2 Observations and data reduction

The observations were performed in May 1998 at the Complejo Astronómico el Leoncito (CASLEO) using the 2.15-m telescope equipped with a REOSC echelle spectrograph and a Tek-1024 CCD. A grating with 1200 lines mm^-1 was used as a cross disperser. A resolving power of 26000 was achieved. Two wavelength ranges were observed (3830-4570 Å; 4520-5230 Å).

The spectra were reduced using the context echelle of the MIDAS reduction package. A typical session of echelle reduction comprises the following steps: bias subtraction, spatial positioning of the spectral orders, flatfield correction (several master flatfield exposures were taken every night), background subtraction, order extraction and wavelength calibration. The wavelength calibration of the stellar spectra was done with thorium-argon comparison spectra. Polynomial calibrations of wavelength as a function of pixel number were calculated for every night. The lower sensitivity at the edges of the orders typical of echelle spectra (ripple effect) was corrected by using Procyon as standard star. A blaze function was derived for each order.

The reliability of the measured equivalent widths depends to a great extent on the accuracy of the continuum placement: an improper placement of the continuum level will lead to systematic errors which can misrepresent the data. Most $\lambda$ Bootis stars are characterized as having broad and often shallow absorption line profiles. In this case, the continuum placement cannot be set by simply connecting the highest points in the observed spectrum, which would produce an underestimation of the equivalent widths. We solved this problem by defining the "true'' continuum level as that of a synthetic spectrum of physical parameters ( $T_{\rm eff}$, $\log\,g$, [M/H], $v \sin i$) similar to those of the observed object. As a first approach, effective temperatures and surface gravities were derived using Moon & Dworetsky (1985). Rotational velocities were estimated using the method described in Sect. 3 where a pseudo-continuum was defined by connecting the highest points in the line profile: the small influence of the continuum level on the method used to calculate rotational velocities permits this approximation. Also, a value of $\rm [M/H] = -1.0$ was used for all the stars, which is justified by the results from our detailed abundance analysis. The normalized spectra were then derived by dividing the extracted spectra by this continuum level. Line identification was performed with the help of Moore et al. (1966).

To have an estimation of the measurements errors in equivalent widths, the standard star Procyon ($\alpha$ CMi, HR 2943) was observed and the spectra compared to the spectrum of the Atlas of Procyon (Griffin & Griffin 1979). It can be seen in Table 1 how the equivalent widths measured in the observed spectra are only slightly larger than those measured in the Atlas. We also compared the equivalent widths of spectral lines present in the overlapping region between spectral orders finding no systematic trend. The list of observed objects is given in Table 2.

 

 

Table 1: Comparison between the equivalent widths measured in the observed spectra of Procyon and in the Atlas (Griffin & Griffin 1979). The relative error is defined as (EW(observed) - EW(atlas))/EW(atlas).

Observing	Relative	Number
date	error	of lines
08/05/1998	$0.05 \pm 0.14$	12
09/05/1998	$0.06 \pm 0.08$	9
10/05/1998	$0.02 \pm 0.12$	11
11/05/1998	$0.04 \pm 0.15$	11
12/05/1998	$0.02 \pm 0.06$	20
13/05/1998	$0.07 \pm 0.11$	17

 

 

Table 2: Target list. Spectral types (excluding HD 184190 for which SIMBAD was used) and visual magnitudes are taken from Paunzen (2000) and SIMBAD, respectively. Surface gravities derived from HIPPARCOS parallaxes are labeled with ($\ast$). Adopted values (in boldface) are the average of Balmer lines and Moon & Dworetsky (1985) ( $T_{\rm eff}$), HIPPARCOS and Moon & Dworetsky (1985) ($\log\,g$) and the weighted mean of the different measurements ($v \sin i$). Steps of 50 ${\rm K}$  and 0.1 dex have been assumed.

