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Astron. Astrophys. 353, L5-L8 (2000)

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2. Observations and continuum images

The observations were carried out in January and March 1998 with the IRAM 5-antenna interferometer at Plateau de Bure, France. Two configurations of the array were used with baselines up to 280 m. The antennae were equipped with SIS receivers operating simultaneously at the frequencies of the CO J=2-1 and J=1-0 lines (230.538 GHz and 115.271 GHz, respectively). The J=1-0 data reveal structure similar to that seen in the 2-1 line, but with a lower S/N ratio and lower angular resolution; it is also affected by nearby H38[FORMULA] emission (Bachiller et al. 1992), so our discussion focuses on the the 2-1 observations. Typical SSB system temperatures were 300 K at this wavelength. Correlator channels free of line emission were combined to measure the continuum with effective bandwidths of 320 MHz at 2.6 mm, and 640 MHz at 1.3 mm. The receiver bandwidths were calibrated using 3C273, and the phase and amplitude using J1923+210 and J2013+370. The final images were produced using natural weighting, and the clean beam at the CO 2-1 frequency is [FORMULA] (at P.A. 30o).

The left hand panels of Fig. 1 present the continuum observations of BD+30o3639. These maps show an elliptical, 6" [FORMULA]5" nebula with enhanced emission to the NW and the SE rims, similar to cm-wave maps obtained at the VLA (e.g., Kawamura & Masson 1996). The total flux at 2.6 mm is 0.41 Jy. The 1.3 mm interferometric data contain only [FORMULA] of the total flux of 0.40 Jy measured by Hoare et al. (1992) with a 19" beam. This total flux has been used to provide zero-spacing information for the map shown in Fig. 1. The continuum fluxes are consistent with free-free radiation. Incomplete uv sampling and limited S/N for the larger uv spacings at 1.3 mm, as well as the inhomogeneous distribution of the gas (Harrington et al. 1997), likely account for the clumpy structure observed in the 1.3 mm map.

[FIGURE] Fig. 1. Maps of BD +30o3639 in the 2.6 and 1.3 mm continuum and the CO 2-1 line. For each map the first contour and the contour intervals are: 5 mJy beam-1 (2.6 mm), 2.5 mJy beam-1 (1.3 mm), and 20 K km s-1 (CO 2-1). The cross marks the position of the central star, 19:34:45.23, +30:30:59.07 (J2000.0), and the ellipses indicate the clean beams. In the CO map, solid and dashed contours denote blue and red shifted emission, respectively; the spectra of the peaks are shown to the right, smoothed to 5 km s-1.

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© European Southern Observatory (ESO) 2000

Online publication: December 17, 1999