arXiv subjects

Jang-Ho Park

Publications and source records attributed to Jang-Ho Park.

At least 19 recordsLinked to original sources

arXiv2026

The Double-lined Eclipsing $γ$ Doradus System AX Draconis in a 0.568-day Orbit

For the near-contact binary AX Dra, we present the first time-series spectroscopy collected with the echelle spectrograph BOES. From spectral analysis, we measured the projected rotation of $v_1 \sin i$ = $120\pm21$ km s$^{-1}$ and effective temperature of $T_{\rm eff,1}$ = $7220\pm150$ K for the brighter primary component, together with radial velocities (RVs) for both stars. To obtain a consistent binary model, the RV curves were analyzed by combining the 2-min cadence photometric data observed in the TESS sectors 15, 21, 22, and 41. The modeling indicates that AX Dra is a semi-detached system exhibiting a total secondary eclipse, with the detached primary component having a large filling factor of 92 \%. The system has masses of $1.717\pm0.026$ $M_\odot$ and $0.804\pm0.014$ $M_\odot$, radii of $1.541\pm0.020$ $R_\odot$ and $1.237\pm0.014$ $R_\odot$, luminosities of $5.78\pm0.50$ $L_\odot$ and $0.83\pm0.05$ $L_\odot$, and a temperature difference of $Δ$($T_{\rm eff,1}$--$T_{\rm eff,2}$) = $2263\pm163$ K. Multi-frequency analyses of the TESS residual lights yielded 35 significant signals in the frequency range below 5 day$^{-1}$. Among them, four frequencies of $f_1$, $f_2$, $f_3$, and $f_5$ are independent $γ$ Dor pulsations of the primary star, for which two acceptable mode-identification solutions were obtained using the frequency ratio method. These results suggest that AX Dra is the shortest-period double-lined eclipsing binary containing a $γ$ Dor-type pulsator and that the pulsating primary is likely an accretor affected by mass transfer.

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arXiv2026

The Pre-He White Dwarfs in Eclipsing Binaries. V. TIC 399725538

We present echelle spectra of TIC 399725538 obtained in Korea and Thailand to investigate the physical properties and evolutionary scenarios of EL CVn-type binaries. The time-series spectra yielded the radial velocities (RVs) of the primary component and its atmospheric parameters, $T_{\rm eff,A}=7194\pm70$ K and $v_{\rm A}\sin i=68\pm9$ km s$^{-1}$. Joint modeling of our RVs and the archival TESS data provided component masses of $M_{\rm A}=1.930\pm0.054$ $M_\odot$ and $M_{\rm B}=0.211\pm0.005$ $M_\odot$, radii of $R_{\rm A}=1.922\pm0.020$ $R_\odot$ and $R_{\rm B}=0.207\pm0.005$ $R_\odot$, and luminosities of $L_{\rm A}=8.87\pm0.39$ $L_\odot$ and $L_{\rm B}=0.546\pm0.034$ $L_\odot$. The surface gravity and distance derived from this modeling are consistent with the model-independent $\log g_{\rm B}$ obtained from the direct observables and with the Gaia distance. The third light of $l_3=0.136\pm0.003$ comes mainly from two neighboring stars, TIC 399725539 and TIC 399725544. Comparison with stellar models indicates that TIC 399725538 A lies within the instability region of $δ$ Sct$-$$γ$ Dor hybrids, whereas its extremely low-mass companion is markedly underluminous compared to theoretical white dwarf (WD) counterparts. Multifrequency analysis of the binary-subtracted residual lights revealed three significant signals, two of which correspond to aliases at two and four times the dominant frequency $f_1=0.0848$ day$^{-1}$. The $f_1$ frequency is likely a $γ$ Dor-type pulsation arising from the brighter A component, though further confirmation is required. Our results demonstrate that TIC 399725538 is a short-period EL CVn system belonging to the thick-disk population, consisting of a main-sequence $γ$ Dor pulsator and a helium-core WD precursor formed through stable mass transfer.

