ACTA ASTRONOMICA Vol. 42 (1992) pp. 343±353 New Color-Magnitude Diagrams and Basic Parameters of the Open Cluster NGC 5749 by Juan J. Clari a 1 and E. Lapasset2 Observatorio Astronomico, Laprida 854, 5000 Cordoba, Argentina Received August 7, 1992 ABSTRACT New photoelectric UBV magnitudes and colors for 112 stars and DDO photometry of two red stars in the ®eld of the open cluster NGC 5749 are presented. Using photometric membership criteria only 30% of the observed stars appear to be cluster members, including one suspected variable star. The cluster does not probably contain any red giant. The reddening is variable across the cluster, (B V ) = ( ) the mean value being E 0 42 0 04 (s.d.). A distance of 1280 118 pc, an age of 7 27 10 yr and other basic cluster parameters are derived. Key words: 1. Introduction = b = NGC 5749 (IAU designation C1445-543, l 319. 5, 4. 5) is a group of stars with little central concentration lying near the south-western edge of the Lupus constellation. This is a poorly populated open cluster with stars in a narrow range of brightness; hence Ruprecht (1966) described it as belonging to class IV1p. NGC 5749 lies in a region of the galactic plane where comparatively large color excessesat modest distances are not unusual (Neckel 1967, Moffat and Vogt 1973). Old distance determinations by Trumpler (1930), Shapley (1930), Collinder (1931), and Barkhatova (1950) place the cluster as lying between 0.9 and 2.7 kpc from the Sun. The most recent reference is from Lynga (1964a), who derived a color excess (B V ) = E 0 35 and a distance of 0.9 kpc. The latter results, however, are rather uncertain since they were derived from UBV photometry of only 15 relatively bright stars in the cluster ®eld (Lynga 1964b). 1 VisitingastronomeratCerroTololoInter-AmericanObservatorysupportedbytheNationalScience Foundation under contract No.AST 74-04128. 2 Visiting astronomer, University of Toronto (David Dunlap Observatory) 24-inch telescope at Las Campanas. 344 A. A. = In this study new photoelectric UBV data of 112 stars brighter than V 14 4, located within about15 0 from the assumedclustercenter, are presented. In addition, DDO photometry of two comparatively bright red stars in the cluster ®eld is also given. These data not only allow the construction of well-de®ned color-magnitude (CM) and color-color (CC) diagrams, but also permit a more accurate determination of the basic cluster parameters, particularly its distance. 2. UBV Photoelectric Observations The UBV measurements were carried out during three observing runs between 1985 and 1987 with the 91 cm telescope of the Cerro Tololo Inter-American Obser- vatory (CTIO) and the 60 cm Canadian telescope of the David Dunlap Observatory located in Las Campanas Observatory (LCO). Dry-ice cooled RCA 31034 and 1P21 photomultipliers in single channel photometers with pulse-counting electron- ics were used at CTIO and LCO, respectively. About 12±15 E-region standards (Cousins 1973, 1974) were observed each night to insure accurate transformations to the standard system. No evidence of systematic differences either in the V mag- nitude or in the colors among the stars measured in CTIO and LCO was detected. Consequently, mean UBV values were computed and listed in Table 1. Table1 UBV photometry for stars in the ®eld of NGC 5749 Star HD/CPD/CD V B-V