scholarly journals Candidate LBV stars in galaxy NGC 7793 found via HST photometry + MUSE spectroscopy

2020 ◽  
Vol 493 (2) ◽  
pp. 2410-2428 ◽  
Author(s):  
Aida Wofford ◽  
Vanesa Ramírez ◽  
Janice C Lee ◽  
David A Thilker ◽  
Lorenza Della Bruna ◽  
...  

ABSTRACT Only about 19 Galactic and 25 extragalactic bonafide luminous blue variables (LBVs) are known to date. This incomplete census prevents our understanding of this crucial phase of massive star evolution which leads to the formation of heavy binary black holes via the classical channel. With large samples of LBVs one could better determine the duration and maximum stellar luminosity which characterize this phase. We search for candidate LBVs (cLBVs) in a new galaxy, NGC 7793. For this purpose, we combine high spatial resolution images from two Hubble Space Telescope (HST) programs with optical spectroscopy from the Multi Unit Spectroscopic Explorer (MUSE). By combining PSF-fitting photometry measured on F547M, F657N, and F814W images, with restrictions on point-like appearance (at HST resolution) and H α luminosity, we find 100 potential cLBVs, 36 of which fall in the MUSE fields. Five of the latter 36 sources are promising cLBVs which have MV ≤ −7 and a combination of: H α with a P-Cygni profile; no [O i]$\, \lambda 6300$ emission; weak or no [O iii]$\, \lambda 5007$ emission; large [N ii]/H α relative to H ii regions; and [S ii]$\, \lambda 6716$/[S ii]$\, \lambda 6731\sim 1$. It is not clear if these five cLBVs are isolated from O-type stars, which would favour the binary formation scenario of LBVs. Our study, which approximately covers one fourth of the optical disc of NGC 7793, demonstrates how by combining the above HST surveys with multi-object spectroscopy from 8-m class telescopes, one can efficiently find large samples of cLBVs in nearby galaxies.

2003 ◽  
Vol 212 ◽  
pp. 38-46
Author(s):  
Roberta M. Humphreys

Current observations of the S Dor/LBVs and candidates and the implications for their important role in massive star evolution are reviewed. Recent observations of the cool hypergiants are altering our ideas about their evolutionary state, their atmospheres and winds, and the possible mechanisms for their asymmetric high mass loss episodes which may involve surface activity and magnetic fields. Recent results for IRC+10420, ρ Cas and VY CMa are highlighted. S Dor/LBVs in eruption, and the cool hypergiants in their high mass loss phases with their optically thick winds are not what their apparent spectra and temperatures imply; they are then ‘impostors’ on the H-R diagram. The importance of the very most massive stars, like η Carinae and the ‘supernovae impostors’ are also discussed.


1984 ◽  
Vol 105 ◽  
pp. 279-297 ◽  
Author(s):  
Roberta M. Humphreys

In this review I will primarily be discussing the observational data relevant to understanding the process of stellar evolution in galaxies of different types. This discussion will focus on the stellar content of the nearer galaxies; those galaxies in which the brightest individual stars are resolved and can be observed.


2014 ◽  
Vol 9 (S307) ◽  
pp. 92-93
Author(s):  
N. Britavskiy ◽  
A. Z. Bonanos ◽  
A. Mehner

AbstractWe present the first systematic survey of dusty massive stars (RSGs, LBVs, sgB[e]) in nearby galaxies, with the goal of understanding their importance in massive star evolution. Using the fact that these stars are bright in mid-infrared colors due to dust, we provide a technique for selecting and identifying dusty evolved stars based on the results of Bonanos et al. (2009, 2010), Britavskiy et al. (2014), and archival Spitzer/IRAC photometry. We present the results of our spectroscopic follow-up of luminous infrared sources in the Local Group dwarf irregular galaxies: Pegasus, Phoenix, Sextans A and WLM. The survey aims to complete the census of dusty massive stars in the Local Group.


