Appendix

HD 3003 Short period binary; both components are of A-type, according to the BSC. An IR excess has been measured from IRAS data by Stencel & Backman (1992) and by Oudmaijer et al. (1992) who derived the [12]-[25] colour index = -1.15.

HD 4065 The spectra of the two components are A0 and A9, according to the BSC; the TD1 colours confirm that the secondary does not affect the UV colours. Recent speckle measures are given by Hartkopf et al. (1996) and by Horch et al. (1996).

HD 4150 The fit of the observed to the computed spectrum is such that this object is suspected to be a binary. Standard star for rotational velocity (Slettebak et al. 1975), but the $v\,\sin\,i=105$ km s^-1 value does not agree with that derived by (Levato 1972) $v\,\sin\,i =60$ km s^-1.

HD 7916 The peculiar spectrum is discussed in the text. The B component is classified A8p? and its peculiarities ascribed to contamination by the brighter companion by Corbally (1984) who gives, for the V magnitudes of the components, $V_{\mathrm{A}}=6.42$ and $V_{\mathrm{B}}=8.26$.

HD 15004 Known shell star with a variable RV of the shell (Levato et al. 1995). Evidence of accreting, circumstellar gas from IUE spectra is discussed by Grady et al. (1996).

HD 21473 We note that among stars of our sample this is the "normal" star with the lowest $T_{\mathrm{eff}}$ value. The star has been tested for photometric variability with negative result by Jorgensen et al. (1971) and confirmed by Hipparcos photometric data.

HD 34968 Slight variability of spectral lines noted by Gray & Garrison (1987) on low resolution spectra. Photometric variable V=4.67-4.72 (SIMBAD data base), while no photometric variability was detected by Jorgensen et al. (1971) and confirmed by Hipparcos photometric data. Old MK classifications give A0 V var.

The Mg II 4481 is slightly asymmetric on the two spectra at our disposal.

HD 38206 The abundance analysis has been made by Lemke (1989 and 1990); the abundances of N and S have been added by Rentzsch-Holm (1997).

HD 45557 (ESA 340) Large differences between the $T_{\mathrm{eff}}$ values derived from various indices have been found by Böhm-Vitense (1982), using visual and UV data. The other stars, in this paper, with similar $T_{\mathrm{eff}}$discrepancies are close binaries or shell stars.

HD 63112 This star has a low logg value for its A0 V spectral classification. A search for binarity by speckle interferometry gave negative results.

HD 67725 The core of H$_\gamma$ is too narrow for the 250 km s^-1 (in agreement with the $v\,\sin\,i=240$ km s^-1 by Dworetsky 1974) fitted by the Mg II 4481 profile. The logg = 3.30 derived from the MD procedure is the lowest of the sample and it is too low to fit the H$_\gamma$ profile. Slight differences of Mg II 4481 profiles are detected on the two observed spectra.

HD 69589 An IRAS colour excess at 12 ${\mu}$m has been derived by Patten & Willson (1991).

HD 71043 Possible variability of the RV and large rotational velocity are noted by Andersen & Nordström (1983).

HD 71155 Standard star for $v\,\sin\,i$ (Slettebak et al. 1975). The IR excess detected from IRAS at 25 ${\mu}$m is interpreted as due to a dust shell (Coté 1987). In the UV, the m₁₅₆₅ is quite high compared with that of other stars of similar $T_{\mathrm{eff}}$ and to the computed colours; the UV flux below 2500 Å agrees with $T_{\mathrm{eff}}=10000$ K, 250 K higher than that obtained from visual data. The four spectra taken by us show some peculiar line profiles.

HD 79108 An IR excess at 60 ${\mu}$m is derived from IRAS data (King 1994); the star is a $\lambda$ Boo candidate, according to Maitzen & Pavlovski (1989).

HD 84461 We did not detect variations on the 3 spectra taken by us. The best fit with computations requires a lower $T_{\mathrm{eff}}$ (9500 K) than that derived from photometric colour indices.

HD 85504 The intriguing properties of this object are summarized by Cacciari (1985). An overabundance of He and C with respect to Sirius has been derived by Wallerstein et al. (1962) who formulate the hypothesis of a composite spectrum by a B8 and an A1 star.

Many metal lines are stronger in the observed, compared to the computed spectrum. We found many, but slight and difficult to prove, indications of binarity (e.g. the H$_\gamma$ profile does not fit well those computed with the photometrically derived parameters; an abnormally large strength of many metal lines; the not rotationally broadened Mg II 4481 profile; the UV flux below 2500 Å fits that computed with $T_{\mathrm{eff}}=10500$ K, while the m₂₇₄₀-V suggests $T_{\mathrm{eff}}=10000$ K).