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arXiv2025

TIC 322208686: An Eclipsing System with $γ$ Doradus Pulsations and a Third Component on a Wider Orbit

TIC 322208686 is known to be a detached binary that exhibits two types of variability: pulsation and eclipse. We present the physical properties of the target star using the short-cadence TESS data from sectors 24, 57, and 58, and our echelle spectra that show the presence of a tertiary companion. The spectral analysis led to the triple-lined radial velocities and the atmospheric parameters of the eclipsing components. Joint modeling of these observations reveals that the eclipsing pair contains two F-type stars with masses $1.564\pm0.012$ $M_\odot$ and $1.483\pm0.012$ $M_\odot$, radii $1.588\pm0.011$ $R_\odot$ and $1.500\pm0.012$ $R_\odot$, effective temperatures $7028\pm100$ K and $7020\pm110$ K, and luminosities $5.51\pm0.32$ $L_\odot$ and $4.90\pm0.32$ $L_\odot$. The light contributions of the three stars obtained from this modeling match well with those calculated from the observed spectra. The binary star parameters are in satisfactory agreement with evolutionary model predictions for age $t$ = 0.4 Gyr and metallicity $Z$ = 0.03. We extracted 11 significant frequencies from the TESS light residuals with the binary effects removed. Of these, five signals between 0.65 day$^{-1}$ and 1.89 day$^{-1}$ can be considered as $γ$ Dor pulsations originating mainly from the primary component, while the other frequencies are likely instrumental artifacts or combination terms. These results suggest that TIC 322208686 is a hierarchical triple, containing a pulsating eclipsing pair and a tertiary companion.

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arXiv2025

The Low Mass Ratio Overcontact Binary GV Leonis and Its Circumbinary Companion

Photometric and spectroscopic observations of GV Leo were performed from 2017 to 2024. The light curves show a flat bottom at the primary eclipse and the conventional O'Connell effect. The echelle spectra reveal that the effective temperature and rotation velocity of the more massive secondary are $T_{\rm eff,2}$ = 5220$\pm$120 K and $v_2 \sin i$ = 223$\pm$40 km s$^{-1}$, respectively. Our binary modeling indicates that the program target is a W-subclass contact binary with a mass ratio of $q$ = 5.48, an inclination angle of $i$ = 81$^\circ$.68, a temperature difference of ($T_{\rm eff,1}-T_{\rm eff,2}$) = 154 K, and a filling factor of $f$ = 36 \%. The light asymmetries were reasonably modeled by a dark starspot on the secondary's photosphere. Including our 26 minimum epochs, 84 times of minimum light were used to investigate the orbital period of the system. We found that the eclipse times of GV Leo have varied by a sinusoid with a period of 14.9 years and a semi-amplitude of 0.0076 days superimposed on a downward parabola. The periodic modulation is interpreted as a light time effect produced by an unseen outer tertiary with a minimum mass of 0.26 M$_\odot$, while the parabolic component is thought to be a combination of mass transfer (secondary to primary) and angular momentum loss driven by magnetic braking. The circumbinary tertiary would have caused the eclipsing pair of GV Leo to evolve into its current short-period contact state by removing angular momentum from the primordial widish binary.

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arXiv2023

Absolute Properties of the Oscillating Eclipsing Algol XZ Ursae Majoris

It is known from archival TESS data that the semi-detached Algol system XZ UMa is one of the candidate binary stars exhibiting short-period oscillations. We secured new high-resolution spectroscopic observations for the program target to better understand its binary and pulsation properties. From the echelle spectra, the radial velocities (RVs) of the eclipsing pair were derived, and the atmosphere parameters of the primary component were measured to be $v_{\rm A}\sin$$i = 80\pm7$ km s$^{-1}$, $T_{\rm eff,A}$ = $7940\pm120$ K, and [M/H] = $-0.15\pm0.20$. The combined solution of our double-lined RVs and the TESS data provides robust physical parameters for XZ UMa with mass and radius measurement precision of better than 2 \%. The outside-eclipse residuals from a mean light curve in the 0.002 phase bin were used for multifrequency analyses, and we extracted 32 significant frequencies (22 in $<$ 5.0 day$^{-1}$ and 10 in 39$-$52 day$^{-1}$). The low frequencies may be mostly aliasing sidelobes, while six of the high frequencies may be pulsation signals arising from the detached primary located inside the $δ$ Sct domain. Their periods, pulsation constants, and pulsational-orbital-period ratios indicate that the mass-accretion primary star is a $δ$ Sct pulsator and, hence, XZ UMa is an oscillating eclipsing Algol.

