Spectroscopic survey of the galactic open cluster NGC 6871. I. New emission-line stars

We analyze spectra of 44 emission-line stars detected in a low-resolution optical spectroscopic survey of the galactic open cluster NGC 6871. The survey of 1217 stars is complete to V=14.9 and includes stars with V<16.5 between the zero-age main sequence and the 10(7) yr pre-main-sequence (PMS) isochrone. Of the 44 emission-line stars in this survey, 28 show obvious emission in Hα and 16 have weak Hα absorption (compared with Hγ). We use the reddening to separate foreground and background stars from the cluster members; the position in the HR diagram or the presence of forbidden emission lines ([N II] and [S II]) then yields the evolutionary status of the emission-line stars. A comparison of the Hα spectral index distribution in NGC 6871 with the distribution of young stars in the Taurus-Auriga molecular cloud indicates that the late-type PMS stars in our sample may be weak-line T Tauri stars. Many of these stars show [S II] ( 36%) and [N II] (45%) emission.