New luminous blue variable candidates in NGC 4736

Abstract

© 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. We have found three new luminous blue variable (LBV) candidates in the star-forming galaxy NGC4736. They show typical well-known LBV spectra, broad and strong hydrogen lines, He I lines, many Fe II lines, and forbidden [Fe II ] and [Fe III ]. Using archival Hubble Space Telescope and ground-based telescope data, we have estimated the bolometric magnitudes of these objects from -8.4 to -11.5, temperatures, and reddening. Source NGC4736 1 (M v = -10.2 ± 0.1 mag) demonstrated variability between 2005 and 2018 as ΔV ≈ 1.1 mag and ΔB ≈ 0.82 mag; the object belongs to LBV stars. NGC4736 2 (M v < -8.6 mag) shows PCyg profiles and its spectrum has changed from 2015 to 2018. The brightness variability of NGC4736 2 is ΔV ≈ 0.5 mag and ΔB ≈ 0.4 mag. In NGC4736-3 (M v =-8.2 ± 0.2 mag), we found strong nebular lines, broad wings of hydrogen; the brightness variation is only ≈0.2 mag. Therefore, the last two objects may reside to LBV candidates.