transient ULX candidate (XT-1) located 6" away from X-7 has a (high) luminosity of $\sim$ 10$^{39}$ erg s$^{-1}$ with no visible optical candidate.

astro-ph.HE↗

arXiv2020

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 $M_1=1.29\pm0.02 M_{\odot}$, $R_{1}=1.47\pm0.03 R_{\odot}$ and $M_{2}=1.19\pm0.02 M_{\odot}$, $R_{2}=1.13\pm0.02 R_{\odot}$ for the primary and secondary components of KIC 5113146; $M_{1}=1.51\pm0.08 M_{\odot}$, $R_{1}=2.02\pm0.05 R_{\odot}$ and $M_{2}=1.19\pm0.07 M_{\odot}$, $R_{2}=1.32\pm0.04 R_{\odot}$ 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 $2.50\pm0.35$ Gyr and $1.95\pm0.40$ Gyr, respectively. Photometric distances were calculated to be $2850\pm 185$ pc for KIC 5113146 and $3120\pm 260$ 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.

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arXiv2020

Empirical Bolometric Correction Coefficients for Nearby Main-Sequence Stars in Gaia Era

Nearby detached double-lined eclipsing binaries with most accurate data were studied and 290 systems were found with at least one main-sequence component having a metallicity $0.008\leq Z\leq 0.040$. Stellar parameters, light ratios, Gaia DR2 trigonometric parallaxes, extinctions and/or reddening were investigated and only 206 systems were selected eligible to calculate empirical bolometric corrections. NASA-IPAC Galactic dust maps were main source of extinctions. Unreliable extinctions at low Galactic latitudes $|b|\leq5^o$ were replaced with individual determinations, if they exist in the literature, else associated systems are discarded. Main-sequence stars of remaining systems were used to calculate bolometric corrections ($BC$) and to calibrate $BC-T_{eff}$ relation, which is valid in the range 3100-36000 K. De-reddened $(B-V)_0$ colours, on the other hand, allowed us to calibrate two intrinsic colour effective temperature relations, where the linear one is valid for $T_{eff}>10000$ K, while the quadratic relation is valid for $T_{eff}<10000$ K, that is, both are valid in the same temperature range $BC-T_{eff}$ relation is valid. New $BC$ computed from $T_{eff}$ and other astrophysical parameters are tabulated, as well.

astro-ph.SR↗

arXiv2018

Interrelated Main-Sequence Mass-Luminosity, Mass-Radius and Mass-Effective Temperature Relations

Absolute parameters of 509 main-sequence stars selected from the components of detached-eclipsing spectroscopic binaries in the Solar neighbourhood are used to study mass-luminosity, mass-radius and mass-effective temperature relations (MLR, MRR and MTR). The MLR function is found better if expressed by a six-piece classical MLR ($L \propto M^α$) rather than a fifth or a sixth degree polynomial within the mass range of $0.179\leq M/M_{\odot}\leq 31$. The break points separating the mass-ranges with classical MLR do not appear to us to be arbitrary. Instead, the data indicate abrupt changes along the mass axis in the mean energy generation per unit of stellar mass. Unlike the MLR function, the MRR and MTR functions cannot be determined over the full range of masses. A single piece MRR function is calibrated from the radii of stars with $M\leq1.5M_{\odot}$, while a second single piece MTR function is found for stars with $M>1.5M_{\odot}$. The missing part of the MRR is computed from the MLR and MTR, while the missing part of the MTR is computed from the MLR and MRR. As a result, we have interrelated MLR, MRR and MTR, which are useful in determining the typical absolute physical parameters of main-sequence stars of given masses. These functions are also useful to estimate typical absolute physical parameters from typical $T_{eff}$ values. Thus, we were able to estimate the typical absolute physical parameters of main-sequence stars observed in the Sejong Open Cluster survey, based on that survey's published values for $T_{eff}$. Since typical absolute physical parameters of main sequence stars cannot normally be determined in such photometric surveys, the interrelated functions are shown to be useful to compute such missing parameters from similar surveys.

