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Astron. Astrophys. 357, L61-L64 (2000)

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2. Observations and data reduction

Observations were carried out at the CFHT on January 29-31, 1997 and December 30, 1997 with the PUEO adaptive optics system equipped with the optical CCD camera STIS2 (pixel size: 0.061"). We used the following narrow-band filters: [O I ] ([FORMULA] 6305Å, [FORMULA] 28 Å), [S II ] (6735 Å, 51 Å), and adjacent continuum (6184 Å, 93 Å). The on-source accumulated times in [O I ](resp. [S II ]) are 900(1100) sec for RW Aur, 1260(630) sec for DG Tau, and 2100(3360) sec for CW Tau.

Individual images were corrected for cosmic ray events, bias and flat-field. Good quality images (core FWHM [FORMULA] 0.3") were selected then summed, after sub-pixel recentering. In RW Aur, a high contrast [S II ] image was obtained by combining short unsaturated exposures with longer core saturated ones according to the procedure in Close et al.   (1997). Dynamical ranges and core FWHM of the combined images before deconvolution are 6000-[FORMULA] and 0.16-0.22" respectively. Due to partial seeing correction in the optical (Strehl ratios of [FORMULA] 5%), strong psf wings are still present. To reduce their contribution, we further deconvolved each image by a high signal to noise estimate of the PSF (either a continuum image or a reference star selected to have similar -within 10%- core FWHM and strehl ratio) using the LUCY algorithm as implemented in the STSDAS/IRAF V2.11 package. The maximum number of iterations (typically 15 to 25) was determined by ensuring that the derived image characteristics (such as jet FWHM) did not change significantly with further deconvolutions. Deconvolved images have typical core FWHM of 0.1-0.13" and significantly improved Strehl ratios of 40-70%, corresponding to a factor 10 increase in dynamic range. Artifacts due to the deconvolution process were identified by comparing results obtained with different psfs. The reconstructed jet intensity distributions within [FORMULA] 0.4" (56 AU) of the strong central unresolved source are not reliable due to psf wing oscillations. Jet widths were computed from gaussian fitting of the transverse intensity profiles in the deconvolved frames. Continuum emission is unresolved in all our targets and has not been subtracted from the line images.

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© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000