HD 33636
Binary star system in the constellation Orion
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HD 33636 is a G-type main-sequence star located approximately 96.5 light-years away in the Orion constellation. It is a 7th magnitude star with a metallicity of −0.05±0.07. A likely substellar companion was discovered in 2002.[7][8]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Orion[1] |
| Right ascension | 05h 11m 46.44941s[2] |
| Declination | +04° 24′ 12.7421″[2] |
| Apparent magnitude (V) | 7.00[3] |
| Characteristics | |
| Evolutionary stage | main sequence[2] |
| Spectral type | G0V_CH-0.3[4] |
| B−V color index | 0.588 ± 0.016[3] |
| Astrometry | |
| Radial velocity (Rv) | 5.66±0.13[2] km/s |
| Proper motion (μ) | RA: 181.259(45) mas/yr[2] Dec.: −138.193(29) mas/yr[2] |
| Parallax (π) | 33.7982±0.0529 mas[2] |
| Distance | 96.5 ± 0.2 ly (29.59 ± 0.05 pc) |
| Absolute magnitude (MV) | 4.71[3] |
| Orbit[5] | |
| Name | HD 33636 B |
| Period (P) | 5.807+0.016 −0.017 yr |
| Semi-major axis (a) | 3.329+0.022 −0.023 AU |
| Eccentricity (e) | 0.483±0.0063 |
| Inclination (i) | 7.07+0.62 −0.54° |
| Longitude of the node (Ω) | 109.9+4.9 −5.0° |
| Periastron epoch (T) | 2455442+12 −13 |
| Argument of periastron (ω) (secondary) | 338.2±1.3° |
| Details | |
| Mass | 1.01±0.02[6] M☉ |
| Radius | 0.97±0.01[6] R☉ |
| Luminosity | 1.08±0.003[6] L☉ |
| Surface gravity (log g) | 4.46±0.02[6] cgs |
| Temperature | 5,979±28[6] K |
| Age | 2.5±1.1[6] Gyr |
| Other designations | |
| BD+04 858, HD 33636, HIP 24205, SAO 112506, G 97-25[4] | |
| Database references | |
| SIMBAD | data |
Companion
HD 33636 b was discovered in 2002 by the Keck telescope in Hawaii using the radial velocity method.[7] It was independently detected at the Haute-Provence Observatory in France.[3] With this method it showed a minimum mass of 9.28 Jupiter masses, and was initially assumed to be a planet and labelled "HD 33636 b" (lower-case).[9]
In 2007, Bean et al. used the Hubble Space Telescope (HST) astrometry to find that this body has an inclination as little as 4.1°±0.1°, which yielded a true mass of 142 MJ. This is too high to be a planet. It was classified by this study as an M-dwarf star of likely spectral type M6V, "HD 33636 B" (upper-case).[10]
This picture was further revised in the 2020s. A 2023 study using astrometry from Hipparcos and Gaia found that the mass had likely been overestimated, and found a lower true mass of about 77.8 MJ. This would place HD 33636 b near the borderline between stars and brown dwarfs.[5] A 2024 study using Gaia astrometry even excluded the possibility of a companion mass greater than 40 MJ, instead finding a mass range more compatible with the initial minimum mass estimate. This study estimated a mass of about 15.4 MJ, near the borderline between brown dwarfs and planets.[8]
This object takes 2,121 days or 5.807 years to orbit at a semimajor axis of 3.33 astronomical units (AU).[5]