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Colour-magnitude diagrams (CMDs)

4.1. Be 64

The CMDs for Be 64 are shown in Fig. 5 (click here). Two nearby fields towards east and west directions tex2html_wrap_inline1299 away from the cluster region have also been observed to estimate contamination of field stars in the cluster region. The CMDs for field regions are shown in Fig. 6 (click here). A clump of red giants appears near V = 16.4, tex2html_wrap_inline1303, tex2html_wrap_inline1305, tex2html_wrap_inline1307. A comparison of the (V, V-R) and (V, V-I) CMDs of the cluster region and nearby fields indicates that in the range of V= 16-17, (V-R)= 1.0-1.2 and (V-I)= 2.0-2.3, there are 7 stars in the cluster region, whereas, in the nearby fields there are 2 and 3 stars respectively. Since the CMDs of nearby fields covers an area which is double as compared to the cluster region, it is expected that at the most 2 field stars can contaminate the sample of the red giant clump. It is rather difficult to identify the MS in the CMDs, however, a well defined blue envelope of the MS can be easily identified in (V, V-I) and (V, V-R) CMDs. A comparison of the (V, V-I) CMD of the cluster with the CMDs of nearby fields manifests that cluster region has large number of stars having tex2html_wrap_inline1335. whereas there are very few stars in the CMD of nearby field regions having tex2html_wrap_inline1337. We have plotted a box using thick dashed line in the CMDs of nearby fields to indicate the main distribution of stars in the CMD. The same box is also plotted in the (V, V-I) CMD of the cluster region. The stars in the cluster region lying in the box mainly belong to the foreground field population. The MS of the cluster region is negligibly affected by the field stars. Since the cluster is located at tex2html_wrap_inline1343, it indicates that the cluster may be located outside the galactic disk.

It is impossible to estimate the BTO and BRGB using (V, B-V) CMD only, however, we have compared the morphology of the (V, B-V), (V, V-I), (V, V-R) CMDs and estimated V magnitude at the turnoff point on the (V, V-I) and (V, V-R) CMDs. Then (B-V) colour corresponding to the so determined V magnitudes was read from the (V, B-V) CMD. The (B-V) colour thus determined was taken as BTO. The BTO colour comes out to be tex2html_wrap_inline1381. The position of BRGB is estimated at tex2html_wrap_inline1383 and tex2html_wrap_inline1385. The CIP comes out to be tex2html_wrap_inline1387 which indicates an age of tex2html_wrap_inline1389.

4.2. Be 69

The CMDs for Be 69 are shown in Fig. 7 (click here). CMDs for two nearby fields towards north and south directions tex2html_wrap_inline1393 away from the cluster region have also been observed to estimate contamination of field stars in the cluster region. The CMDs for field regions are shown in Fig. 8 (click here). The area of the cluster region is tex2html_wrap_inline1395 of the field region. Although the contamination due to field stars is significant, still the main properties of the cluster population can be seen in the CMD of the cluster region. The broadness of the main sequence is due to various causes, among which are the photometric errors, the presence of unresolved binary stars, a possible internal reddening and field stars contamination. The BTO is estimated at tex2html_wrap_inline1397, tex2html_wrap_inline1399, and position of BRGB is estimated at tex2html_wrap_inline1401, tex2html_wrap_inline1403. The colour index parameter comes out to 0.55, which indicates an age of tex2html_wrap_inline1405 for the cluster.

Here we would like to point out that the ages obtained by using this method are approximate. Error in eye estimate of CIP is approximately of the order of tex2html_wrap_inline1407. For a value of tex2html_wrap_inline1409, age estimate can vary from log t= 8.7 to tex2html_wrap_inline1413.


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