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arXiv2023

Improved period variations of 32 contact binaries with rapidly decreasing periods in the Galactic Bulge

We present detailed analyses of updated eclipse timing diagrams for 32 contact binary merger candidates in the Galactic bulge. The photometric data was obtained from 2016 to 2021 using the Korea Microlensing Telescope Network (KMTNet) with the 1.6 m telescopes located at three southern sites (CTIO, SAAO, and SSO). The times of minimum lights were determined by applying the binary star model to full light curves created at half-year intervals from the observations. The orbital period variations of the binary systems were analyzed using the $O-C$ diagrams from our new timings with the others published in the literature (Hong et al.), which are based on the OGLE observations from 2001 to 2015. As results, the orbital periods and period decreasing rates of 32 binary systems were located to be in the ranges of 0.370$-$1.238 days and from $-3.0$ to $-13.1\times10^{-6}$ day yr$^{-1}$, respectively. Out of these stars, 24 systems show a combination effect of a parabola and a light travel time caused by a third body and their outer orbital periods are in the range of 9.1$-$26.5 yr, respectively. We propose that all of our merger candidates need additional monitoring observations to study a luminous red nova (LRN) progenitor.

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arXiv2023

Photometric and Spectroscopic Properties of the Eclipsing System V864 Monocerotis

We present the orbital period variability and evolutionary status of the W UMa-type binary system V864 Mon from accurately measured fundamental parameters. New $BV$ photometric observations of this system were performed in 2019 January and 2022 January, and the first high-resolution spectroscopic observations were carried out on three nights between 2019 January and March. A total of 29 times of minimum light were collected to examine the behavior of the orbital period. Our analysis of these timings indicates a continuous period increase at a rate of $+$2.62$\times$10$^{-7}$ d yr$^{-1}$ over the past 20 years, which can be interpreted as a mass transfer from the less massive primary to the secondary component with a rate of 1.22$\times$10$^{-7}$ M$_\odot$ yr$^{-1}$. We measured the radial velocities (RVs) for both components, and determined the effective temperature and projected rotational velocity of the more massive secondary star to be $T_{\rm eff,2}$ = 5450 $\pm$ 94 K and $v_2 \sin i$ = 192 $\pm$ 40 km s$^{-1}$, respectively, from the comparison of the observed spectrum at the primary minimum and the theoretical models. The individual masses and radii of both components were determined from a simultaneous analysis of the light and RV curves, which are $M_1$ = 0.34 $\pm$ 0.02 M$_\odot$, $R_1$ = 0.69 $\pm$ 0.01 R$_\odot$, and $M_2$ = 1.06 $\pm$ 0.04 M$_\odot$, $R_2$ = 1.16 $\pm$ 0.02 R$_\odot$, respectively. Our results indicate that V864 Mon is a W-subtype of W UMa stars with time-varying spot activity. The positions in the mass-luminosity and mass-radius diagrams indicate that the secondary star belongs to the main sequence region, while the hotter primary is located beyond the terminal-age main sequence.

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arXiv2023

Absolute Properties of the Oscillating Eclipsing Algol X Trianguli

We report results from the TESS photometric data and new high-resolution spectra of the Algol system X Tri showing short-period pulsations. From the echelle spectra, the radial velocities of the eclipsing pair were measured, and the rotational rate and effective temperature of the primary star were obtained to be $v_1$$\sin$$i=84\pm6$ km s$^{-1}$ and $T_{\rm eff,1}=7900 \pm 110$ K, respectively. The synthetic modeling of these observations implies that X Tri is in synchronous rotation and is physically linked to a visual companion TIC 28391715 at a separation of about 6.5 arcsec. The absolute parameters of our target star were accurately and directly determined to be $M_1 = 2.137 \pm 0.018$ $M_\odot$, $M_2 = 1.101 \pm 0.010$ $M_\odot$, $R_1 = 1.664 \pm 0.010$ $R_\odot$, $R_2 = 1.972 \pm 0.010$ $R_\odot$, $L_1 = 9.67 \pm 0.55$ $L_\odot$, and $L_2 = 2.16 \pm 0.09$ $L_\odot$. The phase-binned mean light curve was used to remove the binary effect from the observed TESS data. Multifrequency analysis of the residuals revealed 16 significant frequencies, of which the high-frequency signals between 37 day$^{-1}$ and 48 day$^{-1}$ can be considered probable pulsation modes. Their oscillation periods of 0.021$-$0.027 days and pulsation constants of 0.014$-$0.018 days are typical values of $δ$ Sct variables. The overall results demonstrate that X Tri is an oEA star system, consisting of a $δ$ Sct primary and its lobe-filling companion in the semi-detached configuration.

