An Imaging Search for Post-main-sequence Planets of Sirius B

Abstract

We present deep imaging of Sirius B, the closest and brightest white dwarf, to constrain post-main-sequence planetary evolution in the Sirius system. We use Keck/NIRC2 in L' band (3.776 μm) across three epochs in 2020 using the technique of angular differential imaging. Our observations are speckle-limited out to 1 au and background-limited beyond. The 5σ detection limits from our best-performing epoch are 17-20.4 L' absolute magnitude. We consider multiple planetary formation pathways in the context of Sirius B's evolution to derive mass sensitivity limits, and achieve sub-Jupiter sensitivities at sub-astronomical unit separations, reaching 1.6-2.4 M _J at 0.5 au down to a sensitivity of 0.7-1.2 M _J at >1 au. Consistent with previous results, we do not detect any companions around Sirius B. Our strong detection limits demonstrate the potential of using high-contrast imaging to characterize nearby white dwarfs.