We present the results of BV time-series photometry of the globular cluster NGC 288. Observations were carried out to search for variable stars using the Korea Microlensing Telescope Network (KMTNet) 1.6-m telescopes and a 4k pre-science CCD camera during a test observation from August to December, ...
We present the results of BV time-series photometry of the globular cluster NGC 288. Observations were carried out to search for variable stars using the Korea Microlensing Telescope Network (KMTNet) 1.6-m telescopes and a 4k pre-science CCD camera during a test observation from August to December, 2014. We found a new SX Phe star and confirmed twelve previously known variable stars in NGC 288. For the semi-regular variable star V1, we newly determined a period of 37.3 days from light curves spanning 137 days. The light-curve solution of the eclipsing binary V10 indicates that the system is probably a detached system. The pulsation properties of nine SX Phe stars were examined by applying multiple frequency analysis to their light curves. We derived a new Period-Luminosity (P-L) relation, ${\langle}M_V{\rangle}=-2.476({\pm}0.300){\log}P-0.354({\pm}0.385)$, from six SX Phe stars showing the fundamental mode. Additionally, the period ratios of three SX Phe stars that probably have a double-radial mode were investigated; $P_{FO}/P_F=0.779$ for V5, $P_{TO}/P_{FO}=0.685$ for V9, $P_{SO}/P_{FO}=0.811$ for V11. This paper is the first contribution in a series assessing the detections and properties of variable stars in six southern globular clusters with the KMTNet system.
We present the results of BV time-series photometry of the globular cluster NGC 288. Observations were carried out to search for variable stars using the Korea Microlensing Telescope Network (KMTNet) 1.6-m telescopes and a 4k pre-science CCD camera during a test observation from August to December, 2014. We found a new SX Phe star and confirmed twelve previously known variable stars in NGC 288. For the semi-regular variable star V1, we newly determined a period of 37.3 days from light curves spanning 137 days. The light-curve solution of the eclipsing binary V10 indicates that the system is probably a detached system. The pulsation properties of nine SX Phe stars were examined by applying multiple frequency analysis to their light curves. We derived a new Period-Luminosity (P-L) relation, ${\langle}M_V{\rangle}=-2.476({\pm}0.300){\log}P-0.354({\pm}0.385)$, from six SX Phe stars showing the fundamental mode. Additionally, the period ratios of three SX Phe stars that probably have a double-radial mode were investigated; $P_{FO}/P_F=0.779$ for V5, $P_{TO}/P_{FO}=0.685$ for V9, $P_{SO}/P_{FO}=0.811$ for V11. This paper is the first contribution in a series assessing the detections and properties of variable stars in six southern globular clusters with the KMTNet system.
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제안 방법
For the detection of variable candidates, we used the DIAPL/GETVAR task which finds positions of flux variations based on the standard deviation for each pixel of all series of residual images. By the visual inspection for all light curves of the candidates, we discovered a new SX Phe star, and confirmed twelve already known variable stars: a semi-regular variable star, two RR Lyr stars, an eclipsing binary star, and eight SX Phe stars.
In addition, we performed BV I observations to construct the CMDs for the monitored field. Four different exposure times were used to increase the dynamic range of the sample, including as many stars as possible with a good signal to noise ratio in each band: 14 s, 200s, 600 s, and 1 000 s in the B-band, 6 s, 100 s, 300 s, and 700 s in the V -band, and 4 s, 50 s, 150 s, and 400 s in the I-band. All observed images of NGC 288 were bias corrected and flattened using the IRAF/CCDRED package.
From this study, we intend to check the photometric performance by comparing new light curves with previous results, and we search for new variable stars and improve the physical properties of variable stars using the high cadence and multi-band photometry.
In addition, we performed BV I observations to construct the CMDs for the monitored field. Four different exposure times were used to increase the dynamic range of the sample, including as many stars as possible with a good signal to noise ratio in each band: 14 s, 200s, 600 s, and 1 000 s in the B-band, 6 s, 100 s, 300 s, and 700 s in the V -band, and 4 s, 50 s, 150 s, and 400 s in the I-band.
