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We present optical and near-IR spectroscopy (600--1000 nm) of 8 faint(I$>$18) very red (R--I$>$2.2) objects discovered in a deep CCD survey of thePleiades (Zapatero-Osorio et al. 1996). We compare them with reliable clustermembers like PPl 15 and Teide 1, and with several field very late-type dwarfs(M4--M9.5), which were observed with similar instrumental configurations. Usingpseudocontinuum ratios we classify the new substellar candidates in a spectalsequence defined with reference to field stars of known spectral types. We alsoreclassify PPl 15 and Teide 1 in a self-consistent way. The likelihood ofmembership for the new candidates is assesed via the study of theirphotospheric features, Ha emission, radial velocity, and consistency of theirspectral types and I magnitudes with known cluster members. Four of the newsubstellar candidates are as late or later than PPl~15 (M6.5), but only one,Calar 3 (M8), clearly meets all our membership criteria. It is indeed an objectvery similar to the brown dwarf Teide 1. Calar 3, together with Teide 1, allowsone to compare the spectroscopic characteristics of Pleiades brown dwarfs withthose of old very cool dwarfs. The overall spectral properties are similar, butthere are slight differences in the NaI doublet (818.3 nm, 819.5 nm), VOmolecular band (740 nm), and some spectral ratios, which are probably relatedto lower surface gravity in the young Pleiades brown dwarfs than in fieldstars. Finally, we propose a way of improving future CCD-based brown dwarfsurveys by using narrow-band near-IR pseudocontinuum filters.

Spectroscopy of New Substellar Candidates in the Pleiades: Toward a Spectral Sequence for Young Brown Dwarfs