2 Observations and data reduction

The observational material for this work was obtained during July 6 - July 12, 1999 with the 1.93 m telescope of the Haute-Provence Observatory (OHP), which is equipped with the high resolution (42000) echelle spectrograph ELODIE. Details about the performance and characteristics of the instrument have been thoroughly described by Baranne et al. (1996). We have used one spectrum of HD 172324 taken on June 1995 with the Sandiford echelle spectrograph at 2.1 m telescope of McDonald Observatory. This instrument giving a resolution of 50000 has been described in McCarthy et al. (1993). One spectrum of HD 172481 was obtained with the 2.7 m 2d coudé echelle spectrograph described in Tull et al. (1995). These spectra were reduced using spectroscopic data reduction tasks available in the IRAF package.

2.1 The sample

Table 1 contains the list of stars studied in this work, their spectral types, magnitudes, galactic positions and, when available, the IRAS infrared fluxes.

 

 

Table 1: Basic data and IRAS fluxes of sample stars

Star	Sp.T.	V	l	b	IRAS	12$\mu$	25$\mu$	60$\mu$	100$\mu$
		(mag)	$(^{\rm o})$	$(^{\rm o})$		(Jy)	(Jy)	(Jy)	(Jy)
HD 725	F5Ib-II	7.08	117.56	-5.19	00091+5659	.36	.25	.40	14.43
HD 9167	F1II	8.19	127.73	-0.97	01285+6115	.47	.25	.40	8.14
HD 158616	F8	9.69	13.23	+12.17	17279-1119	3.52	2.90	1.60	1.98
HD 172324	B9Ib	8.16	66.18	+18.58
HD 172481	F2Ia0	9.09	6.72	-10.37	18384-2800	5.41	5.22	.59	1.85
HD 173638	F2Ib-II	5.73	23.38	-3.56	18439-1010	1.41	.39	.67	55.03
HD 218753	A5III	5.69	110.28	-1.02
HD 331319	F3Ib	9.50	67.16	+2.73	19475+3119	.54	37.99	55.83	14.76
HDE 341617	A5	9.40	50.67	+19.79	18062+2410	3.98	19.62	2.90	1.00

2.2 Spectroscopic reductions

All spectra were bias-subtracted and flat-field corrected using standard OHP procedures described by Baranne et al. (1996). The spectra were wavelength calibrated with Th-Ar hollow cathode lamp spectra taken after each stellar exposure. More than one exposure was taken and spectra were combined to attain S/N of at least 50. The ELODIE spectrograph gives a resolution of 42000 and the wavelength coverage goes from 3906 to 6811 Å in 67 echelle orders with some overlaps in adjacent orders.

The equivalent widths were measured using the splot task of the IRAF package and their accuracy is generally better than 10% for spectra with S/N ratio larger than 50. We generally restricted ourselves to unblended weak features and avoided using lines stronger than 200 mÅ.