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Register a new userInterferometric observations of the Mira star o Ceti with the VLTI/VINCI instrument in the near-infrared
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H.C. Woodruff
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We present K-band commissioning observations of the Mira star prototype o Cet obtained at the ESO Very Large Telescope Interferometer (VLTI) with the VINCI instrument and two siderostats. The observations were carried out between 2001 October and December, in 2002 January and December, and in 2003 January. Rosseland angular radii are derived from the measured visibilities by fitting theoretical visibility functions obtained from center-to-limb intensity variations (CLVs) of Mira star models (Bessel et al. 1996, Hofmann et al. 1998, Tej et al. 2003). Using the derived Rosseland angular radii and the SEDs reconstructed from available photometric and spectrophotometric data, we find effective temperatures ranging from T_eff=3192 +/- 200 K at phase phi=0.13 to 2918 +/- 183 K at phi=0.26. Comparison of these Rosseland radii, effective temperatures, and the shape of the observed visibility functions with model predictions suggests that o Cet is a fundamental mode pulsator. Furthermore, we investigated the variation of visibility function and diameter with phase. The Rosseland angular diameter of o Cet increased from 28.9 +/- 0.3 mas (corresponding to a Rosseland radius of 332 +/- 38 R_sun for a distance of D=107 +/- 12 pc) at phi=0.13 to 34.9 +/- 0.4 mas (402 +/- 46 R_sun) at phi=0.4. The error of the Rosseland linear radius almost entirely results from the error of the parallax, since the error of the angular diameter is only approximately 1 %.
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We present a near-infrared spectro-interferometric observation of the non-Mira-type, semiregular asymptotic giant branch star SW Vir. Our aim is to probe the physical properties of the outer atmosphere with spatially resolved data in individual molecular and atomic lines. We observed SW Vir in the spectral window between 2.28 and 2.31 micron with the near-infrared interferometric instrument AMBER at ESOs Very Large Telescope Interferometer (VLTI). Thanks to AMBERs high spatial resolution and high spectral resolution of 12000, the atmosphere of SW Vir has been spatially resolved not only in strong CO first overtone lines but also in weak molecular and atomic lines of H2O, CN, HF, Ti, Fe, Mg, and Ca. Comparison with the MARCS photospheric models reveals that the star appears larger than predicted by the hydrostatic models not only in the CO lines but also even in the weak molecular and atomic lines. We found that this is primarily due to the H2O lines (but also possibly due to the HF and Ti lines) originating in the extended outer atmosphere. Although the H2O lines manifest themselves very little in the spatially unresolved spectrum, the individual rovibrational H2O lines from the outer atmosphere can be identified in the spectro-interferometric data. Our modeling suggests an H2O column density of 10^{19}--10^{20} cm^{-2} in the outer atmosphere extending out to ~2 Rstar. Our study has revealed that the effects of the nonphotospheric outer atmosphere are present in the spectro-interferometric data not only in the strong CO first overtone lines but also in the weak molecular and atomic lines. Therefore, analyses of spatially unresolved spectra, such as for example analyses of the chemical composition, should be carried out with care even if the lines appear to be weak.
We present the first near-infrared K-band long-baseline interferometric measurement of the prototype Seyfert 2 galaxy NGC 1068 with resolution lambda/B ~ 10 mas obtained with the Very Large Telescope Interferometer (VLTI) and the two 8.2m Unit Telescopes UT2 and UT3. The adaptive optics system MACAO was employed to deliver wavefront-corrected beams to the K-band commissioning instrument VINCI. A squared visibility amplitude of 16.3 +/- 4.3 % was measured for NGC 1068 at a sky-projected baseline length of 45.8 m and azimuth angle 44.9 deg. This value corresponds to a FWHM of the K-band intensity distribution of 5.0 +/- 0.5 mas (0.4 +/- 0.04 pc) at the distance of NGC 1068) if it consists of a single Gaussian component. Taking into account K-band speckle interferometry observations (Wittkowski et al. 1998; Weinberger et al. 1999; Weigelt et al. 2004), we favor a multi-component model for the intensity distribution where a part of the flux originates from scales clearly smaller than about 5 mas (<0.4 pc), and another part of the flux from larger scales. The K-band emission from the small (< 5 mas) scales might arise from substructure of the dusty nuclear torus, or directly from the central accretion flow viewed through only moderate extinction.
