Z Canis Majoris (Z CMa) is a B-type

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Canis Major Canis Major is a constellation in the southern celestial hemisphere. In the second century, it was included in Ptolemy's 48 constellations, and is counted among the 88 modern constellations. Its name is Latin for "greater dog" in contrast to C ...

. It has an average

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

of approximately 10, though has brightened by 1-2 magnitudes in irregular outbursts in 1987, 2000, 2004 and 2008. Arville D. Walker of the

Harvard College Observatory The Harvard College Observatory (HCO) is an institution managing a complex of buildings and multiple instruments used for astronomical research by the Harvard University Department of Astronomy. It is located in Cambridge, Massachusetts, United St ...

discovered that the star is a

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

, from the examination of 275 photographs taken between 1899 and 1921. Her discovery was announced in 1921, and the star received its

variable star designation In astronomy, a variable-star designation is a unique identifier given to variable stars. It extends the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constellation in whic ...

, Z Canis Majoris, in 1922. The star is a complex binary system only 300,000 years old with two main components separated by an estimated 100 astronomical units (AU) or 0.1" as seen from Earth. The southeast component is an FU Orionis star (a type of

pre-main-sequence star A pre-main-sequence star (also known as a PMS star and PMS object) is a star in the stage when it has not yet reached the main sequence. Earlier in its life, the object is a protostar that grows by acquiring mass from its surrounding envelope o ...

in a phase of very high mass accretion resulting in an accretion disk which dominates the optical spectrum) that is 1300 times as luminous as the Sun, has 3 times its mass and 13 times its diameter and a surface temperature of 10,000 K. The northwest component is a Herbig Ae/Be star that has been calculated to be 12 times as massive as the Sun with a dust shell photosphere times its diameter and a blackbody temperature of 980 K, the star shines with a luminosity 2,400 times greater than that of the sun, though there is some uncertainty about its properties. It is enveloped in an irregular roughly spherical cocoon of dust that has an inner diameter of 20 and outer diameter of 50 AU. The cocoon has a hole in it through which light shines that covers an angle of 5 to 10 degrees of its circumference. Both stars are surrounded by a large envelope of in-falling material that left over from the original cloud that formed the system. Both stars are emitting jets of material, that of the Herbig Ae/Be star being much larger - up to 11.7 light-years (3.6 parsecs) long. It is unclear whether the most recent (and brightest) brightening in 2008 was due to the Herbig Ae/Be star increasing in luminosity or a hole appearing in the cocoon.

References

{{DEFAULTSORT:Z Canis Majoris FU Orionis stars Herbig Ae/Be stars Canis Major B-type stars 053179 034042 Canis Majoris, Z Durchmusterung objects