VLTI/AMBER spectro-interferometry of the late-type supergiants V766 Cen (=HR 5171 A),<i>σ</i>Oph, BM Sco, and HD 206859

Wittkowski, M.; Arroyo-Torres, B.; Marcaide, J. M.; Abellán, F. J.; Chiavassa, A.; Guirado, J. C.

doi:10.1051/0004-6361/201629349

Cited by 28 publications

(36 citation statements)

References 61 publications

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“…As an example, the contrast of this RHD H-band snapshot is 9%, after convolution to our spatial resolution and correction for the limb-darkening. This value is consistent with our observed value L1, page 3 of 7 shell (Wittkowski et al 2017a), and the companion at positions from C14 (epoch C) and our epochs EII and EIII. Also shown is a plausible Keplerian orbit for a fixed period of 1304 d and semi-major axis of 3 mas.…”

Section: Discussionsupporting

confidence: 92%

“…We used the averaged values and their standard deviations as final fit results as listed in Table 1. Our value of the Rosseland angular diameter Θ Ross of 4.1 ± 0.8 mas is consistent with the estimates of Θ UD = 3.4 ± 0.2 mas by C14 and Θ Ross = 3.9 ± 1.3 mas by Wittkowski et al (2017a).…”

Section: Discussionsupporting

confidence: 91%

“…Previous observations (C14, Wittkowski et al 2017a) indicated the presence of an extended molecular layer, also called MOLsphere (Tsuji 2000). We used a two-component model for the overall stellar disk, consisting of a PHOENIX model atmosphere (Hauschildt & Baron 1999) .1 ± 0.8 0.70 ± 0.14 9.2 ± 3.3 0.28 ± 0.14 from Wittkowski et al (2017a): mass 20 M , effective temperature 3900 K, surface gravity log g = −0.5, and solar metallicity.…”

Section: Discussionmentioning

confidence: 80%

“…We used a two-component model for the overall stellar disk, consisting of a PHOENIX model atmosphere (Hauschildt & Baron 1999) .1 ± 0.8 0.70 ± 0.14 9.2 ± 3.3 0.28 ± 0.14 from Wittkowski et al (2017a): mass 20 M , effective temperature 3900 K, surface gravity log g = −0.5, and solar metallicity. The fit was performed in the same way as in Wittkowski et al (2017a). We treated the flux fractions f Ross and f UD both as free parameters to allow for an additional over-resolved background component.…”

Section: Discussionmentioning

confidence: 99%

“…Chesneau et al (2014, in the following C14) found evidence that the primary component itself (HR 5171 A) has an eclipsing close companion, most likely in a contact or common-envelope phase. Based on VLTI-AMBER spectro-interferometry, Wittkowski et al (2017a) reported that V766 Cen is a high-luminosity (log L/L = 5.8 ± 0.4) source of effective temperature 4290 ± 760 K and radius 1490 ± 540 R , located in the HR diagram close to both the Hayashi and Eddington limits. With this location and radius, it is more likely a RSG before evolving to a YHG, and consistent with a 40 M track of current mass 27−36 M .…”

Section: Introductionmentioning

confidence: 99%

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Multi-epoch VLTI-PIONIER imaging of the supergiant V766 Cen

Wittkowski

Abellán

Arroyo-Torres

et al. 2017

A&A

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Context. The star V766 Cen (=HR 5171A) was originally classified as a yellow hypergiant but lately found to more likely be a 27−36 M red supergiant (RSG). Recent observations indicated a close eclipsing companion in the contact or common-envelope phase. Aims. Here, we aim at imaging observations of V766 Cen to confirm the presence of the close companion. Methods. We used near-infrared H-band aperture synthesis imaging at three epochs in 2014, 2016, and 2017, employing the PIONIER instrument at the Very Large Telescope Interferometer (VLTI). Results. The visibility data indicate a mean Rosseland angular diameter of 4.1 ± 0.8 mas, corresponding to a radius of 1575 ± 400 R . The data show an extended shell (MOLsphere) of about 2.5 times the Rosseland diameter, which contributes about 30% of the H-band flux. The reconstructed images at the 2014 epoch show a complex elongated structure within the photospheric disk with a contrast of about 10%. The second and third epochs show qualitatively and quantitatively different structures with a single very bright and narrow feature and high contrasts of 20−30%. This feature is located toward the south-western limb of the photospheric stellar disk. We estimate an angular size of the feature of 1.7 ± 0.3 mas, corresponding to a radius of 650 ± 150 R , and giving a radius ratio of 0.42 +0.35 −0.10 compared to the primary stellar disk. Conclusions. We interpret the images at the 2016 and 2017 epochs as showing the close companion, or a common envelope toward the companion, in front of the primary. At the 2014 epoch, the close companion is behind the primary and not visible. Instead, the structure and contrast at the 2014 epoch are typical of a single RSG harboring giant photospheric convection cells. The companion is most likely a cool giant or supergiant star with a mass of 5 +15 −3 M .

