HD 178911
Triple star system in the constellation Lyra
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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,[2] 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.[1]
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Lyra |
| Right ascension | 19h 09m 04.35193s[1] |
| Declination | +34° 36′ 01.2420″[1] |
| Apparent magnitude (V) | 6.70[2] (6.89 + 8.96 + 7.88)[3] |
| Characteristics | |
| HD 178911 Aa/Ab | |
| Evolutionary stage | Main sequence |
| Spectral type | G1V + K1V[4] |
| B−V color index | 0.643±0.007[2] |
| HD 178911 B | |
| Spectral type | G5V[5] |
| B−V color index | 0.750±0.015[2] |
| Astrometry | |
| HD 178911 Aa/Ab | |
| Radial velocity (Rv) | −38.09±1.01[1] km/s |
| Proper motion (μ) | RA: 76.618[1] mas/yr Dec.: 207.126[1] mas/yr |
| Parallax (π) | 20.2306±0.3846 mas[1] |
| Distance | 161 ± 3 ly (49.4 ± 0.9 pc) |
| Absolute magnitude (MV) | 3.28[2] |
| HD 178911 B | |
| Radial velocity (Rv) | −40.324±0.0012[6] km/s |
| Proper motion (μ) | RA: 57.177[7] mas/yr Dec.: 195.900[7] mas/yr |
| Parallax (π) | 24.3775±0.0274 mas[7] |
| Distance | 133.8 ± 0.2 ly (41.02 ± 0.05 pc) |
| Absolute magnitude (MV) | 4.90[2] |
| Orbit[4] | |
| Primary | HD 178911 Aa |
| Name | HD 178911 Ab |
| Period (P) | 1,296.984±0.355 d |
| Semi-major axis (a) | 0.074±0.002″ |
| Eccentricity (e) | 0.597±0.003 |
| Inclination (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/s |
| Semi-amplitude (K2) (secondary) | 8.33±0.18 km/s |
| Details | |
| HD 178911 Aa | |
| Mass | 0.802±0.055 M☉[4] 1.234±0.027[8] M☉ |
| HD 178911 Ab | |
| Mass | 0.622±0.053 M☉[4] 0.942±0.021[8] M☉ |
| HD 178911 B | |
| Mass | 1.03±0.02[9] M☉ |
| Radius | 1.05±0.02[9] R☉ |
| Luminosity | 1.00±0.02[9] L☉ |
| Surface gravity (log g) | 4.40±0.02[9] cgs |
| Temperature | 5,642±29[9] K |
| Metallicity [Fe/H] | 0.23[10] dex |
| Rotational velocity (v sin i) | 4.6[10] km/s |
| Age | 4.8±1.3[9] Gyr |
| Other designations | |
| STF2747, HD 178911, HR 7272, WDS 19091+3436[11] | |
| HD 178911 A: BD+34 3439, HIP 94076, SAO 67879, PPM 82386, LTT 15608, NLTT 47474[11] | |
| HD 178911 B: BD+34 3438, HIP 94075, SAO 67875, PPM 82385, LTT 15608, NLTT 47473[12] | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
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°.[3] Component B shares a common motion through space with the primary, and thus they form a wide binary.[13] This secondary is a magnitude 7.88[3] G-type main-sequence star with a stellar classification of G5V.[5] The physical properties of this star are similar to the Sun, although it has a higher metallicity.[9][10]
In 1985, the primary was determined to be a spectroscopic binary pair using the CHARA speckle interferometry program.[14] Designated components Aa and Ab, these have an orbital period of 3.55 yr and an eccentricity (ovalness) of 0.6.[4] They are magnitude 6.89 and 8.96.[3] Based on based on a combined class of G5V for the pair,[8] they have derived main sequence stellar classifications of G1V and K1V, respectively.[4] C. D. Farrington and associates (2014) found dynamic masses for the components of 0.80 and 0.62, respectively.[4] 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.[8]
An additional companion HD 178911 C is a chance optical alignment and is not part of the system.[4]
Planetary system
In 2001 an extrasolar planet was discovered in orbit around HD 178911 B.[15][13]
| 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 | — | — |