WR 120
Binary star system in the constellation Scutum
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WR 120 is a binary containing two Wolf–Rayet stars in the constellation of Scutum, around 10,000 light years away. The primary is a hydrogen-free weak-lined WN7 star, the secondary is a hydrogen-free WN3 or 4 star, and the system is a possible member of the cluster Dolidze 33.[8] From our point of view, WR 120 is reddened by 4.82 magnitudes.
A near-infrared (2.033 micron) light curve for V462 Scuti, adapted from Chené and St-Louis (2007).[1] The left-most point shows the 3 sigma error bar. | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Scutum[2] |
| Right ascension | 18h 41m 00.86701s[3] |
| Declination | −04° 26′ 14.4841″[3] |
| Apparent magnitude (V) | 11.93[4] |
| Characteristics | |
| Evolutionary stage | Wolf–Rayet[5] |
| Spectral type | WN7w[6] + WN3/4[5] |
| U−B color index | 0.13[7] |
| B−V color index | 1.04[7] |
| Astrometry | |
| Proper motion (μ) | RA: −0.489[3] mas/yr Dec.: −2.524[3] mas/yr |
| Parallax (π) | 0.3246±0.0541 mas[3] |
| Distance | approx. 10,000 ly (approx. 3,100 pc) |
| Absolute magnitude (MV) | −3.81[6] |
| Details | |
| Mass | 7[6] M☉ |
| Radius | 3.78[6] R☉ |
| Luminosity | 83,200[6] L☉ |
| Temperature | 50,100[6] K |
| Other designations | |
| MR 89, V462 Scuti, 2MASS J18410086-0426145 | |
| Database references | |
| SIMBAD | data |
Photometric observations obtained in 1995 by Sergey V. Marchenko et al. showed that WR 120 is a variable star.[9] For that reason it was given its variable star designation, V462 Scuti, in the year 2000.[10]
Properties
Analysis of the primary's spectrum with PoWR shows that it has a temperature of around 50,000 Kelvins, and is losing mass at a rate of 10−4.9 M☉/year, or 1 solar mass every 80,000 years, which is being carried away from the surface at a speed of 1,225 kilometres per second.[6] Taking its close distance into account, WR 120 A's luminosity turns out to be a mere 83,200 L☉, which would make it one of the dimmest WN stars known, and one of the only WN stars with a luminosity below 100,000 L☉. Using the Stefan-Boltzmann Law, a radius of 3.78 R☉ is derived, and a "transformed" radius at an optical depth of 2/3, more comparable to other types of stars, is about 6 R☉. Using the WR luminosity-mass ratio, WR 120 may have a mass of just 7 M☉, one of the lowest masses of any WR star. WR 120's absolute magnitude is −3.8, which is also relatively faint for a Wolf–Rayet star.[6]
WR 120 is thought to be a member of Dolidze 33, an open cluster nearly 3,000 pc away.[8]
Binarity
In 2021, WR 120 was found to have a close companion. Previously, it was thought to be a single WR star. The companion is thought to be a WN3/4 WR star and would be located at least 1,700 AU from the primary WN7 WR star. It is about two magnitudes fainter than WR 120.[5]