Binary star in the constellation Cephei
This article is about the star. For the Tunisian newspaper, see
Errai
.
Gamma Cephei
(
γ Cephei
, abbreviated
Gamma Cep
,
γ Cep
) is a
binary star
system approximately 45
light-years
away in the northern
constellation
of
Cepheus
. The primary (designated Gamma Cephei A, officially named
Errai
, the traditional name of the system)
[10]
[11]
is a
stellar class
K1 orange
giant
or
subgiant
star; it has a
red dwarf
companion (Gamma Cephei B). An
exoplanet
(designated
Gamma Cephei Ab
, later named Tadmor) has been confirmed to be orbiting the primary.
Gamma Cephei is the naked-eye star that will succeed
Polaris
as the Earth's northern
pole star
, due to the
precession of the equinoxes
. It will be closer to the northern
celestial pole
than Polaris around 3000 CE and will make its closest approach around 4000 CE. The 'title' will pass to
Iota Cephei
some time around
5200
CE.
Description
[
edit
]
Gamma Cephei has an
apparent magnitude
of 3.21, nearly all of which is accounted for by the primary component, Gamma Cephei A. It is a binary star system with an
orbital period
of 66.8 years and an
eccentricity
(ovalness) of 0.14.
[8]
The pair are orbiting at a separation of
19.6
AU
.
[8]
The primary is about 3.25 billion years old and has evolved off the
main sequence
, having
fused
all of the hydrogen in its core.
[9]
It has 1.3
[8]
times the mass of the Sun and has expanded to 4.9 times the Sun's radius. The star is radiating nearly 12 times the luminosity of the Sun from its
photosphere
at an
effective temperature
of 4,792 K.
[9]
The secondary component, Gamma Cephei B, has a mass approximately 0.40 times that of the
Sun
.
[5]
It is probably a
red dwarf
of
class
M4, 6.2 magnitudes fainter than the primary.
[5]
It is assumed to be of similar age to its primary.
The
spectrum
of this star has served as one of the stable anchor points by which other stars are classified. It was listed as a standard star for the spectral class K1 IV in 1943, 1953 and 1973.
[12]
However, in 1989, it was given as a spectral standard for K1 III-IV. Its spectrum is notable for the strength of the
cyano radical
(CN) bands.
[3]
Analysis of the spectrum in 2018 gave a best match for a spectral type of K1 III.
[9]
γ Cephei is catalogued as a suspected
variable star
with a brightness range between magnitudes 3.18 and 3.24,
[4]
based on its inclusion in an 1884 list of suspected variable stars.
[13]
Nomenclature
[
edit
]
γ Cephei
(
Latinised
to
Gamma Cephei
) is the system's
Bayer designation
. Under the rules for naming objects in multiple star systems the two components are designated A and B.
[14]
Following its discovery the planet was designated Gamma Cephei Ab.
The system bore a traditional name variously spelled as
Errai
,
Er Rai
or
Alrai
, deriving from the
Arabic
?????? (ar-r?‘?), meaning 'the shepherd'. (The star
Beta Ophiuchi
is sometimes also called Alrai, but it is more commonly known as
Cebalrai
or
Kelb Alrai
, meaning 'shepherd's dog'.) In 2016, the
International Astronomical Union
organized a
Working Group on Star Names
(WGSN)
[15]
to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016
[16]
included a table of the first two batches of names approved by the WGSN; which included
Errai
for Gamma Cephei A.
In July 2014 the
International Astronomical Union
launched
NameExoWorlds
, a process for giving proper names to certain exoplanets.
[17]
The process involved public nomination and voting for the new names.
[18]
In December 2015, the IAU announced the winning name was Tadmor for this planet.
[19]
It was submitted by the
Syrian
Astronomical Association and is the ancient
Semitic name
and modern Arabic name for the city of
Palmyra
, a
World Heritage Site
.
[20]
In
Chinese
, the star is named
少衛增八
(Shaowei Z?ng B?, literally, the 8th added star of the
Xingguan
Shaowei
,
Shaowei
: the Minor Guard
[21]
) belonging to the Left Wall of the
Purple Forbidden enclosure
(
紫微左垣
,
Z?w?i Zu?yuan
), which refers to an
asterism
consisting of Gamma Cephei,
Iota Draconis
,
Theta Draconis
,
Eta Draconis
,
Zeta Draconis
,
Upsilon Draconis
,
73 Draconis
and
23 Cassiopeiae
.
