Spatially resolved, high-spectral resolution observation of the K giant Aldebaran in the CO first overtone lines with VLTI/AMBER

Ohnaka, K.

doi:10.1051/0004-6361/201321207

Cited by 16 publications

(29 citation statements)

References 36 publications

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“…We also observe a monotonic decrease beyond 2.3 μm, which may be caused by pseudocontinuum contributions from CO or by contributions from water vapor. We observed the same phenomenon previously for the RSGs VY CMa (Wittkowski et al 2012), AH Sco, UY Sct, and KW Sgr (Arroyo-Torres et al (2013), as well as for the smallamplitude pulsating red giants RS Cap (Marti-Vidal et al 2011), BK Vir (Ohnaka et al 2012), α Tau (Ohnaka 2013), and β Peg (Arroyo-Torres et al 2014).…”

Section: Resultssupporting

confidence: 88%

What causes the large extensions of red supergiant atmospheres?

Arroyo-Torres

Wittkowski²,

Chiavassa

et al. 2015

A&A

108

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Aims. This research has two main goals. First, we present the atmospheric structure and the fundamental parameters of three red supergiants (RSGs), increasing the sample of RSGs observed by near-infrared spectro-interferometry. Additionally, we test possible mechanisms that may explain the large observed atmospheric extensions of RSGs. Methods. We carried out spectro-interferometric observations of the RSGs V602 Car, HD 95687, and HD 183589 in the near-infrared K-band (1.92−2.47 μm) with the VLTI/AMBER instrument at medium spectral resolution (R ∼ 1500). To categorize and comprehend the extended atmospheres, we compared our observational results to predictions by available hydrostatic PHOENIX, available 3D convection, and new 1D self-excited pulsation models of RSGs. Results. Our near-infrared flux spectra of V602 Car, HD 95687, and HD 183589 are well reproduced by the PHOENIX model atmospheres. The continuum visibility values are consistent with a limb-darkened disk as predicted by the PHOENIX models, allowing us to determine the angular diameter and the fundamental parameters of our sources. Nonetheless, in the case of V602 Car and HD 95686, the PHOENIX model visibilities do not predict the large observed extensions of molecular layers, most remarkably in the CO bands. Likewise, the 3D convection models and the 1D pulsation models with typical parameters of RSGs lead to compact atmospheric structures as well, which are similar to the structure of the hydrostatic PHOENIX models. They can also not explain the observed decreases in the visibilities and thus the large atmospheric molecular extensions. The full sample of our RSGs indicates increasing observed atmospheric extensions with increasing luminosity and decreasing surface gravity, and no correlation with effective temperature or variability amplitude. Conclusions. The location of our RSG sources in the Hertzsprung-Russell diagram is confirmed to be consistent with the red limits of recent evolutionary tracks. The observed extensions of the atmospheric layers of our sample of RSGs are comparable to those of Mira stars. This phenomenon is not predicted by any of the considered model atmospheres including available 3D convection and new 1D pulsation models of RSGs. This confirms that neither convection nor pulsation alone can levitate the molecular atmospheres of RSGs. Our observed correlation of atmospheric extension with luminosity supports a scenario of radiative acceleration on Doppler-shifted molecular lines.

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Section: Resultssupporting

confidence: 88%

What causes the large extensions of red supergiant atmospheres?

Arroyo-Torres

Wittkowski²,

Chiavassa

et al. 2015

A&A

108

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“…This extended outer atmosphere, the so-called MOLsphere (Tsuji 2000b), cannot be accounted for by hydrostatic photospheric models. The presence of the MOLsphere in normal (i.e., non-Mira) K-M giants, Mira stars, and red supergiants has been confirmed by IR spectroscopic and interferometric observations of molecules such as CO and H 2 O (e.g., Tsuji et al 1997;Tsuji 2000aTsuji ,b, 2001Perrin et al 2004aPerrin et al ,b, 2005Wittkowski et al 2007Wittkowski et al , 2008Wittkowski et al , 2011Woodruff et al 2008Woodruff et al , 2009Le Bouquin et al 2009;Martí-Vidal 2011;Ohnaka 2004aOhnaka ,b, 2012Ohnaka , 2013Ohnaka et al 2011Ohnaka et al , 2013.…”

Section: Introductionmentioning

confidence: 92%

“…The H 2 O line list was taken from Barber et al (2006) 4 . Details of the computation of the synthetic spectra are described in the Appendix of Ohnaka (2013).…”

