New luminous blue variable candidates in NGC 4736

Abstract

ABSTRACT We have found three new luminous blue variable (LBV) candidates in the star-forming galaxy NGC 4736. 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 NGC 4736_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. NGC 4736_2 (M$v$ < −8.6 mag) shows P Cyg profiles and its spectrum has changed from 2015 to 2018. The brightness variability of NGC 4736_2 is ΔV ≈ 0.5 mag and ΔB ≈ 0.4 mag. In NGC 4736_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.