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Astron. Astrophys. 320, 185-195 (1997)

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2. Observations

All photometric observations were performed at the ESO 1 m-Telescope during two observing runs in 1993 and 1994 at ESO, La Silla.

In the first run, three nights (1993 March 10-12) had been allocated for JHKL photometry using the IR Photometer and a nitrogen-cooled InSb detector, and three more nights (1993 March 14-16) for [FORMULA] [FORMULA] photometry with the single channel photometer and a Hamamatsu R 943-02 detector. All nights were photometric.

In the second run, six nights (1994 May 1-6) had been allocated for [FORMULA] [FORMULA] photometry using the single channel photometer and a RCA 31034A detector, and five more nights (1994 May 7-11) for JHKL photometry with the same setup as in 1993. Due to bad weather during the infrared observations, JHKL photometry could only be obtained during two nights (May 10-11), while during the [FORMULA] [FORMULA] observations all nights were photometric.

For the optical ([FORMULA] [FORMULA]) photometry a diaphragm of 15 arcsec was used in both runs. The usage of two different instrumental systems (due to a technical problem with the Hamamatsu photo-tube at the second run) does not affect the quality of the photometry, since both systems match very well the Cousins standard system (see Table 2 in Covino at al.  1992 ). Moreover, each night at least 20 standard stars from the E-regions by Graham (  1982 ) were observed in order to determine the atmospheric extiction coefficients as well as the colour transformation terms for the tie-in to the standard [FORMULA] system. Data reduction was performed using the VAX/VMS version of the ESO photometric reduction program SNOPY, using the procedure described in Covino et al. (1992 ). Typical standard deviations as determined from measurements of standard stars with comparable brightness as the program stars are: [FORMULA], [FORMULA], [FORMULA], [FORMULA], [FORMULA].

The infrared (JHKL) photometry was measured through a 15 arcsec aperture. For background subtraction standard chopping and beam-switching techniques were applied, using a beam-throw of 20 arcsec in E-W direction. Every night some 12 standard stars from Bouchet et al. (1991 ) were observed. Data reduction was performed with the IR photometry reduction program available at ESO, La Silla.

Photometric data (with individual errors for the JHKL magnitudes) are given in Table 6.

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998