Search for magnetic fields in HgMn stars by using relative strengths of multiplet 74 FeII lines

The anomalous strength of the Fe II X6147.7 line relative to Fe II lambda 6 149.2 in the stars with magnetic fields is used for detecting magnetic fiel ds in very slowly rotating HgMn stars. The diagnosis based on this pair of magnetically sensitive Fe lines is a simple and fast tool, but its applicat ion to more rapidly rotating HgMn stars is hampered by blending with Hg II lambda 6149.5. For spectra of sharp-lined HgMn stars (with v sin i < 4 km s (-1)) taken at high resolving power (R greater than or equal to 100 000) bo th lines, Fe II lambda 6149.25 and Hg II lambda 6149.48, become fully unble nded. The observed relative differences between the equivalent widths of th e two Fe II lines are compared with those derived from synthetic spectra co mputed by neglecting magnetic field effects. This comparison has shown that three HgMn stars, HD 175640, HD 178065 and HD 186122 are very likely to po ssess a magnetic field that could be larger than 2 kG.