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3. Observations

Our photometry was obtained using the 1-m Swope telescope at Las Campanas Observatory on the nights of 9-11 February and 17-18 May 1991. The detector was a Ford2 2048 tex2html_wrap_inline1287 2048 pixel CCD, rebinned 2 tex2html_wrap_inline1287 2. At the Cassegrain focus each rebinned pixel corresponds to 0.87 arcsec on the sky. Observations were made through a Johnson V filter, Gunn r and i filters and a narrow band (70 Å) tex2html_wrap_inline1201 interference filter.

Two cluster fields were observed. Another field, offset approximately 1 degree from the cluster, but at a similar galactic latitude, was also observed in order that some estimate of the contamination by galactic field stars might be made. The suitability of this field for this purpose is discussed in Sect. 6.2 (click here). The coordinates of each of the field centres are given in Table 1 (click here) and their positions on the sky are shown in Fig. 1 (click here).

For each field, four exposures were made, one short and three long to record respectively the bright and faint stars at optimum exposure levels. Exposure times were 15 : 10 : 10 s for the short and 600 : 600 : 600 s for the long through V:R:I filters respectively. Three exposures of 1800 seconds each were made of the first cluster field using the tex2html_wrap_inline1201 filter.

  figure249
Figure 1: The region of IC 2602 showing the positions of the two observed cluster fields

Photometric standard stars chosen from Landolt (1992) to cover a range of spectral types were observed during each night. Dome flat fields for the V, R and I filters, sky flat-fields for the tex2html_wrap_inline1201 filter, and bias frames were also taken.

 

 

Field tex2html_wrap_inline1227 tex2html_wrap_inline1313 l b
(J2000.0)
IC 2602a 10 : 44 : 44.4 -64 : 29 : 04.0 289.792 -4.924
IC 2602b 10 : 41 : 01.5 -64 : 11 : 27.2 289.328 -4.802
"Offset'' 10 : 35 : 15.7 -63 : 54 : 46.6 288.635 -4.853
Table 1: Coordinates of the field centres


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