HD 189733

HD 189733, also catalogued as V452 Vulpeculae, is a binary star system approximately 64.5 light-years away in the constellation of Vulpecula (the Fox). The primary star is suspected to be an orange dwarf star,[2] while the secondary star is a red dwarf star.[5] Given that this system has the same visual magnitude as HD 209458, it promises much for the study of close transiting extrasolar planets. The star can be found with binoculars 0.3 degrees east of the Dumbbell Nebula (M27).

HD 189733 AB

The location of the HD 189733 system.
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Vulpecula
HD 189733 A
Right ascension  20h 00m 43.71s[1]
Declination +22° 42′ 39.1″[1]
Apparent magnitude (V) 7.676[2]
HD 189733 B
Right ascension  20h 00m 42.97s[3]
Declination +22° 42′ 34.2″[3]
Apparent magnitude (V) ~10
Characteristics
Spectral type K1.5V[2]/M[4]
Apparent magnitude (B) 8.609 ±0.016/[2]
Apparent magnitude (J) 6.07[2]/10.116 ±0.041[5]
Apparent magnitude (H) 5.59[2]/9.545 ±0.086[5]
Apparent magnitude (K) 5.54[2]/9.323 ±0.027[5]
Variable type BY Draconis[2][6]
Astrometry
HD 189733 A
Radial velocity (Rv)−2.7 ±0.5[2] km/s
Proper motion (μ) RA: −3.294±0.043[1] mas/yr
Dec.: −250.225±0.049[1] mas/yr
Parallax (π)50.5685 ± 0.0323[1] mas
Distance64.50 ± 0.04 ly
(19.78 ± 0.01 pc)
HD 189733 B
Proper motion (μ) RA: −12.256±0.066[3] mas/yr
Dec.: −253.989±0.078[3] mas/yr
Parallax (π)50.7045 ± 0.049[3] mas
Distance64.32 ± 0.06 ly
(19.72 ± 0.02 pc)
Orbit
CompanionHD 189733 B
Period (P)3,200 yr
Semi-major axis (a)11.38[7]"
(216 AU)
Details
Mass0.846+0.068
−0.049[8] M☉
Radius0.805±0.016[9] R☉
Luminosity0.328±0.011[9] L☉
Surface gravity (log g)4.56±0.03[9] cgs
Temperature4875±43[9] K
Metallicity [Fe/H]−0.03±0.08[10] dex
Rotation11.953±0.009 days[11]
Age4.3±2.8[9] Gyr
Other designations
V452 Vulpeculae, BD+22 3887, Gaia DR2 1827242816201846144, GJ 4130, HIP 98505, SAO 88060, LTT 15851, NLTT 48568, Wolf 864, TYC 2141-972-1, 2MASS J20004370+2242391[2]
Database references
SIMBADdata
Exoplanet Archivedata
Extrasolar Planets
Encyclopaedia		data

As of 2005, it has been confirmed that an extrasolar planet orbits the primary star within the system.[12]

Stellar system

HD 189733 A is an orange dwarf star of the spectral type K1.5V. The star has a mass of 81 percent that of the Sun, a radius 76 percent, and a luminosity of 33 percent. The star is between 89 and 102 percent as enriched in iron as the Sun, making the star more than 600 million years old.

The star has starspots which affect its luminosity by 1.5 percent in visible light.[13] As a result, it is listed in the General Catalogue of Variable Stars as a BY Draconis variable with the variable star designation V452 Vul.[6]

Discovered in 2006 by the infrared 2MASS astronomical survey, 2MASS J20004297+2242342 or HD 189733 B is a dim red dwarf star of spectral type M. The companion was observed at a separation of 216 astronomical units away from the primary star. Orbiting in a clockwise orbit (which is nearly perpendicular to the orbital plane of transiting planet HD 189733 b), the orbital period is estimated around 3,200 years long.[4]

Planetary system

HD 189733 A has one known planet, designated HD 189733 b, a gaseous giant 13% larger than Jupiter close enough to complete an orbit every two days. Using spectrometry it was found in 2007 that this planet contains significant amounts of water vapour. This planet is the second extrasolar planet where definitive evidence for water has been found.[14]

The chemical signature of water vapour was detected in the atmosphere of this planet. Although HD 189733b with atmospheric temperatures rising above 1,000 °C (1,830 °F) is far from being habitable, this finding increases the likelihood that water, an essential component of life, would be found on a more Earth-like planet in the future.[15]

Astronomers have created a rough map of HD 189733b's cloud-top features using data from the Spitzer infrared space telescope.

Although Spitzer could not resolve the planet into a disk, by measuring changes as the planet rotated, the team created a simple longitudinal map. That is, they measured the planet's brightness in a series of pole-to-pole strips across the planet's visible cloud-tops, then assembled those strips into an overall picture.

