A POSSIBLE COMPANION TO PROXIMA-CENTAURI

We report Hubble Space Telescope observations that provide evidence fo r a companion to Proxima Centauri (G1 551), the closest star to the Su n. Data acquired with the Faint Object Spectrograph (FOS), used as a c oronagraphic camera, show excess light that can be interpreted as bein g from a substellar object within 0.'' 5 of Proxima Cen. Two observati ons of Proxima Cen separated by 103 days indicate a point source (or a feature) superposed on the wing of the point-spread function in the F OS images. This feature moves relative to the aperture, and on the pla ne of the sky. Comparisons with other FOS images of stars acquired usi ng the coronagraphic mode reveal no comparable features or evidence th at this feature can be explained by any instrumental anomaly. If this feature denotes a companion to Proxima Cen, it has an apparent separat ion corresponding to similar to 0.5 AU at Proxima Cen and is approxima te to 7 mag fainter than Proxima Cen in the bandpass of the FOS red de tector. The small apparent separation could result from a highly eccen tric orbit, which could project a close companion. Alternately, the sm all separation could imply a short (similar to 1 yr) period. Further c oronagraphic observations, using the Space Telescope Imaging Spectrogr aph, the Near-Infrared Camera and Multiobject Spectrometer, or some ot her instrumentation, are needed to verify this tentative result.