HD 202908

HD 202908, also known as HIP 105200, is a triple star located in the equatorial constellation Equuleus. It has an apparent magnitude of 7.01,^[17] making it readily visible in binoculars but not to the naked eye. When resolved, the components have apparent magnitudes of 7.25 and 8.87 respectively.^[2] The system is located relatively close at a distance of 169 light years based on Gaia DR3 parallax measurements^[9] and it is receding with a heliocentric radial velocity of 6.24 km/s.^[8]

HD 202908

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Equuleus
A
Right ascension	21h 18m 34.85s[1]
Declination	+11° 34′ 08.2″[1]
Apparent magnitude (V)	7.25±0.03[2]
B
Right ascension	21h 18m 34.80s[1]
Declination	+11° 34′ 08.0″[1]
Apparent magnitude (V)	8.87±0.14[2]
Characteristics
Spectral type	G0 V (combined)[3]
U−B color index	+0.07[4]
B−V color index	+0.56[4]
Aa
Spectral type	F9 V[5] or G1 V[6]
Ab
Spectral type	G0 V[5] or G2 V[6]
B
Spectral type	G1.5 V[5] or G6 V[7]
Astrometry
Radial velocity (Rv)	6.24±0.04[8] km/s
Proper motion (μ)	RA: +29.213 mas/yr[9] Dec.: −49.564 mas/yr[9]
Parallax (π)	19.3447±0.0543 mas[9]
Distance	168.6 ± 0.5 ly (51.7 ± 0.1 pc)
A
Absolute magnitude (MV)	+3.73±0.13[2]
B
Absolute magnitude (MV)	+5.35±0.19[2]
Orbit[10]
Primary	A
Companion	B
Period (P)	28,685±173 d
Semi-major axis (a)	0.5177±0.0046″
Eccentricity (e)	0.8651±0.0008
Inclination (i)	100.36±0.16°
Longitude of the node (Ω)	255.03±0.17°
Periastron epoch (T)	24,468,123±3 JD
Argument of periastron (ω) (secondary)	171.9±0.3°
Semi-amplitude (K1) (primary)	6.13±0.07 km/s
Semi-amplitude (K2) (secondary)	13.95±0.09 km/s
Orbit[10]
Primary	Aa
Companion	Ab
Period (P)	3.9660465±0.0000015 d
Eccentricity (e)	0.0033±0.0008
Argument of periastron (ω) (secondary)	271±13°
Semi-amplitude (K1) (primary)	66.03±0.06 km/s
Semi-amplitude (K2) (secondary)	69.69±0.06 km/s
Details
The System
Metallicity [Fe/H]	−0.04[11] dex
Age	6.4±0.7[12] Gyr
The A Subystem
Temperature	6,100±150[13] K
Rotational velocity (v sin i)	10[14] km/s
Aa
Mass	1.14[15] M☉
Radius	1.06±0.08[13] R☉
Luminosity	1.41+0.15 −0.14[13] L☉
Ab
Mass	1.08[15] M☉
Radius	0.97±0.08[13] R☉
Luminosity	1.16+0.13 −0.11[13] L☉
B
Mass	0.97[15] M☉
Radius	0.91±0.08[13] R☉
Luminosity	0.84+0.09 −0.08[13] L☉
Temperature	5,703±1,090[2] K
Rotational velocity (v sin i)	9[14] km/s
Other designations
AG+11°2644, BD+10°4514, GC 29812, HD 202908, HIP 105200, SAO 107015, ADS 14839AB, CCDM J21186+1134AB, WDS J21186+1134AB[16]
Database references
SIMBAD	The system
	A
	B

Stellar system

Aa

Period = 3.966 d

Ab

Separation = 0.5″ Period = 78 y

B

Hierarchy of orbits in the HD 202908 system^[5]

The system was first observed by astronomer S.W. Burnham.^[18]

The "A" component is a double-lined spectroscopic binary that contains two solar-type stars with spectral classifications of F9 V and G0 V respectively.^[5] The pair take roughly 4 days to orbit each other.^[10]

The tertiary companion designated "B" has a class of G1.5 V, indicating that it is an ordinary G-type main-sequence star like the Sun. HD 202908 A and B both complete an eccentric orbit every 78 years.^[10]

Physical characteristics

HD 202908 Aa and Ab have masses 1.08 and 1.14 times that of the Sun^[15] and radii 97% and 106% of the Sun respectively.^[13] The former radiates 1.41 times the luminosity of the Sun from its photosphere and the latter radiates 1.16 times the Sun's luminosity.^[13] The A subsystem has an effective temperature of 6,100 K,^[13] giving it a whitish-yellow hue.

The B component has 97% the mass of the Sun^[15] and 91% of its radius. It radiates 84% of the Sun's luminosity^[13] from its photosphere at an effective temperature of 5,703 K.^[2] The system is estimated to be 6.4 billion years old.^[12]