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arXiv2022

A Photometric and Spectroscopic Study of the Short-Period Algol EW Boötis with a $δ$ Sct Pulsator

In this paper, we present TESS photometry and high-resolution spectra of the short-period Algol EW Boo. We obtained double-lined radial velocities (RVs) from the time-series spectra and measured the effective temperature of the primary star as $T_{\rm{eff,1}}$ = 8560 $\pm$ 118 K. For the orbital period study, we collected all times of minima available for over the last 30 years. It was found that the eclipse timing variation of the system could be represented by a periodic oscillation of 17.6 $\pm$ 0.3 years with a semi-amplitude of 0.0041 $\pm$ 0.0001 d. The orbital and physical parameters were derived by simultaneously analyzing the TESS light and RV curves using the Wilson-Devinney (WD) binary star modeling code. The component masses and radii were showed over 3% precision: $M_{1}$ = 2.67 $\pm $ 0.08 M$_{\odot}$, $M_{2}$ = 0.43 $\pm $ 0.01 M$_{\odot}$, $R_{1}$ = 2.01 $\pm $ 0.02 R$_{\odot}$, and $R_{2}$ = 1.35 $\pm $ 0.01 R$_{\odot}$. Furthermore, multiple frequency analyses were performed for the light-curve residuals from the WD model. As a result, we detected 17 pressure-mode pulsations in the region of 40.15 - 52.37 d$^{-1}$. The absolute dimensions and pulsation characteristics showed that the $δ$ Sct pulsator was the more massive and hotter primary star of the EW Boo.

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arXiv2022

The Pre-He White Dwarfs in Eclipsing Binaries. IV. WASP 1814+48 with Multiperiodic Pulsations

For the EL CVn candidate 1SWASPJ181417.43+481117.0 (WASP 1814+48), we secured the first spectroscopic observations between 2015 April and 2021 March. Using the echelle spectra, the radial velocities (RVs) of the primary star were measured with its atmospheric parameters of $T_{\rm eff,1}=7770\pm130$ K and $v_1$$\sin$$i=47\pm6$ km s$^{-1}$. We fitted our single-lined RVs and the TESS light curve simultaneously. From the binary modeling, we determined the following fundamental parameters for each component: $M_1=1.659\pm0.048$ $M_\odot$, $R_1=1.945\pm0.027$ $R_\odot$, and $L_1=12.35\pm0.90$ $L_\odot$ for WASP 1814+48 A, and $M_2=0.172\pm0.005$ $M_\odot$, $R_2=0.194\pm0.005$ $R_\odot$, and $L_2=0.69\pm0.07$ $L_\odot$ for WASP 1814+48 B. The surface gravity of $\log g_2=5.098\pm0.026$ obtained from $M_2$ and $R_2$ is concurrent with 5.097$\pm$0.025 computed directly from the observable quantities. WASP 1814+48 B is well-matched with the 0.176 M$_\odot$ white dwarf (WD) evolutionary model for $Z=0.01$. The metallicity and our Galactic kinematics indicate that the program target is a thin-disk star. The whole light residuals after removal of the binary trend were analyzed and found to oscillate at a total of 52 frequencies. Among these, most of the low frequencies below 24 day$^{-1}$ are aliases and orbital harmonics. The five significant frequencies between 32 and 36 day$^{-1}$ are the pulsation modes of WASP 1814+48 A located in the $δ$ Sct domain on ZAMS, and the high frequencies of 128$-$288 day$^{-1}$ arise from WASP 1814+48 B in the pre-He WD instability strip. Our results reveal that WASP 1814+48 is the fifth EL CVn star that is composed of a $δ$ Sct-type primary and a pre-ELMV (extremely low-mass pre-He WD variable).

