arXiv subjects

Seung-Lee Kim

Publications and source records attributed to Seung-Lee Kim.

At least 163 records · Page 9Linked to original sources

arXiv2017

Distance and properties of NGC 4993 as the host galaxy of a gravitational wave source, GW170817

Recently, the optical counterpart of a gravitational wave source GW170817 has been identified in NGC 4993 galaxy. Together with evidence from observations in electromagnetic waves, the event has been suggested as a result of a merger of two neutron stars. We analyze the multi-wavelength data to characterize the host galaxy property and its distance to examine if the properties of NGC 4993 are consistent with this picture. Our analysis shows that NGC 4993 is a bulge-dominated galaxy with reff ~ 2-3 kpc and the Sersic index of n = 3-4 for the bulge component. The spectral energy distribution from 0.15 to 24 micron indicates that this galaxy has no significant ongoing star formation, the mean stellar mass of (0.3 - 1.2) times 10^11 Msun,the mean stellar age greater than ~3 Gyr, and the metallicity of about 20% to 100% of solar abundance. Optical images reveal dust lanes and extended features that suggest a past merging activity. Overall, NGC 4993 has characteristics of normal, but slightly disturbed elliptical galaxies. Furthermore, we derive the distance to NGC 4993 with the fundamental plane relation using 17 parameter sets of 7 different filters and the central stellar velocity dispersion from literature, finding an angular diameter distance of 37.7 +- 8.7 Mpc. NGC 4993 is similar to some host galaxies of short gamma-ray bursts but much different from those of long gamma-ray bursts, supporting the picture of GW170817 as a result of a merger of two NSs.

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arXiv2016

KIC 11401845: An Eclipsing Binary with Multiperiodic Pulsations and Light Travel Time

We report the ${\it Kepler}$ photometry of KIC 11401845 displaying multiperiodic pulsations, superimposed on binary effects. Light-curve synthesis represents that the binary star is a short-period detached system with a very low mass ratio of $q$ = 0.070 and filling factors of $F_1$ = 45 % and $F_2$ = 99 %. Multiple frequency analyses were applied to the light residuals after subtracting the synthetic eclipsing curve from the observed data. We detected 23 frequencies with signal to noise amplitude ratios larger than 4.0, of which the orbital harmonics ($f_4$, $f_6$, $f_9$, $f_{15}$) in the low frequency domain may originate from tidally excited modes. For the high frequencies of 13.7$-$23.8 day$^{-1}$, the period ratios and pulsation constants are in the ranges of $P_{\rm pul}/P_{\rm orb}$ = 0.020$-$0.034 and $Q$ = 0.018$-$0.031 d, respectively. These values and the position on the Hertzsprung-Russell diagram demonstrate that the primary component is a $δ$ Sct pulsating star. We examined the eclipse timing variation of KIC 11401845 from the pulsation-subtracted data and found a delay of 56$\pm$17 s in the arrival times of the secondary eclipses relative to the primary eclipses. A possible explanation of the time shift may be some combination of a light-travel-time delay of about 34 s and a very small eccentricity of $e \cos ω <$ 0.0002. This result represents the first measurement of the Rømer delay in non-compact binaries.

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arXiv2016

KIC 6220497: A New Algol-type Eclipsing Binary with Multiperiodic Pulsations

We present both binarity and pulsation of KIC 6220497 from the {\it Kepler} observations. The light curve synthesis shows that the eclipsing system is a semi-detached Algol with parameters of $q$ = 0.243$\pm$0.001, $i$ = 77.3$\pm$0.3 deg, and $ΔT$ = 3,372$\pm$58 K, in which the detached primary component fills its Roche lobe by $\sim$87\%. A multiple frequency analysis of the eclipse-subtracted light residuals reveals 33 frequencies in the range of 0.75$-$20.22 d$^{-1}$ with amplitudes between 0.27 and 4.56 mmag. Among these, four are pulsation frequencies in fundamental ($f_1$, $f_5$) and $p$ ($f_2$, $f_7$) modes, and six are orbital frequency ($f_8$, $f_{31}$) and its harmonics ($f_6$, $f_{11}$, $f_{20}$, $f_{24}$), which can be attributed to tidally excited modes. For the pulsation frequencies, the pulsation constants of 0.16$-$0.33 d and the period ratios of $P_{\rm pul}/P_{\rm orb}$ = 0.042$-$0.089 indicate that the primary component is a $δ$ Sct pulsating star and, thus, KIC 6220497 is an oscillating eclipsing Algol (oEA) star. The dominant pulsation period of 0.1174051$\pm$0.0000004 d is significantly longer than that expected from empirical relations that link the pulsation period with the orbital period. The surface gravity of $\log g_1$ = 3.78$\pm$0.03 is clearly smaller than those of the other oEA stars with similar orbital periods. The pulsation period and the surface gravity of the pulsating primary demonstrate that KIC 6220497 would be the more evolved EB, compared with normal oEA stars.

