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Astron. Astrophys. 361, L29-L32 (2000)

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2. Observations

The speckle interferograms were obtained with the 6 m telescope at the Special Astrophysical Observatory (SAO) in Russia on 19 September 1999. The data were recorded through a [FORMULA]-filter with a central wavelength of 2.165  µm and a bandwidth of 0.328  µm. 5552 speckle interferograms of S140 IRS1 and 5736 speckle interferograms of the reference stars HIP 110410 and HIP 110498 were taken with our Hawaii array speckle camera. The exposure time per frame was 150 ms, the pixel size was 27.0 mas and seeing was [FORMULA]. The images were reconstructed using the bispectrum speckle interferometry method (Weigelt 1977; Lohmann et al. 1983; Weigelt et al. 1991). The object power spectrum was determined with the speckle interferometry method (Labeyrie 1970). The bispectrum of each frame consisted of 100 million elements. The resulting image (Fig. 1, upper right) has a diffraction-limited resolution of 76 mas. In order to increase the SNR we also reconstructed an image with a reduced resolution of 130 mas (60% of the diffraction limit), which is shown in Fig. 1, upper left.

[FIGURE] Fig. 1. Upper left: Color representation of our 160 mas resolution K-band image of S140 IRS1 reconstructed by the bispectrum speckle interferometry method. Blue areas are [FORMULA] mag fainter, red areas (e.g. clumps C and D) are [FORMULA] mag fainter than the peak intensity. Upper right: Contour representation of the diffraction-limited 76 mas resolution K-band image with annotation; the contour level intervals are 0.3 mag, down to 7.9 mag difference relative to the peak intensity. The thin line marks the direction of the symmetry axis of the extended structure with a position angle of [FORMULA]; the thick arrows mark the directions of the red- and blue-shifted CO outflows (position angle [FORMULA]). Lower left: Color representation of the central part of the K-band image with overlaid polarization vectors (for details see Sect. 2) derived from the [FORMULA] data (left) and the [FORMULA] data (right). A [FORMULA] vector appears in the lower right corner for reference. In all images north is up and east is to the left.

The speckle polarimetry observations were carried out on 13 June 1998 using the SAO 6 m telescope, our two-beam polarimeter, and a NICMOS 3 camera. The data recording parameters were as follows: 2800 polarized object speckle frames and 2800 reference star (HIP 109981) frames recorded through a [FORMULA]m-filter with central wavelength / FWHM bandwidth of 2.110 µm / 0.192 µm, 2400 polarized object speckle frames and 2400 reference star (HIP 110498) frames recorded through a [FORMULA]-filter with central wavelength/FWHM bandwidth of 2.165 µm / 0.328 µm, exposure time per frame 150 ms, pixel size 30.1 mas, field of view [FORMULA] (256 [FORMULA] 256 pixels), and seeing [FORMULA]. Our 2-beam speckle polarimeter has the following standard design: achromatic K-band collimator objective to obtain a parallel beam behind the f/4 primary focus of the SAO 6 m telescope, rotatable [FORMULA] plate for rotating the polarization direction, Wollaston prism to obtain two polarized images separated by [FORMULA] on the detector, and a second achromatic K-band objective behind the [FORMULA] plate and Wollaston prism (more technical details of the speckle polarimeter will be described elsewhere). Polarized speckle interferograms were recorded at the four [FORMULA] plate positions [FORMULA], [FORMULA], [FORMULA], and [FORMULA]. For each of these four data sets and the corresponding reference star data sets, polarized images were reconstructed using the bispectrum speckle interferometry method. In each of the four reconstructed images two images of the object were obtained which were polarized parallel and perpendicular to the separation vector of the two images. From these polarized images polarization maps were reconstructed using the standard technique (see e.g. Whitney et al. 1997 and references therein). In order to improve the SNR of the images, the resolution was reduced to 280 mas. In Fig. 1 (lower left) polarization vectors are plotted at the positions where the SNR of the degree of polarization (derived by splitting the data sets) is better than 5 and the error of the polarization vectors is smaller than [FORMULA].

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© European Southern Observatory (ESO) 2000

Online publication: October 2, 2000