emamajek on 19-Aug-2019 17:37:48 GMT about
While HD 20781 has two Gaia DR2 counterparts (separation 0".416, delta(G)=0.0093 mag), and has preliminarily been assigned two entries in SIMBAD ("HD 20781A" = Gaia DR2 5060105892897388288, "HD 20781B" = Gaia DR2 5060105897195702656), the former entry has a Dup=1 "duplicate" flag, and there is NO corroborating evidence for a close <1" stellar companion to HD 20781:
* No sign of proper motion acceleration between Hipparcos and Gaia DR2 epochs (Vtan(anomaly = 12.91+-21.76 m/s; Kervella+2017; 2019A&A...623A..72K).
* No sign of companion in speckle imaging that should have detected a stellar companion: speckle imaging taken by Tokovinin+2015 (2015AJ....150...50T) at epoch 2014.7690 (not far from that of Gaia DR2, 2015.5), which was sensitive to delta(I) = 3.04 mag at separation 0.045" to delta(I)=4.71 mag at 1".
* No sign of additional stellar companion in precise Doppler radial velocity data: RV data is well fit by 4-planet system (K amplitudes 0.9-2.6 m/s) with no long-term acceleration trend over a ~4000 day baseline (Udry+2019 2019A&A...622A..37U; see velocities catalogued by Soubiran+2018; 2018A&A...616A...7S).
* No sign of spectroscopic binarity in high S/N, high-resolution (R=40k) spectroscopy (Mack et al. 2014;
2014ApJ...787...98M
).
Note that HD 20781 does appear to be a wide (253" separation) physical (common proper motion, parallax, radial velocity) companion to HD 20782 (WDS J03201-2851).
So SIMBAD entry for HD 20781A might be worth subsuming into HD 20781, removing any reference to an "A" component, and HD 20781B should probably be removed (with a note attached to HD 20781 that Gaia DR2 5060105897195702656 may be duplicate entry).
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