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Astron. Astrophys. 342, 831-838 (1999)

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2. Observations

In this research work we use spectra obtained during three observing runs: two at the Observatoire de Haute Provence (France), from February 7 to February 11, 1997 and from July 31 to August 6, 1997; one at La Silla (ESO, Chile) in remote mode from Garching (Germany) from May 29 to June 2, 1997.

For northern stars high-resolution spectra (R[FORMULA] 0.17 Å) centered on the Li [FORMULA]6708 Å line were obtained with the Aurélie spectrograph (Gillet et al. 1994) installed on the 1.52m telescope at Observatoire de Haute Provence. This spectrograph uses a cooled 2048-photodiode detector forming a [FORMULA]m pixel linear array. The entrance spherical diaphragm was [FORMULA]. A grating with 1800 grooves mm-1 was used, giving a mean dispersion of 4.7 Å mm-1. The spectral coverage was about 120 Å.

For southern stars, high-resolution spectra (R[FORMULA] 0.10 Å) were obtained with the Coudé Echelle Spectrometer (CES) mounted on the Auxiliary Telescope (CAT) at La Silla, in the Long Camera mode. An RCA high resolution CCD with 640 x 1024 pixels was used as detector. The pixel size was [FORMULA]m corresponding to [FORMULA] and [FORMULA] in the dispersion and slit directions respectively. The spectral coverage was about 77 Å.

Spectrophotometric flux standards recommended by Massey et al. (1988), Breger (1976) and Taylor (1984) were observed several times each night. Thorium lamps were observed before and after each stellar observation for wavelength calibration. At the beginning, the end and the middle of each night, a series of flat-fields were obtained using an internal lamp (Tungstene or quartz). Flat-field corrections and wavelength calibrations were performed at Montpellier using the MIDAS package.

We have selected G and K giants with far infrared excess from the paper of Zuckerman et al. (1995). All these stars are IRAS sources with significant fluxes in 12, 25 and 60 microns and with flux quality flags 3 or 2. The IRAS fluxes of our program stars and their 25 and 60 micron excess can be found in the papers of Zuckerman et al. (1995) and Plets et al. (1997). In all we obtained the spectra of 29 giants (Table 1) in the Li region. All the spectra have a signal to noise ratio about 100.


Table 1. G and K giants observed in the Li region at OHP and ESO.

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© European Southern Observatory (ESO) 1999

Online publication: February 23, 1999