Gemma

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Double star
α Coronae Borealis
Image by Gemma
Image by Gemma
Observation
dates equinox :  J2000.0 , epoch : J2000.0
AladinLite
Constellation Northern crown
Right ascension 15 h 34 m 41.3 s
declination + 26 ° 42 ′ 52.9 ″
Apparent brightness  Coverage variable ( EA )
2.21 to 2.32 mag
Astrometry
parallax (43.46 ± 0.28) mas
distance  (75.0 ± 0.5) ly
((23.0 ± 0.1) pc )
Proper movement :
Rec. Share: (+120.27 ± 0.19) mas / a
Dec. portion: (−89.58 ± 0.20) mas / a
orbit 
period 17.36 d
Major semi-axis 0.2 AU
eccentricity 0.37
Periastron 0.13 AU
Apastron 0.27 AU
Orbit inclination 88 °, 2 ± 0 °, 1
Individual data
Names A; B.
Observation data:
Apparent brightness A. 2.24 mag
B. 7.1 likes
Typing:
Spectral class A. A0 V
B. G5 V
Physical Properties:
Dimensions A. 2.7 M ☉
B. 0.92 M ☉
radius A. 2.7 R ☉
B.
Luminosity A. 67 L ☉
B.
Effective temperature A. 10000 K
B.
Other names
and catalog entries
Bayer name α Coronae Borealis
Flamsteed name 5 Coronae Borealis
Bonn survey BD + 27 ° 2512
Bright Star Catalog HR 5793 [1]
Henry Draper Catalog HD 139006 [2]
SAO catalog SAO 83893 [3]
Tycho catalog TYC 2029-1690-1 [4]
Hipparcos catalog HIP 76267 [5]
Further designations: Alphecca, FK5 578, GJ 9524

α Coronae Borealis ( α CrB for short ) is a double star system about 76.5 light years from Earth and the brightest star in the semicircular constellation Corona Borealis (Northern Crown). It is a variable coverage system of the Algol type . This star is also known as Gemma (Latin: precious stone), Alphekka or Alphecca (from Arabic).

The IAU has the proper name on July 20, 2016 Alphecca defined as standardized proper names.

The main component is a main sequence star of the spectral class A0 (surface temperature of about 9500 Kelvin ) with about 60 times the luminosity of the sun , a mass of 2.6 solar masses and a radius of around 3 solar radii. The companion is a G main sequence star with about 0.9 solar masses.

The brightness of the system fluctuates with a period of 17.36 days between about 2.2 mag and 2.3 mag (hardly noticeable with the naked eye).

The proper motion suggests that α Coronae Borealis belongs to the Ursa Major Current (Bear Current ), a cluster of movements widely scattered in the sky , from whose main stars in the Big Dipper it is 30–40 ° away.

Around 1895 it was assumed from anomalies in the line spectrum that Gemma could be a multiple star . However, recent measurements have not confirmed this.

Star triangle

The star triangle of α CrB (left) with α and γ Bootis

α Coronae Borealis forms an exactly equilateral triangle with the bright stars Arcturus and Seginus (α and γ in the neighboring constellation Bootes). It lies roughly in the extension of the drawbar of the Big Dipper (Alkaid, in the picture above right). In addition, Izar (Epsilon Bootis) is in the center of gravity of the triangle.

See also

Web links

Individual evidence

  1. ^ Hipparcos catalog (ESA 1997)
  2. ^ Hipparcos, the New Reduction (van Leeuwen, 2007)
  3. ↑ a b c d e Alphecca or Gemma. Jim Kaler, accessed September 29, 2018 .
  4. ↑ a b alf CrB. In: VSX. AAVSO, accessed September 29, 2018 .
  5. ↑ In-The-Sky: Alphecca. January 11, 2018, accessed January 18, 2018 .
  6. ↑ Bulletin of the IAU Working Group on Star Names, No. 1, July 2016. (PDF) Retrieved November 9, 2016 (English, 184 KiB).
  7. ↑ Ladislaus Weinek : Atlas der Himmelskunde , Verlag Hartleben, Vienna-Pest-Leipzig 1898, p. 146.