HR 62: A New Evolved Chemically Peculiar Late-B Star?

Abstract

The spectrum of the evolved B8 III giant HR 62 exhibits weak He-lines and strong Mn and P lines. HR 62 therefore resembles both a HgMn star (CP3) and a He-weak PGa star (CP4). This study is a companion project to a high resolution survey of slowly rotationg late-B type stars aiming at finding new chemically peculiar stars. We have analysed the spectra of HR 62 (B8 III) and the dwarf comparison star HR 677 (B8 V) to derive their chemical abundances. Both stars have similar effective temperatures (12500 K) and projected rotational velocities ($\sim$25 km s$^{-1}$). The medium resolution ($R$ $\sim$14000) spectra covering the wavelength range of 4380-7350 Å of HR 62 and HR 677 have been obtained with the échelle spectrograph attached to the 40 cm telescope in Ankara University Kreiken Observatory (AUKR), Turkey. We have used SYNSPEC49/SYNPLOT written by I. Hubeny and T. Lanz to compute grids of synthetic spectra and derive elemental abundances by modeling selected unblended lines. We find that HR 62 exhibits underabundance of Si and remarkable overabundance of P and Mn with respect to the Sun. In contrast, HR 677 does not have abundances departing by more than $\pm$ 0.25 dex from solar abundances. A mass of 5.4 $M_\odot$ and an age of 90 Myr have been estimated for HR 62. We discuss the origin of the chemical peculiarities of HR 62 and its status as a CP star. The effective temperature of the star (12500 K) agrees well with those of HgMn (CP3) stars. Furthermore, the main sequence end of its evolutionary track also intersects the domain of He-weak CP4 stars. Hence these first results suggest that HR 62 may be a transition object between the CP4 to CP3 subgroup. However, a more detailed analysis of higher resolution spectra at shorter wavelengths (< 4380 Å) is necessary to clearly address the nature of this interesting object.