Angular Size Measurements of 18 Mira Variable Stars at 2.2 (?)

Belle, Gerald van; Dyck, H. M.; Benson, J. A.; Lacasse, M. G.

doi:10.1086/118170

Cited by 101 publications

(96 citation statements)

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“…While the effective temperatures of Mira variables are known to show temporal variations with phase (e.g., van Belle et al 1996;Perrin et al 1999;Woodruff et al 2004), the effect of the uncertainty of the effective temperature adopted in our model turns out to be minor as we show below, because the warm water vapor envelope is quite optically thick in the wavelength regions discussed in the present work.…”

Section: Modeling Of the Warm Water Vapor Envelopementioning

confidence: 65%

Warm water vapor envelope in Mira variables and its effects on the apparent size from the near-infrared to the mid-infrared

Ohnaka

2004

A&A

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Abstract.We present a possible interpretation for the increase of the angular diameter of the Mira variables o Cet, R Leo, and χ Cyg from the K band to the 11 µm region revealed by the recent interferometric observations using narrow bandpasses where no salient spectral feature is present (Weiner et al. 2003a,b). A simple two-layer model consisting of hot and cool H 2 O layers for the warm water vapor envelope, whose presence in Mira variables was revealed by previous spectroscopic observations, can reproduce the angular diameters observed with Infrared Spatial Interferometer as well as the high-resolution TEXES spectra obtained in the 11 µm region. The warm water vapor layers are optically thick in the lines, and therefore, strong absorption due to H 2 O can be expected from such a dense water vapor envelope. However, the absorption lines are filled in by emission from the extended part of the envelope, and this results in the high-resolution 11 µm spectra which exhibit only weak, fine spectral features, masking the spectroscopic evidences of the dense, warm water vapor envelope. On the other hand, the presence of the warm water vapor envelope manifests itself as the larger angular diameters in the 11 µm region as compared to those measured in the near-infrared. Furthermore, comparison of the visibilities predicted in the near-infrared (1.5-3.8 µm) with observational results available in the literature demonstrates that our two-layer model for the warm water vapor envelope can also reproduce the observed near-infrared visibilities and angular diameters, and suggests that the wavelength dependence of the angular size of Mira variables in the infrared largely reflects the H 2 O opacity. The radii of the hot H 2 O layers in the three Mira variables are derived to be 1.5-1.7 R with temperatures of 1800-2000 K and H 2 O column densities of (1−5) × 10 21 cm −2 , while the radii of the cool H 2 O layers are derived to be 2.2-2.5 R with temperatures of 1200-1400 K and H 2 O column densities of (1−7) × 10 21 cm −2 .

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Section: Modeling Of the Warm Water Vapor Envelopementioning

confidence: 65%

Warm water vapor envelope in Mira variables and its effects on the apparent size from the near-infrared to the mid-infrared

Ohnaka

2004

A&A

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“…Pulsations certainly help leading to still larger relative extensions, a phenomenon which is not included in their static models. Van Belle et al (1996) have compared visibility curves at 2.2 µm for a sample of oxygen-rich Miras to those computed from the model atmospheres of Scholz & Takeda (1987). They deduced that…”

