CV Serpentis
Binary star system
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CV Serpentis is a binary star system in the equatorial constellation of Serpens. It is a detached eclipsing binary with an orbital period of 29.7 days.[5] The system includes a Wolf–Rayet (WR) star with the identifier WR 113. The system is located at a distance of approximately 6,700 light years from the Sun based on parallax measurements.[2] It is a member of the Serpens OB2 association of co-moving stars.[11]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Serpens |
| Right ascension | 18h 19m 07.363s[2] |
| Declination | −11° 37′ 59.16″[2] |
| Apparent magnitude (V) | 9.08[3] |
| Characteristics | |
| Spectral type | WC8d + O8-9IV[4] |
| B−V color index | 0.724±0.033[3] |
| Variable type | E/D/WR[5] |
| Astrometry | |
| Radial velocity (Rv) | 17±2[3] km/s |
| Proper motion (μ) | RA: −0.691 mas/yr[2] Dec.: −1.568 mas/yr[2] |
| Parallax (π) | 0.4896±0.0157 mas[2] |
| Distance | 6,700 ± 200 ly (2,040 ± 70 pc) |
| Absolute magnitude (MV) | System: −5.1±0.8 WR star: −3.6+1.8 −1.3[6] |
| Orbit[1] | |
| Period (P) | 29.704 d |
| Eccentricity (e) | 0.02±0.02 |
| Inclination (i) | 63.5±2.5[4]° |
| Periastron epoch (T) | 2,455,003±1 HJD |
| Argument of periastron (ω) (secondary) | 330±10° |
| Semi-amplitude (K1) (primary) | 173±1 km/s |
| Details | |
| OB star | |
| Mass | 33.3±2.0[4] M☉ |
| Luminosity | 64,749[7] L☉ |
| Temperature | 27,570[7] K |
| Rotational velocity (v sin i) | 310-330[8] km/s |
| WR star | |
| Mass | 11.7±0.9[4] M☉ |
| Luminosity | 24,018[7] L☉ |
| Temperature | 44,500[9] K |
| Other designations | |
| WR 113, CV Ser, BD−11 4593, HD 168206, HIP 89769, SAO 161325, PPM 234357[10] | |
| Database references | |
| SIMBAD | data |
In 1892, this star was found to be an object of interest based on photographs of its peculiar stellar spectra taken from the Boyden Station in Arequipa, Peru.[12] It was determined to be a carbon-type Wolf–Rayet (WR) star and in 1945 was found to be a spectroscopic binary system by W. A. Hiltner.[13] This system was reported to be an eclipsing binary by S. Gaposchkin in 1949,[14] who found a decrease in brightness of 0.14 magnitude during the first eclipse and 0.08 in the second. R. M. Hjellming and W. A. Hiltner in 1963 measured a much deeper primary eclipse with a decrease of about 0.55 magnitude,[15] then in 1970 K. Stępień saw no evidence of eclipsing.[16] L. V. Kuhi and F. Schweizer confirmed this latter result, hypothesizing that it is the result of a changing Wolf-Rayet envelope.[17]
This is a double-lined spectroscopic binary system in a near circular orbit, meaning that the spectra of both components is visible.[4] The companion of the WR star is a massive OB star with a stellar classification of O8-9IV.[4] A nebulous double-shell centered on CV Ser was discovered in 1984, spanning angular diameters of 4′ and 9′. The diffuse outer ring is incomplete, spanning a radius of 5.4 pc at an approximate distance of two kiloparsecs.[18] Variations in the system's light curve continued to be observed, suggesting changes in the outflow from the Wolf-Rayet star.[19] An emission feature in the spectrum of the system was interpreted as a region between the two stars where their stellar winds are colliding,[20] forming a shock region of plasma.[4]
The system is expected to evolve into a binary with the OB-star and an 8 M☉ black hole following a failed supernova where the WR star collapses with little or no visible explosion.[21] The OB star is observed to be rotating rapidly at between 310 and 330 km/s using spectral lines of neutral helium. Observations using ionized helium absorption lines show a lower velocity, interpreted as showing an oblate shape with gravity darkening causing lower temperatures at the equator.[8]
Speckle interferometry has found a companion star 1.16″ from the bright primary and eight magnitudes fainter. The projected separation of 2,200 AU is much larger than the maximum possible 129 AU separation of the Wolf-Rayet and OB pair. If it is found to be at the same distance as the bright spectroscopic pair, it would likely be an F-type main sequence star in an orbit with a period around 100,000 years and the lowest-luminosity known companion of any WR star at 5 L☉.[22]