emamajek on 25-Mar-2026 08:34:30 GMT about * alf Aql
Several of the 'companions' for Altair in the Washington Double Star catalog (WDS J19508+0852 entries D, E, F, G) either do not yet have entries in SIMBAD, or have entries that are not yet matched to Altair's WDS entry. Unsurprisingly, all appear to be unrelated background stars.
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WDS J19508+0852D (from WDS entry for DAL 27 AD) was listed in Daley 2006 (JDSO, 2, 44; http://www.jdso.org/volume2/number2/Daley1_correction.pdf). With respect to Altair the companion had mag=11.7, PA=95.6deg, sep=32.12" (epoch 2005.838). A later observation by Daley (http://www.jdso.org/volume5/number3/Daley.pdf) had it at PA=98.1deg, sep=31.2" (epoch 2008.800). Malkov (2016; J/BaltA/25/49/ilb_new) estimated the postion of D as RA,Dec = 297.70385, +08.86675. The only star bright enough in the vicinity that matches the brightness and relative position to Altair described for "D" is IDed as:
WDS J19508+0852D = Gaia DR2 4298621664638734592 = Gaia DR3 4298621664638734592 = URAT1 495-521293 = TIC 1906598409
Gaia DR3 position (epoch 2016): 297.70587685490 +08.86802737294
Gmag=12.42, synthetic Vmag=12.72.
The tiny proper motion (pmRA, pmDec = -0.3, -1.2 mas/yr) and parallax (0.48 mas) in Gaia DR3 show WDS J19508+0852D to be a distant background star unrelated to Altair.
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WDS J19508+0852E (from WDS entry for SMR 5 AE) is listed as being an 11th mag star at PA=357deg, sep 157.3" in epoch 2000 compared to Altair, and at final reported epoch 2019 PA=351deg, sep=151.7". A star that well matches this description is found in the Gaia DR3 catalog at sep=157.1" PA=356.4deg from the epoch 2000 position for Altair:
WDS J19508+0852E = Gaia DR3 4298623520076617728 = Gaia DR2 4298623520076617728 = Gaia DR1 4298623515768417536 = UCAC4 495-118188 = URAT1 495-521230 = TIC 408848568 = WISE J195046.33+085442.9 = 2MASS J19504635+0854430
Gaia DR3 position (epoch 2016): 297.69307357668 +08.91188051063
Gmag=10.44, synthetic Vmag=10.77.
The small proper motion (pmRA, pmDec = -6.6, -22.4 mas/yr) and parallax (1.39 mas) are consistent with WDS J19508+0852E being a distant background star unrelated to Altair.
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WDS J19508+0852F (from WDS entry SMR 5 AF) is listed as being mag=10.3, with initial position relative to Altair of PA=47deg, sep=303.7" (epoch 2000) and the most recent position reported at PA=48deg, sep=292.4" (epoch 2015). This is easily cross-IDed with HD 187716 = Gaia DR3 4298623416997887232 (Gmag=12.58), which relative to Altair's epoch 2000.0 position is at sep=303.4" PA=47.0deg.
WDS J19508+0852F = HD 187716 = BD+08 4239 = Gaia DR3 4298623416997887232 (and numerous others)
The star's small proper motion (pmRA, pmDec = -1.35, -6.22 mas/yr) and parallax (1.51 mas) in Gaia DR3 suggest that F is a background star unrelated to Altair.
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WDS J19508+0852G (from WDS entry for GMC 5 AG) is listed in WDS with mag=13.0 and initial position with respect to Altair at epoch 2000 of PA=119deg, sep=189.4", and at final epoch 2012 PA=121deg, sep=185.1". Querying Gaia DR3 around the epoch 2000 position for Altair, one finds a good match in Gaia DR3 4298620633858473344 at PA=118.8deg, sep=189.24". The star does not yet have a SIMBAD entry:
WDS J19508+0852G = UCAC4 495-118297 = URAT1 495-521488 = Gaia DR1 4298620629550367232 = Gaia DR2 4298620633858473344 = Gaia DR3 4298620633858473344
Gaia DR3 position (epoch 2016): 297.74243501000 +8.84297593335
Gmag=11.63, synthetic Vmag=12.08
The small parallax (0.64mas) and proper motion (pmRA, pmDec = 1.9, 1.6 mas/yr) in Gaia DR3 are consistent with it being yet another distant background star unrelated to Altair.
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