HD 189733 b
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| Extrasolar planet | List of extrasolar planets | |
|---|---|---|
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| Parent star | ||
| Star | HD 189733 A | |
| Constellation | Vulpecula | |
| Right ascension | (α) | 20h 00m 43.7133s |
| Declination | (δ) | +22° 42′ 39.070″ |
| Distance | 62.9 ly (19.3 pc) | |
| Spectral type | K1-K2V | |
| Orbital elements | ||
| Semimajor axis | (a) | 0.0313 ± 0.0004 AU |
| Eccentricity | (e) | 0.4007 ± 0.0035 |
| Orbital period | (P) | 116.6884 ± 0.0044 d |
| Inclination | (i) | 85.79° ± 0.2° |
| Longitude of periastron |
(ω) | -° |
| Time of periastron | (T0) | (transit time) JD |
| Semi-amplitude | (K) | 205 ± 6 m/s |
| Physical characteristics | ||
| Mass | (m) | 1.15 ± 0.04 MJ |
| Radius | (r) | 1.154 ± 0.032 RJ |
| Surface gravity | (g) | 2.5 m/s² |
| Temperature | (T) | 1117 ± 42 K |
| Discovery information | ||
| Discovery date | 5 October 2005 | |
| Discoverer(s) | Marcy et al. | |
| Detection method | Doppler Spectroscopy | |
| Discovery site |  United States |
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| Discovery status | Confirmed | |
HD 189733 b is a hot Jupiter class gas giant planet that closely orbits the yellow dwarf star HD 189733 A. The planet was discovered on October 5, 2005 when astronomers in the United States observed the planet transiting across the face of the star.[1] 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.
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%. While transiting the system also clearly exhibits the Rossiter-McLaughlin effect. 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.[2] It and HD 209458 b were the first two planets to be directly spectroscopically observed.[3]
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[edit] Observation
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).
- "A 6-hour photometric sequence using Spitzer's infrared spectrograph in peak-up imaging mode at 16 [micrometers] shows the secondary eclipse depth to be 0.551 ± 0.030%, with accuracy limited by instrumental baseline uncertainties, but with 32-sigma precision (0.017%) on the detection. The 16-[micrometer] brightness temperature of this planet (1117 ± 42 K) is very similar to the Spitzer detections of TrES-1 and HD 209458 b, but the observed planetary flux (660 [micro-janskies]) is an order of magnitude greater. This large signal will allow a detailed characterization of this planet in the infrared. The photometry has sufficient signal-to-noise (~400 per point) to motivate a search for structure in the ingress/egress portions of the eclipse curve, caused by putative thermal structure on the disk of the planet. We show that by binning our 6-second sampling down to 6-minute resolution, we detect the modulation in the intensity derivative during ingress/egress due to the overall shape of the planet, but our sensitivity is not yet sufficient to distinguish between realistic models of the temperature distribution across the planet's disk. We point out the potential for extending Spitzer secondary eclipse detections down to the regime of transiting hot Neptunes, if such systems are discovered among nearby lower dwarf stars."
In 2007 the Spitzer space telescope was used to map the planet's temperature emissions. A temperature range of 973 ± 33 K to 1,212 ± 11 K was discovered, indicating that the star's heat 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.[4]
Its Lambert sphere, Rayleigh-scattering atmosphere, is 1.5+/-.2 Rj: over 30% larger than its transit disc. Its albedo is greater than 0.14. The planet would appear deep blue to our eyes.[5] ([Press release])
The apparent longitude of ascending node of its orbit is 16 degrees +/- 8 away from north-south in our sky.
[edit] Direct spectral observation
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.[3] 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. The findings on HD 189733 b will[when?] appear in an upcoming issue of the Astrophysical Journal Letters. The spectroscopic observations of HD 189733 b were led by Carl Grillmair of NASA's Spitzer Science Center.
| HD 189733 b | Jupiter |
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On 22 October, a team of astrophysicists based in Zurich[who?] managed to "detect and monitor [its] visible light" using polarimetry, the first such success; and sent their findings to The Astrophysical Journal.[citation needed]
In mid January 2008, spectral observation using Rayleigh scattering 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.[6]
[edit] First map of an extra-solar planet
In May 2007 NASA released a map of the surface temperature of HD 189733 b, performed by spectral observations through the Spitzer Space Telescope. This is the first map ever published of an extra-solar planet.[7]
[edit] First evidence of 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.[8] Follow-up observations made using the Hubble Space Telescope confirm the presence of water vapor and also the organic compound methane.[9] It is currently unknown how the methane originated as the planet's high temperature (700°C, 1292°F) favors the formation of carbon monoxide instead.[9][10]
[edit] References
- ^ Bouchy 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. (Preprint)
- ^ HD 189733 page. University of Geneva (2007-03-05). Retrieved on 2008-02-18.
- ^ a b Press Release: NASA's Spitzer First To Crack Open Light of Faraway Worlds
- ^ 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: 183–186. doi:.
- ^ 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. doi:.
- ^ "Rayleigh scattering in the transit spectrum of HD 189733b". Press release. Retrieved on 2008-02-18.
- ^ Image ssc2007-09a
- ^ Press Release: NASA's Spitzer Finds Water Vapor on Hot, Alien Planet
- ^ 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: 329–331. doi:. arXiv.org link
- ^ Stephen Battersby (2008-02-11). Organic molecules found on alien world for first time. Retrieved on 2008-02-12.
