Zeta Puppis

Zeta Puppis (ζ Pup, ζ Puppis) is a star in the constellation of Puppis. It is also known by the traditional names Naos ( /ˈneɪ.ɒs/, from the Greek ναύς "ship") and Suhail Hadar (سهيل هدار, possibly "roaring bright one") in Arabic.

Its spectral class is O5Ia, making it an exceptionally hot star, and it is one of the sky's few naked-eye class O-type stars. Its surface temperature is 42,400 K,^[4] or about seven times hotter than the surface of the Sun. Its mass is 40 solar masses.^[2]

Unlike many other stars at such great distance, the precise parameters for Zeta Puppis including its velocity are known, and can extrapolate back to the region where it was formed, a molecular cloud in Vela.^[2] We can therefore derive a much more accurate distance than we can with, for example, Deneb. 2008 reductions of Hipparcos raw data give a distance of 335 parsecs (1,093 ly) ± 4%, and for Deneb, 475 pc ± 20%.^[5]

Zeta Puppis is an extreme blue supergiant, one of the brightest stars in the Milky Way in terms of absolute magnitude. Visually, it is 21,000 times more powerful than the Sun, but being an extreme blue star most of its radiation is in the ultraviolet, and when this is considered it is approximately 360,000 solar.^[2] Blue stars are never very large, and Naos is no exception, being "merely" 11 times the solar radius.^[2] Red supergiants such as Betelgeuse and Mu Cephei are the largest stars.

For comparison, at the distance of Sirius, Naos would cast strong shadows on Earth, with a visible magnitude of -9 (near that of the quarter moon), but if it were placed at the center of our Solar System, its intense heat at a distance of 1 AU would heat the Earth to an incredible 6100 K, causing it to vaporize slowly and leaving a comet-like trail. It would appear 20 times the Sun's diameter and shine 20,000 times brighter in the sky with an extremely powerful blue-white glow. Its apparent magnitude would be -37.5 and thus even scattered or refracted light would blind a human in seconds, even with a welding mask. In order for Naos to appear equal to the Sun's apparent magnitude of -26.8 combined with Earth-like temperatures, a planet would need to be 450 AU away from Naos, over eleven times the distance from the Sun to Pluto. The star is unlikely to harbor any planets at Earth like distances (1AU).

Zeta Puppis, being typical of O-type stars, is also notable for its extremely strong stellar wind, and it has garnered increasing attention for this over the past decade. Its stellar wind velocity has been estimated at some 2300 km/s, which sees the star shed one millionth () of its solar mass each year, or about 10 million times that shed by our own Sun over a comparable time period. This mass ejection is highly evident in non-visible wavelengths such as radio and X-ray, and it has presented some excellent opportunities for study.

In several hundred thousand years, Naos will cool on its way to becoming a red supergiant and will pass through spectral classes B, A, F, G, K, and M as it cools. When this occurs, the star's output will mostly be in the visible spectrum, and Naos will appear from Earth as one of the brightest stars in the sky. Within 2 million years, Naos will turn into a Class M5 red supergiant bigger than the orbit of the Earth and it will eventually explode into a supernova so powerful and bright that even at 970 light years^[2] it will appear much brighter than the full Moon and could collapse into a black hole. If so, the inwards ejected matter of the supernova will fall back into the black hole and form a powerful accretion disc with gamma rays ejected from the poles.

Origin

It was long thought that Zeta Puppis was formed in the Vela star-forming region, about 1400 light years distant from the position as measured. However, data obtained in 2008 in a revision of Hipparcos data (see above) shows that the star was formed instead with the cluster Trumpler 10 and has been ejected from the cluster. This narrows the question of the age of Zeta Puppis, as Trumpler 10 has been measured to be 47 million years old. There is evidence of an ionization front (a "bow shock") ahead of Naos. Howarth et al. in 1995 determined an anomalously high rotational velocity of 211 km/s at the equator, which also seems to be a common trend in O runaway stars, as well as an apparent enrichment in helium and nitrogen on the surface. Its estimated age is about 4 million years.

Helium

In 1896, Edward C. Pickering observed mysterious spectral lines from ζ Puppis, which fit the Rydberg formula if half-integers were used instead of whole integers. It was later found that these were due to ionized helium.

Namesakes

USS Naos (AK-105) was a United States Navy Crater class cargo ship named after the star.

References

• Schaerer, Daniel; et al. (1997). "Fundamental Stellar Parameters of γ2 Velorum from HIPPARCOS Data". Astrophysical Journal Letters 484: L153–L156. arXiv:astro-ph/9703061. Bibcode 1997ApJ...484L.153S. doi:10.1086/310785.