An Imaging Search for Circumstellar Companions of Sirius B Miles Lucas1, Michael Bottom1, Garreth Ruane2, Sam Ragland3 Why study Sirius B? • Little is known about planetary systems around evolved hosts; we are interested in looking for second-generation companions that form or migrate after the violent RGB and AGB phases • Sirius B is close, which lets us probe sub-AU regions without coronagraphy. It is relatively dim from white dwarf cooling, decreasing the contrast required to image a giant planet. Lastly, it is young (225 Myr), which means giant planets will still be bright from their latent formation heat. • Sirius B is well-characterized: especially its mass, age, and astrometry- reducing uncertainties of companion properties Observations • We took direct images over three epochs in 2020 using Keck/NIRC2 in L’-band (3.776 µm) and narrow FOV (10”x10”) • Sirius A is so bright that diffraction was present in the Sirius B FOV, stalling the AO loop and ruining the coronagraphic pointing algorithm (QACITS) • We were able to close the AO loop by targeting Sirius A using a narrow (~10 nm) laser-line filter in front of the WFS to avoid saturation. We then guided off-axis to Sirius B • We set the field rotator to track the pupil, enabling angular differential imaging (ADI) 0 200 400 x 0 100 200 300 400 500 y 1500 1000 500 0 500 1000 1500 1500 1000 500 0 500 1000 1500 spider diffraction spike from Sirius A 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 projected separation [AU] 2 4 6 8 10 12 14 companion mass [MJ] mean uncertainty from age dynamical stability limit 0.1 0.2 0.3 0.4 0.5 0.6 0.7 separation [arcsec] 2020-02-04 2020-11-21 2020-11-28 model mass limit 0.1 0.2 0.3 0.4 0.5 0.6 0.7 separation [arcsec] Sensitivity Analysis ADI Analysis -2.0 -1.0 0.0 1.0 2.0 -2.0 -1.0 0.0 1.0 2.0 y [AU] median Epoch 2020-02-04 -2.0 -1.0 0.0 1.0 2.0 x [AU] median Epoch 2020-11-21 -2.0 -1.0 0.0 1.0 2.0 annular PCA(2) Epoch 2020-11-28 Results & Discussion • Consistent with previous results, we do not detect any companions around Sirius B • We improve on the sensitivity limits of Sirius B by reaching an average sensitivity of ~2 MJ in the speckle-limited regime (< 1 AU) down to 0.4 MJ in the background-limited regime (> 1 AU). • These sensitivities are the deepest and closest, yet, and only have ~0.1 MJ uncertainty due to Sirius B’s precise age • Future space-based observations can improve the mass sensitivities (if the challenges presented by Sirius A can be overcome), but would be limited by current planetary grid models Acknowledgements The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. 1. Repeatedly inject fake companions at different seperations with a fixed S/N (100) 2. Reduce the injected cube for each ADI algorithm and measure the S/N of the companion in the residual frame 3. Compute the 5σ detection limit in terms of contrast. Dashed curves correct for small-sample statistics 4. Convert the contrast curves to planetary masses using grid models (AMES/COND) 1. Pre-process data with typical ADI workflow: calibration, co-registration, cropping, and parallactic angle calculation 2. Using the following ADI algorithms (median, PCA, NMF, GreeDS), model the stellar PSF and subtract it from the data 3. Derotate and collapse the residual cube using a weighted sum 4. Calculate detection probability using S/N and STIM map; calculate sensitivity using contrast curves 5. Residuals from the best algorithm for each ep