Eta Canis Majoris (η Canis Majoris, abbreviated Eta CMa, η CMa), also named Aludra /əˈluːdrə, əˈljuːdrə/,[10] is a star in the constellation of Canis Major. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[11]

η Canis Majoris

Location of η Canis Majoris (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Canis Major
Right ascension	07h 24m 05.70228s[1]
Declination	–29° 18′ 11.1798″[1]
Apparent magnitude (V)	2.450[2]
Characteristics
Spectral type	B5 Ia[3]
U−B color index	−0.708[2]
B−V color index	−0.087[2]
Variable type	α Cyg[4]
Astrometry
Radial velocity (Rv)	41.1[5] km/s
Proper motion (μ)	RA: −4.14[1] mas/yr Dec.: 5.81[1] mas/yr
Parallax (π)	1.64 ± 0.40 mas[1]
Distance	approx. 2,000 ly (approx. 600 pc)
Absolute magnitude (MV)	−7.0[6]
Details
Mass	18.19[7] M☉
Radius	54[8] R☉
Luminosity	135,000 - 174,000[8] L☉
Surface gravity (log g)	2.00[8] cgs
Temperature	15,000 - 16,000[8] K
Rotational velocity (v sin i)	40[8] km/s
Age	8.3[9] Myr
Other designations
Aludra, 31 Canis Majoris, CD−29°4328, FK5 283, HD 58350, HIP 35904, HR 2827, SAO 173651
Database references
SIMBAD	data

Nomenclature

η Canis Majoris (Latinised to Eta Canis Majoris) is the star's Bayer designation.

The traditional name Aludra originates from the Arabic: العذراء al-adhraa, 'the virgin'. This star, along with Epsilon Canis Majoris (Adhara), Delta Canis Majoris (Wezen) and Omicron² Canis Majoris (Thanih al Adzari), were Al 'Adhārā (العذاري), 'the Virgins'.[12] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[13] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[14] included a table of the first two batches of names approved by the WGSN; which included Aludra for this star.

In Chinese, 弧矢 (Hú Shǐ), meaning Bow and Arrow,[15] refers to an asterism consisting of Eta Canis Majoris, Delta Canis Majoris, HD 63032, HD 65456, Omicron Puppis, k Puppis, Epsilon Canis Majoris, Kappa Canis Majoris and Pi Puppis. Consequently, Eta Canis Majoris itself is known as 弧矢二 (Hú Shǐ èr, English: the Second Star of Bow and Arrow).[16]

Properties

A blue-white supergiant, Eta CMa has been used as a standard for the spectral type of B5Ia.[18]

Eta CMa shines brightly in the skies in spite of a large distance from Earth due to being intrinsically many times brighter than the Sun. It has a luminosity over 100,000 times and a radius around 54 times that of the Sun. It has only been around a fraction of the time the Sun has, less than 10 million years, yet is already in the last stages of its life. It is still expanding and may become a red supergiant, or perhaps has already passed that phase, but in either case it will become a supernova within the next few million years.^{[citation needed]}

Eta CMa is classified as an Alpha Cygni-type variable star and its brightness varies from magnitude +2.38 to +2.48 over a period of 4.7 days.[4][19]

Namesakes

Both USS Aludra (AF-55), an Alstede-class stores ship, and USS Aludra (AK-72), a Crater-class cargo ship, were U.S. Navy vessels named after the star.

References

На других языках

[de] Aludra

[es] Aludra

[ru] Алудра