SiO maser emission in Miras

Gray, M. D.; Wittkowski, M.; Scholz, M.; Humphreys, E. M. L.; Ohnaka, K.; Boboltz, D. A.

doi:10.1111/j.1365-2966.2008.14237.x

Cited by 101 publications

(118 citation statements)

References 56 publications

(109 reference statements)

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“…When meaningful stellar radii such as continuum radii or Rosseland radii were used and were obtained at similar phases as the SiO maps, the radii of the maser emission was consistently found close to two stellar radii (e.g., Boboltz & Wittkowski 2005;Fedele et al 2005;Cotton et al 2010). This location is consistent with theoretical modeling by Humphreys et al (1997) and Gray et al (2009), and is predicted to be located close to the position of a shock front. Among the RSGs observed here, AH Sco is also a known source of SiO maser emission with a mean diameter of 17.2 mas (Chen & Shen 2008).…”

Section: Atmospheric Structuresupporting

confidence: 76%

The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii

Arroyo-Torres

Wittkowski²,

Marcaide

et al. 2013

A&A

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Aims. We present the atmospheric structure and the fundamental properties of the red supergiants (RSGs) AH Sco, UY Sct, and KW Sgr based on VLTI/AMBER observations. Methods. We carried out spectro-interferometric observations of AH Sco, UY Sct, and KW Sgr in the near-infrared K band (1.92-2.47 μm) with the VLTI/AMBER instrument with spatial and spectral resolutions of 3 milliarcsec and 1500, respectively, and compared the data to a new grid of hydrostatic PHOENIX model atmospheres.Results. In our visibility data, we observe molecular layers of water and CO in extended atmospheres. For a uniform disk modeling, we observe size increases at the water band centered at 1.9 μm of 10% to 25% and at the CO bandheads at 2.3-2.5 μm of 20%-35% with respect to the near-continuum bandpass at around 2.20 μm. Our near-infrared spectra of AH Sco, UY Sct, and KW Sgr 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. However, the model visibilities do not predict the large observed extensions of the molecular layers. Comparing the continuum visibility values to PHOENIX models, we estimate the Rosseland-mean photospheric angular diameters of AH Sco, UY Sct, and KW Sgr to be 5.81 ± 0.15 mas, 5.48 ± 0.10 mas, and 3.91 ± 0.25 mas, respectively. Together with the distance and the spectro-photometry, we calculate radii of 1411 ± 124 R for AH Sco, 1708 ± 192 R for UY Sct, and 1009 ± 142 R for KW Sgr and effective temperatures of 3682 ± 190 K for AH Sco, 3365 ± 134 K for UY Sct, and 3720 ± 183 K for KW Sgr. Conclusions. AH Sco, UY Sct, and KW Sgr exhibit extended atmospheric layers of H 2 O and CO. The PHOENIX atmosphere models predict the spectra and the continuum visibility values, but cannot reproduce the large extensions of the molecular layers. This indicates that the opacities of the molecular bands are included, but that the model atmospheres are too compact compared to the observations. The observed extended layers may be levitated by processes such as pulsation or convection, which are not included in the hydrostatic atmospheric models. The location of the targets in the HR-diagram is confirmed to be close to, and possibly slightly to the right of, the Hayashi limit of recent evolutionary tracks corresponding to masses between about 20 M and 40 M .

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Section: Atmospheric Structuresupporting

confidence: 76%

The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii

Arroyo-Torres

Wittkowski²,

Marcaide

et al. 2013

A&A

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“…The impact of dust on SiO masers is not completely clear, however. Gray et al (2009) found that dust can ever play a positive or a negative role on SiO masers, depending on conditions, so that the link between SiO maser and dust formation radii is not straightforward. Our diameter measurements for a sample of stars give a view of the structure of the atmosphere and of where molecular gas is located.…”

Section: Discussionmentioning

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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“…They concluded that this variability points at the presence of differential illumination, or an asymmetric distribution of the circumstellar A&A 564, A88 (2014) material around L 2 Pup. Alternatively, Gray et al (2009) predicted that the centroid of SiO emission would shift in velocity according to the stage in the stellar cycle, as a consequence of the shock behavior and because the SiO maser region is located in a compact region, within a few stellar radii of the central object. Ohnaka (2014) recently observed L 2 Pup in the thermal infrared domain (N band) using the high spectral resolution mode of VISIR, and concluded that its spectrum cannot be reproduced satisfactorily using MARCS atmosphere models.…”

Section: Introductionmentioning

confidence: 99%

An edge-on translucent dust disk around the nearest AGB star, L₂Puppis

Kervella

Montargès

Ridgway

et al. 2014

A&A

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As the nearest known AGB star (d = 64 pc) and one of the brightest (m K ≈ −2), L 2 Pup is a particularly interesting benchmark object to monitor the final stages of stellar evolution. We report new serendipitous imaging observations of this star with the VLT/NACO adaptive optics system in twelve narrow-band filters covering the 1.0−4.0 µm wavelength range. These diffraction-limited images reveal an extended circumstellar dust lane in front of the star that exhibits a high opacity in the J band and becomes translucent in the H and K bands. In the L band, extended thermal emission from the dust is detected. We reproduced these observations using Monte Carlo radiative transfer modeling of a dust disk with the RADMC-3D code. We also present new interferometric observations with the VLTI/VINCI and MIDI instruments. We measured in the K band an upper limit to the limb-darkened angular diameter of θ LD = 17.9 ± 1.6 mas, converting to a maximum linear radius of R = 123 ± 14 R . Considering the geometry of the extended K band emission in the NACO images, this upper limit is probably close to the actual angular diameter of the star. The position of L 2 Pup in the Hertzsprung-Russell diagram indicates that this star has a mass of about 2 M and is probably experiencing an early stage of the asymptotic giant branch. We did not detect any stellar companion of L 2 Pup in our adaptive optics and interferometric observations, and we attribute its apparent astrometric wobble in the H data to variable lighting effects on its circumstellar material. However, we do not exclude the presence of a binary companion, because the large loop structure extending to more than 10 AU to the northeast of the disk in our L-band images may be the result of interaction between the stellar wind of L 2 Pup and a hidden secondary object. The geometric configuration that we propose, with a large dust disk seen almost edge-on, appears particularly favorable to test and develop our understanding of the formation of bipolar nebulae.

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SiO maser emission in Miras

Cited by 101 publications

References 56 publications

The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii

The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii

High-resolution IR and radio observations of AGB stars

An edge-on translucent dust disk around the nearest AGB star, L₂Puppis

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SiO maser emission in Miras

Cited by 101 publications

References 56 publications

The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii

The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii

High-resolution IR and radio observations of AGB stars

An edge-on translucent dust disk around the nearest AGB star, L2Puppis

Contact Info

Product

Resources

About

An edge-on translucent dust disk around the nearest AGB star, L₂Puppis