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Section: Discussionsupporting

confidence: 92%

Section: Discussionsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 80%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Multi-epoch VLTI-PIONIER imaging of the supergiant V766 Cen

Wittkowski

Abellán

Arroyo-Torres

et al. 2017

A&A

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Spatially resolving the thermally inhomogeneous outer atmosphere of the red giant Arcturus in the 2.3 μm CO lines

Ohnaka

Marín

2018

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Aims. The outer atmosphere of K giants shows thermally inhomogeneous structures consisting of the hot chromospheric gas and the cool molecular gas. We present spectro-interferometric observations of the multicomponent outer atmosphere of the well-studied K1.5 giant Arcturus (α Boo) in the CO first overtone lines near 2.3 µm. Methods. We observed Arcturus with the AMBER instrument at the Very Large Telescope Interferometer (VLTI) at 2.28-2.31 µm with a spectral resolution of 12 000 and at projected baselines of 7.3, 14.6, and 21.8 m.Results. The high spectral resolution of the VLTI/AMBER instrument allowed us to spatially resolve Arcturus in the individual CO lines. Comparison of the observed interferometric data with the MARCS photospheric model shows that the star appears to be significantly larger than predicted by the model. It indicates the presence of an extended component that is not accounted for by the current photospheric models for this well-studied star. We found out that the observed AMBER data can be explained by a model with two additional CO layers above the photosphere. The inner CO layer is located just above the photosphere, at 1.04 ± 0.02 R ⋆ , with a temperature of 1600 ± 400 K and a CO column density of 10 20±0.3 cm −2 . On the other hand, the outer CO layer is found to be as extended as to 2.6 ± 0.2 R ⋆ with a temperature of 1800 ± 100 K and a CO column density of 10 19±0.15 cm −2 . Conclusions. The properties of the inner CO layer are in broad agreement with those previously inferred from the spatially unresolved spectroscopic analyses. However, our AMBER observations have revealed that the quasi-static cool molecular component extends out to 2-3 R ⋆ , within which region the chromospheric wind steeply accelerates.

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Pulsations, eruptions, and evolution of four yellow hypergiants

Genderen

Lobel

Nieuwenhuijzen

et al. 2019

A&A

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Aims. We aim to explore the variable photometric and stellar properties of four yellow hypergiants (YHGs), HR 8752, HR 5171A, ρ Cas, and HD 179821, and their pulsations of hundreds of days, and long-term variations (LTVs) of years. We also aim to explore light and colour curves for characteristics betraying evolutionary loops and eruptive episodes and to investigate trends of quasi-periods and the possible need for distance revisions. Methods. We tackled multi-colour and visual photometric data sets, looked for photometric indications betraying eruptions or enhanced mass-loss episodes, calculated stellar properties mainly using a previously published temperature calibration, and investigated the nature of LTVs and their influence on quasi-periods and stellar properties. Results. Based on driven one-zone stellar oscillation models, the pulsations can be characterised as 'weakly chaotic'. The BV photometry revealed a high-opacity layer in the atmospheres. When the temperature rises the mass loss increases as well, consequently, as the density of the high-opacity layer. As a result, the absorption in B and V grow. The absorption in B, presumably of the order of one to a few 0 m . 1, is always higher than in V . This difference renders redder and variable (B − V ) colour indexes, but the absorption law is unknown. This property of YHGs is unpredictable and explains why spectroscopic temperatures (reddening independent) are always higher than photometric ones, but the difference decreases with the temperature. A new (weak) eruption of ρ Cas has been identified. We propose shorter distances for ρ Cas and HR 5171A than the accepted ones. Therefore, a correction to decrease the blue luminescence of HR 5171A by polycyclic aromatic hydrocarbon (PAH) molecules is necessary, and HR 5171A would no longer be a member of the cluster Gum48d. HR 5171A is only subject to one source of light variation, not by two as the literature suggests.Eruptive episodes (lasting one to two years), of YHGs prefer relatively cool circumstances when a red evolutionary loop (RL) has shifted the star to the red on the HR diagram. After the eruption, a blue loop evolution (BL) is triggered lasting one to a few decades. We claim that in addition to HR 8752, also the other three YHGs have shown similar cycles over the last 70 years. This supports the suspicion that HD 179821 might be a YHG (with a possible eruptive episode between 1925 and 1960). The range in temperature of these cyclic T eff variations is 3000 K-4000 K. LTVs mainly consist of such BL and RL evolutions, which are responsible for a decrease and increase, respectively, of the quasi-periods. The reddening episode of HR 5171A between 1960 and 1974 was most likely due to a red loop evolution, and the reddening after the 1975 eruption was likely due to a shell ejection, taking place simultaneously with a blue loop evolution.

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VLTI/AMBER spectro-interferometry of the late-type supergiants V766 Cen (=HR 5171 A),σOph, BM Sco, and HD 206859

Cited by 28 publications

References 61 publications

Multi-epoch VLTI-PIONIER imaging of the supergiant V766 Cen

Multi-epoch VLTI-PIONIER imaging of the supergiant V766 Cen

Spatially resolving the thermally inhomogeneous outer atmosphere of the red giant Arcturus in the 2.3 μm CO lines

Pulsations, eruptions, and evolution of four yellow hypergiants

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