Identification	Spectral.	V mag.	Region	$T_{\rm eff}$	$\log\,g$	$v \sin i$
	type		(Å)	This work	This work	This work
				/Other sources	/Other sources	/Other sources
HD 68758	A1IVp	6.52	3830-4570			$291 \pm 21$ (2)
			3830-4570	8100(H$_\gamma$),8187(H$_\delta$)		$299 \pm 23$ (3)
			3830-4570	8050(H$_\delta$)		$305 \pm 25$ (6)
			3830-4570	8066(H$_\delta$)		$297 \pm 41$ (3)
			4520-5230			285 (1)
				/8300(4)	/3.7($\ast$),3.65(4)
				8150	3.7	299
HD 75654	hF0mA5V	6.38	3830-4570	7256(H$_\gamma$),7214(H$_\delta$)		$45 \pm 4$ (16)
			4520-5230			$43 \pm 5$ (13)
				/7275(4),7200(10)	/3.85($\ast$),3.8(4),3.8(10)	/45(10)
				7250	3.8	44
HD 81290	kA5hF3mA5V	8.89	3830-4570	6775(H$_\gamma$),6862(H$_\delta$)		$53 \pm 6$ (10)
			3830-4570			$57 \pm 8$ (7)
			4520-5230	6800(H$_\beta$)		$56 \pm 8$ (16)
			4520-5230	6750(H$_\beta$)		$57 \pm 8$ (18)
				/6750(4),6760(6)	/3.5(4)
				6800	3.5	56
HD 83041	kA2hF2mA2V	8.80	3830-4570			$105 \pm 15$ (7)
			3830-4570			$106 \pm 17$ (4)
			3830-4570	6800(H$_\delta$)		$121 \pm 33$ (4)
			4520-5230	7050(H$_\beta$)		$77 \pm 10$ (9)
			4520-5230	6975(H$_\beta$)		$83 \pm 14$ (6)
			4520-5230	6843(H$_\beta$)		$78 \pm 10$ (6)
				/6850(4),6900(6)	/3.6(4),3.3(6)
				6900	3.6	95
HD 107233	kA1hF0mA1Va A1V	7.37	3830-4570	7000(H$_\gamma$),6900(H$_\delta$)		$112 \pm 11$ (24)
			3830-4570	6900(H$_\gamma$),6950(H$_\delta$)		$110 \pm 12$ (17)
				/7225(4),7244(5),7200(2)	/4.2($\ast$), 4.05(4), 4.1(2)
				7000	4.1	111
HD 109738	kA1hA9mA1V	8.29	3830-4570	7437(H$_\gamma$),7350(H$_\delta$)		$185 \pm 18$ (10)
			3830-4570	7425(H$_\delta$)		$164 \pm 5$ (3)
				7500(H$_\beta$)		$170 \pm 14$ (2)
				7500(H$_\beta$)		$167 \pm 12$ (6)
				/7575(4),7603(6)	/3.9(4),3.8(6)
				7450	3.9	166
111005	hF0mA3V	7.97	3830-4570	7250(H$_\gamma$),7330(H$_\delta$)		$140 \pm 15$ (12)
			3830-4570	7415(H$_\gamma$),7380(H$_\delta$)		$131 \pm 12$ (10)
			3830-4570	7525(H$_\gamma$),7375(H$_\delta$)		$136 \pm 12$ (8)
			4520-5230	7500(H$_\beta$)		$143 \pm 13$ (5)
			4520-5230	7500(H$_\beta$)		$142 \pm 11$ (6)
					/ 3.8($\ast$)
				7400	3.8	138
HD 142703	kA1hF0mA1Va	6.13	3830-4570	7172(H$_\gamma$),7000(H$_\delta$)		$120 \pm 13$ (16)
			4520-5230			$110 \pm 20$ (12)
				/7200(4), 7400(2),7294(6)	/4.1($\ast$),4.1(2),3.95(4)	/100(10),95(12)
				7100	4.0	117
HD 142994	A3Va	7.18	3830-4570	6900(H$_\gamma$),6962(H$_\delta$)		$202 \pm 14$ (10)
			3830-4570	7035(H$_\gamma$),6803(H$_\delta$)		$212 \pm 14$ (9)
			4520-5230			$204 \pm 10$ (9)
			4520-5230			$207 \pm 17$ (10)
				/7079(1),7244(2),7000(4)	/3.5(1,2,3),3.4(4)	/220(1),195(3)
				6950	3.4	206

 

Table 2: continued.

