The `remarkable' M31 globular cluster 037-B327 revisited

Abstract

The M31 globular cluster candidate 037-B327 has long been known to be an extremely red, non-stellar object. The first published spectrum of this object is used to confirm that it is a globular cluster belonging to M31, with rather typical values of v_r = -338 +/- 12 km/s and [Fe/H]= -1.07 +/- 0.20 dex. Using the spectroscopic metallicity to predict the intrinsic colours, we derive a reddening value of E(B-V)=1.30 +/- 0.04 in good agreement with the value obtained using reddening-free parameters. The extinction-corrected magnitude of 037-B327 is V_0=12.73 (absolute magnitude M_V = -11.74), which makes it the most luminous globular cluster in M31. We examine van den Bergh's (1968) argument regarding the brightest and most-reddened globular cluster in in M31; we find that the brightest clusters are more heavily-reddened than average, but this can be explained by selection effects rather than a different R_V in M31.