2. Observations and data reductions
The spectra were obtained at the Nordic Optical Telescope (NOT) with the SOFIN échelle spectrograph (Tuominen 1992) in February of 1995. The 3rd optical camera was used with an entrance slit width of m, providing a spectral resolving power of . Three stars (F84, F141 and F151) were also observed with the 2nd optical camera, providing a spectral resolving power of (the entrance slit width m). The spectra were recorded with the Astromed-3200 CCD camera (Mackay 1986) equipped with an EEV P88100 UV-coated CCD of pixels operated at the working temperature of 150 K. With the 3rd camera the CCD size covered simultaneously 25 spectral orders, each of 80-150 Å in length, located in the interval of 4500-8750 Å. The 2nd camera gave 15 spectral orders, each of 40-60 Å, in the spectral region from 5650 to 8750 Å. For the F84 and F141 two partly overlapping spectral regions were observed by setting of the échelle and cross-dispersion prism angles in order to extend the wavelength intervals of orders. The concrete numbers of spectrograms received for every star are presented in Table 1. All spectra were exposed to S/N.
Table 1. Atmospheric parameters derived for the programme stars. The last two columns give the resolving powers and number of spectra observed
Reductions of the CCD images were made with the 3A software package (Ilyin 1996). Procedures of bias subtraction, spike elimination, flat field correction, scattered light subtraction, extraction of spectral orders were used for image processing. A Th-Ar comparison spectrum was used for the wavelength calibration. The continuum was defined by a number of narrow spectral regions, selected to be free of lines.
The lines suitable for measurement were chosen using the requirement that the profiles be sufficiently clean to provide reliable equivalent widths. Inspection of the solar spectrum (Kurucz et al. 1984) and the solar line identifications of Moore et al. (1966) were used to avoid blends. Lines blended by telluric absorption lines were omitted from treatment as well. The equivalent widths of lines were measured by fitting of a Gaussian function. 179 atomic lines were selected for the analysis in spectra of the 3rd camera and 132 in spectra obtained on the 2nd camera. The line measurements are listed in Tables 2 and 3 (available in electronic form at CDS).
© European Southern Observatory (ESO) 2000
Online publication: August 17, 2000