We present near-infrared speckle interferometry of the OH/IR star OH 104.9+2.4 in the $K'$ band obtained with the 6m telescope of the Special Astrophysical Observatory (SAO). At a wavelength of λ = 2.12 micron the diffraction-limited resolution of 74 mas was attained. The reconstructed visibility reveals a spherically symmetric, circumstellar dust shell (CDS) surrounding the central star. The visibility function shows that the stellar contribution to the total flux at λ = 2.12 micron is less than ~50%, indicating a rather large optical depth of the CDS. The azimuthally averaged 1-dimensional Gaussian visibility fit yields a diameter of 47 +/- 3 mas (FHWM), which corresponds to 112 +/- 13 AU for an adopted distance of D = 2.38 +\- 0.24 kpc. To determine the structure and the properties of the CDS of OH 104.9+2.4, radiative transfer calculations using the code DUSTY were performed to simultaneously model its visibility and the spectral energy distribution (SED). We found that both the ISO spectrum and the visibility of
OH 104.9+2.4 can be well reproduced by a radiative transfer model with an effective temperature Teff = 2500 +/- 500 K of the central source, a dust temperature Tin = 1000 +/- 200 K at the inner shell boundary Rin = 9.1 Rstar = 25.4 AU, an optical depth tau = 6.5 +/- 0.3 at 2.2 micron, and dust grain radii ranging from amin = 0.005 +/- 0.003 micron to amax = 0.2 +/- 0.02 micron with a power law with index -3.5. It was found that even minor changes in amax
have a major impact on both the slope and the curvature of the visibility function, while the SED shows only minor changes. Our detailed analysis demonstrates the potential of dust shell modeling constrained by both the SED and visibilities.
We present near-infrared (JHK) bispectrum speckle-interferometry monitoring of IRC+10216 obtained with the SAO 6m telescope. The present speckle observations covering baselines up to 6m provide important complementary informations for future long-baseline interferometry. To disentangle the apparent motions of the various IRC+10216 components and to reveal the location of the central star, future high-resolution observations are of utmost value for the interpretation of this astrophysical key object. The J-, H-, and K-band resolutions of our speckle observations are 50 mas, 56 mas, and 73 mas, resp. The K-band observations cover 8 different epochs from 1995 to 2001 and show the dynamical evolution of the dust shell which consists of several compact components within a 200 milli-arcsecond radius. Our recent two-dimensional radiative transfer modelling has shown that the central star is probably not located at the brightest dust-shell component A but at the position of the northern component B. The bright and compact component A is the southern lobe of a bipolar structure. The changes of the dust-shell structure can be related to corresponding changes of the optical depth caused, for instance, by mass-loss variations. The present observations are consistent with the predictions of hydrodynamical models that enhanced dust formation takes place on a timescale of several pulsational cycles.
We present bispectrum speckle interferometric observations of the deeply embedded protostellar outflow source S140 IRS1. Using the SAO 6 m telescope, we obtained a K-band image with diffraction-limited resolution of 76 mas, which is the highest resolution image of a young outflow source ever obtained in the infrared. Our image shows the circumstellar environment of S140 IRS1 in unprecedented detail
and suggests that the central source is marginally resolved with a FWHM diameter of approximately 20 mas (approx 20 AU). The dominant feature is a bright extended and very clumpy structure pointing away from the central source in exactly the same direction as the blue-shifted CO outflow lobe. We interprete this feature as the clumpy inner surface of a partially evacuated cavity in the circumstellar envelope around IRS1, which has been excavated by the strong outflow from IRS1. In addition, we find several arc-like structures north-east of IRS 1, extended diffuse emission south of IRS 1, and four new point sources. The diffuse and fragmentary structures close to IRS 1 appear to trace circumstellar material swept up by energetic outflows. In combination with molecular line emission maps from the literature, our image provides direct confirmation that two distinct bipolar outflow systems continue to be driven from IRS 1 on scales between 3" and 100". Our speckle observations provide important complementary information for future long-baseline interferometric observations, for example with the LBT.
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