emamajek on 15-Mar-2019 05:40:43 GMT about BD+57 793
2013MNRAS.428..182B reports a companion to the exoplanet host star XO-3 at separation 6.059+-0.047 arcseconds, PA = 296.7+-0.3 deg, with delta(z')=8.22+-0.23 and delta(i')=8.57+-0.24 mag, and the pair appears in the Washington Double Star catalog as WDS J04219+5749 or BRG 34.
2013MNRAS.428..182B
reports: "A very faint companion candidate (Delta(z)≈8.2) was found at a large angular separation (ρ≈ 6 arcsec) from the TEP host star XO-3. The (i−z) colour places the companion candidate at a distance of >~860 pc if it is a main-sequence star, and it is hence likely to be a non-related background object. Another possibility is that the companion candidate is a white dwarf at the approximately same distance as the TEP host. The colours and brightness are consistent with a white dwarf with Teff≈4000 K, corresponding to a very hydrogen-deficient white dwarf with cooling age 4 Gyr according to cooling curves by Chen & Hansen (2011). The age of XO-3 has been estimated to be 2.82+0.58−0.82 Gyr (Winn et al. 2008), and it is thus compatible with a 4.6-Gyr white dwarf at 3σ. While the candidate is unlikely to be a coeval comoving white dwarf companion, we cannot exclude the possibility until future proper motion observations can be performed."
The pair are resolved in Gaia DR2:
XO-3 = Gaia DR2 470650560777348352
RA, Dec = 065.46958140194, +57.81720947636 (ICRS, epoch 2015.5)
plx = 4.6660 +- 0.0588 mas
pmRA, pmDec = -2.516, 4.003 (+-0.083, 0.085) mas/yr
G = 9.7389 +- 0.0003
companion = Gaia DR2 470650457698311296
RA, Dec = 065.46674040736, +57.81796486495 (ICRS, epoch 2015.5)
plx = -0.4525 +- 0.4924 mas
pmRA, pmDec = 1.421, -1.091 (+-1.518, 0.657) mas/yr
G = 18.4502 +- 0.0084
However, the companion's parallax differs at the 10.3sigma level from that of XO-2, and the proper motion components differ at the 2.6 and 7.7sigma level, which would seem to support the idea that it is a background star. At this point, the Gaia DR2 astrometry do not seem to corroborate the companion being physically associated with XO-2.
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