4 Results

Our abundance results and the fundamental stellar parameters are listed in Table 3. The abundance patterns are shown in Fig. 1 for the stars we classified as Am and in Fig. 2 for the other objects. Comparisons with other studies are presented in Table 4. The solar abundances are those of Grevesse et al. (1996): Mg, 7.58; Ca, 6.36; Sc, 3.17; Cr, 5.67; Fe, 7.50; Ni, 6.25. The script [X] for any quantity X means log( $X)_{*}\,-\,$ log( $X)_{\hbox{$\odot$ }}$. The dispersion of the values given by different lines is indicated for Ca and Fe when more than two lines are used for the estimate. The v sin i values are deduced from the width of the gaussian fit used for the equivalent width measurements (Hui-Bon-Hoa & Alecian 1998).

 

 

Table 3: Abundance values for the programme stars. A colon (:) denote uncertain values (see text)

Name	HD	Remarks	v sin i	Teff	log g	Vt	[Mg/H]	[Ca/H]	[Sc/H]	[Cr/H]	[Fe/H]	[Ni/H]	Type
			(km s-1)	(K)		(km s-1)
28 And	2628	$\delta$ Scuti	21	7270	3.5	3.0	-0.08	-0.26	-0.41	-0.38	-0.40	-0.19	atyp
								($\pm$0.12)			($\pm$0.06)
9 Aur	32537	SBO	21	7030	4.1	1.5	-0.02	-0.03	-0.06	-0.19	-0.13	-0.35	nl
								($\pm$0.09)			($\pm$0.07)
14 Aur	33959	SBO; $\delta$ Scuti	26	7670	3.5	2.5	0.16	-0.03	-0.16	-0.19	-0.14	-0.09	nl
								($\pm$0.15)			($\pm$0.10)
6 Mon	43760	Var Vr?	13	7170	3.2	2.5	-0.14	-0.15	-0.03	-0.20	-0.05	0.17	nl
								($\pm$0.12)			($\pm$0.11)
RR Lyn A	44691A	A3Vm (1); SB2O	18	8240	4.0	3.0	0.52	-0.13	-1.38	0.43	0.66	0.76	Am
								($\pm$0.13)			($\pm$0.12)
RR Lyn B	44691B		16	7610	4.1	2.5:	-0.66:	0.07:	-0.52:	-0.20:	-0.19:	0.46:	Am
$\rho$ Pup	67523	kF3hF5mF5(Ib-II) (2); $\delta$ Scuti	17	6920	3.7	3.5	0.31	0.14	-0.17	0.38	0.36	0.40	Am
								($\pm$0.07)			($\pm$0.10)
$\tau$ UMa	78362	Am (1); SBO	13	7390	4.2	3.0	0.14	-0.42	-0.56	0.73	0.56	0.85	Am
								($\pm$0.10)			($\pm$0.07)
32 Aqr	209625	A5m (1); SB1O	10	7870	3.9	3.2	-0.02	-0.36	-1.15	0.20	0.26	0.62	Am
								($\pm$0.13)			($\pm$0.12)
o Peg	214994	Am (3); Magnetic field (4)	$\leq$10	9650	3.6	1.5	0.07	0.32	-0.35	0.19	0.42	1.13	Am
											($\pm$0.17)

• References: (1) Hoffleit (1982); (2) Gray & Garrison (1989); (3) Conti & Strom (1968); (4) Mathys & Lanz (1990).

 

 

Table 4: Comparisons with previous studies

HD 209625	Adelman et al. (1997)	This study
[Mg/H]	-0.51	-0.02
[Ca/H]	-0.47	-0.36
[Sc/H]	-1.16	-1.15
[Cr/H]	0.23	0.20
[Fe/H]	0.05	0.26
[Ni/H]	0.53	0.62
Teff	7700	7870
log g	3.65	3.9
Vt	4.5	3.2
HD 214994	Adelman (1988b)	This study
[Mg/H]	-0.07	0.07
[Ca/H]	0.03	0.32
[Sc/H]	-0.47	-0.35
[Cr/H]	0.16	0.19
[Fe/H]	0.18	0.42
[Ni/H]	0.44	1.13
Teff	9600	9650
log g	3.6	3.6
Vt	1.8	1.5

A star is classified as an Am star when its spectral type given by the CaII-K line is earlier than that derived from the metallic lines, the hydrogen line type being in-between (Roman et al. 1948). This reflects the following abundance anomalies: deficiency of Ca and/or overabundance of heavy elements (Conti 1970). The scandium deficiency is at least as typical in Am stars and is considered as a complementary criterion (see Conti 1970 and references therein). Thus, we classified our sample stars as Am stars when Ca and/or Sc are deficient and/or at least two heavy elements are overabundant, whereas normal A stars are those which exhibit normal abundances for Ca, Sc, and at least for two of the elements Cr, Fe, or Ni (abundances are considered as normal when within a factor 2 around the solar value, i.e. $\pm$0.3 dex). Stars that do not belong to the previous groups are denoted "atypical''. This classification is shown in the last column of Table 3 (resp. by the notation Am, nl, and atyp).

Figure 1: Abundance patterns for Am stars. Error bars ended by arrows denote very uncertain values (see text for details)

Figure 2: Same as Fig. 1 for non-Am stars

Figure 3: H-R diagram for the programme stars. Dots (and circles) denote Am stars, squares normal stars, and triangles atypical ones. Open symbols refer to objects studied in Hui-Bon-Hoa et al. (1997). Evolutionary tracks of Schaller et al. (1992) are shown with the corresponding stellar masses in parenthesis. The typical uncertainty on Teff is represented in the lower-left corner. The error bars on Mbol correspond to the standard error on the parallax

4.1 Am stars

Most Am stars show more or less the classical Am abundance pattern. However, some objects deviate obviously from this picture.

RR Lyn (HD 44691) is an SB2 Am system whose brighter component (labelled A) has a classical pattern but that of the companion is very different: Sc is much less deficient and Ni is the only overabundant iron peak element.

$\rho$ Pup (HD 67523) is the prototype of an eponymous group of evolved metallic-line stars (Gray & Garrison 1989). The iron peak elements are enhanced, Ca slightly overabundant and Sc mildly deficient, yielding a pattern of Conti's (1970) type c, i.e. star with only overabundances of heavy elements.

o Peg (HD 214992) is a hot Am star (Conti & Strom 1968) in which a magnetic field of about 2 kG, with a complex structure, has been detected (Mathys 1988; Mathys & Lanz 1990). Our results agree with those of previous studies (see Adelman et al. 1984; Adelman 1988a,b; Hill & Landstreet 1993) but, with almost same atmospheric parameters, our calcium abundance is clearly higher. This may be due to non-LTE effects or reflect an abundance stratification: the CaI lines of Adelman and coworkers have lower excitation potential as ours and may form differently; the results of Hill & Landstreet are obtained by the simultaneous adjustment of both neutral and singly ionized Ca lines and should be considered as values averaged over two ionization stages. With the equivalent widths of Conti & Strom (1968) and our method, we find the same trend of higher values with CaI lines of higher excitation potential (gf-values of Wiese et al. 1969). The strong Ni overabundance should be considered carefully because of the weakness of the lines.

4.2 Other stars

28 And (HD 2628) shows deficiencies for all the studied elements. Here, Sc, Cr, and Fe are obviously underabundant, by an amount comparable to that found in Vega (Adelman & Gulliver 1990) for the two last elements. A study including more elements would be interesting for a more thorough comparison. The remaining sample stars are almost normal. There is however a trend to slight underabundances for all elements. The values are very close to each other for Cr and Fe.