X Cancri is a

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

in the northern

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 origins of the e ...

Cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

. It has a red hue and is visible to the naked eye at its brightest. The distance to this object is approximately 1,860

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s based on

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

measurements, but is drifting closer with a

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

of −5 km/s. It lies very close to the ecliptic and so is subject to lunar occultations. XCncLightCurve

This object is a

carbon star A carbon star (C-type star) is typically an asymptotic giant branch star, a luminous red giant, whose atmosphere contains more carbon than oxygen. The two elements combine in the upper layers of the star, forming carbon monoxide, which consumes mos ...

an aging

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around or ...

star on the

asymptotic giant branch The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) lat ...

that has a higher abundance of carbon than oxygen in its

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

and is one of the brightest carbon stars in the sky. It has a carbon star spectral classification of C-N4.5 C₂5.5 MS3. The first C indicates that it is a carbon star, and the N5 that it is a fairly cool strongly red AGB star. The C₂ index indicates the strength of the Swan bands on a scale of one to eight, which shows the relative abundance of carbon vs oxygen. The MS index, not to be confused with an MS spectral class, indicates the strength of the SiC₂ bands on a scale of one to seven. These bands are thought to be very sensitive to temperature. This is a

semiregular variable star In astronomy, a semiregular variable star, a type of variable star, is a giant or supergiant of intermediate and late (cooler) spectral type showing considerable periodicity in its light changes, accompanied or sometimes interrupted by various irre ...

of subtype SRb that ranges in brightness from visual magnitude 5.52 down to 7.50 with a period of 193 days.

Fourier analysis In mathematics, Fourier analysis () is the study of the way general functions may be represented or approximated by sums of simpler trigonometric functions. Fourier analysis grew from the study of Fourier series, and is named after Josep ...

has shown that the star also pulsates with periods of 350 and 1,870 days. The angular diameter of X Cancri has been measured using both lunar occultations and very long baseline interferometry, both methods giving a diameter around .

References

{{DEFAULTSORT:X Cancri Carbon stars Asymptotic-giant-branch stars Semiregular variable stars Cancer (constellation) Durchmusterung objects 076221 043811 3541 Cancri, X