* Astronomy

Members Login
Username 
 
Password 
    Remember Me  
Home -> Astronomy News -> Stars/galaxy News -> Luminous Blue Variables
Post Info TOPIC: Luminous Blue Variables
Blobrana


L

Posts: 131433
Date:
Luminous Blue Variables
Permalink  
 

Title: Massive star evolution: Luminous Blue Variables as unexpected Supernova progenitors
Authors: Jose H. Groh, Georges Meynet, Sylvia Ekström

Stars more massive than about 8 solar masses end their lives as a Supernova (SN), an event of fundamental importance Universe-wide. Theoretically, these stars have been expected to be either at the red supergiant, blue supergiant, or Wolf-Rayet stage before the explosion. We performed coupled stellar evolution and atmospheric modelling of stars with initial masses between 20 solar masses and 120 solar masses. We found that the 20 solar masses and 25 solar masses rotating models, before exploding as SN, have spectra that do not resemble any of the aforementioned classes of massive stars. Rather, they have remarkable similarities with rare, unstable massive stars known as Luminous Blue Variables (LBV). While observations show that some SNe seem to have had LBVs as progenitors, no theoretical model had yet predicted that a star could explode at this stage. Our models provide theoretical support for relatively low-luminosity LBVs exploding as SN in the framework of single stellar evolution. This is a significant shift in paradigm, meaning that a fraction of LBVs could be the end stage of massive star evolution, rather than a transitory evolutionary phase. We suggest that type IIb SN could have LBV as progenitors, and a prime example could be SN 2008ax.

Read more (119kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
Hen 3-1383
Permalink  
 

Title: Discovery of two new Galactic candidate luminous blue variables with WISE
Authors: V.V. Gvaramadze, A.Y. Kniazev, A.S. Miroshnichenko, L.N. Berdnikov, N. Langer, G.S. Stringfellow, H. Todt, W.-R. Hamann, E.K. Grebel, D. Buckley, L. Crause, S. Crawford, A. Gulbis, C. Hettlage, E. Hooper, T.-O. Husser, P. Kotze, N. Loaring, K.H. Nordsieck, D. O'Donoghue, T. Pickering, S. Potter, E. Romero Colmenero, P. Vaisanen, T. Williams, M. Wolf, D.E. Reichart, K.M. Ivarsen, J.B. Haislip, M.C. Nysewander, A.P. LaCluyze

We report the discovery of two new Galactic candidate luminous blue variable (cLBV) stars via detection of circular shells (typical of known confirmed and cLBVs) and follow-up spectroscopy of their central stars. The shells were detected at 22 um in the archival data of the Mid-Infrared All Sky Survey carried out with the Wide-field Infrared Survey Explorer (WISE). Follow-up optical spectroscopy of the central stars of the shells conducted with the renewed Southern African Large Telescope (SALT) showed that their spectra are very similar to those of the well-known LBVs P Cygni and AG Car, and the recently discovered cLBV MN112, which implies the LBV classification for these stars as well. The LBV classification of both stars is supported by detection of their significant photometric variability: one of them brightened in the R- and I-bands by 0.68±0.10 mag and 0.61±0.04 mag, respectively, during the last 13-18 years, while the second one (known as Hen 3-1383) varies its B,V,R,I and K_s brightnesses by \simeq 0.5-0.9 mag on time-scales from 10 days to decades. We also found significant changes in the spectrum of Hen 3-1383 on a timescale of \simeq 3 months, which provides additional support for the LBV classification of this star. Further spectrophotometric monitoring of both stars is required to firmly prove their LBV status. We discuss a connection between the location of massive stars in the field and their fast rotation, and suggest that the LBV activity of the newly discovered cLBVs might be directly related to their possible runaway status.

Read more (2439kb, PDF)



__________________
Blobrana


L

Posts: 131433
Date:
RE: Luminous Blue Variables
Permalink  
 

Title: The Diversity of Massive Star Outbursts I: Observations of SN 2009ip, UGC 2773 OT2009-1, and Their Progenitors
Authors: Ryan J. Foley, Edo Berger, Ori Fox, Emily M. Levesque, Peter J. Challis, Inese I. Ivans, James E. Rhoads, Alicia M. Soderberg

Despite both being outbursts of luminous blue variables (LBVs), SN 2009ip and UGC 2773 OT2009-1 have very different progenitors, spectra, circumstellar environments, and possibly physical mechanisms that generated the outbursts.
From pre-eruption HST images, we determine that SN 2009ip and UGC 2773 OT2009-1 have initial masses of >60 and >25 M_sun, respectively. Optical spectroscopy shows that at peak SN 2009ip had a 10,000 K photosphere and its spectrum was dominated by narrow H Balmer emission, similar to classical LBV giant outbursts, also known as "supernova impostors." The spectra of UGC 2773 OT2009-1, which also have narrow H alpha emission, are dominated by a forest of absorption lines, similar to an F-type supergiant. Blueshifted absorption lines corresponding to ejecta at a velocity of 2000 - 7000 km/s are present in later spectra of SN 2009ip -- an unprecedented observation for LBV outbursts, indicating that the event was the result of a supersonic explosion, rather than a subsonic outburst. The velocity of the absorption lines increases between two epochs, suggesting that there were two explosions in rapid succession. A rapid fading and rebrightening event concurrent with the onset of the high-velocity absorption lines is consistent with the double-explosion model. A near-infrared excess is present in the spectra and photometry of UGC 2773 OT2009-1 that is consistent with ~2100 K dust emission. We compare the properties of these two events and place them in the context of other known massive star outbursts such as eta Car, NGC 300 OT2008-1, and SN 2008S. This qualitative analysis suggests that massive star outbursts have many physical differences which can manifest as the different observables seen in these two interesting objects.

Read more (320kb, PDF)

__________________
Blobrana


L

Posts: 131433
Date:
Permalink  
 

Title: Luminous Blue Variables as the progenitors of supernovae with quasi-periodic radio modulations
Authors: Rubina Kotak (ESO), Jorick S. Vink (Keele University)

The interaction between supernova ejecta and circumstellar matter, arising from previous episodes of mass loss, provides us with a means with which to constrain the progenitors of supernovae. Radio observations of a number of supernovae show quasi-periodic deviations from a strict power-law decline at late times. Although several possibilities have been put forward to explain these modulations, no single explanation has proven to be entirely satisfactory. Here we suggest that Luminous Blue Variables undergoing S-Doradus type variations give rise to enhanced phases of mass loss which are imprinted on the immediate environment of the exploding star as a series of density enhancements. The variations in mass loss arise from changes in the ionisation balance of Fe, the dominant ion that drives the wind. With this idea, we find that both the recurrence timescale of the variability, as well as the amplitude of the modulations are in line with the observations. Our scenario thus provides a natural, single-star explanation for the observed behaviour that is, in fact, expected on theoretical grounds.

Read more (22kb, PDF)

__________________
Page 1 of 1  sorted by
Quick Reply

Please log in to post quick replies.
Home -> Astronomy News -> Stars/galaxy News -> Luminous Blue Variables


Create your own FREE Forum
Report Abuse 		Powered by ActiveBoard