• Title/Summary/Keyword: UBVI

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The CTIO 4m UBVI & $H{\alpha}$ photometry and spatial variation of the reddening law in the ${\eta}$ Carina nebula

  • Hur, Hyeonoh;Sung, Hwan Kyung;Lim, Beomdu;Chun, Moo-Young;Sohn, Sangmo Tony
    • The Bulletin of The Korean Astronomical Society
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    • v.40 no.1
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    • pp.71.3-71.3
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    • 2015

  • Deep UBVI and $H{\alpha}$ photometry of the ${\eta}$ Carina nebula, one of the brightest nebulae on the sky, was obtained with the CTIO 4m telescope and MOSAIC II CCD Camera to determine the initial mass function down to low-mass (~1 M¤) stars. We modified the spatial variation coefficients in transformation relations of the MOSAIC II CCD. From the cross-identification of optical sources with previous surveys in X-ray, near-infrared, and mid-infrared, a clear PMS sequence is revealed in the optical color-magnitude diagrams down to V=23 mag. Our previous SSO 1m UBVI data for Trumpler 14 (Tr 14) and Trumpler 16 (Tr 16) region, and additional SSO 1m UBVI data for Trumpler 15 (Tr 15) region were combined with the CTIO 4m data to re-examine the reddening law and distance of the young open clusters in the ${\eta}$ Carina nebula. From the new photometric data for Tr 15 region, we report that RV[=AV/E(B-V)], the total-to-selective extinction ratio, decreases from southern part of the nebula (Tr 14 and Tr 16) to northern part (Tr 15) in our field of view.

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UBVI CCD PHOTOMETRY OF THE OPEN CLUSTER NGC 2420 (산개성단 NGC 2420에 대한 UBVI CCD 측광)

  • LEE SANG HYUN;KANG YONG-WOO;ANN HONG BAE
    • Publications of The Korean Astronomical Society
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    • v.14 no.2
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    • pp.61-67
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    • 1999

  • We present a new UBVI CCD photometry of the intermediate-age open cluster NGC 2420. Our photometry covers a field of $7'9\times7.'7$ of the sky centered on the cluster. We determined the reddening and distance to the cluster by the main sequence fitting as $E(B - V) = 0.05\pm0.02$ and $(m-M)_o = 11.9\pm0.1$, along with the age of $\~2$ Gyr by fitting the Padova isochrones to the observed color-magnitude diagrams of the cluster. The fraction of binaries is found to be $44\pm5\%$ and they are likely to locate in the central region of the cluster. The spatial distributions of the binaries and the variation of the cluster luminosity functions along the radius suggest mass segregations due to the dynamical evolution of the cluster.

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UBVI CCD Photometry of NGC 7790 (NGC 7790의 UBVI CCD 측광)

  • Choi, Dong Yeol;Kim, Hee Soo;Lim, Beomdu;Sung, Hwankyung
    • Journal of the Korean earth science society
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    • v.36 no.7
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    • pp.661-673
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    • 2015

  • UBVI CCD photometry of the intermediate age open cluster NGC 7790 has been obtained using AZT-22 1.5 m telescope (f/7.74) at the Maidanak Astronomical Observatory in Uzbekistan. NGC 7790 contains three ${\delta}$ Cep variable stars including CEa Cas, CEb Cas, and CF Cas. PSF photometry was carried out using IRAF/DAOPHOT for all observations. The total number of stars observed both in V and I filter was 1008 and the limiting magnitude was $V{\approx}22$. To determine atmospheric extinction coefficients and photometric zero points, many blue and red standard stars as well as the standard stars in the celestial equator under various airmass were observed. Photometric data were transformed into the standard Johnson-Cousins' UBVI standard system. From the analysis of UBVI color-magnitude diagram and color-color diagram, the color excess in V and I filter [$E(B-V)=0.58{\pm}0.02$], the selective extinction ratio in V and I filter [$R_V{\equiv}A_V/E(B-V)=3.02{\pm}0.09$] and distance modulus ($V_0-M_V=12.65{\pm}0.10$) of the cluster were determined. The age of the cluster was estimated to be log $age=8.05{\pm}0.05$ [yr] based on the position of these three Cepheid variables in the color-magnitude diagram, the isochrone of the Geneva group ($Ekstr{\ddot{o}}m$ et al., 2012-Z=0.019), and the isochrone of the Padova group (Bressan et al., 2012-Z=0.014) were used to compare each other. Of them, the Geneva models that considered stellar rotation well described the position of ${\delta}$ Cepheid variables in the blue loop. Although they were well consistent with standard period-luminosity relation of ${\delta}$ Cepheid variables, three Cepheid variables in NGC 7790 were, on average, brighter by about 0.5 mag than the absolute magnitude estimated from the mean period-luminosity relation at a given period.

  • https://doi.org/10.5467/JKESS.2015.36.7.661 인용 PDF KSCI