Spectral classification of Pleiades brown dwarf candidates

TL;DR

This study spectroscopically analyzed 10 objects previously identified as brown dwarf candidates in the Pleiades, concluding they are actually background dwarf stars rather than brown dwarfs.

Contribution

It provides a detailed spectral classification and membership analysis of brown dwarf candidates in the Pleiades using VLT spectroscopy.

Findings

All candidates are background dwarf stars, not brown dwarfs.

Spectroscopic and proper motion analysis confirmed non-membership.

Objects are late-K to mid-M-type dwarf stars.

Abstract

We report on the results of the spectroscopy of 10 objects previously classified as brown dwarf candidates via RIJHK colors by Eisenbeiss et al. (2009), who performed deep imaging observations on a 0.4 sq.deg. field at the edge of the Pleiades. We describe and judge on classification techniques in the region of M-type stars. To classify and characterise the objects, visual and near infrared spectra have been obtained with VLT FORS and ISAAC. The spectral classification was performed using the shape of the spectra as well as spectral indices that are sensitive to the spectral type and luminosity class of Mtype stars and late M-type brown dwarfs. Furthermore a spectrophotometric distance was calculated and compared the distance of the Pleiades to investigate the membership probability. As a second argument we analyzed the proper motion. The brown dwarf candidates were found not to be brown dwarfs, but late-K to mid-M-type dwarf stars. Based on the obtained distance and tabulated proper motions we conclude that all objects are background dwarf stars.