Identification	Spectral.	V mag.	Region	$T_{\rm eff}$	$\log\,g$	$v \sin i$
	type		(Å)	This work	This work	This work
				/Other sources	/Other sources	/Other sources
HD 156954	hF1mA5V	7.69	3830-4570	6775(H$_\gamma$),7112(H$_\delta$)		$47 \pm 7$ (20)
			3830-4570	7000(H$_\gamma$),		$53 \pm 9$ (21)
			4520-5230	6937(H$_\beta$)		$56 \pm 9$ (32)
				/7050(4),7079(6)	/4.2($\ast$),4.0(4)
				7000	4.1	51
HD 168740	hA7mA2V	6.13	3830-4570	7875(H$_\gamma$),7650(H$_\delta$)		$168 \pm 16$ (12)
			4520-5230	7575(H$_\beta$)		$158 \pm 14$ (10)
				/7650(4),7700(10)	/4.15($\ast$), 3.9(4,12)	/147 (10)
				7700	4.0	162
HD 184190	A8	9.74	4520-5230	7200(H$_\beta$)		$19 \pm 3$ (55)
				7250(4)	4.0(4)
				7250	4.0	19
HD 193281	hA3mA2Vb	6.30	3830-4570	8000(H$_\gamma$),8000(H$_\delta$)		$101 \pm 7$ (5)
			4520-5230			$103 \pm 9$ (7)
			4530-5230			$104 \pm 5$ (6)
				/8100(4), 8100(10), 8080(13)	/3.5(4),3.6(10),3.6(13)	/95(10), 83(13)
				8050 K	3.5	103
HD 204041	A1Vb	6.46	3830-4570	7857(H$_\gamma$),8041(H$_\delta$)		$68 \pm 5$ (8)
			3830-4570	7950(H$_\gamma$),8118(H$_\delta$)		$69 \pm 7$ (10)
			4520-5230	7950(H$_\delta$)		$70 \pm 5$ (7)
				/8100(4),8128(6),8100(7)	/4.0($\ast$),3.95(4),4.03(7)	/65(7),68(8),70(11)
				8000	4.0	69
HD 210111	kA2hA7mA2Vas		3830-4570			$57 \pm 6$ (10)
			3830-4570			$54 \pm 9$ (9)
			4520-5230	7415(H$_\beta$)		$60 \pm 11$ (8)
				/7762(2),7603(5),7450(4)	/3.9($\ast$),3.9(2),3.8(4),3.75(8)	/55(8),60(11)
				7450	3.8	57

References: (1) Paunzen et al. (1998a); (2) Iliev & Barzova (1995); (3) Bohlender et al. (1999); (4) Moon & Dworetsky (1985); (5) Paunzen (1997); (6) Paunzen et al. (1998b); (7) Stürenburg (1993); (8) Holweger & Rentzsch-Holm (1995); (9) North et al. (1994); (10) Paunzen et al. (1999a); (11) Gray & Corbally (1993); (12) Faraggiana & Bonifacio (1999); (13) Holweger et al. (1999).

2.1 Binarity among the observed stars

Five targets of our sample show a composite spectra and no attempt to derive their abundance pattern was done (Fig. 1). All of them are identified as members of binary systems:

• HD111786: Two different hypothesis have been formulated for this star: Holweger & Rentzsch-Holm (1995) recognized a variable narrow absorption in the core of the Ca II K line interpreted as sign of gas dynamic in an accretion disc whereas Faraggiana et al. (1997) proposed a double-line spectroscopic binary system in which the narrow features shown in the spectrum belong to a slow-rotating early F-type star;
• HD141851: Catalogued as visual binary (Faraggiana & Bonifacio 1999). The small separation of the pairs (0.1 $^{\prime\prime}$) makes that ground-based spectra will always be the combined spectrum;
• HD148638: This object is identified in HIPPARCOS as double system with the two components of similar magnitude and a maximum separation of 21.9 $^{\prime\prime}$;
• HD174005: Catalogued as spectroscopic binary (Paunzen 2000), the maximum separation between components is 37.9 $^{\prime\prime}$;
• HD177120: Catalogued as a visual multiple system (Abt 1985), the separation between the primary and secondary being of 8 $^{\prime\prime}$ (Faraggiana & Bonifacio 1999).

Figure 1: Observed stars with composite spectra.