The mechanism of mass loss in late evolutionary stages of low- and intermediate-mass stars is not yet well understood. Therefore, it is crucial to study the dynamics of the region within a few stellar radii, where the wind acceleration is considered to take place. We present three-dimensional diagnosis of the atmospheric dynamics of the closest asymptotic giant branch (AGB) star R Dor from the low photospheric layers to the extended outer atmosphere--for the first time for a star other than the Sun. The images reconstructed with a spatial resolution of 6.8 mas--seven times finer than the stars angular diameter of 51.2 mas in the continuum--using the AMBER instrument at the Very Large Telescope Interferometer show a large, bright region over the surface of the star and an extended atmosphere. The velocity-field maps over the stars surface and atmosphere obtained from the Mg and H2O lines near 2.3 micron forming at atmospheric heights below ~1.5 stellar radii show little systematic motion beyond the measurement uncertainty of 1.7 km/s. In marked contrast, the velocity-field map obtained from the CO first overtone lines reveals systematic outward motion at 7--15 km/s in the extended outer atmosphere at a height of ~1.8 stellar radii. Given the detection of dust formation at ~1.5 stellar radii, the strong acceleration of material between ~1.5 and 1.8 stellar radii may be caused by the radiation pressure on dust grains. However, we cannot yet exclude the possibility that the outward motion may be intermittent, caused by ballistic motion due to convection and/or pulsation.
The prototypical Mira variable, $o$ Cet (Mira), has been observed as a Science Verification target in the 2014 ALMA Long Baseline Campaign with a longest baseline of 15 km. ALMA clearly resolves the images of the continuum and molecular line emission/absorption at an angular resolution of ~30 mas at 220 GHz. We image the data of the $^{28}$SiO v=0, 2 $J$=5-4 and H$_2$O $ u_2$=1 $J(K_a,K_c)$=5(5,0)-6(4,3) transitions and extract spectra from various lines-of-sight towards Miras extended atmosphere. In the course of imaging, we encountered ambiguities in the resulting images and spectra that appear to be related to the performance of the CLEAN algorithm. We resolve Miras millimetre continuum emission and our data are consistent with a radio photosphere with a brightness temperature of 2611$pm$51 K, in agreement with recent results obtained with the VLA. We do not confirm the existence of a compact region (<5 mas) of enhanced brightness. We derive the gas density, kinetic temperature, molecular abundance and outflow/infall velocities in Miras extended atmosphere by modelling the SiO and H$_2$O lines. We find that SiO-bearing gas starts to deplete beyond 4$R_star$ and at a kinetic temperature of $lesssim$600 K. The inner dust shells are probably composed of grain types other than pure silicates. During this observation, Miras atmosphere generally exhibited infall motion, with a shock front of velocity $lesssim$12 km/s outside the radio photosphere. The structures predicted by the hydrodynamical model CODEX can reproduce the observed spectra in astonishing detail; while some other models fail when confronted with the new data. Combined with radiative transfer modelling, ALMA successfully demonstrates the ability to reveal the physical conditions of the extended atmospheres and inner winds of AGB stars in unprecedented detail. (Abbreviated abstract)
Context : The properties of the inner disks of bright Herbig AeBe stars have been studied with near infrared (NIR) interferometry and high resolution spectroscopy. The continuum and a few molecular gas species have been studied close to the central star; however, sensitivity problems limit direct information about the inner disks of the fainter T Tauri stars. Aims : Our aim is to measure some of the properties of the inner regions of disks surrounding southern T Tauri stars. Methods : We performed a survey with the PIONIER recombiner instrument at H-band of 21 T Tauri stars. The baselines used ranged from 11 m to 129 m, corresponding to a maximum resolution of 3mas (0.45 au at 150 pc). Results : Thirteen disks are resolved well and the visibility curves are fully sampled as a function of baseline in the range 45-130 m for these 13 objects. A simple qualitative examination of visibility profiles allows us to identify a rapid drop-off in the visibilities at short baselines in 8 resolved disks. This is indicative of a significant contribution from an extended contribution of light from the disk. We demonstrate that this component is compatible with scattered light, providing strong support to a prediction made by Pinte et al. (2008). The amplitude of the drop-off and the amount of dust thermal emission changes from source to source suggesting that each disk is different. A by-product of the survey is the identification of a new milli-arcsec separation binary: WW Cha. Spectroscopic and interferometric data of AK Sco have also been fitted with a binary and disk model. Conclusions : Visibility data are reproduced well when thermal emission and scattering form dust are fully considered. The inner radii measured are consistent with the expected dust sublimation radii. Modelling of AK Sco suggests a likely coplanarity between the disk and the binarys orbital plane
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