Zeta Puppis (ζ Puppis, abbreviated Zeta Pup, ζ Pup), formally named Naos , is the brightest

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

in the

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 ...

Puppis Puppis ("poop deck, stern") is a constellation in the southern sky. It was originally part of the Former constellations, traditional constellation of Argo Navis (the ship of Jason and the Argonauts), which was divided into three parts, the other ...

. The

spectral class In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

of O4 means this is one of the hottest, and most luminous, stars visible to the naked eye. It is one of the sky's few naked-eye class O-type stars as well as one of the closest to

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. It is a

blue Blue is one of the three primary colours in the RYB color model, RYB colour model (traditional colour theory), as well as in the RGB color model, RGB (additive) colour model. It lies between Violet (color), violet and cyan on the optical spe ...

supergiant Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram, with absolute visual magnitudes between about −3 and −8. The temperatures of supergiant stars range ...

, one of the most luminous stars in the

Milky Way The Milky Way or Milky Way Galaxy is the galaxy that includes the Solar System, with the name describing the #Appearance, galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars in other arms of the galax ...

. Visually it is over 10,000 times brighter than the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

, but its high temperature means that most of its

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes: * ''electromagnetic radiation'' consisting of photons, such as radio waves, microwaves, infr ...

is in the

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

and its bolometric luminosity is over 500,000 times that of the Sun. It is also the 72nd brightest star in terms of

apparent magnitude Apparent magnitude () is a measure of the Irradiance, 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 (astronomy), ...

from Earth. It is a runaway star, meaning it has an unusually large space velocity, probably caused by being ejected from a close binary system when its companion exploded as a supernova. Zeta Puppis is typical of O-type stars in having an extremely strong

stellar wind A stellar wind is a flow of gas ejected from the stellar atmosphere, upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spheri ...

, measured at 2,500 km/s, which sees the star shed more than a millionth of its mass each year, or about 10 million times that shed by the Sun over a comparable time period.

Nomenclature

''ζ Puppis'' ( Latinised to ''Zeta Puppis'') is the star's

Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...

. It bears the name ''Naos'', from the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

''ναύς'' "ship", and in Arabic ''Suhail Hadar'' (سُهَيْل حَضَار). In 2016, the

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

organized a

Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...

(WGSN) to catalogue and standardize proper names for stars. The WGSN approved the name ''Naos'' for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.

Namesake

USS Naos (AK-105) was a

United States Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...

Crater class cargo ship named after the star.

Physical characteristics

Zeta Puppis has been extensively studied because of the rarity of such hot massive stars and its relative closeness to Earth, but its physical parameters and distance are still poorly known. It would be a valuable step on the

cosmic distance ladder The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. A ''direct'' distance measurement of an astronomical object is possible ...

, clarifying the distance of other high luminosity stars in the Milky Way galaxy and external galaxies. The spectral type is O4If(n)p. O4 indicates a hot massive hydrogen-burning star, typically 40,000–44,000K. The "f" indicates that the spectrum has emission lines of ionised Helium and Nitrogen, not uncommon in somewhat evolved hot O stars and typically identified by the composite emission and absorption profile of the 468.6 nm He_II spectral line. The "n" (for nebulous) indicates broadened absorption lines, caused by rapid rotation of the star, in this case over 220 km/s at the equator. The "p" is a general spectral indicator of peculiarity. This combination of spectral characters is unusual because evolved hot stars are expected to rotate relatively slowly after braking by a strong stellar wind, and only 8 stars of this type are known in the Milky Way. The spectral type complicates determination of physical parameters as the standard spectral luminosity indicator lines are peculiar and this type of star cannot be fully modelled. The enhanced Helium and Nitrogen and the lower surface gravity indicates some degree of evolution away from the zero age main sequence and Zeta Puppis is ranked as a supergiant. The angular size of Zeta Puppis has been measured interferometrically to be 0.41 mas, and photometrically to be 0.38 mas.

Variability

The brightness of Zeta Puppis varies slightly but regularly. Its apparent magnitude varies between a peak of 2.24 and a minimum of 2.26 over 1.78 days. The variations had been thought to be the due to the pulsations of an

α Cygni variable Alpha Cygni variables are variable stars which exhibit non-radial pulsations, meaning that some portions of the stellar surface are contracting at the same time other parts expand. They are supergiant stars of Stellar classification, spectral types ...

, but are too predictable and regular. The eclipse-like light curve is now thought to be due to rotation of the star which has large irregular features at the base of its dense

. It also shows variations in H_α spectral line profiles and

x-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

luminosity on timescales less than a day.

Distance

The distance of Zeta Puppis is disputed, most commonly being considered to be based on its Hipparcos parallax, or based on its expected physical properties. Its association with objects such as the Gum nebula and γ² Velorum is also used as a method to establish its distance. The physical properties of the star depend strongly on its distance, with its bolometric luminosity being at and only about at . Its rotational velocity and period constrain the possible distances and inclination of the star. The rotational period was long considered to be just over five days, being the period of certain variations observed in its spectrum. However, it is now thought that less obvious brightness variations with a period of 1.78 days are caused by bright areas on the surface of the star as it rotates. With the projected equatorial rotational velocity of , this means that the star is rotating at close to its break-up velocity and that the equator must be inclined less than about 33° to us.

Helium

In 1896,

Williamina Fleming Williamina Paton Stevens Fleming (15 May 1857 – 21 May 1911) was a pioneering Scottish astronomer, who made significant contributions to the field despite facing gender biases. She was a single mother hired by the director of the Harvard Co ...

observed mysterious spectral lines from Zeta Puppis, which fit the

Rydberg formula In atomic physics, the Rydberg formula calculates the wavelengths of a spectral line in many chemical elements. The formula was primarily presented as a generalization of the Balmer series for all atomic electron transitions of hydrogen. It was ...

if half-integers were used instead of whole integers. It was later found that these were due to ionized

helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...

Origin

Early suggestions for the birthplace of Zeta Puppis were the very young Vela R2 stellar association at around 800pc and the Vela OB2 association at 450pc. Neither origin is satisfactory. A distance of 800pc requires an abnormally high luminosity, while the Vela OB2 association is much older than Zeta Puppis and the space velocity does not lead back to that cluster. Many physical models and the original Hipparcos parallax measurements did lead to a distance value of around 450pc, but the revised Hipparcos reduction gave a much lower distance near 333pc. A recent dynamical study points to Zeta Puppis originating in the Trumpler 10 OB association at around 300pc, but this is also a much older cluster and physical models still lead to a distance of 450-600pc. Zeta Puppis shows a high space velocity and very high rotation rate, and it has been speculated that it is a runaway star resulting from a supernova in a binary system, possibly the progenitor of the Gum Nebula. Models of binary systems are able to reproduce the properties of Zeta Puppis following mass transfer from a companion which then exploded as a supernova. This can explain the observed properties which are inconsistent with single star evolution.

References

{{DEFAULTSORT:Zeta Puppis O-type supergiants Emission-line stars Alpha Cygni variables Runaway stars Puppis Puppis, Zeta Durchmusterung objects 066811 039429 3165 Naos