Section: Direct Effective Temperaturesmentioning

confidence: 99%

The effective temperatures of carbon-rich stars

Bergeat

Knapik

Rutily

2001

A&A

152

207

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Abstract. We evaluate effective temperatures of 390 carbon-rich stars. The interstellar extinction on their lines of sights was determined and circumstellar contributions derived. The intrinsic (dereddened) spectral energy distributions (SEDs) are classified into 14 photometric groups (HCi, CVj and SCV with i = 0,5 and j = 1,7). The new scale of effective temperatures proposed here is calibrated on the 54 angular diameters (measured on 52 stars) available at present from lunar occultations and interferometry. The brightness distribution on stellar discs and its influence on diameter evaluations are discussed. The effective temperatures directly deduced from those diameters correlate with the classification into photometric groups, despite the large error bars on diameters. The main parameter of our photometric classification is thus effective temperature. Our photometric k 1/2 coefficients are shown to be angular diameters on a relative scale for a given photometric group, (more precisely for a given effective temperature). The angular diameters are consistent with the photometric data previously shown to be consistent with the true parallaxes from HIPPARCOS observations (Knapik, et al. 1998, Sect. 6). Provisional effective temperatures, as constrained by a successful comparison of dereddened SEDs from observations to model atmosphere predictions, are in good agreement with the values directly calculated from the observed angular diameters and with those deduced from five selected intrinsic color indices. These three approaches were used to calibrate a reference angular diameter Φ0 and the associated coefficient CT eff . The effective temperature proposed for each star is the arithmetic mean of two estimates, one ("bolometric") from a reference integrated flux F0, the other ("spectral") from calibrated color indices which are representative of SED shapes. Effective temperatures for about 390 carbon stars are provided on this new homogeneous scale, together with values for some stars classified with oxygen-type SEDs with a total of 438 SEDs (410 stars) studied. Apparent bolometric magnitudes are given. Objects with strong infrared excesses and optically thick circumstellar dust shells are discussed separately. The new effective temperature scale is shown to be compatible and (statistically) consistent with the sample of direct values from the observed angular diameters. The effective temperatures are confirmed to be higher than the mean color temperatures (from 140 to 440 K). They are in good agreement with the published estimates from the infrared flux method for T eff ≥ 3170 K, while an increasing discrepancy is observed toward lower temperatures. As an illustration of the efficiency of the photometric classification and effective temperature scale, the C/O ratios and the Merrill-Sanford (M-S) band intensities are investigated. It is shown that the maximum value, mean value and dispersion of C/O increase along the photometric CV-sequence, i.e. with decreasing effective temperature. The M-S bands of SiC2 are sho...

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“…We use a Julian Date of last maximum brightness T 0 = 2 453 190 days, a period P = 430 days (as in Wittkowski et al 2007), and the distance of 480 pc ± 120 pc from van . The broadband near-infrared K UD angular diameter of S Ori has been measured by van Belle et al (1996), Millan-Gabet et al (2005, and Boboltz & Wittkowski (2005) to values between 9.6 mas and 10.5 mas at different phases. Joint VLTI/MIDI and VLBA/SiO maser observations by Wittkowski et al (2007) have shown that S Ori exhibits significant phase-dependencies of the atmospheric extension and dust shell parameters with photospheric angular diameters between 7.9 mas and 9.7 mas.…”

Section: Introductionmentioning

confidence: 99%

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

Wittkowski¹,

Boboltz

Driebe

et al. 2008

A&A

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Aims. We present J, H, K spectrally dispersed interferometry with a spectral resolution of 35 for the Mira variable S Orionis. We aim at measuring the diameter variation as a function of wavelength that is expected due to molecular layers lying above the continuumforming photosphere. Our final goal is a better understanding of the pulsating atmosphere and its role in the mass-loss process. Methods. Visibility data of S Ori were obtained at phase 0.78 with the VLTI/AMBER instrument using the fringe tracker FINITO at 29 spectral channels between 1.29 µm and 2.32 µm. Apparent uniform disk (UD) diameters were computed for each spectral channel. In addition, the visibility data were directly compared to predictions by recent self-excited dynamic model atmospheres. Results. S Ori shows significant variations in the visibility values as a function of spectral channel that can only be described by a clear variation in the apparent angular size with wavelength. The closure phase values are close to zero at all spectral channels, indicating the absence of asymmetric intensity features. The apparent UD angular diameter is smallest at about 1.3 µm and 1.7 µm and increases by a factor of ∼1.4 around 2.0 µm. The minimum UD angular diameter at near-continuum wavelengths is Θ UD = 8.1 ± 0.5 mas, corresponding to R ∼ 420 R . The S Ori visibility data and the apparent UD variations can be explained reasonably well by a dynamic atmosphere model that includes molecular layers, particularly water vapor and CO. The best-fitting photospheric angular diameter of the model atmosphere is Θ Phot = 8.3 ± 0.2 mas, consistent with the UD diameter measured at near-continuum wavelengths. Conclusions. The measured visibility and UD diameter variations with wavelength resemble and generally confirm the predictions by recent dynamic model atmospheres. These size variations with wavelength can be understood as the effects from water vapor and CO layers lying above the continuum-forming photosphere. The major remaining differences between observations and model prediction are very likely due to an imperfect match of the phase and cycle combination between observation and available models.

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Angular Size Measurements of 18 Mira Variable Stars at 2.2 (?)

Cited by 101 publications

References 0 publications

Warm water vapor envelope in Mira variables and its effects on the apparent size from the near-infrared to the mid-infrared

Warm water vapor envelope in Mira variables and its effects on the apparent size from the near-infrared to the mid-infrared

The effective temperatures of carbon-rich stars

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

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