Eta Cassiopeiae

Coordinates: Sky map 00h 49m 06.29070s, +57° 48′ 54.6758″
Source: Wikipedia, the free encyclopedia.
Eta Cassiopeiae

η Cas in optical light
Observation data
Epoch J2000      Equinox J2000
Constellation Cassiopeia
Right ascension 00h 49m 06.29070s[1]
Declination +57° 48′ 54.6758″[1]
Apparent magnitude (V) 3.44[2]/7.51[3]
Characteristics
Spectral type G0 V[4] + K7 V[3]
U−B color index +0.02[2]/1.03
B−V color index +0.58[2]/1.39
Variable type RS CVn?[5]
Distance
19.331 ± 0.002 ly
(5.9270 ± 0.0008 pc)
Argument of periastron
(ω)
(secondary)		88.59°
Details
η Cas A
Gyr
η Cas B
Mass0.57 ± 0.07[3] M☉
Radius0.66[13] R☉
Luminosity0.06[3] L☉
Temperature4,036 ± 150[3] K
LTT 10287, SAO 21732, Wolf 24, Struve 60, GC 962, CCDM J00491+5749[6]
Database references
SIMBADThe system
A
B
η Cassiopeiae is located in the constellation Cassiopeia
η Cassiopeiae is located in the constellation Cassiopeia
Location of η Cassiopeiae in the constellation Cassiopeia

Eta Cassiopeiae (η Cassiopeiae, abbreviated Eta Cas, η Cas) is a binary star system in the northern constellation of Cassiopeia. Its binary nature was first discovered by William Herschel in August 1779. Based upon parallax measurements, the distance to this system is 19.42 light-years (5.95 parsecs) from the Sun.[1] The two components are designated Eta Cassiopeiae A (officially named Achird /ˈeɪtʃərd/)[14] and B.

Nomenclature

η Cassiopeiae (Latinised to Eta Cassiopeiae) is the system's Bayer designation. The designations of the two constituents as Eta Cassiopeiae A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for star systems, and adopted by the International Astronomical Union (IAU).[15]

The proper name Achird was apparently first applied to Eta Cassiopeiae in the

multiple systems.[19] It approved the name Achird for the component Eta Cassiopeiae A on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[14]

In

Chinese name for Eta Cassiopeiae itself is 王良三 (Wáng Liáng sān, English: the Third Star of Wang Liang).[21]

Properties

Eta Cassiopeiae's two components are orbiting around each other over a

apoapsis of about 106 AU. For comparison, the semi-major axis of Neptune
is 30 AU.

There are six dimmer

spectroscopic binary, but this has never been confirmed.[16]

Eta Cassiopeiae A has a

luminosity of the Sun from its outer envelope at an effective temperature of 6,087 K.[3] It appears to be rotating at a leisurely rate, with a projected rotational velocity of 3.15 km s−1.[4]

The cooler and dimmer (magnitude 7.51[3]) Eta Cassiopeiae B is of stellar classification K7 V;[3] a K-type main-sequence star. It has only 57%[3] of the mass of the Sun and 66%[13] of the Sun's radius. Smaller stars generate energy more slowly, so this component radiates only 6%[3] of the luminosity of the Sun. Its outer atmosphere has an effective temperature of 4,036 K.[3]

Compared to the Sun, both components show only half the abundance of elements other than hydrogen and helium—what astronomers term their metallicity.[3]

A necessary condition for the existence of a planet in this system are stable zones where the object can remain in orbit for long intervals. For hypothetical planets in a circular orbit around the individual members of this star system, this maximum orbital radius is computed to be 9.5 AU for the primary and 7.1 AU for the secondary. (Note that the orbit of Mars is 1.5 AU from the Sun.) A planet orbiting outside of both stars would need to be at least 235 AU distant.[23]

  • Cassiopeia constellation
    Cassiopeia constellation
  • Eta Cassiopeiae
    Eta Cassiopeiae

See also

References

  1. ^
    S2CID 18759600
  2. ^
    Bibcode:1966CoLPL...4...99J
  3. ^
    Bibcode:1998A&A...338..455F
  4. ^
    S2CID 43455849, archived from the original
    (PDF) on 2017-09-22, retrieved 2018-11-04
  5. Bibcode:2009yCat....102025S
    .
  6. ^ a b "eta Cas". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2008-04-10.
  7. doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR
    .
  8. S2CID 118577511
    .
  9. ^
    doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR
    .
  10. ^
    doi:10.1086/110853
  11. ^
    S2CID 18993744
    .
  12. ^
    S2CID 14911430
    .
  13. ^
    doi:10.1086/190905
    —see p. 647.
  14. ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017.
  15. arXiv:1012.0707 [astro-ph.SR
    ].
  16. ^
    Bibcode:1995yCat.5050....0H
    .
  17. ISBN 0-486-21079-0
    .
  18. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  19. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  20. ISBN 978-986-7332-25-7
    .
  21. ^ (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived 2010-09-03 at the Wayback Machine, Hong Kong Space Museum. Accessed online November 23, 2010.
  22. ISBN 3-540-42177-7
  23. S2CID 118570249
    .

External links

  • "Eta Cassiopeiae 2". SolStation. Retrieved 2005-11-03.
  • Kaler, Jim. "Achird".
    University of Illinois at Urbana-Champaign
    . Retrieved 2008-04-10.
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