OAO 1657-415
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| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Scorpius |
| Right ascension | 17h 00m 48.884s[1] |
| Declination | −41° 39′ 21.46″[1] |
| Apparent magnitude (V) | >23[2] |
| Characteristics | |
| Spectral type | Ofpe/WN9[3] |
| Apparent magnitude (J) | 14.09[1] |
| Apparent magnitude (H) | 11.68[1] |
| Apparent magnitude (K) | 10.38[1] |
| Variable type | X-ray binary[3] |
| Astrometry | |
| Radial velocity (Rv) | 57.2±3[3] km/s |
| Distance | 7,100[2] pc |
| Orbit[3] | |
| Period (P) | 10.44812±0.00013 days |
| Semi-amplitude (K1) (primary) | 22.1±3.5 km/s |
| Details | |
| Star | |
| Mass | 14.3±0.8[3] M☉ |
| Radius | 24.8±1.5[3] R☉ |
| Luminosity | ~126,000[3] L☉ |
| Temperature | ~20,000[3] K |
| Compact object | |
| Mass | 1.42±0.26[3] M☉ |
| Other designations | |
| AX J1700.7-4139, 2MASS J17004888-4139214 | |
| Database references | |
| SIMBAD | data |
OAO 1657-415 is a high-mass X-ray binary (HMXB) located in the constellation of Scorpius, over 20,000 light years away. It is believed to be composed of a compact object (likely a neutron star) and a highly evolved massive slash star, with Wolf–Rayet and O-type features in its spectrum, with a spectral type of Ofpe/WN9. OAO 1657-415 is special as it has the largest eccentricity and orbital period of any HMXB, and also because its donor star is much more evolved than many other HMXB donor stars.[3]
OAO 1657-415 is very far away, located between 4.4 and 12 kiloparsecs from Earth, most likely being about 7.1 kiloparsecs from Earth. However, recent Gaia data suggests a lower distance of just 2.2 kiloparsecs based on the parallax angle of the optical companion.
OAO 1657-415 is extremely reddened. In the visible wavelength, it is reddened by 20.4 magnitudes.[3] Therefore, it is certainly invisible to the naked eye and likely requires at least a very powerful telescope to be seen in visible light. Despite dedicated efforts to locate OAO 1657-415 in the visible band, no optical component was found with a visible magnitude of under 23.[2]