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arXiv2022

Period Changes of 14,127 Contact Eclipsing Binaries in the Galactic Bulge

We present the orbital period variations of 14,127 contact eclipsing binaries (CEBs) based on the OGLE-III\&IV observations in the Galactic bulge. New times of minimum lights for the CEBs were derived by binary modeling for the full seasonal light curves, which were made from survey observations at an interval of 1 year. The orbital period changes of the systems were classified based on the statistical inference, multiple-hypothesis testing error measure, and visual inspection of the eclipse timing diagrams. As the results, we identified 13,716 CEBs with a parabola, 307 CEBs with a sinusoid, and 104 CEBs with the two variations. The period distributions of the inner close binaries and the outer companions were in the ranges of $0.235-0.990$ days and $5.0-14.0$ years, respectively. In our sample of 13,820 CEBs showing a parabolic variation, the highest decreasing and increasing period rates were determined to be $\dot P=-1.38\pm0.06\times10^{-5}$ day year$^{-1}$ for OGLE-BLG-ECL-169991 and $\dot P=+8.99\pm0.44\times10^{-6}$ day year$^{-1}$ for OGLE-BLG-ECL-189805, respectively. The secular period change rates were distributed almost symmetrically around zero, and most of them lie within $\dot P=\pm5.0\times10^{-6}$ day year$^{-1}$.

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arXiv2022

V608 Cassiopeiae: A W UMa-type eclipsing binary with two possible circumbinary companions

We present the photometric properties of V608 Cas from detailed studies of light curves and eclipse timings. The light curve synthesis indicates that the eclipsing pair is an overcontact binary with parameters of $ΔT$ = 155 K, $q$ = 0.328, and $f$ = 26 %. We detected the third light $\ell_{3}$, which corresponds to about 8 % and 5 % of the total systemic light in $V$ and $R$ bands, respectively. Including our 6 timing measurements, a total of 38 times of minimum light were used for a period study. It was found that the orbital period of V608 Cas has varied in some combination of an upward parabola and two periodic variations. The continuous period increase with a rate of $+$3.99$\times$10$^{-7}$ d yr$^{-1}$ can be interpreted as a mass transfer from the secondary component to the primary star at a rate of 1.51$\times$10$^{-7}$ M$_\odot$ yr$^{-1}$. The periods and semi-amplitudes of the two periodic variations are about $P_3$ = 16.0 yr and $P_4$ = 26.3 yr, and $K_3$ = 0.0341 d and $K_4$ = 0.0305 d, respectively. The most likely explanation of both cycles is a pair of light-traveling time effects operated by the possible presence of third and fourth components with estimated masses of $M_3$ = 2.20 M$_\odot$ and $M_4$ = 1.27 M$_\odot$ in eccentric orbits of $e_3$ = 0.66 and $e_4$ = 0.52. Because the contribution of $\ell_{3}$ is very low compared to the estimated masses of two circumbinary objects, they can be inferred as very faint compact objects.

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arXiv2022

The Pre-He White Dwarfs in Eclipsing Binaries. III. WASP 1625-04

1SWASP J162545.15-043027.9 (WASP 1625-04) has been announced as one of EL CVn candidates showing total primary eclipses and ellipsoidal variations. This paper presents the absolute properties of the binary star, based on our high-resolution spectroscopy conducted from 2015 through 2020. From the spectral analysis, the radial velocities (RVs) for both components were obtained with the effective temperature $T_{\rm eff,1} = 8990 \pm 200$ K and the rotational rate $v_1\sin$$i=53\pm5$ km s$^{-1}$ for the more massive primary. The RV measurements were analyzed with archival WASP photometry. From the modelling we obtained: $M_1 = 1.745 \pm 0.013$ M$_\odot$, $M_2 = 0.187 \pm 0.002$ M$_\odot$, $R_1 = 1.626 \pm 0.008$ M$_\odot$, $R_2 = 0.290 \pm 0.003$ M$_\odot$, $L_1 = 15.5 \pm 1.4$ L$_\odot$, and $L_2 = 1.84 \pm 0.16$ L$_\odot$. In the Hertzsprung-Russell diagram, WASP 1625-04 A lies on the zero-age main sequence and its companion accords well with the helium-core white dwarf models of 0.19 M$_\odot$ in the constant luminosity phase. Our improved results demonstrate that WASP 1625-04 is a typical EL CVn-type binary with a low mass ratio and $M_2$ combination in the thin-disk population and is the product of the stable, non-conservative mass transfer of the precursor binary.

