NU Orionis
NU Orionis is a quadruple star system in the Orion constellation. It is located in the emission nebula Messier 43 and is the main star ionizing it. The distance to the system is, as determined by its stellar parallax.
Location
NU Orionis is within Messier 43, an emission nebula and H II region that is inside the Orion Nebula. It is the main star ionizing M43, with its radiation sculpting the nebula.Due to its faint apparent magnitude of 6.8, NU Orionis cannot be seen with the unaided eye, requiring at least binoculars to be seen. Messier 43 itself is magnitude 9, and can be seen with a small telescope. It culminates and is best seen in January.
NU Orionis was identified to be responsible for photoevaporation of several protoplanetary disks around stars in M43. These objects are also called proplyds. Two proplyds were discovered with the Hubble Space Telescope and later one additional proplyd was discovered with the James Webb Space Telescope.
Variability
NU Orionis is classified as "INSA" in the General Catalogue of Variable Stars. This acronym means that it is an Orion variablea hot star with irregular variationsurrounded in nebulosity. The apparent magnitude varies from 6.80 to 6.93. Such classification is typical of hot, very young stars in the early stages of evolution. The estimated age of NU Ori is 3 million years.Star system
NU Orionis was believed to be a single star until 1991, when spectroscopic observations revealed it to be a close binary with an orbital period of about 19 days. Subsequently, the distant companion HD 37061 B was discovered in 1999, at a distance of 470 milliarcseconds. In 2013, a candidate fourth member named HD 37061 C was announced, discovered using interferometry at a distance of 15 mas from the central pair. It was confirmed in 2018.The primary component, NU Orionis Aa, is a B-type main-sequence star with 16.4 times the mass of the Sun and 5.7 times the radius of the Sun, radiating 27,000 times the solar luminosity. Its companion, NU Orionis Ab, orbits with a period of 14.3027 days and is separated by 0.36 astronomical units; the orbit is nearly circular. The star has 4.4 times the mass and 2.5 times the radius of the Sun, radiating 350 times the radiation the Sun does.
The tertiary NU Orionis C is a B-type main-sequence star with 8.1 times the mass, 3.6 times the radius, and radiates 2,800 times the Sun's luminosity. The star has a strong magnetic field. It orbits the Aa-Ab pair with an orbital period of and is separated by 3.77 au.
The outer companion B is an A or B-main sequence star with 3.8 times the mass, 2.3 times the radius and 190 times the Sun's luminosity. It has a projected separation of 195 au to the inner triple, an orbit too large to currently have its elements measurable.
The components Aa, B and C are rapid rotators, spinning with projected rotational velocities of 190, 180 and 104 km/s respectively. Component C's rotation period has been measured at around 1.09 days.