Crowded field 3D spectroscopy of LBV candidates in M33

Abstract

We present integral field spectroscopy of the LBV candidate stars B416 and v532 in the local group galaxy M33. B416 is surrounded by an elongated ring-like nebula, which has a projected radius of 20x30 pc. From the datacube we create ionization and radial velocity maps of the nebula. The excitation of the gas decreases towards the outer part of the ring, while the inner part of the nebula is filled with a more excited gas. In the EW direction the ring is seen to expand with a maximum projected velocity amplitude of about 40 km/s. The eastern part approaches the observer. We estimate the nebula dynamical lifetime 8*10E5 years. It could be a residual MS bubble, which indicates a main-sequence or pre-LBV status of the star. We classify B416 as an "iron star" or B[e]-supergiant. In v532 an elongated nebula has been marginally detected. The total projected size of the nebula along the main axis is 30 pc, and the total radial velocity gradient is 44+/-11 km/s. v532 exhibits both strong photometric and spectral variability. At the time of our observations it was in an intermediate brightness state with a rich nitrogen spectrum. We classify v532 as an LBV, showing LBV <-> Ofpe/WN transitions. We stress the importance of integral field spectroscopy as the optimal technique for studying nebulae and the evolution of LBV-like stars in nearby galaxies.