Achird

Database links to Achird

Double star Achird
Observation dates equinox :  J2000.0 , epoch : J2000.0
AladinLite
Constellation	Cassiopeia
Apparent brightness	3.44 likes
Astrometry
Radial velocity	+10.0 ± 0.1 km / s
parallax	167.98 ± 0.48 mas
distance	19.42 ± 0.06 ly (5.95 ± 0.02 pc )
Proper movement :
Rec. Share:	1086.59 ± 0.40 mas / a
Dec. portion:	-559.43 ± 0.33 mas / a
orbit
period	480 a
Major semi-axis	71 AU
eccentricity	0.497
Periastron	36 AU
Apastron	107 AU
Orbit inclination	34.76 °
Argument of the node	98.42 °
Epoch of the periastron	1889.6
Argument of the periapsis	88.59 °
Individual data
Names	A; B.
Observation data:
Right ascension	A.	00 h 49 m 05.145 s
	B.	00 h 49 m 05.167 s
declination	A.	+ 57 ° 48 ′ 59.40 ″
	B.	+ 57 ° 49 ′ 03.77 ″
Apparent brightness	A.	3.52 mag
	B.	7.51 likes
Typing:
Spectral class	A.	G0V
	B.	K7V
B − V color index	A.	0.58
	B.	1.39
U − B color index	A.	0.02
	B.	1.03
Physical Properties:
Dimensions	A.	0.972 ± 0.012 M ☉
	B.	0.57 ± 0.07 M ☉
radius	A.	1.0386 ± 0.0038 R ☉
	B.	0.66 R ☉
Luminosity	A.	1.2321 ± 0.0074 L ☉
	B.	0.06 L ☉
Effective temperature	A.	5973 ± 8 K
	B.	4036 ± 150 K
Metallicity [Fe / H]	A.	-0.31
	B.
Age	5.4 ± 0.9 billion a
Other names and catalog entries
Bayer name η Cas Flamsteed name 24 Cas Bonn survey BD + 57 ° 150 Bright Star Catalog HR 219 [1] Henry Draper Catalog HD 4614 [2] SAO catalog SAO 21732 [3] Hipparcos catalog HIP 3821 [4] Tycho catalog TYC 3663-2669-1 [5] TYC 3663-2669-2 [6] WDS catalog WDS J00491 + 5749AB Further designations: Achird, Gliese 34, Wolf 24, Struve 60

Achird ( Bayer name : Eta Cassiopeiae , abbreviated η Cas ) is a binary star system in the constellation Cassiopeia , which is a little more than 19 light years away from the neighbors in the vicinity of the sun . It consists of a sun-like yellow dwarf star of the spectral class G0V and an orange-red dwarf star of the spectral class K7V. In the night sky Achird can easily be found with the naked eye as a single 3rd magnitude star in the celestial W of Cassiopeia between Tsih (γ Cas) and Schedir (α Cas) closer to the latter.

Components

Achird A

The main star Achird A (η Cas A) is like the sun a yellowish main sequence star of the spectral class G and with about 5.4 billion years somewhat older than the sun (4.6 billion years). Its mass is 97% of the solar mass , its radius 101% of the solar radius . The luminosity of Achird A is 129% of the sun's luminosity. The proportion of elements heavier than hydrogen and helium (the metallicity ) is only about half that of the sun.

Achird B

The companion star Achird B (η Cas B) is significantly smaller and fainter than the primary component. It has only 57% of the solar mass and 66% of the solar radius. Its luminosity is only 6% of the sun's luminosity. During the 480-year orbit around their common barycentre , the two stars approach each other by up to 36 AU in the periastron , while in the apastron they diverge up to 107 AU from each other.

Possibility of planets

As early as 1986 and 1987, the radial velocity method was used unsuccessfully to search for massive exoplanets that Achird A could possibly orbit. Measurements carried out over a longer period of time rule out the existence of planets or other substellar companions with a mass of more than 0.878 Jupiter's masses in a circular orbit within three AU of Achird A.

