Showing papers by "Seung-Lee Kim published in 2010"

Technical specifications of the KMTNet observation system

Abstract: Korea Astronomy and Space Science Institute (KASI) has officially started a project to construct an astronomical widefield survey system, namely KMTNet (Korea Micro-lensing Telescope Network), from January 2009. Its primary scientific goal is to discover numerous extra-solar planets, especially earth-mass planets, using the gravitational microlensing technique. This goal requires continuous photometric observations with high cadence of about 10 minutes for tens of millions of stars in dense fields toward the Galactic bulge. KMTNet will comprise three identical systems at southern observatories with different time zones. Each observing system consists of a 1.6 m wide-field optical telescope and a 20k by 20k mosaic CCD camera, which covers a 2 by 2 degrees square field of view. In this proceeding, we present technical specifications, designs and fabrication schedule of the KMTNet system.

Algol-Type Eclipsing Binaries with δ Scuti-Type Pulsating Components: IV Cas

Abstract: We present the results of photometric and spectroscopic observations of the Algol-type eclipsing binary with a δ Scuti-type pulsating component IV Cas This is the first comprehensive study of the absolute proper- ties of the binary system and also of the pulsation characteristics of the primary component The high-resolution spectroscopic data have enabled us to estimate the atmospheric parameters of the primary component Our BV light- curve analysis has revealed that the binary system is in a semidetached configuration, consisting of a detached main- sequence primary of spectral type A3 and an evolved secondary of early-K spectral type, which fills its inner Roche lobe completely We found that the two components are too close to each other to form an accretion disk Spectro- scopic results without an emission feature supported the nonexistence of noticeable disk The rotation of the primary turned out to be nearly synchronized with the revolution, giving a hint that IV Cas is in the middle or late stage of the slow mass transfer phase This coincides well with a slow mass transfer rate deduced from the fact that there was no secular parabolic change of the orbital period for the past ∼100 yr Using residuals subtracted from synthetic eclipsing curves of photometric data, we examined the pulsation properties of the primary component A multiple- frequency analysis was applied to the residuals in the out-of-primary eclipsing phases and this resulted in the detec- tion of four frequencies: f1 ¼ 32:69236 cycles day � 1 , f2 ¼ 36:65999 cycles day � 1 , f3 ¼ 20:71649 cycles day � 1 , and f4 ¼ 30:66072 cycles day � 1 We tentatively identified their pulsation modes on the basis of pulsation con- stants, frequency spacing, mode visibility in eclipsing binaries, phase differences, and amplitude ratios; f1 and f4 (or f1 and f2) appeared to be rotational splitting frequencies The observational properties of IV Cas well matched the empirical relations for Algol-type eclipsing binaries with δ Scuti-type pulsating components

EXOTIME: searching for planets around pulsating subdwarf B stars

Abstract: In 2007, a companion with planetary mass was found around the pulsating subdwarf B star V391 Pegasi with the timing method, indicating that a previously undiscovered population of substellar companions to apparently single subdwarf B stars might exist. Following this serendipitous discovery, the EXOTIME (this http URL) monitoring program has been set up to follow the pulsations of a number of selected rapidly pulsating subdwarf B stars on time-scales of several years with two immediate observational goals: 1) determine Pdot of the pulsational periods P 2) search for signatures of substellar companions in O-C residuals due to periodic light travel time variations, which would be tracking the central star's companion-induced wobble around the center of mass. These sets of data should therefore at the same time: on the one hand be useful to provide extra constraints for classical asteroseismological exercises from the Pdot (comparison with "local" evolutionary models), and on the other hand allow to investigate the preceding evolution of a target in terms of possible "binary" evolution by extending the otherwise unsuccessful search for companions to potentially very low masses. While timing pulsations may be an observationally expensive method to search for companions, it samples a different range of orbital parameters, inaccessible through orbital photometric effects or the radial velocity method: the latter favours massive close-in companions, whereas the timing method becomes increasingly more sensitive towards wider separations. In this paper we report on the status of the on-going observations and coherence analysis for two of the currently five targets, revealing very well-behaved pulsational characteristics in HS 0444+0458, while showing HS 0702+6043 to be more complex than previously thought.

Detection of Variable Stars in the Open Cluster M11 Using Difference Image Analysis Pipeline

Abstract: We developed a photometric pipeline to be used for a wide field survey. This pipeline employs the difference image analysis (DIA) method appropriate for the photometry of star dense field such as the Galactic bulge. To verify the performance of pipeline, the observed dataset of the open cluster M11 was re-processed. One hundred seventy eight variable stars were newly discovered by analyzing the light curves of which photometric accuracy was improved through the DIA. The total number of variable stars in the M11 observation region is 335, including 157 variable stars discovered by previous studies. We present the catalogue and light curves for the 178 variable stars. This study shows that the photometric pipeline using the DIA is very useful in the detection of variable stars in a cluster.

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

Abstract: 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.

New High-Amplitude SX Phœnicis (δ Scuti?) Star in the Direction of the Galactic Anti-Center: 2MASS 06451725 + 4122158

Abstract: The results of extensive time-series photometry of a new variable star, 2MASS 06451725 + 4122158, are presented. The B, V observations (over 4000 individual measurements) were made over 23 nights between 2006 and 2007. To investigate the star's physical characteristics additional Stromgren photometric observations (uvbyHβ) were made on another four nights in 2007 and 2009. Thirteen frequencies were found from a multifrequency analysis of the V and B photometry. All but two of the frequencies, 19.99716 cycles day-1 (corresponding to the pulsation period of 0.0500071 day) and 25.84662 cycles day-1 (0.0386898 day), have been identified as combination frequencies. The ratio of the two frequencies, f1/f3 = 0.77369, and their pulsation constants, Q(f1) = 0.034 and Q(f3) = 0.026, are well matched with theoretical values of the fundamental and the first-overtone radial modes. But the phase shift of f3 was estimated to be a negative value, in contrast to that of f1 to be positive, suggesting that f3 may be a nonradial mode. The period versus amplitude diagram shows that the star has pulsational properties similar to those of high-amplitude SX Phœnicis stars. We obtained its photometric properties from the Stromgren indices: a metal abundance of [Fe/H] = -0.6 dex, an absolute magnitude of MV = 2.7 mag, a distance of ~1.6 kpc in the direction of the Galactic anticenter from the Sun, and a vertical distance from the Galactic plane of ~0.45 kpc. The tangential velocity of 78 km sec-1, which was estimated from the proper motion and the distance, gives us a hint that the star may have high-space motion. Considering these observational properties, we suggest that this new variable is a field SX Phœnicis-type star, although its metallicity value seems not to be low enough for matching the metallicity versus period relation. Future spectroscopic studies would be required to obtain the metallicity more accurately.