Open Clusters in the Third Galactic Quadrant

A&A 370, 436–446 (2001) Astronomy DOI: 10.1051/0004-6361:20010258 & c ESO 2001 Astrophysics Open clusters in the third galactic quadrant I. Photometry A. Moitinho?,?? 1 Observatorio Astronómico Nacional, UNAM, Apdo. Postal 877, CP 22800, Ensenada B.C., México 2 Instituto de Astrof´ısica de Andaluc´ıa (CSIC), Apdo. 3004, 18080 Granada, Spain Received 13 December 2000 / Accepted 14 February 2001 Abstract. We have performed a photometric survey of open clusters in the third Galactic quadrant in order to study the star formation history and spatial structure in the Canis Major-Puppis-Vela region. In this paper we describe a catalogue of CCD UBVRI photometry of approximately 65 000 stars in the fields of 30 open clusters. The data were obtained and reduced using the same telescope, the same reduction procedures, and the same standard photometric system, which makes this catalogue the largest homogeneous source of open cluster photometry so far. In subsequent papers of this series, colour-colour and colour-magnitude diagrams will be presented which, amongst other uses, will allow the determination of an homogeneous set of cluster reddenings, distances, and ages that will constitute the observational basis for our studies of the spatial structure and star formation history in the third Galactic quadrant. Key words. techniques: photometric – stars: fundamental parameters – Galaxy: open clusters and associations: general – Galaxy: structure – ISM: dust, extinction 1. Introduction metalicities), as well as the small number of studies of certain kinds of clusters (e.g. old clusters and distant Open clusters are ideal objects for the investigation of sev- clusters). eral astrophysical problems, since they are groups of stars placed at a common distance, which were formed under The Catalogue of Open Cluster Data (COCD) (Lyng˚a the same conditions, in most cases at approximately the 1981, 1987), which includes information for 1151 clusters same time, and spanning a broad range in mass. These (distances for 422) has been the observational basis for properties allow open cluster distances and ages to be bet- many Galactic structure studies. However, the parameter determined than in the case of isolated stars. Indeed, ters presented in the COCD were derived by different au- there is a virtually endless list of literature on stellar clus- thors using a variety of instrumentation, techniques, cal- ters used as tests for stellar evolution theories, and as ibrations, and analytic criteria, and therefore result in a probes of Galactic structure and evolution. rather inhomogeneous set. An analysis of the precision In the case of Galactic structure studies the existing expected due to the effects of these inhomogeneities has compilations of open cluster parameters have allowed been performed by Janes & Adler (1982) who have found some understanding of the structure and development of a typical difference of 0.55 mag in distance moduli deter- the Galactic disc (Vogt & Moffat 1972; Janes & Adler mined in different UBV photometric studies. But even this 1982; Alfaro et al. 1991; Twarog et al. 1997; Carraro et al. large scatter in distance modulus determinations might 1998). However, many of the conclusions drawn from open be underestimated since several clusters have much larger cluster data have been if not controversial, at least affected ranges in their estimated distances. Cases like NGC 2453 by considerable uncertainty. Among the reasons for this which has distance estimates from 1500 to 5900 pc are not situation are the lack of homogeneity of derived open clus- rare. These problems have been known to the astronom- ter fundamental parameters (reddening, distances, ages, ical community for a long time and have led to several attempts to produce more consistent sets of open cluster parameters. Loktin & Matkin (1994) reanalysed UBV ? e-mail: [email protected] photometry of 330 clusters and obtained a more homoge- ?? Visiting astronomer, Cerro Tololo Inter-American neous, although less numerous, catalogue of open clus- Observatory. CTIO is operated by AURA, Inc., under ter reddenings, distances and ages. However, Loktin & contract to the National Science Foundation. Matkin (1994) used three different sets of isochrones in Article published by EDP Sciences and available at http://www.aanda.org or http://dx.doi.org/10.1051/0004-6361:20010258 A. Moitinho: Open clusters in the third galactic quadrant 437 their age and distance determinations which is likely to af- Table 1. Observed open clusters fect the internal precision of the catalogue. More recently, Dambis (1998) has given another contribution towards an Name lbα(2000) δ(2000) Run homogeneous set of cluster parameters by redetermining Bo 5 232◦. 