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arXiv2020

Physical Nature of the Eclipsing δ Scuti Star AO Serpentis

We present the absolute properties of the eclipsing binary AO Ser with a pulsating component from our $BV$ photometric and high-resolution spectroscopic observations, which were performed between April and May 2017. The radial velocities (RVs) for both components were measured, and the effective temperature and projected rotational velocity of the primary star were determined to be $T_{\rm eff,1}$ = 8,820 $\pm$ 62 K and $v_1 \sin i_{1}$ = 90 $\pm$ 18 km s$^{-1}$, respectively, by comparing the observed spectrum with the Kurucz models. The accurate fundamental parameters of AO Ser were determined by a simultaneous analysis of the light and RV curves. The masses and radii of the primary and secondary components are $M_1$ = 2.55 $\pm$ 0.09 M$_\odot$ and $R_1$ = 1.64 $\pm$ 0.02 R$_\odot$ and $M_2$ = 0.49 $\pm$ 0.02 M$_\odot$ and $R_2$ = 1.38 $\pm$ 0.02 R$_\odot$, respectively. Multiple frequency analyses for the eclipse-subtracted light residuals were conducted. As a result, we detected two frequencies of $f_1$ = 21.852 days$^{-1}$ and $f_2$ = 23.484 days$^{-1}$. The evolutionary position on the HR diagram and the pulsational characteristics indicate that the primary star is a $δ$ Sct pulsator with a radial fundamental mode. On the other hand, the relatively evolved secondary is oversized for its own mass.

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arXiv2020

The Pre-He White Dwarfs in Eclipsing Binaries. I. WASP 0131+28

We report the first $BV$ light curves and high-resolution spectra of the post-mass transfer binary star WASP 0131+28 to study the absolute properties of extremely low-mass white dwarfs. From the observed spectra, the double-lined radial velocities were derived, and the effective temperature and rotational velocity of the brighter, more massive primary were found to be $T_{\rm eff,1} = 10,000 \pm 200$ K and $v_1\sin$$i$ = 55 $\pm$ 10 km s$^{-1}$, respectively. The combined analysis of the {\it TESS} archive data and ours yielded the accurate fundamental parameters of the program target. The masses were derived to about 1.0 \% accuracy and the radii to 0.6 \%, or better. The secondary component's parameters of $M_2 = 0.200 \pm 0.002$ M$_\odot$, $R_2 = 0.528 \pm 0.003$ R$_\odot$, $T_{\rm eff,2}$ = 11,186 $\pm$ 235 K, and $L_2 = 3.9 \pm 0.3$ L$_\odot$ are in excellent agreement with the evolutionary sequence for a helium-core white dwarf of mass 0.203 M$_\odot$, and indicates that this star is halfway through the constant luminosity phase. The results presented in this article demonstrate that WASP 0131+28 is an EL CVn eclipsing binary in a thin disk, which is formed from the stable Roche-lobe overflow channel and composed of a main-sequence dwarf with a spectral type A0 and a pre-He white dwarf.

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arXiv2019

Absolute Properties of the Eclipsing $γ$ Dor Star V404 Lyrae

We present the first high-resolution spectra for the eclipsing binary V404 Lyr showing $γ$ Dor pulsations, which we use to study its absolute properties. By fitting models to the disentangling spectrum of the primary star, we found that it has an effective temperature of $T_{\rm eff,1}=7,330 \pm 150$ K and a rotational velocity of $v_1\sin$$i=148\pm18$ km s$^{-1}$. The simultaneous analysis of our double-lined radial velocities and the pulsation-subtracted ${\it Kepler}$ data gives us accurate stellar and system parameters of V404 Lyr. The masses, radii, and luminosities are $M_1$ = 2.17$\pm$0.06 M$_\odot$, $R_1$ = 1.91$\pm$0.02 R$_\odot$, and $L_1$ = 9.4$\pm$0.8 L$_\odot$ for the primary, and $M_2$ = 1.42$\pm$0.04 M$_\odot$, $R_2$ = 1.79$\pm$0.02 R$_\odot$, and $L_2$ = 2.9$\pm$0.2 L$_\odot$ for the secondary. The tertiary component orbiting the eclipsing pair has a mass of $M_{\rm 3b}$ = 0.71$\pm$0.15 $M_\odot$ in an orbit of $P_{\rm 3b}$ = 642$\pm$3 days, $e_{\rm 3b}$ = 0.21$\pm$0.04, and $a_{\rm 3b}$ = 509$\pm$2 R$_\odot$. The third light of $l_3=4.1\pm0.2\%$ could be partly attributable to the K-type circumbinary object. By applying a multiple frequency analysis to the eclipse-subtracted light residuals, we detected 45 frequencies with signal to noise amplitude ratios larger than 4.0. Identified as independent pulsation modes, seven frequencies ($f_1-f_6$, $f_9$), their new pulsation constants, and the location in the Hertzsprung-Russell diagram indicate that the pulsating primary is a $γ$ Dor-type variable star.

