ALMA and VLA reveal the lukewarm chromospheres of the nearby red supergiants Antares and Betelgeuse

O’Gorman, Eamon; Harper, G. M.; Ohnaka, K.; Feeney-Johansson, A.; Wilkeneit-Braun, K.; Brown, Alexander; Guinan, E. F.; Lim, Jeremy; Richards, A. M. S.; Ryde, Nils; Vlemmings, Wouter

doi:10.1051/0004-6361/202037756

Cited by 16 publications

(11 citation statements)

References 77 publications

(106 reference statements)

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“…An alternative possibility would be the emission of a warm chromosphere which has also been proposed as a source of this continuum emission (Gilman 1974). For our stellar sample, α Ori and α Sco shows clear evidence for having a chromosphere (Linsky 2017;O'Gorman et al 2020). For all others there seems to be no evidence of a chromosphere.…”

Section: The Dust Componentsmentioning

confidence: 64%

“…Most conspicuous are the strong dips in the energy distribution around 4.6 and 2.5 µm from CO (fundamental and first overtone), around 8 and 4.2 µm from SiO (fundamental and first overtone), and around 6.6 µm from H 2 O. This absorption has its origin in a layer above the stellar photosphere located at about 1.5 R * , the so called MOLsphere (Tsuji 2000(Tsuji , 2006Perrin et al 2007;Ohnaka 2014;Montargès et al 2014). It is only observed for massive supergiants.…”

Section: Molecular Bandsmentioning

confidence: 99%

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Non-stoichiometric amorphous magnesium-iron silicates in circumstellar dust shells

Gail¹,

Tamanai

Pucci

et al. 2020

A&A

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Aims. We study the growth of dust in oxygen-rich stellar outflows in order to find out to which extent dust growth models can quantitatively reconcile with the quantities and nature of dust as derived from observations of the infrared emission from circumstellar dust shells. Methods. We use a set of nine well-observed massive supergiants with optically thin dust shells as testbeds because of the relatively simple properties of the outflows from massive supergiants, contrary to the case of AGB stars. Models of the infrared emission from their circumstellar dust shells are compared to their observed infrared spectra to derive the essential parameters that rule dust formation in the extended envelope of these stars. The results are compared with a model for silicate dust condensation. Results. For all objects, the infrared emission in the studied wavelength range, between 6 and 25 μm, can be reproduced rather well by a mixture of non-stoichiometric iron-bearing silicates, alumina, and metallic iron dust particles. For three objects (μ Cep, RW Cyg, and RS Per), the observed spectra can be sufficiently well reproduced by a stationary and (essentially) spherically symmetric outflow in the instantaneous condensation approximation. For these objects, the temperature at the onset of massive silicate dust growth is of the order of 920 K and the corresponding outflow velocity of the order of the sound velocity. This condensation temperature is only somewhat below the vapourisation temperature of the silicate dust and suggests that the silicate dust grows on the corundum dust grains that formed well inside of the silicate dust shell at a much higher temperature. The low expansion velocity at the inner edge of the silicate dust shell further suggests that, for these supergiants, the region inside the silicate dust shell has an only subsonic average expansion velocity, though a high degree of supersonic turbulence is indicated by the widths of spectral lines. Conclusions. Our results suggest that for the two major problems of dust formation in stellar outflows, that is (i) formation of seed nuclei and (ii) their growth to macroscopic dust grains, we are gradually coming close to a quantitative understanding of the second item.

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Section: The Dust Componentsmentioning

confidence: 64%

Section: Molecular Bandsmentioning

confidence: 99%

Non-stoichiometric amorphous magnesium-iron silicates in circumstellar dust shells

Gail¹,

Tamanai

Pucci

et al. 2020

A&A

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“…The distribution and amount of dust in the spread-out layer remain mostly unchanged with time 22,25 , and thus it is unlikely that dust condensation in this layer is related to the large time variation of A(V ) and τ10 during the Dimming that we found. In contrast, the latter, lukewarm region 26 coexists with the warm chromosphere, the temperature of which 9,27 is sufficiently high for dust subli- mation 28 . Therefore, a dust clump that condenses near the photosphere may soon be sublimated by chromospheric heating, or, if the radiative acceleration is insufficient, it may fall back to the photosphere to be sublimated 29 .…”

