Eta Cephei

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Star
η Cephei
Eta Cephei in the constellation Cepheus
AladinLite
Observation
dates equinox :  J2000.0 , epoch : J2000.0
Constellation Cepheus
Right ascension 20 h 45 m 17.37 s
declination + 61 ° 50 ′ 19.6 ″
Apparent brightness 3,426 likes
Typing
B − V color index +0.918 
U − B color index +0.613 
Spectral class K0 IV
Astrometry
Radial velocity -87.45 ± 0.03 km / s
parallax (70.10 ± 0.11)  mas
distance 46.53  ly
14.27  pc
Visual absolute brightness M vis 2,631 likes
Proper movement 
Rec. Share: 86.50  mas / a
Dec. portion: 818.02  mas / a
Physical Properties
Dimensions 1.6  M ☉
radius (4.12 ± 0.07)  R ☉
Luminosity

(9.7 ± 0.5)  L ☉

Effective temperature 4950  K
Metallicity [Fe / H] -0.32
Age 2.5 ± 0.3  a
Other names
and catalog entries
Bayer name η Cephei
Flamsteed name 3 Cephei
Bonn survey BD + 61 ° 2050
Bright Star Catalog HR 7957 [1]
Henry Draper Catalog HD 198149 [2]
Gliese catalog GJ 807 [3]
Hipparcos catalog HIP 102422 [4]
SAO catalog SAO 19019 [5]
Tycho catalog TYC 4246-1967-1 [6]
2MASS catalog 2MASS J20451737 + 6150199 [7]
Other names FK5 783

Eta Cephei (η Cep, η Cephei) is a star of the northern circumpolar constellation Cepheus , it is also called Al Agemim (the sheep farm). The meaning of the wider name Al Kidr , which is also used for the nearby Theta Cephei , is unknown. The Arab astronomer Ulugh Beg called Eta Cephei together with Alpha Cephei (Alderamin) and Beta Cephei (Alfirk) as Al Kawākib al Firḳ ( الكوكب الفرق ), which means "the stars of the herd".

properties

With an apparent magnitude of 3.4 mag, Eta Cephei is a third magnitude star that is easily visible to the naked eye according to the Bortle scale . Parallax measurements show a distance of 46.53 light years .

Eta Cephei is a sub-giant of the spectral class K0 IV, which suggests that it uses up the hydrogen reserves in its core and is in the transition phase to become a giant star . With 1.6 times the mass of the sun and an age of 2.5 billion years, it has reached four times the solar radius and ten times the brightness of the sun. It radiates this energy from its atmosphere at an effective temperature of 4950 K, K, which gives it the typical orange color of a K star . Eta Cephei has a high intrinsic motion , which is associated with a peculiar speed of 112 km / s.

Search for substellar objects

According to Nelson & Angel (1998) Eta Cephei would show two distinct periodicities of 164 days and 10 years, respectively, which indicated the presence of one or more Jupiter- like planets in the orbit of the subgiant. The authors gave an upper limit of 0.64 Jupiter masses for the putative inner planet and 1.2 Jupiter masses for the putative outer planet. Campbell et al. (1988) also concluded the existence of planets or even brown dwarfs with less than 16.3 Jupiter masses.

However, recent studies have not been able to confirm the existence of substellar companions around Eta Cephei. The McDonald Observatory team narrowed the mass of one or more possible planets to 0.13 to 2.4 Jupiter masses and their distances to 0.05 to 5.2 astronomical units .

Web links

Individual evidence

  1. ↑ a b eta Cep. In: SIMBAD . Center de Données astronomiques de Strasbourg , accessed October 29, 2018 .
  2. ↑ a b c P. A. Jennens, HL Helfer: A new photometric metal abundance and luminosity calibration for field G and K giants. . In: Monthly Notices of the Royal Astronomical Society . 172, September 1975, pp. 667-679. bibcode : 1975MNRAS.172..667J . doi : 10.1093 / mnras / 172.3.667 .
  3. ↑ a b c C. Soubiran, O. Bienaymé, TV Mishenina, VV Kovtyukh: Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants . In: Astronomy and Astrophysics . 480, No. 1, 2008, pp. 91-101. arxiv : 0712.1370 . bibcode : 2008A & A ... 480 ... 91S . doi : 10.1051 / 0004-6361: 20078788 .
  4. ^ A b Floor van Leeuwen: Validation of the new Hipparcos reduction . In: Astronomy & Astrophysics . 474, No. 2, November 2007, pp. 653-664. arxiv : 0708.1752v1 . bibcode : 2007A & A ... 474..653V . doi : 10.1051 / 0004-6361: 20078357 . Note: see VizieR catalog I / 311 .
  5. ↑ a b c d e f L. Affer, G. Micela, T. Morel, J. Sanz-Forcada, F. Favata: Spectroscopic determination of photospheric parameters and chemical abundances of 6 K-type stars . In: Astronomy and Astrophysics . 433, No. 2, April 2005, pp. 647-658. bibcode : 2005A & A ... 433..647A . doi : 10.1051 / 0004-6361: 20041308 .
  6. ↑ a b c d e f L. Piau, P. Kervella, S. Dib, P. Hauschildt: Surface convection and red-giant radius measurements . In: Astronomy and Astrophysics . 526, February 2011. arxiv : 1010.3649 . bibcode : 2011A & A ... 526A.100P . doi : 10.1051 / 0004-6361 / 201014442 .
  7. ↑ η Cep (Al Agemim) at SKY-MAP.ORG. Retrieved December 24, 2016 .
  8. ^ RH Allen: Star Names: Their Lore and Meaning . Dover Publications Inc, New York, ISBN 0-486-21079-0 , pp. 157 . Look here 
  9. ^ GA Davis Jr .: The Pronunciations, Derivations, and Meanings of a Selected List of Star Names . In: Popular Astronomy . LII, No. 3, October 1944, p. 16. bibcode : 1944PA ..... 52 .... 8D .
  10. ^ AF Nelson, JRP Angel: The Range of Masses and Periods Explored by Radial Velocity Searches for Planetary Companions . In: Astrophysical Journal . 500, No. 2, June 1998, pp. 940-957. arxiv : astro-ph / 9802194 . bibcode : 1998ApJ ... 500..940N . doi : 10.1086 / 305741 .
  11. ↑ Kaylene A. Murdoch, JB Hearnshaw, M. Clark: A search for substellar companions to southern solar-type stars . In: Astrophysical Journal, Part 1 . 413, No. 1, August 1993, pp. 349-363. bibcode : 1993ApJ ... 413..349M . doi : 10.1086 / 173003 .
  12. ↑ Robert A. Wittenmyer, Michael Endl, William D. Cochran, Artie P. Hatzes, GAH Walker, SLS Yang, Diane B. Paulson: Detection Limits from the McDonald Observatory Planet Search Program . In: The Astronomical Journal . 132, No. 1, July 2006, pp. 177-188. arxiv : astro-ph / 0604171 . bibcode : 2006AJ .... 132..177W . doi : 10.1086 / 504942 .