Astron. Astrophys. 353, L21-L24 (2000)

2. Observations and results

The new mid-infrared object (MIR1) was discovered during the raster imaging observations of the populous cluster NGC 330 with the ISOCAM (Cesarsky et al. 1996) on board the ISO satellite (Kessler et al. 1996). Observations were made on May 22, 1997 using the broad-band CAM filters LW1, LW2 and LW10, corresponding to the effective wavelengths of 4.5, 6.75 and 11.5 µm, respectively. The raster mode was 5 5, with a raster step size equal to 8 pixels (24") and a pixel field of view (PFOV) of 3". The fundamental integration time was set to = 2.1 sec, with a total number of about 15 exposures per single raster position. ISOCAM data were reduced using the CAM Interactive Analysis software (CIA version 3) ¹ and the photometry was performed with the IRAF APPHOT package.

The measured mid-IR fluxes, together with the optical photometry collected from the literature, are given in Table 1. The ISOCAM flux errors given in Table 1 are formal APPHOT errors. The absolute photometric uncertainty of the ISOCAM measurements is estimated to be less than 20% (Biviano, 1998).

Table 1. Optical and mid-infrared photometry of MIR1.
Notes:
1) optical data are averages from the following sources: Balona 1992; Keller et al. 1999c; Sebo & Wood 1994; Vallenari et al. 1994.

The optical counterpart of the infrared source was identified from the instrumental coordinates of MIR1 which were derived with respect to the positions of 8 field stars on LW2 CAM frame (identification accuracy is 1"). The identification chart of MIR1 is given in Fig. 1.

Fig. 1. Identification chart of MIR1 in I-band (north is up and east is left). The frame also covers the central part of SMC cluster NGC 330.

© European Southern Observatory (ESO) 2000

Online publication: January 18, 2000
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