• Title, Summary, Keyword: variable star

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VARIABLE STARS IN THE REGION OF THE OPEN CLUSTER NGC 225 (산개성단 NGC 225 영역의 변광성)

  • JEON, YOUNG-BEOM;PARK, YOON-HO;LEE, SANG-MIN
    • Publications of The Korean Astronomical Society
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    • v.31 no.3
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    • pp.43-56
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    • 2016
  • Through time-series BV CCD photometry of the open cluster NGC 225 region, we have detected 30 variable stars including 22 new ones. They are five ${\delta}$ Scuti-type variable stars, a slowly pulsating B star, six eclipsing binary stars and 18 semi-long periodic or slow irregular variables, respectively. We have performed multiple-frequency analysis to determine pulsation frequencies of the ${\delta}$ Scuti-type stars and a slowly pulsating B star, using the discrete Fourier transform and linear least-square fitting methods. We also have derived the periods and amplitudes of 6 eclipsing binaries and a long-period variable star from the phase fitting method, and presented the light curves of all variable stars. A slowly pulsating B star is a member of NGC 225, but ${\delta}$ Scuti-type stars are not members from the positions in the color-magnitude diagram and the radial distancies from the center of the cluster. From Dias et al. (2014, A&A, 564, 79), only three variable stars including the slowly pulsating B star are members of clusters: two are in NGC 225 and one is in Stock 24. But a variable star in Stock 24 is not a member of the cluster because of its position of color-magnitude diagarm.

VARIABLE STARS IN THE REGION OF THE OPEN CLUSTER NGC 457 (산개성단 NGC 457 영역의 변광성)

  • Jeon, Young-Beom;Park, Yoon-Ho;Lee, Sang-Min
    • Publications of The Korean Astronomical Society
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    • v.32 no.3
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    • pp.421-438
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    • 2017
  • Through the short-period variability survey program, we obtained time-series BV CCD images for $1.5^{\circ}{\times}1.0^{\circ}$ region around the young open cluster NGC 457. As a result, we have detected 61 variable stars including 31 new ones after checking light curves of all stars by eyes. The 61 variable stars were included 14 ${\delta}$ Scuti variable stars, a ${\beta}$ Cephei variable star, 10 variable Be and slowly pulsating B stars, 13 eclipsing binary stars, 21 semi-long periodic or slow irregular variables and an RR Lyrae variable star, respectively. Many variable B-type stars were known through a well-defined zero-age main sequence to the ${\beta}$ Cepheid region of NGC 457. Most of the variable B-type stars found this paper were known variable stars. But, 11 out of 14 ${\delta}$ Scuti variable stars were newly discovered. The new variable stars except for ${\delta}$ Scuti stars were 4 variable B-type stars, 5 eclipsing binaries and 11 semi-long periodic or slow irregular variables. We have performed frequency analysis for all ${\delta}$ Scuti stars, a ${\beta}$ Cepheid star and an RR Lyrae star.

A CONSTRUCTION OF AN AUTOMATIC OBSERVATION SYSTEM FOR BRIGHT AND LONG PERIOD VARIABLE STARS (밝은 장주기 변광성관측을 위한 자동관측시스템 구축)

  • Yoon Joh-Na;Lee Chung-Uk;Cha Sang-Mok;Kim Yong-Gi
    • Journal of Astronomy and Space Sciences
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    • v.23 no.2
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    • pp.143-152
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    • 2006
  • An automatic observation system has been constructed at Chungbuk National University for the purpose of monitoring the bright and long period variable stars effectively. We improved the control part of 40cm telescope of the LX200 and developed n observing software ObsTool II so that the telescope, CCD camera and dome can be controlled in one software. ObsTool II is a COM (Common Object Module) based software, which can be easily reprogrammed in case that a new telescope or CCD camera is installed. Because this system has an additional function in which the telescope can switch the variable, comparison, and check stars respectively as like a photoelectric observation, we can observe the variable star even if the CCD view field does not contain the comparison star with the variable star. In order to check the system stability a W UMa type variable V523 Cas and a magnetic cataclysmic variable TT Ari have been observed with the constructed system and the results have been discussed in context with the possibility of a further application of our automatical observation system.

