HD 147379
Visual binary in constellation Draco
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HD 147379 (Gliese 617) is a wide visual binary between two red dwarfs in the deep northern constellation of Draco. The two stars are located approximately 35.1 light-years (10.8 pc) distant based on Gaia DR3 parallax measurements, and approaching the Solar System at heliocentric radial velocities of −18.962 km/s and −18.36 km/s, respectively. The brighter primary star, HD 147379A, has an apparent magnitude of 8.9,[4] too faint to be seen by the naked eye from Earth but visible using binoculars.[18] The dimmer secondary, B, fluctuates in apparent magnitude between 10.69 and 10.74,[6] making it observable via a telescope with an aperture of 35 mm or larger.[19]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Draco[1][2] |
| HD 147379A | |
| Right ascension | 16h 16m 42.74635s[3] |
| Declination | +67° 14′ 19.8316″[3] |
| Apparent magnitude (V) | 8.9[4] |
| HD 147379B | |
| Right ascension | 16h 16m 45.31448s[5] |
| Declination | +67° 15′ 22.4811″[5] |
| Apparent magnitude (V) | 10.69-10.74[6] |
| Characteristics | |
| HD 147379A | |
| Evolutionary stage | main sequence[3] |
| Spectral type | M0.0V[4] |
| B−V color index | 1.11[4] |
| J−H color index | 0.643[7] |
| J−K color index | 0.826[7] |
| HD 147379B | |
| Spectral type | M3V[8] |
| J−H color index | 0.608[7] |
| J−K color index | 0.842[7] |
| Variable type | BY Draconis variable[6] |
| Astrometry | |
| HD 147379A | |
| Radial velocity (Rv) | −18.962±0.0011[9] km/s |
| Proper motion (μ) | RA: −497.915[3] mas/yr Dec.: 84.047[3] mas/yr |
| Parallax (π) | 92.8766±0.0146 mas[3] |
| Distance | 35.117 ± 0.006 ly (10.767 ± 0.002 pc) |
| Absolute magnitude (MV) | +8.47[1] |
| HD 147379B | |
| Radial velocity (Rv) | −18.36±0.0008[10] km/s |
| Proper motion (μ) | RA: −483.006[5] mas/yr Dec.: 89.049[5] mas/yr |
| Parallax (π) | 92.8985±0.0160 mas[5] |
| Distance | 35.109 ± 0.006 ly (10.764 ± 0.002 pc) |
| Absolute magnitude (MV) | +10.54[2] |
| Orbit[4] | |
| Primary | HD 147379A |
| Name | HD 147379B |
| Semi-major axis (a) | 64.4" (693.4 AU) |
| Details[11] | |
| HD 147379A | |
| Mass | 0.58±0.08 M☉ |
| Radius | 0.57±0.06 R☉ |
| Luminosity | 0.1069±0.0153[12] L☉ |
| Surface gravity (log g) | 4.609±0.012[4] cgs |
| Temperature | 4090±50 K |
| Metallicity [Fe/H] | 0.16±0.16 dex |
| Rotation | 22 d[13] |
| Age | 5.1+3.2 −2.4[14] Gyr |
| HD 147379B | |
| Mass | 0.45±0.02[8] M☉ |
| Radius | 0.460±0.008[8] R☉ |
| Luminosity | 0.02645±0.00645[15] L☉ |
| Surface gravity (log g) | 4.84±0.06[8] cgs |
| Temperature | 3525±31[8] K |
| Metallicity [Fe/H] | 0.20±0.10[8] dex |
| Rotation | 40.4±3.0 d[8] |
| Rotational velocity (v sin i) | 0.50[8] km/s |
| Other designations | |
| GJ 617, HD 147379, WDS J16167+6714 | |
| HD 147379A: AG+67°695, BD+67°935, GC 21949, HIP 79755, G 257-32, G 225-57, G 240-14, LHS 3175, LSPM J1616+6714, LTT 14863, NLTT 42488, TIC 230073581, TYC 4195-721-1, 2MASS J16164280+6714196, WISEA J161641.85+671420.6, Gaia DR3 1642641410934267008[16] | |
| HD 147379B: EW Draconis, HIP 79762, SAO 17026, PPM 19804, G 240-15, G 225-58, G 257-33, LHS 3176, LSPM J1616+6715, LTT 14864, NLTT 42489, TIC 230073588, TYC 4195-1167-1, GSC 04195-01167, 2MASS J16164537+6715224, WISEA J161644.44+671523.3, Gaia DR3 1642642957122493824[17] | |