In advance of commissioning of the science mosaic CCD cameras, we tested the optical performance of the telescopes at each site, and simultaneously performed time-series observations of six globular clusters (NGC 288, NGC 1851, NGC 3201, NGC 4372, NGC 6752, and NGC 6809) using a 4k pre-science CCD camera having a 25×25 arcmin2 FOV.
In conclusion, we discovered a new SX Phe star V13 through BV time-series photometry, and performed a photometric study of all variable stars in NGC 288. We acquired the light curves of the semi-regular variable star V1 observed over 137 days and found a 37.
2003). In order to understand the properties of variable stars in the globular cluster, we performed a time-series photometric study using the Korea Microlensing Telescope Network (hereafter, KMTNet) system.
Firstly, we obtained more than three images per night with 60 s exposure in the B-band and 30 s in the V -band in order to detect relatively bright and long-period variable stars in NGC 288. Secondly, we carried out consecutive observations of more than 4-5 hours with 300 s in the V -band to search for SX Phe stars ranging from 17 mag to 18 mag in the BSS region. Since the pulsation period of SX Phe stars is short, the observation cadence is limited to less than six minutes.
36 arcsec/pixel, covering an FOV of 25 × 25 arcmin2 . To detect various types of variability, the observation strategy was made considering exposure time and cadence. Firstly, we obtained more than three images per night with 60 s exposure in the B-band and 30 s in the V -band in order to detect relatively bright and long-period variable stars in NGC 288.
DIAPL has the advantage of detecting faint variable objects, although it requires a complicated calibration process to convert flux-scale to magnitude-scale. To produce light curves, we stacked the three best images having less than 1 arcsec of seeing and it was convolved with derived kernels to be differenced with each time-series image. Then we obtained the flux-scale light curves from residual images.
To analyze the nature of complex light curves, we performed multiple frequency analysis using the DFT and nonlinear least-squares fitting method (Kim & Lee 1990). We first estimated a pulsation frequency having a strong peak from the maximum power of the DFT, and then we calculdayated the mean magnitude, amplitude, and phase by fitting the time-series data using the identified frequency. Through consecutive prewhitening processes for each frequency peak, we found all possible frequencies.
대상 데이터
We obtained a total of 2 253 CCD frames during 140 hours over a span of four months. For this study, we used an SBIG STX-16803 CCD camera and a JohnsonCousins BV I filter system. The CCD camera has 4 096× 4 096 pixels, with a pixel scale of 0.
2016). The first telescope was installed at Cerro-Tololo Inter-American Observatory (CTIO) in Chile in May 2014, and the second at South African Astronomical Observatory (SAAO) in South Africa in August 2014, and the last at Siding Spring Observatory (SSO) in Australia in November 2014. In advance of commissioning of the science mosaic CCD cameras, we tested the optical performance of the telescopes at each site, and simultaneously performed time-series observations of six globular clusters (NGC 288, NGC 1851, NGC 3201, NGC 4372, NGC 6752, and NGC 6809) using a 4k pre-science CCD camera having a 25×25 arcmin2 FOV.
The observations of NGC 288 were carried out from August 3 to October 6, 2014, at KMTNet-SAAO, and from November 12 to December 24, 2014, at KMTNet-SSO. We obtained a total of 2 253 CCD frames during 140 hours over a span of four months.
Kyeongsoo Hong was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (grant number: NRF-2016R1A6A3A01007139). This research has made use of the KMTNet system operated by KASI and the data were obtained at two host sites of SAAO in South Africa, and SSO in Australia.
이론/모형
Four different exposure times were used to increase the dynamic range of the sample, including as many stars as possible with a good signal to noise ratio in each band: 14 s, 200s, 600 s, and 1 000 s in the B-band, 6 s, 100 s, 300 s, and 700 s in the V -band, and 4 s, 50 s, 150 s, and 400 s in the I-band. All observed images of NGC 288 were bias corrected and flattened using the IRAF/CCDRED package. The point-spread function (PSF) photometry of pre-processed images was performed using the IRAF/DAOPHOT package (Stetson 1987; Massey & Davis 1992) according to standard procedure.
