Piercing the glare: a direct imaging search for planets in the Sirius system

Astrometric monitoring of the Sirius binary system over the past century has yielded several predictions for an unseen third system component, the most recent one suggesting a lsim50 M Jup object in a ~6.3 year orbit around Sirius A. Here we present two epochs of high-contrast imaging observations performed with Subaru IRCS and AO188 in the 4.05 μm narrowband Br α filter. These data surpass previous observations by an order of magnitude in detectable companion mass, allowing us to probe the relevant separation range down to the planetary-mass regime (6-12 M Jup at 1'', 2-4 M Jup at 2'', and 1.6 M Jup beyond 4''). We complement these data with one epoch of M-band observations from MMT/AO Clio, which reach comparable performance. No data set reveals any companion candidates above the 5σ level, allowing us to refute the existence of Sirius C as suggested by the previous astrometric analysis. Furthermore, our Br α photometry of Sirius B confirms the lack of an infrared excess beyond the white dwarf's blackbody spectrum. Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan, and at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution