Project VeSElkA: a search for the vertical stratification of element abundances in HD 157087

Abstract

The new spectropolarimetric spectra of HD157087 obtained recently with ESPaDOnS at CFHT are analysed to verify the nature of this object. The fundamental stellar parameters $T_{\rm eff}$ = 8882 K, $\log{g}$=3.57 have been obtained for HD157087 from the analysis of nine Balmer line profiles in two available spectra. Comparison of the results of our abundance analysis with the previously published data shows a variability of average abundance with time for some chemical species, while the abundance of other elements remains almost the same. The abundance analysis also reveals evidence of a significant abundance increase towards the deeper atmospheric layers for C, S, Ca, Sc, V, Cr, Mn, Co, Ni and Zr. Together with the found enhanced abundance of Ca and Sc this fact contradicts the classification of HD157087 as a marginal Am star. Analysis of the available measurements of radial velocity results in detection of long periodic and short periodic variations. The long periodic variation supports the idea that HD157087 is an astrometric binary system with a period higher than 6 years. The presence of short periodic variation of $V_{\rm r}$, as well as the detection of temporal variation of average abundance suggest that HD157087 may be a triple system, where a short periodic binary rotates around a third star. In this case, the short periodic binary may consist of slowly rotating Am and A (or Ap with weak magnetic field) stars that have similar effective temperature and surface gravity, but different abundance peculiarities.