05h50m30s, +02° 01′ 28.9″
| |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Orion[a] |
| Right ascension | 05h50m 30.03s[1] |
| Declination | 02° 01′ 28.93″[1] |
| Apparent magnitude (V) | 5.976[1] |
| Characteristics | |
| Cool primary | |
| Evolutionary stage | Red giant branch[2] |
| Spectral type | K0II[3] |
| Apparent magnitude (B) | 6.83±0.015[1] |
| Apparent magnitude (G) | 5.64[1] |
| Apparent magnitude (J) | 4.193±0.238[1] |
| Apparent magnitude (H) | 3.502±0.194[1] |
| Apparent magnitude (K) | 3.337±0.19[1] |
| B−V color index | 1.12[3] |
| Hot secondary | |
| Evolutionary stage | B-type main-sequence star + A-type main-sequence star |
| Spectral type | B7V/B8V + A0V[3] |
| B−V color index | -0.09[3] |
| Astrometry | |
| Radial velocity (Rv) | 4.24[3] km/s |
| Proper motion (μ) | RA: 1.097 mas/yr[1] Dec.: -5.161 mas/yr[1] |
| Parallax (π) | 1.47 ± 0.23 mas[4] |
| Distance | 2300+350 −270 ly (707.6+107 −83.3 pc)[4] |
| Absolute magnitude (MV) | –2.53 (–2.3 (primary) + –0.75 (secondary))[3] |
| Orbit | |
| Primary | Cool primary |
| Companion | Hot secondary |
| Period (P) | 2570±13 d 7.04±0.04 year[5] |
| Semi-major axis (a) | 4.7×108 km 3.14 AU[5] |
| Eccentricity (e) | 0.3±0.007[5] |
| Details | |
| K-type giant | |
| Mass | 3.3+0.3 −0.27[2] M☉ |
| Radius | 23.5+3.7 −1.9[2] R☉ |
| Luminosity | 535[6] L☉ |
| Surface gravity (log g) | 1.52[7] cgs |
| Temperature | 4,550[7] K |
| Metallicity [Fe/H] | -0.34[7] dex |
| Rotational velocity (v sin i) | 4.19[8] km/s |
| Age | 257[2] Myr |
| B-type star | |
| Temperature | 11,300[9] K |
| Other designations | |
BD+01 1148, Gaia DR2 3316078695157768448, Gaia DR3 3316078695157768448, HD 39118/39119, HIP 27588, HR 2024, SAO 113198, PPM 149543, TIC 158867386, TYC 120-877-1, GSC 00120-00877, IRAS 05478+0200, 2MASS J05503003+0201290 | |
| Database references | |
| SIMBAD | data |
HD 39118 (HD 39119, HR 2024) is a spectroscopic binary star in the constellation Orion, close to the celestial equator. It is made up from three stars: a cool primary (aK-type giant star) and a hot secondary, which is a binary star formed from a B-type main-sequence star and an A-type main-sequence star. A 2021 estimate derive a distance of 708 parsecs (2,310 ly) to HD 39118, and it is moving away from Earth at a speed of 4.24 km/s. The apparent magnitude is 5.976, making it visible to the naked eye only from dark skies.
HR 2024 is a spectroscopic binary (more precisely a single-lined spectroscopic binary)[10] made up of a cool primary and a hot secondary, which is also a binary star.[3] The designations “cold” and “hot” refer to the effective temperature of the components. They are separated by 4.7×108 kilometres (3.1 AU), and complete an orbit around each other every 2,570 days (7 years).[5] The orbital eccentricity is equivalent to 0.3.[5]
HD 39118 can be seen in the northern celestial hemisphere, close to the celestial equator, at a distance of 708 parsecs (2,310 light-years) in the constellation Orion.[1][4][b] It has an apparent magnitude of 5.976.[1] At this magnitude, it is visible to the naked eye only in dark skies, being close to the limiting magnitude to naked-eye vision of 6.5.[11] The absolute magnitude, i.e. its brightness if it was seen at a distance or 10 parsecs (32.6 ly), is –2.53.[3] It is moving away from Earth at a velocity of 4.24 km/s.[1]
It was double cataloged in the Henry Draper Catalogue, receiving the designations HD 39118 and HD 39119.[1]
The primary has an spectral classification of K0II,[3] meaning that it is a K-type star that has left the main sequence, being now a bright giant star. Currently, it is in the red giant branch of evolution.[2] It is 3.28 times more massive has expanded to 25 times the Sun's size.[2] It emitts a luminosity 535[6] times the solar luminosity from its photosphere at an effective temperature of 4,550 K, which is around 1,200 K cooler than the Sun.[7][c] It has a subsolar metallicity, having an abundance of iron on its surface equivalent to 46% that of the Sun.[7][d] The age of the primary is estimated at 263 million years,[2] much younger than the Sun (4.6 billion years) despite its advanced evolutionary stage. It rotates under its own axis at a velocity of 4.19 km/s.[8] The B-V index is of 1.12,[3] giving it the typical orange hue of a K-type star.[e]
The hot companion is made up of two other stars, one is a late B-type main-sequence star (spectral type B7V/B8V) and the other is an early A-type main-sequence star (spectral type A0V).[3] It has an absolute magnitude about 1.55 magnitudes fainter than the primary companion.[3] The B-type star has an effective temperature of 11,300 K.[9] The B-V index of the hot companion is of –0.09,[3] meaning that it has a typical hue of a B-type star.[e]
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