A coronagraphic survey for companions of stars within 8 parsecs

We present the technique and results of a survey of stars within 8 pc of th e Sun with declinations delta > -35 degrees (J2000.00). The survey, designe d to find without color bias faint companions, consists of optical coronagr aphic images of the 1' field of view centered on each star and infrared dir ect images with a 32 " field of view. The images were obtained through the optical Gunn r and z filters and the infrared J and K filters. The survey a chieves sensitivities up to 4 absolute magnitudes fainter than the prototyp e brown dwarf, Gliese 229B. However, this sensitivity varies with the seein g conditions, the intrinsic brightness of the star observed, and the angula r distance from the star. As a result, we tabulate sensitivity limits for e ach star in the survey. We used the criterion of common proper motion to di stinguish companions and to determine their luminosities. In addition to th e brown dwarf Gl 229B, we have identified six new stellar companions of the sample stars. Since the survey began, accurate trigonometric parallax meas urements for most of the stars have become available. As a result, some of the stars we originally included should no longer be included in the 8 pc s ample. In addition, the 8 pc sample is incomplete at the faint end of the m ain sequence, complicating our calculation of the binary fraction of brown dwarfs. We assess the sensitivity of the survey to stellar companions and t o brown dwarf companions of different masses and ages.