Algol (star)

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Multiple star
Algol (β Persei)
Algol in the constellation Perseus
AladinLite
Observation
dates equinox :  J2000.0 , epoch : J2000.0
Constellation Perseus
Right ascension 03 h 08 m 10.13 s
declination + 40 ° 57 ′ 20.3 ″
Apparent brightness 2.09 (2.09 to 3.30) mag
Typing
B − V color index −0.05 
U − B color index −0.37 
R − I index −0.03 
Spectral class B8 V
Variable star type EA / SD 
Astrometry
Radial velocity (3.7 ± 3.9) km / s
parallax (36.27 ± 1.40)  mas
distance (89.9 ± 3.5)  ly
(27.6 ± 1.1)  pc  
Visual absolute brightness M vis −0.11 mag
Proper movement 
Rec. Share: (2.99 ± 1.42)  mas / a
Dec. portion: (−1.66 ± 1.22)  mas / a
Physical Properties
Dimensions 3.59
0.79
1.67  M ☉
radius 2.3
3.0
0.9  R ☉
Luminosity

98
3.4
4.1  L ☉

Effective temperature 12, 000
4500
8500  K
Age <300 x 10 6  a
Other names
and catalog entries
Bayer name β Persei
Flamsteed name 26 Persei
Bonn survey BD +40 673
Bright Star Catalog HR 936 [1]
Henry Draper Catalog HD 19356 [2]
Gliese catalog FY 9110 [3]
Hipparcos catalog HIP 14576 [4]
SAO catalog SAO 38592 [5]
Tycho catalog TYC 2851-2168-1 [6]
2MASS catalog 2MASS J03081012 + 4057204 [7]
Other names Algol • FK5  111 • ADS 2362 • WDS 03082 + 4057
annotation
  1. ↑ Calculated from apparent brightness and distance.

Algol ( Arabic الغول al-ġūl 'the demon'), also known as β Persei , is a variable star and the second brightest star in the constellation of Perseus . It is about 90 light years away .

Its apparent brightness changes with a period of 2.87 days (2 days, 20 hours, 48 ​​minutes and 56 seconds) between 2.1 and 3.4 mag, which can also be easily observed with free eyes . In the Arab Middle Ages it was also called the " Devil's Star " because of its inexplicable behavior . It is the prototype of the eclipsing stars .

Algol is a three-star system, consisting of Beta Persei (β Per) Aa1, Aa2 and Ab. The two stars β Per Aa1, a bright bluish star (spectral class B8) with one hundred times the brightness of the Sun , and β Per Aa2, a less bright reddish-yellow star (spectral class K2), orbit each other at a distance of about 0.062  AU . A third star, β Per Ab, with an orbital period of 681 days orbits this binary star system at an average distance of 2.69 AU.

Eclipsing star

Animation of the principle of eclipsing double stars with a light curve in the event that the larger star shown in blue is the brighter one (radii, distance and changes are not proportionate)

In a binary star system, a change in apparent brightness occurs when the less bright star, from the point of view of the earth, passes in front of the brighter star and thereby obscures it. A further smaller fluctuation in brightness occurs between two brightness minima when the brighter star partially covers the weaker star. The Algol stars , a class of eclipsing variables, are named after the characteristics of the light curve of Algol .

The discovery of the changes in brightness are attributed to Geminiano Montanari (1667/1669). The period was determined by John Goodricke in 1783. He suspected it was obscured by a large body or an uneven surface with spots similar to those on the sun. In a letter from John Michell to Henry Cavendish in July 1783, the declaration was mentioned with two different stars. In 1889 Hermann Carl Vogel succeeded in Potsdam in demonstrating from shifts in the Fraunhofer lines in the spectrum of the Algol that it has a dark companion and that both move around a common center of gravity.

However, it can be assumed that the Greek and Arab astronomers had already noticed the change in light that can be seen with the naked eye. New findings indicate that the Egyptians already observed this star and adjusted their day selection calendar to it. Around 1200 BC "Calendar of happy and unhappy days", which originated in ancient Egypt in the 4th century BC, contains regularities that are in harmony with the periodic fluctuations in brightness of the "devil's star" Algol. According to a team of Finnish researchers, the calendar would be the oldest recorded document of the discovery of a variable star. In accordance with astrophysical predictions, the period of Algol 3,200 years ago was slightly shorter than it is today.

Naming

Algol is a bright star in the constellation Perseus (the second line-connected star from the top right)

The name Algol is an abbreviation of the original Arabic name»رأس الغول« raʾs al-ġūl 'head of the demon'. It has been used since the 10th century and is one of the oldest Arabic star names in the western world. Ptolemy previously namedthis star Gorgonea Prima ( Latin for "first [star] of the Gorgon") after a Greek legend in which Perseus holdsthe severed head of Medusa (one of the three Gorgons ) in his hands. In astrology, Algol has always been considered a star of disaster.

See also

Web links

Commons : Algol  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b c Hipparcos catalog (ESA 1997)
  2. ↑ a b bet Per. In: VSX. AAVSO, accessed November 2, 2018 .
  3. ↑ a b c Bright Star Catalog
  4. ↑ Pulkovo radial velocities for 35493 HIP stars
  5. ↑ a b c Hipparcos, the New Reduction (van Leeuwen, 2007)
  6. ^ D. Gossman, Light Curves and Their Secrets , Sky & Telescope (October 1989, p.410)
  7. ↑ Eclipsing Binary simulation , Cornell Astronomy
  8. ^ The Philosophical Transactions of the Royal Society of London, from Their Commencement in 1665 to the Year 1800. published 1809, p. 456ff (explanation p. 459); Magazine for the latest in physics and natural history. Volume 2, 2nd St., Gotha 1783, pp. 160f ; Astronomical yearbook for the year 1787. Berlin 1784, p. 145
  9. ↑ Russell McCormmach: Weighing the World: The Reverend John Michell of Thornhill. Verlag Springer Science & Business Media, 2011, p. 360 middle
  10. ^ Emanuel Müller-Baden: Library of general and practical knowledge, Vol. IV, German publishing house Bong & Co.
  11. ↑ Porceddu, S., Jetsu, L., Lyytinen, J., Kajatkari, P., Lehtinen, J., Markkanen, T, Toivari-Viitala, J .: Evidence of Periodicity in Ancient Egyptian Calendars of Lucky and Unlucky Days . In: Cambridge Archaeological Journal . 18, No. 3, 2008, pp. 327-339. doi : 10.1017 / S0959774308000395 .
  12. ↑ Jetsu, L., Porceddu, S., Lyytinen, J., Kajatkari, P., Lehtinen, J., Markkanen, T, Toivari-Viitala, J .: Did the Ancient Egyptians Record the Period of the Eclipsing Binary Algol - The Raging One? . In: The Astrophysical Journal . 773, No. 1, 2013, p. A1 (14pp). bibcode : 2013ApJ ... 773 .... 1J . doi : 10.1088 / 0004-637X / 773/1/1 .