HD 189733b
Credit
X-ray: NASA/CXC/SAO/K.Poppenhaeger et al;
Illustration: NASA/CXC/M.Weiss
The main figure is an artist’s impression showing the HD 189733 system, containing a Sun-like star orbited by HD 189733b, an exoplanet about the size of Jupiter . This "hot Jupiter" is over 30 times closer to its star than Earth is to the Sun
and goes around the star once every 2.2 days, as determined from
previous observations. Also in the illustration is a faint red companion
star, which was detected for the first time in X-rays with these
observations . This star orbits the main star about once every 3,200 years.
The inset contains the Chandra image of HD 189733. The source in
the middle is the main star and the source in the lower right is the
faint companion star. The source at the bottom of the image is a
background object not contained in the HD 189733 system.
The exoplanet itself cannot be seen in the Chandra image, as the
transits involve measuring small decreases in X-ray emission from the
main star. The authors estimate that the percentage decrease in X-ray
light during the transits is about three times greater than the
corresponding decrease in optical light. This tells them that the
region blocking X-rays from the star is substantially larger than the
region blocking optical light from the star, helping to determine the
size of the planet's atmosphere. The extended atmosphere implied by
these results is shown by the light blue color around the planet.
Recent observations of HD 189733b with the Hubble Space Telescope have
confirmed that the lower atmosphere of the planet has a deep blue
color, due to the preferential scattering of blue light by silicate
particles in its atmosphere.
For about a decade astronomers have known that ultraviolet and
X-ray radiation from the main star in HD 189733 are evaporating the
atmosphere of its closely orbiting planet over time. The authors of the
new study estimate that HD 189733b is losing between 100 million and
600 million kilograms per second. This rate is about 25% to 65% higher
than it would be if the planet's atmosphere were not extended.
At a distance of just 63 light years,
HD 189733b is the closest hot Jupiter to Earth, which makes it a prime
target for astronomers who want to learn more about this type of
exoplanet and the atmosphere around it.
Chandra was used to make observations of six transits by HD
189733b and the team also used archival data from XMM-Newton for one
transit. These results are available online and will appear in a future issue of The Astrophysical Journal.
Fast Facts for HD 189733:
Scale:
Image is 1.5 arcmin across (about 0.02 light years)
Category:
Normal Stars & Star Clusters
Coordinates (J2000):
RA 20h 00m 43.70s | Dec +22 42 39.10
Constellation:
Vulpecula
Observation Date:
6 pointings between 5-23 July, 2011
References: Poppenhaeger, K. et al, 2013, ApJ (submitted); arXiv:1306.2311
Color Code:
X-ray (Purple)
Distance Estimate:
About 60 light years
