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Register a new userUBVI CCD Photometry of the Open Cluster NGC 4609 and Hogg 15
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UBVI CCD photometry is obtained for the open clusters NGC 4609 and Hogg 15 in Crux. For NGC 4609, CCD data are presented for the first time. From new photometry we derive the reddening, distance modulus and age of each cluster - NGC 4609 : E(B-V) = 0.37 +/- 0.03, V_0 - M_V = 10.60 +/- 0.08, log tau = 7.7 +/- 0.1; Hogg 15 : E(B-V) = 1.13 +/- 0.11, V_0 - M_V = 12.50 +/- 0.15, log tau <= 6.6. The young age of Hogg 15 strongly implies that WR 47 is a member of the cluster. We have also determined the mass function of these clusters and have obtained a normal slope (Gamma = -1.2 +/- 0.3) for NGC 4609 and a somewhat shallow slope (Gamma = -0.95 +/- 0.5) for Hogg 15.
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We present UBVI photometry of the old open cluster NGC 1193. Color-magnitude diagrams (CMDs) of this cluster show a well defined main sequence and a sparse red giant branch. For the inner region of r<50 arcsec, three blue straggler candidates are newly found in addition to the objects Kaluzny (1988) already found. The color-color diagrams show that the reddening value toward NGC 1193 is E(B-V) =0.19 +/- 0.04. From the ultraviolet excess measurement, we derived the metallicity to be [Fe/H]=-0.45 +/- 0.12. A distance modulus of (m-M)_0 =13.3 +/- 0.15 is obtained from zero age main sequence fitting with the empirically calibrated Hyades isochrone of Pinsonneault et al. (2004). CMD comparison with the Padova isochrones by Bertelli et al. (1994) gives an age of log t =9.7 +/- 0.1.
We present the results of CCD $UBV$ photometric and spectroscopic observations of the open cluster NGC 225. In order to determine the structural parameters of NGC 225, we calculated the stellar density profile in the clusters field. We estimated the probabilities of the stars being physical members of the cluster using the existing astrometric data. The most likely members of the cluster were used in the determination of the astrophysical parameters of the cluster. We calculated the mean radial velocity of the cluster as $V_{r}=-8.3pm 5.0$ km s$^{-1}$ from the optical spectra of eight stars in the clusters field. Using the U-B vs B-V two-colour diagram and UV excesses of the F-G type main-sequence stars, the reddening and metallicity of NGC 225 were inferred as $E(B-V)=0.151pm 0.047$ mag and $[Fe/H]=-0.11pm 0.01$ dex, respectively. We fitted the colour-magnitude diagrams of NGC 225 with the PARSEC isochrones and derived the distance modulus, distance and age of the cluster as $mu_{V}=9.3pm 0.07$ mag, d=585$pm$20 pc and $t=900pm 100$ Myr, respectively. We also estimated the galactic orbital parameters and space velocity components of the cluster and found that the cluster has a slightly eccentric orbit of $e=0.07pm 0.01$ and an orbital period of $P_{orb}= 255pm 5$ Myr.
This paper presents CCD multicolour photometry for the old open cluster NGC 188. The observations were carried out as a part of the Beijing--Arizona--Taiwan--Connecticut Multicolour Sky Survey from 1995 February to 2008 March, using 15 intermediate-band filters covering 3000--10000 AA. By fitting the Padova theoretical isochrones to our data, the fundamental parameters of this cluster are derived: an age of $t=7.5pm 0.5$ Gyr, a distant modulus of $(m-M)_0=11.17pm0.08$, and a reddening of $E(B-V)=0.036pm0.010$. The radial surface density profile of NGC 188 is obtained by star count. By fitting the King model, the structural parameters of NGC 188 are derived: a core radius of $R_{c}=3.80$, a tidal radius of $R_{t}=44.78$, and a concentration parameter of $C_{0}=log(R_{t}/R_{c})=1.07$. Fitting the mass function to a power-law function $phi(m) propto m^{alpha}$, the slopes of mass functions for different spatial regions are derived. We find that NGC 188 presents a slope break in the mass function. The break mass is $m_{rm break}=0.885~M_{odot}$. In the mass range above $m_{rm break}$, the slope of the overall region is $alpha=-0.76$. The slope of the core region is $alpha=1.09$, and the slopes of the external regions are $alpha=-0.86$ and $alpha=-2.15$, respectively. In the mass range below $m_{rm break}$, these slopes are $alpha=0.12$, $alpha=4.91$, $alpha=1.33$, and $alpha=-1.09$, respectively. The mass segregation in NGC 188 is reflected in the obvious variation of the slopes in different spatial regions of this cluster.
