tokens: giants, as can be seen in Fig. A1 (d). These stars are all flagged with suspect broad lines by the ASPCAP pipeline. 5.4 Carbon rich stars Carbon rich stars (discussed in Section 3.4 ) are also detected as outliers. In Fig. A1 (e), we can see the strong CN compared to OH lines for a few carbon enriched stars. The weirdness score increases with the strength of the CN features. 5.5 Young stellar objects Stars in this group show both H-Br emission lines as well as regular metallic absorption lines. They are mostly young stars included in the INfrared Survey of Young Nebulous Clusters (IN-SYNC, Cottaar et al. 2014 ). We detect stars with both broad and narrow emission, and with absorption that can be broad or narrow as well as double lined (SB2s). SIMBAD classification for stars in this group include ‘Variable star of Orion type’, ‘T Tau-type Star’, ‘Pre-main sequence Star’, and ‘Young stellar object’. 5.6 M dwarfs M dwarf stars are also detected as outliers. This is due to the small number of M dwarf stars in the APOGEE sample. Example spectra are in Fig. A1(g). 5.7 Other outliers Some of the objects detected as outliers did not fall into any of the above classes. These include a brown dwarf, a Wolf–Rayet star, a few AGB stars including an OH-IR star, and known variable stars, as well as three red supergiants observed in the massive stars ancillary program. Also detected as outliers are special non-stellar targets, such as the centre of M32, a few M31 globular clusters, and three planetary nebulae. Two outliers show double peaked H-Br emission lines, as well as absorption lines typical to the APOGEE data set. Both of these objects show RV modulations, suggesting they are multiple star systems. For the first, 2M04052624+5304494, the RV modulation of the absorption lines (determined from APOGEE visit spectra) could be modelled with a period of P = 11.152 ± 0.072 d, and amplitude of K = 78 ± 15 km s −1 . The emission lines in the APOGEE spectra show smaller RV modulation, if any. For the second, 2M06415063−0130177, the absorption lines RV changes by ∼160 km s −1 between two APOGEE visits. The visits are separated by 28 d. For the emission lines we could not get a good estimate on the RVs, as the emission line profiles change significantly between the visits. A CoRoT light-curve is available for this system, showing clear periodic modulation. A period of P = 29.04 d was derived for this light-curve by Affer et al. ( 2012 ). We note that this period does not agree with the RV modulation. For both of these systems, additional work is required to determine their nature. We also detect a group of objects with similar, very broad features. Most of these objects have SIMBAD classifications as contact binaries, mainly W Ursae Majoris. A few objects remain unexplained. We divide these objects into two groups. In the first group, we have objects with spectra that seems to have similar features to typical APOGEE red giants (by means of visual inspection). The
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