V901 Orionis


V901 Orionis is a variable star in the equatorial constellation of Orion. It is sometimes known as Landstreet's Star 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, it is a challenge to view with the naked eye. Based on parallax measurements from Earth, it is located at a distance of. The star is drifting further away from the Sun with a radial velocity of 15 km/s.

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. 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.
In 2007, HD 37776 was discovered to undergo change in rotation, probably due to loss of angular momentum from a magnetically-confined stellar wind. The rotational braking in this star is per year, a record level for magnetic chemically-peculiar stars. 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.
This is a massive, helium-strong, magnetic chemically peculiar star with a stellar classification of B2V. It is classified as an SX Arietis variable that ranges in visual magnitude from with a period of 1.5385 days. The light variation is believed due to uneven surface distribution of helium and silicon. The topology of the magnetic field is the most complex ever found for an early-type star.
Stellar models paint this as a young star with an estimated age of four million years, that is spinning with a projected rotational velocity of 101 km/s. It has an estimated 8.3 times the mass of the Sun and 3.2 times the Sun's radius. The star is radiating nearly 2,000 times the luminosity of the Sun from its photosphere at an effective temperature of around 22,000
HD 37776 is a member of the Orion OB1 association of co-moving stars and is embedded in the emission nebula IC 432. It is a candidate member of the Orion [molecular cloud complex|Orion B Complex] star forming region.