Probing the ejecta of evolved massive stars in transition

Oksala, M. E.; Kraus, M.; Cidale, L. S.; Muratore, M. F.; Fernandes, M. Borges

doi:10.1051/0004-6361/201321568

Cited by 70 publications

(166 citation statements)

References 49 publications

(112 reference statements)

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“…Near-infrared spectra of the star display pronounced, apparently stable molecular emission in both 12 CO and 13 CO (McGregor et al 1988b;Liermann et al 2010;Oksala et al 2013). The amount of identified 13 CO implies that the surface of LHA 120-S 73 was strongly enriched in 13 C at the time the material was released.…”

Section: Starmentioning

confidence: 99%

“…LHA 120-S 73 is hence the fourth object with clear signatures of TiO-band emission. Interestingly, all stars with TiO also display strong CO-band emission (see, e.g., Oksala et al 2013). This suggests that the conditions in the environments (in terms of column density and emitting area) of these objects easily enable the production of measurable amounts of molecular emission.…”

Section: Tio-band Emissionmentioning

confidence: 99%

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Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73

Kraus

Cidale

Arias

et al. 2016

A&A

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Context. B[e] supergiants are evolved massive stars, enshrouded in a dense wind and surrounded by a molecular and dusty disk. The mechanisms that drive phases of enhanced mass loss and mass ejections, responsible for the shaping of the circumstellar material of these objects, are still unclear. Aims. We aim to improve our knowledge on the structure and dynamics of the circumstellar disk of the Large Magellanic Cloud B[e] supergiant LHA 120-S 73. Methods. High-resolution optical and near-infrared spectroscopic data were obtained over a period of 16 and 7 yr, respectively. The spectra cover the diagnostic emission lines from [Ca ii] and [O i], as well as the CO bands. These features trace the disk at different distances from the star. We analyzed the kinematics of the individual emission regions by modeling their emission profiles. A lowresolution mid-infrared spectrum was obtained as well, which provides information on the composition of the dusty disk. Results. All diagnostic emission features display double-peaked line profiles, which we interpret as due to Keplerian rotation. We find that the profile of each forbidden line contains contributions from two spatially clearly distinct rings. In total, we find that LHA 120-S 73 is surrounded by at least four individual rings of material with alternating densities (or by a disk with strongly nonmonotonic radial density distribution). Moreover, we find that the molecular ring must have gaps or at least strong density inhomogeneities, or in other words, a clumpy structure. The optical spectra additionally display a broad emission feature at 6160-6180 Å, which we interpret as molecular emission from TiO. The mid-infrared spectrum displays features of oxygen-and carbon-rich grain species, which indicates a long-lived, stable dusty disk.We cannot confirm the previously reported high value for the stellar rotation velocity. He i λ 5876 is the only clearly detectable pure atmospheric absorption line in our data. Its line profile is strongly variable in both width and shape and resembles of those seen in non-radially pulsating stars. A proper determination of the real underlying stellar rotation velocity is hence not possible. Conclusions. The existence of multiple stable and clumpy rings of alternating density recalls ring structures around planets. Although there is currently insufficient observational evidence, it is tempting to propose a scenario with one (or more) minor bodies or planets revolving around LHA 120-S 73 and stabilizing the ring system, in analogy to the shepherd moons in planetary systems.

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Section: Starmentioning

confidence: 99%

Section: Tio-band Emissionmentioning

confidence: 99%

Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73

Kraus

Cidale

Arias

et al. 2016

A&A

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“…Infrared emission at 70 µm was also detected. Recently, this star was included in the K-band SINFONI (Spectrograph for INtegral Field Observations in the Near Infrared) survey presented by Oksala et al (2013), who reported the first detection of the CO band head emission at 2.3 µm. Assuming that CO molecules are located in a narrow ring around the star, they found from model fittings to the observed CO band head emission a CO column number density of N CO ∼ 2 × 10 21 cm −2 and a temperature of T CO ∼ 3 000 K. This temperature is much lower than the CO dissociation temperature (5 000 K) and suggests that the material may be located in a detached disc structure (Liermann et al 2010).…”

Section: Introductionmentioning

confidence: 99%

Resolving the clumpy circumstellar environment of the B[e] supergiant LHA 120-S 35