astro-ph.SR↗

arXiv2015

Towards Understanding the Nature of Young Detached Binary System HD 350731

The young binary system HD 350731 is a noteworthy laboratory for studying early-type binaries with similar components. We present here the analysis of differential multi-color photometric and spectroscopic observations for the double-lined detached system. Accurate absolute parameters were determined from the simultaneous solution of light and radial velocity curves for the first time. HD 350731 consists of two B8V-type components having masses and radii respectively of $M_{1}=2.91\pm0.13$ M$_{\odot}$, $M_{2}=2.80\pm0.14$ M$_{\odot}$, $R_{1}= 2.11 \pm0.05$ R$_{\odot}$ and $R_{2}=2.07\pm0.05$ R$_{\odot}$. The effective temperatures were determined based on analysis of disentangled spectra of the components and derived to be $12000\pm250$ K and $11830\pm300$ K for the primary and secondary components, respectively. The measured projected rotational velocities, 69.2$\pm$1.5 km s$^{-1}$ for primary and 70.1$\pm$1.7 km s$^{-1}$ for secondary, were found closer to the pseudo-synchronous velocities of the components. Comparison with evolutionary models suggests an age of 120$\pm$35 Myr. Kinematic analysis of the unevolved binary system HD 350731 revealed that it belongs to the young thin-disc population of the Galaxy.

astro-ph.SR↗

arXiv2015

The Galactic Kinematics of Cataclysmic Variables

Kinematical properties of CVs were investigated according to population types and orbital periods, using the space velocities computed from recently updated systemic velocities, proper motions and parallaxes. Reliability of collected space velocity data are refined by removing 34 systems with largest space velocity errors. The 216 CVs in the refined sample were shown to have a dispersion of $53.70 \pm 7.41$ km s$^{-1}$ corresponding to a mean kinematical age of $5.29 \pm 1.35$ Gyr. Population types of CVs were identified using their Galactic orbital parameters. According to the population analysis, seven old thin disc, nine thick disc and one halo CV were found in the sample, indicating that 94% of CVs in the Solar Neighbourhood belong to the thin-disc component of the Galaxy. Mean kinematical ages $3.40 \pm 1.03$ and $3.90 \pm 1.28$ Gyr are for the non-magnetic thin-disc CVs below and above the period gap, respectively. There is not a meaningful difference between the velocity dispersions below and above the gap. Velocity dispersions of the non-magnetic thin-disc systems below and above the gap are $24.95 \pm 3.46$ and $26.60 \pm 4.18$ km s$^{-1}$, respectively. This result is not in agreement with the standard formation and evolution theory of CVs. The mean kinematical ages of the CV groups in various orbital period intervals increase towards shorter orbital periods. This is in agreement with the standard theory for the evolution of CVs. Rate of orbital period change was found to be $dP/dt=-1.62(\pm 0.15)\times 10^{-5}$ sec yr$^{-1}$.

astro-ph.SR↗

arXiv2015

Main-Sequence Effective Temperatures from a Revised Mass-Luminosity Relation Based on Accurate Properties

The mass-luminosity (M-L), mass-radius (M-R) and mass-effective temperature ($M-T_{eff}$) diagrams for a subset of galactic nearby main-sequence stars with masses and radii accurate to $\leq 3\%$ and luminosities accurate to $\leq 30\%$ (268 stars) has led to a putative discovery. Four distinct mass domains have been identified, which we have tentatively associated with low, intermediate, high, and very high mass main-sequence stars, but which nevertheless are clearly separated by three distinct break points at 1.05, 2.4, and 7$M_{\odot}$ within the mass range studied of $0.38-32M_{\odot}$. Further, a revised mass-luminosity relation (MLR) is found based on linear fits for each of the mass domains identified. The revised, mass-domain based MLRs, which are classical ($L \propto M^α$), are shown to be preferable to a single linear, quadratic or cubic equation representing as an alternative MLR. Stellar radius evolution within the main-sequence for stars with $M>1M_{\odot}$ is clearly evident on the M-R diagram, but it is not the clear on the $M-T_{eff}$ diagram based on published temperatures. Effective temperatures can be calculated directly using the well-known Stephan-Boltzmann law by employing the accurately known values of M and R with the newly defined MLRs. With the calculated temperatures, stellar temperature evolution within the main-sequence for stars with $M>1M_{\odot}$ is clearly visible on the $M-T_{eff}$ diagram. Our study asserts that it is now possible to compute the effective temperature of a main-sequence star with an accuracy of $\sim 6\%$, as long as its observed radius error is adequately small (<1%) and its observed mass error is reasonably small (<6%).

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arXiv2014

Effective Temperatures of Selected Main-sequence Stars with Most Accurate Parameters

In this study, the distributions of the double-lined detached binaries (DBs) on the planes of mass-luminosity, mass radius and mass-effective temperature have been studied. We improved the classical mass-luminosity relation based on the database of DBs by Eker et al. (2004a). With accurate observational data available to us, a method for improving effective temperatures for eclipsing binaries with accurate masses and radii were suggested.

astro-ph.SR↗

arXiv2014

The Catalogue of Stellar Parameters from the Detached Double-Lined Eclipsing Binaries in the Milky Way

