3 Analysis

 

 

Table 2: Equivalent widths in mÅfor the sample stars (HD numbers). The two sets of values for HD 78362 correspond the two spectra we took

$\lambda$ (Å)	Element	log gf	2628	32537	33959	43760	44691A	44691B	67523	78362 (1)	78362 (2)	209625	214994
5501.47	FeI	-2.95	48	-	44	-	61	-	146	118	120	58	4
5502.09	CrII	-1.92	31	28	35	47	-	22	88	99	100	54	20
5506.79	FeI	-2.80	67	72	58	90	92	-	172	133	134	79	-
5508.64	CrII	-1.98	20	21	27	35	54	23	75	78	81	43	15
5512.99	CaI	-0.29	-	-	38	50	15	57	-	-	-	16	-
5526.82	ScII	0.08	97	84	98	126	8	58	133	61	59	18	14
5528.42	MgI	-0.62	160	143	148	144	167	95	230	179	179	147	37
5543.20	FeI	-1.57	-	30	-	35	38	23	85	72	71	33	-
5543.95	FeI	-1.09	-	31	-	37	50	23	82	72	70	33	-
5554.90	FeI	-0.32	44	48	40	59	69	-	111	103	102	60	12
5560.22	FeI	-1.19	-	19	12	20	27	24	-	53	50	22	-
5569.63	FeI	-0.54	86	87	74	98	124	58	175	158	154	108	16
5576.10	FeI	-0.92	62	67	53	-	84	-	146	128	126	72	8
5578.73	NiI	-2.65	7	8	-	16	16	20	39	50	47	15	3
5581.98	CaI	-0.71	53	60	48	62	22	41	98	30	28	24	-
5586.77	FeI	-0.10	125	117	111	138	-	80	222	206	205	160	31
5588.77	CaI	0.21	128	121	117	-	78	-	189	99	94	86	11
5589.37	NiI	-1.14	5	-	3	14	9	25	31	43	43	16	2
5590.13	CaI	-0.71	50	60	43	56	23	44	94	29	29	22	-
5593.75	NiI	-0.83	10	12	9	22	-	15	48	64	62	26	2
5601.29	CaI	-0.35	62	77	55	73	38	-	128	70	66	37	-

We used the uvby $\beta$ photometry to estimate effective temperatures and gravities (Moon & Dworetsky 1985; Moon 1985; Napiwotzki et al. 1993). The uncertainties in the photometric measurements are the major sources of the errors: $\pm$200 K for T_eff and $\pm$0.14 for log g. A variation of 200 K in T_eff induces a change of 0.07 dex in the abundances, whereas a variation of 0.3 dex in log g (twice the error) induces a change of 0.1 dex for the singly ionized species, the neutrals being almost unchanged. The compilation of Hauck & Mermilliod (1980) provided the photometric data, which are dereddened using the code of Moon (1985). The fundamental parameters of the SB2 system RR Lyn are determined using the data of Popper (1971). The error in T_eff is $\pm$400 K, yielding uncertainties of 0.1 (singly ionized species) and 0.2 dex (neutrals) in the abundances.

The abundance analysis is carried out assuming LTE with the codes of M. Spite (1967, 1996 private communication). We used Kurucz' ATLAS9 code (Kurucz 1993) to build the model atmospheres, the overshooting option being switched off since models computed this way are generally in better agreement with observations (van't Veer & Mégessier 1996; Castelli et al. 1997). The treatment of convection (mixing length theory or Canuto & Mazzitelli 1991, 1992) and the microturbulent velocity of the model have negligible influence on the abundances derived with the present set of lines (Hui-Bon-Hoa 1998, 1999). For most sample stars, the microturbulent velocity ( V_t) minimizes the dispersion among the abundance values from the different lines of FeI. The value for o Peg (which could correspond to a pseudo-microturbulence due to the magnetic field, Adelman 1973) is chosen following recent abundance studies (Adelman et al. 1984; Adelman 1988a,b; Hill & Landstreet 1993). That of the fainter component of RR Lyn uses the relationship between V_t and T_eff of Coupry & Burkhart (1992).

The lines used for the abundance determination and their equivalent widths are listed in Table 2. For each component of RR Lyn, the dilution factors of Popper (1971) are applied (1.5 for the brighter star and 3.0 for the other). We used scaled solar gf-values (Col. 3 of Table 2), obtained by fitting the solar spectrum with the Kurucz solar model, the abundances of Grevesse et al. (1996) and a microturbulent velocity of ${\mathrm{1\,km\,s^{-1}}}$. The equivalent width measurements are carried out with the method of Cayrel et al. (1985) and the smallest values used are equal to the systematic error made on the equivalent widths, estimated using the expression of Cayrel (1988). The hyperfine structure of Sc is neglected.