Angular Size Measurements of Mira Variable Stars at 2.2 Microns. II.

Belle, Gerald van; Thompson, R. R.; Creech‐Eakman, M. J.

doi:10.1086/342282

Cited by 42 publications

(34 citation statements)

References 64 publications

(75 reference statements)

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“…The difference is quite large in the case of RT Aql. We verified that the photospheric radius is consistent with the diameter measured by van Belle et al (2002) in K band: 7.24 ± 0.42 mas. It was measured at V = 84% visibility.…”

Section: Discussionsupporting

confidence: 86%

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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Section: Discussionsupporting

confidence: 86%

High-resolution IR and radio observations of AGB stars

Perrin

Cotton

Millan-Gabet

et al. 2015

A&A

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“…This value is lower than the K-band (λ = 2.2 μm, Δλ = 0.4 μm) UD diameter of θ UD = 10.73 ± 0.66 mas derived by van Belle et al (2002) at a minimum phase of 0.48. This can most likely be explained by the different radius definitions.…”

Section: Midi Model Resultscontrasting

confidence: 56%

Mid-infrared interferometric monitoring of evolved stars

Karovicova

Wittkowski²,

Boboltz³

et al. 2011

A&A

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Aims. We present a unique multi-epoch infrared interferometric study of the oxygen-rich Mira variable RR Aql in comparison to radiative transfer models of the dust shell. We investigate flux and visibility spectra at 8-13 μm with the aim of better understanding the pulsation mechanism and its connection to the dust condensation sequence and mass-loss process. Methods. We obtained 13 epochs of mid-infrared interferometry with the MIDI instrument at the VLTI between April 2004 and July 2007, covering minimum to pre-maximum pulsation phases (0.45-0.85) within four cycles. The data are modeled with a radiative transfer model of the dust shell where the central stellar intensity profile is described by a series of dust-free dynamic model atmospheres based on self-excited pulsation models. We examined two dust species, silicate and Al 2 O 3 grains. We performed model simulations using variations in model phase and dust shell parameters to investigate the expected variability of our mid-infrared photometric and interferometric data. Results. The observed visibility spectra do not show any indication of variations as a function of pulsation phase and cycle. The observed photometry spectra may indicate intracycle and cycle-to-cycle variations at the level of 1-2 standard deviations. The photometric and visibility spectra of RR Aql can be described well by the radiative transfer model of the dust shell that uses a dynamic model atmosphere describing the central source. The best-fitting model for our average pulsation phase of Φ V = 0.64 ± 0.15 includes the dynamic model atmosphere M21n (T model = 2550 K) with a photospheric angular diameter of θ Phot = 7.6 ± 0.6 mas, and a silicate dust shell with an optical depth of τ V = 2.8 ± 0.8, an inner radius of R in = 4.1 ± 0.7 R Phot , and a power-law index of the density distribution of p = 2.6 ± 0.3. The addition of an Al 2 O 3 dust shell did not improve the model fit. However, our model simulations indicate that the presence of an inner Al 2 O 3 dust shell with lower optical depth than for the silicate dust shell can not be excluded. The photospheric angular diameter corresponds to a radius of R phot = 520 +230 −140 R and an effective temperature of T eff ∼ 2420 ± 200 K. Our modeling simulations confirm that significant intracycle and cycle-to-cycle visibility variations are not expected for RR Aql at mid-infrared wavelengths within our uncertainties. Conclusions. We conclude that our RR Aql data can be described by a pulsating atmosphere surrounded by a silicate dust shell. The effects of the pulsation on the mid-infrared flux and visibility values are expected to be less than about 25% and 20%, respectively, and are too low to be detected within our measurement uncertainties.

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“…The Young's type of interference effects were clearly seen at mm l p 2.2 ( eV) light from a source at 1.012 kpc distance, viz., E ≈ 0.56 the star S Ser, using the Infrared Optical Telescope Array, which enabled a radius determination of the star (van Belle, Thompson, & Creech-Eakman 2002). When comparing with equation (13), we see that this result can already be used to completely exclude the model, because for such a value of a and 2 a p 3 for all reasonable values of , Df carries uncertainties k2p, a 0 and the light waves would not have interfered.…”

Section: The Diffraction Of Light From Extragalactic Point Sources: Amentioning

confidence: 82%

The Phase Coherence of Light from Extragalactic Sources: Direct Evidence against First-Order Planck-Scale Fluctuations in Time and Space

Lieu¹,

Hillman²

2003

The Astrophysical Journal

155

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We present a method of directly testing whether time continues to have its usual meaning on scales of ≤ s, the Planck time. According to quantum gravity, the time t of an event cannot 5 1/2 Ϫ44 t p (បG/c ) ≈ 5.4 # 10 P be determined more accurately than a standard deviation of the form , where and a are positive a j /t p a (t /t) a t 0 P 0 constants ∼1; likewise, distances are subject to an ultimate uncertainty , where c is the speed of light. As a cj t consequence, the period and wavelength of light cannot be specified precisely; rather, they are independently subject to the same intrinsic limitations in our knowledge of time and space, so that even the most monochromatic plane wave must in reality be a superposition of waves with varying q and , each having a different phase k velocity . For the entire accessible range of the electromagnetic spectrum this effect is extremely small, but q/k it can cumulatively lead to a complete loss of phase information if the emitted radiation propagated a sufficiently large distance. Since, at optical frequencies, the phase coherence of light from a distant point source is a necessary condition for the presence of diffraction patterns when the source is viewed through a telescope, such observations offer by far the most sensitive and uncontroversial test. We show that the Hubble Space Telescope detection of Airy rings from the active galaxy PKS 1413ϩ135, located at a distance of 1.2 Gpc, excludes all first-order ( ) quantum gravity fluctuations with an amplitude . The same result may be used to deduce that a p 1 a 1 0.003 0 the speed of light in vacuo is exact to a few parts in 10 32 .

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Angular Size Measurements of Mira Variable Stars at 2.2 Microns. II.

Cited by 42 publications

References 64 publications

High-resolution IR and radio observations of AGB stars

High-resolution IR and radio observations of AGB stars

Mid-infrared interferometric monitoring of evolved stars

The Phase Coherence of Light from Extragalactic Sources: Direct Evidence against First-Order Planck-Scale Fluctuations in Time and Space

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