Astron. Astrophys. 343, 273-280 (1999)

2. Observations and data reduction

Radial velocities for the chemically peculiar stars that are listed in Table 1 have been measured with different instruments:

• the 1.4 m Coude Auxiliary Telescope equipped with the Coude Echelle Spectrometer of the European Southern Observatory has been used to observe the stars HD 11753, HD 15144 and HD 25267 in the 545 nm region with a linear dispersion of 1 Å mm^-1, the lines of the wavelength calibration lamp show that the instrumental broadening can be reproduced with a FWHM = 3 km s^-1 Gaussian. This instrument has also been used to observe HD 36485 in the H region and HD 142096 in the D3 region with a 1.4 Å mm^-1 linear dispersion and a FWHM = 5 km s^-1 Gaussian instrumental broadening.

• the 1.5 m ESO telescope equipped with ECHELEC has been used to observe HD 37017 in the H region with a 3 Å mm^-1 linear dispersion and a FWHM = 11 km s^-1 Gaussian instrumental broadening.

• the 2.1 m telescope of the Complejo Astronómico El Leoncito by using a Boller & Chivens Cassegrain spectrograph has been used to observe HD 36485 and HD 37017 in the D3 and H regions at a 10 Å mm^-1 linear dispersion and a FWHM = 25 km s^-1 Gaussian instrumental broadening.

• the 0.9 m telescope of the Catania Astrophysical Observatory , which is fibre linked to a REOSC echelle spectrograph (Frasca & Catalano 1994), has been used to observe the stars HD 37017, HD142096 and HD 189178 in the D3 region with a 6 Å mm^-1 linear dispersion and a FWHM = 24 km s^-1 Gaussian instrumental broadening.

Table 1. Observed CP stars. Spectral and peculiarity classes are from Renson et al. (1991). Spectroscopic observations have been carried out with CAT and 1.5 m telescope of ESO, with the 2.1 m telescope of CASLEO and 0.9 m telescope of the Catania Astrophysical Observatory (SLN).

All data have been reduced using the IRAF package. The achieved S/N was between 100 and 200.

For each observed star, radial velocities have been measured by cross-correlating the observed spectra with SYNTHE (Kurucz & Avrett 1981) spectra. ATLAS9 (Kurucz 1993) model atmospheres have been adopted for these calculations.

Hauck & North (1993) concluded that classical photometric methods can be reliable to infer the effective temperature of helium peculiar stars. Thus we have determined the effective temperatures and gravities of these stars from Strömgren photometry according to the grid of Moon & Dworetsky (1985) as coded by Moon (1985). The photometric colours have been de-reddened with the Moon (1985) algorithm. For the remaining peculiar stars we have determined the effective temperature by using the Napiwotzki et al. (1993) algorithm. The source of the Strömgren photometric data was SIMBAD. Abundances have been changed in order to improve the matching between observed and computed spectra.

To evaluate statistical and systematic errors on our radial velocities, during each night we have observed stars with constant and well known radial velocity. For any of these stars we have computed the average radial velocity and standard deviation (). The largest value is reported in Table 2 to estimate the statistical errors. Systematic errors are quantified with the average difference between radial velocity values from the literature and our measurements (Table 2). Since the errors are smaller than few km s^-1, the measured radial velocities of program stars were not corrected for.

Table 2. A sample of N stars with constant and well known radial velocity has been observed. For any instrument, the average difference between the radial velocity values from the literature and our measurements estimates possible systematic errors. For any template star we have computed the average radial velocity value and standard deviation (). The largest is reported to quantify random errors on our measurements of radial velocity. See the text for a description of the used instrumental configuration.

The measured radial velocities and heliocentric Julian Date are listed in Table 3.

Table 3. Heliocentric Julian Date and measured radial velocities for program stars.

© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999
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