2019 ◽  
Vol 491 (4) ◽  
pp. 6000-6019 ◽  
Author(s):  
Ning-Chen Sun ◽  
Jusytn R Maund ◽  
Ryosuke Hirai ◽  
Paul A Crowther ◽  
Philipp Podsiadlowski

ABSTRACT Type Ibn supernovae (SNe Ibn) are intriguing stellar explosions whose spectra exhibit narrow helium lines with little hydrogen. They trace the presence of circumstellar material (CSM) formed via pre-SN eruptions of their stripped-envelope progenitors. Early work has generally assumed that SNe Ibn come from massive Wolf–Rayet (WR) stars via single-star evolution. In this paper, we report ultraviolet (UV) and optical observations of two nearby Type Ibn SNe 2006jc and 2015G conducted with the Hubble Space Telescope (HST) at late times. A point source is detected at the position of SN 2006jc, and we confirm the conclusion of Maund et al. that it is the progenitor’s binary companion. Its position on the Hertzsprung–Russell (HR) diagram corresponds to a star that has evolved off the main sequence (MS); further analysis implies a low initial mass for the companion star (M2 ≤ 12.3$^{+2.3}_{-1.5}$ M⊙) and a secondary-to-primary initial mass ratio very close to unity (q = M2/M1 ∼ 1); the SN progenitor’s hydrogen envelope had been stripped through binary interaction. We do not detect the binary companion of SN 2015G. For both SNe, the surrounding stellar populations have relatively old ages and argue against any massive WR stars as their progenitors. These results suggest that SNe Ibn may have lower mass origins in interacting binaries. As a result, they also provide evidence that the giant eruptions commonly seen in massive luminous blue variables (LBVs) can also occur in much lower mass, stripped-envelope stars just before core collapse.


1999 ◽  
Vol 193 ◽  
pp. 73-74
Author(s):  
Nicole L. King ◽  
René A.M. Walterbos ◽  
Jay S. Gallagher

We have identified five new candidate LBVs in the NE half of M 31 and provide age limits for these objects through the color-magnitude diagrams of their potential parent OB associations. We note that three of the five candidates are not in OB associations nor are they in prominent H II regions.


2003 ◽  
Vol 212 ◽  
pp. 316-324 ◽  
Author(s):  
Philip Massey

In this paper, I discuss the observational quantities that are useful for judging the successes and failures of current massive star evolutionary theory. The galaxies of the Local Group can serve as important laboratories for providing these diagnostics, as their metallicities vary by a factor of ten. We find that the evolutionary tracks do a good job of matching the distribution of stars in the H-R diagram during the main-sequence phase. However, none of the models produce RSGs that are as cool and as bright as what is observed. The relative number of WC and WN stars is a strong function of metallicity, and the Padova and Geneva ‘normal mass-loss’ models do a reasonably good job of matching the observations at low metallicities, but predict too few WCs at higher metallicity. The ‘enhanced’ mass-loss models of the Geneva group do not match the observations at all. New data is providing excellent statistics on the number of RSGs in these nearby galaxies, and the number ratio of RSGs to WRs is also an extremely sensitive function of metallicity. None of the models reproduce the trend of the RSG/WR ratio with metallicity.


1998 ◽  
Vol 11 (1) ◽  
pp. 381-381
Author(s):  
A.V. Dorodnitsyn

We have considered a stationary outflowing envelope accelerated by the radiative force in arbitrary optical depth case. Introduced approximations provide satisfactory description of the behavior of the matter flux with partially separated radiation at arbitrary optical depths. The obtained systemof differential equations provides a continuous transition of the solution between optically thin and optically thick regions. We analytically derivedapproximate representation of the solution at the vicinity of the sonic point. Using this representation we numerically integrate the system of equations from the critical point to the infinity. Matching the boundary conditions we obtain solutions describing the problem system of differential equations. The theoretical approach advanced in this work could be useful for self-consistent simulations of massive star evolution with mass loss.


2013 ◽  
Vol 63 ◽  
pp. 373-383 ◽  
Author(s):  
G. Meynet ◽  
P. Eggenberger ◽  
S. Ekström ◽  
C. Georgy ◽  
J. Groh ◽  
...  

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