4.2.1. M31

A total of 13 B[e]SGs has been proposed in M31 to date. Twelve of them resulted from optical spectroscopic observations of LBV candidates that display the typical B[e]SG characteristics [99,139]. Infrared spectroscopic observations of a small LBV candidate sample revealed so far that three display CO band emission [136,137], making their classification as B[e]SG very likely, especially since two of the CO band emission objects were also found from optical spectroscopy to be a possible B[e]SG. However, a closer look at this total sample of 13 objects, including the available information from nearand mid-IR photometric observations, reveals that only four stars can be considered as confirmed B[e]SGs. Seven objects require further clarifications, and two appear to be misclassified (see Table 6).


**Table 7.** Confirmed and candidate B[e]SGs in M33. Misclassified objects are listed at the bottom of the table.

**Note:** IR photometry is taken from the 2MASS point source catalog (J, H, and K [104]) and from the WISE All-Sky Data Release (W1, W2, and W4 [105]). Colors resulting from uncertain photometric values are written in italic. a Has CO band absorption [138]. b Has CO band emission [138].