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arXiv2016

Time-series spectroscopy of the pulsating eclipsing binary XX Cephei

Oscillating Algol-type eclipsing binaries (oEA) are very interesting objects that have three observational features of eclipse, pulsation, and mass transfer. Direct measurement of their masses and radii from the double-lined radial velocity data and photometric light curves would be the most essential for understanding their evolutionary process and for performing the asteroseismological study. We present the physical properties of the oEA star XX Cep from high-resolution time-series spectroscopic data. The effective temperature of the primary star was determined to be 7,946 $\pm$ 240 K by comparing the observed spectra and the Kurucz models. We detected the absorption lines of the secondary star, which had never been detected in previous studies, and obtained the radial velocities for both components. With the published $BVRI$ light curves, we determined the absolute parameters for the binary via Wilson-Devinney modeling. The masses and radii are $M_{1} = 2.49 \pm 0.06$ $M_\odot$, $M_{2} = 0.38 \pm 0.01$ $M_\odot$, $R_{1} = 2.27 \pm 0.02$ $R_\odot$, and $R_{2} = 2.43 \pm 0.02$ $R_\odot$, respectively. The primary star is about $45 \%$ more massive and $60 \%$ larger than the zero-age main sequence (ZAMS) stars with the same effective temperature. It is probably because XX Cep has experienced a very different evolutionary process due to mass transfer, contrasting with the normal main sequence stars. The primary star is located inside the theoretical instability strip of $δ$ Sct-type stars on HR diagram. We demonstrated that XX Cep is an oEA star, consisting of a $δ$ Sct-type pulsating primary component and an evolved secondary companion.

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arXiv2015

KIC 4739791: A New R CMa-type Eclipsing Binary with a Pulsating Component

The {\it Kepler} light curve of KIC 4739791 exhibits partial eclipses, inverse O'Connell effect, and multiperiodic pulsations. Including a starspot on either of the binary components, the light-curve synthesis indicates that KIC 4739791 is in detached or semi-detached configurations with both a short orbital period and a low mass ratio. Multiple frequency analyses were performed in the light residuals after subtracting the binarity effects from the original {\it Kepler} data. We detected 14 frequencies: six in the low-frequency region (0.1$-$2.3 d$^{-1}$) and eight in the high-frequency region (18.2$-$22.0 d$^{-1}$). Among these, six high frequencies with amplitudes of 0.62$-$1.97 mmag were almost constant over time for 200 d. Their pulsation periods and pulsation constants are in the ranges of 0.048$-$0.054 d and 0.025$-$0.031 d, respectively. In contrast, the other frequencies may arise from the alias effects caused by the orbital frequency or combination frequencies. We propose that KIC 4739791 is a short-period R CMa binary with the lowest mass ratio in the known classical Algols and that its primary component is a $δ$ Sct pulsating star. Only four R CMa stars have been identified, three of which exhibit $δ$ Sct-type oscillations. These findings make KIC 4739791 an attractive target for studies of stellar interior structure and evolution.