In order to derive the photometric solutions of the binary star, we analyzed simultaneously both their V -band and our BV -bands light curves using the Wilson-Devinney binary code (Wilson & Devinney 1971, hereafter W-D).
Figure 2 shows CMDs from the present work. In order to estimate the cluster parameters of NGC 288 based on our CMDs, we applied the Dartmouth Stellar Evolution Program (DSEP)3 model (Dotter et al. 2008). The red solid lines of each panel represent the best multi-chromatic isochrones fit with respect to our (B − V vs V) and (V − I vs V) CMDs.
The point-spread function (PSF) photometry of pre-processed images was performed using the IRAF/DAOPHOT package (Stetson 1987; Massey & Davis 1992) according to standard procedure.
참고문헌 (32)
Arellano Ferro, A., Bramich, D. M., Giridhar, S., Figuera Jaimes R., Kains N., & Kuppuswamy, K. 2013, Variable Stars in the Globular Cluster NGC 288: [Fe/H] and Distance, AcA, 63, 429
Bolte, M. 1992, CCD Photometry in the Globular Cluster NGC 288. I - Blue Stragglers and Main-Sequence Binary Stars, ApJS, 82, 145
Flower, F. J. 1996, Transformations from Theoretical Hertzsprung-Russell Diagrams to Color-Magnitude Diagrams: Effective Temperatures, B - V Colors, and Bolometric Corrections, AJ, 469, 355
Kim, S.-L., Lee, C.-U., Park, B.-G., et al. 2016, : A Network of 1.6 m Wide-Field Optical Telescopes Installed at Three Southern Observatories, JKAS, 49, 37
Kim, S.-L., & Lee, S.-W. 1990, Pulsational Characteristics of Delta Scuti Variable HR 1170, JKAS, 23, 1
Kopacki, G. 2015, Wide-Field Variability Survey of the Globular Cluster M 79 and a New Period-Luminosity Relation for SX Phe Stars, AcA, 65, 81
Kunder, A., Stetson, P. B., Cassisi, S., et al. 2013, The RR Lyrae Variables and Horizontal Branch of NGC 6656(M22), AJ, 146, 119
Lenz, P., & Breger, M. 2005, Period04 User Guide, CoAst, 146, 53
Martinazzi, E., Kepler, S. O., Costa, J. E. S., Pieres, A., Bonatto, C., Bica, E., & Fraga, L. 2015, New SX Phe Variables in the Globular Cluster NGC 288, MNRAS, 447, 2235
Massey, P., & Davis, L. E. 1992, A User's Guide to Stellar CCD Photometry with IRAF
Mazur, B., Krzeminski, W., & Thompson, I. B. 2003, Variable stars in the globular cluster NGC 3201 - I. Multimode SX Phe type variables, MNRAS, 340, 1205
Nemec, J. M., Linnell Nemec, A. F., & Lutz, T. E. 1994, Period-Luminosity-Metallicity Relations, Pulsation Modes, Absolute Magnitudes, and Distances for Population II Variable Stars, AJ, 108, 222
Oosterhoff, P. Th. 1943, A Semi-Regular Variable in N.G.C. 288, Bulletin of the Astronomical Institutes of the Netherlands, 9, 397
Park, B.-G., Kim, S.-L., Lee, J. W., et al. 2012, Korea Microlensing Telescope Network: Science Cases, Proc. SPIE., 8444, 844447
Petersen, J. O., Quaade, M., Freyhammer, L. M., & Ander- sen, M. I. 2000, Double-Mode SX Phoenicis Variables in Globular Clusters, ASPC, 210, 391
Santolamazza, P., Marconi, M., Bono, G., et al. 2001, Linear Nonadiabatic Properties of SX Phoenicis Variables, ApJ, 554, 1124
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