Pre-Main Sequence Ap Star LkHα 324/B in LDN 988 Star Forming Region

Abstract

We present results of the investigation of the star LkHα 324/B, which belongs to the starforming dark cloud LDN 988. Based on high resolution spectroscopy, we determined its fundamental parameters as Teff=11,175±130 K, log(L*/L⊙)=1.87±0.07. According to these parameters, we found that LkHα 324/B is a pre-main sequence star with mass M≈3M⊙ and age t≈2.9 Myr. Recently, it underwent the phase of actively accreting the Herbig Ae/Be star, but accretion has now ceased in the LkHα 324/B system. This is consistent with the fact that the star is surrounded by a circumstellar disk with an inner cavity, as was determined from its spectral energy distribution. Our analysis revealed the peculiar abundance pattern of LkHα 324/B typical to those of magnetic Ap stars. It possesses mild underabundance of the light elements and excess up to ∼2–4 dex (in comparison to the Sun) of the iron peak and rare earth elements. We found no evidence for abrupt vertical abundances gradients in the lines forming the region of the LkHα 324/B atmosphere, in agreement with the results of the theoretical diffusion calculations in this temperature domain. From the intensification of the magnetically sensitive lines, we deduced that LkHα 324/B probably hosts a global magnetic field of ⟨B⟩≈3.5 kG strength. We suppose that the stabilizing role of this field favored the elements’ separation by diffusion before the star reached the main sequence.