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arXiv2014

The Eclipsing System V404 Lyr: Light-Travel Times and Gamma Doradus Pulsations

We present the physical properties of V404 Lyr exhibiting eclipse timing variations and multiperiodic pulsations from all historical data including the Kepler observations. Detailed analyses of 2,922 minimum epochs showed that the orbital period has varied through a combination with an upward-opening parabola and two sinusoidal variations, with periods of $P_3$=649 d and $P_4$=2,154 d and semi-amplitudes of $K_3$=193 s and $K_4$=49 s, respectively. The secular period increase could be interpreted as a combination of the secondary to primary mass transfer and angular momentum loss. The most reasonable explanation for both sinusoids is a pair of light-travel-time effects due to two circumbinary objects with projected masses of $M_3$=0.47 M$_\odot$ and $M_4$=0.047 M$_\odot$. The third-body parameters are consistent with those calculated using the W-D binary code. For the orbital inclinations higher than 43$^\circ$, the fourth component has a mass within the hydrogen-burning limit of $\sim$0.07 M$_\odot$, which implies that it is a brown dwarf. A satisfactory model for the Kepler light curves was obtained through applying a cool spot to the secondary component. The results demonstrate that the close eclipsing pair is in a semi-detached, but near-contact, configuration; the primary fills approximately 93% of its limiting lobe and is larger than the lobe-filling secondary. Multiple frequency analyses were applied to the light residuals after subtracting the synthetic eclipsing curve from the Kepler data. This revealed that the primary component of V404 Lyr is a $γ$ Dor type pulsating star, exhibiting seven pulsation frequencies in the range of 1.85$-$2.11 d$^{-1}$ with amplitudes of 1.38$-$5.72 mmag and pulsation constants of 0.24$-$0.27 d. The seven frequencies were clearly identified as high-order low-degree gravity-mode oscillations which might be excited through tidal interaction.

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arXiv2014

1SWASP J093010.78+533859.5: A Possible Hierarchical Quintuple System

We present the observational results of this kind of rare object 1SWASP J093010.78+533859.5, for which the doubly eclips- ing feature had been detected previously from the SuperWASP photometric archive. Individual PSF photometry for two objects with a separation of about 1.9 arcsec was performed for the first time in this study. Our time-series photometric data confirms the finding of Lohr et al. (2013) that the bright object A is an Algol-type detached eclipsing binary and the fainter B is a W UMa-type contact eclipsing. Using the high- resolution optical spectra, we obtained well-defined radial velocity variations of system A. Furthermore, stationary spectral lines were detected that must have originated from a further, previously unrecognized stellar component. It was confirmed by the third object contribution from the light curve analysis. No spectral feature of the system B was detected, probably due to motion blur by long exposure time. We obtained the binary parameters and the absolute dimensions of the systems A and B from light curve synthesis with and without radial velocities, respectively. The primary and secondary components of system A have a spectral type of K1 and K5 main sequences, respec- tively. Two components of system B have nearly the same type of K3 main sequence. Light variations for both binaries are satisfactorily modeled by using two-spot models with one starspot on each component. We estimated the distances to systems A and B individually. Two systems may have similar distances of about 70 pc and seem to be gravitationally bound with a separation of about 130 AU. In conclusion, we suggest that 1SWASP J093010.78+533859.5 is a quintuple stellar system with a hierarchical structure of a triple system A(ab)c and a binary system B(ab).

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arXiv2014

Physical Nature and Timing Variations of the Eclipsing System V407 Pegasi

New multiband CCD photometry is presented for V407 Peg; the $R_{\rm C}$ light curves are the first ever compiled. Our light curves, displaying a flat bottom at secondary minimum and an O'Connell effect, were simultaneously analyzed with the radial-velocity (RV) curves given by Rucinski et al. (2008). The light changes of the system are best modeled by using both a hot spot on the secondary star and a third light. The model represents historical light curves also. All available minimum epochs, including our six timing measurements, have been examined and indicate that the eclipse timing variation is mainly caused by light asymmetries due to the spot activity detected in the light-curve synthesis. The hot spot may be produced as a result of the impact of the gas stream from the primary star. Our light and velocity solutions indicate that V407 Peg is a totally-eclipsing A-type overcontact binary with values of $q$=0.251, $i$=87$^\circ.6$, $ΔT$=496 K, $f$=61 $\%$, and $l_3$=11$\sim$16 $\%$. Individual masses and radii of both components are determined to be $M_1$=1.72 M$_\odot$, $M_2$=0.43 M$_\odot$, $R_1$=2.15 R$_\odot$, and $R_2$=1.21 R$_\odot$. These results are very different from previous ones, which is probably caused by the light curves with distorted and inclined eclipses used in those other analyses. The facts that there are no objects optically related with the system and that the seasonal RVs show a large discrepancy in systemic velocity indicate that the third light source most likely arises from a tertiary component orbiting the eclipsing pair.

