A refined analysis of the remarkable Bp star HR 6000
Hubrig, S.; Castelli, F.
Italy, Chile
Abstract
Aims:UVES spectra of the very young (∼ 107 years) peculiar B-type star HR 6000 were analyzed in the near-UV and visual spectral regions (3050-9460 Å) with the aim of extending to other spectral ranges the study made previously in the UV using IUE spectra.
Methods: Stellar parameters T_eff = 12 850 K, log g = 4.10, and ξ=0 km s-1, as determined from Hβ, Hγ, Hδ Balmer profiles and from the Fe I, Fe II ionization equilibrium, were used to compute an individual abundances ATLAS12 model. We identified spectral peculiarities and obtained final stellar abundances by comparing observed and computed equivalent widths and line profiles.
Results: The adopted model fails to reproduce the (b-y) and c color indices. The spectral analysis revealed: the presence of emission lines for Mn II, Cr II, and Fe II; isotopic anomalies for Hg, Ca; the presence of interstellar lines of Na I at λλ 3302.3, 3302.9, 5890, 5896 Å, and of K I at 7665, 7699 Å; the presence of a huge quantity of unidentified lines, which we presume to be mostly due to Fe II transitions owing to the large Fe overabundance amounting to [+0.7]. The main chemical peculiarities are an extreme overabundance of Xe, followed by those of Hg, P, Y, Mn, Fe, Be, and Ti. The most underabundant element is Si, followed by C, N, Al, S, Mg, V, Sr, Co, Cl, Sc, and Ni. The silicon underabundance [ -2.9] is the lowest value for Si ever observed in any HgMn star. The observed lines of He I cannot be reproduced by a single value of the He abundance, but they require values ranging from [ -0.8] to [ -1.6] . Furthermore, when the observed and computed wings of He I lines are fitted, the observed line cores are much weaker than the computed ones. From the present analysis we infer the presence of vertical abundance stratification for He, Mn, and possibly also Fe and P.