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Zeta Puppis (ζ Puppis, abbreviated Zeta Pup, ζ Pup), formally named Naos , is a
star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
in the
constellation A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the earliest constellation ...
of
Puppis Puppis is a constellation in the southern sky. Puppis, the Latin translation of "poop deck", was originally part of an over-large constellation Argo Navis (the ship of Jason and the Argonauts), which centuries after its initial description, wa ...
. 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 An O-type star is a hot, blue-white star of spectral type O in the Yerkes classification system employed by astronomers. They have temperatures in excess of 30,000 kelvin (K). Stars of this type have strong absorption lines of ionised helium, ...
as well as one of the closest to
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...
. It is a blue
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 temperature range of supergiant stars spa ...
, one of the most luminous stars in the
Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...
. Visually it is over 10,000 times brighter than the
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
, 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 through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
is in the
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
and its
bolometric A bolometer is a device for measuring radiant heat by means of a material having a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley. Principle of operation A bolometer ...
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 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 ...
from Earth. It is a runaway star, meaning it has an unusually large pace velocity, probably caused by being ejected from a close binary system when its companion exploded as a supernova. Naos is typical of O-type stars in having an extremely strong
stellar wind A stellar wind is a flow of gas ejected from the 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 spherically symmetric. ...
, 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 or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars ...
. It bears the name ''Naos'', from the
Greek Greek may refer to: Greece 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 ...
''ναύς'' "ship", and in Arabic ''Suhail Hadar'' (سهيل هدار). In 2016, the
International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
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 maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...
Crater class cargo ship The ''Crater''-class cargo ship were converted EC2-S-C1 type, Liberty cargo ships, constructed by the United States Maritime Commission (USMC) for use by the US Navy during World War II. The designation 'EC2-S-C1': 'EC' for Emergency Cargo, '2' fo ...
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 o ...
, 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 HeII 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 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 Hert ...
and Zeta Puppis is ranked as a supergiant.


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 spectral types B or A. Variations in ...
, 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
stellar wind A stellar wind is a flow of gas ejected from the 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 spherically symmetric. ...
. It also shows variations in Hα spectral line profiles and
x-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10  nanometers, corresponding to frequencies in the range 30&nb ...
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 The Gum Nebula (Gum 12) is an emission nebula that extends across 36° in the southern constellations Vela and Puppis. It lies approximately 450 parsecs from the Earth. Hard to distinguish, it was widely believed to be the greatly expanded (an ...
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 Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a ...
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. The angular size of Zeta Puppis has been measured interferometrically to be 0.41 mas, and photometrically to be 0.38 mas.


Helium

In 1896,
Williamina Fleming (15 May 1857 – 21 May 1911) was a Scottish-American astronomer. She was a single mother, hired by the director of the Harvard College Observatory to help in the photographic classification of stellar spectra. She helped develop a common ...
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 wa ...
if half-integers were used instead of whole integers. It was later found that these were due to ionized
helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic ta ...
.


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 Trumpler 10 (also known as C 0846-423) is an open cluster located in the constellation Vela. It was possibly discovered by Nicolas Louis de Lacaille in 1751-52, as the cluster's location data matches well with No. II.6 in his catalog. The clust ...
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 The Gum Nebula (Gum 12) is an emission nebula that extends across 36° in the southern constellations Vela and Puppis. It lies approximately 450 parsecs from the Earth. Hard to distinguish, it was widely believed to be the greatly expanded (an ...
. 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


External links


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