A CO-multilayer outer atmosphere for eight evolved stars revealed with VLTI/AMBER

Hadjara, M.; Cruzalèbes, P.; Nitschelm, Christian; Chen, X; Michael, E A; Moreno, E.

doi:10.1093/mnras/stz2240

Cited by 7 publications

(11 citation statements)

References 87 publications

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“…This sharp increase follows the absorption features that can be seen in the spectrum, with local maxima matching the deep CO band heads. Such variations correlated with the CO optical depth point towards a molecular shell above the photosphere as previously evidenced, for instance, by Perrin et al (2004), Perrin et al (2005), or Hadjara et al (2019) for other evolved stars.…”

Section: Squared Visibilitiessupporting

confidence: 78%

“…The properties of GCIRS 7 are compatible in 2019 within one sigma with all the single shell models, except for Verhoelst et al (2006), and they are also compatible with the outer shell of Antares from Ohnaka et al (2013). On the other hand, 2017 reveals a smaller shell, close to the inner layer of Antares from Hadjara et al (2019).…”

Section: The Molsphere Of Gcirs 7 In Contextmentioning

confidence: 65%

“…For the star Antares, Ohnaka et al (2013) used a similar approach (K-band interferometry) characterizing a double layer model at two different epochs, but without any significant variations in temperature or size. A model consisting in several concentric layers was used in Hadjara et al (2019) to characterize a sample of M stars via K-band interferometry. In the case of Antares, they modeled seven layers between 1.06 and 1.76 stellar radii.…”

Section: The Molsphere Of Gcirs 7 In Contextmentioning

confidence: 99%

“…Thanks to the performance of stellar interferometers, the understanding of the structure and evolution of RSG has improved significantly. The closest ones have been widely studied, not only obtaining measurements of their sizes but also revealing single-layer atmospheres (Perrin et al 2005(Perrin et al , 2007Montargès et al 2014), multi-layer atmospheres (Ohnaka et al 2009(Ohnaka et al , 2011(Ohnaka et al , 2013Hadjara et al 2019), complex structures in the photosphere (Haubois et al 2009;Chiavassa et al 2010;Ravi et al 2011;O'Gorman et al 2017;Ohnaka et al 2017), and even the temporal evolution of the stellar surface (Ohnaka et al 2011(Ohnaka et al , 2013Montargès et al 2016Montargès et al , 2018Climent et al 2020). Moreover, imaging of a RSG was performed in Baron et al (2014), Monnier et al (2014), and more recently, in Wittkowski et al (2017a) and Climent et al (2020).…”

Section: Introductionmentioning

confidence: 99%

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MOLsphere and pulsations of the Galactic Center's red supergiant GCIRS 7 from VLTI/GRAVITY

Rodríguez-Coira,

Paumard,

Perrin

et al. 2021

Preprint

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Context. GCIRS 7, the brightest star in the Galactic central parsec, formed 6 ± 2 Myr ago together with dozens of massive stars in a disk orbiting the central black-hole. It has been argued that GCIRS 7 is a pulsating body, on the basis of photometric variability. Aims. Our goal is to confirm photospheric pulsations based on interferometric size measurements to better understand how the mass loss from these massive stars enriches the local interstellar medium. Methods. We present the first medium-resolution (R = 500), K-band spectro-interferometric observations of GCIRS 7, using the GRAVITY instrument with the four auxiliary telescopes of the ESO VLTI. We looked for variations using two epochs, namely 2017 and 2019. Results. We find GCIRS 7 to be moderately resolved with a uniform-disk photospheric diameter of θ * UD = 1.55 ± 0.03 mas (R * UD = 1368 ± 26 R ) in the K-band continuum. The narrow-band uniform-disk diameter increases above 2.3 µm, with a clear correlation with the CO band heads in the spectrum. This correlation is aptly modeled by a hot (T L = 2368±37 K), geometrically thin molecular shell with a diameter of θ L = 1.74±0.03 mas, as measured in 2017. The shell diameter increased (θ L = 1.89 ± 0.03 mas), while its temperature decreased (T L = 2140 ± 42 K) in 2019. In contrast, the photospheric diameter θ * UD and the extinction up to the photosphere of GCIRS 7 (A K S = 3.18 ± 0.16) have the same value within uncertainties at the two epochs. Conclusions. In the context of previous interferometric and photo-spectrometric measurements, the GRAVITY data allow for an interpretation in terms of photospheric pulsations. The photospheric diameter measured in 2017 and 2019 is significantly larger than previously reported using the PIONIER instrument (θ * = 1.076 ± 0.093 mas in 2013 in the H band). The parameters of the photosphere and molecular shell of GCIRS 7 are comparable to those of other red supergiants that have previously been studied using interferometry. The extinction we measured here is lower than previous estimates in the direction of GCIRS 7 but typical for the central parsec region.

