HD 189733 b

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HD 189733 b
Extrasolar planet List of extrasolar planets
Exoplanet Comparison HD 189733 b.png
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-K2V
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
Semimajor 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 [3] MJ
Radius (r) 1.138 ± 0.027 RJ
Surface gravity (g) 21.2 m/s²
Temperature (T) 1117 ± 42 K
Discovery information
Discovery date 5 October 2005
Discoverer(s) Bouchy et al.
Detection method Doppler spectroscopy
Transit
Discovery site Haute-Provence Observatory
Discovery status Confirmed
Database references
Extrasolar Planets
Encyclopaedia		 data
SIMBAD data

HD 189733 b (or sometimes HD 189733 Ab) is an extrasolar planet approximately 63 light-years away in the constellation of Vulpecula (the Fox). The planet was discovered orbiting the star HD 189733 on October 5, 2005 (more precisely HD 189733 A since a star companion had been confirmed by then), when astronomers in France observed the planet transiting across the face of the star.[4] The planet is classified as a hot Jupiter class Jovian planet, with a close orbit to its parent star. HD 189733 b was the first extrasolar planet to be mapped and the first to be discovered with carbon dioxide in its atmosphere.

HD 189733b's star blasting out a strong X-ray flare, one powerful enough to blow away part of the planet's atmosphere. This artist's interpretation shows what the exoplanet, flare, and atmosphere loss might have looked like.

Contents

Detection and discovery [edit]

Transit and Doppler spectroscopy [edit]

The radial velocity of HD 189733 over time, caused by the presence of HD 189733 b.

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. It is occasionally referred to as HD 189733 Ab to distinguish it from the red dwarf star HD 189733 B. The HD 189733 star system is 63 light years from Earth in the direction of the constellation Vulpecula.

Infrared spectrum [edit]

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.[5] 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.

The infrared spectrum of HD 189733 b.

On October 22, a team of astrophysicists at the ETH Zürich managed to "detect and monitor [its] visible light" using polarimetry, the first such success. The authors claim a radius of 1.5+/-.2 Rj: over 30% larger than its transit disc. Its albedo in blue light is greater than 0.14. The planet would appear deep blue to our eyes.[6][7] This work will need to be confirmed, however, as the estimated radius is much larger than expected from measurements at other wavelengths.

Measured global temperature map of HD 189733 b.

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 to 1540 K.[8] The Rayleigh effect is confirmed in other models,[9] and by the apparent lack of a cooler, shaded stratosphere below its outer atmosphere.

Evaporation [edit]

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.[10]

Satellites [edit]

The transits reveal no moons of 0.8 Earth radius or larger, and no ring system comparable to Saturn's.[11]

Physical characteristics [edit]

An artist's impression of the planet that is in agreement with the global temperature map.[dubious – discuss]

This planet exhibits the largest photometric transit depth (amount of the parent star's light blocked) of any extrasolar planet so far observed, of 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.[5] 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.

The atmosphere was at first predicted "pL class", lacking a temperature-inversion stratosphere; like L dwarfs which lack titanium and vanadium oxides.[12] Follow-up measurements, tested against a stratospheric model, yielded inconclusive results.[13]

The condensates form a haze 1000 km above the surface as viewed in the infrared. A sunset viewed from that surface would be red.[14]

Sodium and potassium signals were predicted by Tinetti 2007. These signals were at first obscured by the condensate haze. Sodium was then found at three times the level of HD 209458 b.[15] This is the first extra solar planet discovered to have carbon dioxide in the atmosphere.[16]

Map of the planet [edit]

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.[17]

An artist's impression of HD 189733 b

Assuming the planet is tidally locked with its star, this suggests that powerful easterly winds moving at more than 9,600 kilometers per hour are responsible for redistributing the heat.[18] 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.[19]

Water vapor, oxygen and organic compounds [edit]

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.[20] Follow-up observations made using the Hubble Space Telescope confirm the presence of water vapor, neutral oxygen and also the organic compound methane.[9][21] [22] Later, Very Large Telescope observations also detected the presence of carbon monoxide on the day side of the planet. [23] It is currently unknown how the methane originated as the planet's high temperature (700°C, 1292°F) should cause the water and methane to react, replacing the atmosphere with carbon monoxide.[21][24]

Evolution [edit]

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.[25]

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.[26] 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 [edit]

References [edit]

