Age and distance for the unstudied open cluster Teutsch 7 In Sung Jang and Myung Gyoon Lee Department of Physics & Astronomy, Seoul National University Abstract We present UBVI CCD photometry of unstudied open cluster Teutsch7. This object is listed in the open cluster catalog(Dias et al 2002), but only their coordinate and size were known. The observation was performed at maidanak observatory, and we find about 420 stars of cluster's member in V filter photometry. Through the radial profile, we determine the cluster's angular size extends out to R = 1.6arcmin. The color magnitude diagram of the cluster shows a well defined main sequence extending at least to the limit of the photometry at Mv=22.5 and small redgient clump. The age of Teutsch7 is estimated to be 6.31Myr using the Padova isochrone and the morphological age indicators. reddening E(B-V)=1.7 and distance 3.16kpc are also determined base on isochrone fitting. 1.Introduction Several famous open clusters, like a M67, tare already well studied. But large proportion of open clusters are not studied yet. According to the open cluster catalog (Dias et al., 2002), there are more than 1700 open clusters in our galaxy. However we know only 37% of them about age or distances. Teutsch7, tiny and faint open cluster, is listed in the open cluster catalog(Dias et al 2002), but only their coordinate and visual size were known. Therefore Teutsch7 is suitable and interesting object for young astronomer. 4. Conclusion 5. Reference Dias et al. 2002, A&A, 389, 871 Myung gyoon lee., 1996, A&A, 422, 205 Montgomery et al 1992, A&A, 181, Data and Photometry Observation was conducted using 1.5m telescope at Maidanak observatory, and standard UBVRI filter set was used. Maidanak observatory is one of the best observation sites in Asia, and especially famous from their good seeing. But when we observed it, because of not good condition, can not get a finest data. We performed a PSF photometry using DAOPHOT, 420 stars consider the clusters members among the 1100 stars. 3. Result 3.1. Size of cluster According to the open cluster catalog, the size of Teutsch7 is 3.2arcmin. but is was determined only visual inspection, so to get more accurate value we draw the radial density profile(Figure 1). From this profile, the radius of Tuetsch7 is estimated 1.58arcmin. It is very similar value of Teutsch’s previous result. The white circle indicate the cluster’s region. After the photometry, we sort the stars that located in the cluster’s region. From I filter photometry we could find at least 420 stars are cluster’s member. 간단한 설명을 쓰세 Figure2. Visual size of Teutsch CMD Through the comparison between left and right diagram, we can determine whether it is real star cluster or not. Left CMD, stars located in the boundary area, we can easily find the mean sequence turn off point. There are some small groups can be founded at (B-V)=2.8 and V=19.3, it is considered the red giant clump Isochrone fitting We have estimated the distance and age using the isochrone fitting. It is hard to exactly know about cluster’s metalicity from isohrone fitting, therefore we adopt the solar metalicity. Teutsch7 locates near the Galactic plane (latitude=0.5) SiteMaidanak observatoryFilterFWHM(arcsec) Telescope1.5m telescopeU1.38 Obs time B1.4 RA/Dec , V1.31 l / b60.75, -0.56I1.27 so we obtain a very high value for the interstellar reddening of E(B- V)=1.7. Distance modulus and age are also estimated : (m-M) 0 =12.5± 0.2mag, age = 6.31Myr. So we can say the Teutsch7 has an intermediate age open cluster. We have studied tiny open cluster Teutsch 7 the first time. From radial density profile, we find a Teutsch 7 is not just optically visible cluster but real star cluster. The radius of cluster is 1.58 arcmin and it is very similar value of Teutsch’s previous result. By using a isochrone fitting, we determine the cluster’s reddening age, distance modulus. These values are listed below table. RadiusAgeE(B-V)DistanceSize Teutsch71.58arcmin631Myear1.7±0.1mag3162±270pc1.45±0.12pc Figure1. Radial number density profile of I filter photometry