Chun-Hwey Kim

The sdB+M Eclipsing System HW Virginis and its Circumbinary Planets

For the very short period subdwarf B eclipsing binary HW Vir, we present new CCD photometry made from 2000 through 2008. In order to obtain consistency of the binary parameters, our new light curves, showing sharp eclipses and a striking reflection effect, were analyzed simultaneously with previously published radial velocity data. The secondary star parameters of M 2 = 0.14 M ?, R 2 = 0.18 R ?, and T 2 = 3084 K are consistent with those of an M6-7 main-sequence star. A credibility issue regarding bolometric corrections is emphasized. More than 250 times of minimum light, including our 41 timings and spanning more than 24 yr, were used for a period study. From a detailed analysis of the O ? C diagram, it emerged that the orbital period of HW Vir has varied as a combination of a downward-opening parabola and two sinusoidal variations, with cycle lengths of P 3 = 15.8 yr and P 4 = 9.1 yr and semiamplitudes of K 3 = 77 s and K 4 = 23 s, respectively. The continuous period decrease with a rate of ?8.28 ? 10?9 days yr?1 may be produced by angular momentum loss due to magnetic stellar wind braking but not by gravitational radiation. Of the possible causes of the cyclical components of the period change, apsidal motion and magnetic period modulation can be ruled out. The most reasonable explanation of both cyclical variations is a pair of light-travel-time effects driven by the presence of two substellar companions with projected masses of M 3sin i 3 = 19.2 M Jup and M 4sin i 4 = 8.5 M Jup. The two objects are the first circumbinary planets known to have been formed in a protoplanetary disk as well the first ones discovered by using the eclipse-timing method. The detection implies that planets could be common around binary stars just as are planets around single stars and demonstrates that planetary systems formed in a circumbinary disk can survive over long timescales. Depending on the thermal inertia of their massive atmospheres, the hemispheres of the planets turned toward the stars can experience substantial reciprocating temperature changes during the minutes-long primary eclipse intervals.

Photometric Studies of the Triple Star ER Orionis

A total of 1637 BVR CCD observations of the overcontact binary ER Ori are used as the basis for new light curves, including the first red one. From these measurements, new timings of minimum light have been calculated. The complex period variation can be sorted into a linear period improvement, a secular period increase of considerable magnitude, and a 50 year cyclical component. This latter is discussed in terms of a light-time contribution from a bound third star, which finds some support from Hipparcos results. The new light curves were synthesized using the Wilson-Divinney code. It was found useful to model a single modest spot in order to minimize the residuals from the observations. Our model is found to agree with previous light curves.

The Chromospherically Active Contact Binary CE Leonis

We present complete VRI light curves of the contact binary CE Leo and provide detailed photometric solutions, as well as an analysis of its period variation. A total of 73 times of minima over 50 years, including our observations, were used for the period study. The complex period variation can be sorted into a linear period improvement, a period of P ¼ 0:30342771 days, a secular period increase at the rate of ˙ P=P ¼þ 3:05 ;10 � 7 days yr � 1 ,a nd a2 2:6 � 0:5 yr periodic component. The � 22.6 yr periodic variation in the OC residuals most likely arises from the light-travel time effect from a low-mass (m3 � 0:3Msini) dM tertiary companion moving in an eccentric (e 0 ¼ 0:61 � 0:04) orbit. However, it is also possible that this periodic variation arises from the effects of a magnetic activity cycle, known as the Applegate mechanism. The light curves show asymmetries in the two different maxima. The 1998 light curves show that primary maximunm was 0.042, 0.038, and 0.038 mag brighter than secondary maximum in V, R ,a ndI, respectively. The durations of totality for three epochs were 18.3 minutes in 1989, 19.7 minutes in 1998, and 18.8 minutes in 2001. The relative depth of primary minimum was found to vary between 1.20 and 1.32 mag. We have analyzed the light curves from the three epochs using the 1993 version of the Wilson-Devinney differential corrections computer code to find a unique solution for CE Leo. The corresponding spectral type of the secondary star from the colors and effective temperature isdK2. The asymmetric light curves can be explained by the effects of starspots. We find that the light curves are best fitted by employing a cool spot on the cooler, larger component of the system. The spot-effect parameter SE ¼ 0:05 found for CE Leo is relatively large for W UMa binaries.

