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A Photometric Study of Unstudied Open Clusters Berkeley 49 & 84 in the SDSS. Jinhyuk Ryu and Myung Gyoon Lee Department of Physics & Astronomy, Seoul National University. Abstract
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Jinhyuk Ryuand Myung Gyoon Lee
Department of Physics & Astronomy, Seoul National University
We present a study of two open clusters Berkeley 49 and Berkeley 84 based on ugriz images of the Sloan Digital Sky Survey (SDSS). These objects were listed in the open cluster candidates(Ruprecht, 1966), but only their coordinates and sizes were known. We derive the photometry of bright stars in these objects using DAOPHOT. We find they are genuine open clusters from the surface number density profiles and Color-Magnitude Diagrams(CMDs). We estimate physical parameters of these clusters using the isochrone fit with the PADOVA models: reddening E(B-V)=1.2±0.1mag for Berkeley 49, and E(B-V)=0.6±0.1mag for Berkeley 84. These two clusters have similar ages of t=700±100Myrs and distance of d=2.6±0.2kpc.
According to the open cluster catalog (Dias et al., 2002), there are more than 1700 open clusters in the Milky Way. However ⅓ of them are not studied yet.
Around 70 open clusters are included in the SDSS, but there is only one previous photometric study about open clusters using the SDSS data (An et al., 2008). Berkeley 49 & 84 are included in the SDSS data and not studied, therefore they are good targets to study using the SDSS.
To compare with other open clusters is also useful to determine parameters. In the figure 5, loci of Ruprecht 115 and NGC 2818 are overlaid on the locus of Berkeley 49 in CMD. These two clusters have similar loci with Berkeley 49, and their ages are also similar. Physical Parameters estimated from the locus fitting are consistent with the isochrone fitting results.
3.2. Berkeley 84
We apply the same method to Berkeley 84. Figure 6 is a radial number density profile of Berkeley 84. In the figure, the radius of Berkeley 84 is 1’.
Figure 7 is a CMD of Berkeley 84. Despite loss of some bright saturated stars, we determine its age t=700±100Myrs, reddening E(B-V)=0.6±0.1mag and distance modulus (m-M)0=12.0±0.2mag.
Berkeley 84 is also compared with Ruprecht 115 and NGC 2818. Figure 8 is loci of these two clusters overlaid on the CMD of Berkeley 84. Parameters estimated from the comparing with Ruprecht 115 and NGC 2818 are consistent with the isochrone fitting also.
Figure 5. Loci are overlaid on the CMD of Berkeley 49. Left yellow dots are the locus of Ruprecht 115, and right red dots are the locus of NGC 2818. Blue dots are core members and a blue arrow is a reddening vector same as Fig. 4.
The SDSS catalog of Berkeley 49 & 84 is incomplete, so we obtain new photometric catalog using DAOPHOT. The standard calibration has done with nearby stars in the SDSS catalog. Figure 1 and 2 are r band images of Berkeley 49 & 84, respectively.
Figure 6. The radial number density profile of Berkeley 84. Density is flattened after radius 1’.
Figure 2. The r band image of Berkeley 84. A red symbol and a circle means same as Fig. 1.
Figure 1. The r band mosaic image of Berkeley 49. The center of the cluster is marked with a red symbol. A red circle represents a radius 2’ from the center.
3. Results3.1. Berkeley 49
We estimate the center of the cluster where is on the peak of surface number density map. Figure 3 shows the radial number density profile of Berkeley 49. From this profile, the radius of Berkeley 49 is 1.5’.
Figure 4 is a CMD of Berkeley 49.It shows that main sequence is scattered. Also there are a few red giant candidates. Overlaid lines are PADOVA isochrones (Girardi et al., 2004) with log age 8.8 and 9.0. We adopt metallicity Z=0.008. From this fitting, we estimate the age t=700±100Myrs, the reddening E(B-V)=1.2±0.1 mag and the distance modulus (m-M)0=12.0±0.2 mag. The green line seems to be well-fitted than the red line when we focused on the red giant branch.
Figure 7. The CMD of Berkeley 84 and PADOVA isochrones. Symbols are same as Fig. 4, but core radius is 0.5’.
Figure 8. Same as Fig. 5, but on the CMD of Berkeley 84.
We found that Berkeley 49 & 84 are genuine open cluster. Their parameters were derived from PADOVA isochrone fitting and loci of clusters comparing. There are no significant differences between results from two methods. Table 1 is the summary of our results.
Figure 3. The radial number density profile of Berkeley 49. Density decreases until 1.5’ and flat after 1.5’.
Table 1. Parameters of Berkeley 49 & 84.
An et al., 2008, ApJs, 179, 326Dias et al. 2002, A&A, 389, 871Girardi et al., 2004, A&A, 422, 205Pedreros, M., 1989, AJ, 98, 2146Piatti et al., 1999, MNRAS, 303, 65
Figure 4. The CMD of Berkeley 49 and PADOVA isochrones. The red dotted line is the log age 9.0, and the green dashed line is the log age 8.8. Blue dots are cluster’s core member whose have the distance less than 0.6’ from the center. A blue arrow is a reddening vector, and error bars below an arrow are error of (g-r) color.