The spectral peculiarities are studied by Adelman & Pintado (1997).

HD 87344 The abundance analysis of this narrow-line star has been made by Lemke (1989 and 1990) and by Rentzsch-Holm (1997). The other component of this visual system, HD 87330, has been recognized to be a SB2; it is identified as HD 87344(2) in the HM Catalog and its photometric values are not correct (see Text).

HD 92845 The TD1 colours are better fitted by undereddened colours.

HD 109573 Star of $\beta$ Pic type with a very strong disk luminosity, even higher than that of $\beta$ Pic itself; a recent discussion of this young object can be found in Mouillet et al. (1997). The spectrum is characterized by weak metal lines; in particular, the Mg II 4481 profile is weak and not rotationally broadened and the UV colours (Fig. 8a) do not fit those predicted with the atmospheric parameters given in Table 2. Moreover, the logg = 4.49 derived from $uvby\beta$ photometry is too high for an A0 dwarf and does not fit the observed H$_\gamma$ profile which better agrees with the logg = 4.30 derived from the parameters obtained from the Geneva undereddened colour indices. The Napiwotzki et al. (1993) correction of the gravity determined by the MD programs gives logg = 4.43, value that does not improve significantly the fit with the spectrum computed with the parameters derived from $uvby\beta$colours.

HD 111519 The cross correlation has a low and flat central part; the Mg II 4481 has a composite profile with a sharp and a broad component, signature of a double-lined spectroscopic binary; the metal lines present an important veiling effect.

HD 111786 Binary $\lambda$ Boo star discussed in the text and in Faraggiana et al. (1997). Among the stars of the present sample, this star has the lowest value of the cross correlation coefficient.

HD 114570 It has a very high colour excess, the H$_\gamma$ profile is peculiar; it core suggests a $v\,\sin\,i$ lower than that obtained from metal lines and the UV dereddened colours fit better a $T_{\mathrm{eff}}$ lower by 250 K than that derived from visual data.

HD 125473 This star is classified A0 III by Gray & Garrison (1987). It is a dusty system on the basis of IRAS data (Cheng et al. 1992). We did not detect differences between the 5 spectra at our disposal. This is the star for which the highest difference in $T_{\mathrm{eff}}$ between MD and Geneva calibrations has been found; the H$_\gamma$ profile is fitted by the spectrum computed with the MD parameters.

HD 129791 It is an X-ray source (Schmitt et al. 1993) difficult to explain since A0-type stars are not X-ray emitters. A relatively high dereddening is requested to reproduce the colours of a normal star. The lines are extremely broadened and their profile suggest a composite spectrum with different $v\,\sin\,i$ of the two components.

HD 139129 The abundance analysis has been made by Lemke (1989, 1990) who adopted $T_{\mathrm{eff}}=9900$ K and log g= 3.7 and derived non solar abundances for several elements. Further discussion on the metal abundances is in Rentzsch-Holm (1997). According to Jaschek et al. (1991), this star has an unexplained IR excess at 12 ${\mu}$m.

HD 151527 No meaningful M_V can be computed owing the high distorted colours from which large and discrepant colour excesses are derived (see Table 2). The peculiarity of the visual and UV colours and of the spectrum suggests that this object is more complex than a simple binary star. The UV TD1 colours are very distorted.

HD 152849 According to Richichi et al. (1997) discussion of this star, the companion has also a spectral type A and is only slightly later than the primary. Recent speckle measures are in Horch et al. (1996).

HD 188228 The $v\,\sin\,i$ value measured by Slettebak et al. (1975) ($v\,\sin\,i=80$ km s^-1) does not agree with that obtained by Levato (1972) ($v\,\sin\,i=140$ km s^-1). A variability is mentioned in old MK classifications.

The Mg II profile is not rotationally broadened; several metal lines have a flat core and the UV fits better $T_{\mathrm{eff}}=10500$ K.

HD 193571 It is a protoplanetary system candidate on the basis of the IR excess detected by IRAS (Cheng et al. 1992); no signatures of CS features have been observed by Holweger & Rentzsch-Holm (1995).

HD 213320 It belongs to the hot extension of the Am sequence according to Adelman & Nasson (1980), but with several abundance anomalies (Adelman et al. 1984); it is an SB according to Dworetsky (1974).

HD 225200 Ambiguous classifications are found in the literature: it is a binary A0 V + A: according to Levato et al. (1979) and B9 IVs + A2n according to AM, but A0 IV^-(shell) according to Gray & Garrison (1987).