The Effects of Sex, Age, and Social Support on Self-Esteem of the Aged. (성, 연령, 사회적 지원에 따른 노인의 자아존중감에 관한 연구)

  • 조옥희
    • Journal of Korean Home Management Association
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    • v.15 no.1
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    • pp.161-172
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    • 1997
  • The purpose of this study was to explore the effect of the sex, age, degree of social support on self-esteem of the old aged and to provide information for finding out ways of developing their self-esteem. The subject of this study were 504 old aged in Kwang-ju and Jun-nam. The statistics used for data analysis were frequency percentage mean standard deviation reliability ANOVA stepwise and multiple regression analysis through the SAS package program, . The major findings of this study can be summarized as follows; 1) The self-esteem of old aged was 27, 2 which was above the median 22.5 2) According to the results related to the old aged the effect were by sex, age, social support, . There were also significant interaction effects by $age^{\star}$social support $sex^{\star}\;age^{\star}$aocial support $sex^{\star}$social support $sex^{\star}$age it was shown that influencing variable on their self-esteem was sex social support $sex^{\star}$social support $sex^{\star}$age age.

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Development of a Period Analysis Algorithm for Detecting Variable Stars in Time-Series Observational Data

  • Kim, Dong-Heun;Kim, Yonggi;Yoon, Joh-Na;Im, Hong-Seo
    • Journal of Astronomy and Space Sciences
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    • v.36 no.4
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    • pp.283-292
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    • 2019
  • The purpose of this study was to develop a period analysis algorithm for detecting new variable stars in the time-series data observed by charge coupled device (CCD). We used the data from a variable star monitoring program of the CBNUO. The R filter data of some magnetic cataclysmic variables observed for more than 20 days were chosen to achieve good statistical results. World Coordinate System (WCS) Tools was used to correct the rotation of the observed images and assign the same IDs to the stars included in the analyzed areas. The developed algorithm was applied to the data of DO Dra, TT Ari, RXSJ1803, and MU Cam. In these fields, we found 13 variable stars, five of which were new variable stars not previously reported. Our period analysis algorithm were tested in the case of observation data mixed with various fields of view because the observations were carried with 2K CCD as well as 4K CCD at the CBNUO. Our results show that variable stars can be detected using our algorithm even with observational data for which the field of view has changed. Our algorithm is useful to detect new variable stars and analyze them based on existing time-series data. The developed algorithm can play an important role as a recycling technique for used data

Light Curve of CVs using KASINICS

  • Han, Jang-Hui;Son, Jeong-Ju;Angeloni, Rodolfo;De Grijs, Richard;Jeon, Yeong-Beom;Seong, Hyeon-Il
    • The Bulletin of The Korean Astronomical Society
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    • v.36 no.1
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    • pp.31.2-31.2
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    • 2011
  • The Vista Variable in the Via Lactea(VVV)는 European Southern Observatory(ESO) Public Survey 중 하나로 Near-IR에서 (주로 K-band)에서 관측되며 1929시간에 걸쳐 은하 중심부의 더 깊은 영역에 대한 관측을 수행할 것이다. VVV Survey를 통해 520 sq. deg에 걸친 영역에서 33개의 잘 알려진 구상성단과 350개의 산개성단을 포함한 ~109개의 별에 대한 광도 곡선을 얻을 수 있을 것으로 예상되며 이들을 분류하기 위해 자동화된 분류 체계가 필요할 것이다. 본 연구는 VVV Survey의 일환으로 보현산 천문대의 근적외선 카메라시스템 KASINICS를 이용하여 Cataclysmic Variable stars에 대한 관측을 시행하고 있다. Cataclysmic Variable stars는 초신성 폭발이나 쌍성계 중 한 쪽 별에서 다른 쪽 별로 대기가 유입되었는 경우 등에 의해 광도가 급격히 증가하는 천체로 아직 많이 연구되지 않은 적외선 파장대로 관측함으로써 적외선영역에서의 물리적 특성에 대한 분석을 하고자 한다. 본 발표에서는 보현산 천문대의 근적외선카메라시스템 KASINICS에서 관측한 결과의 일부를 소개하고자 한다.