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arXiv2012

The Triply Eclipsing Hierarchical Triple Star KIC002856960

In a recent study, Armstrong et al. presented an eclipsing binary star of about 6.2 h period with transit-like tertiary signals occurring every 204.2 d in the {\it Kepler} public data of KIC002856960 and proposed three possible hierarchical structures: (AB)b, (AB)C, and A(BC). We analyzed the {\it Kepler} light curve by including a third light source and one starspot on each binary component. The results represent that the close eclipsing pair is in a low-mass eccentric-orbit, detached configuration. Based on 123 eclipse timings calculated from the Wilson-Devinney binary model, a period study of the close binary reveals that the orbital period has experienced a sinusoidal variation with a period and a semi-amplitude of 205$\pm$2 d and 0.0021$\pm$0.0002 d, respectively. The period variation would be produced by the light-travel-time effect due to a gravitationally-bound third body with a minimum mass of $M_3 \sin i_3$=0.76 M$_\odot$ in an eccentric orbit of $e_3$=0.61. This is consistent with the presence of third light found in our light-curve solution and the tertiary signal of 204.2 d period most likely arises from the K-type star crossed by the close eclipsing binary. Then, KIC002856960 is a triply eclipsing hierarchical system, A(BC), consisting of a close binary with two M-type dwarfs and a more massive K-type component. The presence of the third star may have played an important role in the formation and evolution of the close pair, which may ultimately evolve into a contact system by angular momentum loss.

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arXiv2012

Physical Properties of the Low-Mass Eclipsing Binary NSVS 02502726

NSVS 02502726 has been known as a double-lined, detached eclipsing binary that consists of two low-mass stars. We obtained $BVRI$ photometric follow-up observations in 2009 and 2011 to measure improved physical properties of the binary star. Each set of light curves, including the 2008 data given by \cCakirli et al., was simultaneously analyzed with the previously published radial-velocity curves using the Wilson-Devinney binary code. The conspicuous seasonal light variations of the system are satisfactorily modelled by a two-spot model with one starspot on each component and by changes of the spot parameters with time. Based on 23 eclipse timings calculated from the synthetic model and one ephemeris epoch, an orbital period study of NSVS 02502726 reveals that the period has experienced a continuous decrease of $-5.9\times10^{-7}$ d yr$^{-1}$ or a sinusoidal variation with a period and semi-amplitude of 2.51 yrs and 0.0011 d, respectively. The timing variations could be interpreted as either the light-travel-time effect due to the presence of an unseen third body, or as the combination of this effect and angular momentum loss via magnetic stellar wind braking. Individual masses and radii of both components are determined to be $M_1$=0.689$\pm$0.016 M$_\odot$, $M_2$=0.341$\pm$0.009 M$_\odot$, $R_1$=0.707$\pm$0.007 R$_\odot$, and $R_2$=0.657$\pm$0.008 R$_\odot$. The results are very different from those of \cCakirli et al. with the primary's radius (0.674$\pm$0.006 R$_\odot$) smaller the secondary's (0.763$\pm$0.007 R$_\odot$). We compared the physical parameters presented in this paper with current low-mass stellar models and found that the measured values of the primary star are best fitted to a 79-Myr isochrone. The primary is in good agreement with the empirical mass-radius relation from low-mass binaries, but the secondary is oversized by about 85%.

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arXiv2012

The Light and Period Variations of the Eclipsing Binary BX Draconis

New CCD photometric observations of BX Dra were obtained for 26 nights from 2009 April to 2010 June. The long-term photometric behaviors of the system are presented from detailed studies of the period and light variations, based on the historical data and our new observations. All available light curves display total eclipses at secondary minima and inverse O'Connell effects with Max I fainter than Max II, which are satisfactorily modeled by adding the slightly time-varying hot spot on the primary star. A total of 87 times of minimum light spanning over about 74 yrs, including our 22 timing measurements, were used for ephemeris computations. Detailed analysis of the O-C diagram showed that the orbital period has changed in combinations with an upward parabola and a sinusoidal variation. The continuous period increase with a rate of +5.65 \times 10^-7 d yr^-1 is consistent with that calculated from the Wilson-Devinney synthesis code. It can be interpreted as a mass transfer from the secondary to the primary star at a rate of 2.74 \times 10^-7 M\odot yr^-1, which is one of the largest rates for contact systems. The most likely explanation of the sinusoidal variation with a period of 30.2 yrs and a semi-amplitude of 0.0062 d is a light-traveltime effect due to the existence of a circumbinary object. We suggest that BX Dra is probably a triple system, consisting of a primary star with a spectral type of F0, its secondary component of spectral type F1-2, and an unseen circumbinary object with a minimum mass of M3 = 0.23 M\odot.

