Ho-Il 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.

THE GLOBULAR CLUSTER SYSTEM OF M60 (NGC 4649). II. KINEMATICS OF THE GLOBULAR CLUSTER SYSTEM

We present a kinematic analysis of the globular cluster (GC) system in the giant elliptical galaxy (gE) M60 in the Virgo Cluster, using a photometric and spectroscopic database of 121 GCs (83 blue and 38 red GCs). We have found that the M60 GC system shows a significant overall rotation. The rotation amplitude of the blue GCs is slightly smaller than or similar to that of the red GCs, and the position angles of their rotation axes are similar. The velocity dispersions about the mean velocity and about the best-fit rotation curve for the red GCs are marginally larger than those for the blue GCs. Comparison of observed stellar and GC velocity dispersion profiles with those calculated from the stellar mass profile shows that the mass-to-light ratio should increase as the galactocentric distance increases, indicating the existence of an extended dark matter halo. The sample of all the GCs in M60 is found to have a tangentially biased velocity ellipsoid, unlike the GC systems in other gEs. The two subsamples appear to have different velocity ellipsoids. The blue GC system has a modestly tangentially biased velocity ellipsoid, while the red GC system has a modestly radially biased or an isotropic velocity ellipsoid. We compare the kinematic properties of the M60 GC system to those of other gEs (M87, M49, NGC 1399, NGC 5128, and NGC 4636), and discuss the implication of these results for the formation models of the GC system in gEs.

The Intrinsic Shapes of Low Surface Brightness Dwarf Irregular Galaxies and Comparison to Other Types of Dwarf Galaxies

In this paper, we measure the ellipticities of 30 low surface brightness (LSB) dwarf irregular (dI) galaxies and compare the ellipticity distribution with that of 80 dwarf elliptical (dEs) and 62 blue-compact dwarfs (BCDs). We find that the ellipticity distribution of LSB dIs is very similar to that of BCDs, and marginally different from that of dEs. We then determine the distribution of intrinsic shapes of dI galaxies and compare this to the distributions of other types of dwarf galaxies under various assumptions. First, we assume that LSB dIs are either all oblate or all prolate, and use a nonparametric analysis to find the best-fitting distribution of intrinsic shapes. With this assumption, we find that the scarcity of nearly circular LSB dIs implies, at the 99% confidence level, that they cannot be a population of randomly oriented oblate or prolate objects, implying that LSB dIs are highly unlikely to be disk-shaped systems. Next, we assume that dIs are triaxial, and use a parametric analysis to find permissible distributions of intrinsic shapes. We find that if the intrinsic axis ratios β and γ are distributed according to a Gaussian with means β0 and γ0 and a common standard deviation of σ, the best-fitting set of parameters for LSB dIs is (β0, γ0, σ) = (0.66, 0.50, 0.15), and the best fit for BCDs is (β0, γ0, σ) = (0.66, 0.55, 0.16), while the best fit for dEs is (β0, γ0, σ) = (0.78, 0.69, 0.24). The dIs and BCDs thus have very similar shape distributions, given this triaxial hypothesis, while the dEs peak at a somewhat more spherical shape. Therefore, our results provide strong observational evidence to support the evolutionary scenario in which the three types of dwarf galaxy have a close relation with each other.

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.

A COMPARISON OF THE INTRINSIC SHAPES OF TWO DIFFERENT TYPES OF DWARF GALAXIES BLUE COMPACT DWARFS AND DWARF ELLIPTICALS

We measure the apparent shapes for a sample of 62 blue compact dwarf galaxies (BCDs) and compare them with the apparent shapes for a sample of 80 dwarf elliptical galaxies (dEs). The BCDs are flatter, on average, than the dEs, but the difference is only marginally significant. We then use both nonparametric and parametric techniques to determine possible distributions of intrinsic shapes for the BCDs. The hypothesis that BCDs are oblate spheroids can be ruled out with a high confidence level (>99%), but the hypothesis that they are prolate spheroids cannot be excluded. The apparent shapes of BCDs are totally consistent with the hypothesis that they are triaxial ellipsoids. If the intrinsic axis ratios β and γ are distributed according to a Gaussian with means β0 and γ0 and standard deviation σ, we find that the best-fitting distribution for BCDs has (β0, γ0, σ) = (0.66, 0.55, 0.16), while that for dEs has (β0, γ0, σ) = (0.85, 0.64, 0.24). Our results are consistent with the hypothesis that BCDs have a close evolutionary relation with dEs.

Microlensing Detections of Planets in Binary Stellar Systems

We demonstrate that microlensing can be used for detecting planets in binary stellar systems. This is possible because in the geometry of planetary binary systems, in which the planet orbits one of the binary components and the other binary star is located at a large distance, both planet and secondary companion produce perturbations in a common region around the planet-hosting binary star, and thus the signatures of both planet and binary companion can be detected in the light curves of high-magnification lensing events. We find that identifying planets in binary systems is optimized when the secondary is located within a certain range that depends on the type of the planet. The proposed method can detect planets with masses down to one-tenth of the Jupiter mass in binaries with separations 100 AU. These ranges of planet masses and binary separations are not covered by other methods, and thus microlensing would be able to make the planetary binary sample richer.

Wide-Field Stellar Distributions around the Remote Young Galactic Globular Clusters Palomar 3 and Palomar 4*

In a search for tidal extension features and/or streams of the probable parent satellite galaxies around the remote young globular clusters Pal 3 and Pal 4, we used wide-field VI photometry of an area a ~ 13 × 13 around Pal 3 and an area a ~ 13 × 09 around Pal 4, obtained with the CFH12K mosaic CCD. Applying the CMD-mask algorithm to stars in the vicinity of the clusters, we selected member star candidates that were used to examine the characteristics of the spatial distribution of stars around Pal 3 and Pal 4. The isodensity contours in the Gaussian-smoothed spatial stellar density maps around the clusters, and the Kolmogorov-Smirnov test applied to the corresponding luminosity functions, indicate tidal halos around Pal 3 at distances of up to ~4rt, and around Pal 4 of up to ~6rt. The stellar distribution around Pal 3 suggests north-south elongations along the directions of the Galactic center and anticenter, and a northeast extension in the direction of the clusters proper motion. In the vicinity of Pal 4 an extension of a tail around the cluster in the opposite direction to the Galactic center and a possible extension of stars toward the Galactic center have also been detected in the isodensity maps and in the angular luminosity functions. We discuss the relevance of the spatial distribution of stars in possible streams around Pal 3 and Pal 4 to these spatial correlations and to the space orbits of the possible parent satellite galaxies.

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

LONG-TERM PHOTOMETRIC BEHAVIOR OF THE ECLIPSING BINARY GW CEPHEI

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Raman-scattered He II λ6545 Line in the Symbiotic Star V1016 Cygni

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