HD 148937
Binary star in the constellation Norma
From Wikipedia, the free encyclopedia
HD 148937 is a likely binary star[7] system in the southern constellation of Norma. It has a combined apparent visual magnitude of 6.73,[2] a brightness that is below the limit for being readily visible to the naked eye. Based on parallax measurements, it is located at a distance of approximately 3,900 light years from Sun,[1] but is drifting closer with a radial velocity of about −54 km/s.[2] The star is located in the hourglass-shaped emission nebula NGC 6164/65, which it generated through episodes of mass ejection.[8][9]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Norma |
| Right ascension | 16h 33m 52.387s[1] |
| Declination | −48° 06′ 40.48″[1] |
| Apparent magnitude (V) | 6.73[2] |
| Characteristics | |
| Spectral type | O6f?p[3] |
| B−V color index | 0.316±0.003[2] |
| Astrometry | |
| Radial velocity (Rv) | −53.9±3.0[2] km/s |
| Proper motion (μ) | RA: +0.741 mas/yr[1] Dec.: −3.404 mas/yr[1] |
| Parallax (π) | 0.8417±0.0223 mas[1] |
| Distance | 3,900 ± 100 ly (1,190 ± 30 pc) |
| Orbit[4] | |
| Period (P) | 9,390±300 days |
| Semi-major axis (a) | 33.45±0.73 AU |
| Eccentricity (e) | 0.7782±0.0051 |
| Inclination (i) | 84.07±0.10° |
| Longitude of the node (Ω) | 277.27±0.26° |
| Periastron epoch (T) | 56,958.2±2.8 MJD |
| Argument of periastron (ω) (secondary) | 340.10±0.41° |
| Semi-amplitude (K1) (primary) | 28.4+3.2 −3.6 km/s |
| Semi-amplitude (K2) (secondary) | 31.9+3.7 −3.4 km/s |
| Details | |
| A | |
| Mass | 29.9+3.4 −3.1[4] M☉ |
| Luminosity | 191,000+28,300 −24,600[4] L☉ |
| Surface gravity (log g) | 4.00±0.09[4] cgs |
| Temperature | 37,200+900 −400[4] K |
| Rotational velocity (v sin i) | 165±20 km/s |
| Age | 5[5] Myr |
| B | |
| Mass | 26.6+3.0 −3.4[4] M☉ |
| Luminosity | 155,000+27,000 −23,000[4] L☉ |
| Surface gravity (log g) | 3.61+0.05 −0.09[4] cgs |
| Temperature | 35,000+300 −900[4] K |
| Rotational velocity (v sin i) | 67±15[4] km/s |
| Other designations | |
| BD−47°10855, GC 22246, HD 148937, HIP 81100, SAO 226891, PPM 321879, WDS J16339-4807A[6] | |
| Database references | |
| SIMBAD | data |
Observations
In 1955, C. S. Gum identified HD 148937 and possibly 15 Sagittarii as responsible for the emission from the region of NGC 6164/65.[10] In 1959, K. G. Heinze catalogued NGC 6164/65 as a planetary nebula and placed HD 148937 at its center,[11] with the two nebulae and the star being co-linear.[12] However, the apparent brightness of HD 148937 is brighter than any other nucleus for a nebula of this class, and the spectra of the star raised questions about their evolutionary status.[11] B. E. Westerlund classified the star as class O6fp in 1960,[13] with the 'O' meaning an O-type star, 'f' indicating emission from ionized helium and nitrogen, and the 'p' meaning an unspecified peculiarity.[12] He found a series of symmetrical nebular shells surrounding the star at angular separations of 3′, 4′, and 44′–64′.[13]
In 1970, R. M. Catchpole and M. W. Feast showed that the radial velocities for the two nebulae are consistent with them being ejecta expanding away from the central star.[12] A very luminous absolute visual magnitude of −6 was confirmed for the central star in 1972, which demonstrated that the surroundings are not a planetary nebula.[13] This star lies within an H II region spanning 2°, which is surrounded by a thin dust shell.[5] In 1980, the star showed a mass loss rate of 2×10−7 M☉·yr−1, similar to other O-type main-sequence stars.[14]
An abundance analysis of the surrounding nebulae in 1987 demonstrated a strong overabundance of nitrogen, which most likely comes from stellar processing. This indicates the star is evolved, rather than being in a pre-main-sequence phase. The estimated mass of the NGC 6164/6165 nebulae is twice the mass of the Sun, and it shows a kinetic age of 3×103 yr. The surrounding stellar wind bubble is much older at 2×105 yr.[15]
In 2008, a magnetic field with a longitudinal strength of −276±88 G was detected in the star.[16] It shows spectroscopic variability with a period of 7.031±0.003 d, and has a nitrogen enhancement of about four times that in the Sun. Based on variations in the magnetic field strength, the seven day variance is interpreted as the stellar rotation period.[17] X-ray emission has been detected and is interpreted as originating in hot plasma about one stellar radius from the photosphere.[18]
Observations of the star made between 2015 and 2019 showed a significant change in the spectrum. Radial velocity measurements made during this period suggest that this is a double-lined spectroscopic binary system of high mass stars. Initial measurements suggest they have an eccentric orbit with a period of about 26 years and an orbital eccentricity of 0.75.[7] Only one member of the pair is magnetic, and it appears younger than the companion. This younger star may have been formed by a merger with a third member of the system, an event that can explain both the magnetic field and the surrounding nebula.[4]