emamajek on 24-Aug-2022 07:10:53 GMT about * alf Crv
alf Crv (Alchiba, HD 105452) has a ~3" binary companion reported and analyzed by Scholz (2021,
2021RNAAS...5...40S
) and catalogued as a common proper motion companion by Kervella (2022, 2022A&A...657A...7K). Scholz (2021) estimates the companion to be M4V type and Kervella (2022) estimates the companion mass to be ~0.14 Msun. The binary does not appear yet in WDS. This new nearby binary companion to a bright, nearby star probably deserves a separate SIMBAD entry.
Alchiba A = Gaia DR3 3489338019475637760 (Gmag=3.947)
RA, Dec = 182.10387983595 -24.72905347553 (ICRS, epoch 2016.0)
pmRA, pmDec = 96.976+-0.177, -40.023+-0.211 mas/yr
Alchiba B = Gaia DR3 3489338019474046720 (Gmag=11.967)
RA, Dec = 182.10297084694 -24.72926444101 (ICRS, epoch 2016.0)
pmRA, pmDec = 23.990+-0.285, -59.662+-0.445 mas/yr
Separation 3".0678+-0".0003, Position angle 255.67 deg.
delta(pmRA) = -72.986+-0.335 mas/yr
delta(pmDec) = -19.639+-0.492 mas/yr
At distance d=14.96835 pc (2021AJ....161..147B)
=>
separation = 45.9194 au
delta(Vtan,RA) = -5.179+-0.024 km/s
delta(Vtan,Dec) = -1.394+-0.035 km/s
delta(Vtan) = 5.363+-0.042 km/s
So despite the large mismatch in proper motions, the difference in tangential velocity is reasonable for a stellar binary.
Gliese+1991 (V/70A/catalog) flags Alchiba (Gl 455.3) as a spectroscopic binary, and the Bright Star Catalog 5th edition (Hoffleit+1991 V/50/catalog) flags it "V" for variable radial velocity. From analysis of 20 RV measurements, Holmberg 2007 (V/117A/newcat) and Medeiros+2014 (2014A&A...561A.126D) estimate the probability that the RV of Alchiba is constant at P=0.007 and P=0.011, respectively.
Kervella+2019 analysis of the Hipparcos and Gaia EDR3 astrometry found that Alchiba was subject to a tangential velocity anomaly of 93.67+-19.55 m/s between Hipparcos and Gaia, with a position angle of the velocity anomaly of PA = 258.80+-9.47 deg. This dynamically predicted PA is in perfect agreement with the measured PA using the Gaia DR3 mean epoch positions (PA = 255.67 deg).
The agreement in parallax, RV variability, SB flag, and agreement between the dynamically predicted PA and astrometrically measured PA, are all consistent with the interpretation that the companion at 3" separation is physically related with Alchiba.
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