21 Comae Berenices 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 ...
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 first constellati ...
of
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 hemispher ...
.
It has the
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 ...
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 88 modern constellations, modern constellations visible from southern England. They are named after John Flamsteed, au ...
.
About
According to R. H. Allen, English orientalist Thomas Hyde 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 ...
or dog rose.naked eye
Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or microsc ...
with an 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 ...
that fluctuates around 5.47.parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...
measurements, it is located at a distance of approximately 270 light year
A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...
s away from the Sun.open cluster
An open cluster is a type of star cluster made of tens 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, or 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 classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...
.[ 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 gratin ...
is A3p SrCr,[ where the suffix notation indicates abundance anomalies of the iron-peak element chromium, as well as strontium.
In 1950, Olin Jeuck Eggen reported that the brightness of 21 Comae Berenices is variable.]spots
Spot or SPOT may refer to:
Places
* Spot, North Carolina, a community in the United States
* The Spot, New South Wales, a locality in Sydney, Australia
* South Pole Traverse, sometimes called the South Pole Overland Traverse
People
* Spot Col ...
on its surface created by a magnetic field
A magnetic field (sometimes called B-field) is a physical 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 ...
. 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 am ...
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 class of pulsating star, comprising several sub-classes of object with A- or F-type spectra.
The variables follow a period-luminosity ...
,[ 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 bu ...
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
Solar radius is a unit of distance used to express the size of objects in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3:
1\,R_ = 6.957\ti ...
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. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately , or equivalently, a depth from which 50% of light will esc ...
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
4766
BD+25 2517
Comae Berenices, 21
108945
061071
Comae Berenices, UU