Spectral Synthesis for Classical Ae Stars: Hα and Ca II

Abstract

Classical Ae (CAe) stars are main-sequence, A-type stars with Hα emission but no signature of dust; they are thought to be the cool extension of classical Be (CBe) stars to lower stellar masses. We investigate the use of Hα and the Ca ii IR triplet observed at low spectroscopic resolution ( R=1800 ) as diagnostics for the circumstellar disks of the CAe stars. Using a sample of 159 CAe stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey (Data Release 5), we find that circumstellar disk masses and star/disk viewing inclination angles can be reliably determined from low-resolution Hα profiles. The CAe disk mass distribution agrees well with the previous range found for late-type CBe stars, although there is an apparent increase in disk mass for the latest CAe spectral subtypes (A3 and A4), which we attribute to selection effects. Over the spectral range A2 through B6, the average disk-to-star mass ratio for CAe and CBe stars is consistent with log10(Mdisk/M*)=−9.1 . A minority of the CAe sample (∼16%) also show emission in the Ca ii IR triplet. The observed emission is well within the range predicted by the disk models, and there is statistical evidence that the Ca ii emitters have systematically larger Hα disk masses.