| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Serpens |
| Right ascension | 15h 18m 24.507s[1] |
| Declination | +20° 34′ 21.95″[1] |
| Apparent magnitude (V) | 5.68[2] + 15.3[3] |
| Characteristics | |
| Evolutionary stage | Horizontal branch + white dwarf |
| Spectral type | G8IIIa[4] + DA1.7[3] |
| B−V color index | 0.972±0.004[2] |
| Variable type | Constant[5][6] |
| Astrometry | |
| Radial velocity (Rv) | −7.74±0.07[2] km/s |
| Proper motion (μ) | RA: −12.993 mas/yr[1] Dec.: −22.380 mas/yr[1] |
| Parallax (π) | 7.7902 ± 0.2193 mas[1] |
| Distance | 420 ± 10 ly (128 ± 4 pc) |
| Absolute magnitude (MV) | 0.65±0.15[7] |
| Orbit[7] | |
| Period (P) | 506.45±0.18 d |
| Semi-major axis (a) | 4.14±0.52" (≥ 41.76±0.34 Gm[5]) |
| Eccentricity (e) | 0.3353±0.0056 |
| Inclination (i) | 42.9±6.7° |
| Longitude of the node (Ω) | 207.0±7.4° |
| Periastron epoch (T) | 2,453,240.3±1.3 MJD |
| Argument of periastron (ω) (secondary) | 35.0±1.4° |
| Semi-amplitude (K1) (primary) | 6.340±0.044 km/s |
| Details[7] | |
| A | |
| Mass | 1.84±0.40 M☉ |
| Radius | 10.3 R☉ |
| Luminosity | 56.2 L☉ |
| Surface gravity (log g) | 2.68 cgs |
| Temperature | 4,960±100 K |
| Metallicity [Fe/H] | −0.08±0.09[8] dex |
| Age | 1.45 Gyr |
| B | |
| Mass | 0.59±0.12 or 0.79±0.09 M☉ |
| Surface gravity (log g) | 8.25±0.15 cgs |
| Temperature | 30,400±780 K |
| Other designations | |
| Database references | |
| SIMBAD | data |
HD 136138, or HR 5692, is a binary star system in the Serpens Caput segment of the Serpens constellation. It has a golden hue like the Sun and is dimly visible to the naked eye with an apparent visual magnitude of 5.68;[2] the light contribution from the companion is effectively negligible.[8] This system is located at a distance of approximately 420 light years from the Sun based on parallax.[1] It is drifting closer with a radial velocity of −7.7 km/s[2] and has a proper motion of 23.5 mas·yr−1.[8]
The radial velocity variation of this star was reported by J. R. de Medeiros and M. Mayor in 1999,[5] and it was confirmed as a binary by A. Frankowski and colleagues in 2007 using proper motion measurements.[3] It is an unresolved, single-lined spectroscopic binary system with an orbital period of 1.39 years and an eccentricity (ovalness) of 0.335. Proper motion measurements allow an estimate of the orbital inclination angle as ~43°.[7] Their semimajor axis is around 2.0 AU, or double the distance from the Earth to the Sun.[8]
The stellar classification of the primary component is G8IIIa,[4] indicating this is a evolved G-type giant star that has exhausted the supply of hydrogen at its core. It is a red clump giant that is generating energy through core helium fusion. There is some ambiguous evidence for this being a mild barium star[7] of class Ba0.3,[8] with the spectra showing marginal overabundances of s-process elements.[8] A low level of X-ray emission has been detected, which appears to be coming from the star's corona.[6]
The high level of ultraviolet flux coming from this system strongly suggests the companion is a compact white dwarf. Mass estimates put it in the range of 0.6 to 0.8 times the mass of the Sun, and the temperature is around 30,400 K.[7] It is possible that the earlier evolution of this component contaminated its partner with s-process elements, although the resulting interaction should have circularized the orbit to some degree.[5] The dwarf has a visual magnitude of 15.3 and a hydrogen-dominated atmospheric class of DA1.7.[3]
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