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arXiv2018

KIC 6206751: the first R CMa-type eclipsing binary with $γ$ Doradus pulsations

We present the absolute properties of the double-lined eclipsing binary KIC 6206751 exhibiting multiperiodic pulsations. The ${\it Kepler}$ light curve of this system was simultaneously solved with the radial-velocity data given by Matson et al. (2017). The results indicate that the binary star is a short-period semi-detached system with fundamental parameters of $M_1$ = 1.66$\pm$0.04 M$_\odot$, $M_2$ = 0.215$\pm$0.006 M$_\odot$, $R_1$ = 1.53$\pm$0.02 R$_\odot$, $R_2$ = 1.33$\pm$0.02 R$_\odot$, $L_1$ = 5.0$\pm$0.6 L$_\odot$, and $L_2$ = 0.96$\pm$ 0.09 L$_\odot$. We applied multiple frequency analyses to the eclipse-subtracted light residuals and detected the 42 frequencies below 2.5 d$^{-1}$. Among these, three independent frequencies of $f_2$, $f_3$, and $f_4$ can be identified as high-order (38 $\le n \le$ 40) low-degree ($\ell$ = 2) gravity-mode oscillations, whereas the other frequencies may be orbital harmonics and combination terms. The ratios between the orbital frequency and the pulsation frequencies are $f_{\rm orb}$:$f_{\rm 2-4}$ $\simeq$ 2:3, which implies that the $γ$ Dor pulsations of the detached primary star may be excited by the tidal interaction of the secondary companion. The short orbital period, and the low mass ratio and $M_2$ demonstrate that KIC 6206751 is an R CMa-type star, which is most likely evolving into an EL CVn star. Of seven well-studied R CMa-type stars, our program target is the only eclipsing binary with a $γ$ Dor pulsating component.

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arXiv2018

Absolute dimensions and evolutionary status of the semi-detached Algol W Ursae Minoris

Double-lined eclipsing binaries allow accurate and direct determination of fundamental parameters such as mass and radius for each component, and they provide important constraints on the stellar structure and evolution models. In this study, we aim to determine a unique set of binary parameters for the Algol system W UMi and to examine its evolutionary status. New high-resolution time-series spectroscopic observations were carried out during 14 nights from April 2008 to March 2011, and a total of 37 spectra were obtained using the Bohyunsan Optical Echelle Spectrograph. We measured the radial velocities (RVs) for both components, and the effective temperature of the primary star was found to be $T_{\rm eff,1}$ = 9310 $\pm$ 90 K by a comparison of the observed spectra and the Kurucz models. The physical parameters of W UMi were derived by an analysis of our RV data together with the multi-band light curves of Devinney et al. (1970). The individual masses, radii, and luminosities of both components are $M_1$ = 3.68 $\pm$ 0.10 M$_\odot$ and $M_2$ = 1.47 $\pm$ 0.04 M$_\odot$, $R_1$ = 3.88 $\pm$ 0.03 R$_\odot$ and $R_2$ = 3.13 $\pm$ 0.03 R$_\odot$, and $L_1$ = 102 $\pm$ 1 L$_\odot$ and $L_2$ = 7.3 $\pm$ 0.1 L$_\odot$, respectively. A comparison of these parameters with theoretical stellar models showed that the primary component lies in the main-sequence band, while the less massive secondary is noticeably evolved. The results indicate that the initially more massive star became the present secondary by losing most of its own mass via mass transfer to the companion (present primary).

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