V901 Orionis
Variable star in the constellation Orion
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V901 Orionis is a variable star in the equatorial constellation of Orion.[1] It is sometimes known as Landstreet's Star[10] and has the designation HD 37776 from the Henry Draper Catalogue; V901 Ori is the variable star designation. With an apparent visual magnitude that varies around 6.99,[1] it is a challenge to view with the naked eye. Based on parallax measurements from Earth, it is located at a distance of 1,280 ± 30 light-years (393 ± 8 pc). The star is drifting further away from the Sun with a radial velocity of 15 km/s.[6]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Orion[1] |
| Right ascension | 23h 57m 58.477s[2] |
| Declination | +15° 57′ 10.09″[2] |
| Apparent magnitude (V) | 6.99[1] (6.97 to 7.02[3]) |
| Characteristics | |
| Evolutionary stage | main sequence[4] |
| Spectral type | B2V[5] |
| B−V color index | −0.139±0.007[1] |
| Variable type | SX Ari[3] |
| Astrometry | |
| Radial velocity (Rv) | 14.66±0.25[6] km/s |
| Proper motion (μ) | RA: 2.743 mas/yr[2] Dec.: 1.671 mas/yr[2] |
| Parallax (π) | 2.5463±0.0524 mas[2] |
| Distance | 1,280 ± 30 ly (393 ± 8 pc) |
| Absolute magnitude (MV) | −0.77[1] |
| Details | |
| Mass | 8.3±0.3[7] M☉ |
| Radius | 3.2[8] R☉ |
| Luminosity | 1,995+823 −583[7] L☉ |
| Surface gravity (log g) | 4.04±0.01[9] cgs |
| Temperature | 22,000±1,000[7] K |
| Rotation | 1.539 days[7] |
| Rotational velocity (v sin i) | 101[7] km/s |
| Age | 3.98[4] Myr |
| Other designations | |
| Landstreet's star[10], V901 Ori, BD−01°1005, HD 37776, HIP 26742, SAO 132446, PPM 175998[11] | |
| Database references | |
| SIMBAD | data |
Properties
This object was found to be a helium-rich variable star in 1976. It was shown to have a high rotation rate and display an infrared excess. Magnetic field measurements showed a multipole distribution and a period of 1.5 days.[13] This was the first star discovered in which a quadrupole-like geometry of the magnetic field dominated over the dipole field found in most stars.[14]
In 2007, HD 37776 was discovered to undergo change in rotation, probably due to loss of angular momentum from a magnetically-confined stellar wind.[15] The rotational braking in this star is 0.54±0.02 s per year, a record level for magnetic chemically-peculiar stars.[16] Surprisingly, a long-term study of the rotation period showed a steady increase until 2003, after which the period began to decrease. This may be the result of an interaction between a thin, magnetically-confined outer envelope and a faster rotating inner body.[17]
This is a massive, helium-strong, magnetic chemically peculiar star[18][10] with a stellar classification of B2V.[5] It is classified as an SX Arietis variable that ranges in visual magnitude from 6.97 to 7.02 with a period of 1.5385 days.[3] The light variation is believed due to uneven surface distribution of helium and silicon.[19][20] The topology of the magnetic field is the most complex ever found for an early-type star (i.e. a higher mass main sequence star).[21]
Stellar models paint this as a young star with an estimated age of four million years,[4] that is spinning with a projected rotational velocity of 101 km/s.[7] It has an estimated 8.3[7] times the mass of the Sun and 3.2 times the Sun's radius.[8] The star is radiating nearly 2,000 times the luminosity of the Sun from its photosphere at an effective temperature of around 22,000 [7]
HD 37776 is a member of the Orion OB1 association of co-moving stars[18] and is embedded in the emission nebula IC 432.[10] It is a candidate member of the Orion B Complex star forming region.[9]