HD 189733 b

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HD 189733 b
Exoplanet List of exoplanets
300px
Size comparison of HD 189733 b with Jupiter.
Parent star
Star HD 189733 A
Constellation Vulpecula
Right ascension (α) 20h 00m 43.71s[1]
Declination (δ) +22° 42′ 39.1″[1]
Apparent magnitude (mV) 7.66
Distance 63.4 ± 0.9[1] ly
(19.5 ± 0.3[1] pc)
Spectral type K1–2V
Mass (m) 0.846+0.068
−0.049[2] M☉
Radius (r) 0.781 ± 0.051 R☉
Temperature (T) 4939 ± 158 K
Metallicity [Fe/H] −0.03 ± 0.04
Age >0.6 Gyr
Orbital elements
Semi-major axis (a) 0.03099 ± 0.0006 AU
(4.636 ± 0.09 Gm)
Periastron (q) 0.03096 AU
(4.632 Gm)
Apastron (Q) 0.03102 AU
(4.641 Gm)
Eccentricity (e) 0.0010 ± 0.0002
Orbital period (P) 2.2185733 ± 0.00002 d
    (53.245759 h)
Orbital speed (υ) 152.5 km/s
Inclination (i) 85.76 ± 0.29°
Time of transit (Tt) 2,453,988.80336 ± 0.00024 JD
Semi-amplitude (K) 205 ± 6 m/s
Physical characteristics
Mass (m) 1.162+0.058/-0.039 [2] MJ
Radius (r) 1.138 ± 0.027 RJ
Stellar flux (F⊙) 275 ⊕
Geometric Albedo (Ag) 0.40 ± 0.12 (290–450 nm)
< 0.12 (450–570 nm)
Surface gravity (g) 21.2 m/s²
Temperature (T) 1117 ± 42
Discovery information
Discovery date 5 October 2005
Discoverer(s) Bouchy et al.
Discovery method Doppler spectroscopy
Transit
Other detection methods Polarimetry
Reflection/emission modulations
Discovery site Haute-Provence Observatory
Discovery status Confirmed
Database references
Extrasolar Planets
Encyclopaedia		 data
SIMBAD data
Exoplanet Archive data
Open Exoplanet Catalogue data

HD 189733 b is an extrasolar planet approximately 63 light-years away from the Solar System in the constellation of Vulpecula. The planet was discovered orbiting the star HD 189733 A on October 5, 2005, when astronomers in France observed the planet transiting across the face of the star.[3] With a mass 13% higher than that of Jupiter, HD 189733 b orbits its host star once every 2.2 days at an orbital speed of 152.5 kilometres per second (341,000 mph), making it a hot Jupiter with poor prospects for extraterrestrial life. Being the closest transiting hot Jupiter to Earth, HD 189733 b is a subject for extensive atmospheric examination. HD 189733 b was the first extrasolar planet for which a thermal map was constructed,[4] to be detected through polarimetry, to have its overall colour determined (deep blue),[4][5] to have a transit detected in X-ray spectrum and to have carbon dioxide detected in its atmosphere.

In July, 2014, NASA announced finding very dry atmospheres on three exoplanets (HD 189733b, HD 209458b, WASP-12b) orbiting Sun-like stars.[6]

Detection and discovery

Transit and Doppler spectroscopy

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The infrared spectrum of HD 189733 b.
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A global temperature map of HD 189733 b.
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The planet's blue color was revealed using polarimetry.[4]

On October 6, 2005, a team of astronomers announced the discovery of transiting planet HD 189733 b. The planet was then detected using Doppler spectroscopy. Real-time radial velocity measurements detected the Rossiter–McLaughlin effect caused by the planet passing in front of its star before photometric measurements confirmed that the planet was transiting. In 2006, a team led by Drake Deming announced a detection of strong infrared thermal emission from the transiting extrasolar planet HD 189733 b, by measuring the flux decrement (decrease of total light) during its prominent secondary eclipse (when the planet passes behind the star).

