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Information about Hd 209458

HD 209458

The red circle shows the location of HD 209458 in Pegasus.
Observation data
Epoch J2000
ConstellationPegasus
Right ascension22h 03m 10.8s
Declination+18° 53′ 04″
Apparent magnitude (V)7.65
Characteristics
Spectral typeF8-G0 V
B-V color index0.59
Variable typePlanetary transit
Astrometry
Radial velocity (Rv)-14.8 km/s
Proper motion (μ) RA: 28.90 mas/yr
Dec.: -18.37 mas/yr
Parallax (π)21.24  1.00 mas
Distance154 ly (47.1 pc)
Absolute magnitude (MV)4.29
Details
Mass1.1 M☉
Radius1.2 R☉
Luminosity1.61 L☉
Temperature6000 K
Metallicity109%
Rotation14.4 days
Age4-7 × 109 years
Other designations
BD +18°4917, SAO 107623, V376 Peg, HIP 108859.
Database references
SIMBADdata
HD 209458 is an 8th magnitude star in the constellation Pegasus. It is very similar to our Sun, and it is classified as a yellow dwarf (spectral class G0 V). Because it is located at a distance of about 150 light years, it is not visible to the unaided eye. With good binoculars or small telescope it should be easily detectable.

Enlarge picture
HD 209458


In 1999 two teams working independently (one team consisted of astronomers at the Geneva Observatory, the Harvard-Smithsonian Center for Astrophysics, and the Wise Observatory; the second group was the California and Carnegie Planet Search team) discovered an extrasolar planet orbiting the star by using the radial velocity planet search method. Soon after the discovery, separate teams led by David Charbonneau and Gregory W. Henry were able to detect a transit of the planet across the surface of the star making it the first known transiting extrasolar planet. The planet received the designation HD 209458 b.

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 V376 Pegasi variables, all of which show transits by a planet.[1]

Planetary system

HD 209458 b is an extrasolar planet that orbits the Sun-like star HD 209458 in the constellation Pegasus. Spectroscopic studies first revealed the presence of a planet around HD 209458 on November 5 1999. The planet is now under even more public scrutiny with the announcement that its atmosphere contains water vapor. Astronomers had made careful photometric measurements of several stars known to be orbited by planets, in the hope that they might observe a dip in brightness caused by the transit of the planet across the star's face. This would require the planet's orbit to be inclined such that it would pass between the Earth and the star, and previously no transits had been detected.

Travis Barman at Lowell Observatory in Flagstaff, Arizona, analyzed the emision spectrum of this planet, and believes that its atmosphere contains water (preprint), although previous research (L. J. Richardson et al. Nature 445, 892–895; 2007) suggests that the atmosphere is composed mostly of silicate clouds.

Companion
(In order from star)		 Mass
(MJ)		 Orbital period
(days)		 Semimajor axis
(AU)		 Eccentricity
b0.69 ± 0.053.52474541 ± 0.000000250.0450.00

References

  • Tsevi Mazeh et al, 2000, "The Spectroscopic Orbit of the Planetary Companion Transiting HD 209458", Astrophysical Journal, vol. 532, pp. L55–L58.

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constellation of Orion is the area outlined in the dashed yellow line. Orion contains a striking and well-known star pattern that has the form of a hunter.]] A constellation is any one of the 88 areas into which the sky — or the celestial sphere — is divided.
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Pegasus

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List of stars in Pegasus
Abbreviation: Peg
Genitive: Pegasi
Symbology: the Winged Horse / Pegasus
Right ascension: 23 h
Declination: +20
Area: 1121 sq. deg.
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Right ascension (abbrev. RA; symbol α) is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.
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Variable Star

Author Robert A. Heinlein & Spider Robinson
Cover artist Stephan Martiniere
Country United States
Language English
Genre(s) Science fiction
Publisher Tor Books
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Astrometry is the branch of astronomy that relates to precise measurements and explanations of the positions and movements of stars and other celestial bodies. Although once thought of as an esoteric field with little useful application for the future, the information obtained by
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The proper motion of a star is the measurement of its change in position in the sky over time after improper motions are accounted for. This contrasts with radial velocity which is the measurement of the change in distance toward or away from the viewer over time.
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A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60) of one degree. [1] Since one degree is defined as one three hundred sixtieth (1/360) of a circle, 1 MOA is 1/21600 of the amount of arc in a closed circle, or
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A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60) of one degree. [1] Since one degree is defined as one three hundred sixtieth (1/360) of a circle, 1 MOA is 1/21600 of the amount of arc in a closed circle, or
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A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60) of one degree. [1] Since one degree is defined as one three hundred sixtieth (1/360) of a circle, 1 MOA is 1/21600 of the amount of arc in a closed circle, or
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1 light-year =
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01015 m 01012 km
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0103 AU 0 pc
US customary / Imperial units
01015 ft 01012 mi
A light-year or lightyear (symbol:
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parsec (symbol pc) is a unit of length used in astronomy. The length of the parsec is based on the method of trigonometric parallax, one of the oldest methods for measuring the distances to stars.
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It is equal to the luminosity of the Sun, which is 3.827 × 1026 W, or 3.
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