HD 189733 b

HD 189733 b

Planetbox begin
name = HD 189733 b
Planetbox image



caption = An artist's impression of HD 189733 b about
to block out its parent star.
Planetbox star
star = HD 189733 A
constell = Vulpecula
RA = RA|20|00|43.7133
DEC = DEC|+22|42|39.070
dist_ly = 62.9
dist_pc = 19.3
class = K1-K2V
Planetbox orbit
semimajor = 0.0313 ± 0.0004
eccentricity = 0.0010 ± 0.0002
period = 2.2185733 ± 0.00002
inclination = 85.79° ± 0.2
ang_dist =
long_peri =
t_peri =
semi-amp = 205 ± 6
Planetbox character
mass = 1.15 ± 0.04
radius = 1.154 ± 0.032
gravity = 21.2
temperature = 1117 ± 42
Planetbox discovery
discovery_date = 5 October 2005
discovery_site = flag|France
discoverers = Marcy et al.
discovery_method = Doppler Spectroscopy
discovery_status = Confirmed
Planetbox catalog
names = Gliese 4130 b, HIP 98505 b,
V452 Vulpeculae b

HD 189733 b 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, when astronomers in France observed the planet transiting across the face of the star.cite journal | url=http://www.aanda.org/articles/aa/full/2005/46/aahi291/aahi291.html |author=Bouchy et al.|title=ELODIE metallicity-biased search for transiting Hot Jupiters II. A very hot Jupiter transiting the bright K star HD 189733 | journal = Astronomy and Astrophysics | volume=444 | year=2005 | pages=L15–L19 | doi=10.1051/0004-6361:200500201 ( [http://arxiv.org/abs/astro-ph/0510119 Preprint] )] 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 ever extrasolar planet to be mapped.

Detection and discovery

Transit and Doppler spectroscopy

On October 6 2005, a team of astronomers announced the discovery of transiting planet HD 189733 b. 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).

Planetary radius
radius = 115

The mass of the planet is estimated to be 15% larger than Jupiter's; with the planet completing an orbit around its host star every 2.2 days. 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

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. [http://www.spitzer.caltech.edu/Media/releases/ssc2007-04/release.shtml Press Release: NASA's Spitzer First To Crack Open Light of Faraway Worlds ] ] 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 has been submitted to the "Astrophysical Journal Letters". The spectroscopic observations of HD 189733 b were led by Carl Grillmair of NASA's Spitzer Science Center.

On 22 October, 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.cite journal | url=http://www.astro.phys.ethz.ch/papers/berdyugina/exoplanet_hd189733b.pdf | journal=The Astrophysical Journal | volume=673 | month=20 January | year=2008 | title=First detection of polarized scattered light from an exoplanetary atmosphere | first=Svetlana V.| last=Berdyugina | coauthors=Andrei V. Berdyugin, Dominique M. Fluri, Vilppu Piirola | doi=10.1086/527320 | pages=L83] ( [http://www.eurekalert.org/pub_releases/2007-12/ezfi-ptf122607.php Press release] ) This work will need to be confirmed, however, as the estimated radius is much larger than expected from measurements at other wavelengths.

The blueness 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.cite journal |url=http://www.aanda.org/index.php?option=article&access=standard&Itemid=129&url=/articles/aa/abs/2008/14/aa09388-08/aa09388-08.html |title=Rayleigh scattering in the transit spectrum of HD 189733b |journal=Astronomy & Astrophysics |year=2008 |volume=481 |pages=L83–L86 |accessdate=2008-08-08 |author=A. Lecavelier des Etangs, F. Pont, A. Vidal-Madjar, and D. Sing |doi=10.1051/0004-6361:200809388] The Rayleigh effect is confirmed in other models,Cite arXiv| title =Transits and secondary eclipses of HD 189733 with Spitzer |author= Eric Agol "et al." |year=2008 |eprint=0807.2434v1 |class=astro-ph ] and by the apparent lack of a cooler, shaded stratosphere below its outer atmosphere.

