7 Results of the search for reference stars

7.1 Remarks on cross correlation

The cross correlation shape is highly dominated by the strong H$_\gamma$line which cannot be recorded, at high resolution, on a single order of an echelle spectrograph. Even if great care has been taken in connecting the orders and on the normalization procedures, a doubt remains on the reliability of H$_\gamma$profile, since the continum between the very broad wings has been placed by connecting them with a straight line.

The possibility that instrumental effects are not totally eliminated by the Flat Field correction cannot be discarded, the light path not being the same for the star and for the tungsten lamp. Consequently, it remains a possible source of some of the slight asymmetries of H$_\gamma$profiles and of the cross correlation shape which is dominated by the effect of this strong line profile.

7.2 Remarks on colour excess

There are 7 stars (HD 7916, HD 67725, HD 104039, HD 114570, HD 129791, HD 151527, HD 216931) for which E(b-y) is higher than 0.02. For all, but HD 67725, spectral peculiarities have been detected (see previous section); for HD 67725 we note that the logg value derived from the colours is abnormally low for an A0 V star and the corresponding computed H$_\gamma$ does not fit the observed one.

So all the reddened stars present some spectral peculiarity.

7.3 Remarks on hot Am detection

Among the CP stars the strong lines of Si II and Mn II lie out of our observed spectral range so preventing us to detect hot Ap stars.

We can detect the Am character through one of the classical criteria, the SrII4215/ScII4247 ratio higher than that expected for solar abundances. According to this criterium, the mild hot Am candidates are: HD 32996, HD 63584 and 213320.

We note also that for two suspected binaries, (see Table 3), HD 15646 and HD 113852, the ratio SrII 4215/ScII 4247 is much higher than that expected for solar abundances. A spectral classification based only on this ratio may wrongly assign to the Am class an object that is, in reality, a spectroscopic binary whose components do not differ much in luminosity. This may be the case for HD 60629; several metal lines show an abnormal core.

7.4 Reference stars

We conclude that from our original sample of 71 stars at least 21 (the 8 out of the 10 stars discussed in Sect. 5 (i.e. all, but HD 34968 and HD 213320) and the 13 stars discussed in Sect. 6.1) cannot be considered as reference stars, so that the masses and ages are computed for a reduced sample of 50 stars only.

However, doubts remain on other stars, due to possible binarity as indicated in Sect. 6.2; for several of the remaining stars the peculiarities are not strong enough to exclude any instrumental origin; however, a significant reddening remains difficult to accept for such nearby stars, large discrepancies between results obtained by other authors on $v\,\sin\,i$ (e.g. the discrepant results found for HD 4150) and more subtle discrepancies as those discussed in the Appendix, suggest that the number of binaries and/or peculiar objects may be higher than that selected in this section.

High rotation is expected to affect the photometric colours (Collins & Smith 1985) and the line intensities (Slettebak et al. 1980) of A-type stars. The weakening of Hgamma and Mg II 4481 lines due to rotation is computed in the latter paper; we could not reveal any correlation between the intensities of these lines and the $v\sin i$ values, the rotational effect being probably masked either by the unknown i value and/or by the fact that most of the non binary stars of our sample have $v\sin i$ lower than 200 km s^-1. Also a relation between the spread on the HR diagram (see next section) and the stellar vsini has been searched, but not detected. In particular no trend between logg and $v\,\sin\,i$ appears, nor are the oldest stars those with lower $v\sin i$.