2 Observations and data reduction

 

 

Table 1: Summary of our CCD spectroscopic observations. N indicates the total number of spectra obtained during a run.

Date	Telesc.	Wav. range	N	S/N	Disp.
					(Åmm-1)
July 1986	1.93 m	3875-4320	2	275	33
July 1987	1.93 m	3940-4400	20	280	33
Aug. 1987	1.93 m	4415-4915	1	200	33
Aug. 1989	1.93 m	3875-4915	1	300	130
Sep. 1989	1.93 m	8430-10400	1	25	260
	1.93 m	8440-11130	1	290	260
Aug. 1990	1.93 m	8450-8765	1	240	33
	1.93 m	6830-7130	1	150	33
	1.93 m	6840-9945	2	600	260
Aug. 1991	1.93 m	4250-4660	6	360	33
Oct. 1992	1.93 m	8450-8765	3	200	33
Oct. 1993	1.93 m	3940-4360	2	220	33
Aug. 1994	1.93 m	3930-4360	7	530	33
Aug. 1996	1.52 m	4065-4925	3	230	33
Feb. 1997	1.52 m	6500-6710	4	150	8
July 1997	1.52 m	4100-4960	3	280	33
Sep. 1998	1.52 m	4455-4885	3	400	16
Nov. 1998	1.52 m	4435-4560	15	100	5
July 1999	1.52 m	4060-4930	3	300	33
Aug. 1999	1.52 m	4060-4930	4	300	33
Sep. 2000	1.52 m	4455-4905	11	300	16

An extensive spectroscopic survey of HD108 was conducted from 1986 to 2000 with the Carelec and the Aurélie spectrographs, fed respectively by the 1.93m and 1.52m telescopes of the Observatoire de Haute-Provence. For Carelec, the detector used was a thin back-illuminated RCA CCD with 323$\times$512 pixels of 30 $\mu$m². For Aurélie, it was a TH7832 linear array with a pixel size of 13 $\mu$m² until 1999. In 2000, this detector was replaced by a 2048$\times$1024 CCD EEV 42-20#3, whose pixel size is 13.5 $\mu$m squared. The exact wavelength ranges and mean S/N are given in Table 1, together with the dispersion. All the data were reduced in the standard way using the IHAP and MIDAS softwares developed at ESO. The spectra were normalized by fitting splines through carefully chosen continuum windows. Some older photographic plates taken in 1971-72, 1974 and 1976 at OHP were also used to study the line profile variability.