Beta Cephei
Encyclopedia
Beta Cephei is a third magnitude star
in the constellation
Cepheus
. It has the traditional name Alfirk (Arabic
الفرقة al-firqah), meaning "The Flock" (referring to a flock of sheep) This star, along with α Cep
(Alderamin) and η Cep
(Alkidr), were Al Kawākib al Firḳ (الكوكب الفرق), meaning "the Stars of The Flock" by Ulug Beg. Beta Cephei is the prototype of the Beta Cephei variable
stars.
in the constellation
of Draco
, Alfirk is visible primarily in the northern hemisphere
, given its extreme northern declination
of 70 degrees and 34 minutes. The star is nevertheless visible to most observers throughout the world reaching as far south as cities like Harare
in Zimbabwe
, Santa Cruz de la Sierra
in Bolivia
or other settlements north ± 19° South latitude. The star is circumpolar
throughout all of Europe
, northern Asia, and North American cities as far south as Guadalajara
on the west coast of Mexico
. All other locations around the globe having a latitude
greater than ± 20° North will notice that the star is always visible in the night sky. Because Beta Cephei is a faint third magnitude star, it may be difficult to identify in most light polluted
cities, though in rural locations the star should be easily observable.
8 optical companion. Its magnitude
varies between +3.15 and +3.21 with a period of 0.1904844 days.
Beta Cephei A is a blue giant
star with a stellar classification
listed in the SIMBAD
astronomical database as B2IIIev. The suffix "ev" comes from the Yerkes classification system and stands for "Spectral emission that exhibits variability". This giant star has a radius that has been estimated at 9R☉ and a mass of 12M☉
. Like most high mass B class stars, β Cep is a relatively young star with an estimated age of around 50 million years old. Like the majority of giant stars, Beta Cephei A rotates slowly on its axis with a rotational velocity of 28 km/s, a speed which takes the star approximately 51 days to make one complete revolution.
In 2007, Floor van Leeuwen and his team recalibrated the star's apparent magnitude
at 3.1438 and updated the star's parallax to 4.76 ± 0.30 mas yielding a distance of 210.1 parsecs (pc) or approximately 685 light years (ly) from Earth
. The previous estimate from the Hipparcos
mission had placed the star at about 595 ly. Given a surface temperature of 26,700 Kelvin, theoretical calculations yield a total luminosity for the star of about 36,900L☉.
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Cepheus
Cepheus (constellation)
Cepheus is a constellation in the northern sky. It is named after Cepheus, King of Aethiopia in Greek mythology. It was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and remains one of the 88 modern constellations.-Stars:...
. It has the traditional name Alfirk (Arabic
Arabic language
Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book...
الفرقة al-firqah), meaning "The Flock" (referring to a flock of sheep) This star, along with α Cep
Alpha Cephei
Alpha Cephei is a second magnitude star in the constellation of Cepheus that is relatively close to Earth at only 49 light years...
(Alderamin) and η Cep
Eta Cephei
Eta Cephei is a class K0 third-magnitude giant star in the constellation Cepheus. Eta Cephei is an orange giant star with a very high proper motion on the celestial sphere. It is about 45 light-years from Earth...
(Alkidr), were Al Kawākib al Firḳ (الكوكب الفرق), meaning "the Stars of The Flock" by Ulug Beg. Beta Cephei is the prototype of the Beta Cephei variable
Beta Cephei variable
Beta Cephei variables are variable stars which exhibit variations in their brightness due to pulsations of the stars' surfaces. The point of maximum brightness roughly corresponds to the maximum contraction of the star. Typically, Beta Cephei variables change in brightness by 0.01 to 0.3...
stars.
Visibility
Like the star Epsilon DraconisEpsilon Draconis
Epsilon Draconis is a fourth-magnitude star in the constellation Draco. It has the traditional name Tyl. This star along with Delta Draconis , Pi Draconis and Rho Draconis forms an asterism known as Al Tāis, meaning "the Goat".In Chinese astronomy, , meaning the Celestial Kitchen, refers to an...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
of Draco
Draco (constellation)
Draco is a constellation in the far northern sky. Its name is Latin for dragon. Draco is circumpolar for many observers in the northern hemisphere...