Satellites

The transits reveal no moons of 0.8 Earth radius or larger, and no ring system of 120 times the optical depth.cite arXiv | title=Hubble Space Telescope time-series photometry of the planetary transit of HD189733: no moon, no rings, starspots | author=Frédéric Pont "et al." | year=2008 |eprint=0707.1940v2 |class=astro-ph]

Physical characteristics

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. 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. [cite journal | title=A Unified Theory for the Atmospheres of the Hot and Very Hot Jupiters: Two Classes of Irradiated Atmospheres | author=Fortney, J. J.; Lodders, K.; Marley, M. S.; Freedman, R. S. | year=2008 | journal=Astrophysical Journal | volume=678 |issue=2|pages=1419–1435 | doi=10.1086/528370] Followup measurements, tested against a stratospheric model, yielded inconclusive results. [Cite arXiv| author=Ivan Hubeny, Adam Burrows |title=Spectrum and atmosphere models of irradiated transiting extrasolar giant planets |eprint=0807.3588v1| class=astro-ph|year=2008]

The condensates form a haze 1000 km above the surface as viewed in the infrared. A sunset viewed from that surface would be red. [Cite arXiv| author=F. Pont "et al."|title=Detection of atmospheric haze on an extrasolar planet: The 0.55 – 1.05 micron transmission spectrum of HD189733b with the Hubble Space Telescope |eprint=0712.1374v2| class=astro-ph|year=2008]

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. [cite journal | journal=The Astrophysical Journal Letters |issue=673 |year= 2008 |month=January |day=20 | doi=10.1086/527475 | title=Sodium Absorption from the Exoplanetary Atmosphere of HD 189733b Detected in the Optical Transmission Spectrum |author=Seth Redfield, Michael Endl, William D. Cochran, and Lars Koesterke |pages=L87–L90 | volume=673 ]

Map of the planet

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.

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.cite journal| url=http://www.nature.com/nature/journal/v447/n7141/abs/nature05782.html| journal=Nature| volume= 447| pages= 183–186| month=10 May| year= 2007| doi= 10.1038/nature05782| title=A map of the day–night contrast of the extrasolar planet HD 189733b| first=Heather A.| last=Knutson| coauthors= David Charbonneau, Lori E. Allen, Jonathan J. Fortney, Eric Agol, Nicolas B. Cowan, Adam P. Showman, Curtis S. Cooper & S. Thomas Megeath] 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. [ [http://www.spitzer.caltech.edu/Media/releases/ssc2007-09/ssc2007-09a.shtml Image ssc2007-09a ] ]

Water vapor and organic compounds

On July 11, 2007, a team lead 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. [ [http://www.spitzer.caltech.edu/Media/releases/ssc2007-12/release.shtml Press Release: NASA's Spitzer Finds Water Vapor on Hot, Alien Planet ] ] Follow-up observations made using the Hubble Space Telescope confirm the presence of water vapor and also the organic compound methane.Cite journal | title = The presence of methane in the atmosphere of an extrasolar planet | last = Swain | first = Mark R. | coauthors = Vasisht, Gautam; Tinetti, Giovanna | date = 2008-03-20 | journal = Nature | volume = 452 | pages = 329–331 | url = http://www.nature.com/nature/journal/v452/n7185/abs/nature06823.html | doi = 10.1038/nature06823 [http://arxiv.org/abs/0802.1030 arXiv.org link] ] 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. [cite web|url=http://space.newscientist.com/article/dn13303-organic-molecules-found-on-alien-world-for-first-time.html|title=Organic molecules found on alien world for first time|accessdate=2008-02-12|author=Stephen Battersby|date=2008-02-11]

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. [cite web|url=http://obswww.unige.ch/exoplanets/hd189733.html| title=HD 189733 page| date=2007-03-05| publisher=University of Geneva| accessdate=2008-02-18]

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. [cite journal| title=THE ROTATION PERIOD OF THE PLANET-HOSTING STAR HD 189733
author=Gregory W. Henry "et al." | year= 2008 | journal=The Astronomical Journal | volume=135 | doi=10.1088/0004-6256/135/1/68 |pages=68–71
] 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

* HD 209458 b
* 51 Pegasi b

References

External links

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