Phosphorus Abundances of B-Type Stars in the Solar Neighborhood

Abstract: Phosphorus abundances of ~80 apparently bright sharp-lined early-to-late B-type stars on the upper main sequence are determined by applying the non-LTE analysis to the P II line at 6043.084 A, with an aim of getting information on the P abundance of the galactic gas (from which these young stars were formed) in comparison with the reference solar abundance (A_sun = 5.45). These sample stars turned out to be divided into two distinct groups with respect to their P abundances: (1) chemically peculiar late B-type stars of HgMn group show considerable overabundances of P (supersolar by ~0.5--1.5 dex), the extent of which progressively increases with T_eff. (2) In contrast, the P abundances of normal B-type stars are comparatively homogeneous, though a notable difference is observed between the LTE and non-LTE cases. Although their LTE abundances are near-solar, a slight gradual trend with T_eff is observed. However, after applying the negative non-LTE corrections (amounting ~0.1-0.5 dex), this T_eff-dependence is successfully removed, but the resulting non-LTE abundances (their mean is ~5.20) are appreciably underabundant relative to the Sun by ~0.2--0.3 dex. The cause of this systematic discrepancy (contradicting the galactic chemical evolution) is yet to be investigated.