2011A&A...528A..37Y

In spite of large overabundances of XeII observed in numerous mercury-manganese (HgMn) stars, XeII oscillator strengths are only available for a very limited number of transitions. As a consequence, several unidentified lines in the spectra of HgMn stars could be due to XeII. In addition, some predicted XeII lines are redshifted by about 0.1Å from stellar unidentified lines, raising the question about the wavelength accuracy of the XeII line data available in the literature. For these reasons we investigated the XeII lines lying in the 3900-4521Å, 4769-7542Å, and 7660-8000Å spectral ranges of four well-studied HgMn stars. We compared the XeII wavelengths listed in the NIST database with the position of the lines observed in the high-resolution UVES spectrum of the xenon-overabundant, slowly rotating HgMn star HR6000, and we modified them when needed. We derived astrophysical oscillator strengths for all the XeII observed lines and compared them with the literature values, when available. We checked the stellar atomic data derived from HR6000 by using them to compute synthetic spectra for three other xenon-overabundant, slowly rotating HgMn stars, HD71066, 46Aql, and HD175640. In this framework, we performed a complete abundance analysis of HD71066, while we relied on our previous works for the other stars. We find that all the lines with wavelengths related to the 6d and 7s energy levels have a corresponding unidentified spectral line, blueshifted by the same quantity of about 0.1Å in all the four stars, so that we identified these lines as coming from XeII and modified their NIST wavelength value according to the observed stellar value. We find that the XeII stellar oscillator strengths may differ from one star to another from 0.0dex to 0.3dex. We adopted the average of the oscillator strengths derived from the four stars as final astrophysical oscillator strength.