Delta Cephei
Encyclopedia
Delta Cephei (δ Cep, δ Cephei) is a binary star
system approximately 891 light-year
s away in the constellation
of Cepheus
(the King
). Delta Cephei is the prototype of the Cepheid variable
stars, and it is among the closest stars of this type to the Sun
(with Polaris
being closer). Its variability was discovered by John Goodricke
in 1784, the second Cepheid variable discovered following Eta Aquilae
earlier the same year.
3.48 to 4.37, and its spectral type
also varies, from about F5 to G3. The period is 5.36634 days; rise to maximum is quicker than the subsequent decline to minimum. It was later discovered that there are two types of Cepheid variables, and Delta Cephei is now known as a type I (Classical) Cepheid.
Stars of this type are believed to form with masses of 3–30 times that of our Sun
, and then have passed through the main sequence
as B-class stars. With the hydrogen
burnt up in their core, these unstable stars are now passing through later stages of nuclear burning.
Knowing the distance of Delta Cephei and others in its class is fundamental to calibrating their period-luminosity relationship; unfortunately, these efforts were until recently marred by only fair parallax
accuracy. In 2002 however, the Hubble Space Telescope
was used to determine the distance to Delta Cephei (and RR Lyrae
, another standard candle) within ~4%: 273 parsecs, or 890 light-years. There is a 7.5 magnitude companion star, separated from Delta Cephei by 41 arc seconds and visible in small telescopes.
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
system approximately 891 light-year
Light-year
A light-year, also light year or lightyear is a unit of length, equal to just under 10 trillion kilometres...
s away 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 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:...
(the King
King
- Centers of population :* King, Ontario, CanadaIn USA:* King, Indiana* King, North Carolina* King, Lincoln County, Wisconsin* King, Waupaca County, Wisconsin* King County, Washington- Moving-image works :Television:...
). Delta Cephei is the prototype of the Cepheid variable
Cepheid variable
A Cepheid is a member of a class of very luminous variable stars. The strong direct relationship between a Cepheid variable's luminosity and pulsation period, secures for Cepheids their status as important standard candles for establishing the Galactic and extragalactic distance scales.Cepheid...
stars, and it is among the closest stars of this type to the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
(with Polaris
Polaris
Polaris |Alpha]] Ursae Minoris, commonly North Star or Pole Star, also Lodestar) is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole, making it the current northern pole star....
being closer). Its variability was discovered by John Goodricke
John Goodricke
John Goodricke FRS was an eminent and profoundly deaf amateur astronomer. He is best known for his observations of the variable star Algol in 1782.- Life and work :...
in 1784, the second Cepheid variable discovered following Eta Aquilae
Eta Aquilae
Eta Aquilae is a star in the constellation Aquila. It was also part of the former constellation Antinous. It is a Cepheid variable star, varying from apparent magnitude 3.5 to 4.4 with a period of 7.176641 days...
earlier the same year.
Stellar system
Unlike the eclipsing binary Algol, Delta Cephei's variability is due to pulsation of the star. It varies from 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...
3.48 to 4.37, and its spectral type
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...
also varies, from about F5 to G3. The period is 5.36634 days; rise to maximum is quicker than the subsequent decline to minimum. It was later discovered that there are two types of Cepheid variables, and Delta Cephei is now known as a type I (Classical) Cepheid.
Stars of this type are believed to form with masses of 3–30 times that of our Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, and then have passed through the main sequence
Main sequence
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 Hertzsprung and Henry Norris Russell...
as B-class stars. With the hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
burnt up in their core, these unstable stars are now passing through later stages of nuclear burning.
Knowing the distance of Delta Cephei and others in its class is fundamental to calibrating their period-luminosity relationship; unfortunately, these efforts were until recently marred by only fair parallax
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. The term is derived from the Greek παράλλαξις , meaning "alteration"...
accuracy. In 2002 however, the Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
was used to determine the distance to Delta Cephei (and RR Lyrae
RR Lyrae
RR Lyrae is a variable star in the Lyra constellation. It is the prototype of the RR Lyrae variable class of stars. It has a period of about 13 hours, and oscillates between apparent magnitudes 7 and 8. Its variable nature was discovered by the Scottish astronomer Williamina Fleming at Harvard...
, another standard candle) within ~4%: 273 parsecs, or 890 light-years. There is a 7.5 magnitude companion star, separated from Delta Cephei by 41 arc seconds and visible in small telescopes.