[22]
Planetary system
[
edit
]
A planet orbiting Gamma Cephei A with a 2.7-year period was discovered in 1988.
[23]
Its existence was also announced in 1989.
[24]
This was the
first-confirmed extrasolar planet
and its ostensible discovery was based on the same
radial velocity
technique later used successfully by others. However, the claim was challenged in 1992 by a paper
[25]
which favoured K-giant variability with a period equal to the stellar rotation, but in 2002, the existence of a planet with an orbital period of about 2.5 years was confirmed.
[26]
The secondary star B orbits A at only 9.8 times the
semimajor axis
of A's planet.
[27]
The orbit of the planet is roughly perpendicular to the orbit of the binary. Dynamical modelling suggests that the
Kozai?Lidov mechanism
is at play here.
[28]
References
[
edit
]
- ^
a
b
c
d
Vallenari, A.; et al. (Gaia collaboration) (2023).
"
Gaia
Data Release 3. Summary of the content and survey properties"
.
Astronomy and Astrophysics
.
674
: A1.
arXiv
:
2208.00211
.
Bibcode
:
2023A&A...674A...1G
.
doi
:
10.1051/0004-6361/202243940
.
S2CID
244398875
.
Gaia DR3 record for this source
at
VizieR
.
- ^
a
b
c
Hoffleit, D.; Warren, W. H. (1995). "VizieR Online Data Catalog: Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)".
VizieR On-line Data Catalog: V/50. Originally Published in: 1964BS....C......0H
.
5050
: V/50.
Bibcode
:
1995yCat.5050....0H
.
- ^
a
b
Keenan, Philip C; McNeil, Raymond C (1989). "The Perkins catalog of revised MK types for the cooler stars".
The Astrophysical Journal Supplement Series
.
71
: 245.
Bibcode
:
1989ApJS...71..245K
.
doi
:
10.1086/191373
.
S2CID
123149047
.
- ^
a
b
Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)".
VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S
.
1
: B/gcvs.
Bibcode
:
2009yCat....102025S
.
- ^
a
b
c
Neuhauser, R.; et al. (2007). "Direct detection of exoplanet host star companion γ Cep B and revised masses for both stars and the sub-stellar object".
Astronomy and Astrophysics
.
462
(2): 777?780.
arXiv
:
astro-ph/0611427
.
Bibcode
:
2007A&A...462..777N
.
doi
:
10.1051/0004-6361:20066581
.
S2CID
17530531
.
- ^
a
b
c
d
Jofre, E; Petrucci, R; Saffe, C; Saker, L; Artur de la Villarmois, E; Chavero, C; Gomez, M; Mauas, P. J. D (2015). "Stellar parameters and chemical abundances of 223 evolved stars with and without planets".
Astronomy & Astrophysics
.
574
: A50.
arXiv
:
1410.6422
.
Bibcode
:
2015A&A...574A..50J
.
doi
:
10.1051/0004-6361/201424474
.
S2CID
53666931
.
- ^
Park, Sunkyung; et al. (2013), "Wilson-Bappu Effect: Extended to Surface Gravity",
The Astronomical Journal
,
146
(4): 73,
arXiv
:
1307.0592
,
Bibcode
:
2013AJ....146...73P
,
doi
:
10.1088/0004-6256/146/4/73
,
S2CID
119187733
.
- ^
a
b
c
d
e
f
Mugrauer, Markus; Schlagenhauf, Saskia; Buder, Sven; Ginski, Christian; Fernandez, Matilde (2022). "Follow-up observations of the binary system γ Cep".
Astronomische Nachrichten
.
343
(5).
arXiv
:
2203.04128
.
Bibcode
:
2022AN....34324014M
.
doi
:
10.1002/asna.20224014
.
S2CID
247315574
.
- ^
a
b
c
d
e
f
g
Baines, Ellyn K.; et al. (2018).
"Fundamental Parameters of 87 Stars from the Navy Precision Optical Interferometer"
.
The Astronomical Journal
.
155
(1). 30.
arXiv
:
1712.08109
.
Bibcode
:
2018AJ....155...30B
.
doi
:
10.3847/1538-3881/aa9d8b
.
S2CID
119427037
.
- ^
Rumrill, H. B. (June 1936).
"Star Name Pronunciation"
.
Publications of the Astronomical Society of the Pacific
.
48
(283). San Francisco, California: 139.
