HD 189733 / V452 Vul / BD+22 3887 AB

Zolt Levay, STScI, DSS,
NOAO/REU, ESA, NASA,






Larger composite field image.






HD 189733 can be found near
the Dumbbell Nebula (source).

On October 6, 2005, a team of astronomers announced the discovery of a "hot Jupiter" that transits Sol-type Star A (Observatoire de Genève's page on HD 189733 -- more below). On February 21, 2007, another team of astronomers announced that they had taken an infrared spectrum of the planet with the Spitzer Space Telescope (SSC news release; and CfA press release -- more below). On May 9, 2007, a similar team of astronomers announced the creation of the first thermal map of an extra-Solar planet, with an offset hot spot that be caused by super-high winds (CfA press release; Spitzer image caption; APOD; and Knutson et al, 2007 -- more below). On July 11, 2007, astronomers announced that the presence of water molecules that are too hot to condense into clouds were detected in the planet's atmosphere (Spitzer press release and Tinetti et al, 2007 -- more below). On March 19, 2008, astronomers using the Hubble Space Telescope announced confirmation of the presence of water and the detection of more methane in the atmosphere of the planet than would be predicted by conventional atmospheric models for "hot Jupiters" (Hubble news release and videos; ESA news release and videos; and Swain et al, 2008 -- more below). On December 9, 2008, astronomers using the space telescope announced the detection of carbon dioxide in the planet's atmosphere (Hubble news release). On February 3, 2010, astronomers confirmed the detection of methane (CH4) in the planet's atmosphere using only a ground-based telescope, NASA's Infrared Telescope Facility (Swain et al, 2010; Jason Palmer, BBC News, February 3, 2010; and John Matson, Scientific American, February 3, 2010). (See an animation of the planetary and potentially habitable zone orbits of Star A, with a table of basic orbital and physical characteristics.)

Greg Bacon and
Swain et al, 2008;
STScI, ESA, NASA,





Larger illustration.





HD 189733 A has a
Jupiter-class planet
in a tight orbit, where
methane and water
vapor have been
detected by filtering
the star's light
through the planet's
atmosphere (more).

Today, some astronomers prefer to refer to this Star A as HD 189733, as it is listed in the Henry Draper (1837-82) Catalogue with extension (HDE), a massive photographic stellar spectrum survey carried out by Annie Jump Cannon (1863-1941) and Edward Charles Pickering (1846-1919) from 1911 to 1915 under the sponsorship of a memorial fund created by Henry's wife, Anna Mary Palmer. On the other hand, Star A has an older designation as BD+22 3887 from a catalogue that was originally published in 1863 by Friedrich Wilhelm August Argelander (1799-1875) on the position and brightness of 324,198 stars between +90° and -2° declination that were measured over 11 years from Bonn, Germany with his assistants Eduard Schönfeld (1828-1891) and Aldalbert Krüger (1832-1896). The catalogue became famous as the Bonner Durchmusterung ("Bonn Survey") and is typically abbreviated as BD. It was later expanded and extended during the early 20th Century with the Cordoba (observed from Argentina) then the Cape Photographic Durchmusterung (observed from South Africa).

David A. Aguilar, CfA;
and Grillmair et al, 2007




Larger illustration.




The "hot Jupiter" may
be cloaked in dark
silicate clouds moving
with high winds (more).

HD 189733 A

Star A is an orange-red, main sequence dwarf star of spectral and luminosity type K1-2 V-VI, Bouchy et al, 2005) but was previously catalogued as yellow as G5. The star has a mass around 82 +/-3 percent of Sol's (Bouchy et al, 2005), 0.753 +/- 0.025 percent of its diameter (Winn et al, 2006; Masana et al, 2006; and Bouchy et al, 2005), and a visual luminosity as low as 26.4 percent of Sol's. It may be between 89 and 102 percent as enriched in iron as Sol (Melo et al, 2006). The star is believed to be more than 600 million and probably at least one billion years old (Melo et al, 2006).

Giovanni Tinetti,
University College London,
ESA, NASA,






Larger illustration.






HD 189733 A has an
active chromosphere
with large starspots
that are widespread
enough to dim its
brightness plus or
minus 1.5 percent
at times (more).

Possibly in keeping with its relative youth compared to Sol's 4.6 billion years, Star A has a faster rotation of 13.4 days (Knutson et al, 2007; and Noyes et al, 1984) compared with Sol's 25.4 days, with more chromospheric activity including starspots large and widespread enough to affect its luminosity by about +/- 1.5 percent in visible light (Knutson et al, 2007). As a result, astronomers have classified it as a BY Draconis-type variable with the variable star designation V452 Vulpeculae. Other useful catalogue numbers and designations for the star include: Hip 98505, HD 189733, BD+22 3887, SAO 88060, LTT 15851, and Wolf 854.

Planet "b" or "Ab"

Tim Pyle, SSC,
CalTech, JPL,
NASA,





Larger illustration
or short movie.





Planet b's atmosphere
may have tiny sand
grains (more from
SSC and APOD).

