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Astron. Astrophys. 327, 183-190 (1997)

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2. Observations

2.1. Optical observations

Our optical identification spectra and time-resolved follow-up observations were collected during five observing runs at the European Southern Observatory (ESO) at La Silla, Chile. Low-resolution spectroscopy was obtained with EFOSC2 and CCD#19 at the ESO/MPI 2.2-m telescope in July and November 1995 and with EFOSC1 and CCD#26 at the 3.6-m telescope in January 1992 (discovery spectrum of 0132-65). Slit widths of [FORMULA], [FORMULA] and, [FORMULA] were used to adjust to the different seeing conditions during the individual nights. CCD photometry was performed with CCD#29 at the Dutch 0.9-m telescope in September 1993, with CCD#28 at the

Danish 1.54-m telescope in July 1995, and with CCD#19 at the 2.2-m telescope in November 1995. The details of the observations are given in Table 1. All observations except the July 1995 spectroscopy were done under photometric conditions.


[TABLE]

Table 1. Journal of optical observations of 2022-39 and 0132-65 .


CCD#19 is a front illuminated 1024 [FORMULA] 1024 pixel2 Thompson CCD with 19 [FORMULA] 19  [FORMULA] m2 pixels, CCD#26 and CCD#29 are back illuminated thin 512 [FORMULA] 512 pixel2 Tektronics CCDs with 27 [FORMULA] 27  [FORMULA] m2 pixels, and CCD#28 is a back illuminated thin 1024 [FORMULA] 1024 pixel2 Tektronics CCD with 24 [FORMULA] 24  [FORMULA] m2 pixels.

The long-slit spectroscopic CCD images were reduced using the MIDAS software packages provided by ESO. A flux calibration was obtained from observations of spectrophotometric standard stars (Hamuy et al. 1992, 1994 ).

From the CCD direct images, differential photometry was derived by integrating the fluxes of the object, nearby comparison stars contained in the field of view, and the sky background using circular apertures. An absolute calibration of the V-filter data was derived from observations of photometric standard stars (Landolt 1992 ). The stability of the photometry was checked from the flux differences of the comparison stars. For the comparison stars of 2022-39 flux variations of [FORMULA] 0.006 mag and [FORMULA] 0.008 mag were found for the July 1995 and November 1995 data, respectively.

For those of 0132-65 somewhat larger variations of [FORMULA] 0.04 mag and [FORMULA] 0.03 mag were determined for the September 1993 and November 1995 data, respectively, as weaker comparison stars had to be used. The V-magnitude for 0132-65 was derived from our spectrophotometry.

2.2. X-ray observations

In addition to the RASS observations of 2022-39 and 0132-65 pointed PSPC and HRI observations of 0132-65 were obtained with ROSAT. The details of the X-ray observations (such as observing dates, exposure times, number of observation intervals, mean countrates and hardness ratios) are summarized in Table 2. The hardness ratio HR1 denotes the number of photons above 0.4 keV minus the number of photon below 0.4 keV divided by the total number of photons in the 0.1-2.4 keV ROSAT energy band. All the X-ray data were reduced using the EXSAS software package provided by the MPE Garching (Zimmermann et al. 1993 ).


[TABLE]

Table 2. Journal of ROSAT X-ray observations of 2022-39 and 0132-65 .


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© European Southern Observatory (ESO) 1997

Online publication: April 8, 1998
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