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

Free access article

Issue		A&A Volume 375, Number 3, September 2001


Page(s)		963 - 976
Section		Formation, structure and evolution of stars
DOI		http://dx.doi.org/10.1051/0004-6361:20010894

A&A 375, 963-976 (2001)
DOI: 10.1051/0004-6361:20010894

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

S. Hubrig¹ and F. Castelli²

¹ European Southern Observatory, Casilla 19001, Santiago 19, Chile
e-mail: shubrig@eso.org
² CNR-Gruppo Nazionale Astronomia and Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, 34131 Trieste, Italy

(Received 2 February 2001 / Accepted 18 June 2001 )

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 field 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 FeII $\lambda 6147.7$ Åline relative to the equivalent width of the FeII $\lambda 6149.2$ Åline. The observed relative differences between the equivalent widths of these FeII lines are compared with those derived from synthetic spectra computed by neglecting magnetic field effects. To investigate the effect of oscillator strength uncertainties on the results, we computed equivalent widths by using both FeII $\log gf$ -values taken from Kurucz & Bell (1995) and FeII $\log gf$ -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 field. 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 fields 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 $v\sin i$ (15 km s^-1 and 18 km s^-1, respectively), so that the results for them are the most uncertain ones.

Key words: stars: abundances -- stars: atmospheres -- stars: chemically peculiar -- stars: magnetic fields

Offprint request: F. Castelli, castelli@ts.astro.it

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