The mass of the planet is estimated to be 13% larger than Jupiter's, with the planet completing an orbit around its host star every 2.2 days and an orbital speed of 152.5 km/s.

Infrared spectrum

On February 21, 2007, NASA released news that the Spitzer Space Telescope had measured detailed spectra from both HD 189733 b and HD 209458 b.[7] The release came simultaneously with the public release of a new issue of Nature containing the first publication on the spectroscopic observation of the other exoplanet, HD 209458 b. A paper was submitted and published by the Astrophysical Journal Letters. The spectroscopic observations of HD 189733 b were led by Carl Grillmair of NASA's Spitzer Science Center.

Visible colour

In 2008, a team of astrophysicists managed to detect and monitor the planet's visible light using polarimetry, the first such success.[8] This result was further improved by the same team in 2011.[4] They found that the planet albedo is significantly larger in blue light than in the red, most probably due to Rayleigh scattering and molecular absorption in the red.[4] The blue colour of the planet was subsequently confirmed in 2013,[9] making HD 189733 the first planet to have its overall colour determined by two different techniques.

The blueness of the planet may be the result of Rayleigh scattering. In mid January 2008, spectral observation during the planet's transit using that model found that if molecular hydrogen exists, it would have an atmospheric pressure of 410 ± 30 mbar of 0.1564 solar radii. The Mie approximation model also found that there is a possible condensate in its atmosphere, magnesium silicate (MgSiO3) with a particle size of approximately 10−2 to 10−1 μm. Using both models, the planet's temperature would be between 1340 and 1540 K.[10] The Rayleigh effect is confirmed in other models,[11] and by the apparent lack of a cooler, shaded stratosphere below its outer atmosphere.

X-ray spectrum

In July 2013, NASA reported the first observations of planet transit studied in X-ray spectrum. It was found that the planet's atmosphere blocks three times more X-rays than visible light.[12]

Evaporation

File:Hubble, Swift Detect First-ever Changes in an Exoplanet Atmosphere.ogv
Short narrated video about the evaporation of HD 189733 b's atmosphere.

In March 2010, transit observations using HI Lyman-alpha found that this planet is evaporating at a rate of 1-100 gigagrams per second. This indication was found by detecting the extended exosphere of atomic hydrogen. HD 189733 b is the second planet after HD 209458 b for which atmospheric evaporation has been detected.[13]

Physical characteristics

This planet exhibits one of the largest photometric transit depth (amount of the parent star's light blocked) of extrasolar planets so far observed, approximately 3%. The apparent longitude of ascending node of its orbit is 16 degrees +/- 8 away from north-south in our sky. It and HD 209458 b were the first two planets to be directly spectroscopically observed.[7] The parent stars of these two planets are the brightest transiting-planet host stars, so these planets will continue to receive the most attention by astronomers. Like most hot Jupiters, this planet is thought to be tidally locked to its parent star, meaning it has a permanent day and night.

The planet is not oblate, and has neither satellites with greater than 0.8 the radius of Earth nor a ring system like that of Saturn.[14]

The atmosphere was at first predicted "pL class", lacking a temperature-inversion stratosphere; like L dwarfs which lack titanium and vanadium oxides.[15] Follow-up measurements, tested against a stratospheric model, yielded inconclusive results.[16] Atmospheric condensates form a haze 1000 km above the surface as viewed in the infrared. A sunset viewed from that surface would be red.[17] Sodium and potassium signals were predicted by Tinetti 2007. First obscured by the haze of condensates, sodium was eventually observed at three times the concentration of HD 209458 b's sodium layer.[18] HD 189733 is also the first extrasolar planet confirmed to have carbon dioxide in its atmosphere.[19]

Map of the planet

File:Artist’s impression of the deep blue planet HD 189733b.jpg
An artist's conception of HD 189733 b following the 2013 confirmation of the planet's blue color by the Hubble Space Telescope. The appearance of HD 189733 b beyond the blue color is unknown.