Due to the dual nature of the system, planets can only maintain a stable orbit over a long period of time in a relative proximity to one of the two stars, otherwise they would be thrown out of the system under the influence of the other component. For Achird A, the maximum possible distance for a planet from the star was calculated as 9.54 AU, for Achird B with 7.05 AU. In both cases a planet could also exist in the habitable zone . For component A, this extends at a distance of 0.9 to 1.8 AU from the star, for the weaker component B, on the other hand, at a distance of 0.593 and 1.176 AU. A circumbinary planet orbiting both stars, on the other hand, would have to be at least 235.07 AU away.

Because of Achird's proximity to the sun and the similarity of component A to the sun, the system was also one of the 100 most important target stars of NASA's Terrestrial Planet Finder mission , which was postponed several times and finally canceled in 2011.

Closest neighbors

The closest star to Achird is HR 8832 at a distance of 4.9 light years. It is a single orange dwarf star around which a planetary system with at least four exoplanets was discovered in 2015. The second closest neighbor is My Cassiopeiae , a double system 5.2 light years from Achird, consisting of a cool subdwarf of spectral class G and a red dwarf . Similar to the sun, the stellar environment of Achird is largely characterized by faint red dwarfs. These include EV Lacertae (7.8 light years away), Kruger 60 (8.2 light years away), Groombridge 34 (8.7 light years away), and Stein 2051 (9.2 light years away).

observation

In order to resolve the system into single stars, a telescope with an objective diameter of at least 5 centimeters is required . The color contrast between the lighter white component A and the weaker reddish component B makes Achird an attractive object to observe.

The angular distance and the position angle of component B in relation to component A changes over time as the two stars revolve around the common center of gravity. In 1990 the distance was 12.5 arc seconds or 312 degrees, in 2010 13.2 arc seconds or 322 degrees.

The double star nature of Achird was discovered by Friedrich Wilhelm Herschel on August 19, 1779. In addition to the physically related components A and B, there are also a number of purely optical companion stars (components C to H), which only stand in the same direction when viewed from earth and have an apparent brightness of 8 to 12 mag.

Web links

• SolStation.com: Eta Cassiopeiae (Achird). Retrieved September 13, 2016 .  (English)

Individual evidence

1. ↑ ^{a b c} Simbad: eta Cas - Spectroscopic binary. Retrieved September 13, 2016 . 
2. ^ Strand, KA: The Orbit of Eta Cassiopeiae . bibcode : 1969AJ ..... 74..760S .
3. ↑ ^{a b c d e f} SolStation.com: Eta Cassiopeiae (Achird). Retrieved September 13, 2016 . 
4. ^ Simbad: V * eta Cas. Retrieved September 13, 2016 . 
5. ↑ Martinez-Arnaiz, R. et al .: Chromospheric activity and rotation of FGK stars in the solar vicinity. An estimation of the radial velocity jitter . arxiv : 1002.4391 .
6. ↑ ^{a b c d e f g} Fernandes, J. et al .: Fundamental stellar parameters for nearby visual binary stars: eta Cas, XI Boo, 70 OPH and 85 Peg. Helium abundance, age and mixing length parameters for low mass stars . bibcode : 1998A & A ... 338..455F .
7. ↑ ^{a b} Johnson, HL et al .: UBVRIJKL photometry of the bright stars . bibcode : 1966CoLPL ... 4 ... 99J .
8. ↑ ^{a b c d} Boyajian, TS et al .: Stellar Diameters and Temperatures I. Main Sequence A, F, & G Stars . arxiv : 1112.3316 .
9. ↑ ^{a b c d e} Boyajian, TS et al .: Stellar Diameters and Temperatures III. Main Sequence A, F, G, & K Stars: Additional high-precision measurements and empirical relations . arxiv : 1306.2974 .
10. ^ Johnson, HM et al .: Predicted infrared brightness of stars within 25 parsecs of the sun . bibcode : 1983ApJS ... 53..643J .
11. ↑ McMillan, RS et al .: Nonvariability of the radial velocity of Eta Cassiopeiae A . bibcode : 1987PASP ... 99..849M .
12. ↑ Wittenmyer, R. et al .: Detection Limits from the McDonald Observatory Planet Search Program . arxiv : astro-ph / 0604171 .
13. ^ ^{A b} Jaime, LG et al .: Regions of Dynamical Stability for Discs and Planets in Binary Stars of the Solar Neighborhood . arxiv : 1208.2051 .
14. ↑ epsilon-lyrae.de: Double stars in the constellation Cassiopia. Retrieved September 13, 2016 .