  1. ^ a b c d van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.  Vizier catalog entry
  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. ^ 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
  4. ^ Bouchy, F. et al. (2005). "ELODIE metallicity-biased search for transiting Hot Jupiters II. A very hot Jupiter transiting the bright K star HD 189733". Astronomy and Astrophysics 444: L15–L19. arXiv:astro-ph/0510119. Bibcode:2005A&A...444L..15B. doi:10.1051/0004-6361:200500201. 
  5. ^ a b Press Release: NASA's Spitzer First To Crack Open Light of Faraway Worlds
  6. ^ Berdyugina, Svetlana V.; Andrei V. Berdyugin, Dominique M. Fluri, Vilppu Piirola (20 January 2008). "First detection of polarized scattered light from an exoplanetary atmosphere". The Astrophysical Journal 673: L83. arXiv:0712.0193. Bibcode:2008ApJ...673L..83B. doi:10.1086/527320. [dead link]
  7. ^ "Polarization technique focuses limelight". Retrieved 2009-09-30. See: Svetlana V. Berdyugina, Andrei V. Berdyugin, Dominique M. Fluri, Vilppu Piirola. (Dec. 2007). First detection of polarized scattered light from an exoplanetary atmosphere, Astrophys. J. Lett.
  8. ^ A. Lecavelier des Etangs, F. Pont, A. Vidal-Madjar, and D. Sing (2008). "Rayleigh scattering in the transit spectrum of HD 189733b". Astronomy & Astrophysics 481 (2): L83–L86. arXiv:0802.3228. Bibcode:2008A&A...481L..83L. doi:10.1051/0004-6361:200809388. Retrieved 2008-08-08. 
  9. ^ a b Eric Agol et al. (2008). "Transits and secondary eclipses of HD 189733 with Spitzer". Proceedings of the International Astronomical Union 4: 209. arXiv:0807.2434. doi:10.1017/S1743921308026422. 
  10. ^ Lecavelier des Etangs et al. (2010-03-10). "Evaporation of the planet HD189733b observed in HI Lyman-alpha". Astronomy & Astrophysics 1003: 2206. arXiv:1003.2206. Bibcode:2010arXiv1003.2206L. 
  11. ^ Frédéric Pont et al. (2008). "Hubble Space Telescope time-series photometry of the planetary transit of HD189733: no moon, no rings, starspots". Astronomy and Astrophysics 476 (3): 1347–1355. arXiv:0707.1940. Bibcode:2007A&A...476.1347P. doi:10.1051/0004-6361:20078269. 
  12. ^ Fortney, J. J.; Lodders, K.; Marley, M. S.; Freedman, R. S. (2008). "A Unified Theory for the Atmospheres of the Hot and Very Hot Jupiters: Two Classes of Irradiated Atmospheres". Astrophysical Journal 678 (2): 1419–1435. arXiv:0710.2558. Bibcode:2008ApJ...678.1419F. doi:10.1086/528370. 
  13. ^ Ivan Hubeny, Adam Burrows (2008). "Spectrum and atmosphere models of irradiated transiting extrasolar giant planets". Proceedings of the International Astronomical Union 4: 239. arXiv:0807.3588. doi:10.1017/S1743921308026458. 
  14. ^ F. Pont et al. (2008). "Detection of atmospheric haze on an extrasolar planet: The 0.55 – 1.05 micron transmission spectrum of HD189733b with the Hubble Space Telescope". Monthly Notices of the Royal Astronomical Society 385: 109–118. arXiv:0712.1374. Bibcode:2008MNRAS.385..109P. doi:10.1111/j.1365-2966.2008.12852.x. 
  15. ^ Redfield et al.; Endl, Michael; Cochran, William D.; Koesterke, Lars (2008). "Sodium Absorption from the Exoplanetary Atmosphere of HD 189733b Detected in the Optical Transmission Spectrum". The Astrophysical Journal Letters 673 (1): L87–L90. arXiv:0712.0761. Bibcode:2008ApJ...673L..87R. doi:10.1086/527475. 
  16. ^ Robert Roy Britt (November 24, 2008). "Carbon Dioxide Detected on Faraway World". Space.com. 
  17. ^ Iro, Nicolas; Bruno Bezard, T. Guillot (June 2005). "A time-dependent radiative model of HD 209458b". Astronomy and Astrophysics 436 (2): 719–727. arXiv:astro-ph/0409468. Bibcode:2005A&A...436..719I. doi:10.1051/0004-6361:20048344. 
  18. ^ Knutson, Heather A.; David Charbonneau, Lori E. Allen, Jonathan J. Fortney, Eric Agol, Nicolas B. Cowan, Adam P. Showman, Curtis S. Cooper & S. Thomas Megeath (10 May 2007). "A map of the day–night contrast of the extrasolar planet HD 189733b". Nature 447 (7141): 183–186. arXiv:0705.0993. Bibcode:2007Natur.447..183K. doi:10.1038/nature05782. PMID 17495920. 
  19. ^ "First Map of Alien World". Spitzer Space Telescope. Jet Propulsion Laboratory. 2007-05-09. Retrieved 2009-09-30. 
  20. ^ Press Release: NASA's Spitzer Finds Water Vapor on Hot, Alien Planet
  21. ^ a b Swain, Mark R.; Vasisht, Gautam; Tinetti, Giovanna (2008-03-20). "The presence of methane in the atmosphere of an extrasolar planet". Nature 452 (7185): 329–331. Bibcode:2008Natur.452..329S. doi:10.1038/nature06823. PMID 18354477.  arXiv.org link
  22. ^ Hubble Space Telescope detection of oxygen in the atmosphere of exoplanet HD189733b: Lotfi Ben-Jaffel, Gilda Ballester
  23. ^ 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
  24. ^ Stephen Battersby (2008-02-11). "Organic molecules found on alien world for first time". Retrieved 2008-02-12. 
  25. ^ "HD 189733 page". University of Geneva. 2007-03-05. Retrieved 2008-02-18. 
  26. ^ Gregory W. Henry et al. (2008). "The Rotation Period of the Planet-Hosting Star HD 189733". The Astronomical Journal 135: 68–71. arXiv:0709.2142. Bibcode:2008AJ....135...68H. doi:10.1088/0004-6256/135/1/68. 

External links [edit]

Media related to HD 189733 b at Wikimedia Commons

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

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