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  • 21 Aug, 2019

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HD 178911
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AstrometryHD 178911 Aa/AbRadial velocity (Rv)−38.09±1.01 km/sProper motion (μ) RA: 76.618 mas/yr
Dec.: 207.126 mas/yr Parallax (π)20.2306 ± 0.3846 masDistance161 ± 3 ly
(49.4 ± 0.9 pc)Absolute magnitude (MV)3.28HD 178911 BRadial velocity (Rv)−40.324±0.0012 km/sProper motion (μ) RA: 57.177 mas/yr
Dec.: 195.900 mas/yr Parallax (π)24.3775 ± 0.0274 masDistance133.8 ± 0.2 ly
(41.02 ± 0.05 pc)Absolute magnitude (MV)4.90 OrbitPrimaryHD 178911 AaCompanionHD 178911 AbPeriod (P)1,296.984±0.355 d yrSemi-major axis (a)0.074±0.002″Eccentricity (e)0.597±0.003Inclination (i)147.29±0.99°Longitude of the node (Ω)276.91±1.45°Argument of periastron (ω)
(secondary)83.88±0.87°Semi-amplitude (K1)
(primary)6.47±0.09 km/sSemi-amplitude (K2)
(secondary)8.33±0.18 km/s DetailsHD 178911 AaMass0.802±0.055 M☉
1.234±0.027 M☉HD 178911 AbMass0.622±0.053 M☉
0.942±0.021 M☉ HD 178911 B Mass 1.03±0.02 M☉ Radius 1.05±0.02 R☉ Luminosity 1.00±0.02 L☉ Surface gravity (log g) 4.40±0.02 cgs Temperature 5,642±29 K Metallicity [Fe/H] 0.23 Rotational velocity (v sin i) 4.6 Age 4.8±1.3 Gyr Other designations
STF2747, HD 178911, HR 7272, WDS 19091+3436
HD 178911 A: BD+34 3439, HIP 94076, SAO 67879, PPM 82386, LTT 15608, NLTT 47474HD 178911 B: BD+34 3438, HIP 94075, SAO 67875, PPM 82385, LTT 15608, NLTT 47473 Database referencesSIMBADdata

HD 178911 is a triple star system with an exoplanetary companion in the northern constellation of Lyra. With a combined apparent visual magnitude of 6.70, it is a challenge to view with the naked eye. The system is located at a distance of approximately 161 light years from the Sun based on parallax measurements, but is drifting closer with a radial velocity of −38 km/s.

Stellar system

A companion star, designated component B, was first reported by F. G. W. Struve in 1823. As of 2019, the two have an angular separation of 16.0″ along a position angle of 263°. Component B shares a common motion through space with the primary, and thus they form a wide binary. This secondary is a magnitude 7.88 G-type main-sequence star with a stellar classification of G5V. The physical properties of this star are similar to the Sun, although it has a higher metallicity.

In 1985, the primary was determined to be a spectroscopic binary pair using the CHARA speckle interferometry program. Designated components Aa and Ab, these have an orbital period of 3.55 yr and an eccentricity (ovalness) of 0.6. They are magnitude 6.89 and 8.96. Based on based on a combined class of G5V for the pair, they have derived main sequence stellar classifications of G1V and K1V, respectively. C. D. Farrington and associates (2014) found dynamic masses for the components of 0.80 and 0.62, respectively. However, based on the classes, the expected masses should be around 1.0 and 0.8. Manuel Andrade (2019) derived higher dynamic masses of 1.20 and 0.94.

An additional companion HD 178911 C is a chance optical alignment and is not part of the system.

Planetary system

In 2001 an extrasolar planet was discovered in orbit around HD 178911 B.

The HD 178911 B planetary system
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b >7.35 ± 0.60 MJ 0.345 ± 0.20 71.511 ± 0.011 0.139 ± 0.014 — —

See also