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arXiv2012

Trends of Papers Published from 2006 to 2010 in Journals Nature and Science

We present an analysis of the papers published in the journals Nature and Science in the years from 2006 to 2010. During this period, a total of 7788 papers were published in the two journals. This includes 544 astronomy papers that comprise 7.0% of the papers in `all' research fields and 18.9% of those in the fields of `physical sciences'. The sub-fields of research of the astronomy papers are distributed, in descending order of number of papers, in Solar System, stellar astronomy, galaxies and the universe, the Milky Way Galaxy, and exoplanets. The observational facilities used for the studies are mainly ground-based telescopes (31.1%), spacecrafts (27.0%), and space telescopes (22.8%), while 16.0% of papers did not use any noticeable facilities and 1.7% used other facilities. Korean scientists have published 86 papers (33 in Nature and 53 in Science), which is 1.10% of all the papers (N=7788) in the two journals. The share of papers by Korean astronomers among the scientific papers by Koreans is 8.14%, slightly higher than the contribution of astronomy papers (7.0%) in both journals.

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arXiv2012

The sub-Saturn Mass Transiting Planet HAT-P-12b

We present new photometric data of the transiting planet HAT-P-12b observed in 2011. Our three transit curves are modelled using the JKTEBOP code and adopting the quadratic limb-darkening law. Including our measurements, 18 transit times spanning about 4.2 yr were used to determine the improved ephemeris with a transit epoch of 2,454,187.85560$\pm$0.00011 BJD and an orbital period of 3.21305961$\pm$0.00000035 d. The physical properties of the star-planet system are computed using empirical calibrations from eclipsing binary stars and stellar evolutionary models, combined with both our transit parameters and previously-known spectroscopic results. We found that the absolute dimensions of the host star are $M_{\rm A}$=0.73$\pm$0.02 M$_\odot$, $R_{\rm A}$=0.70$\pm$0.01 R$_\odot$, log $g_{\rm A}$=4.61$\pm$0.02, $ρ_{\rm A}$=2.10$\pm$0.09 $ρ_{\odot}$, and $L_{\rm A}$=0.21$\pm$0.01 L$_\odot$. The planetary companion has $M_{\rm b}$=0.21$\pm$0.01 M$_{\rm Jup}$, $R_{\rm b}$=0.94$\pm$0.01 R$_{\rm Jup}$, log $g_{\rm b}$=2.77$\pm$0.02, $ρ_{\rm b}$=0.24$\pm$0.01 $ρ_{\rm Jup}$, and $T_{\rm eq}$=960$\pm$14 K. Our results agree well with standard models of irradiated gas giants with a core mass of 11.3 M$_{\oplus}$.

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arXiv2011

The Algol System SZ Herculis: Physical Nature and Orbital Behavior

Multiband CCD photometric observations of SZ Her were obtained between 2008 February and May. The light curve was completely covered and indicated a significant temperature difference between both components. The light-curve synthesis presented in this paper indicates that the eclipsing binary is a classical Algol-type system with parameters of $q$=0.472, $i$=87$^\circ$.57, and $Δ$($T_{1}$--$T_{2}$)=2,381 K; the primary component fills approximately 77% of its limiting lobe and is slightly larger than the lobe-filling secondary. More than 1,100 times of minimum light spanning more than one century were used to study an orbital behavior of the binary system. It was found that the orbital period of SZ Her has varied due to a combination of two periodic variations with cycle lengths of $P_3$=85.8 yr and $P_4$=42.5 yr and semi-amplitudes of $K_3$=0.013 d and $K_4$=0.007 d, respectively. The most reasonable explanation for them is a pair of light-time effects (LITEs) driven by the possible existence of two M-type companions with minimum masses of $M_3$=0.22 M$_\odot$ and $M_4$=0.19 M$_\odot$, that are located close to the 2:1 mean motion resonance. If two additional bodies exist, then the overall dynamics of the multiple system may provide a significant clue to the formation and evolution of the eclipsing pair.

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arXiv2011

WZ Cygni: a Marginal Contact Binary in a Triple System?