Section: Time Variations Of the Photospheric Parametersmentioning

confidence: 99%

The Great Dimming of Betelgeuse seen by the Himawari-8 meteorological satellite

Taniguchi,

Yamazaki,

Uno

2022

Preprint

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Betelgeuse, one of the most studied red supergiant stars 1,2 , dimmed in the optical by ∼1.2 mag between late 2019 and early 2020, reaching an historical minimum 3,4,5 called "the Great Dimming." Thanks to enormous observational effort to date, two hypotheses remain that can explain the Dimming 1 : a decrease in the effective temperature 6,7 and an enhancement of the extinction caused by newly produced circumstellar dust 8,9 . However, the lack of multi-wavelength monitoring observations, especially in the mid infrared where emission from circumstellar dust can be detected, has prevented us from closely examining these hypotheses. Here we present 4.5-year, 16-band photometry of Betelgeuse between 2017-2021 in the 0.45-13.5 µm wavelength range making use of images taken by the Himawari-8 10 geostationary meteorological satellite. By examining the optical and near-infrared light curves, we show that both a decreased effective temperature and increased dust extinction may have contributed by almost the same amount to the Great Dimming. Moreover, using the mid-infrared light curves, we find that the enhanced circumstellar extinction actually contributed to the Dimming. Thus, the Dimming event of Betelgeuse provides us an opportunity to examine the mechanism responsible for the mass loss of red supergiants, which affects the fate of massive stars as supernovae 11 .Himawari-8 is a Japanese geostationary meteorological satellite orbiting 35, 786 km above the equator at 140.7 • east 10 . Since 7 July 2015, Himawari-8 has taken images of the entire disk of the Earth once every ten minutes using its optical and infrared imager, the Advanced Himawari Imager (AHI; Extended Data Fig. 1). The Himawari-8 satellite also observes the region of outer space around the edge of the Earth's disk during every scan; this motivated us to develop a brand-new concept: using meteorological satellites as "space telescopes" for astronomy (Fig. 1).One of the unique aspects of this concept to use the Himawari-8 for astronomy is that it enables us to obtain high-cadence time series of mid-infrared images, which is hard to acquire with the usual astronomical instruments. Small ground-based telescopes can acquire time-series measurements 12 , but the observations only cover wavelengths within the atmospheric window, and they are interrupted by the Sun for several months in most cases 13,14 . In contrast, astronomical satellites and aircraft-carrying telescopes can observe stars in most wavelength ranges 15,16,17 , but the observations require higher costs than ground-based telescopes. Survey telescopes orbiting the Earth for non-astronomical purposes-like the Himawari-8 meteorological satellite-have the potential to overcome these problems. In this work, we demonstrate that the mystery of the Great Dimming of Betelgeuse can be solved with the aid of the time-series observations from the Himawari-8, especially that in the mid infrared, with which the amount of dust around Betelgeuse can be determined.

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“…The main characteristic of this profile is a temperature inversion in the chromosphere of the star, that peaks at ∼ 1.4 R , and decreases again. ALMA and VLA observations of the RSGs Antares and Betelgeuse by Lim et al (1998);O'Gorman et al (2017O'Gorman et al ( , 2020 confirm the presence of such a lukewarm chromospheric temperature inversion, peaking at a radius of 1.3 − 1.5 R with a peak temperature of ∼3800 K. However, Lim et al (1998) pointed out that optical and ultraviolet chromospheric signatures required higher temperatures of ∼5000 K at similar radii (Uitenbroek et al 1996). Conversely, modelling of spectroscopic and interferometric data of the CO MOLsphere derived gas temperatures of only 2000 K at 1.2 − 1.4 R (Ohnaka et al 2013).…”

Section: Modelsmentioning

confidence: 99%

The effect of winds on atmospheric layers of red supergiants I. Modelling for interferometric observations

González-Torà,

Wittkowski,

Davies

et al. 2022

Preprint

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Context. Red supergiants (RSGs) are evolved massive stars in a stage preceding core-collapse supernova. The physical processes that trigger mass loss in their atmospheres are still not fully understood, and remain one of the key questions in stellar astrophysics. Based on observations of α Ori, a new semi-empirical method to add a wind to hydrostatic model atmospheres of RSGs was recently developed. This method can reproduce many of the static molecular shell (or 'MOLsphere') spectral features. Aims. We use this method of adding a semi-empirical wind to a MARCS model atmosphere to compute synthetic observables, comparing the model to spatially resolved interferometric observations. We present a case study to model published interferometric data of HD 95687 and V602 Car obtained with the AMBER instrument at the Very Large Telescope Interferometer (VLTI). Methods. We compute model intensities with respect to the line of sight angle (µ) for different mass-loss rates, spectra and visibilities using the radiative transfer code Turbospectrum. We can convolve the models to match the different spectral resolutions of the VLTI instruments, studying a wavelength range of 1.8 − 5 µm corresponding to the K, L and M-bands for GRAVITY and MATISSE data. The model spectra and squared visibility amplitudes are compared with the published VLTI/AMBER data. Results. The synthetic visibilities reproduce observed drops in the CO, SiO, and water layers that are not shown in visibilities based on MARCS models alone. For the case studies, we find that adding a wind on to the MARCS model with simple radiative equilibrium dramatically improves the agreement with the squared visibility amplitudes as well as the spectra, the fit being even better when applying a steeper density profile than predicted from previous studies. Our results reproduce observed extended atmospheres up to several stellar radii. Conclusions. This paper shows the potential of our model to describe extended atmospheres in RSGs. It can reproduce the shapes of the spectra and visibilities with better accuracy in the CO and water lines than previous models. The method can be extended to other wavelength bands for both spectroscopic and interferometric observations. We provide temperature and density stratifications that succeed for the first time in reproducing observed interferometric properties of red supergiant atmospheres.

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ALMA and VLA reveal the lukewarm chromospheres of the nearby red supergiants Antares and Betelgeuse

Cited by 16 publications

References 77 publications

Non-stoichiometric amorphous magnesium-iron silicates in circumstellar dust shells

Non-stoichiometric amorphous magnesium-iron silicates in circumstellar dust shells

The Great Dimming of Betelgeuse seen by the Himawari-8 meteorological satellite

The effect of winds on atmospheric layers of red supergiants I. Modelling for interferometric observations

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