21 Comae Berenices 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 ...

Coma Berenices Coma Berenices is an ancient asterism in the northern sky, which has been defined as one of the 88 modern constellations. It is in the direction of the fourth galactic quadrant, between Leo and Boötes, and it is visible in both hemisphere ...

. It has the

variable star designation In astronomy, a variable star designation is a unique identifier given to variable stars. It uses a variation on the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constell ...

UU Comae Berenices, while 21 Comae Berenices is the

Flamsteed designation A Flamsteed designation is a combination of a number and constellation name that uniquely identifies most naked eye stars in the modern constellations visible from southern England. They are named for John Flamsteed who first used them while co ...

About

According to R. H. Allen, English orientalist

Thomas Hyde Thomas Hyde (29 June 163618 February 1703) was an English linguist, historian, librarian, classicist, and orientalist. His chief work was the 1700 'On the Ancient Religion of the Persians'' the first attempt to use Arab and Persian sources ...

attributed the ancient title Kissīn to this star, a name that comes from a climbing plant – either

bindweed Bindweed may refer to: * Some species of Convolvulaceae (bindweed family or morning glory family): ** ''Calystegia'' (bindweed, false bindweed, morning glory), a genus of about 25 species of flowering plants ** ''Convolvulus'' (bindweed, morning ...

dog rose ''Rosa canina'', commonly known as the dog rose, is a variable climbing, wild rose species native to Europe, northwest Africa, and western Asia. Description The dog rose is a deciduous shrub normally ranging in height from , though sometimes it ...

. This star has a white hue and is just visible to the naked eye with an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...

that fluctuates around 5.47. Based upon

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, it is located at a distance of approximately 270

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 away from the Sun. It is a single star but is a confirmed physical member of the Melotte 111

open cluster An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

History

This object has been studied extensively since 1953, producing some occasionally contradictory results such as hints of pulsational behavior or a binary companion. It is a weakly magnetic chemically peculiar star of type CP2, or

Ap star Ap and Bp stars are chemically peculiar stars (hence the "p") of spectral types A and B which show overabundances of some metals, such as strontium, chromium and europium. In addition, larger overabundances are often seen in praseodymium and neodym ...

, that is most likely on the

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

. The

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...

is A3p SrCr, where the suffix notation indicates abundance anomalies of the

iron-peak element The iron peak is a local maximum in the vicinity of Iron, Fe (Chromium, Cr, Manganese, Mn, Fe, Cobalt, Co and Nickel, Ni) on the graph of the abundances of the chemical elements. For elements lighter than iron on the periodic table, nuclear fusio ...

chromium, as well as strontium. This is an Alpha² Canum Venaticorum (ACV) variable, which indicates it varies in luminosity as it rotates due to spots on its surface created by a

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

. The range of variation has an

amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of amplit ...

of 0.02 magnitude and a period of just over two days. Samus et al. (2017) have it classified as a low-amplitude

Delta Scuti variable A Delta Scuti variable (sometimes termed dwarf cepheid when the V-band amplitude is larger than 0.3 mag.) is a subclass of young pulsating star. These variables as well as classical cepheids are important standard candles and have been used to e ...

, although this is disputed. The age of the Melotte 111 cluster, and therefore this star, lies in the range of 400–800 million years. The star has a

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bulge ...

of 63 km/s, with a polar inclination of 64° or greater, resulting in a rotation period of 2.05 days. Stellar evolutionary models yield a mass of around 2.3 times that of the Sun and 2.6 times the Sun's radius for this object. It is radiating 38 times the

luminosity of the Sun The solar luminosity (), is a unit of radiant flux (power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal s ...

from its

photosphere The photosphere is a star's outer shell from which light is radiated. The term itself is derived from Ancient Greek roots, φῶς, φωτός/''phos, photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it ...

at an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 8,900 K.

References

{{DEFAULTSORT:21 Comae Berenices A-type main-sequence stars Ap stars Alpha2 Canum Venaticorum variables Delta Scuti variables Coma Berenices 4968 BD+18 2697 Comae Berenices, 42 0501 114378 064241 Comae Berenices, UU