Bibcode
:
1936PASP...48..139R
.
doi
:
10.1086/124681
.
S2CID
120743052
.
- ^
"IAU Catalog of Star Names"
. Retrieved
28 July
2016
.
- ^
Garrison, R. F. (December 1993),
"Anchor Points for the MK System of Spectral Classification"
,
Bulletin of the American Astronomical Society
,
25
: 1319,
Bibcode
:
1993AAS...183.1710G
, archived from
the original
on 2019-06-25
, retrieved
2012-02-04
- ^
Gore, J. E (1884). "A Catalogue of Suspected Variable Stars. With Notes and Observations".
Proceedings of the Royal Irish Academy. Science
.
4
: 267?410.
Bibcode
:
1885PRIA....4..411G
.
JSTOR
20635921
.
- ^
Hartkopf, William I.; Mason, Brian D.
"Addressing confusion in double star nomenclature: The Washington Multiplicity Catalog"
.
U.S. Naval Observatory
. Archived from
the original
on 2011-05-17
. Retrieved
2016-01-19
.
- ^
"IAU Working Group on Star Names (WGSN)"
. Retrieved
22 May
2016
.
- ^
"Bulletin of the IAU Working Group on Star Names, No. 1"
(PDF)
. Retrieved
28 July
2016
.
- ^
NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars
. IAU.org. 9 July 2014
- ^
"NameExoWorlds The Process"
. Archived from
the original
on 2015-08-15
. Retrieved
2015-09-05
.
- ^
Final Results of NameExoWorlds Public Vote Released
, International Astronomical Union, 15 December 2015.
- ^
"NameExoWorlds The Approved Names"
. Archived from
the original
on 2018-02-01
. Retrieved
2015-12-30
.
- ^
Richard Hinckley Allen: Star Names ? Their Lore and Meaning: Cepheus
- ^
(in Chinese)
中國星座神話
, written by 陳久金. Published by 台灣書房出版有限公司, 2005,
ISBN
978-986-7332-25-7
- ^
Campbell, Bruce; et al. (1988).
"A search for substellar companions to solar-type stars"
.
The Astrophysical Journal
.
331
: 902?921.
Bibcode
:
1988ApJ...331..902C
.
doi
:
10.1086/166608
.
- ^
Lawton, A. T.; Wright, P. (1989). "A planetary system for Gamma Cephei?".
British Interplanetary Society
.
42
: 335?336.
Bibcode
:
1989JBIS...42..335L
.
- ^
Walker, Gordon A.H.; Bohlender, David A.; Walker, Andrew R. (1992). "Gamma Cephei: Rotation or Planetary Companion?".
Astrophysical Journal Letters
.
396
: L91?L94.
Bibcode
:
1992ApJ...396L..91W
.
doi
:
10.1086/186524
.
- ^
Hatzes, Artie P.; et al. (2003). "A Planetary Companion to Gamma Cephei A".
The Astrophysical Journal
.
599
(2): 1383?1394.
arXiv
:
astro-ph/0305110
.
Bibcode
:
2003ApJ...599.1383H
.
doi
:
10.1086/379281
.
S2CID
11506537
.
- ^
Torres, Guillermo (2007). "The Planet Host Star γ Cephei: Physical Properties, the Binary Orbit, and the Mass of the Substellar Companion".
The Astrophysical Journal
.
654
(2): 1095?1109.
arXiv
:
astro-ph/0609638
.
Bibcode
:
2007ApJ...654.1095T
.
doi
:
10.1086/509715
.
S2CID
13255217
.
- ^
Huang, Xiumin; Ji, Jianghui (2022).
"Extremely Inclined Orbit of the S-type Planet γ Cep Ab Induced by the Eccentric Kozai?Lidov Mechanism"
.
The Astronomical Journal
.
164
(5): 177.
arXiv
:
2209.01472
.
Bibcode
:
2022AJ....164..177H
.
doi
:
10.3847/1538-3881/ac8f4c
.
S2CID
252089858
.
- ^
Endl, Michael; et al. (2011).
News from the γ Cephei Planetary System
. PLANETARY SYSTEMS BEYOND THE MAIN SEQUENCE: Proceedings of the International Conference. AIP Conference Proceedings. Vol. 1331. pp. 88?94.
arXiv
:
1101.2588
.
Bibcode
:
2011AIPC.1331...88E
.
doi
:
10.1063/1.3556187
.
External links
[
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]