57 +00◦. 69 07h30m. 9 −17◦040 1998 the reddenings, distances and ages of 203 open clusters, Cz 29 230◦. 80 +00◦. 93 07h28m. 3 −15◦240 1998 younger than log t<8.2 to avoid chemical composition Haf 10 230◦. 82 +01◦. 00 07h28m. 6 −15◦230 1998 effects, using a single set of isochrones and an empirical ◦ ◦ h m − ◦ 0 ZAMS. Haf 16 242. 07 +00. 47 07 50. 3 25 27 1994 ◦ ◦ ◦ 0 Although the works of Loktin & Matkin (1994) and Haf 18 243. 11 +00. 42 07h52m. 5 −26 22 1994 Dambis (1998) have generated improved sets of cluster Haf 19 243◦. 04 +00◦. 52 07h52m. 7 −26◦150 1994 parameters by using the same kind of data (UBV pho- NGC 2302 219◦. 28 −03◦. 10 06h51m. 9 −07◦040 1998 tometry), and were analysed in an homogeneous fashion, NGC 2309 219◦. 89 −02◦. 22 06h56m. 2 −07◦120 1998 at least two effects still contribute to degrade the precision ◦ ◦ ◦ 0 NGC 2311 217. 73 −00. 68 06h57m. 8 −04 35 1998 of their results. The first one is that both works used UBV ◦ − ◦ h m − ◦ 0 data from different sources, nominally on the UBV system NGC 2335 223. 62 01. 26 07 06. 6 10 05 1998 ◦ − ◦ h m − ◦ 0 but in fact were calibrated using various sets of standard NGC 2343 224. 31 01. 15 07 08. 3 10 39 1998 ◦ ◦ ◦ 0 stars which can produce considerably different photome- NGC 2353 224. 73 +00. 38 07h14m. 6 −10 18 1994 try (see Table 8 in this paper, and also Bessel 1995 for a NGC 2367 235◦. 64 −03◦. 85 07h20m. 1 −21◦560 1994 detailed comparison of some versions of the UBVRI sys- NGC 2383 235◦. 27 −02◦. 43 07h24m. 8 −20◦560 1998 tem). The second and perhaps most important factor is NGC 2384 235◦. 39 −02◦. 42 07h25m. 1 −21◦020 1998 the effect of photometric depth. Photoelectric photome- ◦ ◦ ◦ 0 NGC 2401 229. 67 +01. 85 07h29m. 4 −13 58 1998 try is usually limited to V ∼ 16 mag, which in many cases ◦ ◦ h m − ◦ 0 is not enough for reliable distance determinations: evo- NGC 2414 231. 41 +01. 97 07 33. 3 15 27 1998 ◦ ◦ h m ◦ 0 lutionary effects will produce redder colours and lead to NGC 2425 231. 49 +03. 31 07 38. 3 −14 52 1998 ◦ ◦ ◦ 0 underestimated distances. Also, for the younger clusters, NGC 2432 235. 48 +01. 78 07h40m. 9 −19 05 1998 the nearly vertical shape of the upper main sequence will NGC 2439 246◦. 41 −04◦. 43 07h40m. 8 −31◦390 1994 introduce large uncertainties in distance determinations NGC 2453 243◦. 33 −00◦. 93 07h47m. 8 −27◦140 1998 via ZAMS fitting. NGC 2533 247◦. 80 +01◦. 29 08h07m. 0 −29◦540 1998 In the light of the above mentioned problems with the ◦ ◦ ◦ 0 NGC 2571 249. 10 +03. 54 08h18m. 9 −29 44 1998 current open cluster parameter compilations and of our ◦ ◦ h m − ◦ 0 interest in studying the star formation history and spa- NGC 2588 252. 28 +02. 45 08 23. 2 32 59 1998 ◦ ◦ h m ◦ 0 tial structure of the Canis Major-Puppis-Vela region, we NGC 2635 255. 60 +03. 97 08 38. 5 −34 46 1998 ◦ ◦ ◦ 0 have performed a deep CCD UBVRI photometric survey Rup 18 239. 94 −04. 92 07h24m. 8 −26 13 1998 of open clusters using the same instruments, reduction Rup 55 250◦. 68 +00◦. 76 08h12m. 3 −32◦360 94/98 methods and standard stars. In this paper we describe the Rup 72 259◦. 55 +04◦. 37 08h52m. 1 −37◦360 1998 photometric database. Reddenings, distances and ages will Rup 158 259◦. 55 +04◦. 42 08h52m. 3 −37◦340 1998 be determined in forthcoming papers using the same Zero ◦ ◦ ◦ 0 Tr 7 238. 28 −03. 39 07h27m. 3 −24 02 94/98 Age Main Sequence (ZAMS) and evolutionary models. In the next sections we describe the observations and data reductions, and present the photometric database. 00 Later, in Sect. 6 a comparison with previously published images presented higher values (∼2.0 ). The cluster photometry is shown. Finally, Sect. 7 is a discussion of the names, coordinates and observing run are presented in interstellar extinction law in the direction of our sample. Table 1. In both runs, images were taken with a 2048 × 2048 Tek CCD and the standard set of UBVRI filters avail- 2. Observations 00 able at CTIO. The 0.39 /pixel plate scale resulted 0 0 Open clusters in the galactic range 217◦ <l<260◦ in a field of view of 13 × 13 . Images were acquired and −5◦ <b<5◦, with angular diameters of approxi- using the CTIO ARCON operating in Quad mode mately 50 and with estimated ages lesser than 1.3108 yr (http://www.ctio.noao.edu/instruments/arcon/ − (log(age) ∼ 8.1) were selected from the COCD. 24 ob- arcon.html). The gain was set at 3.2 e /adu and the − jects were selected following these criteria. To extend the readout noise was determined to be 4.0 e .

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