Almaaz

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Double star
Almaaz (ε Aurigae)
AladinLite
Observation
dates equinox :  J2000.0 , epoch : J2000.0
Constellation Carter
Right ascension 05 h 01 m 58.13 s
declination + 43 ° 49 ′ 23.9 ″
Apparent brightness 3.03 (2.92 to 3.83) mag
Typing
B − V color index +0.54 
U − B color index +0.33 
R − I index +0.45 
Spectral class F0 Ia
Variable star type EA / GS 
Astrometry
Radial velocity (−10.4 ± 0.4) km / s
parallax (2.41 ± 0.51)  mas
distance (approx. 1300)  ly
approx. 400  pc  
Visual absolute brightness M vis −5.95 mag
Proper movement 
Rec. Share: (−0.86 ± 1.38)  mas / a
Dec. portion: (−2.66 ± 0.75)  mas / a
Physical Properties
Effective temperature 7800  K
Other names
and catalog entries
Bayer name ε Aurigae
Flamsteed name 7 Aurigae
Bonn survey BD + 43 ° 1166
Bright Star Catalog HR 1605 [1]
Henry Draper Catalog HD 31964 [2]
Hipparcos catalog HIP 23416 [3]
SAO catalog SAO 39955 [4]
Tycho catalog TYC 2907-1275-1 [5]
2MASS catalog 2MASS J05015812 + 4349241 [6]
Other names Almaaz, FK5 183, ADS 3605
annotation
  1. ↑ a b Only rough values
  2. ↑ Calculated from apparent brightness and distance.

Almaaz (from Arabic الماعز, DMG al-māʿiz  'goat (nbock)'; also Al Anz or Haldus ) is the name of the star ε Aurigae (Epsilon Aurigae) in the constellation Fuhrmann .

Overview

Almaaz is an eclipse-shifting star of the Algol type about 1,300 light years away. At around 27 years (9892 days), ε Aurigae has a very long period for stars with variable eclipses. A special feature of the supergiant of the spectral class F0 are the type and duration of the coverage, which suggest a very large companion.

Exploring the system

The first eclipse of Almaaz was observed in 1821 by the German amateur astronomer JH Fritsch , making this star one of the first eclipsing stars to be discovered. The periodicity of the light curve was, however, only proven and examined by Hans Ludendorff in 1903 . The coverage phase lasts a total of exactly two years, the minimum between the so-called second and third contact lasts about 330 days. The last occultation started in 2009 and lasted until 2011.

Light curve of Almaaz during the last occultation in the years 2009-2011 ( AAVSO )

For a long time, little was known about the nature of the secondary component because it could not be observed. It was only the explanation for the periodic darkening of the main component. One suspected, however, that it is a binary star system in a dark cloud. Direct observation of the course of the eclipse in 2009 showed that a dark disk of dust surrounding a small, invisible star is passing in front of Epsilon Aurigae. This was achieved with the help of the Michigan Infra-Red Combiner (MIRC), an interferometer that combines the light from four individual telescopes of the CHARA array at Georgia State University .

Mass of stars

Earlier studies assumed a very massive main component with 15 M ☉ or more, later studies suggested a model with significantly lower mass components as an alternative. Thanks to observation with the astrometry satellite Gaia , the distance to the system can be narrowed down much more than before. Based on the now favored distance of around 1300 light years, the lower-mass model seems to be preferred. Accordingly, the main component has a mass of only 2.2 M ☉ , while the darker secondary component would have 5.9 M ☉ and would therefore be more massive. However, further measurements are likely to be necessary before the system is fully understood.

Web links

Individual evidence

  1. ↑ a b eps Aur. In: SIMBAD . Center de Données astronomiques de Strasbourg , accessed June 13, 2020 .
  2. ↑ a b c Hipparcos catalog (ESA 1997)
  3. ↑ a b c eps Aur. In: VSX. AAVSO , accessed June 13, 2020 .
  4. ↑ a b c Bright Star Catalog
  5. ↑ Pulkovo radial velocities for 35493 HIP stars
  6. ^ Hipparcos, the New Reduction (van Leeuwen, 2007)
  7. ↑ Almaaz. Jim Kaler, accessed June 13, 2020 .
  8. ↑ Epsilon Aurigae. AAVSO , accessed June 13, 2020 .
  9. ↑ Mystery of the star eclipse solved. April 8, 2010, accessed June 13, 2020 .
  10. ^ Brian Kloppenborg et al .: Infrared images of the transiting disk in the ε Aurigae system . In: Nature . 464, 2010, pp. 870-872. doi : 10.1038 / nature08968 .
  11. ↑ P. Chadima et al .: Spectral and photometric analysis of the eclipsing binary epsilon Aurigae prior to and during the 2009-2011 eclipse . In: Astronomy & Astrophysics . 530, No. 530, 2011, p. A146. arxiv : 1105.0107 . bibcode : 2011A & A ... 530A.146C . doi : 10.1051 / 0004-6361 / 201116739 .
  12. ^ Solving the 200-Year-Old Mystery of a Strange Eclipsing Star. Space.com, June 18, 2018, accessed June 13, 2020 .