HD 209458

HD 209458
	HD 209458 (100x100); HD 209458 (circled) in the constellation Pegasus.
Observation data; Epoch J2000 Equinox J2000
Constellation	Pegasus
Right ascension	22h 03m 10.77275s
Declination	+18° 53′ 03.5494″
Apparent magnitude (V)	7.65
Characteristics
Evolutionary stage	main sequence
Spectral type	F9 V or G0 V
Apparent magnitude (B)	8.244
Apparent magnitude (K)	6.308±0.026
B−V color index	+0.574±0.014
Variable type	EP
Astrometry
Radial velocity (Rv)	−14.78±0.16 km/s
Proper motion (μ)	RA: 29.766(28) mas/yr ; Dec.: −17.976(25) mas/yr
Parallax (π)	20.7694 ± 0.0266 mas
Distance	157.0 ± 0.2 ly ; (48.15 ± 0.06 pc)
Absolute magnitude (MV)	4.28±0.10
Details
Mass	1.148±0.022 M☉
Radius	1.203±0.061 R☉
Luminosity	1.77±0.14 L☉
Temperature	6071±20 K
Metallicity [Fe/H]	0.00±0.02 dex
Rotation	14.4 days[citation needed]
Rotational velocity (v sin i)	4.228±0.007 km/s
Age	3.5±1.4 Gyr
Other designations
	V376 Peg, BD+18°4917, HIP 108859, SAO 107623, 2MASS J22031077+1853036
Database references
SIMBAD	data
Exoplanet Archive	data

HD 209458 is a star with an orbiting exoplanet in the constellation Pegasus. It has an apparent visual magnitude of 7.65^[2] and an absolute magnitude of 4.28.^[5] Because it is located at a distance of 157 light-years (48 parsecs) from the Sun as measured via parallax, it is not visible to the unaided eye. With good binoculars or a small telescope it should be easily detectable. The system is drifting closer with a heliocentric radial velocity of −14.8 km/s.^[1]

The spectrum of HD 209458 presents as a late F- or early G-type main-sequence star with a stellar classification of F9 V^[3] or G0 V,^[4] respectively. It is roughly 3.5^[7] billion years old and is spinning with a projected rotational velocity of 4.2 km/s.^[8] The star displays a moderate amount of magnetic activity in its chromosphere.^[10] It has a 15% greater mass than the Sun and a 20% larger radius. The abundance of iron, a measure of the metallicity of the star, is solar.^[7] HD 209458 is radiating 1.8 times the luminosity of the Sun from its photosphere at an effective temperature of 6,071 K.^[7]

Because the planet transits the star, the star is dimmed by about 2% every 3.5 days making it an extrinsic variable. The variable star designation for HD 209458 is V376 Pegasi. It is the prototype of the variable class "EP" in the General Catalogue of Variable Stars, defined as stars showing eclipses by their planets.^[6]^[11]

^ ^a ^b ^c ^d ^e ^f Cite error: The named reference GaiaDR3 was invoked but never defined (see the help page).
^ ^a ^b ^c ^d Cite error: The named reference Anderson_Francis_2012 was invoked but never defined (see the help page).
^ ^a ^b Cite error: The named reference Gray_et_al_2001 was invoked but never defined (see the help page).
^ ^a ^b Cite error: The named reference Charbonneau2000 was invoked but never defined (see the help page).
^ ^a ^b ^c ^d Cite error: The named reference mazeh was invoked but never defined (see the help page).
^ ^a ^b Cite error: The named reference gcvs was invoked but never defined (see the help page).
^ ^a ^b ^c ^d ^e ^f ^g ^h Cite error: The named reference Del Burgo2016 was invoked but never defined (see the help page).
^ ^a ^b Cite error: The named reference Bonomo2017 was invoked but never defined (see the help page).
^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
^ Cite error: The named reference Ben-Jaffel_2007 was invoked but never defined (see the help page).
^ Samus, N. N. (2009). "GCVS Variability Types and Distribution Statistics of Designated Variable Stars According to their Types of Variability". Retrieved 2010-08-02.

[GaiaDR3-1] ^ ^a ^b ^c ^d ^e ^f Cite error: The named reference GaiaDR3 was invoked but never defined (see the help page).

[Anderson_Francis_2012-2] Cite error: The named reference Anderson_Francis_2012 was invoked but never defined (see the help page).

[Gray_et_al_2001-3] Cite error: The named reference Gray_et_al_2001 was invoked but never defined (see the help page).

[Charbonneau2000-4] Cite error: The named reference Charbonneau2000 was invoked but never defined (see the help page).

[mazeh-5] Cite error: The named reference mazeh was invoked but never defined (see the help page).

[gcvs-6] Cite error: The named reference gcvs was invoked but never defined (see the help page).

[Del_Burgo2016-7] ^ ^a ^b ^c ^d ^e ^f ^g ^h Cite error: The named reference Del Burgo2016 was invoked but never defined (see the help page).

[Bonomo2017-8] Cite error: The named reference Bonomo2017 was invoked but never defined (see the help page).

[SIMBAD-9] Cite error: The named reference SIMBAD was invoked but never defined (see the help page).

[Ben-Jaffel_2007-10] Cite error: The named reference Ben-Jaffel_2007 was invoked but never defined (see the help page).

[11] Samus, N. N. (2009). "GCVS Variability Types and Distribution Statistics of Designated Variable Stars According to their Types of Variability". Retrieved 2010-08-02.

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Observation data Epoch J2000 Equinox J2000
HD 209458 (100x100) HD 209458 (circled) in the constellation Pegasus.
Constellation	Pegasus
Right ascension	22^h 03^m 10.77275^s^[1]
Declination	+18° 53′ 03.5494″^[1]
Apparent magnitude (V)	7.65^[2]
Characteristics
Evolutionary stage	main sequence
Spectral type	F9 V^[3] or G0 V^[4]
Apparent magnitude (B)	8.244^[2]
Apparent magnitude (K)	6.308±0.026^[2]
B−V color index	+0.574±0.014^[5]
Variable type	EP^[6]
Astrometry

Radial velocity (R_v)	−14.78±0.16^[1] km/s
Proper motion (μ)	RA: 29.766(28) mas/yr^[1] Dec.: −17.976(25) mas/yr^[1]
Parallax (π)	20.7694 ± 0.0266 mas^[1]
Distance	157.0 ± 0.2 ly (48.15 ± 0.06 pc)
Absolute magnitude (M_V)	4.28±0.10^[5]

Details

Mass	1.148±0.022^[7] `M`_☉
Radius	1.203±0.061^[7] `R`_☉
Luminosity	1.77±0.14^[7] `L`_☉
Temperature	6071±20^[7] K
Metallicity [Fe/H]	0.00±0.02^[5] dex
Rotation	14.4 days^{[citation needed]}
Rotational velocity (v sin i)	4.228±0.007^[8] km/s
Age	3.5±1.4^[7] Gyr

Other designations
V376 Peg, BD+18°4917, HIP 108859, SAO 107623, 2MASS J22031077+1853036^[9]
Database references
SIMBAD	data
Exoplanet Archive	data