NGC 5822 is a richly populated, moderately nearby, intermediate-age open cluster covering an area larger than the full moon on the sky. A CCD survey of the cluster on the UBVI and uvbyCaHbeta systems shows that the cluster is superposed upon a heavily reddened field of background stars with E(B-V) > 0.35 mag, while the cluster has small and uniform reddening at E(b-y) = 0.075 +/- 0.008 mag or E(B-V) = 0.103 +/- 0.011 mag, based upon 48 and 61 probable A and F dwarf single-star members, respectively. The errors quoted include both internal photometric precision and external photometric uncertainties. The metallicity derived from 61 probable single F-star members is [Fe/H] = -0.058 +/- 0.027 (sem) from m_1 and 0.010 +/- 0.020 (sem) from hk, for a weighted average of [Fe/H] = -0.019 +/- 0.023, where the errors refer to the internal errors from the photometry alone. With reddening and metallicity fixed, the cluster age and apparent distance modulus are obtained through a comparison to appropriate isochrones in both VI and BV, producing 0.9 +/- 0.1 Gyr and 9.85 +/- 0.15, respectively. The giant branch remains dominated by two distinct clumps of stars, though the brighter clump seems a better match to the core-He-burning phase while the fainter clump straddles the first-ascent red giant branch. Four potential new clump members have been identified, equally split between the two groups. Reanalysis of the UBV two-color data extending well down the main sequence shows it to be optimally matched by reddening near E(B-V) = 0.10 rather than the older value of 0.15, leading to [Fe/H] between -0.16 and 0.00 from the ultraviolet excess of the unevolved dwarfs. The impact of the lower reddening and younger age of the cluster on previous analyses of the cluster is discussed.
Precision uvbyCaHbeta photometry of the nearby old open cluster, NGC 752, is presented. The mosaic of CCD fields covers an area ~42 on a side with internal precision at the 0.005 to 0.010 mag level for the majority of stars down to V~15. The CCD photometry is tied to the standard system using an extensive set of published photoelectric observations adopted as secondary standards within the cluster. Multicolor indices are used to eliminate as nonmembers a large fraction of the low probability proper-motion members near the faint end of the main sequence, while identifying 24 potential dwarf members between V=15.0 and 16.5, eight of which have been noted before from Vilnius photometry. From 68 highly probable F dwarf members, we derive a reddening estimate of E(b-y)= 0.025 +/- 0.003 (E(B-V) = 0.034 +/- 0.004), where the error includes the internal photometric uncertainty and the systematic error arising from the choice of the standard (b-y), Hbeta relation. With reddening fixed, [Fe/H] is derived from the F dwarf members using both m_1 and hk, leading to [Fe/H] = -0.071 +/-0.014 (sem) and -0.017 +/- 0.008 (sem), respectively. Taking the internal precision and possible systematics in the standard relations into account, [Fe/H] for NGC 752 becomes -0.03 +/-0.02. With the reddening and metallicity defined, we use the Victoria-Regina isochrones on the Stromgren system and find an excellent match for (m-M) = 8.30 +/- 0.05 and an age of 1.45 +/- 0.05 Gyr at the appropriate metallicity.
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