, Alfirk is visible primarily in the northern hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
, given its extreme northern declination
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
of 70 degrees and 34 minutes. The star is nevertheless visible to most observers throughout the world reaching as far south as cities like Harare
Harare
Harare before 1982 known as Salisbury) is the largest city and capital of Zimbabwe. It has an estimated population of 1,600,000, with 2,800,000 in its metropolitan area . Administratively, Harare is an independent city equivalent to a province. It is Zimbabwe's largest city and its...
in Zimbabwe
Zimbabwe
Zimbabwe is a landlocked country located in the southern part of the African continent, between the Zambezi and Limpopo rivers. It is bordered by South Africa to the south, Botswana to the southwest, Zambia and a tip of Namibia to the northwest and Mozambique to the east. Zimbabwe has three...
, Santa Cruz de la Sierra
Santa Cruz de la Sierra
Santa Cruz de la Sierra, commonly known as Santa Cruz, is the capital of the Santa Cruz department in eastern Bolivia and the largest city in the country...
in Bolivia
Bolivia
Bolivia officially known as Plurinational State of Bolivia , is a landlocked country in central South America. It is the poorest country in South America...
or other settlements north ± 19° South latitude. The star is circumpolar
Circumpolar star
A circumpolar star is a star that, as viewed from a given latitude on Earth, never sets , due to its proximity to one of the celestial poles...
throughout all of Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, northern Asia, and North American cities as far south as Guadalajara
Guadalajara
Guadalajara may refer to:In Mexico:*Guadalajara, Jalisco, the capital of the state of Jalisco and second largest city in Mexico**Guadalajara Metropolitan Area*University of Guadalajara, a public university in Guadalajara, Jalisco...
on the west coast of Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
. All other locations around the globe having a latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
greater than ± 20° North will notice that the star is always visible in the night sky. Because Beta Cephei is a faint third magnitude star, it may be difficult to identify in most light polluted
Light pollution
Light pollution, also known as photopollution or luminous pollution, is excessive or obtrusive artificial light.The International Dark-Sky Association defines light pollution as:...
cities, though in rural locations the star should be easily observable.
Properties
Beta Cephei is a triple star comprising a spectroscopic binary with a magnitudeApparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
8 optical companion. Its magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
varies between +3.15 and +3.21 with a period of 0.1904844 days.
Beta Cephei A is a blue giant
Blue giant
In astronomy, a blue giant is a star with a spectral type of O or B and a luminosity class of III...
star with a stellar classification
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
listed in the SIMBAD
SIMBAD
SIMBAD is an astronomical database of objects beyond the Solar System...
astronomical database as B2IIIev. The suffix "ev" comes from the Yerkes classification system and stands for "Spectral emission that exhibits variability". This giant star has a radius that has been estimated at 9R☉ and a mass of 12M☉
Solar mass
The solar mass , , is a standard unit of mass in astronomy, used to indicate the masses of other stars and galaxies...
. Like most high mass B class stars, β Cep is a relatively young star with an estimated age of around 50 million years old. Like the majority of giant stars, Beta Cephei A rotates slowly on its axis with a rotational velocity of 28 km/s, a speed which takes the star approximately 51 days to make one complete revolution.
In 2007, Floor van Leeuwen and his team recalibrated the star's apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
at 3.1438 and updated the star's parallax to 4.76 ± 0.30 mas yielding a distance of 210.1 parsecs (pc) or approximately 685 light years (ly) from Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. The previous estimate from the Hipparcos
Hipparcos
Hipparcos was a scientific mission of the European Space Agency , launched in 1989 and operated between 1989 and 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky...
mission had placed the star at about 595 ly. Given a surface temperature of 26,700 Kelvin, theoretical calculations yield a total luminosity for the star of about 36,900L☉.
See also
- List of stars in Draco
- Class B Stars
- Variable starVariable starA star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
- Star systemStar systemA star system or stellar system is a small number of stars which orbit each other, bound by gravitational attraction. A large number of stars bound by gravitation is generally called a star cluster or galaxy, although, broadly speaking, they are also star systems.-Binary star systems:A stellar...
External links
- Jim Kaler's Stars, University of Illinois:ALFIRK (Beta Cephei)
- AAVSO Variable Star of the Month, Winter 2005: The Beta Cephei Stars and Their Relatives
- An Atlas of the Universe: Multiple Star Orbits