Antonio J. Delgado

Spectroscopy of Pre-Main-Sequence Candidates of Spectral Type AF in the Young Galactic Cluster IC 4996

We present the results of a spectroscopic analysis of the pre–main-sequence (PMS) candidates in IC 4996, proposed by Delgado et al. Spectral types and heliocentric radial velocities are calculated for 16 stars in the field observed by these authors, 13 of them located in the region of the color-magnitude diagram where their proposed PMS stars are located. The estimated heliocentric radial velocity of the cluster is centered around -12 ± 5 km s-1. From the radial velocity distribution, six stars are rejected as cluster members, one of them showing spectral features characteristic of an Am star. The remaining 10 stars are confirmed as cluster members: three B-type stars and seven PMS stars of spectral types A4–F0 (six stars) and early G (one star). One of the proposed PMS members clearly shows radial velocity and spectral type variations, as well as relatively broad Hα absorption. The G-type cluster member is a weak-lined T Tauri star with strong Li I λ6708 absorption [Wλ(Li I) 0.26 A]. These results strongly support the presence in the cluster of a populated sequence of PMS stars of AF spectral type.