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The JCMT Transient Survey: Examination of Periodic Variability in nearby Star-forming Regions

  • Lee, Yong-Hee;Lee, Jeong-Eun;Johnstone, Doug;Herczeg, Gregory J.;Mairs, Steve
    • The Bulletin of The Korean Astronomical Society
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    • v.44 no.1
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    • pp.43.1-43.1
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    • 2019
  • We perform the Lomb-Scargle Periodogram analysis to protostars identified by the JCMT Transient Survey, which monitors 8 nearby star forming regions. The observations have been done monthly for over 3 years using SCUBA-2 (the Submillimetre Common User Bolometer Array 2) in two wavelengths, 450 and $850{\mu}m$. Under the threshold of 1% False Alarm Probability, we found 16 variable sources including EC53, which is the first variable protostar detected by the JCMT Transient Survey. Most of the variable sources are cataloged as protostars (classified via the Spitzer data, Megeath et al. 2012; Dunham et al. 2015), but SerpS-MM19, which has a clear 1-year period, is a candidate of a first hydrostatic core (Maury et al. 2011; Young et al. 2018).

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Retrieval of Nighttime Aerosol Optical Thickness from Star Photometry (별 측광을 통한 야간 에어로졸의 광학적 두께 산출)

  • Oh, Young-Lok
    • Atmosphere
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    • v.25 no.3
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    • pp.521-528
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    • 2015
  • In this study star photometry was applied to retrieve aerosol optical thickness (AOT) at night. The star photometry system consisted of small refractor, optical filters, CCD camera, and driving mount and was located in Suwon. The calibration constants were retrieved from the astronomical Langley method but standard deviations of these were more than 10% of the mean values. After the calibration the nighttime AOT was retrieved and cloud-screened in clear six days from 25 Nov. 2014 to 17 Jan. 2015. To estimate the quality of the measurements the nighttime AOT was combined with daytime AOT retrieved from sky-radiometer that was located in Seoul and 17 km away from the star photometry system. In spite of the uncertainty of the calibration constants and the spatial difference of two observation systems, the temporal changes of the nighttime AOT coincided with the daytime. The nighttime ${\AA}ngstr{\ddot{o}}m$ exponent was about 20% lower and more variable than the daytime because of the uncertainty of the calibration constants. If the calibration process is more precise, the combination of star and sun or sky photometry system can monitor the air pollution day and night constantly.

SPECTRAL FEATURES OF THE SYMBIOTIC VARIABLE STAR CH CYGNI IN 2005 - 2006

  • Yoo, Kye-Hwa;Yoon, Tae-Seog
    • Journal of The Korean Astronomical Society
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    • v.42 no.4
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    • pp.93-103
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    • 2009
  • This article reports the spectral behavior of CH Cygni, using data obtained in October 2005 and June 2006. In these epochs, CH Cygni showed emission lines of H I, Fe II, [Fe II], [O III], [N II], [Ne III] and [S II]. Many of these lines were more enhanced since 2004. The underlying M-type spectrum was removed to get the intrinsic emission profile, and the resulting profiles were deconvoluted into several Gaussian components. Also, the radial velocities for all the lines that appeared in these spectra of CH Cygni were measured. The resultant lines were compared with each other and with those obtained in 2004; the findings are explained in terms of an accretion disk and jets.

Functional Data Classification of Variable Stars

  • Park, Minjeong;Kim, Donghoh;Cho, Sinsup;Oh, Hee-Seok
    • Communications for Statistical Applications and Methods
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    • v.20 no.4
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    • pp.271-281
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    • 2013
  • This paper considers a problem of classification of variable stars based on functional data analysis. For a better understanding of galaxy structure and stellar evolution, various approaches for classification of variable stars have been studied. Several features that explain the characteristics of variable stars (such as color index, amplitude, period, and Fourier coefficients) were usually used to classify variable stars. Excluding other factors but focusing only on the curve shapes of variable stars, Deb and Singh (2009) proposed a classification procedure using multivariate principal component analysis. However, this approach is limited to accommodate some features of the light curve data that are unequally spaced in the phase domain and have some functional properties. In this paper, we propose a light curve estimation method that is suitable for functional data analysis, and provide a classification procedure for variable stars that combined the features of a light curve with existing functional data analysis methods. To evaluate its practical applicability, we apply the proposed classification procedure to the data sets of variable stars from the project STellar Astrophysics and Research on Exoplanets (STARE).