The High Galactic Latitude Early-type Star Feige 89's Abundance Analysis

Feige89 is a B star in the high galactic latitudes.It is labeled as a hot subdwarf candidate in the SIMBAD database.The apparent magnitude of Feige89 is V=14.36,The data released by Gaia DR2 does not provide the star's trigonometric parallax.Recently,this star was reclassified as normal B2 ? star based on the LAMOST low-resolution spectrum.To further confirm the star's physical properties and investigate its possible origin,based on the low-resolution(R = 1800)spectrum of LAMOST and the high-resolution(R = 48000)spectrum observed by the SUBARU telescope in Japan,the atmospheric parameters and the abundance of some light elements of the special B-star Feige89 with high galactic latitude were measured,and analyzed the possible origin mechanism.Firstly,based on LAMOST's low-resolution spectrum(R=1800),using the NLTE stellar atmosphere model grid provided by TLUSTY,the theoretical spectrum was generated by the spectrum synthesis procedure SYNSPEC,The atmospheric parameters of Feige89 are obtained.Teff=19000K,log g=3.0,?sini =150km/s,log?(He)=11.8 ? 0.2.Then,the abundance of some light elements was measured by high-resolution spectroscopy based on the observation of SUBARU telescope.log?(N)=9.0 ?0.1,log?(O)=9.0 ?0.1,log?(Mg)=7.3 ?0.5,log?(Si)=8.6 ?0.25.Based on the atmospheric parameters and element abundance of Feige89,this paper firstly rules out the possibility that the star belongs to BHB stars,because the rotation speed of BHB stars is slow(tens of kilometers per second)and the metallicity is low([Fe/H]<-1.0)By comparison,it is found that though the effective temperature of Feige89 Teff = 19000 K is close to the lower temperature limit of the thermal subdwarf,it is surface gravity log g = 3.0 is significantly lower than the lower limit of the thermal subdwarf log g = 5.0,so it can be concluded that Feige89 can not be a thermal subdwarf.For the possibility that it is a post-AGB star,it is found by comparison that its effective temperature of 19000 k falls within the scope of the post-AGB star,that is,log g = 3.0 is slightly higher than that of post-AGB stars' typical value 2.5.Its rotation speed 150 km/s is much higher than the known post-AGB stars' maximum of 40 km/s;1.0Z? metallicity is slightly higher than-0.3,the metallicity upper limit of post-AGB stars;and Feige89's high abundance [Si/H] = 1.05 also supports the rich metal features.Besides,using the infrared star information provided by the SIMBAD website,it is not found that Feige89 has an obvious infrared overshooting phenomenon,which was also inconsistent with the bright infrared feature of post-AGB,thus ruling out the possibility that Feige89 is an aged post-AGB star.After ruling out the possibility that Feige89 belongs to a special old star,this paper compared with the element abundance of B star from the Population I given by the literature.We infer Feige89 is also a "normal" B star which means that Its quality should be around 10M?.This makes it difficult to understand that it came from the escape of the galactic disk,Because more mass means a shorter star life.So we infer that Feige89 is more likely to belong to the binary system of Population I that escaped from the galactic disk,Because the material transfer between the two stars can extend its life.