U-B n Remarks 1 11.895 0.460 0.177 1 nm 2 12.346 0.750 0.172 1 nm 3 13.011 0.509 0.123 2 nm 4 13.132 0.553 0.413 2 pm 5 a 13.394 0.551 0.293 2 pm 6 13.643 0.511 0.351 1 m 7 130348 9.720 1.025 0.777 2 G8III/IV,nm 8 12.564 0.468 0.284 2 pm 9 12.019 0.386 0.184 2 m 10 13.160 0.712 0.256 2 nm 11 13.198 0.599 0.421 2 nm 12 13.329 0.453 0.335 2 m 13 12.336 0.375 0.105 3 m 14 13.847 0.498 0.330 2 m 15 12.142 0.320 -0.006 3 m 16 13.714 0.622 0.098 3 nm 17 12.144 0.490 0.304 2 nm 18 13.915 0.731 0.137 2 nm 19 13.282 0.620 0.044 3 nm 20 14.015 0.692 0.080 2 nm Vol. 42 345 Table1 continued Star HD/CPD/CD V B-V U-B n Remarks 21 14.159 0.798 0.200 2 nm 22 -54 6170 11.273 0.266 -0.276 3 m 23 -54 6169 10.852 0.260 -0.206 3 m 24 13.314 0.602 0.211 3 nm 25 -53 6114 11.143 0.308 -0.113 2 m 26 -53 6117 10.891 0.216 -0.268 2 m 27 12.535 0.329 0.195 3 m 28 11.941 1.428 1.292 2 nm 29 -53 6112 10.285 1.260 1.325 2 nm 30 12.304 1.345 1.091 1 nm 31 11.644 2.037 2.363 2 nm 32 b 13.373 0.634 0.024 2 nm 33 13.043 0.421 0.200 2 m 34 13.031 0.361 0.240 4 m 35 14.184 0.667 0.080 1 nm 36 12.763 0.430 0.250 3 m 37 13.643 0.637 0.097 3 nm 38 -53 6113 11.594 0.259 -0.060 4 m 39 130244 10.398 0.112 0.059 4 A0V,nm 40 -53 6119 11.496 0.256 -0.035 4 m 41 13.284 0.455 0.291 1 m 42 13.592 0.681 0.095 2 nm 43 13.945 0.536 0.338 1 m 44 13.134 0.573 0.226 1 nm 45 13.208 0.643 0.352 1 nm 46 11.873 1.289 0.988 3 nm 47 13.710 0.683 0.130 2 nm 48 14.336 0.713 0.093 2 nm 49 12.179 1.454 1.299 2 nm 50 c 12.566 0.510 0.027 2 nm 51 13.690 0.778 0.257 3 nm 52 13.652 0.660 0.168 1 nm 53 13.629 0.750 0.339 2 nm 54 b 12.767 0.407 0.210 1 m 55 12.444 0.658 0.053 2 nm 56 11.660 0.278 0.129 2 m 57 10.924 1.328 1.200 1 nm 58 12.444 0.658 0.053 2 nm 59 d -53 6110 10.701 0.313 0.166 2 nm 60 11.776 0.928 0.527 1 nm 61 11.390 0.438 0.129 2 nm 62 12.143 0.455 0.082 2 nm 63 12.840 0.415 0.263 2 m 64 13.445 0.613 0.341 2 pm 65 12.429 1.381 1.156 2 nm 66 -53 5709 11.162 1.015 0.646 4 nm 67 12.042 0.647 0.184 3 nm 68 12.844 0.574 0.083 3 nm 69 11.896 0.377 0.285 2 pm 70 -53 6105 10.171 0.170 -0.478 4 m 71 d 13.018 0.700 0.318 2 nm 346 A. A. Table1 concluded. Star HD/CPD/CD V B-V U-B n Remarks 72 130152 9.676 0.167 -0.332 4 B6Ib-II,m 73 13.919 0.894 0.462 1 nm 74 e 13.016 0.417 0.252 3 m 75 12.390 0.352 0.074 2 m 76 14.082 0.642 0.199 1 nm 77 -54 6168 10.861 0.230 -0.259 3 m 78 13.949 0.666 0.250 2 nm 79 12.558 0.289 0.130 3 m 80 12.960 0.380 0.213 3 m 81 11.776 0.483 0.020 2 nm 82 11.843 0.502 0.160 3 nm 83 13.079 0.709 0.265 1 nm 84 13.506 0.623 0.078 2 nm 85 13.908 0.643 0.053 2 nm 86 12.521 0.550 0.012 1 nm 87 13.070 1.125 0.928 2 nm 88 12.738 0.496 0.196 2 nm 89 13.183 1.138 1.036 1 nm 90 -54 6165 10.937 0.619 0.074 1 nm 91 f 12.569 1.457 1.684 2 nm 92 12.961 0.382 0.201 3 m 93 11.971 1.273 0.947 2 nm 94 d 11.815 1.826 2.178 1 nm 95 13.729 0.486 0.090 2 nm 96 12.659 0.683 0.126 2 nm 97 13.506 0.577 0.051 3 nm 98 13.447 0.828 0.216 2 nm 99 13.522 0.722 0.152 3 nm 100 13.423 0.483 0.319 3 m 101 13.601 0.649 0.038 2 nm 102 10.701 1.173 0.968 3 nm 103 13.448 0.602 0.090 1 nm 104 11.874 0.352 0.136 1 m 105 12.268 0.733 0.248 2 nm 106 12.772 0.444 0.250 1 m 107 11.916 0.246 0.004 2 m 108 13.098 0.496 0.002 1 nm 109 12.284 0.235 -0.273 1 nm 110 10.017 2.023 1.606 1 nm 111 -53 6101 9.575 1.089 0.963 2 nm 112 129793 8.500 0.112 0.108 2 A0IV,nm a: Variable star No.