We present new multiband CCD photometry for WZ Cyg made on 22 nights in two observing seasons of 2007 and 2008. Our light-curve synthesis indicates that the system is in poor thermal contact with a fill-out factor of 4.8% and a temperature difference of 1447 K. Including our 40 timing measurements, a total of 371 times of minimum light spanning more than 112 yr were used for a period study. Detailed analysis of the $O$--$C$ diagram showed that the orbital period has varied by a combination with an upward parabola and a sinusoid. The upward parabola means the continuous period increase and indicates that some stellar masses are thermally transferred from the less to the more massive primary star at a rate of about 5.80$\times10^{-8}$ M$_\odot$ yr$^{-1}$. The sinusoidal variation with a period of 47.9 yr and a semi-amplitude of 0.008 d can be interpreted most likely as the light-travel-time effect due to the existence of a low-mass M-type tertiary companion with a projected mass of $M_3 \sin i_3$=0.26 M$_\odot$. We examined the evolutionary status of WZ Cyg from the absolute dimensions of the eclipsing pair. It belongs to the marginal contact binary systems before broken-contact phase, consisting of a massive primary star with spectral type of F4 and a secondary with the type K1.

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arXiv2010

The EXOTIME project: a status report on PG 1325+101 (QQ Vir)

After the discovery of V391 Peg b, the first planet detected around a post Red Giant phase star (Silvotti et al. 2007), the EXOTIME (EXOplanet search with the TIming MEthod) project is focused on the search for new planets with similar characteristics. The aim of the project is to organize a global observing network to collect as much data as possible for a sample of five subdwarf B (sdB) stars and share them in order to obtain a more precise analysis. These evolved pulsators may have extremely regular oscillation periods. This feature makes these stars suitable to search for planetary companions with the timing method as in the case of pulsars. In this contribution we present the project and some preliminary results for the star PG 1325+101 (QQ Vir) after the first two years of activity.

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arXiv2010

Physical Properties of the Transiting Planetary System TrES-3

We present four new transits of the planetary system TrES-3 observed between 2009 May and 2010 June. Among these, the third transit by itself indicates possible evidence for brightness disturbance, which might be the result of the planet blocking a cool starspot on the stellar surface. A total of 109 transit times, including our measurements, were used to determine the improved ephemeris with a transit epoch of 2454185.910944$\pm$0.000072 HJED and an orbital period of 1.30618700$\pm$0.00000015 d. We analyzed the transit light curves using the JKTEBOP code and adopting the quadratic limb-darkening law. In order to derive the physical properties of the TrES-3 system, the transit parameters are combined with the empirical relations from eclipsing binary stars and stellar evolutionary models. The stellar mass and radius obtained from a calibration using $T_A$, log $ρ_{\rm A}$ and [Fe/H] are consistent with those from the isochrone analysis. We found that the exoplanet TrES-3b has a mass of 1.93$\pm$0.07 M$_{\rm Jup}$, a radius of 1.30$\pm$0.04 R$_{\rm Jup}$, a surface gravity of log $g_{\rm b}$=3.45$\pm$0.02, a density of 0.82$\pm$0.06 $ρ_{\rm Jup}$, and an equilibrium temperature of 1641$\pm$23 K. The results are in good agreement with theoretical models for gas giant planets.

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arXiv2010

The Light and Period Variations of the Eclipsing Binary AA Ursae Majoris

We present new multiband CCD photometry for AA UMa made on 8 nights between January and March 2009; the $R$ light curves are the first ever compiled. Historical light curves, as well as ours, display partial eclipses and inverse O'Connell effects with Max I fainter than Max II. Among possible spot models, a cool spot on either of the component stars and its variability with time permit good light-curve representations for the system. A total of 194 eclipse timings over 81 yrs, including our five timings, were used for ephemeris computations. We found that the orbital period of the system has varied due to a periodic oscillation overlaid on an upward parabolic variation. The continuous period increase at a fractional rate of $+$1.3$\times$10$^{-10}$ is consistent with that calculated from the W-D code and can be interpreted as a thermal mass transfer from the less to the more massive secondary star at a rate of 6.6$\times$10$^{-8}$ M$_\odot$ yr$^{-1}$. The periodic component is in satisfactory accord with a light-time effect due to an unseen companion with a period of 28.2 yrs, a semi-amplitude of 0.007 d, and a minimum mass of $M_3 \sin i_3$=0.25 $M_\odot$ but this period variation could also arise from magnetic activity.

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