Alioth (star)
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Star Alioth (ε Ursae Majoris) |
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| ε UMa in the constellation "Great Bear" | |||||||||||||||||||||
| AladinLite | |||||||||||||||||||||
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Observation dates equinox : J2000.0 , epoch : J2000.0 |
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| Constellation | Big Bear | ||||||||||||||||||||
| Right ascension | 12 h 54 m 1.75 s | ||||||||||||||||||||
| declination | + 55 ° 57 ′ 35.4 ″ | ||||||||||||||||||||
| Apparent brightness | 1.75 likes | ||||||||||||||||||||
| Typing | |||||||||||||||||||||
| B − V color index | −0.02 | ||||||||||||||||||||
| U − B color index | 0.01 | ||||||||||||||||||||
| R − I index | −0.03 | ||||||||||||||||||||
| Spectral class | A1 III-VIp | ||||||||||||||||||||
| Variable star type | ACV | ||||||||||||||||||||
| Astrometry | |||||||||||||||||||||
| Radial velocity | (−12.7 ± 0.2) km / s | ||||||||||||||||||||
| parallax | (39.51 ± 0.20) mas | ||||||||||||||||||||
| distance | (82.6 ± 0.4) ly (25.3 ± 0.1) pc |
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| Visual absolute brightness M vis | −0.21 mag | ||||||||||||||||||||
| Proper movement | |||||||||||||||||||||
| Rec. Share: | (+111.91 ± 0.23) mas / a | ||||||||||||||||||||
| Dec. portion: | (−8.24 ± 0.19) mas / a | ||||||||||||||||||||
| Physical Properties | |||||||||||||||||||||
| Dimensions | 2.8 M ☉ | ||||||||||||||||||||
| radius | 3.9 R ☉ | ||||||||||||||||||||
| Luminosity |
137 L ☉ |
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| Effective temperature | 9550 K | ||||||||||||||||||||
| Metallicity [Fe / H] | 0.00 | ||||||||||||||||||||
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Other names and catalog entries |
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Alioth (from Arabic ألية, DMG alya , fat tail [of the sheep], buttocks') is the proper name of the star Epsilon Ursae Maioris (ε UMa) in the constellation Great Bear . It is the closest to the “wagon” of the three drawbar stars of the big wagon . Alioth has an apparent magnitude of 1.8 mag and is about 83 light years away. It is slightly brighter than Dubhe and Alkaid , making it the brightest star in the constellation and one of the 50 brightest stars in the night sky.
Alioth is a white subgiant of almost 3 times the mass, 4 times the diameter and over 130 times the luminosity of the sun . Its surface temperature is around 9500 K.
Alioth belongs to a group of variable stars , the Alpha-2-Canum Venaticorum variables, whose characteristic feature is magnetic field fluctuations. Alioth also shows slight fluctuations in brightness with an amplitude of 0.03 mag and a period of 5.09 days.
With four other of the seven bright chariot stars, Alioth belongs to the so-called group of bears , a cluster of over a hundred stars spread across half the sky. Our sun is in the range of this group, but moves in a different direction.
According to the “IAU Catalog of Star Names” of the Working Group on Star Names (WGSN) of the IAU for the standardization of star names, the name “Alioth” was officially assigned to the star ε Ursae Maioris in 2016.
Scientific research
The spectrum of the star shows peculiarities according to which it was classified as an abnormal Ap star . Relative to the standard stars, it shows stronger lines of silicon , strontium and metals, but weaker lines of calcium and magnesium .
As is typical for such stars, a relatively low value of about 30 km / s was measured for the projected equatorial rotation speed v ∙ sin i .
Individual evidence
- ^ A b c d VizieR: Hipparcos, the New Reduction (van Leeuwen, 2007) - The Astrometric Catalog
- ↑ a b c VizieR: Stellar Photometry in Johnson's 11-color system (Ducati, 2002)
- ↑ Vizier: NStars project: the Northern sample. I. (Gray +, 2003)
- ↑ eps UMa. In: VSX. AAVSO, accessed September 18, 2018 .
- ↑ VizieR: Pulkovo radial velocities for 35493 HIP stars (Gontcharov, 2006)
- ↑ a b c d VizieR: Fundamental parameters of stars (Allende Prieto +, 1999)
- ↑ a b VizieR: Extended Hipparcos Compilation (XHIP) (Anderson +, 2012)
- ↑ VizieR: AAVSO International Variable Star Index VSX (Watson +, 2006-2014)
- ↑ Bulletin of the IAU Working Group on Star Names, No. 2. IAU Division C Education, Outreach and Heritage, 2016 ( PDF; 158 kB ).
- ^ HA Abt, NI Morrell: The relation between rotational velocities and spectral peculiarities among A-type stars. In: The Astrophysical Journal Supplement Series. Vol. 99, 1995, doi: 10.1086 / 192182 , pp. 135-172 ( bibcode : 1995ApJS ... 99..135A ).
- ^ VizieR: Catalog of Stellar Rotational Velocities (Glebocki + 2005) - Mean V * sin (i) values for stars