New results of magnetic field diagnosis in HgMn stars and normal late B-type stars

Abstract

We suggested in a previous paper that three HgMn stars, HD 175640, HD 178065, and HD 186122, may be suspected to possess a magnetic eld that could be larger than 2 kG. We report here new observations of these three stars, three more HgMn stars, and four normal late B-type stars. The search was carried out by measuring the equivalent width of the Fe II 6147:7 A line relative to the equivalent width of the Fe II 6149:2 A line. The observed relative dierences between the equivalent widths of these Fe II lines are compared with those derived from synthetic spectra computed by neglecting magnetic eld eects. To investigate the eect of oscillator strength uncertainties on the results, we computed equivalent widths by using both Fe II log gf-values taken from Kurucz & Bell (1995) and Fe II log gf-values taken from Raassen & Uylings (2000). The comparison of the computed and observed equivalent widths based on the Kurucz & Bell (1995) atomic data leads us to conclude that all the stars of our sample, except HD 175640, are very likely to possess a magnetic eld. On the other hand, the comparison of the computed and observed equivalent widths based on the Raassen & Uylings (2000) log gf-values suggests the possible presence of magnetic elds only in three stars, the HgMn star HD 16717 and the two normal B-type stars HD 179761 and HD 186568. The latter two are those in the sample with the largest v sini (15 km s 1 and 18 km s 1 , respectively), so that the results for them are the most uncertain ones.