HD 209458 is a

star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...

with an orbiting

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...

in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Pegasus Pegasus (; ) is a winged horse in Greek mythology, usually depicted as a white stallion. He was sired by Poseidon, in his role as horse-god, and foaled by the Gorgon Medusa. Pegasus was the brother of Chrysaor, both born from Medusa's blood w ...

. It has an

apparent visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...

of 7.65 and an absolute magnitude of 4.28. Because it is located at a distance of from the Sun as measured via

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...

, it is not visible to the unaided eye. With good

binoculars Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...

or a small

telescope A telescope is a device used to observe distant objects by their emission, Absorption (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally, it was an optical instrument using len ...

it should be easily detectable. The system is drifting closer with a heliocentric

radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...

of −14.8 km/s. The

spectrum A spectrum (: spectra or spectrums) is a set of related ideas, objects, or properties whose features overlap such that they blend to form a continuum. The word ''spectrum'' was first used scientifically in optics to describe the rainbow of co ...

of HD 209458 presents as a

late Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudonym used by Dave Groh ...

F- or early

G-type main-sequence star A G-type main-sequence star (spectral type: G-V), also often, and imprecisely, called a yellow dwarf, or G star, is a main sequence, main-sequence star (luminosity class V) of stellar classification, spectral type G. Such a star has about 0.9 to ...

with a

stellar classification In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...

of F9 V or G0 V, respectively. It is roughly 3.5 billion years old and is spinning with a

projected rotational velocity Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bu ...

of 4.2 km/s. The star displays a moderate amount of

magnetic activity A stellar magnetic field is a magnetic field generated by the motion of conductive Plasma (physics), plasma inside a star. This motion is created through convection, which is a form of energy transport involving the physical movement of material ...

in its

chromosphere A chromosphere ("sphere of color", from the Ancient Greek words χρῶμα (''khrôma'') 'color' and σφαῖρα (''sphaîra'') 'sphere') is the second layer of a Stellar atmosphere, star's atmosphere, located above the photosphere and below t ...

. It has a 15% greater mass than the Sun and a 20% larger radius. The abundance of iron, a measure of the

metallicity In astronomy, metallicity is the Abundance of the chemical elements, abundance of Chemical element, elements present in an object that are heavier than hydrogen and helium. Most of the normal currently detectable (i.e. non-Dark matter, dark) matt ...

of the star, is solar. HD 209458 is radiating 1.8 times the luminosity of the Sun from its

photosphere The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately , or equivalently, a depth from which 50% of light will esc ...

at an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 6,071 K. 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 A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

designation for HD 209458 is V376 Pegasi. It is the

prototype A prototype is an early sample, model, or release of a product built to test a concept or process. It is a term used in a variety of contexts, including semantics, design, electronics, and Software prototyping, software programming. A prototype ...

of the variable class "EP" in the

General Catalogue of Variable Stars The General Catalogue of Variable Stars (GCVS) is a list of variable stars in the Milky Way Galaxy. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR, edited by and Pavel Parenago. Second a ...

, defined as stars showing eclipses by their planets.

Planetary system

In 1999, two teams working independently (one team consisted of astronomers at the Geneva Observatory, the Center for Astrophysics Harvard & Smithsonian, and the

Wise Observatory The Florence and George Wise Observatory (IAU code 097) is an astronomy, astronomical observatory owned and operated by Tel Aviv University. It is located west of the town of Mitzpe Ramon in the Negev desert near the edge of the Ramon Crater, an ...

; the second group was the California and Carnegie Planet Search team) discovered an

extrasolar planet An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first detect ...

orbiting the star by using the

planet A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...

search method. Soon after the discovery, separate teams led by David Charbonneau and Gregory W. Henry were able to detect a

transit Transit may refer to: Arts and entertainment Film * ''Transit'' (1980 film), a 1980 Israeli film * ''Transit'' (1986 film), a Canadian short film * ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countrie ...

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 HD 209458 b is an exoplanet, specifically a hot Jupiter, that orbits the solar analog HD 209458 in the constellation Pegasus, some from the Solar System. The radius of the planet's orbit is , or one-eighth the radius of Mercury's orbit (). Th ...

. 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

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 emission spectrum of this planet in 2007, and believes that its atmosphere contains water vapor, although previous research in 2007 suggests that the atmosphere is composed mostly of silicate clouds. A spectrum taken in 2020 detected either sodium or

titanium oxide Titanium oxide may refer to: * Titanium dioxide (titanium(IV) oxide), TiO2 * Titanium(II) oxide (titanium monoxide), TiO, a non-stoichiometric oxide * Titanium(III) oxide (dititanium trioxide), Ti2O3 * Ti3O * Ti2O * δ-TiOx (x= 0.68–0.75) * Ti ...

in the planet's atmosphere. A later study in 2021 did not find any molecular absorption features in the planetary atmosphere at all.

References

External links

* {{DEFAULTSORT:HD 209458 F-type main-sequence stars G-type main-sequence stars Planetary transit variables Planetary systems with one confirmed planet Pegasus (constellation) BD+18 4917 209458 108859 Pegasi, V376 J22031077+1853036

Planetary system

See also

References

External links