Torres

Cidale

Kraus

et al. 2018

A&A

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Context. B[e] supergiants are massive post-main-sequence stars, surrounded by a complex circumstellar environment where molecules and dust can survive. The shape in which the material is distributed around these objects and its dynamics as well as the mechanisms that give rise to these structures are not well understood. Aims. The aim of this work is to deepen our knowledge of the structure and kinematics of the circumstellar disc of the B[e] supergiant LHA 120-S 35. Methods. High-resolution optical spectra were obtained in three different years. Forbidden emission lines, that contribute to trace the disc at different distances from the star, are modelled in order to determine the kinematical properties of their line-forming regions, assuming Keplerian rotation. In addition, we used low-resolution near-infrared spectra to explore the variability of molecular emission. Results. LHA 120-S 35 displays an evident spectral variability in both optical and infrared regions. The P-Cygni line profiles of H i, as well as those of Fe ii and O i, suggest the presence of a strong bipolar clumped wind. We distinguish density enhancements in the P-Cygni absorption component of the first Balmer lines, which show variations in both velocity and strength. The P-Cygni profile emission component is double-peaked, indicating the presence of a rotating circumstellar disc surrounding the star. We also observe line-profile variations in the permitted and forbidden features of Fe ii and O i. In the infrared, we detect variations in the intensity of the H i emission lines as well as in the emission of the CO band-heads. Moreover, we find that the profiles of each [Ca ii] and [O i] emission lines contain contributions from spatially different (complete or partial) rings. Globally, we find evidence of detached multiring structures, revealing density variations along the disc. We identify an inner ring, with sharp edge, where [Ca ii] and [O i] lines share their forming region with the CO molecular bands. The outermost regions show a complex structure, outlined by fragmented clumps or partial-ring features of Ca ii and O i. Additionally, we observe variations in the profiles of the only visible absorption features, the He i lines. Conclusions. We suggest that LHA 120-S 35 has passed through the red-supergiant (RSG) phase and evolves back bluewards in the Hertzsprung-Russell diagram. In this scenario, the formation of the complex circumstellar structure could be the result of the windwind interactions of the post-RSG wind with the previously ejected material from the RSG. The accumulation of material in the circumstellar environment could be attributed to enhanced mass-loss, probably triggered by stellar pulsations. However, the presence of a binary companion can not be excluded. Finally, we find that LHA 120-S 35 is the third B[e] supergiant belonging to a young stellar cluster.

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“…In our study, the more luminous are also those with the least dust. Furthermore, no measurable CO bandhead emission was detected in those with luminosities below 10 5 L ⊙ (Oksala et al 2013), and the three B[e]sgs with the lower C 12 /C 13 ratios tend to have the lower luminosities. Since the lower luminosity B[e]sgs are also the dustiest with a higher fraction of their luminosities in the infrared, these would be the more likely candidates for post-RSG evolution.…”

Section: Concluding Remarks -Lbvs and B[e] Supergiantsmentioning

confidence: 98%

“…Oksala et al (2013) concluded that the C 12 /C 13 ratios measured from the CO bandheads in ten B[e]sgs in the Clouds and the Milky Way are consistent with a pre-RSG stage. Only three stars had the low ratios (5 -14) (Milam et al 2009) expected for oxygen-rich evolved RSGs and post-RSG or YSG stars.…”

Section: Concluding Remarks -Lbvs and B[e] Supergiantsmentioning

confidence: 99%

Luminous and Variable Stars in M31 and M33. V. The Upper HR Diagram

Humphreys

Davidson

Hahn

et al. 2017

ApJ

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We present HR Diagrams for the massive star populations in M31 and M33 including several different types of emission-line stars: the confirmed Luminous Blue Variables (LBVs), candidate LBVs, B[e] supergiants and the warm hypergiants. We estimate their apparent temperatures and luminosities for comparison with their respective massive star populations and to evaluate the possible relationships of these different classes of evolved, massive stars, and their evolutionary state. Several of the LBV candidates lie near the LBV/S Dor instability strip which supports their classification. Most of the B[e] supergiants, however, are less luminous than the LBVs. Many are very dusty with the infrared flux contributing one-third or more to their total flux. They are also relatively isolated from other luminous OB stars. Overall, their spatial distribution suggests a more evolved state. Some may be post-RSGs like the warm hypergiants, and there may be more than one path to becoming a B[e] star. There are sufficient differences in the spectra, luminosities, spatial distribution, and the presence or lack of dust between the LBVs and B[e] supergiants to conclude that one group does not evolve into the other.

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Probing the ejecta of evolved massive stars in transition

Cited by 70 publications

References 49 publications

Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73

Inhomogeneous molecular ring around the B[e] supergiant LHA 120-S 73

Resolving the clumpy circumstellar environment of the B[e] supergiant LHA 120-S 35

Luminous and Variable Stars in M31 and M33. V. The Upper HR Diagram

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