2 Observations

The spectroscopic observations were carried out with the 2.15 m telescope at the Complejo Astronómico El Leoncito, CASLEO (San Juan, Argentina). Medium-low resolution spectrograms were obtained with a Boller & Chivens spectrograph using a photon-counting Reticon, called Z-Machine, during 1990 and 1991 and a Thompson CCD (500$\times$592 pixels) in 1992. Since 1994 high resolution spectrograms were obtained with a REOSC echelle spectrograph using a Tek CCD (1024$\times$1024 pixels). A log of the observations is shown in Table 1.

  

Table 1: Log of the spectroscopic observations of Hen 1761

Details about the Z-Machine observations and data reduction procedures were given by Barbá et al. (1992). The CCD data were reduced with standard IRAF packages, CCDRED and ONEDSPEC and all the spectra were measured using the SPLOT task within IRAF.

To obtain the flux calibration, standard stars from Stone & Baldwin's (1983) and Baldwin & Stone's (1984) lists, were observed each night. An analysis of the flux calibration errors, by flux comparisons of the standard stars, shows that they may be estimated at about 15% for the Z-Machine images, 5% for the Thomson CCD images and 20% in the central part of each order for the REOSC echelle images. However, it must be kept in mind that true flux errors are largely dependent on the tracing of the continuum and the emission line strengths.