Epsilon Canis Majoris
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| Observation data Epoch J2000 |
|
|---|---|
| Constellation (pronunciation) |
Canis Major |
| Right ascension | 06h 58m 37.6s |
| Declination | −28° 58' 19" |
| Apparent magnitude (V) | 1.51 |
| Characteristics | |
| Spectral type | B2 Iab |
| U-B color index | −0.93 |
| B-V color index | −0.13 |
| Astrometry | |
| Radial velocity (Rv) | +27.3 km/s |
| Proper motion (μ) | RA: 2.63 mas/yr Dec.: 2.29 mas/yr |
| Parallax (π) | 7.57 ± 0.57 mas |
| Distance | 430 ± 30 ly (132 ± 10 pc) |
| Absolute magnitude (MV) | −4.11 |
| Details | |
| Mass | 10 M☉ |
| Luminosity | 20,000 L☉ |
| Temperature | 24,750 K |
| Metallicity | 20% Sun |
| Other designations | |
| Database references | |
| SIMBAD | data |
Epsilon Canis Majoris (ε CMa / ε Canis Majoris), is the second brightest star in the constellation Canis Major, and one of the brightest stars in the nighttime sky. It has the Bayer designation "epsilon" despite being the second brightest and not the fifth brightest star in its constellation. It also has the traditional name Adhara (sometimes spelled Adara). The name is from the Arabic word عذارى ‘aðāra’, "virgins". It is known as 弧矢七 (the Seventh Star of the Bow and Arrow) in Chinese.
Adhara is a binary star, about 430 light years distant from Earth. The main star possesses an apparent magnitude of +1.5 and belongs to the spectral classification B2. It has a surface temperature of 25,000 K and emits a total radiation equal to 20,000 times that of the Sun. If this star were at the same distance as Sirius, it would appear 15 times brighter than the planet Venus. This star is also one of the brightest known extreme ultraviolet sources in the sky.
The +7.5 magnitude companion star (the absolute magnitude amounts to −5.0) is at 7.5" away with a position angle of 161° of the main star. Despite the relatively large angular distance the components can only be resolved in large telescopes, since the main star is approximately 250 times brighter than its companion.
A few million years ago, Adhara was much closer to the Sun than it is at present, causing it to be a much brighter star in the night sky. About 4,700,000 years ago, Adhara was 34 light years from the Sun, and was the brightest star in the sky with a magnitude of –3.99. No other star has attained this brightness since, nor will any other star attain this brightness for at least five million years.[1]
[edit] References
- E. Wilkinson, J.C. Green, R. McLean, and B. Welsh, "Extreme Ultraviolet Spectrum of epsilon Canis Majoris between 600-920 Å", Bull. American Astron. Soc., 188, #58.02.
- ^ Sky and Telescope, April 1998.
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