Probably due to strong winds, the hottest point on the planet seems to be "offset by about 30 degrees longitudinally" from the substellar point ("high noon").[16]

In late 2008, the spectral signature of carbon dioxide was found in HD 189733b's atmosphere.[17]

In 2013, albedo measurements at visible wavelengths in the range of 290–570 nm using the Hubble Space Telescope STIS (Space Telescope Imaging Spectrograph) instrument, reported in the Astrophysical Journal Letters, determine the planet to have a deep blue hue due to optically thick reflective clouds containing silicates (glass) "rain".[18][19] The paper detailing the results reports measurement of "geometric albedos of Ag = 0.40 ± 0.12 at 290–450 nm [near ultraviolet to blue in the visible light region of the electromagnetic spectrum] and Ag < 0.12 at 450–570 nm ... with sodium absorption suppressing the scattered light signal beyond ∼450 nm as predicted by models of hot Jupiter atmospheres." [19]

The HD 189733 planetary system
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b 1.162+0.058
−0.039 MJ		 0.03099 ± 0.0006 2.21857 ± 0.00002 0.0010 ± 0.0002 — —

Star-Planet Interaction Controversy

In 2008, a team of astronomers first described how as the exoplanet orbiting HD 189733 A reaches a certain place in its orbit, it causes increased stellar flaring. In 2010, a different team found that every time they observe the exoplanet at a certain position in its orbit, they also detected X-ray flares. Theoretical research since 2000 suggested that an exoplanet very near to the star that it orbits may cause increased flaring due to the interaction of their magnetic fields, or because of tidal forces. In 2019, astronomers analyzed data from Arecibo Observatory, MOST, and the Automated Photoelectric Telescope, in addition to historical observations of the star at radio, optical, ultraviolet, and X-ray wavelengths to examine these claims. They found that the previous claims were exaggerated and the host star failed to display many of the brightness and spectral characteristics associated with stellar flaring and solar active regions, including sunspots. Their statistical analysis also found that many stellar flares are seen regardless of the position of the exoplanet, therefore debunking the earlier claims. The magnetic fields of the host star and exoplanet do not interact, and this system is no longer believed to have a "star-planet interaction."[20] Some researchers had also suggested that HD 189733 accretes, or pulls, material from its orbiting exoplanet at a rate similar to those found around young protostars in T Tauri Star systems. Later analysis demonstrated that very little, if any, gas was accreted from the "hot Jupiter" companion.[21]

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See also

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. "HD 189733". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2013-07-11.
  3. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  4. Bakos, Gáspár Á.; et al. (2006). "A Stellar Companion in the HD 189733 System with a Known Transiting Extrasolar Planet". The Astrophysical Journal Letters. 641 (1): L57–L60. arXiv:astro-ph/0602136. Bibcode:2006ApJ...641L..57B. doi:10.1086/503671.
  5. "HD 189733B". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2013-07-11.
  6. "GCVS query result: V452 Vul". General Catalog of Variable Stars. Sternberg Astronomical Institute, Moscow, Russia. Retrieved 2009-05-22.
  7. "20 00 43.71347 +22 42 39.0645". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2013-07-11.
  8. de Kok, R. J.; et al. (2013). "Detection of carbon monoxide in the high-resolution day-side spectrum of the exoplanet HD 189733b". Astronomy and Astrophysics. 554: A82. arXiv:1304.4014. Bibcode:2013A&A...554A..82D. doi:10.1051/0004-6361/201321381.
  9. Boyajian, T.; et al. (2015). "Stellar diameters and temperatures - VI. High angular resolution measurements of the transiting exoplanet host stars HD 189733 and HD 209458 and implications for models of cool dwarfs". Monthly Notices of the Royal Astronomical Society. 447 (1): 846–857. arXiv:1411.5638. Bibcode:2015MNRAS.447..846B. doi:10.1093/mnras/stu2502.
  10. Torres, Guilermo; et al. (2008). "Improved Parameters for Extrasolar Transiting Planets". Astrophysical Journal. 677 (2): 1324–1342. arXiv:0801.1841. Bibcode:2008ApJ...677.1324T. doi:10.1086/529429.
  11. Henry, Gregory W.; Winn, Joshua N. (2008). "The Rotation Period of the Planet-Hosting Star HD 189733". The Astronomical Journal. 135 (1): 68–71. arXiv:0709.2142. Bibcode:2008AJ....135...68H. doi:10.1088/0004-6256/135/1/68.
  12. 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 (1): L15–L19. arXiv:astro-ph/0510119. Bibcode:2005A&A...444L..15B. doi:10.1051/0004-6361:200500201.
  13. Winn, J. N.; et al. (2007). "The Transit Light Curve Project. V. System parameters and stellar rotation period of HD 189733". The Astronomical Journal. 133 (4): 1828–1835. arXiv:astro-ph/0612224. Bibcode:2007AJ....133.1828W. doi:10.1086/512159.
  14. "Water vapour found on exoplanet". BBC News. 2007-07-11. Retrieved 2007-07-12.
  15. "'Clear Signs of Water' on Distant Planet". 2007-07-11. Retrieved 2008-02-02.
  16. "CfA Press Release - First Map of an Extrasolar Planet". 2007-05-09. Retrieved 2008-12-06.
  17. "Carbon dioxide discovered on distant planet". Nature News. 2008-11-25. Retrieved 2008-11-25.
  18. "Glass rain may give planet blue hue". BBC News. 2013-07-11. Retrieved 2013-07-12.
  19. "The deep blue color of HD 189733b: albedo measurements with HST /STIS at visible wavelengths" (PDF). Retrieved 2013-07-12.
  20. Route, Matthew (February 10, 2019). "The Rise of ROME. I. A Multiwavelength Analysis of the Star-Planet Interaction in the HD 189733 System". The Astrophysical Journal. 872 (1): 79. arXiv:1901.02048. Bibcode:2019ApJ...872...79R. doi:10.3847/1538-4357/aafc25.
  21. Route, Matthew; Looney, Leslie (December 20, 2019). "ROME (Radio Observations of Magnetized Exoplanets). II. HD 189733 Does Not Accrete Significant Material from Its Exoplanet Like a T Tauri Star from a Disk". The Astrophysical Journal. 887 (2): 229. arXiv:1911.08357. Bibcode:2019ApJ...887..229R. doi:10.3847/1538-4357/ab594e.

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