| Database references | |
| SIMBAD | A |
| B | |
HD 147379A
HD 147379A (HIP 79755) is a red dwarf with a spectral type of M0.0V, about 58% the mass of the Sun, 57% the radius, and an age of 5.1+3.2
−2.4 billion years. It emits just over a tenth of the luminosity of the Sun from its photosphere at an effective temperature of 4,090 K (3,820 °C; 6,900 °F). It has a high metallicity of [Fe/H]=0.16±0.16 dex, meaning it has an iron content somewhere around 45% higher than the Sun.[11] It is also enriched in cobalt, but is depleted in calcium and titanium. The star shows slight variations in the TiO spectral lines.[20]
Planetary system
In 2018, two teams independently reported the discovery of an exoplanet orbiting HD 147379A, both via the radial-velocity method.[11][12] This was the first exoplanet found by the CARMENES survey.[11] The planet, commonly referred to as HD 147379 b, has a minimum mass of 21.6 ± 1.1 M🜨, slightly more massive than Neptune (17.147 M🜨[21]). It orbits its host star once every 86.58 days at about a third of the distance from Earth to the Sun, placing it within the conservative habitable zone of the star, where liquid water could exist.[4]
One of the teams that discovered HD 147379 b proposed another candidate planet, this one with a minimum mass of 27 M🜨 and a 500-day period, orbiting at a distance of about 1 AU.[12] However, a 2023 follow-up study did not detect such a signal. Instead, they detected a signal with a 12.3-day period, but discarded it due to the high chance of it being a false positive. Nevertheless, it is highly likely that a second planet exists interior to b's orbit.[4]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | ≥21.6 ± 1.1 M🜨 | 0.3315 ± 0.0024[22] | 86.58 ± 0.14 | 0.0630+0.0470 −0.0380 |
— | — |
HD 147379B
HD 147379B (HIP 79762) is a gravitationally bound companion to HD 147379A at a separation of 64.4 arcseconds, which corresponds to a distance of 693.4 AU.[4]
This is a red dwarf with a spectral type of M3V, about 45% the mass of the Sun and 46% the radius. It has a "partially convective" structure, meaning that the outer convection zone does not reach down to the core,[8] as opposed to "fully convective" stars weighing less than 0.35 M☉ that are convective throughout.[24] It too has a high metallicity of [M/H]=0.20±0.10 dex, translating to a roughly 60% excess in elements heavier than hydrogen and helium compared to the Sun. At an effective temperature of 3,525 K (3,252 °C; 5,885 °F),[8] it radiates just 2.6% the luminosity of the Sun from its photosphere.[15] It rotates on its axis once every 40.4 days at a relatively slow projected equatorial velocity of 0.50 km/s.[8]
It has a magnetic field that fluctuated in strength between 36-75 G between 2020-2022, approximately 100 times stronger than Earth's magnetic field (0.22-0.67 G[25]) and similar to those of faster-rotating red dwarfs. The variations in strength are smaller than those seen in fully convective red dwarfs such as Gliese 1151.[8]
In 1994, the star was reported to have a high likelihood (99%) of exhibiting long-term variability, albeit the author noted that this may be suspect.[26] It was formally classified as a BY Draconis variable in 1997, receiving the variable-star designation EW Draconis.[6]