| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cassiopeia |
| Right ascension | 02h 40m 31.6643s[1] |
| Declination | +61° 13′ 45.592″[1] |
| Apparent magnitude (V) | 10.61–10.83[2] |
| Characteristics | |
| Spectral type | B0Ve[3] |
| U−Bcolor index | −0.34[4] |
| B−Vcolor index | +0.86[4] |
| Variable type | High-mass X-ray binary[2] |
| Astrometry | |
| Radial velocity (Rv) | −41.41 km/s |
| Proper motion (μ) | RA: 0.27[5]mas/yr Dec.: 2.38[5]mas/yr |
| Parallax (π) | 0.45±0.23 mas[1] |
| Distance | approx. 7,000 ly (approx. 2,000 pc) |
| Other designations | |
| V615 Cas,1RXS J024033.5+611358,TYC 4047-1917-1,HIP 12469 | |
| Database references | |
| SIMBAD | data |
LS I +61 303 is abinary system containing a massivestar and a compact object. The compact object is a pulsar[6] and the system is around 7,000light-years away.
LS I +61 303 is an 11th-magnitude star that was recognised as aluminous object and catalogued as anOB star in 1959.[7] It was included in theHipparcos survey as HIP 12469 and had itsparallax measured at5.65±2.28milliarcseconds (mas), revised to −0.29±2.99 mas in the new reduction.[5] The firstGaia data release gave a parallax of0.45±0.23 mas.[1]
The Galactic radio source GT 0236+610 was found at the same position as LS I +61 303. Agamma-ray source 2CG 135+01 was found within a degree of its position, and theMAGIC telescope confirmed that LS I +61 303 was the source of the gamma rays. PeriodicX-ray outbursts also occur.[8]
LS I +61 303 shows the spectrum of aBe star, a B0main sequence star with disk that producesemission lines in its spectrum. Variations in its radial velocity show that it is in orbit with an unseen compact object having a mass between 1 and 4 M☉. The pair orbit every 26.496 days.[8] Although the uncertain mass of the compact object would allow it to be aneutron star, it was often suggested to be ablack hole.[11] In March 2022, a period of ~0.27 s was reported to be detected in observations using the FAST telescope, confirming the neutron star nature of the compact object. This promotes the possibility that the system is indeed the first one detected containing a pulsar with magnetar behavior in it.[6][12]
In 1979, Philip C. Gregoryet al. discovered that the star's brightness varies, after examining decades ofHarvard College Observatoryphotographic plates.[9] LS I +61 303 varies slightly at optical wavelengths, but measurements going back to 1887 show no obvious period. It also shows regular X-ray outbursts coinciding with its orbital period, and strong radio variability.[9] It was given thevariable star designation V615 Cassiopeiae.[2]
LS I +61 303 emitsHE andVHE (High Energy and Very High Energy) gamma rays.[3][8] It is only one of several knownstar systems that produce such energetic rays. Other such systems arePSR B1259–63,LS 5039 and HESS J0632+057.
