Search for LBVs in the Local Volume galaxies: study of four stars in NGC 4449

TL;DR

This study identifies and characterizes four luminous stars in NGC 4449, confirming two as LBVs and suggesting the others as LBV candidates or B[e]-supergiants, expanding knowledge of massive star evolution in external galaxies.

Contribution

First detailed spectral and photometric analysis of LBV candidates in NGC 4449, including modeling of stellar winds and variability, in galaxies outside the Local Group.

Findings

Two stars confirmed as LBVs based on spectral features and variability.

Estimated bolometric luminosities range from log(L/L_sun)=5.24 to 6.42.

Modeled mass loss rate for one LBV candidate as 5.2×10^{-3} M_sun/yr.

Abstract

We continue to search for LBV stars in galaxies outside the Local Group. In this work, we have investigated four luminous stars in NGC 4449. Multiple spectral observations carried out for J122810.94+440540.6, J122811.70+440550.9, and J122809.72+440514.8 revealed the emission features in their spectra that are characteristic of LBVs. Photometry showed noticeable brightness changes of J122809.72+440514.8 ($\Delta I=0.69\pm0.13^m$) and J122817.83+440630.8 ($\Delta R=2.15\pm0.13^m$), while the variability of J122810.94+440540.6 and J122811.70+440550.9 does not exceed $0.3^m$ regardless of the filter. We have obtained estimates of the interstellar reddening, photosphere temperatures, and bolometric luminosities $\log(\text{L}_\text{Bol}/\text{L}_{\odot}) \approx 5.24-6.42$. Using the CMFGEN code, we have modelled the spectrum of the cold state of J122809.72+440514.8 ($T_{\text{eff}}=9300\,$K) and have obtained possible value of the mass loss rate $\dot{M} = 5.2\times10^{-3}\,M_{\odot}\,yr^{-1}$. Based on the observational properties, J122809.72+440514.8 and J122817.83+440630.8 were classified as LBVs, while the other two stars were classified as LBV candidates or B[e]-supergiants candidates