The most accurate stellar astrophysical parameters were collected from the solutions of the light and the radial velocity curves of 257 detached double-lined eclipsing binaries in the Milky Way. The catalogue contains masses, radii, surface gravities, effective temperatures, luminosities, projected rotational velocities of the component stars and the orbital parameters. The number of stars with accurate parameters increased 67 per cent in comparison to the most recent similar collection by Torres et al. (2010). Distributions of some basic parameters were investigated. The ranges of effective temperatures, masses and radii are $2750<T_{eff}$(K)$<43000$, $0.18<M/M_{\odot}<33$ and $0.2<R/R_{\odot}<21.2$, respectively. Being mostly located in one kpc in the Solar neighborhood, the present sample covers distances up to 4.6 kpc within the two local Galactic arms Carina-Sagittarius and Orion Spur. The number of stars with both mass and radius measurements better than 1 per cent uncertainty is 93, better than 3 per cent uncertainty is 311, and better than 5 per cent uncertainty is 388. It is estimated from the Roche lobe filling factors that 455 stars (88.5 per cent of the sample) are spherical within 1 per cent of uncertainty.

astro-ph.SR↗

arXiv2013

The early-type near-contact binary system V337 Aql revisited

The close binary V337 Aql consists of two early B-type components with an orbital period of 2.7339 d. New multi-band photometric observations of the system together with published radial velocities enabled us to derive the absolute parameters of the components. The simultaneous light and radial velocity curves solution yields masses and radii of \emph{M$_{1}$}=17.44$\pm$0.31 \emph{M$_\odot$} and \emph{R$_{1}$}=9.86$\pm$0.06 \emph{R$_\odot$} for the primary and \emph{M$_{2}$}=7.83$\pm$0.18 \emph{M$_\odot$} and \emph{R$_{2}$}=7.48$\pm$0.04 \emph{R$_\odot$} for the secondary component. Derived fundamental parameters allow us to calculate the photometric distance as 1355$\pm$160 pc. The present analysis indicates that the system is a near-contact semi-detached binary, in which a primary star is inside its Roche lobe with a filling ratio of 92 percent and the secondary star fills its Roche lobe. From \emph{O-C} data analysis, an orbital period decrease was determined with a rate of -7.6 $\times$ 10$^{-8}$ yr$^{-1}$. Kinematic analysis reveals that V337 Aql has a circular orbit in the Galaxy and belongs to a young thin-disc population.

astro-ph.SR↗

arXiv2009

The Spectroscopic Orbits of Three Double-lined Eclipsing Binaries: I. BG Ind, IM Mon, RS Sgr

We present the spectroscopic orbit solutions of three double-lines eclipsing binaries, BG Ind, IM Mon and RS Sgr. The first precise radial velocities (RVs) of the components were determined using high resolution echelle spectra obtained at Mt. John University Observatory in New Zealand. The RVs of the components of BG Ind and RS Sgr were measured using Gaussian fittings to the selected spectral lines, whereas two-dimensional cross-correlation technique was preferred to determine the RVs of IM Mon since it has relatively short orbital period among the other targets and so blending of the lines is more effective. For all systems, the Keplerian orbital solution was used during the analysis and also circular orbit was adopted because the eccentricities for all targets were found to be negligible. The first precise orbit analysis of these systems gives the mass ratios of the systems as 0.894, 0.606 and 0.325, respectively for BG Ind, IM Mon and RS Sgr. Comparison of the mass ratio values, orbital sizes and minimum masses of the components of the systems indicates that all systems should have different physical, dynamical and probable evolutionary status.

astro-ph.SR↗

arXiv2008

New absolute magnitude calibrations for detached binaries

Lutz-Kelker bias corrected absolute magnitude calibrations for the detached binary systems with main-sequence components are presented. The absolute magnitudes of the calibrator stars were derived at intrinsic colours of Johnson-Cousins and 2MASS (Two Micron All Sky Survey) photometric systems. As for the calibrator stars, 44 detached binaries were selected from the Hipparcos catalogue, which have relative observed parallax errors smaller than 15% ($σ_π/π\leq0.15$). The calibration equations which provide the corrected absolute magnitude for optical and near-infrared pass bands are valid for wide ranges of colours and absolute magnitudes: $-0.18<(B-V)_{0}<0.91$, $-1.6<M_{V}<5.5$ and $-0.15<(J-H)_{0}<0.50$, $-0.02<(H-K_{s})_{0}<0.13$, $0<M_{J}<4$, respectively. The distances computed using the luminosity-colours (LCs) relation with optical (BV) and near-infrared ($JHK_{s}$) observations were compared to the distances found from various other methods. The results show that new absolute magnitude calibrations of this study can be used as a convenient statistical tool to estimate the true distances of detached binaries out of Hipparcos' distance limit.

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