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Section: Squared Visibilitiessupporting

confidence: 78%

Section: The Molsphere Of Gcirs 7 In Contextmentioning

confidence: 65%

Section: The Molsphere Of Gcirs 7 In Contextmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

MOLsphere and pulsations of the Galactic Center's red supergiant GCIRS 7 from VLTI/GRAVITY

Rodríguez-Coira,

Paumard,

Perrin

et al. 2021

Preprint

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“…Despite being a decommissioned instrument, by the end of 2017, a large number of observations performed with AMBER are still used in very recent works about circumstellar environments (e.g., Koutoulaki et al 2018;Adam & Ohnaka 2019;Ohnaka et al 2019;Hadjara et al 2019), and it yielded the largest number of articles among the VLTI instruments to date. the interesting science cases pointed out by Millour et al (2018) for a future visible spectro-interferometric instrument on VLTI.…”

Section: Vlti/ambermentioning

confidence: 99%

Probing the weak wind phenomenon in Galactic O-type giants

Almeida

Marcolino

Bouret

et al. 2019

A&A

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Aims. Analyses of Galactic late O dwarfs (O8-O9.5V stars) raised the "weak wind problem": spectroscopic mass-loss rates (Ṁ) are up to two orders of magnitude lower than the theoretical values. We investigated the stellar and wind properties of Galactic late O giants (O8-O9.5III stars). These stars have luminosities log(L /L ) ∼ 5.2, which is the critical value (onset of weak winds) proposed in the literature. Methods. We performed a spectroscopic analysis of nine O8-O9.5III stars in the ultraviolet (UV) and optical regions using the model atmosphere code CMFGEN. Results. Stellar luminosities were adopted using calibrations from the literature. Overall, our model spectral energy distributions agree well with the observed ones considering parallaxes from the latest GAIA data release (DR2). The effective temperature derived from the UV region agrees well with the ones from the optical. As expected, the analysis of the Hertzsprung-Russell (HR) diagram shows that our sample is more evolved than late O dwarfs. From the UV region, we foundṀ ∼ 10 −8 − 10 −9 M yr -1 overall. This is lower by ∼ 0.9 − 2.3 dex than predicted values based on the (global) conservation of energy in the wind. The mass-loss rates predicted from first principles, based on the moving reversing layer theory, agree better with our findings, but it fails to match the spectroscopiċ M for the most luminous OB stars. The region of log(L /L ) ∼ 5.2 is critical for both sets of predictions in comparison with the spectroscopic mass-loss rates. CMFGEN models with the predictedṀ (the former one) fail to reproduce the UV wind lines for all the stars of our sample. We reproduce the observed Hα profiles of four objects with ourṀ derived from the UV. Hence, lowṀ values (weak winds) are favored to fit the observations (UV + optical), but discrepancies between the UV and Hα diagnostics remain for some objects. Conclusions. Our results indicate weak winds beyond the O8-9.5V class, since the region of log(L /L ) ∼ 5.2 is indeed critical to the weak wind phenomenon. Since O8-O9.5III stars are more evolved than O8-9.5V, evolutionary effects do not seem to play a role in the onset of the weak wind phenomenon. These findings support that theṀ (for low luminosity O stars) in use in the majority of modern stellar evolution codes must be severely overestimated up to the end of the H-burning phase. Further investigations must evaluate the consequences of weak winds in terms of physical parameters for massive stars (e.g., angular momentum and CNO surface abundances).

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MOLsphere and pulsations of the Galactic Center’s red supergiant GCIRS 7 from VLTI/GRAVITY

Rodríguez-Coira¹,

Paumard²,

Perrin³

et al. 2021

A&A

View full text Add to dashboard Cite

Context. GCIRS 7, the brightest star in the Galactic central parsec, formed 6 ± 2 Myr ago together with dozens of massive stars in a disk orbiting the central black-hole. It has been argued that GCIRS 7 is a pulsating body, on the basis of photometric variability. Aims. Our goal is to confirm photospheric pulsations based on interferometric size measurements to better understand how the mass loss from these massive stars enriches the local interstellar medium. Methods. We present the first medium-resolution (R = 500), K-band spectro-interferometric observations of GCIRS 7, using the GRAVITY instrument with the four auxiliary telescopes of the ESO VLTI. We looked for variations using two epochs, namely 2017 and 2019. Results. We find GCIRS 7 to be moderately resolved with a uniform-disk photospheric diameter of θUD* = 1.55 ± 0.03 mas (RUD* = 1368 ± 26 R⊙) in the K-band continuum. The narrow-band uniform-disk diameter increases above 2.3 μm, with a clear correlation with the CO band heads in the spectrum. This correlation is aptly modeled by a hot (TL = 2368 ± 37 K), geometrically thin molecular shell with a diameter of θL = 1.74 ± 0.03 mas, as measured in 2017. The shell diameter increased (θL = 1.89 ± 0.03 mas), while its temperature decreased (TL = 2140 ± 42 K) in 2019. In contrast, the photospheric diameter θUD* and the extinction up to the photosphere of GCIRS 7 (AKS = 3.18 ± 0.16) have the same value within uncertainties at the two epochs. Conclusions. In the context of previous interferometric and photo-spectrometric measurements, the GRAVITY data allow for an interpretation in terms of photospheric pulsations. The photospheric diameter measured in 2017 and 2019 is significantly larger than previously reported using the PIONIER instrument (θ* = 1.076 ± 0.093 mas in 2013 in the H band). The parameters of the photosphere and molecular shell of GCIRS 7 are comparable to those of other red supergiants that have previously been studied using interferometry. The extinction we measured here is lower than previous estimates in the direction of GCIRS 7 but typical for the central parsec region.

show abstract

A CO-multilayer outer atmosphere for eight evolved stars revealed with VLTI/AMBER

Cited by 7 publications

References 87 publications

MOLsphere and pulsations of the Galactic Center's red supergiant GCIRS 7 from VLTI/GRAVITY

MOLsphere and pulsations of the Galactic Center's red supergiant GCIRS 7 from VLTI/GRAVITY

Probing the weak wind phenomenon in Galactic O-type giants

MOLsphere and pulsations of the Galactic Center’s red supergiant GCIRS 7 from VLTI/GRAVITY

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