On October 6, 2005, a team of astronomers (François Bouchy, Stephane Udry, Michel Mayor, C. Moutou, F. Pont, R. Da Silva, S. Ilovaisky, Didier Queloz, Nuno C. Santos, Damien Ségransan, and S. Zucker) using the Geneva-Haute-Provence-Marseille Elodie spectrograph announced the discovery of transiting planet "b" (Observatoire de Genève's page on HD 189733). The planet has 1.15 +/- 0.04 Jupiter-masses and a diameter of 1.26 +/- 0.03 of Jupiter's; and at an inferred density of (0.75 gram per cubic centimeter), the planet is believe to be a "bloated" gas giant). It orbits HD 189733 A at an average distance (semi-major axis) of 0.0313 +/- 0.0004 AUs, with a period of 2.2 days in a circular orbit with an eccentricity of 0.0 and an inclination of 85.76 (± 0.29) degrees to Earth's line of sight. The planet has also been detected with the photometric transit method.

Carl J. Grillmair,
SSC, CalTech,
JPL, NASA,





Larger illustration.





The spectrum of
planet b was obtained
through subtraction
when Star A eclipsed
the planet (more).

On February 21, 2007, another team of astronomers announced that analysis of the spectrum of the planet's atmosphere obtained with the Spitzer Space Telescope's infrared spectrograph indicates the presence of high but dry clouds. On July 11, 2007, astronomers announced that the presence of water molecules that are too hot to condense into clouds was detected in the planet's atmosphere (Spitzer press release and Tinetti et al, 2007). The planetary's atmosphere also appeared to have silicate dust or "tiny sand grains" like the spectrum of the similar planet found around more distant HD 209458). Although the planet is tidally locked with one hot side facing the star, high winds may be redistributing heat on the dayside of the atmosphere rapidly to the planet's nightside (more from SSC; CfA; APOD; Grillmair et al, 2007; and Deming et al, 2006).

On March 19, 2008, astronomers using the Hubble Space Telescope announced confirmation of the presence of water and the detection of more methane in the atmosphere of HD 189733's planet than would be predicted by conventional atmospheric models for such a hot Jupiter-class planet (Hubble news release and videos; ESA news release and videos; and Swain et al, 2008). One possible explanation is that the Hubble observations were more sensitive to the perpetual dark nightside of the planet where the atmosphere is slightly colder and the photochemical mechanisms that destroy methane are less efficient than on the dayside. The astronomers used spectroscopy to split light that travelled through the planet's atmosphere into its component "colors" to see which wavelengths were being absorbed by organic molecules such as methane. On December 9, 2008, astronomers using the space telescope announced the detection of carbon dioxide in the planet's atmosphere (Hubble news release). The successful detection of such as carbon dioxide and methane in the atmosphere of the planet around HD 1989733 demonstrates that astronomers should be able to use spectroscopy to detect organic molecules in the atmospheres of planets around other stars in the search for Earth-like planets and Earth-type life.

Heather A. Knutson, CfA
CalTech, JPL, NASA,





Larger illustration.





6,000-mile-per-hour
winds may have offset
the planet's hot spot
by 30 degrees from
the planet's substellar
"high noon" (more).

On May 9, 2007, a team of astronomers announced that the difference in planet b's cloud-top temperatures between the perpetual day and night sides only differs by around 500° F (or 260° C), which is much less than expected. Creating the first ever thermal map of an extra-Solar planet, the team determined that the planet's dayside hot spot had a temperature of 1,700° F (927° C). Surprisingly, the hot spot was found to be offset by about 30 degrees longitudinally east from the substellar point of the planet where "high noon" would be. This offset may be a result of the winds redistributing heat across the face of the planet at some 6,000 miles (9,700 kilometers) per hour, according to some computer models. Hence, the coldest regions on the night side may still be as hot as 1,200° F, or 659° C (CfA press release; Spitzer image caption; APOD; and Knutson et al, 2007).

David A. Aguilar, CfA;
and Knutson et al, 2007



Larger illustration.




Another depiction of
HD 189733 b with a
bright (if offset),
dayside hot spot
explains why some
astronomers call it
the "bulls-eye"
planet (more).

Astronomers have also observed that planet b is eclipsed by its star by about two minutes (120 +/- 24 seconds) later than would be expected if it has a perfectly circular orbit. They suggest that the planet's slightly eccentric orbit could be caused other planets too small to be detected which tug at its orbit (Knutson et al, 2007). For an Earth-type planet around HD 189733 A to have liquid water at its surface, it would need a stable orbit centered around 0.5 AU -- between the orbital distances of Mercury and Venus in the Solar System (with an orbital period around 150 days assuming a stellar mass around 82 percent of Sol's. However, the presence of planet b may perturb the orbit of such a hypothetical Earth-mass planet. Astronomers would find it very difficult to detect an Earth-sized planet around this star using present methods. (See an animation of the planetary and potentially habitable zone orbits of Star A, with a table of basic orbital and physical characteristics.)

Martin Kornmesser,
STScI, ESA, NASA,




Larger and jumbo illustrations.




Carbon dioxide and monoxide, water vapor,
and methane have been detected in the
planet's atmosphere (more).

HD 189733 B (2MASS J20004297+2242342)

NASA -- larger image


Star B is a dim red dwarf star, less like Gliese
623 A (M2.5V) than B (M5.8Ve) at lower right.

In 2006, astronomers discovered a very dim ("mid-range"), red dwarf companion to HD 189733 A of spectral and luminosity type M V. Observed at a separation of 216 AUs from Star A, the companion star has a clockwise orbit that is nearly perpendicular to the orbital plane of transiting planet b around Star A (HD 189733 b or Ab). The orbital period is estimated around 3,200 years (Bakos, et al, 2006).

The following table includes all star systems known to be located within 10 light-years (ly), plus more bright stars within 10 to 20 ly, of HD 189733 AB.