BATC 15 Band Photometry of the Open Cluster NGC 188

Abstract

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 Å. By fitting the Padova theoretical isochrones to our data, the fundamental parameters of this cluster are derived: an age of $t=7.5\pm 0.5$ Gyr, a distant modulus of $(m-M{)}_0=11.17\pm 0.08$, and a reddening of $E(B-V)=0.036\pm 0.010$. 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 $R_c=3.80^{\prime }$, a tidal radius of $R_t=44.78^{\prime }$, and a concentration parameter of $C_0=\log (R_t/R_c)=1.07$. Fitting the mass function to a power-law function $\varphi (m)\propto m^{\alpha }$, 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 $m_{\mathrm{break}}=0.885M_{\odot }$. In the mass range above $m_{\mathrm{break}}$, 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 $m_{\mathrm{break}}$, 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.

Accepted for Publication in AJ, 11 pages, 9 figures and 4 tables

References in corpus (3)

• BATC 13-band Photometry of Open Cluster NGC 7789
• A Survey of Open Clusters in the u'g'r'i'z' Filter System: III. Results for the Cluster NGC 188
• Membership Determination of Open Cluster M48 Based on BATC Thirteen-Band Photometry

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