3 Results

The 1200 $\mu$m image of the $\beta ~ {\rm Pic}$ region is displayed in Fig. 2, where the displayed contours are chosen in compliance with Holland et al. (1998). The flux maximum, designated as feature A in the figure, is centered on the position of the star $\beta ~ {\rm Pic}$ (0 $^{\prime \prime }$, 0 $^{\prime \prime }$). At position angle 237$^{\circ}$ relative to A, an elongation of the emission in the NE-SW direction is discernable. For an assumed Gaussian source flux distribution, the deconvolved minor and major axes are $\le$10 $^{\prime \prime }$ and 26 $^{\prime \prime }$, respectively, the latter corresponding to 500 AU. The disk emission extends to at least 55 $^{\prime \prime }$ (1050 AU) in the SW direction. In addition, faint emission protrudes south toward a "blob'' at (-27 $^{\prime \prime }$, -44 $^{\prime \prime }$). This feature C, at position angle 211 $.\!\!^\circ$5, is 52 $^{\prime \prime }$ (1000 AU) distant from the star and is thus not (whether real or not) positionally coincident with the 850 $\mu$m-SW blob of Holland et al. 1998 at (-21 $^{\prime \prime }$, -26 $^{\prime \prime }$) and identified as B in Fig. 2, but we note the following important facts: (1) this faint emission, extending straight south, is also apparent in the 850 $\mu$m image, (2) as is evident in Fig. 2, the position angle to blob C coincides with that of the midplane of the $\beta ~ {\rm Pic}$ disk inferred from optical data (= 31 $.\!\!^\circ$5 + 180$^{\circ}$; Kalas & Jewitt 1995, Heap et al. 2000), and (3) faint dust scattered light in this direction has been observed far from the star (1450 AU, Larwood & Kalas 2001). Toward the NE, the scattering disk has been claimed to extend even further from the star, to 1835 AU.

An about $2\sigma$ feature at (+48 $^{\prime \prime }$, +32 $^{\prime \prime }$) and PA = 57$^{\circ}$ (1100 AU) is discernable in our image, but which would again be significantly offset from a similar blob at (+28 $^{\prime \prime }$, +25 $^{\prime \prime }$) in the 850 $\mu$m data. In order to assess the reality of these faint features we have divided the raw data into different portions and then applied the same reduction procedures to these subsamples. The result of this exercise indicates that the (+48 $^{\prime \prime }$, +32 $^{\prime \prime }$) feature is an artefact introduced by the noise, as it is not seen in all frames, whereas blob C is persistently present in the final sub-maps. The flux densities of both the $\beta ~ {\rm Pic}$ disk (A) and the SW features (B and C) are presented in Table 1. The result for the peak flux obtained by Chini et al. (1991) with a single element bolometer at the SEST at 1300 $\mu$m, viz. $24.9 \pm 2.6$ mJy/beam, is in agreement with our array value of $24.3 \pm 3.0$ mJy/beam at 1200 $\mu$m (cf. Fig. 3). The ratio of the peak flux A to that of blob C is $2.5 \pm 0.8$.