A Period Study and Light Synthesis for the W Ursae Majoris Type Binary SS Arietis

Numerous new CCD measures of the cool overcontact binary SS Arietis are compiled into six well-covered light curves. The confusing history of the binarys period variability is laid out in order to consider the diverse interpretations that have been presented previously. It is concluded that the period activity can be ascribed to no fewer than three separate causes. There is some little support for a magnetic cycle functioning in phase with one of the components of the period variability. The three light curves from 1996 have responded satisfactorily to a modern synthesis code, and the characterization of the binary characterization is better constrained than was the case from earlier light-curve studies. Light curves from 1999 have not been so satisfactorily represented. Conditioning the light-curve results with published radial velocities has very little effect on the light-curve parameters. It does, however, reveal a curious distribution of the velocity residuals, and we offer some possible interpretations. Low-level spot activity is also modeled. There is no evidence of a third star contributing significant light to the system.

A Possible Detection of a Second Light-Time Orbit for the Massive, Early-Type Eclipsing Binary Star AH Cephei

All published and newly observed times of minimum light of the massive, early-type eclipsing binary star AH Cep were analyzed. After subtracting the light-time effect due to the well-known third body from the residuals of the observed times of minimum light, it was found that the second-order O - C residuals varied in a cyclical way. It was assumed that the secondary oscillations were produced by a light-time effect due to a fourth body so all the times of minimum light were reanalyzed with a differential least-squares scheme in order to obtain the light-time orbits due to both the third and fourth bodies. The periods, eccentricities, and semiamplitudes of the light-time orbits for the third and fourth bodies were derived as P3 = 67.6 and P4 = 9.6 yr, e3 = 0.52 and e4 = 0.64, and K3 = 0.0608 and K4 = 0.0040 days, respectively. The radial velocities of AH Cep published so far do not conflict with the hypothesis of the multiplicity of the system, but their accuracies are not high enough to support the interpretation. Other properties of the distant bodies are discussed for assorted possible inclinations of their orbits.

Photometric Studies of the Near‐Contact Binary AX Draconis

ABSTRACT We have obtained CCD photometric observations of the near‐contact binary AX Dra during two observing seasons from 2001 March through May and from 2003 April and May. From these measurements, the seasonal light curves of AX Dra for 2001 and 2003 were compiled, and a total of 13 new timings of minimum light were calculated. An analysis of the resulting \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

A Long-term Photometric Study of the Near-contact Binary RU Ursae Minoris

O-C

THE FIRST COMPREHENSIVE PHOTOMETRIC STUDY OF THE ALGOL-TYPE SYSTEM CL AURIGAE

\end{document} diagram reveals evidence for a periodic change with a semiamplitude of 0.0061 days and a period of 56.1 ...

A period study of AR Lacertae

New CCD photometric observations of the near-contact binary RU UMi were obtained from1999 December to 2000 April and later during 2003 March. All available times of minimum light, including our own measurements, have been examined and indicate that the orbital period of the system has experienced a continuous period decrease with a rate of (dP/dt)obs = -1.6 × 10-8 d yr-1. This period decrease cannot be explained trivially by mass transfer from the more massive primary to the less massive secondary, because our light-curve synthesis indicates that RU UMi is in a semidetached configuration with the primary star filling 95% of its inner Roche lobe and the secondary filling its limiting lobe completely. We present the case that the observed period change may be produced by a combination of AML due to magnetic braking with a rate of (dP/dt)mb = -1.0 × 10-7 d yr-1 and of mass transfer from the secondary to the primary at a rate of 2 = -6.0 × 10-8 M⊙ yr-1. Historical light curves of RU UMi over a 32-yr interval display variably asymmetrical secondary minima. From analyses of velocity and light curves and of the light curves alone, the light variations are best represented by a variable cool spot that has consistently existed on the inner hemisphere of the secondary component. There is a weak indication that the hot star is no longer a main sequence one.

Minimum Number of Observation Points for LEO Satellite Orbit Estimation by OWL Network

We present the first extensive photometric results of CL Aur from our BVRI CCD photometry made on 22 nights from 2003 November to 2005 February. Fifteen new timings of minimum light were obtained. During the past 104 yr, the orbital period has varied due to a periodic oscillation superposed on a continuous period increase. The period and semi-amplitude of the oscillation are about 21.6 yr and 0.0133 day, respectively. This detail is interpreted as a light-travel-time effect due to a low-luminosity K-type star gravitationally bound to the CL Aur close system. Our photometric study indicates that CL Aur is a relatively short-period Algol-type binary with values of q = 0.602 and i = 882. Mass transfer from the secondary to the primary eclipsing component is at least partly responsible for the observed secular period change with a rate of dP/dt = +1.4 × 10–7 days yr–1. A cool spot model has been calculated but we think that an alternative hot-spot model resulting from a gas stream impact on the hot star is more reasonable despite two difficulties with the explanation. Absolute dimensions of the eclipsing system are deduced and its present state is compared with tracks for single star and conservative close binary evolution. Finally, we examine the possible reconciliation of two different calculations of the luminosity of the hot spot and a re-interpretation of the secular term of the period variability.