J, H, K spectro-interferometry of the Mira variable S Orionis

Wittkowski, M.; Boboltz, D. A.; Driebe, T.; Bouquin, J.-B. Le; Millour, F.; Ohnaka, K.; Scholz, M.

doi:10.1051/0004-6361:20079237

Cited by 62 publications

(99 citation statements)

References 24 publications

(36 reference statements)

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“…One goal of the current paper is to add three RSGs and thus to increase this sample. On the other hand, our previous works showed that the observed visibility data of the RSGs and of one of the red giants, β Peg, indicate large extensions of the molecular layers, similar as those previously observed for Mira variable stars (Wittkowski et al 2008. This was not predicted by hydrostatic PHOENIX model atmospheres.…”

Section: Introductionsupporting

confidence: 79%

“…Observations of Mira variable stars using the IOTA or VLTI interferometers show evidence of molecular layers lying above the photospheric layers (e.g., Perrin et al 2004;Wittkowski et al 2008Wittkowski et al , 2011). Theoretical dynamic model atmospheres (Ireland et al 2004a(Ireland et al ,b, 2008Scholz et al 2014) can explain reasonably well these molecular layers for Miras.…”

Section: Introductionmentioning

confidence: 99%

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What causes the large extensions of red supergiant atmospheres?

Arroyo-Torres

Wittkowski²,

Chiavassa

et al. 2015

A&A

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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: Introductionsupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

What causes the large extensions of red supergiant atmospheres?

Arroyo-Torres

Wittkowski²,

Chiavassa

et al. 2015

A&A

Self Cite

108

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“…Observations in specific narrow-band filters pointed to CO and H 2 O vapors as potential major contributors to the opacity in K band, with water vapor being the main contributor. Spectrally dispersed observations in the near-infrared confirmed this finding (Eisner et al 2007;Wittkowski et al 2008;Le Bouquin et al 2009). At the lowest opacity (in J and H bands), the impact of the envelope is reduced and the diameter of the object is close to that of the photosphere.…”

Section: Near-infraredsupporting

confidence: 59%

“…Except for S Ser, for which only one baseline was available for both Kand N-band measurements, for all other sources χ 2 values are indicative of the quality of the fits. The χ 2 is usually higher in the 11.55−13.26 µm sub-band than in other sub-bands probably because the structure of the envelope is more complex: water maybe present at different altitudes and farther away, which may explain the larger radii as shown in comparisons between nearinfrared data and dynamical model atmospheres (see, e.g., result on S Orionis by Wittkowski et al 2008). RX Tau seems to be a particular case with quite high χ 2 values and a larger spread in envelope diameter values that indicates a more extended envelope contributing at a wider range of distances from the star.…”

Section: Discussion Of Modeling Resultsmentioning

confidence: 99%

High-resolution IR and radio observations of AGB stars

Perrin

Cotton

Millan-Gabet

et al. 2015

A&A

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Aims. We present the results of observations with interferometers of a sample of pulsating asymptotic giant branch (AGB) stars in the infrared and at radio wavelengths. The goal of these observations is to explore the extended stellar atmospheres and to establish links between the spatial scales of molecular envelopes and of the dust shell. This is the key to better understand the process of dust formation and therefore of mass loss. Methods. We used the ESO VLTI/MIDI interferometer in the N band, the Keck Interferometer in the K band, and NRAO VLBA observations of SiO masers at 7 mm wavelength of a sample of AGB stars: U Ari, W Cnc, RX Tau, RT Tau, RT Aql, S Ser, and V Mon. The various instruments probe different altitudes of the atmosphere of the AGB stars. They are sensitive to regions below the silicate dust condensation distance and provide the opportunity of finding hints about how dust and its precursors form in the extended atmosphere of an AGB star. The K-band observations are sensitive to water and carbon-monoxyde vapors. Unfortunately, we were only able to observe S Ser in this wavelength range. Results. We find a ratio of 2.2 between the molecular envelope radius and the photospheric size, which is consistent with previous results. The N-band observations are mostly sensitive to vapors of SiO and water and to dust (alumina and silicate). The silicate dust shell is fully resolved, and no precise parameters can be deduced from the N-band observations other than a spatial extension of at least 12-16 R for our sample. The sizes found for the SiO region are consistent with the radii of the SiO maser rings provided by the VLBA observations. The sizes of the alumina and water vapor regions are systematically found to be larger. There is clear evidence that SiO is absent from regions farther from the star where silicate dust condenses. Conclusions. These observations support a possible scenario in which SiO is adsorbed by species such as corundum. An alternative explanation could be that SiO has chemically disappeared at this range of distances.

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“…Wittkowski et al 2008). For each observation mentioned in Table 1, only some of the individual frames were selected for further analysis.…”

Section: Data Reductionmentioning

confidence: 99%

Ellipsoidal primary of the RS CVn binaryζ Andromedae

Korhonen

Wittkowski

Kővári³

et al. 2010

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Aims. We have obtained high-resolution spectroscopy, optical interferometry, and long-term broad band photometry of the ellipsoidal primary of the RS CVn-type binary system ζ And. These observations are used to obtain fundamental stellar parameters and to study surface structures and their temporal evolution. Methods. Temperature maps of the stellar surface were obtained from high-resolution spectra with Doppler imaging techniques. These spectra were also used to investigate the chromospheric activity using the Hα line and to correlate it with the photospheric activity. The possible cyclicity in the spot activity was investigated from the long-term broad band photometry. Optical interferometry was obtained during the same time period as the high-resolution spectra. These observations were used to derive the size and fundamental parameters of ζ And. Results. Based on the optical interferometry the apparent limb darkened diameter of ζ And is 2.55 ± 0.09 mas using a uniform disk fit. The expected ∼4% maximum difference between the long and short axes of the ellipsoidal stellar surface cannot be confirmed from the current data which have 4% errors. The Hipparcos distance and the limb-darkened diameter obtained with a uniform disk fit give stellar radius of 15.9 ± 0.8 R , and combined with bolometric luminosity, it implies an effective temperature of 4665 ± 140 K. The temperature maps obtained from Doppler imaging show a strong belt of equatorial spots and hints of a cool polar cap. The equatorial spots show a concentration around the phase 0.75, i.e., 0.25 in phase from the secondary, and another concentration spans the phases 0.0-0.4. This spot configuration is reminiscent of the one seen in the earlier published temperature maps of ζ And. Investigation of the Hα line reveals both prominences and cool clouds in the chromosphere. These features do not seem to have a clearly preferred location in the binary reference frame, nor are they strongly associated with the cool photospheric spots. The investigation of the long-term photometry spanning 12 years shows hints of a spot activity cycle, which is also implied by the Doppler images, but the cycle length cannot be reliably determined from the current data.

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J, H, K spectro-interferometry of the Mira variable S Orionis

Cited by 62 publications

References 24 publications

What causes the large extensions of red supergiant atmospheres?

What causes the large extensions of red supergiant atmospheres?

High-resolution IR and radio observations of AGB stars

Ellipsoidal primary of the RS CVn binaryζ Andromedae

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