HD 136118
Star in the constellation Serpens
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HD 136118 is a star in the Serpens Caput section of the Serpens constellation. The star is too dim to be readily visible to the naked eye, having an apparent visual magnitude of 6.93.[1] It is located at a distance of 165 light years from the Sun based on parallax,[2] and is drifting closer with a radial velocity of −3 km/s.[1]
Telescope image of HD 136118 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Serpens[1] |
| Right ascension | 15h 18m 55.47227s[2] |
| Declination | −01° 35′ 32.5926″[2] |
| Apparent magnitude (V) | 6.93[1] |
| Characteristics | |
| Evolutionary stage | main sequence[3] |
| Spectral type | F7V[4] |
| B−V color index | 0.553±0.007[1] |
| Astrometry | |
| Radial velocity (Rv) | −3.07±0.13[2] km/s |
| Proper motion (μ) | RA: −123.024(31) mas/yr[2] Dec.: 22.180(30) mas/yr[2] |
| Parallax (π) | 19.8116±0.0341 mas[2] |
| Distance | 164.6 ± 0.3 ly (50.48 ± 0.09 pc) |
| Absolute magnitude (MV) | 3.60[5] |
| Details | |
| Mass | 1.84±0.23[6] M☉ |
| Radius | 1.70±0.02[7] R☉ |
| Luminosity | 3.717±0.018[7] L☉ |
| Surface gravity (log g) | 4.08[5] cgs |
| Temperature | 6,148+38 −43[7] K |
| Metallicity [Fe/H] | −0.06±0.01[1] dex |
| Rotational velocity (v sin i) | 8.5[5] km/s |
| Age | 3.5±0.4[1] Gyr |
| Other designations | |
| BD−01° 3045, HD 136118, HIP 74948, SAO 140452[8] | |
| Database references | |
| SIMBAD | data |
This object is an F-type main-sequence star with a stellar classification of F7V.[4] The absolute visual magnitude of this star suggests that it has begun to evolve away from the main sequence.[3] The abundances of the stellar atmosphere are similar to the Sun, and it has only a modest level of chromospheric activity.[9] HD 136118 has 84% more mass compared to the Sun,[6] and is 70%[7] larger in radius. The star is an estimated 3.5[1] billion years old and is spinning with a projected rotational velocity of 8.5 km/s.[5]
Brown dwarf companion
The astronomer Debra Fischer discovered a substellar companion, originally thought to be a very massive exoplanet, which was announced on February 7, 2002.[3] Designated HD 136118 b, it is orbiting the host star with a period of 3.25 years.[9] This object has a minimum mass of 11.9 MJ.[3] On November 25, 2009, its inclination was calculated to be 163.1° and its true mass 42 MJ, classifying it as a brown dwarf.[9] Later studies in 2022 and 2023 found true masses of about 13-16 MJ, closer to the minimum mass, but still classifying the companion as a brown dwarf by most definitions.[10][11]
Due to its high mass the object is likely to be very hot and possibly glowing faintly. The orbit of the object has a semimajor axis of 1.45 astronomical units from the parent star, taking 1,188 days (3.25 years) to complete one eccentric orbit.
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (years) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 16.5+1.7 −1.8 MJ |
2.353+0.046 −0.045 |
3.262+0.053 −0.051 |
0.35+0.027 −0.026 |
134.0+4.7 −7.5° |
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