6. Results and error estimates
The final abundances are presented in Table 5 for the blue stragglers and in Table 6 for the main sequence stars. For CMa in Table 7 we also give for comparison the results obtained by Sadakane & Ueta 1989and the more recent results of spectral synthesis by Hill & Landstreet (1993). In this study we did not aim to update the list of measured elemental abundances for CMa, which has been the subject of several investigations. Nevertheless, note that we are in very good agreement with other investigators.
Table 5. Final relative elemental abundances [El/H] for blue straggler stars.
Table 6. Final relative elemental abundances [El/H] for main sequence stars
It is quite likely that some of the abundances are influenced by NLTE effects. Some errors may also come 1) from uncertainties in the continuum level within the echelle orders (especially for rapidly rotating stars), 2) from oscillator strengths (in particular from those that can not be checked using the solar spectrum), 3) from Stark broadening constants, which strongly affect abundances derived from the lines of ionized species (prevalent in the blue straggler spectra), but which are poorly known for the bulk of the lines. To this list we should also add the unavoidable errors introduced by temperature, gravity, microturbulence parameter and projected rotational velocity determination which are discussed below.
As an example, in Table 8 we give error estimates for the and abundances in the blue straggler HD 170054 based on the analysis of two selected lines: 4471 Å and 4481 Å . In each individual case presented in Table 8, the abundance correction should be regarded as the largest necessary to compensate for the visible differences between the observed and calculated profiles.
Table 8. Parameter variation and abundance corrections ()
Inspecting Table 8 and taking into account that the temperature and gravity values for our blue stragglers are probably more accurate than the extreme cases supposed for Table 8, one can conclude that the elemental abundances for the stars with narrow-lined spectra are reliable with an accuracy better than 0.15-0.20 dex. This is not the case for the main sequence stars with broadened and blended lines, where errors connected with the continuum placement are more pronounced than for the blue stragglers. We would be optimists if we could say that in this case abundances are known with an accuracy better than 0.2 dex.
© European Southern Observatory (ESO) 2000
Online publication: April 10, 2000