In 2007, the Spitzer space telescope was used to map the planet's temperature emissions. The planet+star system was observed for 33 consecutive hours, starting when only the night side of the planet was in view. Over the course of one-half of the planet's orbit, more and more of the day side came into view. A temperature range of 973 ± 33 K to 1,212 ± 11 K was discovered, indicating that the absorbed energy from the parent star is distributed fairly evenly through the planet's atmosphere. Interestingly, the region of peak temperature was offset 30 degrees east of the substellar point, as predicted by theoretical models of hot Jupiters taking into account a parameterized day to night redistribution mechanism.[20]

File:HD 189733b's atmosphere.jpg
An artist's impression of HD 189733 b showing rapid evaporation of the atmosphere

Scientists at the University of Warwick determined that it has winds of up to 8,700 km/h (5,400 mph) blowing from the day side to the night side.[21] NASA released a brightness map of the surface temperature of HD 189733 b; it is the first map ever published of an extra-solar planet.[22]

Water vapor, oxygen and organic compounds

On July 11, 2007, a team led by Giovanna Tinetti published the results of their observations using the Spitzer Space Telescope concluding there is solid evidence for significant amounts of water vapor in the planet's atmosphere.[23] Follow-up observations made using the Hubble Space Telescope confirm the presence of water vapor, neutral oxygen and also the organic compound methane.[11][24][25] Later, Very Large Telescope observations also detected the presence of carbon monoxide on the day side of the planet.[2] It is currently unknown how the methane originated as the planet's high 700 °C temperature should cause the water and methane to react, replacing the atmosphere with carbon monoxide.[24][26]

Evolution

While transiting the system also clearly exhibits the Rossiter–McLaughlin effect, the shifting in photospheric spectral lines caused by the planet occulting a part of the rotating stellar surface. Due to its high mass and close orbit the parent star has a very large semi-amplitude (K), the "wobble" in the star's radial velocity, of 205 m/s.[27]

The Rossiter–McLaughlin effect allows the measurement of the angle between the planet's orbital plane and the equatorial plane of the star. These are well aligned.[28] By analogy with HD 149026 b, the formation of the planet was peaceful and probably involved interactions with the protoplanetary disc. A much larger angle would have suggested a violent interplay with other protoplanets.

See also

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References

  1. ↑ 1.0 1.1 1.2 1.3 Lua error in package.lua at line 80: module 'strict' not found. Vizier catalog entry
  2. ↑ 2.0 2.1 2.2 Detection of carbon monoxide in the high-resolution day-side spectrum of the exoplanet HD 189733b: Remco J. de Kok, Matteo Brogi, Ignas A.G. Snellen, Jayne Birkby, Simon Albrecht, Ernst J. W. de Mooij
  3. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ 7.0 7.1 Press Release: NASA's Spitzer First To Crack Open Light of Faraway Worlds
  8. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ First distant planet to be seen in colour is blue Nature 11 July 2013
  10. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ 11.0 11.1 Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ NASA's Chandra Sees Eclipsing Planet in X-rays for First Time
  13. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  14. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  15. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  16. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  17. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  18. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  19. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  20. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  21. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  22. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  23. ↑ Press Release: NASA's Spitzer Finds Water Vapor on Hot, Alien Planet
  24. ↑ 24.0 24.1 Lua error in package.lua at line 80: module 'strict' not found. arXiv.org link
  25. ↑ Hubble Space Telescope detection of oxygen in the atmosphere of exoplanet HD189733b: Lotfi Ben-Jaffel, Gilda Ballester
  26. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  27. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  28. ↑ Lua error in package.lua at line 80: module 'strict' not found.

External links

Media related to Lua error in package.lua at line 80: module 'strict' not found. at Wikimedia Commons

Coordinates: Sky map 20h 00m 43.7133s, +22° 42′ 39.07″

es:HD 189733#HD 189733b

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