Section: Comparison Between Visir Spectra and Marcs Modelsmentioning

confidence: 99%

“…This can make the resultant, spatially unresolved spectrum appear nearly unchanged. For example, Ohnaka et al (2012) and Ohnaka (2013) demonstrate that although the spatially unresolved spectra of the 2.3 μm CO first overtone lines in K and M giants can be reproduced well by the MARCS photospheric models alone and show very little signature of the MOLsphere, spatially resolved spectrointerferometric observations clearly reveal the presence of the extended MOLsphere. This means that constraining the parameters of the MOLsphere from spatially unresolved spectra alone is not necessarily straightforward.…”

Section: Optically Bright Red Supergiantsmentioning

confidence: 99%

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High spectral resolution spectroscopy of the SiO fundamental lines in red giants and red supergiants with VLT/VISIR

Ohnaka

2013

A&A

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Context. The mass-loss mechanism in red giants and red supergiants is not yet understood well. The SiO fundamental lines near 8 μm are potentially useful for probing the outer atmosphere, which is essential for clarifying the mass-loss mechanism. However, these lines have been little explored until now. Aims. We present high spectral resolution spectroscopic observations of the SiO fundamental lines near 8.1 μm in 16 bright red giants and red supergiants. Our sample consists of seven normal (i.e., non-Mira) K-M giants (from K1.5 to M6.5), three Mira stars, three optically bright red supergiants, two dusty red supergiants, and the enigmatic object GCIRS3 near the Galactic center. Methods. Our program stars were observed between 8.088 μm and 8.112 μm with a spectral resolution of 30 000 using VLT/VISIR. Results. We detected SiO fundamental lines in all of our program stars except for GCIRS3. The SiO lines in normal K and M giants as well as optically bright (i.e., not dusty) red supergiants do not show P-Cyg profiles or blueshifts, which means the absence of systematic outflows in the SiO line forming region. We detected P-Cyg profiles in the SiO lines in the dusty red supergiants VY CMa and VX Sgr, with the latter object being a new detection. These SiO lines originate in the outflowing gas with the thermal dust continuum emission seen as the background. The outflow velocities of the SiO line forming region in VY CMa and VX Sgr are estimated to be 27 km s −1 and 17 km s −1 , respectively. We derived basic stellar parameters (effective temperature, surface gravity, luminosity, and mass) for the normal K-M giants and optically bright red supergiants in our sample and compared the observed VISIR spectra with synthetic spectra predicted from MARCS photospheric models. Most of the SiO lines observed in the program stars warmer than ∼3400 K are reasonably reproduced by the MARCS models, which allowed us to estimate the silicon abundance as well as the 28 Si/ 29 Si and 28 Si/ 30 Si ratios. However, we detected possible absorption excess in some SiO lines. Moreover, the SiO lines in the cooler red giants and red supergiant cannot be explained by the MARCS models at all, even if the dust emission is taken into account. This disagreement may be a signature of the dense, extended molecular outer atmosphere.

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“…Dust shell parameters were measured in particular by mid-infrared interferometry (e.g. ; Danchi et al 1994;Monnier et al 1997Monnier et al , 2000Weiner et al 2006;Lopez et al 1997;Ohnaka et al 2005;Wittkowski et al2007;Sacuto & Chesneau 2009, Karovicova et al 2011, 2013Zhao-Geisler et al 2011Sacuto et al 2013). There are mainly three scenarios that are being discussed, as recently outlined in more detail by Karovicova et al (2013): 1.…”

Section: Dust Shells and Winds From Cool Evolved Starsmentioning

confidence: 99%

From the atmosphere to the circumstellar environment in cool evolved stars

Wittkowski¹,

Paladini

2014

EAS Publications Series

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Abstract. We discuss and illustrate contributions that optical interferometry has made on our current understanding of cool evolved stars. We include red giant branch (RGB) stars, asymptotic giant branch (AGB) stars, and red supergiants (RSGs). Studies using optical interferometry from visual to mid-infrared wavelengths have greatly increased our knowledge of their atmospheres, extended molecular shells, dust formation, and winds. These processes and the morphology of the circumstellar environment are important for the further evolution of these stars toward planetary nebulae (PNe) and core-collapse supernovae (SNe), and for the return of material to the interstellar medium.

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Spatially resolved, high-spectral resolution observation of the K giant Aldebaran in the CO first overtone lines with VLTI/AMBER

Cited by 16 publications

References 36 publications

What causes the large extensions of red supergiant atmospheres?

What causes the large extensions of red supergiant atmospheres?

High spectral resolution spectroscopy of the SiO fundamental lines in red giants and red supergiants with VLT/VISIR

From the atmosphere to the circumstellar environment in cool evolved stars

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