R Monocerotis

R Monocerotis, abbreviated R Mon, is a very young binary star^[5] system in the equatorial constellation of Monoceros. The apparent magnitude of R Mon varies between 10 and 12 and the spectral type is B8IIIe.^[3]

R Monocerotis

R Monocerotis is at the bottom left of this photo. Credit: HST/NASA/JPL
Observation data Epoch J2000      Equinox J2000
Constellation	Monoceros
Right ascension	06h 39m 09.954s[1]
Declination	+08° 44′ 09.56″[1]
Apparent magnitude (V)	11.85[2]
Characteristics
Spectral type	B8IIIev[3]
Variable type	T Tauri[2]
Astrometry
Distance	2600 ly (800[4] pc)
Details
Mass	~2–10[5] M☉
Age	~105 yr[5] years
Other designations
R Mon, BD+08°1427, 2MASS J06390995+0844097, NGC 2261[2]
Database references
SIMBAD	data

This is a massive Herbig Ae/Be star, a type of pre-main-sequence star that is surrounded by an orbiting circumstellar disk of gas and dust. This disk has a mass of ~0.007 M_☉ and extends outward to a distance of under 150 AU from the host. Because of this dust, the star is obscured from direct visual sight but can still be observed in the infrared.^[5] R Mon is still in the accretion phase of star formation and it is driving an optically opaque bipolar outflow with a velocity of 9 km/s. The northern flow is blue-shifted, and thus moving more toward the Sun.^[7] There is a T Tauri-type stellar companion at an angular separation of 0.69″ from the primary.^[5]

This system is located in a diffuse nebula called "Hubble's Variable Nebula" (NGC 2261), which is being illuminated by a conical beam of light from the primary.^[5]