2 Observations and data reduction

The field of PSR B0950+08 was observed on Jan. 21, 2001 with the wide field camera Suprime-Cam at the primary focus of the Subaru telescope. The Suprime-Cam (Miyazaki et al. 1998) is equipped with ten MIT/LL $2048 \times 4096$ CCDs arranged in a $5\times 2$ pattern to provide $34^{\prime} \times 27^{\prime}$ FOV with a pixel size on the sky of $0.201^{\prime\prime} \times 0.201^{\prime\prime}$. The pulsar was exposed in one of the CCD chips, si006s, with the gain = 1.17. Nine 600 s exposures were taken using the B filter with the bandpass close to the Johnson system. The mean seeing was about $0.7^{\prime\prime}$. The 2nd, 7th, and 9th exposures were removed from further consideration because of the problems with the telescope guiding system. The observational conditions for the rest six exposures are listed in Table 2.

Figure 1: Top Left a) 24 $^{\prime \prime }$ $\times$ 24 $^{\prime \prime }$ fragment of the Subaru 2001 image of the PSR B0950+08 field in the B band. Larger and smaller boxes show the FOV of the HST 1994 observations (see the right panel) and the borders of the bottom panel containing the pulsar, respectively. Right b) $7\hbox{$.\!\!^{\prime\prime}$ }4\times7\hbox{$.\!\!^{\prime\prime}$ }4$ HST 1994 image of the pulsar field. The pulsar counterpart and an extended object o1, both visible in the HST and Subaru images, are marked. The HST image is aligned with the Subaru image using o1 as a reference. The Subaru contour map is overlaid. The pulsar close vicinity, $\sim$ $0\hbox{$.\!\!^{\prime\prime}$ }9\times0\hbox{$.\!\!^{\prime\prime}$ }6$, with the closest Subaru contour and the radioposition at the epoch of the FOC observations marked by "+", is zoomed in the inset. Bottom c) 2 $^{\prime \prime }$ $\times$ 2 $^{\prime \prime }$ neighbourhood of the pulsar in the B band. The HST contour map is overlaid. It is shifted for the pulsar proper motion for 6.75 yr passed between the observations. The arrow points out the radio position of the pulsar at the epoch of the Subaru observations, its length corresponds to the pulsar shift due to the proper motion for 10 yr. The circle shows 1$\sigma$ uncertainty of the pulsar position in the Subaru image; "+" marks the center of the Gaussian fitted to the pulsar counterpart profile in this image.

The standard data reduction, including bias subtraction and flatfielding, was performed making use of the ccdproc task of the IRAF software. To combine the individual dithered images and to get rid of cosmic rays, as well as of a trace of an unknown minor object or a dust clump with an orbit close to the Earth, crossing our image E-W approximately 8 $^{\prime \prime }$ away of the pulsar position, we made use of the IRAF dither package. A fragment of the combined image of the pulsar field with the total integrated exposure time of 3600 s is shown in Fig. 1a.